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Articles 1 - 20 of 20
Full-Text Articles in Physics
Sufficient Condition For The Coherent Control Of N -Qubit Systems, R. Cabrera, Chitra Rangan, W.E. Baylis
Sufficient Condition For The Coherent Control Of N -Qubit Systems, R. Cabrera, Chitra Rangan, W.E. Baylis
Physics Publications
We study quantum systems with even numbers N of levels that are completely state controlled by unitary transformations generated by Lie algebras isomorphic to sp(N) of dimension N(N+1) 2 as discussed by Albertini and D'Allesandro [IEEE Trans. Autom. Control 48, 1399 (2003)]. These Lie algebras are smaller than the corresponding su(N) with dimension N2 -1. We show that this reduction constrains the field-free Hamiltonian to have symmetric energy levels. An example of such a system is an n -qubit system with state-independent interaction terms. Using Clifford's geometric algebra to represent the quantum wave function of a finite system, we present …
A Multiplet Table For Neutral Helium (4he I) With Transition Rates, Gordon W. F. Drake, D. C. Morton
A Multiplet Table For Neutral Helium (4he I) With Transition Rates, Gordon W. F. Drake, D. C. Morton
Physics Publications
This paper combines the precise determination of the energy levels of 4He I from calculations and experiments with theoretical transition probabilities to present multiplet tables and finding lists for the fine structure of the helium atom. The tabulated transition rates and oscillator strengths include corrections for singlet-triplet mixing and spin-orbit coupling, but not the higher order relativistic terms nor the finite nuclear mass, although the latter are tabulated for future use. The results are consistent with laboratory lifetimes and oscillator strengths, but very few measurements are accurate enough to be stringent tests. An Appendix discusses the corrections for finite nuclear …
Escherichia Coli Identification And Strain Discrimination Using Nanosecond Laser-Induced Breakdown Spectroscopy, J. Diedrich, Steven J. Rehse, S. Palchaudhuri
Escherichia Coli Identification And Strain Discrimination Using Nanosecond Laser-Induced Breakdown Spectroscopy, J. Diedrich, Steven J. Rehse, S. Palchaudhuri
Physics Publications
Three strains of Escherichia coli, one strain of environmental mold, and one strain of Candida albicans yeast have been analyzed by laser-induced breakdown spectroscopy using nanosecond laser pulses. All microorganisms were analyzed while still alive and with no sample preparation. Nineteen atomic and ionic emission lines have been identified in the spectrum, which is dominated by calcium, magnesium, and sodium. A discriminant function analysis has been used to discriminate between the biotypes and E. coli strains. This analysis showed efficient discrimination between laser-induced breakdown spectroscopy spectra from different strains of a single bacteria species.
Detection Of Trace Al In Model Biological Tissue With Laser-Induced Breakdown Spectroscopy, M.D. Adamson, Steven J. Rehse
Detection Of Trace Al In Model Biological Tissue With Laser-Induced Breakdown Spectroscopy, M.D. Adamson, Steven J. Rehse
Physics Publications
Laser-induced breakdown spectroscopy (LIBS), which is an excellent tool for trace elemental analysis, was studied as a method of detecting sub-part-per-106 (ppm) concentrations of aluminum in surrogates of human tissue. Tissue was modeled using a 2% agarose gelatin doped with an Al2O3 nanoparticle suspension. A calibration curve created with standard reference samples of known Al concentrations was used to determine the limit of detection, which was less than 1 ppm. Rates of false negative and false positive detection results for a much more realistic sampling methodology were also studied, suggesting that LIBS could be a candidate for the real-time in …
Pathogenic Escherichia Coli Strain Discrimination Using Laser-Induced Breakdown Spectroscopy, J. Diedrich, Steven J. Rehse, S. Palchaudhuri
Pathogenic Escherichia Coli Strain Discrimination Using Laser-Induced Breakdown Spectroscopy, J. Diedrich, Steven J. Rehse, S. Palchaudhuri
Physics Publications
A pathogenic strain of bacteria, Escherichia coli O157:H7 (enterohemorrhagic E. coli or EHEC), has been analyzed by laser-induced breakdown spectroscopy (LIBS) with nanosecond pulses and compared to three nonpathogenic E. coli strains: a laboratory strain of K-12 (AB), a derivative of the same strain termed HF4714, and an environmental strain, E. coli C (Nino C). A discriminant function analysis (DFA) was performed on the LIBS spectra obtained from live colonies of all four strains. Utilizing the emission intensity of 19 atomic and ionic transitions from trace inorganic elements, the DFA revealed significant differences between EHEC and the Nino C strain, …
Hyperfine Structure Of The 23p State Of 3he With And Without An External Magnetic Field, Q. Wu, Gordon W. F. Drake
Hyperfine Structure Of The 23p State Of 3he With And Without An External Magnetic Field, Q. Wu, Gordon W. F. Drake
Physics Publications
The hyperfine structure of the 23P state of 3He with and without an external magnetic field is precisely calculated. All the linear terms, diamagnetic terms and the α2 relativistic correction terms are included in the Zeeman Hamiltonian. The values of the fields for 32 crossings and 5 anticrossings of the magnetic sublevels are theoretically predicted for magnetic field strengths up to 10 000 gauss. The results are compared with experimental data and other theoretical works. All related matrix elements are calculated with high accuracy by the use of double basis set Hylleraas-type variational wavefunctions. © 2007 IOP Publishing Ltd.
