The document summarizes research on the optical properties of molecular beam epitaxy grown (InGa)MnAs thin films with varying Mn concentration. Spectroscopic ellipsometry was used to determine the dielectric functions of the films. Analysis showed the fundamental band gap energy (E0 critical point) blueshifted with increasing Mn concentration, while the E1 critical point showed a redshift. This indicates the electronic structure is changing with Mn incorporation. Specifically, the band structure transitions in the Brillouin zone are affected by the Mn doping level in this quaternary semiconductor system.
48 Measurement of the Σ beam asymmetry for the ω photo-production off the pro...Cristian Randieri PhD
Measurement of the Σ beam asymmetry for the ω photo-production off the proton and the neutron at GRAAL - June 2013
di V. Vegna, A. D'Angelo, O. Bartalini, V. Bellini, J. P. Boquet, M. Capogni, L. E. Casano, M. Castoldi, F. Curciarello, V. De Leo, J. P. Didelez, R. Di Salvo, A. Fantini, D. Franco, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, A. Lapik, P. Levi Sandri, A. Lleres, F. Mammoliti, G. Mandaglio, M. Manganaro, D. Moricciani, A. Mushkarenkov, V. Nedorezov, C. Randieri, D. Rebreyend, N. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, I. Zonta (2013)
Abstract
We report on new measurements of the beam asymmetry for ω photo-production on proton and neutron in Hydrogen and Deuterium targets from the GRAAL collaboration. The beam asymmetry values are extracted from the reaction threshold (E = 1.1 GeV in the free nucleon kinematics) up to 1.5 GeV of incoming photon energy. For the first time both the radiative and the three- pion decay channels are simultaneously investigated on the free proton. Results from the two decay channels are in agreement and provide important constraints for the determination of resonant state contributions to the ω production mechanism. First experimental results on the deuteron allow the extraction of the _ beam asymmetry on quasi-free nucleons. Comparison of the results for free and quasi-free kinematics on the proton shows a generally reasonable agreement, similar to the findings in pseudo-scalar meson photo-production reactions. For the first time measurements on quasi-free neutrons are available, showing that both the strength and the angular distributions of the beam asymmetry are sensibly different from the results on the proton target.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Molecular dynamics (MD) simulations calculate particle trajectories by integrating Newton's equations of motion. This document discusses the history and basic principles of MD, force fields, the NAMD simulation package, and applications. NAMD is a parallelized MD program for biomolecular simulations that uses spatial decomposition and multithreading. It supports features like CHARMM force fields, ensembles, and interactive modeling with VMD for structure visualization. MD simulations are useful for modeling protein structures, comparing protein templates, and predicting protein behavior through refinement of simulation approaches.
This document discusses using density functional theory with different basis sets (Gaussian, plane waves, numerical) to calculate exchange coupling constants in transition metal complexes. It compares the accuracy and reliability of these approaches by calculating exchange coupling constants and spin distributions for three test complexes. The plane wave and numerical basis set approaches are found to be accurate alternatives to the more established Gaussian basis functions for calculating these properties, while also allowing for larger system sizes to be studied. Pseudopotentials are also found to not significantly affect the calculation of exchange coupling constants.
2015 New trans-stilbene derivatives with large TPA valuesvarun Kundi
This document discusses a theoretical study of the linear and non-linear optical properties of 13 new trans-stilbene derivatives designed to have large two-photon absorption cross-sections. The study uses density functional theory and time-dependent density functional theory calculations with the CAM-B3LYP functional to evaluate properties like hyperpolarizability and one- and two-photon absorption. It finds that derivatives TSBD-10, TSBD-11, TSBD-12, and TSBD-13 have particularly large non-linear optical susceptibilities and two-photon absorption cross-sections, with the largest being 5560 GM for TSBD-13.
This document summarizes a study investigating compositional modulations in AlxGa1-xAs thin films using solid-state NMR and DFT calculations. The researchers were able to identify all possible As coordination sites in AlxGa1-xAs using 75As NMR experiments. Spectral deconvolution complied with an absence of long-range ordering, but an unconstrained fit showed a deviation from the imposed ordering parameter. NMR and DFT showed that the electric field gradients experienced by arsenic sites are distributed due to compositional variation in the higher coordination spheres of Al and Ga atoms. DFT calculations reproduced the experimentally observed electric field gradient distributions and showed NMR is sensitive to compositional modulations up to the 7th coordination shell
Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of el...Sérgio Sacani
High-energy cosmic-ray electrons and positrons (CREs), which
lose energy quickly during their propagation, provide a probe of
Galactic high-energy processes1–7 and may enable the observation
of phenomena such as dark-matter particle annihilation or
decay8–10. The CRE spectrum has been measured directly up to
approximately 2 teraelectronvolts in previous balloon- or spaceborne
experiments11–16, and indirectly up to approximately 5
teraelectronvolts using ground-based Cherenkov γ-ray telescope
arrays17,18. Evidence for a spectral break in the teraelectronvolt
energy range has been provided by indirect measurements17,18,
although the results were qualified by sizeable systematic
uncertainties. Here we report a direct measurement of CREs in the
energy range 25 gigaelectronvolts to 4.6 teraelectronvolts by the
Dark Matter Particle Explorer (DAMPE)19 with unprecedentedly
high energy resolution and low background. The largest part of
the spectrum can be well fitted by a ‘smoothly broken power-law’
model rather than a single power-law model. The direct detection of
a spectral break at about 0.9 teraelectronvolts confirms the evidence
found by previous indirect measurements17,18, clarifies the behaviour
of the CRE spectrum at energies above 1 teraelectronvolt and sheds
light on the physical origin of the sub-teraelectronvolt CREs.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
48 Measurement of the Σ beam asymmetry for the ω photo-production off the pro...Cristian Randieri PhD
Measurement of the Σ beam asymmetry for the ω photo-production off the proton and the neutron at GRAAL - June 2013
di V. Vegna, A. D'Angelo, O. Bartalini, V. Bellini, J. P. Boquet, M. Capogni, L. E. Casano, M. Castoldi, F. Curciarello, V. De Leo, J. P. Didelez, R. Di Salvo, A. Fantini, D. Franco, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, A. Lapik, P. Levi Sandri, A. Lleres, F. Mammoliti, G. Mandaglio, M. Manganaro, D. Moricciani, A. Mushkarenkov, V. Nedorezov, C. Randieri, D. Rebreyend, N. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, I. Zonta (2013)
Abstract
We report on new measurements of the beam asymmetry for ω photo-production on proton and neutron in Hydrogen and Deuterium targets from the GRAAL collaboration. The beam asymmetry values are extracted from the reaction threshold (E = 1.1 GeV in the free nucleon kinematics) up to 1.5 GeV of incoming photon energy. For the first time both the radiative and the three- pion decay channels are simultaneously investigated on the free proton. Results from the two decay channels are in agreement and provide important constraints for the determination of resonant state contributions to the ω production mechanism. First experimental results on the deuteron allow the extraction of the _ beam asymmetry on quasi-free nucleons. Comparison of the results for free and quasi-free kinematics on the proton shows a generally reasonable agreement, similar to the findings in pseudo-scalar meson photo-production reactions. For the first time measurements on quasi-free neutrons are available, showing that both the strength and the angular distributions of the beam asymmetry are sensibly different from the results on the proton target.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Molecular dynamics (MD) simulations calculate particle trajectories by integrating Newton's equations of motion. This document discusses the history and basic principles of MD, force fields, the NAMD simulation package, and applications. NAMD is a parallelized MD program for biomolecular simulations that uses spatial decomposition and multithreading. It supports features like CHARMM force fields, ensembles, and interactive modeling with VMD for structure visualization. MD simulations are useful for modeling protein structures, comparing protein templates, and predicting protein behavior through refinement of simulation approaches.
This document discusses using density functional theory with different basis sets (Gaussian, plane waves, numerical) to calculate exchange coupling constants in transition metal complexes. It compares the accuracy and reliability of these approaches by calculating exchange coupling constants and spin distributions for three test complexes. The plane wave and numerical basis set approaches are found to be accurate alternatives to the more established Gaussian basis functions for calculating these properties, while also allowing for larger system sizes to be studied. Pseudopotentials are also found to not significantly affect the calculation of exchange coupling constants.
