bluuebunny/crossref_metadata_2025 huggingface dataset:
Luminescence of CsCl: Tl Single Crystals
Authors: Nagirnyi V. , Zazubovich S. , Jaanson N.
Published: July 2007

Spectral, polarization, and kinetic characteristics of CsCl:Tl luminescence are studied between 4.2 and 350 K. The Ax band at 3.88 eV and the AT band at 3.65 eV are observed in the triplet emission spectrum of Tl+ centres. It is shown that in the triplet relaxed excited state (RES) the trigonal (X) minima are of higher energy than the tetragonal (T) ones. The symmetry of both the emitting and the metastable states in each (X or T) minimum is the same, and in many respects their structure is similar to that of other ns2 ions in alkali halides. However, some peculiarities are observed in the luminescence characteristics of CsCl:Tl crystals (e.g. very small quantum efficiency of triplet emission at excitation in high‐energy absorption bands; population of the lower (T) minima mainly in the process of vibronic relaxation in the triplet excited state; too large polarization degree of the slow decay component of the Ax emission, exceeding 1.5 times its theoretical limit; large difference in the spin‐orbit splitting energies δ of the triplet RES in the × and the T minima as well as in radiative decay probabilities y1 of their metastable states; the absence of an off‐centre displacement of the excited Tl+ ion from the crystal lattice site, etc.). Possible reasons for these features are discussed.
Expansion of Free Energy in Terms of Correlation Functions Within the Landau‐Ginzburg Model I. Fundamental Relations
Authors: Madzhulis I. , Kaupužs J.
Published: July 2007

The free energy can be expanded in terms of correlation functions on the basis of the Landau‐Ginzburg phase transition model for ferroelectrics. An equation for the two‐point correlation function is obtained from the extremum condition of the free energy function. A new criterion is proposed to choose skeleton diagrams for the free energy with an account of fluctuations. Results obtained for any functional integral in statistical physics can be generalized.
Some Typical Features of Relativistic Tunnelling through a Double Barrier System with δ‐Function Potentials
Authors: Roy C. L.
Published: July 2007

A comparative study of relativistic and non‐relativistic tunnelling of electrons through double‐barrier systems is reported considering potentials of rectangular barrier and δ‐function barrier types. Among other things, it is found that, for δ‐function barriers, the relativistic treatment predicts resonant tunnelling at all energies for certain quantised values of the strength of the δ‐function barriers, while the corresponding non‐relativistic treatment is not involved with a situation of this sort.
Electronic Structure of α‐Quartz. A XANES Study of Empty States
Authors: Bart F. , Jollet F. , Duraud J. P. , Douillard L.
Published: July 2007

X‐ray absorption spectra of α‐quartz in the XANES region are presented both at oxygen and silicon K edges. The consequences of the electric dichroism of the samples on XANES structures are investigated. Polarization effects are detected when the electric field of the incident beam is parallel or perpendicular to the crystallographic c‐axis. The structures after the absorption edges are discussed both in the frame of the Natoli's rule and from a density of states point of view.
Elastic Constants for the H. C. P. Lattice
Authors: Pasianot R. , Savino E. J.
Published: July 2007

The analytic expressions for the five elastic constants of an h. c. p. lattice are deduced. These expressions are appropriate for fitting empirical many‐body interatomic potentials of the embedded atom type. The uniform deformation method is used together with the lattice symmetry properties. These greatly simplify algebraic manipulations and provide for an easy inclusion of the contribution of inner strains.
Polaron Theory of the Image Potential Considering the Spatial Dispersion
Authors: Beril S. I. , Pokatilov E. P. , Goryachkovskii E. R. , Semenovskaya N. N.
Published: July 2007

The quantum‐mechanical theory of the image potential, which was developed recently on the basis of the polaronic approach is completed now with the consideration of the spatial dispersion of dielectric permittivity describing the microscopic inhomogeneity of a crystal lattice. The presence of nonmonotonicity in the coordinate dependence of the image potential energy obtained in the previous theory occurred to take place in our theory as well, but now it is less pronounced.
Anomalous Field Dependence of the Hole Mobility in a Molecular Doped Polymer
Authors: Novo M. , van der Auweraer M. , de Schryver F. C. , Borsenberger P. , Bässler H.
Published: July 2007

Photocurrent transients are determined in polycarbonate doped with 17 wt% of p‐p‐EFTP (see structure below) as a function of the electric field strength and the temperature. The hole mobilities are obtained both by a graphical method and by computational analysis based on an analytical expression for the transient photocurrent which has been recently proposed by Scott et al. The comparison of the results obtained with the two methods shows that, although the absolute values of the mobilities differ by a factor of 1.5, the field and temperature dependencies of the hole mobility are similar. The system studied shows an anomalous field dependence of the mobility which at low fields increases with increasing field to a maximum above which it decreases with increasing field. Such a behaviour is analysed in the framework of two different theoretical models: one based on the Marcus theory of electron‐transfer processes and Bässler's model which takes into account the fluctuations in hopping sites due to the simultancous presence of diagonal and off‐diagonal disorder. While the first model does not provide a satisfactory description of the experimental data, the latter cannot explain qualitatively the observed field dependence over a wide range of applied fields. The predicted saturation of the drift velocity of the holes at high fields does not agree with the observed temperature dependence of the mobility high fields. This disagreement with the conventional models is probably due to the large dimensions of the molecules allowing a change in the free energy for nearest‐neighbour hops which is large compared to the polaron binding energy or the width of the distribution of the density of states.
Magnetic Properties of New Layered Heisenberg Antiferromagnets
Authors: Du A. , Wei G. Z.
Published: July 2007

