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1.
The results of electrical resistance (R), thermoelectric power (TEP) and X-ray diffraction measurements on praseodymium (Pr) and its alloys with thorium under pressure
are reported. The maximum inR vsP curve exhibited by Pr persists only in the dhcp phase of PrTh alloy. X-ray measurements confirmed that in the alloys also
the maximum inR vsP curve is due to the dhcp → fcc transition. Thus the behaviour of Pr and Pr-Th alloys is different from that of La and its
alloys with Ce and Th where the maximum in theR vsP curve is electronic in origin and is exhibited by the dhcp, fcc and dist fcc phases. 相似文献
2.
A. V. Tsvyashchenko A. V. Nikolaev A. I. Velichkov A. V. Salamatin L. N. Fomicheva G. K. Ryasny A. A. Sorokin O. I. Kochetov M. Budzynski 《Journal of Experimental and Theoretical Physics》2010,111(4):627-634
We use the time-differential perturbed angular correlation technique to study nuclear electric quadupole hyperfine interactions
of probe 111Cd nuclei in cerium lattice sites at room temperature under pressures up to 8 GPa. We have found that the well known γ → α
phase transition in cerium is not isostructural. In α-Ce, the probe 111Cd nuclei reveal a quadrupole electron charge density component that is absent in γ-Ce. The hidden spacial structure of electronic
quadrupoles in α-Ce is triple-q antiferroquadrupolar, as was suggested in [14]. We relate our findings to the current understanding
of the γ → α phase transition and also report on nuclear quadrupole interactions in other high-pressure phases of cerium:
α″ (C2/m space symmetry) and α′ (α-U structure). 相似文献
3.
Hao Chen Yongchang Liu Zesheng Yan Yanli Li Lifang Zhang 《Applied Physics A: Materials Science & Processing》2010,98(1):211-217
The three cooling rates of 10, 100, 200 K/min dilatometry experiments are used to investigate the kinetics of the isochronal
austenite (γ) to ferrite (α) transformation of Fe–0.0036wt.%C alloy. “Normal transformation” and “abnormal transformation” have both been observed for
transformations at different cooling rates. In accordance with the thermodynamic characteristics of the γ→α transformation investigated here and previous kinetic considerations, a JMAK-like approach for the kinetics of isochronal
phase transformations was developed that incorporates three overlapping processes: site saturation nucleation, alternate growth
modes (from interface-controlled to diffusion-controlled to interface-controlled growth), as well as impingement for random
distribution nuclei. The JMAK-like approach has been employed to fit the experimental results, and the fitting results show
that for the γ→α transformation of the Fe–C alloy at all applied cooling rates, the growth mode evolves in the corresponding order: from interface-controlled
to diffusion-controlled growth; from interface-controlled to diffusion-controlled to interface-controlled growth; and interface-controlled
growth. 相似文献
4.
In 1964 Davis and Adams established that the large increase of the thermal expansion and compressibility in the critical region
of the γ-to α-Ce phase transition occurs predominantly in the α phase. This provides strong evidence that a tricritical point
is realized in Ce. This also means that the aforementioned transition is not isomorphic and that α-Ce should have a distorted
fcc structure. A careful examination of Jayaraman’s data (1965) shows that a second-order transition line continues beyond
the tricritical point to the vicinity of a triple point on the melting curve. The phase boundary with the tricritical point
and the minimum of the melting curve are reconstructed within the framework of Landau theory.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 111–117 (25 January 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
5.
W.-D. Zeitz S. Unterricker F. Schneider V. Samokhvalov K. Potzger A. Weber M. Dietrich 《Hyperfine Interactions》2004,158(1-4):437-441
The magnetic response of europium in γ-cerium and in platinum was studied by applying the perturbed angular correlation spectroscopy.
The probe nuclei were 147Eu(11/2−) and 149Eu(11/2−). The response in γ-Ce was determined by the electronic S = J = 7/2 ground state of divalent Eu. In Pt, on the other hand, Eu is trivalent (J = 0 ground state). Here the magnetic contributions originate from Van Vleck terms of the whole multiplet system. 相似文献
6.
