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- Enantiomer separation (2)
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- Physics Faculty Research & Creative Works (31)
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Articles 1 - 30 of 70
Full-Text Articles in Physical Sciences and Mathematics
Semiquantal Modeling Of Thermal Vibrational Relaxation Of Diatomic Molecules, Ronald James Bieniek, Steven J. Lipson
Semiquantal Modeling Of Thermal Vibrational Relaxation Of Diatomic Molecules, Ronald James Bieniek, Steven J. Lipson
Physics Faculty Research & Creative Works
Vibrationally excited molecules play an important role in the spectroscopy, energetics, and chemical behavior of a wide range of gaseous systems of scientific and applied interest. Unfortunately, many desired collisional relaxation rates have not yet been experimentally measured, and current theoretical methods are often inadequate or too cumbersome for practical application. We report a semiquantal two-parameter scaling method for predicting relaxation rates that is very simple to employ, and impressively fits the temperature and vibrational dependencies of quantum mechanical and experimental collisional relaxation rates for several diatomic molecules (e.g., N2, HF, OH, NO) over many orders of magnitude.
Angle-Resolved X-Ray Circular And Magnetic Circular Dichroisms: Definitions And Applications, Sy Y. Tong, X. Q. Guo, James G. Tobin, George Daniel Waddill
Angle-Resolved X-Ray Circular And Magnetic Circular Dichroisms: Definitions And Applications, Sy Y. Tong, X. Q. Guo, James G. Tobin, George Daniel Waddill
Physics Faculty Research & Creative Works
We introduce definitions of angle-resolved x-ray circular dichroism (ARXCD) and magnetic x-ray circular dichroism (ARMXCD). As defined, the much larger effect of circular dichroism (ARXCD) is separated from the smaller magnetic (ARMXCD) effect. In all materials, ARXCD is zero along mirror planes while nonzero elsewhere. ARMXCD is nonzero only in magnetic materials. The measurement and analysis of ARMXCD allow element specific surface magnetism and surface structure as well as their inter-relationship to be studied as functions of the outgoing electron's direction.
Elucidation Of Vancomycin's Enantioselective Binding Site Using Its Copper Complex, Usha B. Nair, Samuel S.C. Chang, Daniel W. Armstrong, Yasir Y. Rawjee, Drake S. Eggleston, James V. Mcardle
Elucidation Of Vancomycin's Enantioselective Binding Site Using Its Copper Complex, Usha B. Nair, Samuel S.C. Chang, Daniel W. Armstrong, Yasir Y. Rawjee, Drake S. Eggleston, James V. Mcardle
Chemistry Faculty Research & Creative Works
Vancomycin forms a stable complex with Cu2+ in neutral aqueous solutions. The enantioselectivity of native vancomycin was compared to that of the copper-vancomycin complex using capillary electrophoresis (CE). There were significant differences in their enantioselectivities. This can be attributed to the fact that copper ion coordinates with some of the same functional groups in vancomycin that are essential for chiral recognition and enantioresolution. An amine moiety that provides one of the more important enantioselective interactions was identified. This chiral interaction site was illustrated using a color-coded, space-filling model of the X-ray crystal structure of the copper-vancomycin complex. Successful enantioselective interactions …
Cycle Symmetry And Its Causes, Cisco Group (Virgilian And Wolfcampian), Texas, Wan Yang
Cycle Symmetry And Its Causes, Cisco Group (Virgilian And Wolfcampian), Texas, Wan Yang
Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works
181 transgressive-regressive cycles composed of nonmarine and marine carbonate and siliciclastic rocks of the Cisco Group on the Eastern Shelf, Texas, display complex characteristics at both hemicycle and full-cycle scales. They are delineated on the basis of successive changes of depositional environments, stratal boundary relations, and stratigraphic position. Transgressive and regressive stratigraphic environment gradients are defined as the magnitude of environmental shift divided by thickness for each hemicycle. They indicate the rates of lateral environmental shifts during transgression and regression. Cycle symmetry index is defined as the ratio between transgressive and regressive stratigraphic environment gradients. It provides a measure of …
Some Global Bifurcation Results For Variational Inequalities, Vy Khoi Le
Some Global Bifurcation Results For Variational Inequalities, Vy Khoi Le
Mathematics and Statistics Faculty Research & Creative Works
No abstract provided.