2015 New trans-stilbene derivatives with large TPA valuesvarun Kundi
This document discusses a theoretical study of the linear and non-linear optical properties of 13 new trans-stilbene derivatives designed to have large two-photon absorption cross-sections. The study uses density functional theory and time-dependent density functional theory calculations with the CAM-B3LYP functional to evaluate properties like hyperpolarizability and one- and two-photon absorption. It finds that derivatives TSBD-10, TSBD-11, TSBD-12, and TSBD-13 have particularly large non-linear optical susceptibilities and two-photon absorption cross-sections, with the largest being 5560 GM for TSBD-13.
This document summarizes a study investigating compositional modulations in AlxGa1-xAs thin films using solid-state NMR and DFT calculations. The researchers were able to identify all possible As coordination sites in AlxGa1-xAs using 75As NMR experiments. Spectral deconvolution complied with an absence of long-range ordering, but an unconstrained fit showed a deviation from the imposed ordering parameter. NMR and DFT showed that the electric field gradients experienced by arsenic sites are distributed due to compositional variation in the higher coordination spheres of Al and Ga atoms. DFT calculations reproduced the experimentally observed electric field gradient distributions and showed NMR is sensitive to compositional modulations up to the 7th coordination shell
Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of el...Sérgio Sacani
High-energy cosmic-ray electrons and positrons (CREs), which
lose energy quickly during their propagation, provide a probe of
Galactic high-energy processes1–7 and may enable the observation
of phenomena such as dark-matter particle annihilation or
decay8–10. The CRE spectrum has been measured directly up to
approximately 2 teraelectronvolts in previous balloon- or spaceborne
experiments11–16, and indirectly up to approximately 5
teraelectronvolts using ground-based Cherenkov γ-ray telescope
arrays17,18. Evidence for a spectral break in the teraelectronvolt
energy range has been provided by indirect measurements17,18,
although the results were qualified by sizeable systematic
uncertainties. Here we report a direct measurement of CREs in the
energy range 25 gigaelectronvolts to 4.6 teraelectronvolts by the
Dark Matter Particle Explorer (DAMPE)19 with unprecedentedly
high energy resolution and low background. The largest part of
the spectrum can be well fitted by a ‘smoothly broken power-law’
model rather than a single power-law model. The direct detection of
a spectral break at about 0.9 teraelectronvolts confirms the evidence
found by previous indirect measurements17,18, clarifies the behaviour
of the CRE spectrum at energies above 1 teraelectronvolt and sheds
light on the physical origin of the sub-teraelectronvolt CREs.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Monte Carlo Simulations & Membrane Simulation and DynamicsArindam Ghosh
Monte Carlo simulations and molecular dynamics simulations are common computational methods to study membrane proteins and lipid bilayers. Monte Carlo simulations use random sampling to explore the behavior of complex systems. Molecular dynamics simulations numerically simulate particle motions under internal and external forces based on empirical energy functions. There are different levels of molecular dynamics simulations including atomistic, united atom, and coarse grained simulations, each with varying degrees of atomic detail and accessible timescales. Parameterized force fields are used to model interactions in lipid and protein systems. These computational methods provide insights into membrane and protein dynamics that are difficult to obtain experimentally.
This document summarizes a theory for analyzing microstrip transmission lines on artificial periodic substrates. It proposes a double vector integral equation method involving two stages: 1) solving for the Green's function of the periodic structure, and 2) using this Green's function in a second integral equation to determine the fields and parameters of the microstrip line. Key aspects of the microstrip that can be determined include the propagation constant, characteristic impedance, and propagation bandgaps due to the periodic elements. The theory is validated through numerical comparisons to effective medium approximations and experimental data on a three-layer periodic substrate structure.
High-Resolution Infrared and Electron-Diffraction Studies of Trimethylenecycl...Corey Wright
This document presents a study combining high-resolution spectroscopy, electron diffraction, and quantum theoretical methods to determine the structure of trimethylenecyclopropane ([3]-radialene). High-resolution infrared spectroscopy was used to obtain an accurate rotational constant of 0.1378629(8) cm-1. Electron diffraction data and theoretical predictions were then used to determine bond lengths of C-H = 1.072(17) Å, C-C = 1.437(4) Å, and C=C = 1.330(4) Å, indicating π-electron delocalization shortens the C-C bond by approximately 0.05 Å compared to ethane. While an accurate hydrogen-carbon
This work studied the manipulation of ferromagnetic behavior in gallium manganese nitride (GaMnN) epilayers and heterostructures. Key findings include:
1) GaMnN/p-GaN heterostructures exhibited room temperature ferromagnetism that increased with p-type GaN thickness and hole concentration.
2) GaMnN i-p-n structures showed electric field controlled ferromagnetism at room temperature, with magnetization decreasing under reverse bias due to p-GaN layer depletion.
3) Ferromagnetism in the structures depended on p-GaN layer thickness and GaMnN thickness, demonstrating manipulation of room temperature ferromagnetic properties.
1) Raman spectroscopy was used to study the thermal maturity of solid bitumen from a sample with low maturity (0.61% reflectance). However, initial measurements showed intense fluorescence that obscured the typical Raman bands.
2) Repeated measurements at the same location caused the fluorescence background to decrease over time, revealing the Raman bands more clearly without artificially altering the sample.
3) Multiple measurements allowed the fluorescent component to be isolated from the Raman spectrum, producing a clean spectrum free of background interference. This method provides a way to apply Raman spectroscopy to samples that normally exhibit strong fluorescence.
This document provides an overview of molecular dynamics (MD) simulations and their analysis. MD simulations calculate the time-dependent behavior of molecules and can be used to study conformational changes in proteins and nucleic acids. The document outlines various analyses that can be done on MD simulations including root mean square deviation (RMSD), root mean square fluctuation (RMSF), radius of gyration, hydrogen bonding, secondary structure analysis using Ramachandran plots, free energy surfaces, and principal component analysis. It also provides examples of running MD simulations using VMD and applications of MD simulations such as understanding allostery and molecular docking.
This document summarizes a study that demonstrates the use of equally-sloped tomography (EST) to improve electron tomography reconstruction. EST acquires projection images at constant slope increments, allowing the use of a pseudo-polar fast Fourier transform to directly relate the projection and volume grids. The study applied EST to reconstruct frozen keyhole limpet hemocyanin molecules and a bacterial cell from tilt-series data. EST reconstructions exhibited higher contrast, less noise, clearer boundaries, and reduced missing wedge effects compared to other reconstruction methods. Surprisingly, EST reconstructions using only two-thirds of the original projections appeared to have the same resolution as full reconstructions using other methods, suggesting EST can reduce radiation dose requirements or allow higher resolutions.
This study analyzed the electronic properties of methyl-terminated germanane (GeCH3) flakes using surface photovoltage spectroscopy (SPS). Previous studies showed GeCH3 has a p-type response and band gap of 1.7 eV. The SPS data in this study showed GeCH3 surfaces can exhibit both p-type and n-type character, and humidity and oxidation can affect the results. The findings have implications for relating SPS features to sample structure to synthesize materials without defects. The study of defects in 2D GeCH3 is important because it is a direct bandgap semiconductor with applications in optoelectronics.
Stillwell_ Strongly coupled electronic, magnetic, and lattice degrees of free...Ryan Stillwell, Ph.D.
This document summarizes research on the ferromagnetic compound LaCo5 under high pressure. X-ray diffraction measurements show an anisotropic lattice collapse of the c axis near 10 GPa, consistent with theoretical predictions. High-pressure magnetotransport measurements reveal changes in the Hall effect signatures near 10 GPa, providing the first experimental evidence of changes in the electronic and magnetic properties associated with the predicted magnetoelastic collapse. The coupling of structural, electronic, and magnetic behaviors in LaCo5 under pressure substantiates the theoretical model of an electronic topological transition driving the magnetoelastic collapse.