V. A. Kulbachinski? V. G. Kytin P. M. Tarasov 《Journal of Experimental and Theoretical Physics》2010,110(4):618-621
The effect of gallium on the temperature dependences (5 K ≤ T ≤ 300 K) of Seebeck coefficient α, electrical conductivity σ, thermal conductivity k, and thermoelectric efficiency Z of mixed p-(Bi0.5Sb0.5)2Te3 semiconductor single crystals is studied. The hole concentration decreases upon gallium doping; that is, gallium causes a
donor effect. The Seebeck coefficient increases anomalously, i.e., much higher than it should be at the detected decrease
in the hole concentration. This leads to an enhancement of the thermoelectric power. The observed changes in the Seebeck coefficient
indicate a noticeable gallium-induced change in the density of states in the valence band. 相似文献
7.
Igor E. Protsenko 《Journal of Russian Laser Research》2010,31(5):481-494
The thermoelectric (Seebeck) coefficient α and thermoelectric quality factor (figure of merit) ZT are estimated for a tunnel junction in metals. It is shown that α can be of the order of hundreds of μV/K while ZT can approach values ∼0.1–1. The maxima of α(h) and ZT(h) correspond to a certain width h of the tunnel junction; such h is about a few nanometers. The results we obtained can find applications in the constructions of novel thermoelectric generators. 相似文献
8.
Benjamin Lindner 《Journal of statistical physics》2008,130(3):523-533
Nonequilibrium biological systems like moving cells or bacteria have been phenomenologically described by Langevin equations
of Brownian motion in which the friction function depends on the particle’s velocity in a nonlinear way. An important subclass
of such friction functions is given by power laws, i.e., instead of the Stokes friction constant γ
0 one includes a function γ(v)∼v
2α
. Here I show using a recent analytical result as well as a dimension analysis that the diffusion coefficient is proportional
to a simple power of the noise intensity D like D
(1−α)/(1+α) (independent of spatial dimension). In particular the diffusion coefficient does not depend on the noise intensity at all,
if α=1, i.e., for a cubic friction F
fric=−γ(v)v∼v
3. The exact prefactor is given in the one-dimensional case and a fit formula is proposed for the multi-dimensional problem.
All results are confirmed by stochastic simulations of the system for α=1, 2, and 3 and spatial dimension d=1, 2, and 3. Conclusions are drawn about the strong noise behavior of certain models of self-propelled motion in biology. 相似文献
9.
On the basis of the concepts of an intermediate-valence (IV) regime, an empirical model is proposed that quantitatively describes
the magnetic susceptibility, specific heat, and effective atomic volume of the low-temperature α phase and the gallium or
aluminum-stabilized face-centered cubic (fcc) δ phase of plutonium metal. The results of the paper allow one to estimate the
entropy change associated with the α → δ structural phase transition, the value of this change being very close to the experimental
value. According to the model, both phases of plutonium are systems with multiple intermediate valence, whose ground state
is a many-particle Kondo singlet, and fluctuations occur between 5f electron configurations with integer valences of 3+, 4+, and 2+. 相似文献
10.
Recent X-ray diffraction studies on α-quartz (SiO2) by Kingmaet al [1], have shown the occurrence of a reversible, crystalline-to-crystalline, phase transition just prior to amorphization
at ≈ 21 GPa. This precursor transition has also been confirmed by our recent molecular dynamics simulation study [2]. In order
to investigate the possibility of a similar behaviour in other isostructural compounds, which also undergo pressure induced
amorphization, α-GeO2 and α-AlPO4 (berlinite form) were studied using energy dispersive X-ray diffraction. In either of these materials, no such phase transition
is detected prior to amorphization. The onset of amorphization and its reversal is found to be time dependent in GeO2. 相似文献
11.