The magnetic properties of layered Heisenberg antiferromagnets with antiferromagnetic interaction between spins within a layer and ferromagnetic interaction between layers are studied by using a spin‐wave theory and double time‐temperature spin Green's function theory. At low temperatures a characteristic temperature is defined reflecting the layered features of the system and the low‐temperature region is divided into two new ones, giving asymptotic expressions of sublattice magnetization and parallel suseeptibility in different temperature region, including the low‐temperature region. the vicinity of the Néel temperature, and the high‐temperature region. Also given is the Néel temperature in an asymptotic form when the interlayer coupling is weak. It is shown that the characteristies of dimensional cross‐over for physical quantities exists at low temperatures. The interlayer coupling is essential to keep long‐range ordering and the properties of this king of antiferromagnets are very similar to those of normal antiferromagnets.
Stability Studies of the AlLiCu Icosahedral Quasicrystal by Means of the Embedded‐Atom Method
Authors: Nie Xiliang , Wang Renhui , Ye Yiying
Published: July 2007

Total energies of the T2‐Al6Li3 Cu icosahedral quasicrystal and its crystalline approximant are calculated by means of the embedded‐atom method and are compared with the fictitious AlLiCu solid solutions and mixtures. For such a calculation, the real atomic structure of the icosahedral T2‐Al6Li3 Cu phase is obtained by the projection method and special cubic spline knots for the embedding function FLi(ϱ) are selected to overcome the difficulty that the local electron density in Al‐Li‐Cu alloys is much larger than that in the pure Li crystal. The results show that both quasicrystalline T2‐Al6Li3 Cu and crystalline R‐Al5Li3 Cu are stable phases compared with the fictitious corresponding solid solutions and mixtures of pure Al, Li, and Cu crystals. These results are consistent with the experiments within the theoretical error.
Empirical Tight‐Binding Total Electronic Energy Calculation for SinH2m (n = 1 to 6, m = 1 to 3) Clusters
Authors: Katircioḡlu S. , Erkoç S.
Published: July 2007

The stable structures of SinH2m (n = 1 to 6, m = 1 to 3) clusters are investigated by the total electronic energy calculation using an empirical tight‐binding (ETB) method. It seems that bridged H‐bond models are also possible for small sinHm clusters.
The Influence of the Vector Potential on the Conductance of a 1D Quantum Wire in the Ballistic Transport Regime
Authors: Kováč M.
Published: July 2007

The influence of a vector potential on 1D ballistic transport in the region where the magnetic induction is zero is confirmed theoretically. The conductance is expressed by the reflection coefficient calculated by Babikov's method of phase functions.
Long‐Wavelength Limit of the Structure Factor of Liquid Metals from the Charged Hard‐Sphere Reference System
Authors: Akinlade O.
Published: July 2007

A detailed study of the long‐wavelength limit S(0) of the structure factor of alkali metals and some polyvalent metals at their freezing points using the charged hard‐sphere reference system is made. In order to investigate the role of refinements in the description of the electron‐ion interaction, use is made of both the Ashcroft empty‐core model (ECM) potential and a non‐local pseudopotential which incorporates high‐order perturbation corrections. The results obtained from the random‐phase approximation (RPA) are compared with those using the mean‐density approximation (MDA). Our calculations indicate that to obtain an accurate description of S(0) within the present framework, a good method of dealing with the electron‐ion pseudopotential is essential. It is also observed that the MDA correction in most cases does not lead to a remarkable improvement on those obtained from the RPA.
Static Lattice Defects in a Quasi‐Continuum
Authors: Vörös G. , Kovács I.
Published: July 2007

A new method for the description of the properties of lattice defects in a quasi‐continuum with long‐range elastic interactions is presented. The method is based on the application of the Fourier transformation for the solution of the equation of classical elasticity and takes into account the fact that the wavelength of the elastic waves in a real material cannot be arbitrarily small. The method is applied for the description of the properties of a dilatation centre and a screw dislocation.
On the Hot Phonon Spot Dynamics in Thin Films
Authors: Agaev F. F. , Guseinov N. M. , Rustamov K. A.
Published: July 2007

The hot phonon spot (HPS) formation and development in thin semiconductor films as a result of photoexcited charge‐carrier cooling is discussed. The film is assumed to be thin enough so that the thickness d follows d/v ≪ τ1, (ω), where v is a mean phonon group speed and τ1,(ω) a spontaneous decay time of nonequilibrium longitudinal phonons. Phonon scattering on defects is neglected. The light pumping parameter values that lead to the HPS formation are obtained. The equations that describe the dynamics of spot development are also discussed.
Deformation Potential Approach to the Estimation of the Peierls Phase Transition Temperature
Authors: Zhang Hongqun , Huang Yuanhe , Liu Ruozhuang
Published: July 2007

