1) The document describes an experiment using two-color quantum interference to inject photocurrents in films of the topological insulator Bi2Se3.
2) High-quality Bi2Se3 films were grown by molecular beam epitaxy and characterized using reflection high-energy electron diffraction, X-ray reflectivity, and diffraction.
3) Photocurrents were injected in the Bi2Se3 films using two ultrashort optical pulses at different frequencies, and the emitted terahertz radiation was measured. The injection current followed the expected dependences on the relative phase and irradiances of the optical pulses, confirming the third-order nonlinear optical mechanism.
This document discusses electrospinning as a process for creating nanofibers. It begins with an introduction to nanofibers and electrospinning. The document then describes the electrospinning apparatus and working principle, including how a high voltage is applied to create charged polymer jets that dry into fibers. It discusses how fiber diameter, mesh size, porosity and other variables can be controlled. The document outlines applications of electrospun nanofibers such as air filtration and drug delivery. It concludes by discussing opportunities for further research to optimize electrospinning techniques and fiber properties.
Nanotechnology involves manipulating matter at the nanoscale (1 billionth of a meter) to create new materials and devices. There are two main approaches to synthesizing nano-phase materials: top-down, which breaks down bulk materials into nano sizes, and bottom-up, which builds materials atom by atom. Electrospinning is a commonly used bottom-up technique to produce nanofibers less than 500 nm in diameter for applications such as filters, protective fabrics, and tissue scaffolds. Nanotechnology has applications in fields like electronics, energy, materials, medicine, and textiles. It promises to revolutionize industries and improve lives through targeted drug delivery, artificial organs, stronger/lighter materials, pollution cleanup, and more.
Electrospinning Technique on PEO Nanofibersjosearzon99
This document discusses a study on the effects of a rotating and translating target on the alignment of electrospun nanofibers. The study aimed to determine if using a rotational and translational target during electrospinning would produce more uniformly aligned fibers compared to non-aligned electrospinning. The procedure involved electrospinning nanofibers with and without target rotation/translation. The fibers were then characterized and analyzed to evaluate if rotational electrospinning better aligned the fibers. Future work is proposed to calcine the fibers to isolate palladium shells deposited on them during sputtering, and later determine the fibers' potential for sensor applications.
The document discusses nanofiber technology for protein purification using electrospun nanofibers and simulated moving bed chromatography. Specifically, it notes that electrospun nanofibers can produce high surface area materials allowing for rapid convective flow and high binding capacities. When packed into a filter and used with simulated moving bed chromatography, it allows for continuous high throughput protein purification at lower costs compared to traditional bead-based methods. The technology has potential for scaling up antibody purification for the biopharmaceutical industry.
STUDY OF ABSORPTION IN CARBON NANOTUBE COMPOSITES FROM 1HZ TO 40GHZjmicro
Absorption performances in High Density Polyethylene (HDPE) and polycarbonate (PC) polymer matrices
containing various loads of carbon nanotubes were analysed. It depends on electrical conductivity,
dielectric constant and thickness of the polymer composites. These parameters can be easily controlled.
Significant absorption, which can reach between 60 and 90%, hence occurs at particular combinations of
these last parameters (in a frequency range from 1Hz to GHz). These new results are really useful in
various applications, and are considered in low scale systems as a major technological solution against
electromagnetic interferences.
The document discusses electrospinning, a technique for creating nanofibers. Electrospinning uses high voltage to draw charged polymer solutions or melts into fibers that can be deposited on a collector. Key parameters that affect the electrospinning process and fiber properties are described. Common polymers used in electrospinning are also listed. The document outlines various applications of electrospun nanofibers, including their use in filtration, tissue engineering scaffolds, and drug delivery. Recent research on modifying the surface of electrospun nanofibers to optimize their performance for tissue engineering and controlled drug release is also summarized.
Electrospinning is a nanofiber fabrication technique that uses electrostatic forces to produce fibers with diameters as small as 1 nanometer. The process involves applying a high voltage to a polymer solution or melt, which is extruded through a spinneret to form fibers that are deposited onto a grounded collector. Key parameters that affect fiber morphology include solution properties like concentration and viscosity, as well as process parameters like voltage, flow rate, and working distance. Electrospinning can be used to produce a variety of nanofibers from polymers, ceramics, and composites for applications like filtration, energy storage, and tissue engineering. Scale-up methods involve using multiple spinnerets or continuous systems like rotating drums to produce
This document discusses electrospinning as a process for creating nanofibers. It begins with an introduction to nanofibers and electrospinning. The document then describes the electrospinning apparatus and working principle, including how a high voltage is applied to create charged polymer jets that dry into fibers. It discusses how fiber diameter, mesh size, porosity and other variables can be controlled. The document outlines applications of electrospun nanofibers such as air filtration and drug delivery. It concludes by discussing opportunities for further research to optimize electrospinning techniques and fiber properties.
Nanotechnology involves manipulating matter at the nanoscale (1 billionth of a meter) to create new materials and devices. There are two main approaches to synthesizing nano-phase materials: top-down, which breaks down bulk materials into nano sizes, and bottom-up, which builds materials atom by atom. Electrospinning is a commonly used bottom-up technique to produce nanofibers less than 500 nm in diameter for applications such as filters, protective fabrics, and tissue scaffolds. Nanotechnology has applications in fields like electronics, energy, materials, medicine, and textiles. It promises to revolutionize industries and improve lives through targeted drug delivery, artificial organs, stronger/lighter materials, pollution cleanup, and more.
Electrospinning Technique on PEO Nanofibersjosearzon99
This document discusses a study on the effects of a rotating and translating target on the alignment of electrospun nanofibers. The study aimed to determine if using a rotational and translational target during electrospinning would produce more uniformly aligned fibers compared to non-aligned electrospinning. The procedure involved electrospinning nanofibers with and without target rotation/translation. The fibers were then characterized and analyzed to evaluate if rotational electrospinning better aligned the fibers. Future work is proposed to calcine the fibers to isolate palladium shells deposited on them during sputtering, and later determine the fibers' potential for sensor applications.
