476 research outputs found
On the perturbation propagation in the initial-boundary value problem for quasilinear first order equations
The paper deals with initial-boundary value problem for generalized solutions of single quasilinear nonautonomous conservation law. For the case so-called "processes with aggravation" the localization property and inner boundedness are studied. Also in case when boundary function tends to zero as t => + ∞ the localization effect is regarded
Anisotropic phonon DOS: the application of Rietveld and Mossbauer texture analysis in aligned powders
While synthesizing the single crystals of novel materials is not always
feasible, orienting the layered polycrystals becomes an attractive method in
the studies of angular dependencies of inelastic scattering of x-rays or
neutrons. Putting in use the Rietveld analysis of layered structures in novel
manganites and cuprates we develop the studies of their anisotropic properties
with oriented powders instead of single crystals. Densities of phonon states
(DOS) and atomic thermal displacememts (ATD) are anisotropic in the A-site
ordered manganites LnBaMn2Oy of both y=5 and y=6 series (Ln=Y, La, Sm, Gd). We
establish the angular dependence of DOS on textures of arbitrary strengths,
link the textures observed by x-ray and gamma-ray techniques, and solve the
problem of disentanglement of Goldanskii-Karyagin effect (GKE) and texture in
Moessbauer spectra.Comment: 6 pages; 5 figures, revise
Novel dynamic scaling regime in hole-doped La2CuO4
Only 3% hole doping by Li is sufficient to suppress the long-range
3-dimensional (3D) antiferromagnetic order in La2CuO4.
The spin dynamics of such a 2D spin liquid state at T << J was investigated
with measurements of the dynamic magnetic structure factor S(omega,q), using
cold neutron spectroscopy, for single crystalline La2Cu0.94Li0.06O4.
S(omega,q) peaks sharply at (pi,pi) and crosses over around 50K from omega/T
scaling to a novel low temperature regime characterized by a constant energy
scale. The possible connection to a crossover from the quantum critical to the
quantum disordered regime of the 2D antiferromagnetic spin liquid is discussed.Comment: 4 pages, 4 figure
СИСТЕМНЫЕ АСПЕКТЫ МОРФОЛОГИИ ПЕРЕХОДНЫХ КРИЗИСНЫХ ЯВЛЕНИЙ В ОРГАНИЗАЦИЯХ
Characteristics of the two main approaches to modeling of management processes are described. The first of them is the system-cybernetic (separation of the control procedures in processes), the second is modeling stages of the company development by L. Greiner (partition of the cycle stages of organization). Each approach of business process modeling is viewed using simple charts and tables. The purpose of research is to acquaint managers of companies with the most effective management systems in order to the enterprise the correct organizational development of the company. The general laws of building optimal crisis management mechanisms now is given.Выделены и описаны характерные особенности двух основных подходов к моделированию процессов менеджмента. Первый – системно-кибернетический (разделение процедуры управления на процессы), второй – моделирование этапов развития фирмы по Л. Грейнеру (разбиение жизненного цикла компании на этапы). Каждый подход к моделированию бизнес-процессов подробно рассматривается с использованием простых схемы и таблицы. Цель исследования – познакомить руководителей компаний с наиболее эффективными системами управления на предприятии для правильного организационного развития фирмы, для преодоления кризисов организаций и минимализации их последствий. Приведены общие закономерности оптимального построения механизмов антикризисного управления компанией
Dilution and clustering of Fe in the rutile phases of TiO2 and SnO2
ABSTRACT: Dilute magnetic semiconductors of Fe-doped SnO2 and TiO2 with the structure of rutile were prepared in forms of powder and thin films using the techniques of sol gel and pulsed-laser deposition. We present the results of measurement of vibrational density of states of Fe impurity dopants in these oxides and demonstrate the cases of dilution and clustering. The oxygen pressure during the film deposition was varied between 10−1 and 10−8 Torr. In TiO2 films made at 10−1 Torr, Fe is diluted, however, in films made at 10−8 Torr Fe is clustered. The case of true Fe dilution in SnO2 is also shown. In spite of larger mass defect for Fe in SnO2 than that for Fe in TiO2 the dilute Fe species probe the phonon states in SnO2 more faithfully than in TiO2. This result is understood in terms of the combined effect of mass defect and nearest-neighbor force-constant changes. The impurity modes are more pronounced in TiO2 than in SnO2 due to ca. 10% difference of the lattice cell volumes between these two rutile oxides
Dispersion of the odd magnetic resonant mode in near-optimally doped Bi2Sr2CaCu2O8+d
We report a neutron scattering study of the spin excitation spectrum in the
superconducting state of slightly overdoped Bi2Sr2CaCu2O8+d system (Tc=87 K).