The effect of mechanical contacts between γ-Fe2O3 particles on the temperature of the γ-α structural transition in them is established by magnetic studies and differential
thermal analysis (DTA). The sample in which γ-Fe2O3 particles had no mechanical contacts with one another remained in the ferromagnetic state up to T
C = 630°C and had two exothermal DTA peaks. The first peak almost coincided with the Curie temperature, while the second peak
attributed to the γ → α structural transition corresponded to 760°C. The magnetic transition for particles with a larger number
of contacts was shadowed by the γ → α structural transition with a temperature lowered to 550°C. 相似文献
12.
The thermoelectric performance of a thermoelement is ideally defined in terms of the so-called figure-of-meritZ = α2σ/λ, where α,σ and λ refer respectively to the Seebeck coefficient, electrical conductivity and thermal conductivity of the thermoelement
material. However, there are other parameters which are fairly good indicators of a material’s thermoelectric ‘worth’. A simple
yet useful performance indicator is possible with only two parameters — energy gap and lattice thermal conductivity. This
indicator can outline all potentially useful thermoelectric materials. Thermal conductivity in place of lattice thermal conductivity
can provide some additional information about the temperature range of operation. Yet another performance indicator may be
based on the slope of α vs. ln σ plots. α plotted against ln σ shows a linear relationship in a simplified model, but shows
a variation with temperature and carrier concentration. Assuming that such a relationship is true for a narrow range of temperature
and carrier concentration, one can calculate the slope m of α vs. ln σ plots against temperature and carrier concentrations.
A comparison between the variation ofZT and slopem suggests that such plots may be useful to identify potential thermoelectric materials. 相似文献
13.
An emulsion chamber was used to study the characteristics of high energy nuclear interactions from the production spectra
ofγ-rays. The emulsion chamber, which comprised of two parts, namely the detector and the graphite producer unit, was exposed
to cosmic rays for about 7 hr at an atmospheric depth of 10 g cm−2 at Hyderabad (geomagnetic latitude 7·6°N). 720 electromagnetic cascades due toγ-rays were recorded in the detector. These cascades were classified into three groups; (a)γ-rays from nuclear interactions in the detector (b)γ-rays from nuclear interactions in the producer unit and (c)γ-rays of atmospheric origin. The energies of the cascades were determined using photometric method. The spectra ofγ-rays from groups (a) and (c) were determined and compared with similar spectra obtained at greater atmospheric depths. The
spectra were found to obey a power law. The spectrum ofγ-rays of atmospheric origin was found to steepen at high energies,E
r>2200 GeV. 相似文献
14.
Sunanda Banerjee 《Pramana》2000,55(1-2):85-100
Several studies have been made to the hadronic final states in e
+
e
− collisions at LEP. Studies of the annihilation process at LEP2 have given rise to results on jet rate, event shape, heavy
flavour production, inclusive momentum spectra, Bose-Einstein correlation and colour reconnection effects. Event shape studies
have given rise to accurate determination of the strong coupling constant α
s using O (α
s
2
) with resummed leading and next-to-leading log calculation and also with power law corrections. Studies of 2-photon processes
have yielded results on γγ cross-section, heavy flavour production, photon structure function and γ*γ* scattering. 相似文献
15.
V. A. Lisovskii 《Technical Physics》1998,43(5):526-534
It is found that the region for the stable existence of the aregime of a radio-frequency (rf) discharge is bounded not only
on the moderate-pressure side, but also on the low-pressure side. One feature of the α-γ transition in a low-pressure rf discharge is that the criterion for breakdown of the electrode sheath is not satisfied. It
is shown that at low pressures the α-γ transition of an rf argon discharge takes place abruptly and exhibits hysteresis. At intermediate pressures the α-γ transition is continuous and lacks jumps; negative differential conductivity appears, double layers form, and nonmonotonic
behavior of the plasma density is observed at the center of the discharge. The role of stochastic (collisionless) electron
heating in sustaining an rf discharge at intermediate gas pressures is discussed.
Zh. Tekh. Fiz. 68, 52–60 (May 1998) 相似文献
16.