Breakdown Of Landau-Ginzburg-Wilson Theory For Certain Quantum Phase Transitions, Thomas Vojta, Dietrich Belitz, Rajesh S. Narayanan, Theodore R. Kirkpatrick
Breakdown Of Landau-Ginzburg-Wilson Theory For Certain Quantum Phase Transitions, Thomas Vojta, Dietrich Belitz, Rajesh S. Narayanan, Theodore R. Kirkpatrick
Physics Faculty Research & Creative Works
The quantum ferromagnetic transition of itinerant electrons is considered. It is shown that the Landau-Ginzburg-Wilson theory described by Hertz and others breaks down due to a singular coupling between fluctuations of the conserved order parameter. This coupling induces an effective long-range interaction between the spins of the form 1/r2d-1. It leads to unusual scaling behavior at the quantum critical point in 1 < d ≤ 3 dimensions, which is determined exactly.
Mechanism Of Signal Suppression By Anionic Surfactants In Capillary Electrophoresis-Electrospray Ionization Mass Spectrometry, Kimber L. Rundlett, Daniel W. Armstrong
Mechanism Of Signal Suppression By Anionic Surfactants In Capillary Electrophoresis-Electrospray Ionization Mass Spectrometry, Kimber L. Rundlett, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
Micellar-mediated capillary electrophoresis (CE) is used for a wide variety of applications, including the separation of pharmaceuticals, environmental contaminants, illicit drugs, DNA fragments, and many other biological samples. The electrospray ionization interface is one of the most common CE-MS interfaces. Coupling micellar-mediated CE separations with MS detection combines two very powerful, widely applicable analytical techniques. Some types of surfactants strongly interfere with electrospray ionization mass spectrometric (ESI-MS) detection of analytes, and in many cases the ESI-MS analyte signals are completely quenched. Only a few reports have appeared that describe the ESI-MS detection of analytes in the presence of surfactants; however, …
Run-Time Security Evaluation: Can We Afford It?, Cristina Serban, Bruce M. Mcmillin
Run-Time Security Evaluation: Can We Afford It?, Cristina Serban, Bruce M. Mcmillin
Computer Science Faculty Research & Creative Works
The use of the run-time security evaluation (RTSE) method for a distributed application takes a toll in overall application performance. The associated overhead and its major sources are discussed, along with possible solutions for improvements, and questions that remain still open.
Investigation On Enantiomeric Separations Of Fluorenylmethoxycarbonyl Amino Acids And Peptides By High-Performance Liquid Chromatography Using Native Cyclodextrins As Chiral Stationary Phases, Y. Tang, J. Zukowski, Daniel W. Armstrong
Investigation On Enantiomeric Separations Of Fluorenylmethoxycarbonyl Amino Acids And Peptides By High-Performance Liquid Chromatography Using Native Cyclodextrins As Chiral Stationary Phases, Y. Tang, J. Zukowski, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
A systematic study was carried out to investigate enantiomeric separations of fluorenylmethoxycarbonyl (FMOC) amino acids and their peptides. Twenty amino acids were derivatized by 9-fluorenylmethyl chloroformate (FMOC-Cl) and its analogues, FMOC-glycyl-Cl and FMOC-β-alanyl-Cl. All derivatives were chromatographed on native β- and γ-cyclodextrin columns using acetonitrile as the main mobile phase component. The results indicated that glycyl and β-alanyl groups between FMOC and amino acid moieties enhanced chiral selectivities of amino acid derivatives. The addition of modifiers, triethylamine, acetic acid and methanol, into the mobile phase caused alterations in retention, enantiorecognition and elution order. The structures of amino acids and the …
Theory Of The Seebeck Coefficient In Lacro₃ And Related Perovskite Systems, D. B. Marsh, Paul Ernest Parris
Theory Of The Seebeck Coefficient In Lacro₃ And Related Perovskite Systems, D. B. Marsh, Paul Ernest Parris
Physics Faculty Research & Creative Works