By means of the deformation potential theory, an expression for the electron‐phonon coupling constant g is derived, thereby a formula for the calculation of the Peierls phase transition temperature is obtained. As an illustration, this formula with the data calculated by a semiempirical crystal orbital method is used to compute the Peierls phase transition temperature of TTF‐TCNQ.
Pressure Dependent Donor Ionization Energies in a Quantum Well
Authors: Benedictal A. , Sukumar B. , Navaneethakrishnan K.
Published: July 2007

Donor ionization energies in a GaAs quantum well of the GaAs/Ga1−xAlxAs superlattice are obtained for different hydrostatic pressures up to 40 × 108 Pa. It is found that the ionization energy increases with pressure. While the conduction band nonparabolicity increases, the ionization energy generally decreases (the maximum change by 18% occurring at zero pressure), for high pressures this effect is negligible. The effect of replacing the static dielectric constant by a suitable screening function has the effect of enhancing the ionization energy by about 2%, the maximum contribution arising at high pressures.
Diamagnetic and Dielectric Susceptibilities of AlSb and GaSb
Authors: Sahu T. , Nayak S. K. , Acharya R. N.
Published: July 2007

The magnetic susceptibility (χ) and dielectric constant (ϵ0) of AlSb and GaSb are calculated by adopting a linear combination of hybrids (LCH) method developed by us. We have constructed basis functions for the valence and conduction bands and used them in the general expression for χ of intrinsic semiconductors to derive an expression for χ of these A NB8‐N semiconductors. Our LCH basis states are also used in the Kramers‐Kronig relation at ω = 0 to obtain an expression for ϵ0. The Hall‐Weaire‐Thorpe approximation is used to calculate the matrix elements between different hybrids and made an average energy gap ansatz (Eg) for energy gap denominator occuring in the expression for χ and ϵ0. Our expressions for χ and ϵ0, which are obtained in terms of matrix elements between intrasite hybrids and between adjacent hybrids forming a bond, are free from any scaling parameter, whereas in the earlier theories arbitrary scaling parameters have been used to fit with the experimental results. Our results agree well with the available experimental results.
Fine Structure of the Triplet Relaxed Excited State of Ga+ Centres in Alkali Chlorides Induced by the Off‐Centre Position of the Excited Ga+ Ion
Authors: Kalder K. , Korrovits V. , Nagirnyi V. , Zazubovich S.
Published: July 2007

The luminescence of a RbCl:Ga crystal is investigated by the methods of time‐resolved polarization spectroscopy in the temperature range 0.09 to 400 K. Manifestations of an off‐centre displacement of an excited Ga+ ion and its tunnelling motion are found in the decay kinetics of the triplet AT emission of the Ga+ centre. No such manifestations are observed for the Ax emission. A comparison of luminescence characteristics and peculiarities of the triplet relaxed excited state (RES) structure of the Ga+ centre in RbCl:Ga crystal with those of NaCl:Ga and KCl:Ga crystals is performed. The fine structure of the tetragonal Jahn‐Teller minima of the triplet RES of Ga+ centres in RbCl:Ga is found to be analogous to that of KCl:Ga: the metastable state is split due to tunnelling transitions between various equivalent off‐centre positions of the excited Ga+ ion, but in the emitting state the spin splitting caused by the off‐centre displacement of Ga+ ion considerably dominates over the tunnel splitting of this state. Basing on the analysis of the ODMR spectra as well as of the circular polarization of Ga+ triplet luminescence and its decay kinetics, the assumption is made that the tunnel splitting energy of the triplet metastable state of Ga+ centres is less than 10−5 eV.
Electronic and Magnetic Structure of B.C.C. FeMn Alloys
Authors: Elzain M. E. , Yousif A. A.
Published: July 2007

The first principle discrete variational method in the local density approximation is employed to calculate the electronic and magnetic properties of 15‐atom clusters representing b.c.c. FeMn alloys. The occupation numbers and local densities of states are found to be unaffected by alloying in the case of paramagnetic clusters. When spin polarization is included the local magnetic moments at Fe sites are found to depend on the number of neighbouring Mn atoms and the FeMn coupling. The local moment components Eg and T2g at a site show different orientations. This is explained in terms of coupling T2g moments to nearest neighbours and of Eg moments to next‐nearest neighbours. The average magnetic moment and hyperfine field were calculated and compared with experimental data.
Correlated Effective‐Field Treatment of Spin‐1 Ising Models; Susceptibility
Authors: Sarmento E. F. , Kaneyoshi T.
Published: July 2007

The initial susceptibility of the Blume‐Emery‐Griffiths model is investigated by the use of the new correlated‐effective‐field theory. The general expression for evaluating the paramagnetic susceptibility is obtained. In particular, the present formulation is illustrated in a honeycomb lattice by examining the susceptibility (or the inverse susceptibility) numerically. We find many characteristic phenomena in the system with z = 3, where z is the coordination number.
Static and Dynamic Properties of Vacancies in H.C.P. Metals Many‐Body versus Pair Potentials
Authors: Fernández J. R. , Monti A. M.
Published: July 2007