42 Beam Asymmetry Σ of the π- Photoproduction off Neutron - International Jou...Cristian Randieri PhD
Beam Asymmetry Σ of the π- Photoproduction off Neutron - International Journal of Modern Physics E, June 2010, Vol. 19, N. 5-6, pp. 965-976, doi: 10.1142/S0218301310015412
di G. Mandaglio, V. Bellini, J. P. Bocquet, L. Casano, A. D'Angelo, R. Di Salvo, A. Fantini, D. Franco, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, A. S. Ignatov, A. M. Lapik, P. Levi Sandri, A. Lleres, F. Mammoliti, M. Manganaro, D. Moricciani, A. N. Mushkarenkov, V. G. Nedorezov, C. Randieri, D. Rebreyend, N. V. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna (2010)
Abstract
We present the analysis of data performed in order to identify the events of the γ + n → π- + p reaction obtained by bombarding a liquid Deuterium target with a polarised γ beam of 0.55-1.5 GeV at the Graal-experiment. We show the effect of different kinematic and hardware constraints used to reduce the contamination coming from the concurrent reaction channels. By the simulation we estimate the contamination degree due to the other reaction channels so we can test the reliability of our method. We describe a new three-dimensional cut based on the Fermi momentum reconstruction and its effect on the suppression of the concurrent double charged pion photoproduction. We present the preliminary beam asymmetry Σ of the π- fotoproduction off quasi-free neutron up to about θc.m., π- = 165° together with some theoretical multipolar analysis. For a comparison we also report the data present in literature on the same reaction for Eγ =850-1740 MeV and θc.m., π- ≤105°.
This document summarizes the results of a Monte Carlo simulation comparing electron transport properties in GaSb and GaAs semiconductors at high electric fields. The simulation includes nonparabolic band structures, acoustic and polar optical phonon scattering, and ionized impurity scattering. It finds that GaAs has a higher peak electron drift velocity of around 2.2x105 m/s compared to 1.2x105 m/s for GaSb. Both materials show velocity saturation at high fields due to increased intervalley scattering. Temperature is also found to decrease peak velocity and increase the critical field for velocity overshoot.
protein sturcture prediction and molecular modellingDileep Paruchuru
This document discusses molecular modeling and protein structure prediction. It begins by introducing molecular modeling as a combination of computational chemistry and computer graphics that allows scientists to generate and present molecular data. It then discusses the two main computational methods for molecular modeling - molecular mechanics and quantum mechanics. The document goes on to discuss molecular mechanics in more detail and its applications. It also discusses protein structure and function, the challenges of protein structure prediction, and the goals of protein structure prediction.
The document discusses solid state nuclear magnetic resonance (NMR) spectroscopy. It provides examples of applications of solid state NMR including structure determination of organic and inorganic complexes as well as biological molecules, minerals, ceramics, polymers and more. It describes several interactions observed in solid state NMR spectra such as chemical shift anisotropy, dipole-dipole coupling, J-coupling, quadrupolar interactions and magic angle spinning which is a technique to average anisotropic interactions and improve resolution.
49 First Measurement of the Σ Beam Asymmetry in η' Photoproduction off the Pr...Cristian Randieri PhD
First Measurement of the Σ Beam Asymmetry in η' Photoproduction off the Proton near Threshold - July 2014
di P. Levi Sandri, G. Mandaglio, O. Bartalini, V. Bellini, J. P. Bocquet, M. Capogni, F. Curciarello, A. D’Angelo, V. De Leo, J. P. Didelez, R. Di Salvo, A. Fantini, D. Franco, C. Gaulard, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, A. Lapik, A. Lleres, F. Mammoliti, M. Manganaro, D. Moricciani, A. Mushkarenkov, V. Nedorezov, C. Randieri, D. Rebreyend, N. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna and I. Zonta (2014)
Abstract
The Σ beam asymmetry in η' photoproduction off the proton was measured at the GRAAL polarized photon beam with incoming photon energies of 1.461 and 1.480 GeV. For both energies the asymmetry as a function of the meson emission angle shows a clear structure, more pronounced at the lowest one, with a change of sign around 90°. The results are compared to the existing theories that fail to account for the data.
This document discusses molecular mechanics force fields, specifically the Merck Molecular Force Field (MMFF). It provides details on the functional form and parameters of MMFF, including that it is a Class II force field designed to accurately model conformational energies and non-bonded interactions of pharmaceutical compounds. The total energy expression for MMFF is provided, including terms for internal interactions like bonds, angles, and torsions, as well as nonbonded van der Waals and electrostatic terms. Application of MMFF in the CHARMM program is also described.
The document summarizes a study of the electronic transport properties of carbon nanobuds (CNBs) using density functional theory calculations. CNBs are hybrid carbon nanostructures formed by attaching fullerenes to single-walled carbon nanotubes. The study finds that attaching fullerenes to form CNBs with a (14,0) carbon nanotube reduces electron transmission across the structure compared to the pristine nanotube. Localized states near the bud region cause strong backscattering, lowering transmission. Current-voltage characteristics show that while the pristine nanotube is semiconducting, CNB formation does not change this behavior. CNBs may have applications in nanoelectronics
This document outlines a graduate student's thesis work on multi-scale modeling of micro-coronas. There are wide variations in both time and length scales involved in plasma modeling, from picoseconds to hours/days and from molecular to macroscopic scales. A multi-scale modeling technique of domain decomposition is proposed, using microscopic models locally where needed and macroscopic models for the rest. The goals are to develop a modeling tool that can span micro- to macro-scales and simulate plasmas in complex geometries. Challenges include bridging between scales and incorporating particle and fluid models.
Hamiltonian Approach for Electromagnetic Field in One-dimensional Photonic Cr...IRJET Journal
1) The document presents a novel Hamiltonian approach for determining the classical electromagnetic field distribution in one-dimensional photonic crystals.
2) The approach starts from a microscopic Hamiltonian describing the interaction between quantized electromagnetic fields and medium oscillators. Approximations are made to derive a macroscopic Hamiltonian in terms of averaged field operators and material susceptibilities.
3) Using the macroscopic Hamiltonian and coherent states of the electromagnetic field, the electric field operator for the photonic crystal is obtained. The expectation value of this operator gives the classical electric field distribution inside the photonic crystal.
4) As an example, the electric field distribution in a one-dimensional photonic crystal of alternating dielectric layers is determined and a phot
Performance analysis of a monopole antenna with fluorescent tubes at 4.9 g hz...Alexander Decker
This document describes the analysis of a monopole antenna design with fluorescent tubes at an operating frequency of 4.9 GHz. The antenna structure consists of 12 commercial fluorescent tubes surrounding a monopole antenna located in the center of a circular ground plane. The performance of the antenna design is analyzed using CST Microwave Studio software. Parameters like return loss, radiation pattern, and gain are evaluated to analyze the antenna's performance. The fluorescent tubes act as plasma reflectors when electrified, trapping radiation inside and improving the antenna's performance for potential military applications.
Results of a series of tests designed by the National Renewable Energy Laboratory (NREL) and conducted by PV Evolution Labs (PVEL) to measure the performance of various inverter technologies in various shading conditions were published today. The test determined the annual percentage of energy recovered by power optimizers and micro inverters when compared to traditional string inverter systems in shaded conditions.The results indicate that the SolarEdge optimized system generates 2%, 5% and over 8% more energy than traditional string inverters in light, medium and heavy shading scenarios, respectively.The SolarEdge system outperformed all systems in annual energy production demonstrating higher results than the leading micro inverter solution as well.
"The SolarEdge system yielded more energy than the string inverter system in all tests. On an annual average, the SolarEdge system recovered 24.8% of energy lost due to shading, while the microinverter system recovered 23.2%," says Matt Donovan, PV Evolution Labs.
Exchange biasing of the ferromagnetic semiconductor Ga,Mn As by MnOOleg Maksimov
This document summarizes research on exchange biasing of the ferromagnetic semiconductor Ga1−xMnxAs with an antiferromagnetic MnO layer. Characterization using RBS, XPS, TEM, and XRR showed the formation of a MnO layer on Ga1−xMnxAs. SQUID magnetometry measurements exhibited an exchange field and enhanced coercivity, indicating exchange bias. The exchange and coercive fields varied with temperature and cooling field. Both cases where the Néel temperature of MnO was similar to or greater than the Curie temperature of Ga1−xMnxAs were investigated.
