CAIs define a brief formation interval corresponding to an age of 4567.30 ± 0.16 million years, whereas chondrules range from 4567.32 ± 0.42 to 4564.71 ± 0.30 million years. U-Pb dating refutes the long-held view of an age gap between CAIs and chondrules, instead indicating chondrule formation started contemporaneously with CAIs and lasted ~3 million years. This timeline is similar to protoplanetary disk lifetimes from astronomy, suggesting CAI and chondrule formation occurred during the evolution of the solar protoplanetary disk.
- Comet C/2011 N3 (SOHO) was observed by the Solar Dynamics Observatory as it passed through the low solar corona in July 2011.
- The comet survived within the corona until it came within 0.146 solar radii (approximately 100,000 km) of the solar surface, at which point its extreme ultraviolet signal disappeared.
- Before being destroyed, material released from the comet was first seen in absorption against the solar corona, then formed an emission nebula as it interacted with the coronal plasma.
This document summarizes a scientific paper published in Science in 2011 about the discovery that the large, oxygen-rich halos surrounding star-forming galaxies are a major reservoir of heavy elements ejected from galaxies. The paper presents evidence that these halos contain a significant portion of metals produced by massive stars. It also describes how these findings help scientists better understand the cycling of matter on large scales throughout the universe.
Evidence for a Dynamo in the Main Group Pallasite Parent BodyCarlos Bella
Evidence is presented that the parent body of pallasite meteorites hosted a dynamo. Pallasite olivines contain tiny magnetic inclusions that can record magnetic fields. Paleointensity measurements from these inclusions indicate strong ancient magnetic fields, suggesting the parent body generated its own magnetic field through dynamo action. Thermal modeling suggests pallasites formed when liquid iron-nickel from the core of an impactor was injected as dikes into the shallow mantle of a ~200 km radius protoplanet that remained intact long enough to sustain a dynamo.
This article reports the detection of two gas clouds with no discernible elements heavier than hydrogen, representing the lowest heavy-element abundance observed in the early universe. One cloud at z=3.4 exhibits a deuterium abundance matching predictions from Big Bang nucleosynthesis, providing direct evidence for the standard cosmological model. The sparse metal enrichment of these clouds implies an inhomogeneous process for transporting heavy elements from galaxies into the surrounding intergalactic medium.
This document describes a new technique for wide-field background-free fluorescence imaging in vivo using magnetic modulation of fluorescent nanodiamond emission. Fluorescent nanodiamonds are promising probes for in vivo imaging but are limited by autofluorescence. The technique uses a rotating magnetic field to selectively modulate nanodiamond fluorescence, which is then detected using phase-sensitive lock-in detection to improve signal-to-background ratio up to 100-fold. This overcomes autofluorescence and improves nanodiamond imaging capabilities for in vivo applications.
Seasonal erosion and restoration of mars’ northern polar dunesSérgio Sacani
The document discusses seasonal erosion and restoration of dunes in Mars' northern polar regions. High-resolution images show that substantial sediment transport occurs today on martian north polar dune slipfaces via grainflow triggered by seasonal carbon dioxide sublimation. Every year, Mars' polar regions are covered by seasonal caps of carbon dioxide frost. In northern spring, sublimation of this frost causes sediment transport that erodes dunes, and restoration occurs over the martian year as winds replenish the dunes with new sediment.
Measurements of a_massive_galaxy_clusterSérgio Sacani
This document reports on observations of IDCS J1426.5+3508, a galaxy cluster located at a redshift of 1.75. A Sunyaev-Zeldovich decrement was detected towards this cluster, indicating a total mass of 4.3×1014 solar masses. This makes it the most distant cluster detected via the Sunyaev-Zeldovich effect to date and the most massive cluster found at a redshift greater than 1.4. Despite its rarity, the cluster is not unexpected given cosmological models and the large area surveyed. However, it remains one of the rarest and most extreme clusters discovered and provides insight into the early formation of the most massive clusters.
This document summarizes a study that used anionic photoelectron spectroscopy to investigate the electronic structures of six [MoOS4]- complexes. The study revealed new information about how the energy separations between the highest occupied molecular orbitals depend on ligand types and dihedral angles. It also showed that the threshold photoelectron feature observed in all six complexes is due to detaching an unpaired electron that is mainly of Mo 4d character, consistent with previous theoretical calculations. The results provide insights into the electronic structures and chemical bonding of these molybdenum-containing complexes.
- Comet C/2011 N3 (SOHO) was observed by the Solar Dynamics Observatory as it passed through the low solar corona in July 2011.
- The comet survived within the corona until it came within 0.146 solar radii (approximately 100,000 km) of the solar surface, at which point its extreme ultraviolet signal disappeared.
- Before being destroyed, material released from the comet was first seen in absorption against the solar corona, then formed an emission nebula as it interacted with the coronal plasma.
This document summarizes a scientific paper published in Science in 2011 about the discovery that the large, oxygen-rich halos surrounding star-forming galaxies are a major reservoir of heavy elements ejected from galaxies. The paper presents evidence that these halos contain a significant portion of metals produced by massive stars. It also describes how these findings help scientists better understand the cycling of matter on large scales throughout the universe.
Evidence for a Dynamo in the Main Group Pallasite Parent BodyCarlos Bella
Evidence is presented that the parent body of pallasite meteorites hosted a dynamo. Pallasite olivines contain tiny magnetic inclusions that can record magnetic fields. Paleointensity measurements from these inclusions indicate strong ancient magnetic fields, suggesting the parent body generated its own magnetic field through dynamo action. Thermal modeling suggests pallasites formed when liquid iron-nickel from the core of an impactor was injected as dikes into the shallow mantle of a ~200 km radius protoplanet that remained intact long enough to sustain a dynamo.
This article reports the detection of two gas clouds with no discernible elements heavier than hydrogen, representing the lowest heavy-element abundance observed in the early universe. One cloud at z=3.4 exhibits a deuterium abundance matching predictions from Big Bang nucleosynthesis, providing direct evidence for the standard cosmological model. The sparse metal enrichment of these clouds implies an inhomogeneous process for transporting heavy elements from galaxies into the surrounding intergalactic medium.
This document describes a new technique for wide-field background-free fluorescence imaging in vivo using magnetic modulation of fluorescent nanodiamond emission. Fluorescent nanodiamonds are promising probes for in vivo imaging but are limited by autofluorescence. The technique uses a rotating magnetic field to selectively modulate nanodiamond fluorescence, which is then detected using phase-sensitive lock-in detection to improve signal-to-background ratio up to 100-fold. This overcomes autofluorescence and improves nanodiamond imaging capabilities for in vivo applications.
Seasonal erosion and restoration of mars’ northern polar dunesSérgio Sacani
The document discusses seasonal erosion and restoration of dunes in Mars' northern polar regions. High-resolution images show that substantial sediment transport occurs today on martian north polar dune slipfaces via grainflow triggered by seasonal carbon dioxide sublimation. Every year, Mars' polar regions are covered by seasonal caps of carbon dioxide frost. In northern spring, sublimation of this frost causes sediment transport that erodes dunes, and restoration occurs over the martian year as winds replenish the dunes with new sediment.
Measurements of a_massive_galaxy_clusterSérgio Sacani
This document reports on observations of IDCS J1426.5+3508, a galaxy cluster located at a redshift of 1.75. A Sunyaev-Zeldovich decrement was detected towards this cluster, indicating a total mass of 4.3×1014 solar masses. This makes it the most distant cluster detected via the Sunyaev-Zeldovich effect to date and the most massive cluster found at a redshift greater than 1.4. Despite its rarity, the cluster is not unexpected given cosmological models and the large area surveyed. However, it remains one of the rarest and most extreme clusters discovered and provides insight into the early formation of the most massive clusters.
This document summarizes a study that used anionic photoelectron spectroscopy to investigate the electronic structures of six [MoOS4]- complexes. The study revealed new information about how the energy separations between the highest occupied molecular orbitals depend on ligand types and dihedral angles. It also showed that the threshold photoelectron feature observed in all six complexes is due to detaching an unpaired electron that is mainly of Mo 4d character, consistent with previous theoretical calculations. The results provide insights into the electronic structures and chemical bonding of these molybdenum-containing complexes.
Edri And Regev 2009 “Shaken, Not Stable”: Dispersion Mechanism and Dynami...edrier
This study examines the dispersion dynamics of single-walled carbon nanotubes (SWNTs) stabilized by bovine serum albumin (BSA) protein. The researchers investigated how BSA properties like charge and conformation affect SWNT exfoliation during sonication and subsequent recovery after centrifugation. They found that bulkier BSA conformations led to faster exfoliation and higher SWNT recovery, while higher BSA-to-SWNT ratios resulted in slower exfoliation dynamics and lower recoveries. The study links the unstable state during sonication to the stable state achieved after centrifugation removal of bundles and impurities.
Color and albedo_heterogeneity_on_vestaSérgio Sacani
The document summarizes findings from the Dawn spacecraft about the composition and geology of Vesta. It found that Vesta's surface has significant heterogeneity in color and albedo. Spectroscopic data revealed variations in the mineralogy and composition, with the Oppia region showing differences possibly related to mass movements. Craters exposed layers with different mineral and chemical compositions, providing insights into Vesta's complex, stratified crust formed from magmatic processes during planetary differentiation.
The document outlines the schedule for Science Day 2012 hosted by Govinda Bhisetti on December 28, 2012. The day-long event includes an introduction, a tribute to Dr. Yellapragada SubbaRow, a discussion of the 2012 Nobel Prizes, a screening of a movie, and presentations on breakthroughs in science from the past year. It also provides background information on Dr. SubbaRow and how Nobel Prize winners are selected.