We consider the Seebeck coefficient in LaCrO3 and related transition-metal-oxide perovskites using a model for electronic conduction based on the electronic structure of the 3d orbitals of the B-site transition-metal cations. Relations for the Seebeck coefficient are presented for those perovskite systems in which electronic conduction is through the t2g states of the B-site transition-metal cations. High- and low-temperature limits for the Seebeck coefficient are identified for the cases of both strong and weak magnetic coupling between electron spins. In these high- and low-temperature limits, the Seebeck coefficient is determined as a function of carrier concentration. Results are …
Localized Amplification Of Seismic Waves And Correlation With Damage Due To The Northridge Earthquake: Evidence For Focusing In Santa Monica, Stephen S. Gao, Kelly H. Liu, Paul M. Davis, Leon Knopoff
Localized Amplification Of Seismic Waves And Correlation With Damage Due To The Northridge Earthquake: Evidence For Focusing In Santa Monica, Stephen S. Gao, Kelly H. Liu, Paul M. Davis, Leon Knopoff
Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works
The analysis of seismograms from 32 aftershocks recorded by 98 seismic stations installed after the Northridge earthquake in the San Fernando Valley, the Santa Monica Mountains, and Santa Monica, California, indicates that the enhanced damage in Santa Monica is explained in the main by focusing due to a lens structure at a depth of several kilometers beneath the surface and having a finite lateral extent. The diagnosis was made from the observation of late-arriving S phases with large amplitudes, localized in the zones of large damage. The azimuths and angles of incidence of the seismic rays that give rise to …
Proton Spin-Lattice Relaxation Of Water Molecules In Ferrous-Ferric/Agarose Gel System, Tadashi Tokuhiro, Alan Appleby, Armin A. Leghrouz, Rodney Metcalf, Robert Tokarz
Proton Spin-Lattice Relaxation Of Water Molecules In Ferrous-Ferric/Agarose Gel System, Tadashi Tokuhiro, Alan Appleby, Armin A. Leghrouz, Rodney Metcalf, Robert Tokarz
Chemistry Faculty Research & Creative Works
Proton spin-lattice relaxation time (T1) of water in aqueous solutions of ferrous and ferric ions and in the corresponding agarose gel systems have been studied in the light of NMR relaxation theory. The theoretical analysis of 1/T1's has revealed that, at the microscopic level, changes in the solvation states of paramagnetic ions in aqueous or gel environment are greater than difference in the paramagnetism between ferric and ferrous ions. The former change is the primary factor for the exhibition of radiation effect. At the phenomenological level, we have confirmed and demonstrated that: (1) Radiation effect is …
Higher-Order Binding Corrections To The Lamb Shift Of 2p States, Ulrich D. Jentschura, Krzysztof Pachucki
Higher-Order Binding Corrections To The Lamb Shift Of 2p States, Ulrich D. Jentschura, Krzysztof Pachucki
Physics Faculty Research & Creative Works
We present an improved calculation of higher-order corrections to the one-loop self-energy of 2P states in hydrogenlike systems with small nuclear charge Z. The method is based on a division of the integration with respect to the photon energy into a high- and a low-energy part. The high-energy part is calculated by an expansion of the electron propagator in powers of the Coulomb field. The low-energy part is simplified by the application of a Foldy-Wouthuysen transformation. This transformation leads to a clear separation of the leading contribution from the relativistic corrections and removes higher-order terms. The method is applied to …
Relation Between Charge-Dipole Interactions And The Sqrt(E)-Dependent Mobility In Molecularly Doped Polymers, Paul Ernest Parris
Relation Between Charge-Dipole Interactions And The Sqrt(E)-Dependent Mobility In Molecularly Doped Polymers, Paul Ernest Parris
Physics Faculty Research & Creative Works