Many‐body interatomic potentials based on the embedded atom method are used to study the static properties of small vacancy clusters and dynamic properties of monovacancies in Mg, α‐Ti, and α‐Zr. In agreement with pair potential predictions, quantitative differences due to the elastic material properties characterize the static calculations. Diffusion constants for the monovacancy mechanism described in terms of the Arrhenius law are found to be strongly dependent on the potential barrier at distances below a, the basal lattice parameter.
The Electronic Structure and the Chemical Bonding in NiO and La2NiO4 Crystals. A Comparison with CuO and La2CuO4
Authors: Choisnet J. , Evarestov R. A. , Tupitsin I. I. , Veryazov V. A.
Published: July 2007

Modelling from quantum chemical data of the chemical bonding in NiO and La2NiO4 crystals comparatively to CuO and La2CuO4, is proposed. The increase of the ionicity degree of the Ni(II)–O bonding in comparison with Cu(II)‐O bonding is observed. The covalency is low and equally distributed in the equatorial plane and apical direction in the NiO6 octahedra in La2NiO4. As a supplementary data, which is common to La2CuO4 and La2NiO4, the covalency of the apical La(III)–O bonding plays an important role in increasing the overall covalent character of the apical oxygen and triggering a further elongation of MO6 octahedra.
Pressure Dependent Hydrogen Diffusion in the Intermetallic Compound Fe0.5 Ti0.5
Authors: Alfred Raj S. Cecil , Lawrence N. , Sebastian R. , Haridasan T. M.
Published: July 2007

The Green's function technique is used in the scattering matrix formalism to compute the mean square displacement (MSD) of hydrogen interstitials and the reaction coordinate technique is used to calculate the hydrogen diffusion parameters in the intermetallic compound Fe0.5 Ti0.5 from normal pressure to 2.5 GPa pressure for low concentration of hydrogen. The MSD of the metal atoms surrounding the interstitial are found to be smaller than those of the host crystal in agreement with NbHx. The diffusion of hydrogen into the alloy is found to decrease with increase in pressure as experimentally observed in PdHx.
Pertubative Approach to Spin‐1/2 Heisenberg Antiferromagnet
Authors: Trimper S.
Published: July 2007

The temperature Green's function matrix for a two‐sublatticc antiferromagnet is studied taking into account the complete algebraic properties of spin operators. The non‐diagonal part of Green's functions gives rise to a temperature dependent effective interaction. The staggered magnetization is calculated by summing up additional diagrams originated from the spin commutation relations.
On the Nucleation of Dislocations at a Crystal Surface
Authors: Beltz G. E. , Freund L. B.
Published: July 2007

An exact expression for the elastic energy associated with a semicircular shear dislocation loop emanating from a free surface is derived (within continuum dislocation theory) and compared with an earlier approximation. The energy required to activate a semicircular dislocation loop into its unstable “saddle‐point” configuration is then re‐calculated, based on the modified expression for the self‐energy. It is found that the shear stress necessary to emit the loop, as a function of temperature, is almost 50% less than earlier estimates. The principal drawback to this type of calculation is also discussed, namely, that the critical radius of an incipient dislocation loop is on the order of one atomic spacing, which is too small for a continuum theory to be valid.
Electronic and Chemical Properties of Barium and Indium Clusters
Authors: Onwuagba B. N.
Published: July 2007

The ground state electronic and chemical properties of divalent barium and trivalent indium are investigated in a self‐consistent manner using the spin‐polarized local density approximation in the framework of the density functional theory. A jellium model is adopted in the spirit of Gunnarsson and Lundqvist's exchange and correlation energies and the calculated properties primarily associated with the s‐p orbitals in barium and p orbitals in indium provide deepend insight towards the understanding of the mechanisms to the magic numbers in both clusters.
Magnetic and EPR Studies of Oxygenated and Non‐Oxygenated LaBaSrCu3O6+x Compounds in the Tetragonal Phase
Authors: Guskos N. , Likodimos V. , Calamiotou M. , Kuriata J. , Wabia M. , Paraskevas S. M. , Windsch W. , Metz H. , Koufoudakis A. , Mitros C. , Gamari‐Seale H. , Psyharis V. , Niarchos D.
Published: July 2007

Oxygenated and non‐oxygenated LaBaSrCu3O6+x ceramics in the tetragonal phase are studied using X‐ray, EPR, and magnetic measurements. A Meissner signal for the oxygenated sample corresponding to almost perfect diamagnetism is measured below 35 K. However, EPR data indicate that at least some parts of the sample become superconducting already below 62 K. Magnetic susceptibility of the non‐oxygenated sample exhibit a significant paramagnetic contribution attributed to Cu(1) ions ferromagneticall coupled to the Cu(2) planes.
Thermal Conductivity of Ice
Authors: Ahmad N.
Published: July 2007

The thermal conductivity of ice, formed at different cooling rates during the solidification process, is measured between 2 and 80 K. It is found that the thermal conductivity depends upon the cooling rate. The density of vibrational states is determined from the heat capacity data available in literature and is used in the analysis of thermal conductivity. The umklapp processes, boundary scattering, and point defects are considered along with dislocations or tunnelling states as scattering mechanisms. It is found that the model based on two‐level tunnelling states provides a better fit to the experimental data than the model based on the presence of dislocations.
EPR Study of Phase Transitions and Modulated Structure in [Mg(H2O)6]GeF6 Crystals
Authors: Hrabański R.
Published: July 2007