SiD Letter of Intent_Linear Collider DetectorCARMEN IGLESIAS
This document presents the current status of SiD's e®ort to develop an optimized design for
an experiment at the International Linear Collider. It presents detailed discussions of each
of SiD's various subsystems, an overview of the full GEANT4 description of SiD, the status
of newly developed tracking and calorimeter reconstruction algorithms, studies of subsystem
performance based on these tools, results of physics benchmarking analyses, an estimate
of the cost of the detector, and an assessment of the detector R&D needed to provide the
technical basis for an optimised SiD.
Chris Dube_Publications_Conference Proceedings_PatentsChris Dub
This document lists 43 publications and conference presentations by Christopher E. Dubé. The publications span from 1990 to 2015 and cover topics related to solar cell fabrication and characterization using techniques like ion implantation, aluminum oxide passivation, selective emitters, and contact resistance modeling. Many of the publications involve collaboration with researchers from institutions including MIT, Fraunhofer ISE, and University of Konstanz.
This year marked significant progress in gene therapy with successful clinical trials demonstrating its potential to treat devastating genetic diseases like blindness, brain disorders, and "bubble boy" disease. Researchers were able to halt progression or cure patients by inserting corrected genes to repair malfunctioning cells. This helped gene therapy turn a corner after struggles with safety issues in early trials.
1) Apatite samples from the Grand Canyon basement were analyzed using 4He/3He thermochronometry to constrain the near-surface cooling history associated with canyon incision.
2) Data from eastern Grand Canyon apatites indicate substantial canyon incision by ~70 million years ago, earlier than conventional models suggesting incision began 5-6 million years ago.
3) Similar data from western Grand Canyon provide evidence that it was excavated to within a few hundred meters of its modern depth by ~70 million years ago, challenging the view that the entire canyon was carved only in the last 5-6 million years.
1) Researchers used CT scans and finite element modeling to create a highly accurate 3D biomechanical model of the Allosaurus skull.
2) The model showed that forces during feeding were distributed throughout the skull. Bite forces were surprisingly low compared to estimates for Tyrannosaurus rex, indicating Allosaurus had a different feeding strategy of inflicting rapid bites to soft tissues.
3) Contrary to views of its skull being delicate, the analysis found the Allosaurus skull was strongly built to absorb forces from prey impacts and tooth dragging, though its exact adaptations require more study.
Topography of northern_hemisphere_of_mercury_from_messenger_altimeterSérgio Sacani
The document describes a study that used laser altimetry from the MESSENGER spacecraft to create a topographic model of Mercury's northern hemisphere. The study found that Mercury has a much smaller range of elevations compared to Mars or the Moon, likely due to Mercury's higher density and gravitational acceleration smoothing out topographic features. The model revealed numerous large impact structures that influence the shape of the hemisphere but do not significantly affect the distribution of elevations.
This CV summarizes the academic and professional background of Paul L. Edmiston. He received his B.S. in Chemistry from Pepperdine University in 1993 and Ph.D. in Chemistry from the University of Arizona in 1997. He is currently a Professor of Chemistry at the College of Wooster where he conducts research exclusively with undergraduate students. He has founded a company, ABS Materials, and his research focuses on developing new hybrid organic-inorganic materials for applications including water treatment. He has received significant research funding and awards for his work developing swellable organosilica materials.
This study examines a reservoir of ionized gas in the galactic halo that can sustain star formation in the Milky Way. The authors detect a substantial amount of warm-hot gas in the halo of a star-forming galaxy at z=0.2 through detection of Ne VIII absorption lines. This warm-hot gas reservoir contains as much mass as the galaxy's stars and can replenish its supply of cool gas to sustain star formation over billions of years.
Bright and dark_polar_deposits_on_mercury_evidence_for_surface_volatilesSérgio Sacani
1) Measurements from MESSENGER's Mercury Laser Altimeter revealed regions of unusually dark and bright surface deposits near Mercury's north pole.
2) These deposits are concentrated on pole-facing slopes and spatially correlate with areas exhibiting high radar backscatter, suggesting the presence of near-surface water ice.
3) Analysis found the bright deposits are consistent with surface water ice, while the dark regions likely overlie buried ice and provide thermal insulation, such as from complex organic materials delivered by comets or asteroids.
The document discusses three individuals who were awarded the 2012 Nobel Memorial Prize in Economic Sciences: Alvin Roth, Lloyd Shapley, and John Nash. Alvin Roth and Lloyd Shapley were recognized for their work on stable allocation and market design theory. Roth developed theory for matching markets and practical market applications. Shapley pioneered game theory and made foundational contributions to mathematical economics. The third laureate, John Nash, developed the concept of Nash equilibrium.
This document discusses the x-ray crystal structure of the mammalian Shaker family potassium ion channel Kv1.2 determined by the authors. Three key conclusions are presented:
1) The voltage sensors that allow the channel to switch between conductive and nonconductive states are independent domains within the membrane.
2) The voltage sensors perform mechanical work on the pore via the S4-S5 linker helices, positioned to constrict or dilate the pore.
3) In the open conformation, two of the four conserved arginine residues on S4 are on a lipid-facing surface while two are buried within the voltage sensor.
This document provides biographical information on Peter Agre, a Nobel Prize-winning American scientist. It notes that Peter Agre is a Professor of Biological Chemistry and Medicine at Johns Hopkins University, where he is also the Director of the Johns Hopkins Malaria Research Institute. He was awarded the 2003 Nobel Prize in Chemistry for his discovery of aquaporins, which are water channels in cell membranes. The document provides details on Agre's scientific career and accomplishments, as well as his work in scientific diplomacy and public engagement with science.
Pamela L. Gordon is a scientist with an active Top Secret clearance from the Department of Defense. She has published numerous refereed journal articles and book chapters on topics related to actinide chemistry, including studies of neptunium, plutonium, and uranium speciation under various conditions. Gordon also has other publications, presentations, and reports on emerging chemical threats and nanotechnology.
This document discusses histotaphonomic analysis and its application to understanding mortuary context. It provides an overview of histological analysis and taphonomic processes. Three case studies are presented that use histo-taphonomic analysis to make inferences about fragmented remains in South-East Arabia, diagenesis of early Holocene skeletons in North India, and the Donner Party camp site. The document argues that microstructural changes observed through histo-taphonomic analysis can help reveal information about mortuary practices and social context.
This patent document describes a microfluidic electrochemical reactor. It includes an electrode with one or more microfluidic channels on the electrode surface. The microfluidic channels are covered by a membrane containing a gas-permeable polymer. The distance between the electrode and membrane is less than 500 micrometers. This design allows for increased reaction rates in electrochemical reactions using a gaseous reactant compared to conventional electrochemical cells. Microfluidic electrochemical reactors can be incorporated into devices for applications such as fuel cells, electrochemical analysis, and pH gradient formation.
This document lists 29 publications authored or co-authored by S. Azad related to surface chemistry and materials science research. The publications span the years 2000-2014 and cover topics including the reaction pathways of hydrocarbons on metal surfaces, the adsorption and reaction of gases on metal oxide surfaces, nanoscale effects on ion conductivity in oxide thin films, and the oxidation properties of lubricating greases and graphite.
Engineering Research Publication
Best International Journals, High Impact Journals,
International Journal of Engineering & Technical Research
ISSN : 2321-0869 (O) 2454-4698 (P)
www.erpublication.org
Este documento trata sobre la competencia lingüística. Define la competencia lingüística como la capacidad de realizar tareas efectivamente en un contexto determinado mediante la movilización integrada de actitudes, habilidades y conocimientos. Explora los ámbitos de la competencia en comunicación lingüística como la comprensión lectora, el habla y la escucha, y la composición de textos. Finalmente, discute los cambios requeridos en las aulas y centros para desarrollar la competencia lingüística de los estudiantes
An Earth-mass planet orbiting a Centauri BCarlos Bella
1) Researchers detected an Earth-mass planet orbiting the star Alpha Centauri B.
2) The planet has a minimum mass similar to Earth and orbits its star with a period of 3.236 days, within 0.04 astronomical units.
3) This makes it the lightest planet detected orbiting a Sun-like star and the closest exoplanet to our solar system found to date.
Edri And Regev 2009 “Shaken, Not Stable”: Dispersion Mechanism and Dynami...edrier
This study examines the dispersion dynamics of single-walled carbon nanotubes (SWNTs) stabilized by bovine serum albumin (BSA) protein. The researchers investigated how BSA properties like charge and conformation affect SWNT exfoliation during sonication and subsequent recovery after centrifugation. They found that bulkier BSA conformations led to faster exfoliation and higher SWNT recovery, while higher BSA-to-SWNT ratios resulted in slower exfoliation dynamics and lower recoveries. The study links the unstable state during sonication to the stable state achieved after centrifugation removal of bundles and impurities.
Color and albedo_heterogeneity_on_vestaSérgio Sacani
The document summarizes findings from the Dawn spacecraft about the composition and geology of Vesta. It found that Vesta's surface has significant heterogeneity in color and albedo. Spectroscopic data revealed variations in the mineralogy and composition, with the Oppia region showing differences possibly related to mass movements. Craters exposed layers with different mineral and chemical compositions, providing insights into Vesta's complex, stratified crust formed from magmatic processes during planetary differentiation.
The document outlines the schedule for Science Day 2012 hosted by Govinda Bhisetti on December 28, 2012. The day-long event includes an introduction, a tribute to Dr. Yellapragada SubbaRow, a discussion of the 2012 Nobel Prizes, a screening of a movie, and presentations on breakthroughs in science from the past year. It also provides background information on Dr. SubbaRow and how Nobel Prize winners are selected.