Time-of-flight measurements on a wide variety of molecularly-doped polymers reveal carrier mobilities that exhibit an exponential dependence on the square root of the applied electric field. Recent attempts to explain the observed field dependence have focused on the role played by spatial and energetic disorder. It as also been conjectured that the charge-dipole interactions often identified as the source of energetic disorder could be of sufficient range to lead to correlations in the energies of neighboring hopping sites. We have analytically explored the effect of such correlations on high field carrier transport in random potentials, and discuss how particular features …
Neutron Diffraction Structural Study Of Ce₂Fe₁₇₋ₓgaₓ, H. Luo, Z. Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow
Neutron Diffraction Structural Study Of Ce₂Fe₁₇₋ₓgaₓ, H. Luo, Z. Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow
Physics Faculty Research & Creative Works
Six samples of Ce2Fe17-xGax with nominal Ga content x equal to 0, 0.3, 0.5, 0.7, 1.0, 2.0 have been studied by powder neutron diffraction at room temperature. Both crystalline and magnetic refinements have been carried out. All six samples adopt the Th2Zn17-type rhombohedral structure. The only additional phase found is α-iron. Gallium atoms are found to have high affinity for the iron 18h site, and are absent from the 9d and 18f sites. The Ga substitution for Fe leads to an expansion of both the a and c axes. The Curie …
Comparison And Modeling Study Of Vancomycin, Ristocetin A, And Teicoplanin For Ce Enantioseparations, Mary P. Gasper, Alain Berthod, Usha B. Nair, Daniel W. Armstrong
Comparison And Modeling Study Of Vancomycin, Ristocetin A, And Teicoplanin For Ce Enantioseparations, Mary P. Gasper, Alain Berthod, Usha B. Nair, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
The structurally related glycopeptide antibiotics vancomycin, ristocetin A, and teicoplanin can all be used as chiral selectors in capillary electrophoresis (CE). Both experimental and modeling studies were done to elucidate their similarities and differences. There are identifiable morphological differences in the aglycon macrocyclic portions of these three compounds. In addition, there are other structural distinctions that can affect their CE enantioselectivity, migration times, and efficiency. Teicoplanin is the most distinct of the three and is the only one that is surface active. Its aggregational properties appear to affect its enantioselectivity among other things. The similar but not identical structures of …
Anisotropy And Polarization In Charge Changing Collisions Of C⁴⁺ With Na(3s) And Laser Aligned Na(3p), S. Schippers, R. Hoekstra, R. Morgenstern, Ronald E. Olson
Anisotropy And Polarization In Charge Changing Collisions Of C⁴⁺ With Na(3s) And Laser Aligned Na(3p), S. Schippers, R. Hoekstra, R. Morgenstern, Ronald E. Olson
Physics Faculty Research & Creative Works
Absolute cross sections for C3+(6→5) emission at 465.7 nm after collisions of C4+ ions with ground state Na(3s) and laser excited aligned Na(3p) atoms are measured over the collision energy range of 3-7 keV amu-1. For Na(3s) polarizations are observed by measuring the linear polarization of the emitted light. In these collisions the polarization is found to be 0.33 and almost independent of the collision energy. Cross sections for collisions with the Na(3p) target are up to five times larger than for collisions with Na(3s). Slightly larger cross sections are measured when the laser excited Na(3p) target is Π-aligned as …
Charge-Dipole Model For The Universal Field Dependence Of Mobilities In Molecularly Doped Polymers, David H. Dunlap, Paul Ernest Parris, Vasudev M. Kenkre
Charge-Dipole Model For The Universal Field Dependence Of Mobilities In Molecularly Doped Polymers, David H. Dunlap, Paul Ernest Parris, Vasudev M. Kenkre
Physics Faculty Research & Creative Works
Using the general result that the mobility μ, of charge carriers driven in a spatially correlated random potential by an electric field E can be expressed in terms of the Laplace transform of a particular correlation function related to the random potential, we demonstrate that the exponential dependence of μ on √E universally observed in molecularly doped polymers arises naturally from the interaction of charge carriers with randomly distributed permanent dipoles.