The document discusses nanofiber technology for protein purification using electrospun nanofibers and simulated moving bed chromatography. Specifically, it notes that electrospun nanofibers can produce high surface area materials allowing for rapid convective flow and high binding capacities. When packed into a filter and used with simulated moving bed chromatography, it allows for continuous high throughput protein purification at lower costs compared to traditional bead-based methods. The technology has potential for scaling up antibody purification for the biopharmaceutical industry.
STUDY OF ABSORPTION IN CARBON NANOTUBE COMPOSITES FROM 1HZ TO 40GHZjmicro
Absorption performances in High Density Polyethylene (HDPE) and polycarbonate (PC) polymer matrices
containing various loads of carbon nanotubes were analysed. It depends on electrical conductivity,
dielectric constant and thickness of the polymer composites. These parameters can be easily controlled.
Significant absorption, which can reach between 60 and 90%, hence occurs at particular combinations of
these last parameters (in a frequency range from 1Hz to GHz). These new results are really useful in
various applications, and are considered in low scale systems as a major technological solution against
electromagnetic interferences.
The document discusses electrospinning, a technique for creating nanofibers. Electrospinning uses high voltage to draw charged polymer solutions or melts into fibers that can be deposited on a collector. Key parameters that affect the electrospinning process and fiber properties are described. Common polymers used in electrospinning are also listed. The document outlines various applications of electrospun nanofibers, including their use in filtration, tissue engineering scaffolds, and drug delivery. Recent research on modifying the surface of electrospun nanofibers to optimize their performance for tissue engineering and controlled drug release is also summarized.
Electrospinning is a nanofiber fabrication technique that uses electrostatic forces to produce fibers with diameters as small as 1 nanometer. The process involves applying a high voltage to a polymer solution or melt, which is extruded through a spinneret to form fibers that are deposited onto a grounded collector. Key parameters that affect fiber morphology include solution properties like concentration and viscosity, as well as process parameters like voltage, flow rate, and working distance. Electrospinning can be used to produce a variety of nanofibers from polymers, ceramics, and composites for applications like filtration, energy storage, and tissue engineering. Scale-up methods involve using multiple spinnerets or continuous systems like rotating drums to produce
Drug delivery system based on gold nanostarsCarlos Maranje
This document summarizes a student's design of a photodelivery drug system using gold nanostars covered with polyacrylic acid modified with β-cyclodextrin. The system aims to have nanoparticles with strong near-infrared absorption and high light-to-heat conversion. β-cyclodextrin would store the drug (e.g. doxorubicin), and the coating would provide stability. The student's experiments show the system has over 90% drug loading capacity and can release 6% of the drug under near-infrared light irradiation.
Nanofibers are fibers with diameters less than 1000 nanometers. They have a very high surface area to volume ratio and unique physical and chemical properties. Nanofibers can be produced through various methods like melt processing, electrospinning, and interfacial polymerization, with electrospinning being the most common. Electrospinning uses a high voltage electric field to draw charged polymer solutions or melts into fibers that are deposited onto a collector. Nanofibers find applications in areas like drug delivery, wound dressings, tissue engineering scaffolds, filtration, protective clothing, sensors, and energy storage due to their small size and large surface area.
Performance Characteristics of the MIT Epithermal Neutron Irradiation Facilitykent.riley
This document summarizes the performance characteristics of the first fission converter-based epithermal neutron beam (FCB) designed for boron neutron capture therapy (BNCT) at the Massachusetts Institute of Technology (MIT). Key findings include:
1) The FCB provides an epithermal neutron flux of 4.6 × 109 n cm-2 s-1, making it the most intense BNCT source in the world. It achieves low specific photon and fast neutron absorbed doses.
2) Measurements confirm the beam achieves a therapeutic dose rate of 1.7 RBE Gy min-1 at a depth of 97 mm using boronated phenylalanine, with an average therapeutic ratio of
Surface Plasmon Hybridization of Whispering Gallery Mode Microdisk LaserOka Kurniawan
This document summarizes research on using a plasmonic microdisk laser to efficiently generate and couple surface plasmon polaritons. The microdisk laser exhibits high-intensity whispering gallery modes that are hybridized with surface plasmon modes by attaching metal layers. This creates a surface plasmon source with over 20,000 times electric field enhancement. Simulation shows 60% coupling efficiency between the plasmonic microdisk laser and an adjacent metal-insulator-metal waveguide to transport surface plasmon polaritons. The structure could enable both high-speed and miniaturized plasmonic devices and circuits.
LET, Linear Energy Transfer, Relative Biologic Effectiveness, Oxygen enhancement ratio,
Dr. Vandana, KGMU, CSMMU, Lucknow, Radiation Oncology, Radiotherapy
This document discusses several key concepts in radiation oncology:
1. The Law of Bergonie and Tribondeau states that radiosensitivity varies with cell maturation and metabolism, with stem cells being most radiosensitive. Younger and more metabolically active tissues are also more radiosensitive.
2. Factors like linear energy transfer (LET), relative biological effectiveness (RBE), fractionation, and oxygenation level impact radiation response. High LET radiation like alpha particles is more effective due to dense ionization.
