bluuebunny/crossref_metadata_2025_split huggingface dataset:
Progress in Understanding Plasma‐Propellant Interaction
Authors: Kappen Klaus , Beyer Richard 
Published: March 2003

AbstractTo explore the phenomena of the plasma‐propellant interaction (PPI) and to point out the role of radiation, a series of experiments have been performed at the U.S. Army Research Laboratory. For this, the plasma radiation to the propellant has been separated from all other energy transfer mechanisms. The results clearly indicate that the observed structural damage of translucent JA2 samples is due to radiation only. An other aim of this work is to clarify some misunderstandings in analyzing plasma‐propellant interaction. By variation of the electrical pulse length it will be shown that electrical energy is in no way a useful parameter to characterize propellant response to variable plasma igniter systems.
Acceleration and Viscoplastic Deformation of Spherical and Cylindrical Casings under Explosive Loading
Authors: Tan Duowang , Sun Chengwei , Wang Yanping 
Published: March 2003

AbstractA theoretical model to predict continuous deformation and acceleration of spherical or cylindrical metallic casings driven by detonation products inwards or outwards before fracture occurring is proposed in this paper. The casing materials are assumed to be rigid viscoplastic medium and the geometries are one dimension i.e., the explosive charge is initiated at the spherical center or on the cylindrical axis in the divergent case, or uniformly on the explosive shell's outer surface in the convergent case. The acceleration movements of spherical and cylindrical casings calculated with this model are in good agreement with experimental and numerical results performed with the finite element hydrocode DYNA2D. It is concluded that this model describes well one‐dimensional divergent and convergent movements of spherical or cylindrical casings under explosive loading, and provides a useful method to explore related problems, such as shell's fragmentation, its maximum velocity before fracture, blast wave in the near area adjacent to the casing and solid liner implosion.
An elementary aspect of the Weyl‐Wigner representation
Authors: Dahl J.P. , Schleich W.P. 
Published: March 2003

AbstractIt is an elementary aspect of the Weyl‐Wigner representation of quantum mechanics that the dynamical phase‐space function corresponding to the square of a quantum‐mechanical operator is, in general, different from the square of the function representing the operator itself. We call attention to some conceptual consequences of this fact.
Coherent states for hydrogen‐like atom in the presence of Aharonov‐Bohm effect
Authors: Drăgănescu Gh.E. , Avram N.M. 
Published: March 2003

AbstractFor a hydrogenlike atom introduced in an Aharonov‐Bohm potential due a infinite solenoid it was established different operators corresponding to different representations of the system. For this system we studied the the displacement coherent states and harmonic oscillatorlike coherent states. The average values of some observables in different coherent states have been done.
Quantum cloning of orthogonal qubits
Authors: Fiurášek J. , Iblisdir S. , Massar S. , Cerf N.J. 
Published: March 2003

AbstractAn optimal universal cloning transformation is derived that produces M copies of an unknown qubit from a pair of orthogonal qubits. For M>6, the corresponding cloning fidelity is higher than that of the optimal copying of a pair of identical qubits.
Quantum operators in Weyl quantization procedure via Wigner representation of quantum mechanics ‐ quantum phase operator as a special case
Authors: Davidović M. 
Published: March 2003

AbstractCoherent states, in Wigner representation of quantum mechanics which is classical in structure with Wigner function playing the role of classical phase space probability distribution, and standard quantum mechanical expression for average values of corresponding Weyl quantum operators, general expression for matrix elements of the operator corresponding to phase of the oscillator by Weyl procedure, are obtained in the |n〉 basis. The general expression for matrix elements in the same basis of any other operator is also obtained. As the only mathematical technique necessary in the proposed procedure is a simple change of variables to polar coordinates in the corresponding integrals, this way to introduce Weyl phase operator, and some other operators in Weyl quantization, greatly simplifies necessary derivations and calculations.
Self‐dressing in classical and quantum electrodynamics
Authors: Compagno G. , Passante R. , Persico F. 
Published: March 2003

AbstractA short review is presented of the theory of dressed states in nonrelativistic QED, encompassing fully and partially dressed states in atomic physics. This leads to the concept of the reconstruction of the cloud of virtual photons and of self‐dressing. Finally some recent results on the classical counterpart of self‐dressing are discussed and a comparison is made with the QED case. Attention is drawn to open problems and future lines of research are briefly outlined.
The quantum way to diagonalize hermitean matrices
Authors: Weigert S. 
Published: March 2003