The Indices of Refraction of Molecular-Beam Epitaxy–Grown BexZn1–xTe Ternary ...Oleg Maksimov
This document discusses a study that uses a combination of prism-coupling, reflectivity, and ellipsometric techniques to determine the indices of refraction (n) of molecular-beam epitaxy grown BexZn1-xTe thin films. Initially, prism-coupling measurements were used to obtain discrete n values and film thicknesses at specific wavelengths. Reflectivity data was then analyzed using the prism-coupling results to determine n dispersion below the bandgap. Ellipsometry was finally used to model n dispersion both below and above the bandgap, guided by the prior thickness and below-bandgap n data from the other techniques. The combination of these three methods allowed for accurate determination of n over a wide wavelength
Monte Carlo Simulations & Membrane Simulation and DynamicsArindam Ghosh
Monte Carlo simulations and molecular dynamics simulations are common computational methods to study membrane proteins and lipid bilayers. Monte Carlo simulations use random sampling to explore the behavior of complex systems. Molecular dynamics simulations numerically simulate particle motions under internal and external forces based on empirical energy functions. There are different levels of molecular dynamics simulations including atomistic, united atom, and coarse grained simulations, each with varying degrees of atomic detail and accessible timescales. Parameterized force fields are used to model interactions in lipid and protein systems. These computational methods provide insights into membrane and protein dynamics that are difficult to obtain experimentally.
This document summarizes a theory for analyzing microstrip transmission lines on artificial periodic substrates. It proposes a double vector integral equation method involving two stages: 1) solving for the Green's function of the periodic structure, and 2) using this Green's function in a second integral equation to determine the fields and parameters of the microstrip line. Key aspects of the microstrip that can be determined include the propagation constant, characteristic impedance, and propagation bandgaps due to the periodic elements. The theory is validated through numerical comparisons to effective medium approximations and experimental data on a three-layer periodic substrate structure.
High-Resolution Infrared and Electron-Diffraction Studies of Trimethylenecycl...Corey Wright
This document presents a study combining high-resolution spectroscopy, electron diffraction, and quantum theoretical methods to determine the structure of trimethylenecyclopropane ([3]-radialene). High-resolution infrared spectroscopy was used to obtain an accurate rotational constant of 0.1378629(8) cm-1. Electron diffraction data and theoretical predictions were then used to determine bond lengths of C-H = 1.072(17) Å, C-C = 1.437(4) Å, and C=C = 1.330(4) Å, indicating π-electron delocalization shortens the C-C bond by approximately 0.05 Å compared to ethane. While an accurate hydrogen-carbon
This work studied the manipulation of ferromagnetic behavior in gallium manganese nitride (GaMnN) epilayers and heterostructures. Key findings include:
1) GaMnN/p-GaN heterostructures exhibited room temperature ferromagnetism that increased with p-type GaN thickness and hole concentration.
2) GaMnN i-p-n structures showed electric field controlled ferromagnetism at room temperature, with magnetization decreasing under reverse bias due to p-GaN layer depletion.
3) Ferromagnetism in the structures depended on p-GaN layer thickness and GaMnN thickness, demonstrating manipulation of room temperature ferromagnetic properties.
1) Raman spectroscopy was used to study the thermal maturity of solid bitumen from a sample with low maturity (0.61% reflectance). However, initial measurements showed intense fluorescence that obscured the typical Raman bands.
2) Repeated measurements at the same location caused the fluorescence background to decrease over time, revealing the Raman bands more clearly without artificially altering the sample.
3) Multiple measurements allowed the fluorescent component to be isolated from the Raman spectrum, producing a clean spectrum free of background interference. This method provides a way to apply Raman spectroscopy to samples that normally exhibit strong fluorescence.
This document provides an overview of molecular dynamics (MD) simulations and their analysis. MD simulations calculate the time-dependent behavior of molecules and can be used to study conformational changes in proteins and nucleic acids. The document outlines various analyses that can be done on MD simulations including root mean square deviation (RMSD), root mean square fluctuation (RMSF), radius of gyration, hydrogen bonding, secondary structure analysis using Ramachandran plots, free energy surfaces, and principal component analysis. It also provides examples of running MD simulations using VMD and applications of MD simulations such as understanding allostery and molecular docking.
This document summarizes a study that demonstrates the use of equally-sloped tomography (EST) to improve electron tomography reconstruction. EST acquires projection images at constant slope increments, allowing the use of a pseudo-polar fast Fourier transform to directly relate the projection and volume grids. The study applied EST to reconstruct frozen keyhole limpet hemocyanin molecules and a bacterial cell from tilt-series data. EST reconstructions exhibited higher contrast, less noise, clearer boundaries, and reduced missing wedge effects compared to other reconstruction methods. Surprisingly, EST reconstructions using only two-thirds of the original projections appeared to have the same resolution as full reconstructions using other methods, suggesting EST can reduce radiation dose requirements or allow higher resolutions.
This study analyzed the electronic properties of methyl-terminated germanane (GeCH3) flakes using surface photovoltage spectroscopy (SPS). Previous studies showed GeCH3 has a p-type response and band gap of 1.7 eV. The SPS data in this study showed GeCH3 surfaces can exhibit both p-type and n-type character, and humidity and oxidation can affect the results. The findings have implications for relating SPS features to sample structure to synthesize materials without defects. The study of defects in 2D GeCH3 is important because it is a direct bandgap semiconductor with applications in optoelectronics.
Stillwell_ Strongly coupled electronic, magnetic, and lattice degrees of free...Ryan Stillwell, Ph.D.
This document summarizes research on the ferromagnetic compound LaCo5 under high pressure. X-ray diffraction measurements show an anisotropic lattice collapse of the c axis near 10 GPa, consistent with theoretical predictions. High-pressure magnetotransport measurements reveal changes in the Hall effect signatures near 10 GPa, providing the first experimental evidence of changes in the electronic and magnetic properties associated with the predicted magnetoelastic collapse. The coupling of structural, electronic, and magnetic behaviors in LaCo5 under pressure substantiates the theoretical model of an electronic topological transition driving the magnetoelastic collapse.
42 Beam Asymmetry Σ of the π- Photoproduction off Neutron - International Jou...Cristian Randieri PhD
Beam Asymmetry Σ of the π- Photoproduction off Neutron - International Journal of Modern Physics E, June 2010, Vol. 19, N. 5-6, pp. 965-976, doi: 10.1142/S0218301310015412
di G. Mandaglio, V. Bellini, J. P. Bocquet, L. Casano, A. D'Angelo, R. Di Salvo, A. Fantini, D. Franco, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, A. S. Ignatov, A. M. Lapik, P. Levi Sandri, A. Lleres, F. Mammoliti, M. Manganaro, D. Moricciani, A. N. Mushkarenkov, V. G. Nedorezov, C. Randieri, D. Rebreyend, N. V. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna (2010)
Abstract
We present the analysis of data performed in order to identify the events of the γ + n → π- + p reaction obtained by bombarding a liquid Deuterium target with a polarised γ beam of 0.55-1.5 GeV at the Graal-experiment. We show the effect of different kinematic and hardware constraints used to reduce the contamination coming from the concurrent reaction channels. By the simulation we estimate the contamination degree due to the other reaction channels so we can test the reliability of our method. We describe a new three-dimensional cut based on the Fermi momentum reconstruction and its effect on the suppression of the concurrent double charged pion photoproduction. We present the preliminary beam asymmetry Σ of the π- fotoproduction off quasi-free neutron up to about θc.m., π- = 165° together with some theoretical multipolar analysis. For a comparison we also report the data present in literature on the same reaction for Eγ =850-1740 MeV and θc.m., π- ≤105°.
This document summarizes the results of a Monte Carlo simulation comparing electron transport properties in GaSb and GaAs semiconductors at high electric fields. The simulation includes nonparabolic band structures, acoustic and polar optical phonon scattering, and ionized impurity scattering. It finds that GaAs has a higher peak electron drift velocity of around 2.2x105 m/s compared to 1.2x105 m/s for GaSb. Both materials show velocity saturation at high fields due to increased intervalley scattering. Temperature is also found to decrease peak velocity and increase the critical field for velocity overshoot.
protein sturcture prediction and molecular modellingDileep Paruchuru
This document discusses molecular modeling and protein structure prediction. It begins by introducing molecular modeling as a combination of computational chemistry and computer graphics that allows scientists to generate and present molecular data. It then discusses the two main computational methods for molecular modeling - molecular mechanics and quantum mechanics. The document goes on to discuss molecular mechanics in more detail and its applications. It also discusses protein structure and function, the challenges of protein structure prediction, and the goals of protein structure prediction.