3. The oxygen enhancement ratio (OER) compares radiation doses needed under hypoxic vs aerated conditions. It is typically 2.5-3.0 for X-rays but 1 for high
Analysis on The Impact of Reflectance in Optical Fiber Linksijtsrd
An optical fiber link is a part of an optic fiber communication system. Other components of the optic fiber link include the transmitter, connectors, and the receiver. The optical fiber could be single-mode (for long distance transmission) or multi-mode (for short distance transmission). This paper however, majors on the impact of reflectance in the single-mode optical fiber. Reflectance is a hidden threat that increases Bit Error Rate, BER, (rate at which errors occur in transmission system) and reduces system performance if not monitored or controlled. Optical Time Domain Reflectometer (OTDR) was used to measure the reflectance in single-mode fiber. Events measurements in OTDR heavily depend on good reflectance. The OTDR was able to establish the reflectance in every portion of the fiber under test. An average reflectance level of -14.9275 dB of 1550 nm signal over the span length of 20.422 km was achieved which is within the acceptable standard range. Hence, good quality performance transmissions can be achieved along these routes. J. Ilouno | M. Awoji | J. Sani"Analysis on The Impact of Reflectance in Optical Fiber Links" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-2 | Issue-4 , June 2018, URL: http://www.ijtsrd.com/papers/ijtsrd14378.pdf http://www.ijtsrd.com/physics/other/14378/analysis-on-the-impact-of-reflectance-in-optical-fiber-links/j-ilouno
STUDY ON FIBER GRATINGS AND ITS CHARACTERIZATIONDr. Ved Nath Jha
Good potential uses in fiber and fiber lasers have been seen through Random Fiber Gratings (RFGs). However, a quantitative link has never been studied between the RFG's randomness and spectral reaction. This paper first experimentally characterizes two RFGs of varying degrees of randomness by optical frequency reflectometry (OFDR). The high degree of randomness indicates that the grating intensity is limited and the strength variations in spatial domain are large. The experimental findings show. Study establishes the theoretical basis for the optimization configuration and implementation of the long-term fiber grating in the area of fiber optics sensing and communication.
The document discusses applications of nanofibers in tissue engineering. It describes three main techniques to produce nanofibers - self-assembly, phase separation, and electrospinning. Several natural and synthetic polymers that can be used to create nanofibers are discussed, including collagen, elastin, polyglycolic acid and polylactic acid. The document also outlines how nanofibers can be applied as scaffolds in tissue engineering and their ability to mimic natural extracellular matrix fibers at the nanoscale level.
It contains some basic concept of radiobiology like linear energy transfer , relative biologic effectiveness and oxygen enhancement ratio and their interrelationship
X-rays and neutrons interact differently with biological material based on their ionizing ability. X-rays produce sparse ionization while neutrons produce more dense ionization. Linear energy transfer (LET) quantifies the energy deposited over track length and is used to compare radiation types. Higher LET radiation like alpha particles are more biologically effective due to producing denser ionization over shorter tracks. The relative biological effectiveness (RBE) of radiation depends on factors like dose, fractions, and biological system and is calculated as the ratio of doses needed for equal effect compared to a reference radiation like x-rays. RBE increases with increasing LET up to 100keV/μm then decreases with further increases in LET. Oxygen enhancement ratio (
Beam generation and planar imaging at energies below 2.40 MeV with carbon and...David Parsons
This study investigated generating low-energy x-ray beams below 2.40 MeV using carbon and aluminum linear accelerator targets for improved planar imaging quality. The authors were able to lower the incident electron energy to between 1.90 and 2.35 MeV by adjusting the bending magnet current on a Varian linac. They measured an increase in contrast-to-noise ratio of cortical bone of 3.7-7.4 times compared to a standard 6 MV therapy beam, with only a slight degradation of spatial resolution at lower energies. Monte Carlo simulations showed that 46-54% of the generated photons were in the diagnostic energy range.
20180323 electrospinning and polymer nanofibersTianyu Liu
Electrospinning uses electric fields to produce polymer nanofibers. It works by applying a high voltage to a polymer solution, forming a Taylor cone and whipping jet that dries into nanofibers collected on a grounded target. Key parameters that affect fiber diameter are polymer concentration and viscosity, applied voltage, injection rate, and collector pattern. Electrospun nanofibers have various applications including tissue engineering scaffolds, filtration membranes, sensors, and energy storage devices like batteries.
Comparison of electrical, optical and plasmonic on chip interconnectsHarish Peta
This document compares electrical, optical, and plasmonic interconnects for on-chip communication based on delay and energy. Plasmonic interconnects can be used for local connections using metal structures that support surface plasmon polaritons for propagation. Optical interconnects are better suited for global connections due to their higher bandwidth compared to electrical interconnects. The document analyzes the delay and energy of different interconnect types and defines a critical length beyond which optical interconnects perform better than electrical interconnects.
Temperature Dependence of the Band-Edge Transitions of ZnCdBeSeOleg Maksimov
This study characterized the temperature dependence of band-edge transitions in three ZnCdBeSe films with varying concentrations of beryllium (Be) using contactless electroreflectance (CER) and piezoreflectance (PzR) measurements from 15-450K. The CER and PzR spectra showed doublet features near the band edge, indicating light-hole and heavy-hole excitonic transitions. Comparing the relative intensities of the PzR and CER spectra allowed identification of the transitions. Analysis of the temperature dependence provided information on how the energy and broadening of the transitions varied with temperature and Be concentration. The results showed that incorporating Be effectively reduced the rate of temperature variation of the energy
NOVEL ELECTROSPUN NANOFIBERS IN DRUG DELIVERYVenkatesh Reddy
This document presents information on electrospinning nanofibers for drug delivery applications. It defines nanofibers as solid fibers with diameters less than 100nm. The electrospinning process uses electrostatic and mechanical forces to spin polymer fibers into nanofibers. It requires a high voltage supply, syringe with needle, and metal collector. Both natural and synthetic polymers can be used to form nanofibers with properties like large surface area and small diameter that make them useful for controlled drug release over long periods of time and targeting specific body areas. The document discusses using electrospun nanofibers to alter drug dissolution rates and protect drugs from decomposition in the body.
This document describes how researchers used optical tweezers to stretch and measure the elasticity of DNA strands. Optical tweezers use refracted and reflected laser light to apply tiny forces (piconewtons) to manipulate microscopic objects like DNA. The researchers attached one end of a DNA strand to a bead trapped by the tweezers and the other end to a movable stage. By varying the stage position and measuring the counteracting force from the tweezers, they could determine how much force was required to stretch the DNA and analyze its mechanical properties.
Content
■ History of Nanofibers.