AbstractAn entirely quantum mechanical approach to diagonalize hermitean matrices has been presented recently. The method is based on the measurement of quantum mechanical observables which provides the computational resource. In brief, quantum mechanics is able to directly address and output eigenvalues of hermitean matrices. Here, the example of (2×2) matrices is considered in detail. This simple case allows one to illustrate the conceptual features of the general method which is applicable to (N×N) hermitean matrices.
Dipole‐dipole coupling in the presence of dispersing and absorbing bodies
Authors: Welsch D.‐G. , Dung H.T. , Knöll L. 
Published: March 2003

AbstractAn effective Hamiltonian and equations of motion for treating both the resonant dipole‐dipole interaction between two‐level atoms and the resonant atom‐field interaction are derived, which can suitably be used for studying the influence of arbitrary dispersing and absorbing material surroundings on these interactions. It is shown that the dipole‐dipole interaction and the atom‐field interaction, respectively, are closely related to the real part and the imaginary part of the (classical) Green tensor. The theory is applied to the study of the transient behavior of two atoms that initially share a single excitation, with special emphasis on the role of the two competing processes of virtual and real photon exchange in the energy transfer between the atoms. To illustrate the powerfulness of the theory, specific results for the case of the atoms being near a dispersing and absorbing microsphere are presented. In particular, the regimes of weak and strong atom‐field coupling are addressed.
Quantum‐mechanical description of polarized and unpolarized light
Authors: Wünsche A. 
Published: March 2003

AbstractThe restrictions for density operators of unpolarized quasiplane and quasimonochromatic two‐mode light are determined by invariance with respect to SU(2) polarization transformations and it is shown that this leads only to the type of unpolarized light established in [6]. In this connection, it is clarified and underlined by group‐theoretical considerations that the “type II of unpolarized light'' derived in [8‐11] is in reality a type of polarized light with second‐order polarization (or hidden polarization in first order) and that it is obtained by invariance with respect to an axial subgroup C∞v of SU(2) or of U(2).
Photoluminescence studies of isotopically enriched silicon
Authors: Karaiskaj D. , Thewalt M.L.W. , Ruf T. , Cardona M. 
Published: March 2003

AbstractIn this issue's Editor's Choice, the first high resolution photoluminescence (PL) investigations of isotopically pure silicon are reported. The cover figure shows the PL spectrum of the no‐phonon transitions of an exciton bound to the neutral aluminum acceptor in 28Si, compared with the corresponding result from natural Si. It is seen that in the isotopically purified material the lines are shifted (as indicated by the horizontal arrow) and are sharper than in natural Si. Moreover, the splitting of the A0 ground state, as shown in the level scheme of the inset, is clearly absent in the 28Si sample, demonstrating that this splitting results from the random isotopic composition in natural Si. The paper is an invited presentation from the 10th International Conference on Shallow Level Centers in Semiconductors (SLCS‐10) held in Warsaw, Poland, 24‐27 July 2002.This issue of phys. stat. sol. (b) contains a second paper selected as Editor's Choice, entitled “Tunable spin‐injection and magnetoconductance in a novel 2DEG‐ferromagnet structure” by Y. Jiang and M. B. A. Jalil [2].
Spin related effects in magnetic mesoscopic systems
Authors: Barnaś J. , Dugaev V. , Krompiewski S. , Martinek J. , Rudziński W. , Świrkowicz R. , Weymann I. , Wilczyński M. 
Published: March 2003

AbstractSpin effects in transport properties of double‐barrier mesoscopic junctions are analyzed and their possible applications in spintronics devices are discussed. In a general case, external electrodes of the junctions are ferromagnetic and the central electrode is either a nonmagnetic metallic grain or a semiconducting quantum dot. Transport characteristics depend then on magnetic configuration of the system. When the spin relaxation time on the central electrode is sufficiently long, measurable spin effects can also occur in entirely nonmagnetic devices.
Ferromagnetic Kondo‐lattice model: Application to thin ferromagnetic and semiconducting local moment films
Authors: Nolting W. , Santos C. 
Published: March 2003

