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1.
FePS3 is a layered antiferromagnet (T
N=123 K) with a marked Ising anisotropy in magnetic properties. The anisotropy arises from the combined effect of the trigonal
distortion from octahedral symmetry and spin-orbit coupling on the orbitally degenerate5
T
2g
ground state of the Fe2+ ion. The anisotropic paramagnetic susceptibilities are interpreted in terms of the zero field Hamiltonian, ℋ=Σi [δ(L
iz
2
−2)+|λ|L
i
.S
i
]−Σ
ij
J
ij
S
i
.S
j
. The crystal field trigonal distortion parameter Δ, the spin-orbit coupling λ and the isotropic Heisenberg exchange,J
ij, were evaluated from an analysis of the high temperature paramagnetic susceptibility data using the Correlated Effective
Field (CEF) theory for many-body magnetism developed by Lines. Good agreement with experiment were obtained for Δ/k=215.5 K; λ/k=166.5 K;J
nn
k=27.7 K; andJ
nnn
k=−2.3 K. Using these values of the crystal field and exchange parameters the CEF predicts aT
N=122 K for FePS3, which is remarkably close to the observed value of theT
N. The accuracy of the CEF approximation was also ascertained by comparing the calculated susceptibilities in the CEF with
the experimental susceptibility for the isotropic Heisenberg layered antiferromagnet MnPS3, for which the high temperature series expansion susceptibility is available. 相似文献
2.
E. Elizalde S. D. Odintsov L. Sebastiani S. Zerbini 《The European Physical Journal C - Particles and Fields》2012,72(2):1843
Oscillations of the F(R) dark energy around the phantom divide line, ω
DE=−1, both during the matter era and also in the de Sitter epoch are investigated. The analysis during the de Sitter epoch
is revisited by expanding the modified equations of motion around the de Sitter solution. Then, during the matter epoch, the
time dependence of the dark energy perturbations is discussed by using two different local expansions. For high values of
the red shift, the matter epoch is a stable point of the theory, giving the possibility to expand the F(R)-functions in terms of the dark energy perturbations. In the late-time matter era, the realistic case is considered where
dark energy tends to a constant. The results obtained are confirmed by precise numerical computation on a specific model of
exponential gravity. A novel and very detailed discussion is provided on the critical points in the matter era and on the
relation of the oscillations with possible singularities. 相似文献
3.
Zhe Chang Ming-Hua Li Xin Li Sai Wang 《The European Physical Journal C - Particles and Fields》2012,72(3):1915
We investigate the possible effect of cosmological-constant type dark energy during the inflation period of the early universe.
This is accommodated by a new dispersion relation in de Sitter space. The modified inflation model of a minimally coupled
scalar field is still able to yield an observation-compatible scale-invariant primordial spectrum, simultaneously having the
potential to generate a spectrum with lower power at large scales. A qualitative match to the WMAP 7-year data is presented.
We obtain an Ω
Λ
of the same order of that in the Λ-CDM model. Possible relations between the de Sitter scenario and Doubly Special Relativity (DSR) are also discussed. 相似文献
4.
Yu. G. Chukalkin A. E. Teplykh A. N. Pirogov D. G. Kellerman 《Physics of the Solid State》2010,52(12):2545-2551
The specific features of the crystal structure and the magnetic state of stoichiometric lithium manganite in the structurally
ordered Li[Mn2]O4 and disordered Li1 − δMnδ[Mn2 − δLiδ]O4 (δ = 1/6) states have been investigated using neutron diffraction, X-ray diffraction, and magnetic methods. The structurally
disordered state of the manganite was achieved under irradiation by fast neutrons (E
eff ≥ 1 MeV) with a fluence of 2 × 1020 cm−2 at a temperature of 340 K. It has been demonstrated that, in the initial sample, the charge ordering of manganese ions of
different valences arises at room temperature, which is accompanied by orthorhombic distortions of the cubic spinel structure,
and the long-range antiferromagnetic order with the wave vector k = 2π/c(0, 0, 0.44) is observed at low temperatures. It has been established that the structural disordering leads to radical changes
in the structural and magnetic states of the LiMn2O4 manganite. The charge ordering is destroyed, and the structure retains the cubic symmetry even at a temperature of 5 K. The
antiferromagnetic type of ordering transforms into ferrimagnetic ordering with local spin deviations in the octahedral sublattice
due to the appearance of intersublattice exchange interactions. 相似文献
5.