Editorial: The Scope Of Physical Review A And Editorial Procedures, Gordon W. F. Drake
Editorial: The Scope Of Physical Review A And Editorial Procedures, Gordon W. F. Drake
Physics Publications
No abstract provided.
Ionization Energy Of Li 6,7 Determined By Triple-Resonance Laser Spectroscopy, B. A. Bushaw, W. Nortershauser, Gordon W. F. Drake, H. J. Kluge
Ionization Energy Of Li 6,7 Determined By Triple-Resonance Laser Spectroscopy, B. A. Bushaw, W. Nortershauser, Gordon W. F. Drake, H. J. Kluge
Physics Publications
Rydberg level energies for Li7 were measured using triple-resonance laser excitation, followed by drifted field ionization. In addition to the principal n P2 series, weak Stark mixing from residual electric fields allowed observation of n S2 and hydrogenic Stark manifold series at higher n. Limit analyses for the series yield the spectroscopic ionization energy EI (Li7) =43 487.159 40 (18) cm-1. The Li 6,7 isotope shift (IS) was measured in selected n P2 Rydberg levels and extrapolation to the series limit yields IS (EI) 7,6 =18 067.54 (21) MHz. Results are compared with recent theoretical calculations: EI values from experiment …
Theoretical Study Of Deep-Defect States In Bulk Pbte And In Thin Films, Khang Hoang, S. D. Mahanti, Puru Jena
Theoretical Study Of Deep-Defect States In Bulk Pbte And In Thin Films, Khang Hoang, S. D. Mahanti, Puru Jena
Physics Publications
The nature of neutral defect states in PbTe, a narrow band-gap semiconductor, has been studied using density functional theory and supercell models. We find that the defect states associated with different substitutional impurities and native point defects found in bulk PbTe are preserved in the film geometry, but get modified as one goes from the surface to the subsurface layers and then to the bulklike layers. These modifications, which usually occur in the neighborhood of the band gap, will impact the transport properties of the films. Energetic studies of different impurities and native defects embedded in bulk PbTe and in …
Ab Initio Study Of Electronic And Magnetic Properties Of The C-Codoped Ga1−Xmnxn (101¯0) Surface, Q. Wang, Q. Sun, Puru Jena
Ab Initio Study Of Electronic And Magnetic Properties Of The C-Codoped Ga1−Xmnxn (101¯0) Surface, Q. Wang, Q. Sun, Puru Jena
Physics Publications
First principles calculations based on gradient corrected density functional theory have been carried out to study the magnetic coupling between Mn atoms in pure and carbon doped Ga1−xMnxN thin films. We show that the ground state of Mn-doped GaN (101¯0) thin film, with Mn replacing the Ga sites, is antiferromagnetic but becomes ferromagnetic when it is codoped with C. The interaction between the Mn spins via the delocalized holes introduced by codoping of C at N sites is responsible for this transition. The overlap between Mn 3d and C 2p in the spin-up band renders half-metallic character to the C …
Ground State Structures And Photoelectron Spectroscopy Of [Co-M(Coronene)](-) Complexes, Anil K. Kandalam, Boggavarapu Kiran, Puru Jena, Xiang Li, Andrej Grubisic, Kit H. Bowen
Ground State Structures And Photoelectron Spectroscopy Of [Co-M(Coronene)](-) Complexes, Anil K. Kandalam, Boggavarapu Kiran, Puru Jena, Xiang Li, Andrej Grubisic, Kit H. Bowen
Physics Publications