SiD Letter of Intent_Linear Collider DetectorCARMEN IGLESIAS
This document presents the current status of SiD's e®ort to develop an optimized design for
an experiment at the International Linear Collider. It presents detailed discussions of each
of SiD's various subsystems, an overview of the full GEANT4 description of SiD, the status
of newly developed tracking and calorimeter reconstruction algorithms, studies of subsystem
performance based on these tools, results of physics benchmarking analyses, an estimate
of the cost of the detector, and an assessment of the detector R&D needed to provide the
technical basis for an optimised SiD.
Chris Dube_Publications_Conference Proceedings_PatentsChris Dub
This document lists 43 publications and conference presentations by Christopher E. Dubé. The publications span from 1990 to 2015 and cover topics related to solar cell fabrication and characterization using techniques like ion implantation, aluminum oxide passivation, selective emitters, and contact resistance modeling. Many of the publications involve collaboration with researchers from institutions including MIT, Fraunhofer ISE, and University of Konstanz.
This year marked significant progress in gene therapy with successful clinical trials demonstrating its potential to treat devastating genetic diseases like blindness, brain disorders, and "bubble boy" disease. Researchers were able to halt progression or cure patients by inserting corrected genes to repair malfunctioning cells. This helped gene therapy turn a corner after struggles with safety issues in early trials.
1) Apatite samples from the Grand Canyon basement were analyzed using 4He/3He thermochronometry to constrain the near-surface cooling history associated with canyon incision.
2) Data from eastern Grand Canyon apatites indicate substantial canyon incision by ~70 million years ago, earlier than conventional models suggesting incision began 5-6 million years ago.
3) Similar data from western Grand Canyon provide evidence that it was excavated to within a few hundred meters of its modern depth by ~70 million years ago, challenging the view that the entire canyon was carved only in the last 5-6 million years.
1) Researchers used CT scans and finite element modeling to create a highly accurate 3D biomechanical model of the Allosaurus skull.
2) The model showed that forces during feeding were distributed throughout the skull. Bite forces were surprisingly low compared to estimates for Tyrannosaurus rex, indicating Allosaurus had a different feeding strategy of inflicting rapid bites to soft tissues.
3) Contrary to views of its skull being delicate, the analysis found the Allosaurus skull was strongly built to absorb forces from prey impacts and tooth dragging, though its exact adaptations require more study.
Topography of northern_hemisphere_of_mercury_from_messenger_altimeterSérgio Sacani
The document describes a study that used laser altimetry from the MESSENGER spacecraft to create a topographic model of Mercury's northern hemisphere. The study found that Mercury has a much smaller range of elevations compared to Mars or the Moon, likely due to Mercury's higher density and gravitational acceleration smoothing out topographic features. The model revealed numerous large impact structures that influence the shape of the hemisphere but do not significantly affect the distribution of elevations.
This CV summarizes the academic and professional background of Paul L. Edmiston. He received his B.S. in Chemistry from Pepperdine University in 1993 and Ph.D. in Chemistry from the University of Arizona in 1997. He is currently a Professor of Chemistry at the College of Wooster where he conducts research exclusively with undergraduate students. He has founded a company, ABS Materials, and his research focuses on developing new hybrid organic-inorganic materials for applications including water treatment. He has received significant research funding and awards for his work developing swellable organosilica materials.
This study examines a reservoir of ionized gas in the galactic halo that can sustain star formation in the Milky Way. The authors detect a substantial amount of warm-hot gas in the halo of a star-forming galaxy at z=0.2 through detection of Ne VIII absorption lines. This warm-hot gas reservoir contains as much mass as the galaxy's stars and can replenish its supply of cool gas to sustain star formation over billions of years.
Bright and dark_polar_deposits_on_mercury_evidence_for_surface_volatilesSérgio Sacani
1) Measurements from MESSENGER's Mercury Laser Altimeter revealed regions of unusually dark and bright surface deposits near Mercury's north pole.
2) These deposits are concentrated on pole-facing slopes and spatially correlate with areas exhibiting high radar backscatter, suggesting the presence of near-surface water ice.
3) Analysis found the bright deposits are consistent with surface water ice, while the dark regions likely overlie buried ice and provide thermal insulation, such as from complex organic materials delivered by comets or asteroids.
The document discusses three individuals who were awarded the 2012 Nobel Memorial Prize in Economic Sciences: Alvin Roth, Lloyd Shapley, and John Nash. Alvin Roth and Lloyd Shapley were recognized for their work on stable allocation and market design theory. Roth developed theory for matching markets and practical market applications. Shapley pioneered game theory and made foundational contributions to mathematical economics. The third laureate, John Nash, developed the concept of Nash equilibrium.
This document discusses the x-ray crystal structure of the mammalian Shaker family potassium ion channel Kv1.2 determined by the authors. Three key conclusions are presented:
1) The voltage sensors that allow the channel to switch between conductive and nonconductive states are independent domains within the membrane.
2) The voltage sensors perform mechanical work on the pore via the S4-S5 linker helices, positioned to constrict or dilate the pore.
3) In the open conformation, two of the four conserved arginine residues on S4 are on a lipid-facing surface while two are buried within the voltage sensor.
This document provides biographical information on Peter Agre, a Nobel Prize-winning American scientist. It notes that Peter Agre is a Professor of Biological Chemistry and Medicine at Johns Hopkins University, where he is also the Director of the Johns Hopkins Malaria Research Institute. He was awarded the 2003 Nobel Prize in Chemistry for his discovery of aquaporins, which are water channels in cell membranes. The document provides details on Agre's scientific career and accomplishments, as well as his work in scientific diplomacy and public engagement with science.
Pamela L. Gordon is a scientist with an active Top Secret clearance from the Department of Defense. She has published numerous refereed journal articles and book chapters on topics related to actinide chemistry, including studies of neptunium, plutonium, and uranium speciation under various conditions. Gordon also has other publications, presentations, and reports on emerging chemical threats and nanotechnology.
This document discusses histotaphonomic analysis and its application to understanding mortuary context. It provides an overview of histological analysis and taphonomic processes. Three case studies are presented that use histo-taphonomic analysis to make inferences about fragmented remains in South-East Arabia, diagenesis of early Holocene skeletons in North India, and the Donner Party camp site. The document argues that microstructural changes observed through histo-taphonomic analysis can help reveal information about mortuary practices and social context.
This patent document describes a microfluidic electrochemical reactor. It includes an electrode with one or more microfluidic channels on the electrode surface. The microfluidic channels are covered by a membrane containing a gas-permeable polymer. The distance between the electrode and membrane is less than 500 micrometers. This design allows for increased reaction rates in electrochemical reactions using a gaseous reactant compared to conventional electrochemical cells. Microfluidic electrochemical reactors can be incorporated into devices for applications such as fuel cells, electrochemical analysis, and pH gradient formation.
This document lists 29 publications authored or co-authored by S. Azad related to surface chemistry and materials science research. The publications span the years 2000-2014 and cover topics including the reaction pathways of hydrocarbons on metal surfaces, the adsorption and reaction of gases on metal oxide surfaces, nanoscale effects on ion conductivity in oxide thin films, and the oxidation properties of lubricating greases and graphite.
Engineering Research Publication
Best International Journals, High Impact Journals,
International Journal of Engineering & Technical Research
ISSN : 2321-0869 (O) 2454-4698 (P)
www.erpublication.org
Este documento trata sobre la competencia lingüística. Define la competencia lingüística como la capacidad de realizar tareas efectivamente en un contexto determinado mediante la movilización integrada de actitudes, habilidades y conocimientos. Explora los ámbitos de la competencia en comunicación lingüística como la comprensión lectora, el habla y la escucha, y la composición de textos. Finalmente, discute los cambios requeridos en las aulas y centros para desarrollar la competencia lingüística de los estudiantes
An Earth-mass planet orbiting a Centauri BCarlos Bella
1) Researchers detected an Earth-mass planet orbiting the star Alpha Centauri B.
2) The planet has a minimum mass similar to Earth and orbits its star with a period of 3.236 days, within 0.04 astronomical units.
3) This makes it the lightest planet detected orbiting a Sun-like star and the closest exoplanet to our solar system found to date.
1) PSR J033711715 is a millisecond pulsar discovered to be in a hierarchical triple system with two white dwarf companions, making it the first known millisecond pulsar triple system.
2) Precise timing observations using multiple radio telescopes determined the masses of the pulsar (1.4378 solar masses), inner white dwarf companion (0.19751 solar masses), and outer white dwarf companion (0.4101 solar masses) to high precision.
3) The unexpectedly coplanar and nearly circular orbits of the system indicate an exotic evolutionary history and provide an opportunity to test theories of general relativity by studying the interactions between the bodies.
Detection of Radio Emission from FireballsCarlos Bella
This document summarizes the detection of radio emissions from fireballs (very bright meteors) using the Long Wavelength Array radio telescope. A search of over 11,000 hours of all-sky radio images found 49 long-duration radio transients. Ten of these transients correlated spatially and temporally with fireballs detected by an optical meteor monitoring network. This provides evidence that fireballs emit previously undiscovered low frequency radio pulses. Further analysis found characteristics inconsistent with expected radio reflections from meteor trails, suggesting a non-thermal radio emission mechanism from the fireballs. This identifies a new class of natural radio transients and provides a new probe to study meteor physics.
A Complete Skull from Dmanisi, Georgia, and the Evolutionary Biology of Early...Carlos Bella
The article describes a newly discovered complete skull (D4500) from the site of Dmanisi, Georgia dating to 1.8 million years ago. It represents the earliest known completely preserved adult hominin skull. The skull possesses a small braincase of 546 cubic centimeters but also exhibits a large, prognathic face. This combination of features had not been seen before in the human fossil record. Analysis of this new skull and comparison to other remains from Dmanisi provides direct evidence of wide morphological variation within early members of the genus Homo, implying a single evolving lineage across continents.