Binary Nucleation Kinetics. Iii. Transient Behavior And Time Lags, Barbara Ellen Wyslouzil, Gerald Wilemski
Binary Nucleation Kinetics. Iii. Transient Behavior And Time Lags, Barbara Ellen Wyslouzil, Gerald Wilemski
Physics Faculty Research & Creative Works
Transient binary nucleation is more complex than unary because of the bidimensionality of the cluster formation kinetics. To investigate this problem qualitatively and quantitatively, we numerically solved the birth-death equations for vapor-to-liquid phase transitions. Our previous work [J. Chem. Phys 103, 1137 (1995)] showed that the customary saddle point and growth path approximations are almost always valid in steady state gas phase nucleation and only fail if the nucleated solution phase is significantly nonideal. The current work demonstrates that in its early transient stages, binary nucleation rarely, if ever, occurs via the saddle point. This affects not only the number …
Structural And Magnetic Studies On Prba2fe3o8, V. P.S. Awana, Latika Menon, S. K. Malik, Apurva Mehta, Sanjay Mishra, William B. Yelon
Structural And Magnetic Studies On Prba2fe3o8, V. P.S. Awana, Latika Menon, S. K. Malik, Apurva Mehta, Sanjay Mishra, William B. Yelon
Physics Faculty Research & Creative Works
It is known that Fe moments order antiferromagnetically with Néel temperature, TN, above 700 K in RBa2Fe3O7-δ with R=Y and Eu, and Pr moments order antiferromagnetically in PrBa2Cu3,O7-δ, with TN of 17 K. We have synthesized PrBa2Fe3O8 to study the ordering of Pr and Fe moments. From X-ray and neutron diffraction studies, this compound is found to crystallize in the tetragonal structure (space group P4/mmm). 57Fe Mössbauer studies show a complex hyperfine split pattern at 77 K, but a doublet superimposed on a six-line pattern at 300 K implying that some of the Fe moments order magnetically between 77 and …
A Classical Analysis Of Proton Collisions With Ground-State And Excited, Aligned Sodium Targets, C. J. Lundy, Ronald E. Olson
A Classical Analysis Of Proton Collisions With Ground-State And Excited, Aligned Sodium Targets, C. J. Lundy, Ronald E. Olson
Physics Faculty Research & Creative Works
The dependence of electron capture and ionization processes on the pre-collision electronic distribution is examined for the systems H+ + Na(3s, 3pΣ, 3pΠ) primarily in the energy range 1-15 keV. Populations of the capture and ionization channels as well as the coherence of the post-collision electronic distribution of the capture product are formulated using the classical trajectory Monte Carlo (CTMC) method. Total capture and ionization cross sections arising from initially aligned Na(3p) targets exhibit transient behaviour near the velocity-matching energy of 5.7 keV. This observation is described in terms of anisotropy parameters; anisotropy effects are also analysed for the capture …
State-Selective Electron Capture In Low Velocity Multiply Charged Ion, Helium Collisions, A. Cassimi, S. Duponchel, X. Flechard, P. Jardin, P. Sortais, D. Hennecart, Ronald E. Olson
State-Selective Electron Capture In Low Velocity Multiply Charged Ion, Helium Collisions, A. Cassimi, S. Duponchel, X. Flechard, P. Jardin, P. Sortais, D. Hennecart, Ronald E. Olson
Physics Faculty Research & Creative Works
Recoil ion momentum spectroscopy has been applied to study low energy, state-selective single electron capture by highly charged projectiles. The specific systems investigated are fully stripped 6.82 keV/u Ne10+ 6.82 keV/u Ar18+ on He. Measurements of the He+ recoil ion longitudinal momenta are used to determine the final n-state dependence of the captured electron. Simultaneous measurement of the transverse momenta of the recoil ion yields information about the impact parameter dependence of the reaction and the reaction window for electron capture. © 1996 The American Physical Society.