The phase transitions in [Mg(H2O)6]GeF6 are investigated with an Mn2+ EPR probe substituted for Mg2+ ions in the lattice. An axial symmetry phase with space group R 3 is observed above 403 K. The ferroelastic phase transition at 318 K is of first order and leads to monoclinic symmetry and to the development of a domain structure. In the intermediate phase the spectra exhibit anomalous changes of the lineshapes resulting from incommensurate modulation of the crystal field fine structure tensor. The results of EPR studies are interpreted both in terms of the plane‐wave and multi‐soliton models.
On a New Type of Dynamic Quantum Wells and Quantum Dots
Authors: Tralle I. E.
Published: July 2007

Electron movement in a spatially periodic high‐frequency electric field is considered. If the spatial period is small enough and the frequency is sufficiently high, the effect of this field on the charge particle is in a sense equivalent to the effect of a time‐independent effective potential that is a sequence of deep ‘dynamic’ quantum wells where the electrons are confined. The physical model is proposed which could be described in terms of such a Hamiltonian. Also the influence of an external quantizing magnetic field on such quantum well is considered and the existence of a quantum dot in this system is demonstrated.
Interference between Parametric and Coherent Bremsstrahlung Radiation Mechanisms of a Fast Charged Particle in a Crystal
Authors: Kleiner V. L. , Nasonov N. N. , Safronov A. G.
Published: July 2007

Parametric and coherent Bremsstrahlung radiation of a fast charged particle, moving in a crystal is studied from a single point of view. Such an approach permits to observe the essential change of the radiation structure in the region where CBR and PXR radiation patterns overlap that may be interpreted as an interference of these two radiation mechanisms. The dependence of interference items from charge sign is predicted. The PXR expression admitting a continuous transition from the dynamic regime of radiation to the kinematic one and the parameter of this transition are given.
Analysis of Magnetic Point‐Defect Relaxations in Electron‐Irradiated Magnetite
Authors: Walz F. , Kronmüller H.
Published: July 2007

Pronounced relaxation peaks occurring in the magnetic after‐effect (MAE) spectra of low‐temperature electron‐irradiated single‐crystalline magnetite (Fe3O4) are numerically analyzed and associated with anisotropic point defect configurations. As basic defects, cation interstitials and octahedral vacancies have been identified to exist, each in two closely related configurations, giving rise to reorientation‐type double peaks at 230 K (interstitials) and 300 K (vacancies). The analysis of these relaxations yields reorientation (migration) enthalpies of 0.69 eV and 0.73 eV for the interstitials and of 0.86 eV and 0.93 eV for the vacancies. The role of radiation damage for the relaxation mechanisms below the Verwey temperature (Tv = 125 K), i.e. tunnelling (4 K < T < 35 K) and hopping (45 K < T < 125 K) of electrons is discussed and a consistent recovery model, comprising all types of radiation‐induced lattice defects, developed.
Infrared Spectra of Solid Chlorodifluoromethane
Authors: Anderson A. , Beardsall A. J. , Fraser J. M.
Published: July 2007

Infrared spectra of solid Chlorodifluoromethane (CHClF2 or Freon 22) at temperatures between 12 and 105 K are presented and discussed. The evidence for a reversible solid state phase transition at (55 ± 5) K is described, confirming the results of a previous Raman study. Two metastable phases are also detected. Multiplet structure is observed for all nine internal modes and interpreted in terms of crystal field effects. This confirms that both phases are ordered, with rather large unit cells, and that the transition is of a displacive type. Coincidences with Raman frequencies suggest that both structures are probably non‐centrosymmetric. The lattice spectra are compatible with these conclusions and are tentatively assigned on the basis of inertia and intensity arguments.
Free Carrier Absorption in Quantum Well Structures Due to Confined and Interface Optical Phonons
Authors: Bhat J. S. , Mulimani B. G. , Kubakaddi S. S.
Published: July 2007

A theory of free carrier absorption in quantum wells when electrons are scattered by confined LO phonons described by the Huang and Zhu model, Fuchs‐Kliewer slab modes, and Ridley's guided mode models is given. The effect of interface phonon modes on free carrier absorption is also studied. Numerical results for frequency and well width dependence are given for parameters characteristic of the GaAs/AlAs quantum well. A comparison is made with the calculations based on a bulk description of phonons.
On the M‐Centre Luminescence in Alkali Halides. The Case of NaF and LiF
Authors: Bosi L. , Gallo D.
Published: July 2007

New results concerning the M luminescence in NaF and LiF are presented. The ageing of the samples is investigated particularly in connection with MA‐centre formation in NaF : Li. Trends and correlations are proposed between halfwidths, effective modes, and Huang‐Rhys factors in alkali halides.
Augmented Space Formalism for Diagonal and Off‐Diagonal Disordered Alloys
Authors: Cordelli A. , Grosso G. , Parravicini G. Pastori
Published: July 2007

A general treatment for electronic states of disordered alloys, including composition‐dependent off‐diagonal Hamiltonian matrix elements is presented. The recursion method within the augmented space of a disordered lattice is exploited. The main novelty is the simple description of the states of this space by a binary logic to allow a manageable use of recurrence relations. Several examples of one‐dimensional disordered alloys are considered, and comparison is performed between the electronic structure obtained with our procedure and numerical simulation of small clusters.
A Numerical Analysis of the Thermal Conductivity in the ab‐Plane of YBa2Cu3O7‐δ
Authors: Eversmann K. , Kopte T. , Dörr M. , Hegenbarth E.
Published: July 2007