This document is the introduction to The Skeptic Encyclopedia of Pseudoscience. It provides an overview of the encyclopedia, which aims to objectively analyze prominent scientific and pseudoscientific claims. The introduction discusses the relationship between facts and theories in science. It notes that observations must be viewed through theoretical lenses, and references Darwin's view that observations are only useful if they are for or against some view. The introduction also discusses how views of science have changed over time between seeing it as progressively approaching truth, and as a relativistic social construct. It argues the field has moved to a more balanced middle view. The goal of the encyclopedia is to explore the borderlands where theory and data intersect, with the aim of achieving a
Offshore fresh groundwater reserves as a global phenomenonCarlos Bella
There is mounting evidence that vast reserves of fresh and brackish groundwater exist below continental shelves around the world. These offshore fresh groundwater reserves (OFGRs) were formed when sea levels were lower during glacial periods, exposing continental shelf areas that became recharged with precipitation and glacial meltwater. While some OFGRs may still be connected to modern coastal groundwater systems, many appear to be relics of past hydrological conditions and are termed "palaeo-groundwater". The largest documented OFGR is below the New Jersey shelf, where freshwater has been found over 100km offshore. Global occurrences of OFGRs have also been identified through borehole and geophysical data in locations such as the North
Revealing letters in rolled Herculaneum papyri by X-ray phase-contrast imagingCarlos Bella
X-ray phase-contrast tomography was used to read letters hidden inside two unopened Herculaneum papyri without damaging them. In a fragment of one papyrus, two Greek words were identified on a hidden layer. In an intact rolled papyrus, several letter sequences were revealed, including "APN", "HEY", and "KI". This non-destructive technique opens opportunities to read many rolled Herculaneum papyri and enhance knowledge of ancient Greek literature.
Baryons at the edge of the x ray–brightest galaxy clusterSérgio Sacani
This article discusses observations of the outskirts of the Perseus galaxy cluster, which is the brightest extended X-ray source. The observations find evidence of gas beyond the virial radius that has been shock heated to high temperatures by accretion and mergers. The results provide insights into the formation and evolution of large-scale structure in the universe.
The gravity field_and_interior_structure_of_enceladusSérgio Sacani
The gravity field and interior structure of Enceladus were determined using Doppler data from three Cassini flybys. There is a negative mass anomaly in the south polar region, largely compensated by a positive subsurface anomaly consistent with a regional subsurface sea at depths of 30-40 km extending to 50° south latitude. Enceladus deviates mildly from hydrostatic equilibrium, with estimated quadrupole coefficients indicating a differentiated body with a low-density core.
The gravity fieldandinteriorstructureofenceladusGOASA
The Cassini spacecraft measured Enceladus' gravity field during three flybys. The results indicate a negative mass anomaly over the south pole, likely compensated by a subsurface sea of water 30-40 km deep extending to 50° south latitude. Analysis of the gravity data suggests Enceladus has differentiated into a low-density core with a moment of inertia around 0.335 times its mass times the square of its radius, consistent with the presence of liquid water beneath the surface. The endogenic heat output and gravity data are best explained by models involving tidal heating of Enceladus' interior through past or current orbital resonances.
Citizen science projects have the potential to transform earthquake detection by greatly increasing the number of seismic sensor locations. Individuals can host sensors in their homes and buildings to record ground motion data during quakes. However, data quality standards must be maintained and networks need to remain operational long-term for the data to be scientifically useful. If these challenges can be addressed, dense citizen sensor networks may provide new insights into earthquake processes.
The Dawn spacecraft's VIR instrument obtained hyperspectral images of Vesta's surface. Analysis of the spectra showed considerable regional variations in mineralogy. The south polar region, including the Rheasilvia basin, displayed a higher diogenitic component with deeper pyroxene absorption bands. Equatorial regions showed a higher eucritic component with shallower bands. This lithological distribution indicates Vesta had a deeper diogenitic crust exposed by the Rheasilvia impact, overlain by an upper eucritic crust. Evidence for layering was observed on crater walls and in ejecta, broadly consistent with magma ocean differentiation models. However, spectral variability also highlighted local variations, suggesting a complex crustal
The study examines a post-starburst galaxy outflow using ultraviolet spectroscopy of multiple ions including hydrogen. It finds the outflow extends at least 160,000 light-years from the galaxy and contains a hidden mass of at least 6x10^9 times the mass of our Sun. This challenges previous assumptions about the extent and mass of galaxy outflows, suggesting they may play a larger role in regulating galaxy evolution than thought.
The document summarizes findings from a study published in Science about the detection of water ice in the protoplanetary disk surrounding the young star TW Hydrae. Using the Herschel Space Observatory, researchers detected a large reservoir of water stored as ice in the disk. This suggests icy planetesimals could form in the outer parts of the disk beyond the "snow line." The water vapor observed likely originates from ultraviolet light releasing water molecules trapped in the ice grains. The results provide insights into the distribution and transport of water in protoplanetary disks, which influenced the formation of planets like Earth.
This study examines lunar basalt sample 10020, which is approximately 3.7 billion years old. Paleomagnetic measurements and petrologic analysis reveal the sample contains a stable natural remanent magnetization acquired in a magnetic field of at least 12 microteslas. This provides evidence the lunar dynamo, which was likely present 4.2 billion years ago, persisted for at least another 500 million years. A long-lived lunar dynamo would have required an energy source beyond secular cooling of the lunar interior. The findings extend knowledge of the lunar dynamo and present a challenge to current dynamo theory.
Observations of ejecta_clouds_produced_by_impacts_onto_saturn_ringsSérgio Sacani
Three key points from the document:
1. Cassini observations detected dusty ejecta clouds above Saturn's rings that were produced by impacts onto the rings 1 to 50 hours prior.
2. The largest cloud was observed twice, and its brightness and position evolved consistently with this impact hypothesis.
3. The responsible interplanetary meteoroids were initially between 1 cm and several meters in size, and their influx rate is consistent with prior knowledge of smaller meteoroids in the outer solar system.
1) The document studied the stability of tubular DNA origami structures in different protein crystallization buffers using three methods: abrupt buffer exchange, gradient buffer exchange, and gradual overnight dialysis.
2) Only the abrupt and gradient buffer exchange methods were successful in maintaining the DNA origami structure, and only for the catalase crystallization buffer.
3) Further experiments examined the impact of individual components in crystallization buffers - salts, buffers, precipitants, and pH - on the stability of the DNA origami structures. The results provide a strategy for screening suitable buffer conditions for using DNA nanostructures to promote protein crystallization.
This document reports the detection of five planets orbiting the star Kepler-62, including two super-Earth-size planets (Kepler-62e and Kepler-62f) in the habitable zone of the star. Kepler-62e receives 1.2 times the solar flux at Earth's orbit, while Kepler-62f receives 0.41 times the solar flux. Theoretical models suggest that both planets could be solid, with either a rocky composition or composed mostly of solid water.
Minor Planet Evidence for Water in the Rocky Debris of a Disrupted Extrasolar...Carlos Bella
Evidence has been found for water in the debris of a disrupted extrasolar minor planet orbiting a white dwarf star. Spectroscopic analysis of the white dwarf's atmosphere revealed an excess of oxygen that cannot be explained by oxide minerals alone, indicating the parent body was originally composed of about 26% water by mass. This demonstrates that water-bearing planetesimals can form around higher mass stars that eventually become white dwarfs. The disrupted planetesimal is the source of a circumstellar debris disk closely orbiting the white dwarf remnant.
Superconducting qubits for quantum information an outlookGabriel O'Brien
The document discusses the progress and future directions of quantum information processing using superconducting qubits. It describes the stages needed to build a functional quantum computer, from controlling individual qubits to implementing error correction. Superconducting qubits are well-suited for this task as their Hamiltonians can be designed using circuit elements like inductors and Josephson junctions. While full fault-tolerant quantum computing has yet to be achieved, the performance of superconducting qubits has improved dramatically in recent years, suggesting the goals may be within reach this century.
This document reports on the detection of Berry's phase in the bulk Rashba semiconductor bismuth telluride iodide (BiTeI). The researchers analyzed Shubnikov-de Haas oscillations from spin-split inner and outer Fermi surfaces in BiTeI under an external magnetic field. They observed a systematic pi-phase shift in the oscillations from both Fermi surfaces, consistent with the theoretically predicted non-trivial pi Berry's phase in Rashba systems. This provides direct experimental evidence of a non-trivial Berry's phase in the bulk states of a physical-spin Rashba system.
Measurements of energetic_particle_radiation_in_transit_to_mars_on_the_mars_s...Sérgio Sacani
The Radiation Assessment Detector on the Mars Science Laboratory measured the radiation environment inside the spacecraft during its 253-day cruise to Mars. It found a galactic cosmic ray dose rate of 332 mGy/day in silicon or 481 mGy/day in water. The quality factor for the radiation field was 3.82, indicating it was more biologically damaging than an equal dose of low-LET radiation. Integrating the measured energy and linear energy transfer spectra against quality factors yielded a total mission dose equivalent of 0.66 sievert for the round-trip cruise, posing health risks for future human Mars missions with current propulsion technologies and shielding.
Chenglin Zhang is a research scientist at Rice University with over 12 years of experience in synthesizing magnetic and superconducting materials. He has grown many new single crystal materials and published over 70 peer-reviewed papers. His expertise includes material fabrication, neutron and X-ray scattering, transport characterization, and data analysis. He received his Ph.D from Rutgers University and has held positions at the University of Tennessee and Rice University, where he managed research groups.
A comparative study of living cell micromechanical properties by oscillatory ...Angela Zaorski
This study used an oscillatory optical tweezer-based technique to measure the frequency-dependent viscoelastic properties of cultured alveolar epithelial cells. Both the storage modulus and complex shear modulus followed a weak power law dependence on frequency. Measurements were taken by oscillating either an intracellular organelle or a bead attached to the cell's exterior through membrane receptors. The exponents of the power law were similar between the two measurement methods, but the modulus magnitudes differed significantly. Comparing intracellular and extracellular probing provided insights into cell mechanical properties.