The document discusses solid state nuclear magnetic resonance (NMR) spectroscopy. It provides examples of applications of solid state NMR including structure determination of organic and inorganic complexes as well as biological molecules, minerals, ceramics, polymers and more. It describes several interactions observed in solid state NMR spectra such as chemical shift anisotropy, dipole-dipole coupling, J-coupling, quadrupolar interactions and magic angle spinning which is a technique to average anisotropic interactions and improve resolution.
49 First Measurement of the Σ Beam Asymmetry in η' Photoproduction off the Pr...Cristian Randieri PhD
First Measurement of the Σ Beam Asymmetry in η' Photoproduction off the Proton near Threshold - July 2014
di P. Levi Sandri, G. Mandaglio, O. Bartalini, V. Bellini, J. P. Bocquet, M. Capogni, F. Curciarello, A. D’Angelo, V. De Leo, J. P. Didelez, R. Di Salvo, A. Fantini, D. Franco, C. Gaulard, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, A. Lapik, A. Lleres, F. Mammoliti, M. Manganaro, D. Moricciani, A. Mushkarenkov, V. Nedorezov, C. Randieri, D. Rebreyend, N. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna and I. Zonta (2014)
Abstract
The Σ beam asymmetry in η' photoproduction off the proton was measured at the GRAAL polarized photon beam with incoming photon energies of 1.461 and 1.480 GeV. For both energies the asymmetry as a function of the meson emission angle shows a clear structure, more pronounced at the lowest one, with a change of sign around 90°. The results are compared to the existing theories that fail to account for the data.
This document discusses molecular mechanics force fields, specifically the Merck Molecular Force Field (MMFF). It provides details on the functional form and parameters of MMFF, including that it is a Class II force field designed to accurately model conformational energies and non-bonded interactions of pharmaceutical compounds. The total energy expression for MMFF is provided, including terms for internal interactions like bonds, angles, and torsions, as well as nonbonded van der Waals and electrostatic terms. Application of MMFF in the CHARMM program is also described.
The document summarizes a study of the electronic transport properties of carbon nanobuds (CNBs) using density functional theory calculations. CNBs are hybrid carbon nanostructures formed by attaching fullerenes to single-walled carbon nanotubes. The study finds that attaching fullerenes to form CNBs with a (14,0) carbon nanotube reduces electron transmission across the structure compared to the pristine nanotube. Localized states near the bud region cause strong backscattering, lowering transmission. Current-voltage characteristics show that while the pristine nanotube is semiconducting, CNB formation does not change this behavior. CNBs may have applications in nanoelectronics
This document outlines a graduate student's thesis work on multi-scale modeling of micro-coronas. There are wide variations in both time and length scales involved in plasma modeling, from picoseconds to hours/days and from molecular to macroscopic scales. A multi-scale modeling technique of domain decomposition is proposed, using microscopic models locally where needed and macroscopic models for the rest. The goals are to develop a modeling tool that can span micro- to macro-scales and simulate plasmas in complex geometries. Challenges include bridging between scales and incorporating particle and fluid models.
Hamiltonian Approach for Electromagnetic Field in One-dimensional Photonic Cr...IRJET Journal
1) The document presents a novel Hamiltonian approach for determining the classical electromagnetic field distribution in one-dimensional photonic crystals.
2) The approach starts from a microscopic Hamiltonian describing the interaction between quantized electromagnetic fields and medium oscillators. Approximations are made to derive a macroscopic Hamiltonian in terms of averaged field operators and material susceptibilities.
3) Using the macroscopic Hamiltonian and coherent states of the electromagnetic field, the electric field operator for the photonic crystal is obtained. The expectation value of this operator gives the classical electric field distribution inside the photonic crystal.
4) As an example, the electric field distribution in a one-dimensional photonic crystal of alternating dielectric layers is determined and a phot
Performance analysis of a monopole antenna with fluorescent tubes at 4.9 g hz...Alexander Decker
This document describes the analysis of a monopole antenna design with fluorescent tubes at an operating frequency of 4.9 GHz. The antenna structure consists of 12 commercial fluorescent tubes surrounding a monopole antenna located in the center of a circular ground plane. The performance of the antenna design is analyzed using CST Microwave Studio software. Parameters like return loss, radiation pattern, and gain are evaluated to analyze the antenna's performance. The fluorescent tubes act as plasma reflectors when electrified, trapping radiation inside and improving the antenna's performance for potential military applications.
Results of a series of tests designed by the National Renewable Energy Laboratory (NREL) and conducted by PV Evolution Labs (PVEL) to measure the performance of various inverter technologies in various shading conditions were published today. The test determined the annual percentage of energy recovered by power optimizers and micro inverters when compared to traditional string inverter systems in shaded conditions.The results indicate that the SolarEdge optimized system generates 2%, 5% and over 8% more energy than traditional string inverters in light, medium and heavy shading scenarios, respectively.The SolarEdge system outperformed all systems in annual energy production demonstrating higher results than the leading micro inverter solution as well.
"The SolarEdge system yielded more energy than the string inverter system in all tests. On an annual average, the SolarEdge system recovered 24.8% of energy lost due to shading, while the microinverter system recovered 23.2%," says Matt Donovan, PV Evolution Labs.
Exchange biasing of the ferromagnetic semiconductor Ga,Mn As by MnOOleg Maksimov
This document summarizes research on exchange biasing of the ferromagnetic semiconductor Ga1−xMnxAs with an antiferromagnetic MnO layer. Characterization using RBS, XPS, TEM, and XRR showed the formation of a MnO layer on Ga1−xMnxAs. SQUID magnetometry measurements exhibited an exchange field and enhanced coercivity, indicating exchange bias. The exchange and coercive fields varied with temperature and cooling field. Both cases where the Néel temperature of MnO was similar to or greater than the Curie temperature of Ga1−xMnxAs were investigated.
The Indices of Refraction of Molecular-Beam Epitaxy–Grown BexZn1–xTe Ternary ...Oleg Maksimov
This document discusses a study that uses a combination of prism-coupling, reflectivity, and ellipsometric techniques to determine the indices of refraction (n) of molecular-beam epitaxy grown BexZn1-xTe thin films. Initially, prism-coupling measurements were used to obtain discrete n values and film thicknesses at specific wavelengths. Reflectivity data was then analyzed using the prism-coupling results to determine n dispersion below the bandgap. Ellipsometry was finally used to model n dispersion both below and above the bandgap, guided by the prior thickness and below-bandgap n data from the other techniques. The combination of these three methods allowed for accurate determination of n over a wide wavelength
Analysis Of High Resolution FTIR Spectra From Synchrotron Sources Using Evolu...Heather Strinden
This document discusses the analysis of a high resolution FTIR spectrum of trimethylene sulfide (TMS) using evolutionary algorithms (EA). The spectrum was collected at the Canadian Light Source with a resolution of 0.00096 cm-1. Preliminary analysis using traditional methods assigned 2358 transitions. EA was also applied and yielded spectroscopic constants that similarly reproduced the complex experimental spectrum. As a test, EA was also successfully applied to a previously analyzed spectrum of azetidine, demonstrating the robustness of the EA method for automated assignment of dense rovibrational spectra.
Annealing Dependence of Exchange Bias in MnO/Ga1−xMnxAs HeterostructuresOleg Maksimov
The document discusses the annealing dependence of exchange bias in MnO/Ga1-xMnxAs heterostructures. It finds that as-grown Mn overlayers do not produce exchange coupling, and annealing is essential to create exchange bias signatures like loop shifting. X-ray photoelectron spectroscopy shows the cleanest exchange bias arises when the Mn overlayer is completely converted to MnO during annealing. Rapid thermal annealing of samples bonded with indium provides sufficient heating to oxidize the Mn layer to MnO and produce exchange bias, while unannealed samples do not exhibit this behavior.
The document describes a Monte Carlo simulation of electron transport properties in InAsxP1-x, InAs, and InP semiconductors at high electric fields and room temperature. It finds that electron velocity overshoot only occurs above a critical electric field that is material dependent. The simulation includes non-parabolic bands and scattering mechanisms. It calculates drift velocities and finds InAs has the highest peak velocity followed by InAsxP1-x alloys then InP. Occupancy of satellite valleys increases with field strength more substantially in InAs. Transient transport shows larger overshoot velocities and faster relaxation in InAs compared to other materials.