Measurements of the thermal conductivity in the ab‐plane of different YBa2Cu3O7‐δ single crystals in the temperature range 2 K < T < 120 K are presented. The crystals differ in oxygen content and density of defects like point defects and twin boundaries. A numerical analysis of the phonon thermal conductivity is described. It allows to separate the scattering rates for phonons due to the scattering mechanisms being effective in YBa2Cu3O7‐δ. The phonon thermal conductivity is considered only in the range of T < 1/3 Tc and T > Tc, because separation of the electron thermal conductivity from the measured total value is complicated between these two limits. The results of analyzing some crystals provide a useful characterization of the mean densities of defects and show the dependence of the scattering mechanisms on the oxygen content.
Effect of the uniaxial compression on the phase transitions in Sn2P2S6‐type ferroelectrics
Authors: Rizak V. M. , Rizak I. M. , Perechinskii S. I. , Vysochanskii Yu. M. , Slivka V. Yu.
Published: July 2007

The effect of uniaxial compression on the temperature dependences of birefringence and dielectric constant is studied for the proper uniaxial ferroelectrics Sn2P2S6 and Sn2P2Se6. The influences of compression on the ferroelectric phase transition (PT) in Sn2P2S6 and on the PT which restricts the incommensurate (IC) phase in Sn2P2Se6 are compared. The observed variations of PT temperature and IC‐phase range with pressure agree with those calculated in an approximation which takes into account the presence of a tricritical point on the phase diagram of the crystals under study along with the Lifshits point. The variation of the ratio of the rates of PT temperature change for different uniaxial mechanical stresses on the replacement of sulphur by selenium as well as the weak sensitivity of the IC‐phase to compression along the structure modulation axis are found. It is suggested that these manifestations of the anisotropy are related to the special features of the linear interaction of soft optical and acoustic phonon branches.
Crystal anharmonicity in Li(H,D) and Na(H,D) systems
Authors: Islam A. K. M. A. , Haque E. , Azad A. S.
Published: July 2007

The reliability of a recently developed potential model is tested by extending the study to various anharmonic properties, e.g., third and fourth‐order elastic constants, Grüneisen parameters, and the pressure derivatives of second‐order elastic constants of hydrides and deuterides of lithium and sodium. A comparison of the calculated properties with the limited experimental results and other theoretical estimates gives an indication of the applicability of the derived potential in the study of crystal anharmonicity. However, the need for further experimental data is stressed in order to judge clearly the reliability of the present calculations for all the compounds.
Thermal properties of Si and Ge under pressure
Authors: Kagaya H.‐Matsuo , Soma T.
Published: July 2007

Thermal properties of Si and Ge under pressure are studied theoretically from first principles using the lattice dynamical method developed recently. The volume dependence of the anharmonic coefficient for the specific heat A, defined by C/3Nk = 1 + AT, is calculated. Then, numerical calculations of the anharmonic contributions to the thermal expansion coefficient are performed for Si and Ge.
Reservoir hypothesis for the quantum hall effect
Authors: Raymond A. , Sibari H.
Published: July 2007

It is assumed that in modulation‐doped heterojunctions the 2D electron gas is in thermodynamical equilibrium with an external reservoir. In a quantizing magnetic field energy gaps appear in the density of states of the 2D system. This produces, when the magnetic field B increases, oscillations of the density of the free 2D electrons, because of the transfer of electrons into (and out of) the reservoir. It is shown that these oscillations of N8 induce the formation of plateaus of the Hall resistivity ϱxy with the exact quantization in h/ie2 and vanishing values of the resistivity ϱxx, when the Fermi energy is between Landau levels. The model developed in the triangular well approximation accounts well for the width and shape of the Hall steps and for the ϱxx behaviour in a magnetic field, in a large range of temperatures.
Electrosoliton dynamics in a thermalized chain
Authors: Kadantsev V. N. , Lupichcv L. N. , Savin A. V.
Published: July 2007

A numerical study of the electrosoliton dynamics in a thermalized molecular chain with asymmetric electron‐phonon interaction is carried out. The effect of thermal vibrations of the chain molecules is taken into account in terms of classical mechanics. It is shown that electrosoliton in α‐helical protein molecules exists at room temperature (300 K).
Theoretical investigation of the self‐trapped hole in alkali halides. I. Long‐range effects within the model hamiltonian approach
Authors: Kantorovich L. N. , Zapol P. B.
Published: July 2007

A small‐radius polaron model of the self‐trapped hole (Vk‐center) in alkali halide crystals is presented. Along with the usual contributions, the electronic polarization is also included in accordance with the electronic polaron theory of Toyozawa. It is shown that the exact solution of the problem within the Landau‐Pekar approximation leads to multi‐hole quantum states accompanied by the relevant electronic and lattice polarizations. As an example the KCl crystal is considered, for which the Vk‐center structure as well as the self‐trapping energy are computed. While solving our equations, the local symmetry of the defect is taken into account allowing us to consider a comparatively spread wave function of the hole. The results obtained demonstrate the importance of chemical‐type interactions within the Vk‐center.
Optical properties of fullerite thin films in the 0.4 to 32 eV energy range
Authors: Guizzetti G. , Marabelli F. , Patrini M. , Capozzi V. , Lorusso G. F. , Minafra A. , Manfredini M. , Milani P.
Published: July 2007