1) The EPOXI mission flew by comet Hartley 2 in 2010, obtaining over 105 images and spectra.
2) Hartley 2 has an unusually small but very active bi-lobed nucleus with dimensions of 2.33 km and a rotation period of about 18 hours.
3) The nucleus shows substantial differences in volatile composition between its lobes and waist region.
This document provides an overview of key concepts covered in Chapter 2 of the textbook, including:
1. It defines science and the scientific method, and describes the major components and behaviors of complex systems.
2. It outlines the basic forms of matter - elements, compounds, atoms, ions - and states of matter. Matter can change forms through physical and chemical changes.
3. It discusses the major forms of energy, how energy is transferred, and the electromagnetic spectrum. The two laws of thermodynamics govern energy changes.
4. It summarizes models of cells and DNA, and explains genes and chromosomes. Quality and states of matter, chemical and physical changes in matter are also covered.
This document discusses microfluidic devices for DNA analysis. It summarizes that:
1) Microfabricated electrophoresis devices allow for faster DNA analysis and sequencing - in under 2 minutes for short-tandem-repeat genotyping assays and under 15 minutes for single-stranded DNA sequencing.
2) The microdevice format is a natural extension of improvements to electrophoresis over 100 years, operating in an almost perfect way limited only by the sieving medium.
3) Procedures for making the microfluidic devices are simple using current semiconductor fabrication technology, requiring one or two lithography steps at low resolution.
Similar to The absolute chronology and thermal processing of solids in the solar protoplanetary disk (20)
Animal behaviour: Incipient tradition in wild chimpanzeesCarlos Bella
This study observed the adoption of a new tool use behavior, moss sponging, by chimpanzees at the Sonso community in Uganda's Budongo Forest. The dominant male was first observed using a moss sponge to drink from a small flooded waterhole. Over the next six days, six other chimpanzees began displaying this behavior after observing the dominant male and female. The researchers used a statistical technique called network-based diffusion analysis to show the spread of this innovation was consistent with social learning along social network pathways, providing the first direct evidence of cultural diffusion in wild chimpanzees.
Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075...Carlos Bella
1) The asteroid (29075) 1950 DA is rotating faster than would be allowed without cohesive forces, with a rotation period of just over 2 hours.
2) Thermal infrared observations and measurements of its orbital drift were used to determine it has a low bulk density of 1.7 g/cm3, indicating it is a rubble pile asteroid made of smaller pieces held together weakly.
3) For it to retain its fine-grained surface and resist breaking up from centrifugal forces at its rate of rotation, cohesive van der Waals forces between the grains comparable to lunar regolith are required, with a minimum cohesive strength of 64 Pa.
Preserved flora and organics in impact melt brecciasCarlos Bella
This document discusses the preservation of organic matter and plant remains in impact melt breccias found in Argentina. Analyses found centimeter-scale leaf fragments encapsulated in the impact glass that exhibited remarkable cellular-level preservation. Organic matter was also detected, including polycyclic aromatic hydrocarbons, alkanes, and pigment-like structures similar to chlorophyll. Heating experiments showed temperatures above 1500°C were required to preserve morphology, suggesting the impact process rapidly quenched and encapsulated the organic material. These findings demonstrate the potential for impact events to preserve biomarkers of early life on Mars.
A Sedna-like body with a perihelion of 80 astronomical unitsCarlos Bella
1) The document reports the discovery of 2012 VP113, the second known object after Sedna with an extremely distant perihelion of 80 AU, confirming that Sedna is not isolated.
2) Simulation results suggest there may be few inner Oort cloud objects with perihelia between 50-75 AU, and the population increases with perihelion distances greater than 75 AU.
3) Both Sedna and 2012 VP113 have similar arguments of perihelion, as do all other objects beyond 150 AU, suggesting they were perturbed by a possible unseen super-Earth mass perturber in the outer solar system that could restrict their arguments of perihelion.
Fuel gain exceeding unity in an inertially confined fusion implosionCarlos Bella
The document summarizes key results from experiments achieving fusion fuel gains exceeding unity using a "high-foot" laser pulse shape on the National Ignition Facility. Specifically:
1) Experiments achieved fusion fuel gains over unity for the first time, representing a 10x improvement over past experiments, and showed significant alpha heating and evidence of ignition requirements being met.
2) The "high-foot" pulse shape reduces instability during implosions by increasing ablation velocity and density scale length, improving stability compared to past "low-foot" experiments.
3) Improved performance is attributed to reduced mix from the ablator, with experiments pushing higher velocities through laser power and pattern optimization while maintaining hotspot shape control.
This document summarizes meteor phenomena and bodies. It discusses the different types of interactions that can occur when meteoroids collide with Earth's atmosphere, including meteors, fireballs, bolides, explosive impacts, and meteoric dust particles. It also describes the various stages of a meteoroid's trajectory through the atmosphere, including orbital motion, preheating, ablation, dark flight, and impact. Finally, it provides an overview of the size ranges and velocities associated with different meteor phenomena.
The Origin Of The 1998 June BoöTid Meteor ShowerCarlos Bella
The document analyzes the origin of the 1998 June Boötid meteor shower through comparing orbital elements and simulating particle release from the potential parent comet 7P/Pons–Winnecke. It finds that:
1) 7P/Pons–Winnecke best matches the shower orbit based on the Tisserand invariant and D-discriminant.
2) Simulations show particles released from 7P/Pons–Winnecke in 1819 and 1869 were Earth-crossing in 1998 after Jovian perturbations altered their orbits starting in the 1940s.
3) This identifies 7P/Pons–Winnecke as the parent comet and 1819 and 1869 as the active returns
Physics first spectrum of ball lightningCarlos Bella
Researchers in China measured the first spectrum of ball lightning. They observed ball lightning form after a cloud-to-ground lightning strike about 900 meters away. The spectrum contained emission lines from silicon, iron, and calcium, elements common in soil. This supports the theory that ball lightning is formed when lightning vaporizes soil, producing glowing nanoparticles. It was about 2 meters wide and drifted horizontally for 30 meters before rising a few meters. This is the first direct observation of ball lightning forming from a lightning strike and the first measurement of its emission spectrum.
Transient Water Vapor at Europa’s South PoleCarlos Bella
1) Hubble Space Telescope images from November and December 2012 of Europa's atmosphere detected statistically significant surpluses of hydrogen Lyman-α and oxygen OI130.4 nm emissions above Europa's southern hemisphere in December 2012.
2) These emissions were observed in the same region over a period of ~7 hours, suggesting an inhomogeneous atmosphere, consistent with two 200-km-high plumes of water vapor with column densities of about 1020 m−2.
3) No plumes were detected in November 2012 images or previous 1999 images, indicating variable plume activity possibly related to Europa's changing orbital phases and surface stresses. The December 2012 plume was seen when Europa was near apocenter.
Solid-state plastic deformation in the dynamic interior of a differentiated a...Carlos Bella
This document summarizes a study that analyzed the microstructural properties of olivine grains in the diogenite meteorite Northwest Africa 5480 using electron backscatter diffraction techniques. The study found evidence of solid-state plastic deformation in the olivine-dominated zones, represented by a well-defined lattice-preferred orientation that is best explained by high-temperature deformation via the pencil-glide slip system, typically seen on Earth in dry ultramafic rocks deformed in the mantle. Numerical modeling indicates this observation in the meteorite can be explained by large-scale downwelling in the asteroid's mantle within the first 50 million years after formation, providing evidence of dynamic planet-like processes occurring in the interior of
Broadband high photoresponse from pure monolayer graphene photodetectorCarlos Bella
This document summarizes a research article that reports on the development of a high-performance photodetector using pure monolayer graphene. The researchers introduced electron trapping centers and created a bandgap in graphene through band structure engineering. This allowed them to achieve a high photoresponsivity of 8.61 A/W, about three orders of magnitude higher than previous graphene photodetectors. Additionally, they demonstrated broadband photoresponse from visible to mid-infrared wavelengths, the broadest reported for a pure graphene photodetector. By introducing defects and quantum confinement effects, they were able to greatly increase the lifetime of photo-generated carriers and achieve carrier multiplication, resulting in high photoresponsivity across a wide spectrum
Formation SiO2 Mass-Independent Oxygen Isotopic Partitioning During Gas-PhaseCarlos Bella
This document summarizes an experimental study that investigated oxygen isotopic partitioning during gas-phase silicon dioxide (SiO2) formation. The experiments involved laser ablation of silicon monoxide (SiO) in the presence of oxygen (O2) with and without hydrogen (H2). SiO2 formed in experiments without H2 showed normal mass-dependent isotopic fractionation, whereas those with H2 exhibited anomalous mass-independent fractionation. The extent of mass-independent fractionation in SiO2 increased with higher H2/O2 ratios. This provides the first experimental evidence that gas-to-particle conversion reactions can produce solids like SiO2 with oxygen isotopic compositions similar to early solar system materials like calcium-
Unique chemistry of a diamond-bearing pebble from the Libyan Desert Glass str...Carlos Bella
This document summarizes research on a unique black, shiny, and intensely fractured stone named "Hypatia" found in the Libyan Desert Glass strewnfield in southwest Egypt. Analysis showed the stone is composed primarily of amorphous carbonaceous matter containing nanodiamonds. Isotopic signatures of carbon and noble gases rule out a terrestrial origin and match cometary materials. The researchers propose Hypatia is a remnant of a comet nucleus fragment that was incorporated into the bolide that created the Libyan Desert Glass in an atmospheric airburst event 28.5 million years ago. Its shock transformation produced a weathering-resistant material that has been exceptionally preserved.