Numerical Simulation of 퐒퐢ퟏ−퐱퐆퐞퐱 Thin Film Solar Cell Using AMPS - 1DIOSR Journals
This document describes a numerical simulation of thin film silicon-germanium solar cells using the AMPS-1D simulation program. The simulation varied the germanium concentration in the intrinsic layer between 0-100% to determine the optimal band gap for maximum efficiency. The results showed that a germanium concentration of 90% produced the highest efficiency of 19.68% for device thicknesses under 6 micrometers. Above 6 micrometers, pure silicon performed equally well or better than silicon-germanium alloys.
Computational electromagnetics in plasmonic nanostructuresAliakbarMonfared1
This document summarizes computational methods for simulating the optical response of plasmonic nanostructures, specifically focusing on finite-difference time-domain (FDTD), finite element method (FEM), discrete dipole approximation (DDA), and boundary element method (BEM). It discusses these numerical approaches from both theoretical and practical perspectives. FDTD is described as explicitly calculating electric and magnetic fields on a grid over time to solve Maxwell's equations. Its applications include simulating optical properties and enhancing solar cell efficiency by tuning nanoparticle geometry. The document provides several examples of research using FDTD for these purposes.
Study of Microstructural, Electrical and Dielectric Properties of La0.9Pb0.1M...Scientific Review SR
The present work studies the microstructural and electrical properties of La0.9Pb0.1MnO3 and La0.8Y0.1Pb0.1MnO3 ceramics synthesized by solid-state route method. Microstructure and elemental analysis of both samples were carried out by field emission scanning electron microscope (FESEM) and energy dispersive spectroscopy (EDS) method, respectively. Phase analysis by X-ray diffraction (XRD) indicated formation of single phase distorted structure. The XRD data were further analyzed by Rietveld refinement technique. Raman analysis reveals that Y atom substitutes La site into the LPMO with shifting of phonon modes. The temperature variation of resistivity of undoped and Y-doped La0.9Pb0.1MnO3 samples have been investigated. The electrical resistivity as a function of temperature showed that all samples undergo an metal-insulator (M-I) transition having a peak at transition temperature TMI. Y-doping increases the resistivity and the metal-insulator transition temperature (TMI) shifts to lower temperature. The temperature-dependent resistivity for temperatures less than metal-insulator transition is explained in terms the quadratic temperature dependence and for T > TMI, thermally activated conduction (TAC) is appropriate. Variation of frequency dispersion in permittivity and loss pattern due to La-site substitution in LPMO was observed in the dielectric response curve.
The document presents a comprehensive evaluation and comparison of four machine learning interatomic potential (ML-IAP) methods: the Gaussian approximation potential (GAP), moment tensor potential (MTP), high-dimensional neural network potential (NNP), and spectral neighbor analysis potential (SNAP). It assesses the accuracy, data requirements, and computational cost of each method using standardized density functional theory data sets of six materials (Li, Mo, Cu, Ni, Si, Ge) spanning different crystal structures and bonding types. The evaluation shows that all ML-IAP methods achieve near density functional theory accuracy in predicting energies and forces, with trade-offs between accuracy and computational cost depending on the model complexity.
The document describes a new broadband permeameter technique for measuring the complex permeability and permittivity of rectangular magnetic samples in-situ from 130 MHz to 7 GHz. The technique uses S-parameter measurements of an asymmetrical stripline containing the sample under test, and employs an optimization method to extract the electromagnetic properties of the sample by matching theoretical and measured effective parameters. Experimental results are presented to validate the quasistatic electromagnetic analysis approach used in the permeameter.
28 Measurement of η photoproduction on the proton from threshold to 1500-MeV ...Cristian Randieri PhD
Measurement of η photoproduction on the proton from threshold to 1500-MeV - The European Physical Journal A, Hadrons and Nuclei, August 2007, Vol. 33, N. 2, pp. 169-184, ISSN: 1434-6001, doi: 10.1140/epja/i2007-10439-9
di O. Bartalini, V. Bellini, J. P. Bocquet, P. Calvat, M. Capogni, L. Casano, M. Castoldi, A. D'Angelo, J. P. Didelez, R. Di Salvo, A. Fantini, D. Franco, C. Gaulard, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, M. Guidal, E. Hourany, R. Kunne, A. Lapik, P. Levi Sandri, A. Lleres, F. Mammoliti, G. Mandaglio, D. Moricciani, A. N. Mushkarenkov, V. Nedorezov, L. Nicoletti, C. Perrin, C. Randieri, D. Rebreyend, F. Renard, N. Rudnev, T. Russew, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna (2007).
Abstract
Beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy. The two dominant neutral decay modes of the eta meson, eta->2g and eta->3pi0, were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.
Equation of state for technetium from x‐ray diffraction and first principle c...Konstantin German
This document presents an experimental and theoretical study of the equation of state (EoS) of technetium metal under high pressure. Key points:
1) X-ray diffraction was used to measure the structure of technetium up to 67 GPa in a diamond anvil cell. The hexagonal close-packed structure was found to be stable over this pressure range.
2) First-principles calculations were also performed to model the compression behavior of technetium up to 273 GPa.
3) By fitting both the experimental and calculated volume-pressure data to different equations of state, the Vinet equation of state with B0 = 288 GPa and B' = 5.9(
Enhancing the Performance of P3HT/Cdse Solar Cells by Optimal Designing of Ac...IOSRJEEE
The present study examined the influence of different condition like as doping , in active layer, on the performance of P3HT/CdSe Solar cells .In this work, we analyzed the best doping for the configuration of P3HT/ CdSe in order to improve the performance of the solar cell. For this aim, we investigated the current density of electrons, the electric field, the short-circuit current and the open-circuit voltage in different doping . The results indicate that when the doping is increased in P3Ht and is decreased in CdSe, the current density of electrons, the electric field, the short-circuit current, and the open-circuit voltage are increased. Finally, we obtained doping of and for electron and hole donor respectively as the best doping for this configuration
Efficiency Improvement of p-i-n Structure over p-n Structure and Effect of p-...iosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
The International Journal of Engineering and Sciencetheijes
This document summarizes a study on enhancing the properties of porous gallium nitride (GaN) using different intensities of ultraviolet (UV) electrochemical etching. GaN samples were etched at various current densities of UV illumination and characterized using scanning electron microscopy, photoluminescence spectroscopy, and Raman spectroscopy. The results showed that increasing the current density led to larger pore sizes, higher photoluminescence intensity, and small blue shifts and peak broadening in the Raman spectra, indicating relaxation of stress in the porous GaN layers.
Malcolm Jardine completed a summer placement project to set up an optical magnetometer using a cesium gas cell. Tri-axial Helmholtz coils were constructed and modeled in MATLAB to create a controlled magnetic field for testing the magnetometer. The magnetometer was able to correctly measure magnetic fields with an initial sensitivity of 0.3μT. MATLAB was also used to develop programs for modeling the magnetic fields of the coils and performing linear regression analysis of experimental data.
Amorphous-nano-crystalline silicon composite thin films (a-nc-Si:H) samples were synthesized by
Plasma Enhanced Chemical Vapor Deposition technique. The measurement of DC conductivities was
accomplished using Dielectric spectroscopy (Impedance Spectroscopy) in wide frequency and temperature range.
In analysis of impedance data, two approaches were tested: the Debye type equivalent circuit with two parallel R
and CPEs (constant phase elements) and modified one, with tree parallel R and CPEs including crystal grain
boundary effects. It was found that the later better fits to experimental results properly describes crystal grains
dielectric effect and hydrogen concentration indicating presence of strain. The amorphous matrix showed larger
resistance and lower capacity than nano-crystal phase. Also it was found that composite silicon thin film cannot
be properly described by equivalent circuit only with resistors and constant phase elements in serial relation
This document summarizes a study on the effect of dipolar interactions in iron-based magnetic nanoparticles. It finds that increasing the concentration of nanoparticles leads to higher blocking temperatures, as observed in the ZFC-FC curves. This is consistent with dipolar interactions enhancing the orientational disorder of magnetic moments. The experimental data for the most dilute sample could be well modeled without considering interactions. For more concentrated samples, the coercive field behavior was also consistent with dipolar interactions playing a role. The document proposes that dipolar interactions can be modeled by introducing an effective temperature T* in theories of superparamagnetism.