■ What is Nanofibers
■ Properties of Nanofibers
■ Production of Nanofibers
■ Advantage and Disadvantage of Nanofibers
■ Application of nanofibers
DEVELOPMENT OF OPTICAL PARAMETER CALCULATIONS OF THE PROBES IN WATERDr. Ved Nath Jha
This document describes the development of optical parameter calculations for probes used in water sensing. Three probes (a, b, c) of varying nanoparticle size were developed and their plasma and collision wavelengths were calculated based on experimental measurements in water and air. The probes showed decreasing collision wavelength but nearly constant plasma wavelength with increasing nanoparticle size. Models were developed to calculate output intensity based on the dielectric constant of the surrounding medium. Distinct dips in output intensity correlated with different dielectric components when mixtures were tested, showing ability to detect multiple impurities simultaneously. The probes function best for dielectric constants between 1.4-2.0 and silver nanoparticles provide sensitivity towards targeted impurities in water quality monitoring.
An over massive_black_hole_in_a_typical_star_forming_galaxy_2_billion_years_a...Sérgio Sacani
Uma equipe internacional de astrofísicos, liderada por Benny Trakhtenbrot, um pesquiador no Instituto para Astronomia de Zurique ETH, descobriu um gigantesco buraco negro em uma galáxia outrora normal, usando o telescópio Keck I de 10 metros de diâmetro do Observatório W. M. Keck no Havaí. A equipe, conduzindo uma pesquisa rotineira de caça por antigos e massivos buracos negros, foi surpreendida quando encontrou um com uma massa mais de 7 bilhões de vezes a massa do Sol, figurando assim entre os buracos negros mais massivos já descobertos. E pelo fato da galáxia onde ele foi descoberto ser uma galáxia típica em tamanho, o estudo levantou algumas questões sobre as premissas prévias no desenvolvimento das galáxias. As descobertas foram publicadas na revista Science.
Os dados, coletado com o novíssimo instrumento MOSFIRE do observatório Keck, revelou um gigantesco buraco negro na galáxia chamada CID-947 que está a 11 bilhões de anos-luz de distância da Terra. A incrível sensibilidade do MOSFIRE acoplada ao maior telescópio óptico/infravermelho do mundo permitiu que os cientistas pudessem observar e caracterizar esse buraco negro como ele era quando o universo tinha somente 2 bilhões de anos de vida, ou seja, apenas 14% da sua idade atual.
Ainda mais surpreendente que a massa recorde do buraco negro, foi a massa relativamente comum da galáxia que o contém.
A maior parte das galáxias abrigam buracos negros com massas de menos de 1% da massa da galáxia. Na CID 947, a massa do buraco negro é 10% da massa total da galáxia hospedeira. Devido a essa grande disparidade, a equipe deduziu que esse buraco negro cresceu tão rapidamente que a galáxia não foi capaz de pará-lo, levantando assim uma questão sobre o pensamento prévio na co-evolução de galáxias e de seus buracos negros centrais.
1. The document describes a microstrip diplexer design inspired by electromagnetically induced transparency (EIT). EIT allows wave propagation within a medium's absorption spectrum through quantum interference between atomic transition pathways.
2. The proposed diplexer exploits an analogous EIT-like interference mechanism using pairs of unequal open-circuit stubs on a microstrip transmission line. This creates separate transparent passbands for diplexing action at different frequencies.
3. A prototype was fabricated at C-band frequencies with passbands centered at 4.6 GHz and 5.5 GHz, achieving insertion losses of 0.59 dB and 0.61 dB respectively. High isolation of 40 dB was observed between the passbands due
Electrostatic Edge Plasma Turbulence in the Uragan-3M torsatronAleksey Beletskii
The document summarizes electrical probe measurements of electrostatic edge plasma turbulence in the Uragan-3M torsatron. Key findings include: (1) plasma density fluctuations in the scrape-off layer and divertor region exhibit a spectral splitting depending on position relative to the last closed magnetic surface; (2) formation of radial electric field shear decreases turbulence and anomalous transport at the plasma edge; (3) turbulence data from Uragan-3M is included in the International Stellarator/Heliotron Edge Turbulence Database. Future work involves direct measurements of plasma potential and electron temperature fluctuations using a new combined probe.
Drug delivery system based on gold nanostarsCarlos Maranje
This document summarizes a student's design of a photodelivery drug system using gold nanostars covered with polyacrylic acid modified with β-cyclodextrin. The system aims to have nanoparticles with strong near-infrared absorption and high light-to-heat conversion. β-cyclodextrin would store the drug (e.g. doxorubicin), and the coating would provide stability. The student's experiments show the system has over 90% drug loading capacity and can release 6% of the drug under near-infrared light irradiation.
Nanofibers are fibers with diameters less than 1000 nanometers. They have a very high surface area to volume ratio and unique physical and chemical properties. Nanofibers can be produced through various methods like melt processing, electrospinning, and interfacial polymerization, with electrospinning being the most common. Electrospinning uses a high voltage electric field to draw charged polymer solutions or melts into fibers that are deposited onto a collector. Nanofibers find applications in areas like drug delivery, wound dressings, tissue engineering scaffolds, filtration, protective clothing, sensors, and energy storage due to their small size and large surface area.
Performance Characteristics of the MIT Epithermal Neutron Irradiation Facilitykent.riley
This document summarizes the performance characteristics of the first fission converter-based epithermal neutron beam (FCB) designed for boron neutron capture therapy (BNCT) at the Massachusetts Institute of Technology (MIT). Key findings include:
1) The FCB provides an epithermal neutron flux of 4.6 × 109 n cm-2 s-1, making it the most intense BNCT source in the world. It achieves low specific photon and fast neutron absorbed doses.
2) Measurements confirm the beam achieves a therapeutic dose rate of 1.7 RBE Gy min-1 at a depth of 97 mm using boronated phenylalanine, with an average therapeutic ratio of
Surface Plasmon Hybridization of Whispering Gallery Mode Microdisk LaserOka Kurniawan
This document summarizes research on using a plasmonic microdisk laser to efficiently generate and couple surface plasmon polaritons. The microdisk laser exhibits high-intensity whispering gallery modes that are hybridized with surface plasmon modes by attaching metal layers. This creates a surface plasmon source with over 20,000 times electric field enhancement. Simulation shows 60% coupling efficiency between the plasmonic microdisk laser and an adjacent metal-insulator-metal waveguide to transport surface plasmon polaritons. The structure could enable both high-speed and miniaturized plasmonic devices and circuits.