We focus on the dispersion of the resonance peak in the superconducting state
that is due to a S=1 collective mode. The measured spin excitation spectrum
bears a strong similarity to the spectrum of the YBa2Cu3O6+x system for a
similar doping level i.e. x= 0.95-1), which consists of intersecting upward-
and downward-dispersing branches. A close comparison of the threshold of the
electron-hole spin flip continuum, deduced from angle resolved photo-emission
measurements in the same system, indicates that the magnetic response in the
superconducting state is confined, in both energy and momentum, below the
gapped Stoner continuum. In contrast to YBa2Cu3O6+x, the spin excitation
spectrum is broader than the experimental resolution. In the framework of an
itinerant-electron model, we quantitatively relate this intrinsic energy width
to the superconducting gap distribution observed in scanning tunnelling
microscopy experiments. Our study further suggests a significant in-plane
anisotropy of the magnetic response.Comment: 10 figure
Condensation of a tetrahedra rigid-body libration mode in HoBaCo4O7 : the origin of phase transition at 355 K
Rietveld profiles, Moessbauer spectra and x-ray absorption fine structure
(XAFS) were analyzed through the structural phase transition at Ts = 355 K in
HoBaCo4O7. Excess of the oxygen content over O7 was avoided via annealing the
samples in argon flow at 600 degree C. Space groups (S.G.) Pbn21c and P63mc
were used to refine the structure parameters in the low- and high-temperature
phases, respectively. Additionally, the Cmc21 symmetry was considered as a
concurrent model of structure of the low-temperature phase. In the
high-temperature phase, severe anisotropy of thermal motion of the major part
of the oxygen atoms was observed. This anisotropic motion turns to be quenched
as the sample is cooled below Ts. The variation of quadrupole splitting near Ts
is not similar to a steplike anomaly frequently seen at the charge-ordering
transition. We observe instead a dip-like anomaly of the average quadrupole
splitting near Ts. Narrow distribution of the electric field gradient (EFG)
over different cobalt sites is observed and explained on the basis of
point-charge model. XAFS spectra show no evidence of significant difference
between YBaCo4O7 (T > Ts) and HoBaCo4O7 (T < Ts). The origin of the transition
at Ts is ascribed to the condensation of the libration phonon mode associated
with the rigid-body rotational movements of the starlike tetrahedral units, the
building blocks of kagome network. It is shown that the condensation of the
libration mode is not compatible with translation symmetry for the hexagonal
S.G., but compatible for the orthorhombic S.G. The orthorhombic lattice
parameters and EFG components (Vxx, Vyy, Vzz) vary smoothly with temperature at
approaching Ts and closely follow each other.Comment: 13 figure
Two Pseudogaps in the Cuprates: Meingast et al. Reply
In classical superconductors Cooper-pair formation and phase coherence occur
simultaneously as the temperature is lowered below Tc. In high-temperature
superconductors (HTSC), on the other hand, the small superfluid density and low
associated phase stiffness of the superconducting condensate are expected to
lead to a separation of the Cooper-pair formation and the phase-coherence
temperatures, especially in underdoped materials [3]. The only real phase
transition in this scenario is the 3d-XY phase-ordering transition at Tc [3,4].
In our Letter [2] we showed that Tc in underdoped and optimally doped YBCO is
just such a phase-ordering temperature, and then the question naturally arises
- where do the Cooper pairs form? The observed 3d-XY scaling of our thermal
expansion data over a wide temperature range [2] suggests that pairing occurs
at temperatures considerably above Tc, and it thus appeared quite natural for
us to associate the opening of the pseudogap at T*.Comment: 3 pages, 1 Figure (Reply to Comment by R. S. Markiewicz, Phys. Rev.
Lett. 89, 229703 (2002
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