This document summarizes a heat-pipe model for early Earth's lithospheric dynamics and heat transport. Numerical simulations show that frequent volcanic eruptions could have advected surface materials downwards, developing a thick cold lithosphere. Declining heat sources over time would lead to an abrupt transition to plate tectonics. Evidence from the geologic record, such as rapid volcanic resurfacing and contractional deformation before 3.2 billion years ago, is consistent with predictions of the heat-pipe model. The model provides a framework for understanding Earth's evolution before the onset of plate tectonics.
Analysis of Surface Materials by Curiosity Mars Rover - Special CollectionCarlos Bella
Curiosity used its instruments to analyze materials along its traverse on Mars, yielding three key results:
1) It found a unique alkaline volcanic rock called "Jake_M" that is compositionally similar to rare mugearite rocks on Earth.
2) It analyzed windblown deposits and found two soil types - a common mafic type similar to global Martian soils, and a locally derived felsic type from broken down bedrock.
3) Chemical analysis of the soils found evidence of hydration in the amorphous soil components, suggesting absorbed water plays a role in Mars' global hydration signal detected from orbiters.
Adaptation of an Antarctic lichen to Martian niche conditions can occur withi...Carlos Bella
The study exposed the Antarctic lichen Pleopsidium chlorophanum to simulated Martian conditions in a Mars simulation chamber for 34 days to test its ability to adapt. Under conditions simulating the unprotected Martian surface, the fungal symbiont decreased metabolic activity and it was unclear if the algal symbiont was still photosynthesizing. However, under conditions simulating a protected niche environment, the entire lichen survived, remained photosynthetically active, and even increased its photosynthetic activity over the 34 days, demonstrating its ability to adapt to Martian conditions within a protected environment.
The internal energy and thermodynamic behaviour of a boson gas below the Bose...Carlos Bella
This document presents a new theory for the internal energy and thermodynamic behavior of an ideal boson gas below the Bose-Einstein temperature. The existing theory assumes particles lose kinetic energy when dropping into the ground state, leading to problems like infinite compressibility below TB. The new theory assumes particles retain their kinetic energy of 0.77kTB at TB. This yields expressions for internal energy and pressure below TB that are finite and agree with experiments. For liquid helium, the theory predicts a density maximum at 1.88K, close to the observed value of 2.18K.
Sequencing y chromosomes resolves discrepancy in time to common ancestor of m...Carlos Bella
The study sequenced the complete Y chromosomes of 69 males from diverse global populations. This identified over 11,000 genetic variants, resolving the phylogeny of male lineages. Applying molecular clock methods calibrated to the peopling of the Americas, the estimated time to the most recent common ancestor (TMRCA) of the Y chromosome was 120 to 156 thousand years, similar to estimates for the mitochondrial genome TMRCA of 99 to 148 thousand years. This challenges previous suggestions that male lineages coalesce more recently than female lineages.
1. Researchers injected mice with a virus that causes neurons activated during exploration of a novel context to express channelrhodopsin-2 (ChR2). They labeled dentate gyrus neurons activated during exploration of context A with ChR2.
2. On a later day, they optically stimulated the neurons labeled in context A while delivering a foot shock in a different context B, to test if this could generate a false fear memory for context A.
3. When later tested, mice that received optical stimulation of dentate gyrus neurons showed increased freezing in context A, where no shock was delivered, demonstrating the creation of a false fear memory through artificial means.
Level 3 NCEA - NZ: A Nation In the Making 1872 - 1900 SML.pptHenry Hollis
The History of NZ 1870-1900.
Making of a Nation.
From the NZ Wars to Liberals,
Richard Seddon, George Grey,
Social Laboratory, New Zealand,
Confiscations, Kotahitanga, Kingitanga, Parliament, Suffrage, Repudiation, Economic Change, Agriculture, Gold Mining, Timber, Flax, Sheep, Dairying,
Beyond Degrees - Empowering the Workforce in the Context of Skills-First.pptxEduSkills OECD
Iván Bornacelly, Policy Analyst at the OECD Centre for Skills, OECD, presents at the webinar 'Tackling job market gaps with a skills-first approach' on 12 June 2024
Elevate Your Nonprofit's Online Presence_ A Guide to Effective SEO Strategies...TechSoup
Whether you're new to SEO or looking to refine your existing strategies, this webinar will provide you with actionable insights and practical tips to elevate your nonprofit's online presence.
Chapter wise All Notes of First year Basic Civil Engineering.pptxDenish Jangid
Chapter wise All Notes of First year Basic Civil Engineering
Syllabus
Chapter-1
Introduction to objective, scope and outcome the subject
Chapter 2
Introduction: Scope and Specialization of Civil Engineering, Role of civil Engineer in Society, Impact of infrastructural development on economy of country.
Chapter 3
Surveying: Object Principles & Types of Surveying; Site Plans, Plans & Maps; Scales & Unit of different Measurements.
Linear Measurements: Instruments used. Linear Measurement by Tape, Ranging out Survey Lines and overcoming Obstructions; Measurements on sloping ground; Tape corrections, conventional symbols. Angular Measurements: Instruments used; Introduction to Compass Surveying, Bearings and Longitude & Latitude of a Line, Introduction to total station.
Levelling: Instrument used Object of levelling, Methods of levelling in brief, and Contour maps.
Chapter 4
Buildings: Selection of site for Buildings, Layout of Building Plan, Types of buildings, Plinth area, carpet area, floor space index, Introduction to building byelaws, concept of sun light & ventilation. Components of Buildings & their functions, Basic concept of R.C.C., Introduction to types of foundation
Chapter 5
Transportation: Introduction to Transportation Engineering; Traffic and Road Safety: Types and Characteristics of Various Modes of Transportation; Various Road Traffic Signs, Causes of Accidents and Road Safety Measures.
Chapter 6
Environmental Engineering: Environmental Pollution, Environmental Acts and Regulations, Functional Concepts of Ecology, Basics of Species, Biodiversity, Ecosystem, Hydrological Cycle; Chemical Cycles: Carbon, Nitrogen & Phosphorus; Energy Flow in Ecosystems.
Water Pollution: Water Quality standards, Introduction to Treatment & Disposal of Waste Water. Reuse and Saving of Water, Rain Water Harvesting. Solid Waste Management: Classification of Solid Waste, Collection, Transportation and Disposal of Solid. Recycling of Solid Waste: Energy Recovery, Sanitary Landfill, On-Site Sanitation. Air & Noise Pollution: Primary and Secondary air pollutants, Harmful effects of Air Pollution, Control of Air Pollution. . Noise Pollution Harmful Effects of noise pollution, control of noise pollution, Global warming & Climate Change, Ozone depletion, Greenhouse effect
Text Books:
1. Palancharmy, Basic Civil Engineering, McGraw Hill publishers.
2. Satheesh Gopi, Basic Civil Engineering, Pearson Publishers.
3. Ketki Rangwala Dalal, Essentials of Civil Engineering, Charotar Publishing House.
4. BCP, Surveying volume 1
The absolute chronology and thermal processing of solids in the solar protoplanetary disk
1. The Absolute Chronology and Thermal Processing of Solids in the
Solar Protoplanetary Disk
James N. Connelly et al.
Science 338, 651 (2012);
DOI: 10.1126/science.1226919
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2. REPORTS
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In contrast, chronologies based on long-lived
The Absolute Chronology and
Downloaded from www.sciencemag.org on November 6, 2012
radioisotope systems rely on the knowledge of
the present-day abundances of the parent and
Thermal Processing of Solids daughter isotopes in a sample and therefore are
free from assumptions of parent nuclide homo-
in the Solar Protoplanetary Disk geneity. Of the various long-lived radioisotope
systems, the Pb-Pb dating method is the most
powerful tool to establish a high-resolution chro-
James N. Connelly,1* Martin Bizzarro,1* Alexander N. Krot,1,2 Åke Nordlund,3 nology of the first 10 My of the solar system.