LET, Linear Energy Transfer, Relative Biologic Effectiveness, Oxygen enhancement ratio,
Dr. Vandana, KGMU, CSMMU, Lucknow, Radiation Oncology, Radiotherapy
This document discusses several key concepts in radiation oncology:
1. The Law of Bergonie and Tribondeau states that radiosensitivity varies with cell maturation and metabolism, with stem cells being most radiosensitive. Younger and more metabolically active tissues are also more radiosensitive.
2. Factors like linear energy transfer (LET), relative biological effectiveness (RBE), fractionation, and oxygenation level impact radiation response. High LET radiation like alpha particles is more effective due to dense ionization.
3. The oxygen enhancement ratio (OER) compares radiation doses needed under hypoxic vs aerated conditions. It is typically 2.5-3.0 for X-rays but 1 for high
Analysis on The Impact of Reflectance in Optical Fiber Linksijtsrd
An optical fiber link is a part of an optic fiber communication system. Other components of the optic fiber link include the transmitter, connectors, and the receiver. The optical fiber could be single-mode (for long distance transmission) or multi-mode (for short distance transmission). This paper however, majors on the impact of reflectance in the single-mode optical fiber. Reflectance is a hidden threat that increases Bit Error Rate, BER, (rate at which errors occur in transmission system) and reduces system performance if not monitored or controlled. Optical Time Domain Reflectometer (OTDR) was used to measure the reflectance in single-mode fiber. Events measurements in OTDR heavily depend on good reflectance. The OTDR was able to establish the reflectance in every portion of the fiber under test. An average reflectance level of -14.9275 dB of 1550 nm signal over the span length of 20.422 km was achieved which is within the acceptable standard range. Hence, good quality performance transmissions can be achieved along these routes. J. Ilouno | M. Awoji | J. Sani"Analysis on The Impact of Reflectance in Optical Fiber Links" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-2 | Issue-4 , June 2018, URL: http://www.ijtsrd.com/papers/ijtsrd14378.pdf http://www.ijtsrd.com/physics/other/14378/analysis-on-the-impact-of-reflectance-in-optical-fiber-links/j-ilouno
STUDY ON FIBER GRATINGS AND ITS CHARACTERIZATIONDr. Ved Nath Jha
Good potential uses in fiber and fiber lasers have been seen through Random Fiber Gratings (RFGs). However, a quantitative link has never been studied between the RFG's randomness and spectral reaction. This paper first experimentally characterizes two RFGs of varying degrees of randomness by optical frequency reflectometry (OFDR). The high degree of randomness indicates that the grating intensity is limited and the strength variations in spatial domain are large. The experimental findings show. Study establishes the theoretical basis for the optimization configuration and implementation of the long-term fiber grating in the area of fiber optics sensing and communication.
The document discusses applications of nanofibers in tissue engineering. It describes three main techniques to produce nanofibers - self-assembly, phase separation, and electrospinning. Several natural and synthetic polymers that can be used to create nanofibers are discussed, including collagen, elastin, polyglycolic acid and polylactic acid. The document also outlines how nanofibers can be applied as scaffolds in tissue engineering and their ability to mimic natural extracellular matrix fibers at the nanoscale level.
It contains some basic concept of radiobiology like linear energy transfer , relative biologic effectiveness and oxygen enhancement ratio and their interrelationship
X-rays and neutrons interact differently with biological material based on their ionizing ability. X-rays produce sparse ionization while neutrons produce more dense ionization. Linear energy transfer (LET) quantifies the energy deposited over track length and is used to compare radiation types. Higher LET radiation like alpha particles are more biologically effective due to producing denser ionization over shorter tracks. The relative biological effectiveness (RBE) of radiation depends on factors like dose, fractions, and biological system and is calculated as the ratio of doses needed for equal effect compared to a reference radiation like x-rays. RBE increases with increasing LET up to 100keV/μm then decreases with further increases in LET. Oxygen enhancement ratio (
Beam generation and planar imaging at energies below 2.40 MeV with carbon and...David Parsons
This study investigated generating low-energy x-ray beams below 2.40 MeV using carbon and aluminum linear accelerator targets for improved planar imaging quality. The authors were able to lower the incident electron energy to between 1.90 and 2.35 MeV by adjusting the bending magnet current on a Varian linac. They measured an increase in contrast-to-noise ratio of cortical bone of 3.7-7.4 times compared to a standard 6 MV therapy beam, with only a slight degradation of spatial resolution at lower energies. Monte Carlo simulations showed that 46-54% of the generated photons were in the diagnostic energy range.
20180323 electrospinning and polymer nanofibersTianyu Liu
Electrospinning uses electric fields to produce polymer nanofibers. It works by applying a high voltage to a polymer solution, forming a Taylor cone and whipping jet that dries into nanofibers collected on a grounded target. Key parameters that affect fiber diameter are polymer concentration and viscosity, applied voltage, injection rate, and collector pattern. Electrospun nanofibers have various applications including tissue engineering scaffolds, filtration membranes, sensors, and energy storage devices like batteries.
Comparison of electrical, optical and plasmonic on chip interconnectsHarish Peta
This document compares electrical, optical, and plasmonic interconnects for on-chip communication based on delay and energy. Plasmonic interconnects can be used for local connections using metal structures that support surface plasmon polaritons for propagation. Optical interconnects are better suited for global connections due to their higher bandwidth compared to electrical interconnects. The document analyzes the delay and energy of different interconnect types and defines a critical length beyond which optical interconnects perform better than electrical interconnects.