Enhanced Exchange Pinning Field For Fe Mn Spin Valvesguestc57e7ed
This document discusses enhanced exchange pinning fields observed in spin-valve structures with ultra-thin magnetic pinned layers and FeMn antiferromagnetic layers. Spin-valves using CoNiFe/Cu, NiFe/Cu, and CoFe/Cu multilayer systems were investigated. Those with ultra-thin pinned layers of approximately 0.5 nm exhibited high pinning fields of 800-900 Oe for CoNiFe/Cu and CoFe/Cu, and around 500 Oe for NiFe/Cu. Enhanced pinning fields were inversely related to pinned layer thickness. Giant magnetoresistance was also measured, decreasing from 3-4% to less than 2% for pinned layers below 0.8 nm
Enhanced Exchange Pinning Field For Fe Mn Spin Valvesguestc57e7ed
This document discusses enhanced exchange pinning fields observed in spin-valve structures with ultra-thin magnetic pinned layers and FeMn antiferromagnetic layers. Three material systems - CoNiFe/Cu, NiFe/Cu, and CoFe/Cu - were investigated. Spin-valves with pinned layers as thin as 0.5 nm exhibited exchange pinning fields as high as 800-900 Oe for CoNiFe/Cu and CoFe/Cu multilayers, while NiFe/Cu multilayers achieved a pinning field of around 500 Oe. Using ultra-thin pinned layers reduced demagnetizing effects and improved spin-valve performance in terms of linearity.
Similar to Optical properties of molecular-beam-epitaxy-grown InGaMnAs thin films (20)
Giant LO oscillation in the Zn1yxBex(Se,Te) multi-phonons percolative alloysOleg Maksimov
This document discusses Raman scattering experiments on ZnBe(Se,Te) alloys. It finds that within the percolation regime of 0.19<x<0.81:
1) The low-frequency LO component is overdamped.
2) The high-frequency LO component exhibits a red asymmetry and apparent blue shift compared to predictions.
3) These anomalies can be explained by a discrete multi-mode description for the low- and high-frequency components, where coupling between modes via the macroscopic polarization field results in a transfer of oscillator strength building a "giant" LO oscillation.
Effect of nitridation on crystallinity of GaN grown on GaAs by MBEOleg Maksimov
1) GaN films were grown on GaAs substrates using plasma-assisted molecular beam epitaxy. The growth process involved substrate nitridation, deposition of a low-temperature buffer layer, and high-temperature film growth.
2) The effect of nitridation temperature on film crystallinity was studied using X-ray diffraction. Low-temperature (400°C) nitridation promoted the growth of c-oriented hexagonal α-GaN, while higher nitridation temperatures resulted in mis-oriented domains and inclusions of cubic β-GaN.
3) It was demonstrated that controlling the nitridation temperature is critical for achieving high quality GaN crystal growth, and nitridation must be performed at
Observation of free-to-acceptor-type photoluminescence in chlorine-doped Zn(B...Oleg Maksimov
The document summarizes photoluminescence studies of chlorine-doped Zn1-xBexSe alloys. At low temperatures, photoluminescence is dominated by neutral donor-bound excitons. At high temperatures, a free-to-acceptor transition emerges, involving recombination of free electrons and holes localized at acceptors. The acceptor ionization energy increases with beryllium concentration, suggesting an effective mass defect.
Properties of MBE-Grown ZnBeSe: Study of Be Isoelectronic Traps and of Dopant...Oleg Maksimov
This document summarizes a study of the properties of MBE-grown ZnBeSe, including its undoped, Cl-doped, and N-doped forms. Key findings include:
1) PL from undoped ZnBeSe is attributed to isoelectronic bound excitons formed by a Be-related isoelectronic trap, based on its effective mass behavior under temperature and pressure.
2) For Cl- and N-doped ZnBeSe, the binding energies of donor and acceptor impurities increase with Be concentration, following hydrogenic behavior.
3) Reported values for the ZnBeSe bandgap from one reference seem too low to explain the observed PL peaks
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
High reflectivity symmetrically strained ZnxCdyMg1ÀxÀySe-based distributed Br...Oleg Maksimov
This summary provides the key details from the document in 3 sentences:
The document describes the growth and characterization of distributed Bragg reflector (DBR) structures made of alternating ZnCdSe and ZnCdMgSe layers grown on InP substrates by molecular beam epitaxy. Undoped DBR structures with up to 24 periods achieved a maximum reflectivity of 99%, while a chlorine-doped 12-period DBR achieved 89% reflectivity. Structural characterization confirmed high crystalline quality and layer thicknesses close to the designed optical thickness of λ/4n, demonstrating the suitability of these materials for applications requiring highly reflective mirrors such as vertical cavity surface emitting lasers.
Temperature dependence of the energy gap of MgxZnyCd1–x–ySe alloyOleg Maksimov
This document reports on a study of the temperature dependence of the band gap energy in MgxZnyCd1–x–ySe alloys. Reflectivity measurements were taken between 4.2K and 300K. The data was fitted to a Bose-Einstein relationship. A similar temperature dependence was observed for MgxZnyCd1–x–ySe and Zn0.5Cd0.5Se, indicating that quantum confinement in MgxZnyCd1–x–ySe/Zn0.5Cd0.5Se quantum wells does not significantly change with temperature. This stability of quantum confinement could simplify the design of light emitting devices using these materials.
Efficient free exciton emission at room temperature in Zn0.5Cd0.5Se/MgxZnyCd1...Oleg Maksimov
This document summarizes research on efficient free exciton emission at room temperature in Zn0.5Cd0.5Se/MgxZnyCd1KxKySe quantum wells. Photoluminescence spectroscopy shows that at low temperatures, luminescence is dominated by bound exciton emission, but free exciton emission becomes dominant above 100 K and persists up to room temperature at 40% of the low-temperature intensity. This is attributed to the deep confinement potential stabilizing excitons and preventing thermal escape. Calculations estimate the increase in exciton binding energy due to quantum well confinement.
Reflectance and photoluminescence characterization of BexZn1Oleg Maksimov
This document summarizes research on the optical properties of BexZn1-xTe thin films grown by molecular beam epitaxy. Reflectance and photoluminescence measurements were performed on the epilayers as a function of BeTe content and temperature. An increase in emission line broadening was observed with higher BeTe content, which is attributed to alloy disorder. Temperature-dependent reflectance data showed a reduction in the variation of band gap energy with increasing BeTe content. This effect is proposed to be due to lattice hardening from BeTe decreasing the lattice contribution to the temperature dependence.
Exciton localization in MgxZnyCd1–x–ySe alloyOleg Maksimov
The document summarizes photoluminescence and reflectivity measurements of MgxZnyCd1–x–ySe epitaxial layers with varying Mg content (x). As Mg content increases, significant emission line broadening, an increase in activation energy, and a large Stokes shift are observed. For samples with high Mg content (x > 0.3), an anomalous temperature dependence of emission energy and line broadening is seen, attributed to exciton localization. Exciton localization on statistical CdSe clusters within the alloy is proposed as the most likely localization mechanism.
Percolation-based vibrational picture to estimate nonrandom N substitution in...Oleg Maksimov
This document discusses using Raman spectroscopy to estimate the degree of nonrandom nitrogen (N) substitution in GaAsN alloys. It finds evidence of two distinct Ga-N vibrational modes: one at around 475 cm-1 representing isolated Ga-N bonds, and another lower frequency mode at around 428 cm-1 representing Ga-N bonds within nitrogen-rich regions. This is interpreted using a model of mechanical contrast between the nitrogen-rich and nitrogen-poor regions, similar to models used for Be-chalcogenide alloys. Estimating the relative strengths of the two Ga-N modes suggests the nitrogen-rich regions incorporate around 30% of the total nitrogen, much higher than the approximately 4% seen in random Be
Magnetoresistance anomalies in (Ga,Mn)As epilayers with perpendicular magneti...Oleg Maksimov
This document summarizes magnetoresistance anomalies observed in tensile-strained (Ga,Mn)As epilayers with perpendicular magnetic anisotropy. The researchers observed "spikes" in the longitudinal magnetoresistance that are antisymmetric with respect to the direction of the magnetic field. These anomalies occur during magnetization reversal and are accompanied by a change in sign of the anomalous Hall effect. Angular sweeps of the magnetic field reveal that the anomalies have an antisymmetric dependence on the helicity of the field sweep. The data suggest that the antisymmetric anomalies originate from anomalous Hall effect contributions to the longitudinal resistance when domain walls are located between the voltage probes.