A synergistic approach involving theory and experiment has been used to study the structure and properties of neutral and negatively charged cobalt-coronene [Com(coronene)] complexes. The calculations are based on density functional theory with generalized gradient approximation for exchange and correlation potential, while the experiments are carried out using photoelectron spectroscopy of mass selected anions. The authors show that the geometries of neutral and anionic Co(coronene) and Co2(coronene) are different from those of the corresponding iron-coronene complexes and that both the Co atom and the dimer prefer to occupy η2-bridge binding sites. However, the magnetic coupling between the Co atoms remains …
On The Structural And Energetic Properties Of The Hydrogen Absorber Li2mg(Nh)2, C. Moysés Araújo, Ralph H. Scheicher, Puru Jena, Rajeev Ahuja
On The Structural And Energetic Properties Of The Hydrogen Absorber Li2mg(Nh)2, C. Moysés Araújo, Ralph H. Scheicher, Puru Jena, Rajeev Ahuja
Physics Publications
The authors have performed density functional theory based calculations of several possible conformations for the crystal structure of Li2Mg(NH)2 and they confirm the α phase, resolved from both x-ray and neutron diffraction data, as the ground-state configuration. It is also found that although the N–H bond is stronger in Li2Mg(NH)2 than in Li2NH, hydrogen release from Li2Mg(NH)2/LiH mixture displays more favorable thermodynamics than that from the Li2NH∕LiH mixture. The insights gained from this seemingly counterintuitive result should prove helpful in the search for promising hydrogen storage materials.
First-Principles Study Of Magnetic Properties In V-Doped Zno, Qian Wang, Qiang Sun, Puru Jena, Zheng Hu, R. Note, Y. Kawazoe
First-Principles Study Of Magnetic Properties In V-Doped Zno, Qian Wang, Qiang Sun, Puru Jena, Zheng Hu, R. Note, Y. Kawazoe
Physics Publications
A comprehensive theoretical study of electronic and magnetic properties of V-doped ZnO in bulk as well as (112¯0)thin films has been performed using density functional theory. Vanadium atoms substituted at Zn sites show very little selectivity of site occupancy. More importantly, different geometries with ferromagnetic, ferrimagnetic, and antiferromagnetic configurations are found to be energetically nearly degenerate both in Zn1−xVxO bulk and subsurface layers of the thin film. On the other hand, V atoms couple ferromagnetically when they occupy surface sites of the thin film. The diverse magnetic behaviors in V-doped ZnO account for the many reported conflicting experimental results.
Dehydrogenation From 3d-Transition-Metal-Doped Naalh4: Prediction Of Catalysts, A. Blomqvist, C. Moysés Araújo, Puru Jena, R. Ahuja
Dehydrogenation From 3d-Transition-Metal-Doped Naalh4: Prediction Of Catalysts, A. Blomqvist, C. Moysés Araújo, Puru Jena, R. Ahuja
Physics Publications
A fundamental understanding of the role of catalysts in improving the kinetics and thermodynamics of hydrogen sorption in NaAlH4 is the key for using this material in hydrogen storage. The authors present a systematic theoretical study of energies needed to desorb hydrogen in 3dtransition metal (Sc–Cu)-doped NaAlH4. They show that Cr and Fe atoms can be far more effective catalysts than Ti in desorbing hydrogen. The role of the 3d metal atoms in improving the thermodynamics of dehydrogenation is attributed to a significant shortening of the bond length with neighboring Al atoms.