Temperature Dependence of the Band-Edge Transitions of ZnCdBeSeOleg Maksimov
This study characterized the temperature dependence of band-edge transitions in three ZnCdBeSe films with varying concentrations of beryllium (Be) using contactless electroreflectance (CER) and piezoreflectance (PzR) measurements from 15-450K. The CER and PzR spectra showed doublet features near the band edge, indicating light-hole and heavy-hole excitonic transitions. Comparing the relative intensities of the PzR and CER spectra allowed identification of the transitions. Analysis of the temperature dependence provided information on how the energy and broadening of the transitions varied with temperature and Be concentration. The results showed that incorporating Be effectively reduced the rate of temperature variation of the energy
NOVEL ELECTROSPUN NANOFIBERS IN DRUG DELIVERYVenkatesh Reddy
This document presents information on electrospinning nanofibers for drug delivery applications. It defines nanofibers as solid fibers with diameters less than 100nm. The electrospinning process uses electrostatic and mechanical forces to spin polymer fibers into nanofibers. It requires a high voltage supply, syringe with needle, and metal collector. Both natural and synthetic polymers can be used to form nanofibers with properties like large surface area and small diameter that make them useful for controlled drug release over long periods of time and targeting specific body areas. The document discusses using electrospun nanofibers to alter drug dissolution rates and protect drugs from decomposition in the body.
This document describes how researchers used optical tweezers to stretch and measure the elasticity of DNA strands. Optical tweezers use refracted and reflected laser light to apply tiny forces (piconewtons) to manipulate microscopic objects like DNA. The researchers attached one end of a DNA strand to a bead trapped by the tweezers and the other end to a movable stage. By varying the stage position and measuring the counteracting force from the tweezers, they could determine how much force was required to stretch the DNA and analyze its mechanical properties.
Content
■ History of Nanofibers.
■ What is Nanofibers
■ Properties of Nanofibers
■ Production of Nanofibers
■ Advantage and Disadvantage of Nanofibers
■ Application of nanofibers
DEVELOPMENT OF OPTICAL PARAMETER CALCULATIONS OF THE PROBES IN WATERDr. Ved Nath Jha
This document describes the development of optical parameter calculations for probes used in water sensing. Three probes (a, b, c) of varying nanoparticle size were developed and their plasma and collision wavelengths were calculated based on experimental measurements in water and air. The probes showed decreasing collision wavelength but nearly constant plasma wavelength with increasing nanoparticle size. Models were developed to calculate output intensity based on the dielectric constant of the surrounding medium. Distinct dips in output intensity correlated with different dielectric components when mixtures were tested, showing ability to detect multiple impurities simultaneously. The probes function best for dielectric constants between 1.4-2.0 and silver nanoparticles provide sensitivity towards targeted impurities in water quality monitoring.
An over massive_black_hole_in_a_typical_star_forming_galaxy_2_billion_years_a...Sérgio Sacani
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Similar to Bas et al. - 2015 - Coherent control of injection currents in high-qua (20)
Bas et al. - 2015 - Coherent control of injection currents in high-qua
1. Coherent control of injection currents in high-quality films of Bi2Se3
D. A. Bas, K. Vargas-Velez, S. Babakiray, T. A. Johnson, P. Borisov, T. D. Stanescu, D. Lederman, and A. D.
Bristow
Citation: Applied Physics Letters 106, 041109 (2015); doi: 10.1063/1.4907004
View online: http://dx.doi.org/10.1063/1.4907004
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/106/4?ver=pdfcov
Published by the AIP Publishing
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2. Coherent control of injection currents in high-quality films of Bi2Se3
D. A. Bas, K. Vargas-Velez, S. Babakiray, T. A. Johnson, P. Borisov, T. D. Stanescu,
D. Lederman, and A. D. Bristowa)
Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506-6315,
USA
(Received 24 December 2014; accepted 19 January 2015; published online 28 January 2015)
Films of the topological insulator Bi2Se3 are grown by molecular beam epitaxy with in-situ
reflection high-energy electron diffraction. The films are shown to be high-quality by X-ray reflec-
tivity and diffraction and atomic-force microscopy. Quantum interference control of photocurrents
is observed by excitation with harmonically related pulses and detected by terahertz radiation. The
injection current obeys the expected excitation irradiance dependence, showing linear dependence
on the fundamental pulse irradiance and square-root irradiance dependence of the frequency-
doubled optical pulses. The injection current also follows a sinusoidal relative-phase dependence
between the two excitation pulses. These results confirm the third-order nonlinear optical origins of
the coherently controlled injection current. Experiments are compared to a tight-binding band
structure to illustrate the possible optical transitions that occur in creating the injection current.
VC 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4907004]
Bi2Se3 is a well-known thermoelectric material1
and
currently of great interest in condensed matter physics
because the surface states exhibit massless Dirac dispersions
in the gaps between the bulk valence and conduction bands.2
The surface states have an electron spin structure defined by
strong spin-orbit coupling which locks the spin vector per-
pendicular to the momentum vector.3,4
Fundamental proper-
ties of Bi2Se3 have been widely investigated because of the
potential opportunities for developing spintronic and opti-
cally controlled devices.
A great deal of attention has been paid to the light-matter
interactions because the surface states of Bi2Se3 are obscured
in electrical measurements, due to inherent n-doping in the
as-grown material. This means that the Fermi level is in the
bulk conduction band above the 0.3-eV band gap. Despite
this fact, optical measurements have been widely explored in
the near infrared, revealing anomalous absorption coefficients
with film thickness,5
strong coupling between electrons and
phonons,6,7
and a second set of massless surface states at
about 1.7 eV above the commonly studied Dirac point below
the Fermi level.8
These developments, among others,9
indi-
cate that near-infrared optical interactions provide mecha-
nisms that can be exploited for photonic devices and also
access surface-surface state excitations. In which case, cou-
pling of optical radiation to inject and control photocurrents
is then relevant for the performance of this material system
and coupling to the all-important surface states.
Photocurrents in Bi2Se3 have been predicted10
and
measured11
using circular polarization, through the circular
photogalvanic effect. Experimental studies have been per-
formed in exfoliated Bi2Se3 patterned with contacts that are
sensitive to both photocurrents and photo-thermal currents.