Daniel Wielandt,1 Marina A. Ivanova4 This chronometer is based on two isotopes of
U, 238U and 235U, that decay in a chain to stable
Transient heating events that formed calcium-aluminum–rich inclusions (CAIs) and chondrules Pb isotopes, 206Pb and 207Pb, respectively, result-
are fundamental processes in the evolution of the solar protoplanetary disk, but their chronology ing in 207PbR/206PbR (where R = radiogenic) ra-
is not understood. Using U-corrected Pb-Pb dating, we determined absolute ages of individual tios that correspond to the amount of time passed
CAIs and chondrules from primitive meteorites. CAIs define a brief formation interval corresponding since the system closed, by Eq. 1
to an age of 4567.30 T 0.16 million years (My), whereas chondrule ages range from 4567.32 T 0.42 235 l1 t
to 4564.71 T 0.30 My. These data refute the long-held view of an age gap between CAIs and 207
PbR U ðe − 1Þ
¼ ð1Þ
chondrules and, instead, indicate that chondrule formation started contemporaneously with 206 Pb
R
238
U ðel2 t − 1Þ
CAIs and lasted ~3 My. This time scale is similar to disk lifetimes inferred from astronomical
observations, suggesting that the formation of CAIs and chondrules reflects a process intrinsically where l1 and l2 reflect the decay constants for 235U
linked to the secular evolution of accretionary disks. and 238U, respectively; t, time. The 207PbR/206PbR
ratio of an inclusion is calculated by extrapolat-
he only record of our solar system’s form- tures (9). In contrast, most chondrules represent ing from an array of measured Pb isotopic values
T ative stages comes from the earliest sol-
ids preserved from the protoplanetary disk
that now reside as millimeter- to centimeter-
coalesced dust aggregates that were subsequent-
ly rapidly melted and cooled in lower-temperature
regions (1000 K) and higher ambient vapor
that represent varying mixtures of radiogenic
Pb and its initial Pb isotopic composition, which
should approximate that of the solar system de-
sized objects—calcium-aluminum–rich inclusions pressures (≥10−3 bar) than CAIs, resulting in ig- fined by the Nantan iron meteorite (14). However,
(CAIs) and chondrules—in chondrite meteorites. neous porphyritic textures (10). Despite their for- attempts to date individual CAIs and chondrules
These complex objects have been the subject mation by different mechanisms (condensation by this approach have historically been frustrated
of intense study in an attempt to decipher their versus dust accretion) in distinct environments by the difficulties in analyzing the small amounts
origins and, in turn, use them as records of the (11), these objects share common histories of ex- of Pb in these inclusions. In addition, the 238U/235U
dynamics of the protoplanetary disk that led posure to brief, high-temperature events at least ratio required for Eq. 1, which has traditionally
to the formation of the solar system (1–8). Most once in their respective evolutions. been assumed to be 137.88 in all solar system
CAIs formed as fine-grained condensates from a The current perception of the relative tim- materials, was demonstrated to vary in CAIs by
gas of approximately solar composition in a high- ing of CAI and chondrule formation is based on 35 e units (deviations in parts per 104), correspond-
temperature environment (1300 K) at total the short-lived 26Al-26Mg chronometer [26Al de- ing to offsets in calculated Pb-Pb ages of up to
pressure ≤10–4 bar, with a subset experiencing cays to 26Mg with a half-life of 0.73 million 5 My (15). The observation of U isotope varia-
re-melting to form distinct coarser igneous tex- years (My)], which has led to a growing con- bility, attributed to the decay of the short-lived
247
sensus that chondrules formed 1 to 2 My after Cm nuclide (247Cm decays to 235U with a half-
1 CAIs (12). This age difference has long been life of 15.6 My) voided all published Pb-Pb ages
Centre for Star and Planet Formation and Natural History
Museum of Denmark, University of Copenhagen, DK-1350 used as a central observation in defining mod- for solar system materials that were based on an
Copenhagen, Denmark. 2Hawai‘i Institute of Geophysics and els of chondrule formation and, in addition, im- assumed 238U/235U ratio and made clear the need to
Planetology, University of Hawai‘i at Manoa, HI 96822, USA. plies that the melting of CAIs and chondrules have measurements of the U isotopic composi-
3
Centre for Star and Planet Formation and Niels Bohr Institute, was produced by different mechanisms and/or tions for all materials dated by the Pb-Pb method.
University of Copenhagen, DK-2100 Copenhagen, Denmark.
4
Vernadsky Institute of Geochemistry and Analytical Chem- heat sources. However, the 26Al-26Mg dating meth- To establish an assumption-free absolute chro-
istry, Moscow 119991, Russia. od critically depends on the disputed assump- nology of CAI and chondrule formation, we have
*To whom correspondence should be addressed. E-mail: tion of homogeneous distribution of 26Al in space developed improved methods for the precise anal-
connelly@snm.ku.dk ( J.N.C.); bizzarro@snm.ku.dk (M.B.) and time within the protoplanetary disk (13). ysis of small amounts of Pb and U by thermal
www.sciencemag.org SCIENCE VOL 338 2 NOVEMBER 2012 651
3. REPORTS
ionization mass spectrometry and high-resolution ing the best estimate of the bulk 238U/235U ratio on the CV chondrite parent body. The ages we
inductively coupled plasma source mass spec- of the solar system and hence that of the Sun. report for Efremovka CAIs overlap with the age
trometry, respectively (16). We measured the To constrain the timing and duration of CAI of 4567.18 T 0.50 My recently obtained for the
238 235
U/ U ratios of three CAIs from the reduced and chondrule formation, we have obtained coarse-grained type B CAI SJ101 from Allende
CV chondrite Efremovka, three chondrules from Pb isotope data for a suite of three CAIs from (19), which is the only CAI age currently avail-
the oxidized CV chondrite Allende, and whole- Efremovka (22E, 31E, and 32E), two ferro- able in the literature calculated with a measured
238 235
rock chondrites and differentiated meteorites in magnesian porphytitic olivine-pyroxene chon- U/ U ratio. Pooling the ages we obtained
an attempt to understand the extent and origin drules from Allende (C20 and C30), and three for Efremovka CAIs with that of the SJ101 CAI
of 238U/235U variations in the early solar system ferromagnesian porphyritic olivine (C1) and from Allende yields a weighted mean age of
(Fig. 1 and Table 1). The Efremovka CAIs show barred olivine-pyroxene chondrules (C2 and C3) 4567.30 T 0.16 My, suggesting that the time
a range of 238U/235U ratios (Table 1), confirm- from the unequilibrated ordinary chondrite NWA scale of the CAI-forming event inferred from
ing the presence of U isotope variability in re- 5697. 22E is a fine-grained inclusion with a our absolute chronology may be as short as
fractory inclusions. In contrast, our analyses of porous, nearly monomineralic hibonite core sur- 160,000 years. Therefore, these data collectively
meteorites derived from chondritic and differen- rounded by a mantle composed of concentrically support a single and brief time interval for the
tiated asteroids as well as three individual chon- zoned objects having a spinel-hibonite-perovskite formation of CV CAIs, in agreement with the
drules from Allende show identical 238U/235U core rimmed by the layers of melilite T anorthite rapid time scales of less than 50,000 years re-
ratios within analytical uncertainty (Fig. 1), de- and pyroxene. The texture and mineralogy of quired for their condensation and evaporative
fining a weighted mean of 137.786 T 0.013. 22E indicate that it is an unmelted nebular con- melting based on bulk 26Al-26Mg systematics
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These observations indicate a uniform 238U/235U densate. 31E is a coarse-grained type B1 CAI (6, 13). However, our preferred age for the CAI-
ratio in the inner solar system outside the CAI- with a pyroxene-melilite-spinel core surrounded forming event and, by extension, the formation of
forming region. This is consistent with an earlier by a melilite mantle and a multilayered Wark- the solar system, is based on the best-constrained
study (17) but at odds with the solar system Lovering rim sequence of spinel, melilite, py- age of 4567.35 T 0.28 My obtained for the 22E
initial 247Cm/235U value of ~1.1 × 10−4 inferred roxene, and forsterite. 32E is a coarse-grained CAI (Fig. 2A). This interpretation is founded
from 238U/235U variability in Allende CAIs (15). type B1 CAI with a melilite-pyroxene-anorthite- on the petrographic features of this inclusion,
Moreover, our analyses of Efremovka CAIs show spinel core surrounded a melilite mantle, thin suggesting an origin as a gas-solid condensate,
significant departure from the apparent correla- Wark-Lovering rim layers of pyroxene and spinel,
tion between the 144Nd/238U [an assumed proxy and a forsterite-rich accretionary rim. Both coarse-
for Cm/U (18)] and 235U/238U ratios of Allende grained CAIs experienced melting after their
CAIs (15), similarly to another recent study (19). initial formation by condensation and evapora-
Thus, we infer that the 238U/235U variability in tion processes. To calculate the Pb-Pb ages of
CAIs largely reflects mass-dependent fraction- the Efremovka CAIs, we used their measured
238 235
ation associated with the CAI-forming process U/ U ratios, which are characterized by a
and not 247Cm decay (supplementary materials range of ~15 e units (Table 1) with compositions
text 1). that are both isotopically heavy and light rela-
The subset of chondrite meteorites we ana- tive to the bulk solar 238U/235U value of 137.786.
lyzed includes the Ivuna carbonaceous chondrite, The three CAIs yield ages of 4567.35 T 0.28 My
a member of the rare clan of primitive mete- (22E), 4567.23 T 0.29 My (31E), and 4567.38 T
orites referred to as CI chondrites. Composed 0.31 My (32E) (Table 1), with uncertainties in-
of matrix material with the highest abundances cluding errors associated with both the Pb and
of presolar grains, CI chondrites are generally U isotope measurements. The age concordancy
considered to represent the least chemically frac- of these inclusions, despite the wide range of
tionated and least thermally processed mete- their 238U/235U ratios, supports our interpreta-
orites: They have solar abundances of most tion that the 238U/235U variability was imparted
elements (20) and, by extension, have the solar during CAI formation and does not represent a
247
Cm/235U ratio. Therefore, we interpret the secondary event such as, for example, mass-
U/ U value of 137.786 T 0.013 obtained for
238 235
dependent fractionation resulting from varia-
bulk inner solar system materials as represent- ble redox conditions during alteration processes
Table 1. Summary of Pb-Pb ages, 238U/235U ratios used in age calculations, and 54Cr compositions
of individual CAIs and chondrules. The Pb concentrations are based on the total amount of Pb
analyzed. m = 238U/204Pb. The e54Cr values represent 104 deviation of the 54Cr/52Cr value of a sample
relative to the terrestrial chromium reference standard and were acquired following Trinquier et al.
(41). Uncertainties reflect the external reproducibility of 9 ppm. The e54Cr value for the 31E CAI is from
Larsen et al. (13).
Sample Type Weight (mg) m Pb (ppb) Age (My) 238
U/235U e54Cr Fig. 1. 238U/235U ratios of individual chondrules,
22E CAI 25.9 46 178.8 4567.35 T 0.28 137.627 T 0.022 bulk chondrites, and achondrites. These samples
31E CAI 57.6 247 119.4 4567.23 T 0.29 137.770 T 0.022 6.8 T 1.2 define a mean of 137.786 T 0.013 [mean square
32E CAI 18.0 116 322.3 4567.38 T 0.31 137.832 T 0.022 of weighted deviations (MSWD) = 1.2], which we
C30 Chondrule 29.7 246 24.1 4567.32 T 0.42 137.786 T 0.013 –0.58 T 0.09 interpret as the present-day solar 238U/235U ratio.