AbstractWe present a many‐body approach to the electronic and magnetic properties of the Kondo‐lattice model. This model is considered a candidate for the description of magnetic materials the characteristic properties of which are mainly determined by an exchange coupling of itinerant electrons to a system of localized magnetic moments. This coupling leads to a distinct temperature‐dependence of the electronic quasiparticle spectrum and to magnetic properties, as e.g. the Curie temperature TC or magnon dispersions, which are strongly influenced by the band electron selfenergy. The model studies are applied to thin ferromagnetic EuO(100) films. For a realistic description we present a multiband extension of the Kondo‐lattice model with a single‐electron part taken from a tight‐binding‐LMTO bandstructure calculation. The proposed method avoids the double counting of relevant interactions and takes into account the correct symmetry of atomic orbitals. The layer‐dependent magnetization as well as quasiparticle density of states are discussed as functions of the film thickness. For a 20‐layer film the existence of a surface state is predicted, which may lead to a temperature‐driven surface halfmetal‐insulator transition.
Ferromagnetic ordering in UFe0.5Ni0.5Al
Authors: Tran V. H. , Troć R. , André G. , Bourée F. , Baenitz M. 
Published: March 2003

AbstractThe alloy UFe0.5Ni0.5Al crystallizing in the hexagonal ZrNiAl‐type structure has been studied by means of neutron powder diffraction and specific heat measurements. The Ni atoms occupy preferentially the (1b) sites. The transition into a ferromagnetic state at TC ∼ 55 K reported previously is corroborated by the occurrence of specific heat anomaly and magnetic reflections. The magnetic structure consists of the ferromagnetic (001)‐planes with the magnetic moments parallel to the c‐axis. At 1.4 K, the ordered uranium moment is about 0.6 μB. The low‐temperature dependence of Cp may be described by an expression involving an energy gap in the magnon spectrum. The electronic coefficient of the specific heat is modestly enhanced and amounts to about 47 mJ/mol K2. This feature together with a small value of μord point to the strongly 5f–d hybridized character of the magnetism in UFe0.5Ni0.5Al.
Jahn–Teller effect and superexchange in half‐doped manganites
Authors: Sikora O. , Oleś A. M. 
Published: March 2003

AbstractWe investigate the stability of the charge exchange (CE) phase within a microscopic model which describes a single plane as in La0.5Sr1.5MnO4. The model includes Coulomb interactions (on‐site and intersite), the Jahn–Teller term and the superexchange interactions due to eg and t2g electrons. By investigating the phase diagram at T = 0 in mean‐field approximation we conclude that the superexchange interactions can stabilize the CE phase, but only if they are stronger than estimated from spectroscopy.
Electronic transport through large quantum dots in the Kondo regime
Authors: Stefański P. , Bułka B. R. 
Published: March 2003

AbstractConductance through a large two‐level quantum dot is investigated theoretically in the strong coupling regime. In large quantum dots the separation between discrete levels becomes smaller than the level width due to strong hybridization with electrodes. In such circumstances, apart from strong electronic correlations in the quantum dot, the indirect interaction between both the spatial levels comes into play. It takes place in lateral quantum dots, where the spatial level index is not conserved during the hybridization process with electrodes. This interaction shifts the Kondo resonance peak in the density of states out of the Fermi surface and alters its intensity. This feature can be observed in the differential conductance dependence vs. bias voltage. The virtual inter‐level mixing is suppressed for temperatures above the Kondo temperature of the system. The results of theoretical predictions are compared with the results of experimental conductance measurements performed on large quantum dots and some non‐typical conductance features are clarified.
Ground states of the spin‐1/2 Falicov–Kimball model
Authors: Lemański R. , Wojtkiewicz J. 
Published: March 2003

AbstractThe spin‐1/2 Falicov–Kimball model is analyzed perturbatively in the large U limit. In the case of 2D square lattice, the effective Hamiltonian up to terms proportional to U–3 has been obtained, and its ground states have been determined for a range of chemical potentials. The resulting phase diagram appeared to be qualitatively the same as that one for the spinless model. This is rather surprising result, because the effective Hamiltonians are quite different in the both cases.
Magnetization plateaux in S = 1 spin ladder
Authors: Sakai T. , Okazaki N. , Okamoto K. , Kindo K. , Narumi Y. , Hosokoshi Y. , Kato K. , Inoue K. , Goto T. 
Published: March 2003