Nonetheless, this study has demonstrated that photocurrents
can indeed be controlled. A more discrete scheme has been
proposed for coherent control of the surface states using two-
color quantum interference.12
Quantum interference uses
harmonically related pulses to link the same initial and final
states via single and two-photon absorption, such that it is a
quantum analogue of the classical Young’s double slit
experiment. The two-color proposal is based on undoped
Bi2Se3 where an injection current is created by quantum in-
terference control of carriers being promoted from below the
Dirac point to above it. In order to achieve this experimen-
tally, mid-infrared light pulses would be required to impinge
as-grown Bi2Se3 devices with adjustable Fermi levels,
through precise gate-voltage control. Alternatively, one
could exploit surface-state to surface-state transitions from
the well-known Dirac cone to the newly discovered Dirac
cone at higher energies. To date, these transitions have gen-
erally not been factored into many of the optical measure-
ments performed with commercially available near-infrared
lasers, despite the propensity with which they have been
used. One exception is the investigation of carrier dynamics
by differential reflection.13
Here, we demonstrate the use of the two-color excitation
scheme14
to inject ballistic photocurrents in high-quality
Bi2Se3 films. We also show that the currents can be con-
trolled by the relative phase between the fundamental and
frequency doubled excitation pulses. Moreover, we confirm
that the injection current follows the expected dependences
on irradiance of the two excitation pulses.
Bi2Se3 films of various thickness were grown by molec-
ular beam epitaxy15
on double-side polished 0.5-mm Al2O3
(0001) substrates by a two-step process.16
In the first step,
three quintuple layers (QLs) were grown at 140
C to help
deposition of the film with the correct stoichiometry. The re-
mainder of the film is grown in a second step at a tempera-
ture of 275
C to produce a smoother film. Figure 1(a) shows
the oscillations of layer growth during the high-temperature
growth stage, monitored by the in-situ reflection high-energy
electron diffraction (RHEED). The inset of the figure shows
the striping associated with a high-quality film. RHEEDa)
E-mail: alan.bristow@mail.wvu.edu
0003-6951/2015/106(4)/041109/4/$30.00 VC 2015 AIP Publishing LLC106, 041109-1
APPLIED PHYSICS LETTERS 106, 041109 (2015)
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3. oscillations confirm growth of the 12 additional QLs of
Bi2Se3 to form a 15-QL thick sample.
It is suspected that selenium vacancies17,18
quickly alter
the surface potential and subsequently lead to oxidation
when exposed to air. Consequently, a 10-nm thick MgF2 cap-
ping layer is sputtered onto the samples without removing
them from the growth chamber. The result is an encapsulated
and highly stable film of Bi2Se3. A schematic diagram of the
sample structure is shown in the inset of Fig. 2.
Bi2Se3 film thicknesses were then confirmed with X-ray
reflectivity (XRR); see Fig. 1(b). Fitting the XRR pattern
indicates roughness of 0.2 nm. Fitting of the XRR data is per-
formed using the open-source program GenX. The inset
shows an atomic force micrograph of the Bi2Se3 film with
MgF2 layer. The triangles reveal the expected degree of dis-
locations in the Bi2Se3 film. Figure 1(c) shows X-ray diffrac-
tion (XRD), which is used to determine the degree of the
out-of-plane disorder. The 003 XRD Bragg peak observed at
low angle corresponds to that observed in the XRR data.
Overall, characterization indicates high-quality films with
which to perform optical measurements.
Figure 2 shows the experimental setup for the current
injection measurements. A laser amplifier system with optical
parametric amplifier (OPA) provides $80-fs pulses at a reple-
tion rate of 1 kHz. Signal pulses from the OPA are centered
at 1540 nm (0.8 eV). A b-barium borate crystal frequency
doubles the fundamental pulses, generating second-harmonic
pulses at 770 nm (1.6 eV). These fundamental (x) and
frequency-doubled (2x) pulses feed a two-color Mach-
Zehnder interferometer that allows for independent control of
the phase and polarization for each color. The two colors are
set to collinear polarization and their time delay is adjusted to
be close to the center of their envelopes, as measured with an
interferometric cross-correlation. Measurements presented
here are performed on the 15-QL thick Bi2Se3 sample at nor-
mal incidence. Measurements have also been performed on
samples ranging from 6 QL to 40 QL showing qualitatively
consistent behavior.
The acceleration of charge in the production of the pho-
tocurrent on a picosecond timescale re-radiates light at tera-
hertz (THz) frequencies.19,20
The sample is oriented such
FIG. 1. (a) Reflection high-energy electron diffraction during the second
growth stage of the Bi2Se3 film. The oscillations indicate growth of 12 quin-
tuple layers (QL) in the formation of a 15-QL sample. [1 QL is approxi-
mately 1 nm]. The inset shows clean stripes indicating good sample quality.
(b) X-ray reflection of the 15-QL sample. The inset shows an atomic force
micrograph of the sample. (c) Out-of-plane X-ray diffraction showing fea-
tures from the substrate and Bi2Se3 film.
FIG. 2. Experimental setup of the all-optical injection current excitation and
detection scheme. BBO ¼ beta-barium borate crystal, PBC ¼ polarization
beam cube, k/2 ¼ half-wave plate, M ¼ mirror, D/ ¼ relative phase between
fundamental (x), second-harmonic (2x) pulses, HCM ¼ hot-cold mirror,
u ¼ azimuthal angle, LPF ¼ low-pass filter, EOX ¼ electro-optic sampling
crystal, k/4 ¼ quarter-wave plate, WP ¼ Wollaston prism, A-B ¼ balanced
detection signal feed to lock-in amplifier. The top inset shows the structure
of the sample. The lower inset shows the band structure for a slab of Bi2Se3.