Facile Liquid Chromatographic Enantioresolution Of Native Amino Acids And Peptides Using A Teicoplanin Chiral Stationary Phase, Alain Berthod, Youbang Liu, Christina Bagwill, Daniel W. Armstrong
Facile Liquid Chromatographic Enantioresolution Of Native Amino Acids And Peptides Using A Teicoplanin Chiral Stationary Phase, Alain Berthod, Youbang Liu, Christina Bagwill, Daniel W. Armstrong
Chemistry Faculty Research & Creative Works
The glycopeptide antibiotic teicoplanin is shown to be a highly effective stationary phase chiral selector for the resolution of underivatized amino-acid and imino-acid enantiomers. Fifty four of these compounds (including all chiral protein amino acids) as well as a number of dipeptides were resolved. Hydro-organic mobile phases are used and no buffers or added salts are needed in most cases. Hence the purified analytes are easily isolated in pure form, if needed, by evaporating of the solvent. The effect of pH, organic modifier type and amount are discussed. The enantioselective separation mechanism is examined using both molecular modeling and retention …
Neutron Diffraction And Magnetic Studies Of Rfe₁₂₋ₓtₓcY (R=Y,Er; T=V,Ti,Mo) Alloys, Z. Hu, William B. Yelon, X. D. Zhang, William Joseph James
Neutron Diffraction And Magnetic Studies Of Rfe₁₂₋ₓtₓcY (R=Y,Er; T=V,Ti,Mo) Alloys, Z. Hu, William B. Yelon, X. D. Zhang, William Joseph James
Physics Faculty Research & Creative Works
RFe12-xTxCy, (R=Y,Er; T=V,Ti,Mo) alloys were prepared by rf induction melting and analyzed using neutron powder diffraction and superconducting quantum interference device (SQUID) measurements. Rietveld analysis of the neutron diffraction data indicates that V, Ti, and Mo atoms all prefer the 8i sites. The refined amount of carbon atoms found in the interstitial sites from neutron diffraction data is significantly less than the nominal carbon content. All samples have the easy direction along the c axis. The Er sublattice couples to the Fe sublattice antiferromagnetically. The average Fe site moments range from 1.3 to 2.8 …
Neutron Diffraction Studies Of Ndₙfeₘ₋ₓ₋YVₓalY [(N,M)=(1,12), (2,17), (3,29)], Z. Hu, William B. Yelon, William Joseph James
Neutron Diffraction Studies Of Ndₙfeₘ₋ₓ₋YVₓalY [(N,M)=(1,12), (2,17), (3,29)], Z. Hu, William B. Yelon, William Joseph James
Physics Faculty Research & Creative Works
Several NdnFem-x-yVxAly [(n,m)=(1,12), (2,17), (3,29)] samples were prepared and analyzed using neutron powder diffraction. Rietveld analysis of the neutron diffraction data indicates that the V and Al substituents take those sites with similar environments in all three phases, as observed in our previous study of Ti-substituted compounds. It was confirmed that the diffraction data of the 3:29 compound can be better refined using the A2/m space group than using the P21/c space group. The SQUID measurements show that all samples have Curie temperatures well above room temperature. The neutron diffraction results …
Site Affinity Of Substituents In Nd₂Fe₁₇₋ₓtₓ (T=Cu,Zr,Nb,Ti,V) Alloys, William B. Yelon, Z. Hu, William Joseph James, G. K. Marasinghe
Site Affinity Of Substituents In Nd₂Fe₁₇₋ₓtₓ (T=Cu,Zr,Nb,Ti,V) Alloys, William B. Yelon, Z. Hu, William Joseph James, G. K. Marasinghe
Physics Faculty Research & Creative Works
In order to understand the magnetic properties of the substituted rare-earth-iron alloys, it is especially important to know the location of the substitutional atoms within the iron lattice. The site distributions of some nontransition-metal substituents in the substituted Nd2Fe17-xTx alloys have previously been reported. Here we report the site distributions of some transition-metal substituents (Cu,Zr,Nb,Ti,V) in the Nd2Fe17-xTx alloys and compare them with those of the nontransition-metal substituted compounds. Rietveld analysis of neutron powder diffraction data indicates that the nontransition-metal substituents show very similar site affinity at low substituent content. …