The optical properties of C60 thin films are investigated in the energy range 0.4 to 32 eV using reflectance, transmittance, and ellipsometric spectroscopies. The complex dielectric constant and the associated functions are determined by a combination of photometric and ellipsometric data and by Kramers‐Kronig transformations. Spectral features above the fundamental absorption edge (at ≈ 1.8eV) are related to both one‐electron interband transitions and collective electron effects. A comparison is made with recent results of electron energy loss spectroscopy and of theoretical calculations on the f.c.c. fullerite structure.
Behaviour of the optical indicatrix and small‐angle light scattering in the case of “Devil's Staircase”
Authors: Sveleba S. , Kapustianik V. , Polovinko I. , Bublyk M. , Zhmurko V.
Published: July 2007

The deformation and rotation of the optical indicatrix and the scattering of light in the incommensurate phases which consist of a sequence of phases with superstructures are investigated. The periods of such superstructures are large but commensurate with the period of the crystalline lattice. The values of deformation and rotation of the optical indicatrix are determined on the basis of the analysis of light passed through [N(CH3)4]2FeCl4 and [N(CH3)4]2CuCl4 crystals. The pulsing deformation of the optical indicatrix and its rotation in the commensurate regions are found in the incommensurate phase. It is shown that the investigated scattering of light is connected with the scattering on the phason.
Type‐II GaAs/AlAs superlattices under high excitation
Authors: Boujdaria K. , Scalbert D. , la Guillaume C. Benoit À
Published: July 2007

High‐intensity photoluminescence data on GaAs/AlAs superlattices and multi‐quantum wells of type‐II at low temperature are reported. The variation with density of the renormalized band gap reveals the competition between the Hartree energy, a consequence of non‐local neutrality, which tends to open the gap and the many‐body effects (mainly exchange). Preliminary analysis for a lot of samples with widely different periods provides a satisfactory fit with the Hartree‐Fock model. The kinetics of luminescence and total decay in the electron‐hole plasma regime is measured. In some samples, a phase transition is observed which is tentatively interpreted in terms of the electron‐hole liquid condensation.
Polarization dependence of the V K edge in VO2 through the phase transition at 68 °C
Authors: Poumellec B. , Cortés R. , Loisy E. , Berthon J.
Published: July 2007

X‐ray absorption measurements in the low (pseudo‐rutile) and high (rutile) temperature phases of VO2 are described. Investigations are made versus temperature and polarization. The analysis of the results leads to conclusions concerning the scattering mechanisms at the origin of the pre‐edge, the edge, and the first peak of the edge. Specifically, the angular dependence of the pre‐edge of the monoclinic form is different from the rutile form. A new peak on the edge appears for e ‖ cr at low temperature and the pre‐edge and the first peak appears to be sensitive to the asymmetry of the local environment.
The nonlinear paradigm: Advancing paradigmatic progress in the policy sciences
Authors: Douglas L.
Published: July 2007

This paper responds to Daneke 's call for a new systems paradigm in the policy sciences. The nonlinear paradigm is presented as one perspective that may add to this new paradigm. The nonlinear paradigm explores the complex, uncertain, and sometimes unstable time evolution of nonlinear systems. The paper identifies and examines elements of the nonlinear paradigm that have particular relevance for understanding and contending with policy problems. The lessons learned and the tools utilized by this emerging perspective are presented as a means for furthering paradigmatic progress in the policy sciences.
Main dimensions of human practical directives system
Authors: Lewicka‐Strzalecka Anna
Published: July 2007

A hypothesis is made that due to the uncertainty and complexity of the practical inference schemes, the acting subject exerts his/her own system of beliefs about efficient ways of attaining the given goals. These beliefs are termed here: Practical Directives, and their system: Practical Attitude. An attempt was made to reconstruct such a system and its main dimensions. To this end, an instrument was constructed: the Questionnaire of Practical Directives (QPD), which is meant as an operational definition of Practical Attitude. A group of 218 subjects was tested with the aid of QPD and the factor analysis of the results revealed nine factors interpreted as main dimensions of the system of Practical Directives.
Projecting military housing needs with decision support systems
Authors: Forgionne Guisseppi A.
Published: July 2007

The Department of the Army must provide its personnel with acceptable housing within the vicinity of military installations. To achieve this housing goal, the Army must often enter into agreements for the construction of housing or for leasing of existing housing. Any housing construction or leasing request must be accompanied by a Segmented Housing Market Analysis (SHMA), a time‐consuming and costly forecasting process that requires many manual labor tasks. As described elsewhere, a Housing Analysis System (HANS) was developed to support these tasks on a micro computer with very user‐friendly computer programs. Recently, the original version of HANS has been modified and incorporated into a larger computer system now under development. At the heart of both the original and modified systems is a set of econometric and heuristic programming models that deliver the required analyses and evaluations. This paper describes these models, explains how they drive the modified HANS, and presents the results and benefits of the use of the modified computer system.