C1 Chondrule 30.0 23 78.3 4566.67 T 0.43 137.786 T 0.013 –0.60 T 0.09 The vertical gray band reflects the 2 SD uncer-
tainty of the 238U/235U solar value. Uncertainties
C20 Chondrule 28.5 26 40.8 4566.24 T 0.63 137.786 T 0.013 –0.36 T 0.09
of sample measurements reflect external repro-
C3 Chondrule 107.6 183 27.6 4566.02 T 0.26 137.786 T 0.013 –0.87 T 0.09
ducibility or the internal precision of individual
C2 Chondrule 58.9 63 77.7 4564.71 T 0.30 137.786 T 0.013 –0.24 T 0.09
analyses, whichever is larger.
652 2 NOVEMBER 2012 VOL 338 SCIENCE www.sciencemag.org
4. REPORTS
together with the combined effect of the slightly ments used to define the array (table S4), and the Allende meteorite (Fig. 1), we used the well-
smaller errors on the age due to the greater spread low amount of terrestrial Pb contamination (21). constrained solar 238U/235U value of 137.786 T
in Pb-Pb data to define the 207PbR/206PbR ratio, Because of the lack of 238U/235U variability 0.013 to calculate the absolute Pb-Pb ages of our
greater number of points defining the isochron, among bulk inner solar system reservoirs, in- subset of chondrules. In contrast to the narrow
acceptable sample/blank ratios for all measure- cluding three individual chondrules from the age span defined by CAIs, the chondrule ages
Downloaded from www.sciencemag.org on November 6, 2012
Fig. 2. Pb-Pb isochron diagrams for Efremovka CAI 22E (A), Allende chon-
drule C30 (B), and NWA 5697 chondrule C2 (C).
Fig. 3. Initial Pb isotopic compositions of individual
chondrules. The initial Pb isotope compositions are defined
by the intersection of the individual isochrons and a Pb
evolution array anchored on the solar system initial Pb
isotope composition defined by the Nantan iron meteorite
(14). The m values (238U/204Pb) of chondrules are indicated
in parentheses. Chondrule C30 was displaced to the right-
hand side of the solar system initial Pb array for clarity. The
uncertainty of the solar system initial Pb value is smaller
than the symbol.
www.sciencemag.org SCIENCE VOL 338 2 NOVEMBER 2012 653
5. REPORTS
range from 4567.32 T 0.42 My to 4564.71 T thermal history involving multiple heating and substantial radiogenic Pb by the time the last
0.30 My (Fig. 2, B and C, and Table 1). The melting events. The isochron for the oldest melting event occurred at 4564.71 T 0.30 My.
oldest chondrule age overlaps with our estimate Allende chondrule (C30) projects back to an ini- Chondrules from the Allende and NWA
of CAI formation and thus requires that ag- tial Pb isotopic composition that is less radio- 5697 chondrites define age ranges (Fig. 4) that
gregation of the chondrule precursor material genic than the most primitive estimate of the indicate the presence of multiple generations of
and its thermal processing occurred within the initial Pb isotopic composition of the solar sys- chondrules in individual chondrite groups. To
uncertainty of its Pb-Pb age. Moreover, the age tem (Fig. 3), based on the Nantan iron meteorite explore the spatial significance of this age range,
of the oldest chondrule indicates that it was not (14). The low m value of the precursor material we have measured the 54Cr/52Cr ratios of these
heated to temperatures above the Pb closure tem- for chondrules in general and the antiquity of chondrules, because 54Cr/52Cr variations within
perature after 4567.32 T 0.42 My and therefore this chondrule in particular indicate that the the inner solar system track genetic relationships
has a formation and thermal history indistinguish- Pb isotopic composition of the Nantan iron me- between early-formed solids and their respective
able from that of CAIs. These data demonstrate teorite does not represent the initial Pb isotopic reservoirs (25). The five chondrules analyzed
that chondrule formation started contemporane- composition of the solar system, but instead an here show significant 54Cr variability (Table 1)
ously with CAIs (within the uncertainty of our mea- evolved composition inherited after accretion that is not correlated with their ages. Moreover,
surements) and continued for at least ~3 My. and differentiation of its parent body before most chondrules have 54Cr/52Cr ratios that are
The majority of chondrules are believed to core formation. Similar to chondrule C30, three distinct from those of their host chondrites (26).
have formed as dust aggregates of near-solar of the four younger chondrules we analyzed Collectively, these observations indicate that
composition subsequently thermally processed define isochron relationships that project back chondrules from individual chondrite groups
Downloaded from www.sciencemag.org on November 6, 2012
by a flash heating mechanism creating the ig- to Pb isotopic compositions that are more pri- formed from isotopically diverse precursor ma-
neous textures we observe today (10). However, mitive than the current estimate of the solar terial in different regions of the protoplanetary
the presence of relict grains, igneous rims, and system initial Pb composition. This implies that disk and were subsequently transported to the ac-
compound chondrules suggests that some chon- the precursor material of these chondrules, es- cretion regions of their respective parent bodies.
drules may have grown by collisions and re- pecially C3 with its high m value of ~183, were This is consistent with the proposal that radial
melting (22, 23). Given the low solar 238U/204Pb not thermally processed until at or near the transport of material in the protoplanetary disk,
ratio (m) of ~0.15 (24), the Pb isotopic com- derived Pb-Pb age. Thus, the range of ages we such as by radial diffusion (27) and/or stellar
position of a chondrule precursor is not expected observe for individual chondrules reflects pri- outflows (3), was important during the epoch of
to evolve measurably during the lifetime of the mary ages associated with a chondrule-forming CAI and chondrule formation (28).
protoplanetary disk (~3 My) until its m value is event and not secondary disturbance of the Some models of chondrule formation such
increased by Pb devolatilization during ther- Pb-Pb chronometer. Only the youngest chon- as current sheets (29), colliding molten planet-
mal processing. As such, internal isochron rela- drule, C2, yields an isochron that projects to a esimals (30), and recycling of fragmented dif-
tionships of chondrules are expected to project more evolved Pb isotopic composition, requiring ferentiated planetesimals (31) are based on the
back to nonevolved initial Pb isotopic compo- that this inclusion was thermally processed for presumed offset of 1 to 2 My between the for-
sitions, unless an object experienced a complex the first time early enough to have accumulated mation of CAIs and chondrules and therefore
are inconsistent with the contemporaneous for-
Fig. 4. Time scales of sol- mation of CAIs and the oldest chondrules in-
id formation and disk evo- ferred from our study. Moreover, differentiated
lution. The brief formation planetesimals typically have enhanced U/Pb val-
interval of 160,000 years ues (32), which would result in chondrules with
for the CAI-forming event radiogenically evolved initial Pb isotopic com-
is similar to the median positions. However, the initial Pb isotopic com-
lifetimes of class 0 proto- position of individual chondrules suggests that,
stars of ~0.1 to 0.2 My in most cases, chondrule precursors retained the
inferred from astronomical solar U/Pb value up to the chondrule-forming
observation of star-forming event(s).
regions (37). Therefore, Nebular shock waves are currently the fav-
the thermal regime re- ored mechanism for chondrule formation. The pro-
quired for CAI condensa- posed sources of shock waves include infalling
tion may only have existed
clumps of dust and gas (33), bow shocks gen-
during the earliest stages
erated by planetary embryos (34), spiral arms
of disk evolution typified
by high mass accretion rates and clumps in a gravitationally unstable proto-
(~10−5 M☉ year–1) to the planetary disk (35), and x-ray flares (3). Similar
central star. to the colliding planetesimals model, the forma-
tion of chondrules by bow shocks requires at
least 1 My to allow for the growth of planetary
embryos of adequate size and therefore cannot
explain the existence of old chondrules. Accretion-
driven shock models, including models based on
a gravitationally unstable disk, require copious mass
accretion rates to the central star on the order of
~10−5 solar mass (M☉) year–1 to be plausible
(36). Astronomical observations indicate that such
high accretion rates are achieved only in the deeply
embedded class 0 phase of star formation (37),
and such accretion rates can only last for ~0.1 My.
Thus, chondrule formation via accretion-driven
654 2 NOVEMBER 2012 VOL 338 SCIENCE www.sciencemag.org
6. REPORTS
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transient mass-accretion events. Indeed, models
of the innermost structure of protoplanetary disks
predict temperatures in excess of 1400 K within
1 astronomical unit for mass accretion rates as Chloroplast Biogenesis Is Regulated
low as ~10−6 M☉ year−1 (40). Because the con-
servation of energy requires dissipation per unit
of area of the disk that scales as the inverse cube
by Direct Action of the
of the distance from the central star, accretion-
based processes may produce similar thermal re- Ubiquitin-Proteasome System
gimes over a large range of accretion rates, albeit Qihua Ling,* Weihua Huang,*† Amy Baldwin,‡ Paul Jarvis§
at different orbital radii. Whether accretion-based
processes can provide thermal histories for CAIs Development of chloroplasts and other plastids depends on the import of thousands of nucleus-encoded
and chondrules that are consistent with their proteins from the cytosol. Import is initiated by TOC (translocon at the outer envelope of chloroplasts)
heating and cooling rates, as well as the chro- complexes in the plastid outer membrane that incorporate multiple, client-specific receptors. Modulation
nology provided here, requires robust numerical of import is thought to control the plastid’s proteome, developmental fate, and functions. Using forward
simulations of the evolving thermal structure of genetics, we identified Arabidopsis SP1, which encodes a RING-type ubiquitin E3 ligase of the chloroplast
accreting disks. outer membrane. The SP1 protein associated with TOC complexes and mediated ubiquitination of TOC
components, promoting their degradation. Mutant sp1 plants performed developmental transitions that
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www.sciencemag.org SCIENCE VOL 338 2 NOVEMBER 2012 655