Local Electronic And Optical Behaviors Of A-Plane Gan Grown Via Epitaxial Lateral Overgrowth, J. C. Moore, V. Kasliwal, A. A. Baski, X. Ni, Ü. Özgür, Hadis Morkoç
Local Electronic And Optical Behaviors Of A-Plane Gan Grown Via Epitaxial Lateral Overgrowth, J. C. Moore, V. Kasliwal, A. A. Baski, X. Ni, Ü. Özgür, Hadis Morkoç
Physics Publications
Conductive atomic force microscopy and near-field optical microscopy (NSOM) were used to study the morphology, conduction, and optical properties of a-plane GaNfilmsgrown via epitaxial lateral overgrowth (ELO) by metal organic chemical vapor deposition. The AFM images for the coalesced ELOfilms show undulations, where the window regions appear as depressions with a high density of surface pits. At reverse bias below 12V, very low uniform conduction (2pA) is seen in the window regions. Above 20V, a lower-quality sample shows localized sites inside the window regions with significant leakage, indicating a correlation between the presence of surface pits and leakage sites. Room …
Magnetic Endohedral Metallofullerenes With Floppy Interiors, Meichun Qian, Stephen V. Ong, Shiv N. Khanna, Mark B. Knickelbein
Magnetic Endohedral Metallofullerenes With Floppy Interiors, Meichun Qian, Stephen V. Ong, Shiv N. Khanna, Mark B. Knickelbein
Physics Publications
It is shown that Gd3N@C80 is a highly magnetic and very stable motif that allows enhanced contrast magnetic resonance imaging and electric dipole moment with potential for cancer treatment. Using a synergistic approach combining Stern-Gerlach experiments in beams and first-principles electronic structure studies, it is demonstrated that an isolated Gd3N has a ground state spin moment of 23μBfollowed by a noncollinear state of 17.2μB only 88meV above the ground state. The large moment is largely due to localized f electrons. As a Gd3N is embedded inside a C80 cage, the localized felectrons maintain the magnetic character while the hybridization between …
Structure Of Siau(16): Can A Silicon Atom Be Stabilized In A Gold Cage?, Qiang Sun, Qian Wang, Gang Chen, Puru Jena
Structure Of Siau(16): Can A Silicon Atom Be Stabilized In A Gold Cage?, Qiang Sun, Qian Wang, Gang Chen, Puru Jena
Physics Publications
Nanostructures of Au and Si as well as Au–Si hybrid structures are topics of great current interest from both scientific and technological points of view. Recent discovery of Au clusters having fullerenelike geometries and the possibility of endohedral complexes with Si atoms inside the Au cage opens new possibilities for designing Au–Si nanostructures. Using ab initio simulated annealing method we have examined the stability of Si–Au16 endohedral complex. Contrary to what we believed, we find that the endohedral configuration is metastable and the structure where Si atom binds to the exterior surface of the Au16 cage is the lowest energy …
An Ab Initio Investigation On The Endohedral Metallofullerene Gd 3 N – C 80, M. C. Qian, S. N. Khanna
An Ab Initio Investigation On The Endohedral Metallofullerene Gd 3 N – C 80, M. C. Qian, S. N. Khanna
Physics Publications
First-principles electronic structure studies on the ground state geometry and electronic and magnetic properties of bare and hydrogen coated metallofullerene Gd3N–C80 have been carried out within a density functional formalism. The correlation effects are incorporated either through a generalized gradient corrected functional or through an on-site Coulomb interaction (LDA+U). It is shown that the bare Gd3N–C80 possess a ferromagnetic ground state with a large spin moment of 21μB that is highly stable against spin fluctuations. The simulated Raman spectrum shows that the low-energy peaks are contributed by the floppy movement of N atom. As to the effect of addition of …
Temperature-Dependent Characterization Of Thin-Film Filters For Optical Communications, Corneliu Rablau, Christopher Schenk
Temperature-Dependent Characterization Of Thin-Film Filters For Optical Communications, Corneliu Rablau, Christopher Schenk
Physics Publications
The explosive increase in the demand for transmission capacity for optical communications networks has resulted in a widespread deployment of dense wavelength division multiplexing (DWDM). Thin film filters are a critical component of DWDM devices. They consist of Fabry-Perot resonant cavities obtained by vacuum deposition on a glass substrate of alternating layers of two dielectric materials of different indices of refraction. The performance requirements for these filters are determined by the density of channels to be multiplexed. For the 100 GHz ITU grid, these channels are spaced 100 GHz (0.8 nm) apart. Typical figures of merit include the insertion loss …
Ferromagnetic To Ferrimagnetic Crossover In Cr-Doped Gan Nanohole Arrays, Q. Wang, Q. Sun, Puru Jena, Y. Kawazoe
Ferromagnetic To Ferrimagnetic Crossover In Cr-Doped Gan Nanohole Arrays, Q. Wang, Q. Sun, Puru Jena, Y. Kawazoe
Physics Publications
Using spin-polarized density-functional theory with exchange and correlation potential, approximated by both the generalized gradient approximation (GGA) and the GGA+U methods, we show that the coupling between a pair of Cr atoms substituted in GaN nanoholes is ferromagnetic. The interaction between the two Cr atoms, each carrying an average magnetic moment of around 2.5μB, is short ranged and mediated by the neighboring N atom. As the concentration of Cr increases, clustering ensues and the coupling changes from ferromagnetic to ferrimagnetic resulting in a significant reduction in the average magnetic moment per Cr atom.