Biographical Sketch — Guisseppi A. Forgionne is Professor of Information Systems at the University of Maryland Baltimore County (UMBC). Professor Forgionne holds a B.S. in Commerce and Finance, an M.A. in Econometrics, an M.B.A., and a Ph.D. in Management Science and Econometrics. He has published 16 books and approximately 70 research articles and consulted for a variety of public and private organizations on decision support systems theory and applications. Dr. Forgionne has also served as department chair at UMBC, Mount Vernon College, and Cal Poly Pomona. He has received several national and international awards for his work.
Relevance, formality, and process: Toward a theory of soft systems practice
Authors: Ledington Paul
Published: July 2007

This paper argues that Relevance, Formality, and Process are themes that form an intellectual structure for making sense of the application of systems methodologies to real‐world problem situations and hence provide a starting point for a theory of soft systems practice. These themes are developed from a consideration of the development and use of Soft Systems Methodology. The core concepts and structure of Soft Systems Methodology are described and then a view of Soft Systems Methodology as a tool for managing inquiry‐based intervention into action‐oriented communities is developed and illustrated. The case studies are then used to explore the themes of relevance, formality, and process and to analyse areas of strength and weakness in Soft Systems Methodology.
The concept of coherence considered as a systems isomorphism
Authors: Wolkowski Zbigniew William
Published: July 2007

The concept of coherence has gained a considerable extension from its primary domain of quantum optics over the last quarter of a century. In particular, it offers the possibility of a new conceptual tool for understanding the living state and of biological systems. Considered as a systems isomorphism, it may represent a significant epistemological contribution.
The effects of strategic decision making structure and computerization on organizational performance
Authors: Hoffman James J. , Carter Nancy M. , Cullen John B.
Published: July 2007

Findings indicate that the effects from a manager's decision to computerize operations and change the organization's strategic decision making structure are not immediately felt. These findings support the idea that performance needs to be measured on a long‐term basis rather than on a short‐term basis. The results also suggest that it may be erroneous to evaluate managers strictly on a short‐term basis since the effects from strategic decisions may not be fully felt for one or more years.
Morphodynamics Ergodic Theory of Complex Systems
Authors: Fivaz Roland
Published: July 2007

Morphodynamics is a general theory of stationay complex system, such as living systems, or mental and social systems it is based on the thermodynamics of physical systems and built on the same lines. By means of the ergodic hypothesis thermodynamics is known to connect the particle dynamics to the energence of order parameters in the equation of state. In the same way, morphodynamics connects order parameters to the emergence of higher level variables; through recurrent applications of the ergodic hypothesis, a hierarchy of equations of state is established which describes a series of successive levels of organization. The equation support a cogmitiveist interpretation that leads to general principles of evolution: the principles determine thespontaneous and irreversible complexification of systems living in their natural environment.
Criticality Analysis of Mis Architecture
Authors: Gupta M. P. , Sushil
Published: July 2007

Abstract The Design of Management Information System (MIS) architecture has been the subject of the first phase of the methodology INFLOS reported in the previous article of the current issue of the journal. Sequel to this is the second phase which deals with the criticality analysis of the MIS architecture. In this, from a design point of view, it is aimed to identify critical decision units in terms of their direct and indirect informational impact on overall MIS. The methodology also facilitates the identification of varying possibility levels of informational interaction among the decision units. The results provide important inputs for systematic physical system design.
The nature of order in complex systems
Authors: Fivaz Roland
Published: July 2007

Order in complex systems is investigated within morphodynamics, a theory of evolution considering such systems as ensembles of selectively adaptable components embedded in a random environment. Accordingly, components are specified by pairs of configurational and functional variables submitted to repulsive and attractive interactions; statistical methods of thermodynamics then apply formally. Many order parameters emerge alternatively in the functional space and in the configurational space: a multi‐levelled hierarchy is built that describes organization among functions as well as order among structures. Morphodynamics shows that such coordinations arise spontaneously in absense of computations or instructions; instead, they are selected on a basis of internal stability that warrants both high performance and subsidiary adaptation to environmental constraints. Examples are discussed concerning biological order and sensori‐motor coordinations.
The individual and the collective in health care: A problem of systems ethics
Authors: Strijbos S.
Published: July 2007

Our society seems to be characterized by certain imbalances between the individual and the collective, between people and the organizational‐technical systems they manage. In the health care sector this is reflected for example in the pressing problems concerning the control of costs. To clarify these imbalances they are placed in a broader framework, namely, that of the changing nature of our technical‐industrial societies. The role of systems ethics in solving them is explored.
War, hypercomplexity and computer simulation
Authors: Geeraerts Gustaaf
Published: July 2007

The scientific study of war has not yet shown any indication of a major breakthrough. For such a breakthrough to materialize it is paramount to approach the war phenomenon from a dynamic systems perspective. Perceived from this angle, war is placed in both an evolutionary and systems point of view, specifically implying a vision of war as one aspect of the international political process, connected in various ways with other injurious forms of interaction as serious disputes and low level conflict behavior, but also supportive behavior like trade and co‐operation. War constitutes a ‘normal’ event: no less than other social phenomena, it is the result of different over‐time conjunctures of common underlying behavioral mechanisms and resulting processes of interaction occurring within the higher level system's structure. In view of the ‘hypercomplex’ nature of the concerned dynamics, the development of computer (simulation) models will become essential in the study of war and peace.