Direct-to-indirect band gap crossover for the BexZn1-xTe alloyOleg Maksimov
The document investigates the growth and optical properties of BexZn1-xTe epitaxial layers with Be concentrations ranging from 0-0.7. Reflectivity and photoluminescence spectra were used to determine the direct-indirect band gap crossover. The results indicate the crossover occurs at around x=0.28 Be concentration. Above this concentration, BexZn1-xTe behaves as an indirect semiconductor, while below it has direct band gap characteristics. The direct band gap increases linearly with Be content, while the indirect gap can be modeled by a quadratic equation related to composition.
High-Brightness 9XX-nm Pumps with Wavelength StabilizationOleg Maksimov
This document summarizes the development of high-power, high-brightness laser diode pumps for fiber lasers. It describes pumps capable of outputting over 100W of continuous wave power while maintaining high efficiency and beam quality. Key points discussed include:
1. Single emitter pumps have advantages over bar stacks in cost, reliability, and performance for applications requiring kilowatt-class output.
2. New pumps achieve over 65% efficiency and output over 100W while maintaining a beam numerical aperture below 0.13.
3. Wavelength stabilized pumps provide over 50W within a 1.5nm window, suitable for pumping specific gain media.
4. 100W-class pumps demonstrate high reliability with
This document summarizes research on developing high-power, high-brightness fiber coupled diode pumps. [1] New diode chips with cavity lengths of 4.5mm instead of the previous 3mm allow output power over 20W continuously while maintaining high efficiency and reliability. [2] Optimization of the layered semiconductor structure and ridge waveguide geometry achieved a peak power efficiency of over 72% and average efficiency over 60% up to 14W output. [3] Further optimization targeted high output power, demonstrating over 20W continuously with good efficiency at room temperature operation.
Hanle Effect Measurements of Spin Lifetime in Zn0.4Cd0.6Se Epilayers Grown on...Oleg Maksimov
This document summarizes a study that used the Hanle effect to measure spin lifetimes in ZnCdSe epilayers grown on InP substrates with varying n-doping levels. Four samples were studied: three Zn0.4Cd0.6Se samples with carrier densities of 8.0×1016 cm-3, 4.3×1017 cm-3, and 1.1×1018 cm-3, as well as an undoped Zn0.5Cd0.5Se sample. Measurements showed that spin lifetime varied non-monotonically with carrier density, reaching a maximum of ~10.5 ns for the sample near the metal-insulator transition.
Patterned three-color ZnCdSe/ZnCdMgSe quantum-well structures for integrated ...Oleg Maksimov
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2. 1088 Peiris et al.: Optical properties of molecular-beam-epitaxy-grown InGaMnAs 1088
While the Mn concentrations were obtained using elec-
tron probe microanalysis and x-ray photoelectron spectros-
copy, the In and Ga concentrations were determined using
the lattice parameters obtained by x-ray diffraction experi-
ments and comparing them to previously calibrated samples.
The thickness of the quaternary film was estimated from
RHEED oscillations and verified by x-ray reflectivity and
ellipsometry. Ellipsometric spectra were obtained using two
ellipsometers; a rotating analyzer ellipsometer operating be-
tween 200 and 1800 nm and a rotating compensator ellip-
someter operating between 2 and 30 m. For a given
sample, once the spectra were taken separately in each of
these instruments, they were merged together for the analy-
sis. Additionally, for each sample, room temperature ellipso-
metric data were obtained for at least two different incident
angles.
III. RESULTS AND DISCUSSION FIG. 1. Real part ͑⑀1͒ of the complex dielectric function of four different
Spectroscopic ellipsometry generally measures two pa- samples of ͑In0.5Ga0.5͒1−xMnxAs.
rameters, ⌿ and ⌬, at each wavelength that are related to the
ratio of reflection coefficients by
nonzero values for ⑀2͒ seems to blueshift as a function of the
Rp Mn concentration. In order to fully recognize the dependence
= = tan͑⌿͒ei⌬ ,
Rs of the critical point energies with respect to the Mn concen-
where R p is the complex reflection coefficient for light po- tration of the quaternary system, ⑀ for each sample was rep-
larized parallel to the plane of incidence, and Rs is the coef- resented using a parametric semiconductor model.19 In this
ficient for light polarized perpendicular to the plane of inci- method, ⑀ is expressed as a summation of energy-bounded,
dence. One must note that both ⌿ and ⌬ obtained from Gaussian-broadened continuous functions, accounting for
ellipsometry depend on the optical properties of the entire absorption effects that occur outside the model region.
structure, and since the technique is an inverse problem, a The ⑀ for all of the films were modeled according to the
suitable model has to be formulated to arrive at a reliable above stated scheme. This allowed us to determine two of
solution.17,18 the critical points associated with the electronic transition in
The ͑In0.5Ga0.5͒1−xMnx samples used in this study were the ͑In0.5Ga0.5͒1−xMnxAs quaternary system. In Fig. 3, E0 and
represented by a four layer model ͑i.e., InP substrate, E1 critical point energies are plotted as a function of Mn
In0.5Ga0.5As buffer, quaternary layer, and a surface oxide concentration. It is important to note that since the excitonic
layer͒. Using the sample in which the quaternary layer was effects dominate near the E1 critical point, the measurement
absent, ⑀ of the In0.5Ga0.5As buffer layer was first deter-
mined. The results obtained for the buffer layer were consis-
tent with the literature values for this particular alloy.19 For
the samples with the quaternary alloy, the thicknesses and ⑀
of the ͑In0.5Ga0.5͒1−xMnx layer were adjusted to match the
experimental data. This was achieved in two steps. First,
focusing only on the ⌿ and ⌬ spectra obtained in the trans-
parent region, ⑀ in the transparent region ͑i.e., below the
fundamental E0 band gap͒ as well as the thicknesses of the
quaternary system were determined. The thicknesses ob-
tained from this method fell within 10% of the values re-
corded by RHEED and x-ray reflectivity. After the layer
thickness and the transparent region optical properties were
determined, the next step was to simulate the above band gap
optical properties of this layer.15
The components of the complex dielectric function, ⑀1
and ⑀2, determined from the above procedure are plotted in
Figs. 1 and 2, respectively. In both figures, ⑀ of In0.5Ga0.5As
is shown as solid lines. As is evident from both Fig. 1 and 2,
the incorporation of Mn into the lattice alters ⑀, particularly FIG. 2. Imaginary part ͑⑀2͒ of the complex dielectric function of four differ-
as noted in Fig. 2, the onset of the initial absorption ͑i.e., ent samples of ͑In0.5Ga0.5͒1−xMnxAs.
J. Vac. Sci. Technol. B, Vol. 25, No. 3, May/Jun 2007
3. 1089 Peiris et al.: Optical properties of molecular-beam-epitaxy-grown InGaMnAs 1089
these dielectric functions were represented by a parametric
semiconductor model which accounts for absorption effects
outside the model region. Our analysis indicates that in
͑In0.5Ga0.5͒1−xMnxAs, while the critical point associated with
the fundamental gap, E0, blueshifts as a function of Mn con-
centration, the E1 critical point shows a redshift with respect
to the Mn concentration.
ACKNOWLEDGMENTS
The work at Kenyon was supported by grants from Re-
search Cooperation ͑CC-6027͒, American Chemical Society
͑PRF-41803B͒, and National Science Foundation ͑DMR-
0521147͒. The work at Penn State was supported by the Na-
tional Science Foundation.
1
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͑R1͒.15 It is evident that the fundamental band gap, repre- 8
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several diluted magnetic systems ͓see, for example, results 10
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K. S. Burch et al., Phys. Rev. Lett. 97, 087208 ͑2006͒.
14
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band structure calculations that would verify this phenom- 15
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JVST B - Microelectronics and Nanometer Structures