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991.
High-temperature and high-pressure behaviours of β-Ga2O3 powder are studied by energy-dispersive x-ray diffrac- tion in a diamond anvil cell (DAC). It is found that the phase transition from the monoclinic β-Ga2O3 to the trigonal α-Ga2O3 occurs at around 19.2 GPa under cold compression. By heating the powder to 2000 K at 30 GPa, we confirm that α-Ga2O3 is the most stable structure at the high pressure. Furthermore, the structural transition from β-Ga2O3 to α-Ga2O3 is irreversible. After laser heating, the recrystallized Ga2O3 has a preferable (012) orientation. This interesting behaviour is also discussed. 相似文献
992.
Development of Simple Dip-Stick-Type Uniaxial Stress Actuator for Alternating-Current Susceptibility Measurements 下载免费PDF全文
A simple dip-stick type uniaxial stress actuator for ac-susceptibility measurement is designed. Target pressure can be achieved by smooth and continues work carried out using a combination of light weight micrometer and spring. The magnitude of the pressure is directly calculated from the force constant of the spring and the surface atea of the sample. Benchmark on the quality of the data under uniaxial pressure is confirmed by the Piezo resistance measurements on [100] oriented n-type Si. The system is examined and calibrated with the standard paramagnetic Gd2O3. Further, the device performance, generation of constant uniaxial pressure against temperature variations, is assured by investigating the ac-magnetic susceptibility measurements on highly anisotropic La1.25Sr1.75Mn2O7 bilayer single crystal. 相似文献
993.
V.V. Bannikov I.R. SheinV.L. Kozhevnikov A.L. Ivanovskii 《Journal of magnetism and magnetic materials》2008
Using the full-potential linearized augmented plane-wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential, we studied spin polarization induced by replacement of oxygen atoms by non-magnetic 2p impurities (B, C and N) in non-magnetic cubic SrMO3 perovskites, where M=Ti, Zr and Sn. The results show that the magnetization may appear because of the spin–split impurity bands inside the energy gap of the insulating SrMO3 matrix. Large magnetic moments are found for the impurity centers. Smaller magnetic moments are induced on the oxygen atoms around impurities. It is shown that SrTiO3:C and SrSnO3:C should be magnetic semiconductors while other compounds in this series (SrTiO3:B, SrTiO3:N and SrZrO3:C) are expected to exhibit magnetic half-metallic or pseudo-half-metallic properties. 相似文献
994.
Magnetoelastic (ME) waves and thickness-shear modes in the ferromagnetic plate are studied. Coupled vibrations of magnetization and shear elastic deformations excited simultaneously by a variable magnetic field propagate in two mutually perpendicular directions: parallel and normal to a surface. For parameters characteristic of isotropic ferromagnet with the sample magnetization and Zeeman field parallel to the surface, resonant frequencies of shear modes are computed and their dispersion law is examined. It is shown that the dependence of dimensional resonances frequencies on wave number kz of ME wave propagating along saturating field direction occurs. The possibility of excitation of ME waves with different kz explains multimode character of thickness ME resonances. 相似文献
995.
We investigate the entropy bound for local quantum field theory in this Letter. Both the bosonic and fermionic fields confined to an asymptotically flat space–time are examined. By imposing the non-gravitational collapse condition, we find both of them are limited by the same entropy bound A3/4, where A is the boundary area of the region where the quantum fields are contained in. The gap between this entropy bound and the holographic entropy has been verified. 相似文献
996.
T. J. Bullard J. Das G. L. Daquila U. C. T?uber 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(4):469-484
In order to characterize flux flow through disordered type-II superconductors, we investigate the effects of columnar and
point defects on the vortex velocity/voltage power spectrum in the driven non-equilibrium steady state. We employ three-dimensional
Metropolis Monte Carlo simulations to measure relevant physical observables including the force-velocity/current-voltage (I-V)
characteristics, vortex spatial arrangement and structure factor, and mean flux line radius of gyration.Our simulation results
compare well to earlier findings and physical intuition.We focus specifically on the voltage noise power spectra in conjunction
with the vortex structure factor in the presence of weak columnar and point pinning centers. We investigate the vortex washboard
noise peak and associated higher harmonics,and show that the intensity ratios of the washboard harmonics are determined bythe
strength of the material defects rather than the type of pins present.Through varying columnar defect lengths and pinning
strengths as well as magnetic flux density we further explore the effect of the material defects on vortex transport.It is
demonstrated that the radius of gyration displays quantitatively uniquefeatures that depend characteristically on the type
of material defects presentin the sample. 相似文献
997.
Saurabh Gupta R. P. Malik 《The European Physical Journal C - Particles and Fields》2008,58(3):517-529
We demonstrate that the four-dimensional (4D) ((3+1)-dimensional) free Abelian 2-form gauge theory presents a tractable field-theoretical
model for the Hodge theory where the well-defined symmetry transformations correspond to the de Rham cohomological operators
of differential geometry. The conserved charges, corresponding to the above continuous symmetry transformations, obey an algebra
that is reminiscent of the algebra obeyed by the cohomological operators. The discrete symmetry transformation of the theory
represents the realization of the Hodge duality operation that exists in the relationship between the exterior and co-exterior
derivatives of differential geometry. Thus, we provide the realizations of all the mathematical quantities, associated with
the de Rham cohomological operators, in the language of the symmetries of the present 4D free Abelian 2-form gauge theory. 相似文献
998.
Ultrafast optical response in the films of poly(3-dodecylthiophene) (P3DT) and blue-and red-phase polydiacetylenes (PDA-4BCMU) has been investigated by femtosecond absorption and picosecond luminescence spectroscopies. Several nonlinear optical processes, i.e., hole burning, Raman gain, inverse Raman scattering, and induced-frequency shift, have been observed. The relaxation processes from photoexcited free excitons to self-trapped excitons (STEs) has been observed. The time constant is estimated as 140±40 fs in the blue-phase PDA-4BCMU and 100±50 fs in P3DT. The generated unthermalized STEs thermalize with the time constant of about 1 ps. The STEs in the blue-phase PDA-4BCMU decay exponentially with lifetime of 1.6±0.1 ps at 290 K and 2.1±0.2 ps at 10 K. The decay curves in the red-phase PDA-4BCMU and P3DT are not single exponential but can be fitted to biexponential functions with time constants of slightly shorter than 1 ps and about 5 ps. These two decay time constants correspond to relaxations to the ground state, respectively, from the free exciton and unthermalized STE and from the thermalized STE. 相似文献
999.
1000.
Given p () , we determine when a product of quasi-p-pseudocompact spaces preserves this property. In particular, we analyze the product of quasi-p-pseudocompact subspaces of () containing . We give examples of spaces X, Y,
X
s
, Ys which are quasi-p-pseudocompact for every p *, but X Y is not pseudocompact, and X
s
Y
s is pseudocompact and it is not quasi-s-pseudocompact for each s *. Besides, we prove that every pseudocompact space X of with X, is quasi-p-pseudocompact for some p *. Finally, we introduce, for each p *, the class P
p
of all spaces X such that X × Y is quasi-p-pseudocompact when so is Y; and we prove: (1) the intersection of classes P
p
(
p
*) coincides with the Frol"ik class; (2) every class P
p
is closed under arbitrary products; (3) the partial ordered set ( P
p
p ,) is isomorphic to the set of equivalence classes of free ultrafilters on with the Rudin–Keisler order. A topological characterization of RK-minimal ultrafilters is also given. 相似文献