041109-2 Bas et al. Appl. Phys. Lett. 106, 041109 (2015)
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4. that the optical pulses transmit through the sapphire substrate
before they arrive at the Bi2Se3 film, so as to not distort the
emitted THz radiation.21
The THz radiation is collected
using off-axis parabolic mirrors and focused onto a 1-mm
thick electro-optic crystal (ZnTe), which is gated by an 80-fs
pulse from the laser amplifier. The quasi-static electric field
of the THz induces birefringence in the ZnTe that is seen by
the gate pulse and measured by projecting the orthogonal
polarization components onto balanced photodetectors.22
The signal is extracted using lock-in detection referenced to
a mechanical chopper placed close to the laser source, which
modulates the light at 250 Hz. The THz signal is mapped out
in the time domain by varying the relative time delay
between the emitted THz and the gate pulse.
Figure 3(a) shows THz transients recorded for two exci-
tation conditions of the relative phase (D/ ¼ 2/x À /2x)
between the x and 2x optical pulses. It can be seen that for
an excitation condition of D/ ¼ 3p/2 the transient has the op-
posite sign to that for D/ ¼ p/2. Figure 3(b) shows a sinusoi-
dal dependence of the THz amplitude versus D/, measured
at the peak of the THz transient indicated by the dashed
vertical line in Fig. 3(a). In Fig. 3(b) a slight offset from zero
is observed indicating that there exists a weak background
that is phase independent and results from excitation due to
only one pulse.
Figure 3(c) shows the dependence of the emitted THz
amplitude on irradiance (or average power) of one excitation
pulse while holding the other constant and vice versa. Fixing
the average power of the x pulse and varying the average
power of the 2x pulse results in a sub-linear slope on the
log-log plot, with a ͱI2x dependence. In this case, the THz
amplitude scales because of single-photon absorption of the
2x pulse. In contrast, fixing the average power of the 2x
pulse and varying the average power of the x pulse results in
a linear slope, with an Ix dependence. In this case, the THz
amplitude scales due to two-photon absorption of the x
pulse. Overall, the emitted field amplitude of the THz signal
follows a ͱI3
(or I1.5
) dependence, confirming that it is gov-
erned by a third-order nonlinear optical process.
The relative-phase dependence and average-power de-
pendence of the emitted THz signals are the expected signa-
tures of a signal derived from an injection current.23
Injection
currents arise from an imbalance of the total number of car-
riers excited to positive and negative states in k-space. The net
momentum is equivalent to excitation of a ballistic photocur-
rent. In this all-optical method of injecting charge currents,
the emitted THz follows the derivative of the injection current
Ji, such that dJi=dt ¼ 2gijklð0; x; x; À2xÞjEx
jkj2
E2x
l sin D/,
where gijkl is a fourth-rank tensor related to the imaginary part
of v(3)
, Ex
jk is the x electric field, E2x
l is the 2x electric field,
and i; j; k, and l are numerical indices.24
Using the above
equation, the relative-phase dependence and average power-
dependences have been fit, shown as solid lines in Figs. 3(b)
and 3(c) respectively. Overall, the theoretical comparison
qualitatively fits the experimental data well. At present, quan-
titative analysis cannot be performed because little is known
about the nonlinear absorption coefficients for this material
due to saturable absorption.9
Nonetheless, theoretical verifica-
tion of the irradiance and relative phase dependence exclude
other THz generation processes such as optical rectification22
and shift currents.20
Third-order nonlinear processes are expected from all
materials and injection currents have been observed in a
range of solids, including unbiased and unstrained silicon,14
direct-gap GaAs,19
nanowires,25
and graphene.26
The pro-
cess in Bi2Se3 may be similar to that in graphene if Dirac
surface states are involved. In which case, quantum interfer-
ence between single and two-photon absorption at 2x occurs
in the presence of simultaneous single-photon absorption of
the x pulse. In graphene, the absorption at x does not affect
the injection current, as would be expected in this case as
well.
The inset of Fig. 2 shows a band structure for a 15-QL
Bi2Se3 thin film calculated using a phenomenological tight-
binding model, based on eight bands to capture both sets of
surface states and Dirac cones. The parameters are optimized
for a bulk system using results from local-density approxi-
mation calculations27,28
and two-photon photoemission
measurements.8
Confinement-induced bands are determined
by solving the model in the slab geometry. The 2x frequency
is also illustrated and is commensurate with excitations from
FIG. 3. (a) Terahertz (THz) transients recorded with relative phase condi-
tions between the x and 2x excitation pulses of p/2 and 3p/2. (b) Phase de-
pendence recorded at the peak of the THz transient indicated in (a). (c)
Average power (or irradiance) dependence of the x and 2x excitation pulses
individually, while fixing the average power (or irradiance) of the other.
041109-3 Bas et al. Appl. Phys. Lett. 106, 041109 (2015)
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5. the surface states near the C-point of the band structure
below the Fermi surface to states in the newly discovered set
of surface states at close to 1.7 eV.
At the wavelength of excitation, transitions depend on
the character of the bulk and surface states. There are a
variety of transitions that include surface, bulk, and both
types of states. Indeed, the surface-surface transitions and
bulk-bulk transitions should have very different characteris-
tics. Moreover, bulk-surface or surface-bulk transitions lead
to a charge displacement in the thin films. Finally, in thin
films confinement can lead to new bands in the band struc-
ture drastically changing the ratio of surface and bulk states
suitable for optical transitions.29
In summary, Bi2Se3 films have been grown to sufficient
quality that injection currents have been observed and con-
trolled using all-optical methods. All-optical methods of
charge current excitation and detection are non-invasive and
avoid problems with contacts, such as local modification of
band structures and slow read-outs that can confuse current
signals. The ability to inject and control these photocurrents
offers a powerful method for characterization of topological
insulator materials based on as-grown Bi2Se3.
The authors wish to thank John Sipe and Rodrigo Muniz
for useful discussions. This work was supported by the
West Virginia Higher Education Policy Commission
(HEPC.dsr.12.29) and WVU Shared Research Facilities.
K.V.V. was supported by the National Science Foundation
through the Research Experience for Undergraduates program
(DMR-1262075).
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