AbstractThe experimental magnetization curve of the first synthesized S = 1 organic spin ladder compound BIP‐TENO is presented. It reveals a clear plateau at 1/4 of the saturation magnetization. We propose a mechanism of the 1/4 plateau formation based on the frustration due to third‐neighbor exchange interactions. We also compare the numerically calculated magnetization curve and susceptibility with the experimental results to estimate the exchange coupling constants.
The structural instabilities of ferronematic based on liquid crystal with low negative magnetic susceptibility
Authors: Kopčanský P. , Potočová I. , Koneracká M. , Timko M. , Jadzyn J. , Czechowski G. , A. M. G. Jansen  
Published: March 2003

AbstractThe Fredericksz transition in ferronematic based on liquid crystal ZLI 1695 (extremely low anisotropy of diamagnetic susceptibility χa = –3 × 10–8) was studied. The decrease of the Fredericksz transition critical magnetic fields BFN with increasing magnetic particles volume concentration was found. The surface density of anchoring energy of liquid crystal molecules on magnetic particles surfaces was experimentally estimated falling into the range (0.3–5.2) × 10–6. These estimations confirm the soft‐anchoring considered within the Burylov and Raikher's theory.
Neutron diffraction study of crystal and magnetic structure of (La0.7Ca0.3)1–xMn1+xO3 (x = 0, 0.1) systems
Authors: Bażela W. , Dyakonov V. , Pashchenko V. , Penc B. , Szymczak H. , Hernandez‐Velasco J. H. , Szytuła A. 
Published: March 2003

AbstractThe evolution of crystal and magnetic structures of (La0.7Ca0.3)1–xMn1+xO3 (x = 0, 0.1) as a function of temperature was determined. For both compounds the crystal structure is orthorhombic (space group Pnma) with the following sequence of the lattice constants: b/√2< a < c for x = 0 and c < a < b/√2 for x = 0.1. The para‐ferromagnetic transitions at Tc = 265 K for x = 0 and 260 K for x = 0.1 are accompanied by structural distortions. For x = 0 the ferromagnetic ordering of the Mn moments equal to 3.57(10)μB and parallel to the b‐axis is stable in the temperature range from 1.5 K to Tc. For x = 0.1 at 1.5 K the magnetic order has two components: the ferromagnetic one with the magnetic moment μ = 3.46(12)μB parallel to the b‐axis and the antiferromagnetic one with μ = 0.66(23)μB parallel to the c‐axis. This order is stable up to Tt = 45 K. Then the ferromagnetic order only exists up to Tc = 260 K. These results correlate well with macroscopic magnetic data. At Tc and Tt the anomalies in the thermal dependence of Mn–O bond lengths and Mn–O–Mn bond angles are observed.
Two‐step mean‐field renormalization group results for the large square Ising clusters
Authors: Kamieniarz G. , Musiał G. , Tomecka D. 
Published: March 2003

AbstractA transfer matrix approach has been worked out to test the predictions of the improved three‐step mean‐field renormalization group approach to square Ising clusters with linear size up to L = 11. Performing the asymptotic analysis, the convergence of the finite‐size critical couplings and the critical exponents towards the exact values is shown.
Ferromagnetism in diluted magnetic semiconductors at low carrier density
Authors: Dugaev V. K. , Litvinov V. I. , Barnaś J. , Slobodskyy A. H. , Dobrowolski W. , Vieira M. 
Published: March 2003

AbstractWe present a general approach to the problem of a ferromagnetic phase transition in diluted magnetic semiconductors with free carriers. The Curie temperature of ferromagnetic transition is calculated in the mean field approximation. The approach allows to analyze the effects of magnetic fluctuations and disorder on the Curie temperature. We also propose a new mechanism of exchange interaction between magnetic impurities at vanishing concentration of free carriers.
Marginal synchronization of spin‐wave amplitudes in a model for chaos in parallel pumping
Authors: Krawiecki A. , Sukiennicki A. 
Published: March 2003