Three-Body Collision Dynamics For Single Ionization Of Helium By Protons And Antiprotons, C. J. Wood, Ronald E. Olson
Three-Body Collision Dynamics For Single Ionization Of Helium By Protons And Antiprotons, C. J. Wood, Ronald E. Olson
Physics Faculty Research & Creative Works
All momentum components of the three outgoing particles are calculated for 100 keV p and p- + He single-ionization collisions. Differential ejected electron cross sections are evaluated for a fixed collision plane defined by the incident momentum vector of the projectile and the final momentum vector of the He+ recoil ion. For proton impact the electron spectra display saddle-point ionization when the transverse recoil ion momentum is small, whereas the electrons are ejected in the backward direction for large transverse recoil ion momenta. The antiproton collisions primarily show backward ejected electrons. However, for the antiproton system there is a decided …
Critical Behavior Of A Quantum Spherical Model In A Random Field, Thomas Vojta, Michael Schreiber
Critical Behavior Of A Quantum Spherical Model In A Random Field, Thomas Vojta, Michael Schreiber
Physics Faculty Research & Creative Works
We consider the influence of a quenched random field on the critical behavior of a quantum spherical model at the zero-temperature quantum phase transition. We find a complete solution of the model for arbitrary translationally invariant pair interactions. It turns out that the critical behavior for zero as well as finite temperatures is dominated by static random field fluctuations rather than by quantum or thermal fluctuations. Therefore the critical behavior close to the zero-temperature quantum phase transition is identical to that close to a finite-temperature transition. The system does not show a crossover from quantum to classical behavior.
Neutron Diffraction And Mössbauer Spectral Study Of The Nd₂Fe₁₆Ticₓ Solid Solutions, Gaya Kanishka Marasinghe, Peter C. Ezekwenna, William Joseph James, Gary J. Long, Oran Allan Pringle, Zhongbo Hu, William B. Yelon, Fernande Grandjean
Neutron Diffraction And Mössbauer Spectral Study Of The Nd₂Fe₁₆Ticₓ Solid Solutions, Gaya Kanishka Marasinghe, Peter C. Ezekwenna, William Joseph James, Gary J. Long, Oran Allan Pringle, Zhongbo Hu, William B. Yelon, Fernande Grandjean
Chemistry Faculty Research & Creative Works
Three samples of , with x equal to 0.0, 0.3, and 2.8, with the Th2Zn17-type rhombohedral structure, have been studied by powder x-ray and neutron diffraction, magnetic measurements, and Mössbauer spectroscopy. Nd2Fe16Ti and Nd2Fe16TiC0.3 were synthesized by induction melting stoichiometric amounts of the constituent elements, whereas Nd2Fe16TiC2.8 was synthesized by methane-derived gas phase insertion of carbon into finely ground Nd2Fe16Ti at 600 K. The neutron diffraction determined titanium site occupancies are similar in both Nd2Fe16 …
A Spin Reorientation In Pr₂Fe₁₇D₃ As Revealed By Mössbauer Spectroscopy, Fernande Grandjean, Dimitri Hautot, Gary J. Long, Olivier Isnard, Salvatore Miraglia, Daniel Fruchart
A Spin Reorientation In Pr₂Fe₁₇D₃ As Revealed By Mössbauer Spectroscopy, Fernande Grandjean, Dimitri Hautot, Gary J. Long, Olivier Isnard, Salvatore Miraglia, Daniel Fruchart
Chemistry Faculty Research & Creative Works
The Mössbauer effect spectra of Pr2Fe17D3, which have been measured between 85 and 295 K, indicate the presence of a spin reorientation of the iron magnetic moments at 105±5 K. At this magnetic transition a large increase of ~50 kOe in the 6c iron magnetic hyperfine field and abrupt changes in all of the remaining hyperfine fields are observed. A study of the changes in the quadrupole shifts at the transition indicates that this spin reorientation takes place within the basal plane of this rhombohedral compound. As expected, the temperature dependence of the isomer …