D. B. Gin V. G. Kiptily A. A. Pasternak I. N. Chugunov A. E. Shevelev G. Gorini M. Tardocchi M. Nocente JET-EFDA contributors 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(7):931-936
A parametrization of the partial cross section of the 9Be(α, nγ)12C reaction in the α-particle energy range of 0.3–7.9 MeV is presented, along with the count rates of γ quanta. The need to
consider subbarrier (Eα < 1.9 MeV) α-particles in plasma for temperatures T
α < 0.2 MeV is substantiated. The shapes of the Doppler-broadened 4.44 MeV γ line and the count rates of γ quanta in the plasma
of the JET tokamak are measured for the first time and compared to the calculated values. An estimated T
α ≲ 160 keV is obtained. 相似文献
17.
本文采用第一性原理框架下的赝势平面波方法结合振动类德拜模型研究了α,β和γ-Si3N4在高温下的点阵常数,弹性常数和弹性模量.研究发现三种同质异相体的体模量都很高.β-Si3N4在低温下表现出脆性,在高温下则表现出延展性.γ-Si3N4在低温和高温下都是脆性的共价化合物.β → γ 相变的相界斜率为正值,说明在较高温度时合成γ-Si3N4所需的压强也较高.α → γ 相变的相界可以表示成 P=16.29- 1.835-10-2 T+9.33945-10-5T2-2.16759-10-7T3+2.91795-10-10T4.本文还分析了Si3N4同质异相体在高压下的态密度和能带.在α-Si3N4中主要是Si-s, p和N-s,p的轨道杂化对晶体的稳定性起作用.α和β-Si3N4都具有ΓV-ΓC类型的间接带隙(分别是4.9~eV和4.4~eV)而γ-Si3N4具有直接带隙(3.9~eV). 研究还发现α-Si3N4和β-Si3N4的价带顶分别沿着Γ-M和Γ-A方向.本文的计算结果和已有的实验数据是一致的. 相似文献
18.
The principles of construction and the results of testing of a system for measuring P-odd asymmetries in nuclear reactions with polarized cold neutrons by the integrated method of recording events at the neutron
polarization switching frequency above the fundamental frequencies of the reactor power fluctuation spectrum are presented.
It is shown experimentally that if the signal under investigation is characterized by the spectral density of power decreasing
with increasing frequency, switching of the equipment at a higher frequency decreases the measuring error. The dependence
of the error of measurements of P-odd asymmetry in the emission of γ quanta in the 10B(n, α)7Li* ⟹ γ ⟹ 7Li(g.s.) reaction on the neutron polarization switching frequency is derived. The system described here is implemented experimentally
for the first time. 相似文献
19.
The results of numerical analysis of the Brownian movement of a particle in the force field of the potential corresponding
to interacting subcritical and supercritical phase transitions are considered. If the white noise intensity corresponds to
the critical intensity of the noise-induced transition, the system of stochastic differential equations describes random steady-state
processes with fluctuation power spectra inversely proportional to frequency f, S(f) ∼ 1/f
α, where exponent α varies in the interval 0.8 ≤ α ≤ 1.8. Exponent β of distribution function P(τ) ∼ τ−β for the duration of low-frequency extremal fluctuations, which are analogous to avalanches considered in the models of self-organized
criticality in many respects, varies between the same limits. It is shown that exponents α and β are connected through the
relation α + β = 2. 相似文献
20.
Yu. P. Gangrsky F. F. Karpeshin M. B. Trzhaskovskaya 《Physics of Atomic Nuclei》2011,74(12):1665-1670
We consider spectra of γ, internal conversion and α transitions in (n, γ) and (n, γα) reactions on 60143Nd. Probabilities of mixing of neutron resonances with different spins and parities arising due to internal and resonance
conversion are also considered from the point of view of studying the P-violating processes. Arguments are presented in favor of that the α decay of the 55-eV neutron resonance 4− to the ground state, observed earlier, may be due to such interaction. 相似文献