AbstractA model for chaos in high‐power parallel pumping is considered, based on nonlinear interactions of two groups of parametric spin wave pairs. If spin wave pairs within each group have identical damping, frequencies, and interaction coefficients with other pairs, all of them are excited in the chaotic regime and marginal synchronization of amplitudes of spin wave pairs belonging to the same group is observed. In the case of small differences between spin wave pairs only a low number of pairs from each group is excited. On the basis of this result, possible explanation of the origin of low dimensional chaos usually observed experimentally in parallel pumping is proposed.
Spin waves in La2CuO4: band structure and correlation effects
Authors: Peres N. M. R. , Araújo M. A. N. 
Published: March 2003

AbstractWe calculate the antiferromagnetic spin wave dispersion in the half‐filled (electronic density n = 1) Hubbard model for a two‐dimensional square lattice, using the random phase approximation (RPA) in a broken symmetry (spin density wave) ground state. Our results for the spin wave dispersion, ω (q), are compared with high‐resolution inelastic neutron scattering performed on La2CuO4. The effects of different band structures and different values of the on‐site Coulomb interaction on the spin wave spectrum are studied. Particular attention is put on the high energy dispersion values ω (π/2, π/2) and ω (0, π).
Properties of the UFe5Sn compound: electronic structureand X‐ray photoemission
Authors: Szajek A. , Malinowski W. L. 
Published: March 2003

AbstractThe UFe5Sn compound crystallizes in the orthorhombic CeCu5Au‐type structure having the Pnma space group with iron atoms located in four inequivalent sites. The electronic structure UFe5Sn compound has been studied using spin‐polarized tight binding version of the linear muffin‐tin orbital method in the atomic sphere approximation (TB LMTO ASA). The calculations showed that the magnetic moments on uranium atoms are antiparallel to the moments formed on Fe atoms, whose values depend on local environments. The X‐ray photoemission spectra were calculated.
Frontier orbital and density functional study of the variation of the hard–soft behavior of monoborane (BH3) and boron trifluoride (BF3) as a function of angles of reorganization from planar (D3h) to pyramidal (C3v) shape
Authors: Ghosh Dulal C. , Jana Jibanananda 
Published: March 2003

AbstractIn chemical response the BH3 and BF3 molecules undergo the physical process of planar (D3h) to pyramidal (C3v) reorganization in shape as the condition precedent to the event of chemical reaction under the requirement of symmetry. A frontier orbital and density functional study of the variation of the stability of electronic structures and chemical reactivity of associated with the physical process of D3h to C3v geometry reorganization has been performed. The theoretical parameters viz. eigenvalues of HOMO and LUMO, the HOMO and LUMO energy gap, the global hardness and global softness, the chemical potential, the condensed Fukui function, and local softness of B atom, the reaction site, have been computed over a wide range of ∠XBX angles. The nature of variation in the intrinsic chemical reactivity, global and local, of the molecules associated with their geometry reorganization during the chemical event of charge transfer interaction involving their frontier molecular orbitals has been quantitatively explored. The hardness profiles as a function of reaction coordinates are consistent with the principle of maximum hardness (PMH). Results demonstrate that the hardness and softness are not a static and invariable property of molecules but a dynamic and variable function of molecular structure. The hardness parameters and the HOMO–LUMO gap of the molecules are so modified with the distortion of molecular geometry that, after a certain stage of molecular deformation, the profiles of such parameters of the molecules intersect and cross each other, signifying that the relative order of the intrinsic hardness of their equilibrium geometry is reversed. The intrinsically hard molecule BF3 becomes softer than the intrinsically soft molecule BH3 as a consequence of structural distortion. The increase in chemical reactivity computed in terms of density functional parameters are transparent and justified in terms of the profiles of the eigenvalues of the frontier orbitals. The profiles of chemical potential reveal the inherent difference in the tendency of backdonation from two molecules. The computed values of Fukui functions and local softness parameters of the B atom site demonstrate that the concept of local softness can be exploited for a theoretical analysis and understanding of the characteristic chemical events of the molecules under consideration. The profiles of the Fukui functions and local softness parameters of the two molecules seem to reflect and reveal their intrinsic difference in the tendency of receiving donation in the LUMO (electrophilicity) and that of backdonation from the HOMO (nucleophilicity) and the inherent difference of overall reactivity of the two molecules by a simultaneous operation of two opposing processes of charge transfer. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003