We have obtained a generalization of the hydrodynamic theory of vacuum in the context of general relativity. While retaining
the Lagrangian character of general relativity, the new theory provides a natural alternative to the view that the singularity
is inevitable in general relativity and the theory of a hot Universe. We show that the macroscopic source-sink motion as a
whole of ordinary (dark) matter that emerges during the production of particles out of the vacuum can be a new source of gravitational
vacuum polarization (determining the variability of the cosmological term in general relativity). We have removed the well-known
problems of the cosmological constant by refining the physical nature of dark energy associated precisely with this hydrodynamically
initiated variability of the vacuum energy density. A new exact solution of the modified general relativity equations that
contains no free (fitting) parameter additional to those available in general relativity has been obtained. It corresponds
to the continuous and metric-affecting production of ultralight dark matter particles (with mass m
0 = (ħ/c
2) $
\sqrt {12\rho _0 k}
$
\sqrt {12\rho _0 k}
≈ 3 × 10−66 g, k is the gravitational constant) out of the vacuum, with its density ρ0, constant during the exponential expansion of a spatially flat Universe, being retained. This solution is shown to be stable
in the regime of cosmological expansion in the time interval −∞ < t < t
max, when t = 0 corresponds to the present epoch and t
max= 2/3H
0
cΩ0m
≈ 38 × 109 yr at Ω0m
= ρ0/ρc ≈ 0.28 (H
0 is the Hubble constant, ρc is the critical density). For t > t
max, the solution becomes exponentially unstable and characterizes the inverse process of dark matter particle absorption by
the vacuum in the regime of contraction of the Universe. We consider the admissibility of the fact that scalar massive photon
pairs can be these dark matter particles. Good quantitative agreement of this exact solution with the cosmological observations
of SnIa, SDSS-BAO, and the decrease in the acceleration of the expansion of the Universe has been obtained. 相似文献
6.
In the framework of a simple spin-boson Hamiltonian we study an interplay between dynamic and spectral roots to stochastic-like
behavior. The Hamiltonian describes an initial vibrational state coupled to discrete dense spectrum reservoir. The reservoir
states are formed by three sequences with rationally independent periodicities 1; 1 ± δ typical for vibrational states in
many nanosize systems (e.g., large molecules containing CH2 fragment chains, or carbon nanotubes). We show that quantum evolution of the system is determined by a dimensionless parameter
δΓ, where Γ is characteristic number of the reservoir states relevant for the initial vibrational level dynamics. When δΓ
> 1 spectral chaos destroys recurrence cycles and the system state evolution is stochastic-like. In the opposite limit δΓ
< 1 dynamics is regular up to the critical recurrence cycle k
c
and for larger k > k
c
dynamic mixing leads to quasi-stochastic time evolution. Our semi-quantitative analytic results are confirmed by numerical
solution of the equation of motion. We anticipate that both kinds of stochastic-like behavior (namely, due to spectral mixing
and recurrence cycle dynamic mixing) can be observed by femtosecond spectroscopy methods in nanosystems in the spectral window
1011–1013 s−1 相似文献
7.
We develop a renormalization group approach for cyclizing polymers for the case when chain ends are initially close together
(ring initial conditions). We analyze the behavior at times much shorter than the longest polymer relaxation time. In agreement
with our previous work (Europhys. Lett.
73, 621 (2006)) we find that the leading time dependence of the reaction rate k(t) for ring initial conditions and equilibrium initial conditions are related, namely k
ring(t) ∝ t
-δ and k
eq(t) ∝ t
1-δ for times less than the longest polymer relaxation time. Here δ is an effective exponent which approaches δ = 5/4 for very
long Rouse chains. Our present analysis also suggests a “sub-leading” term proportional to (ln t)/t which should be particularly significant for smaller values of the renormalized reaction rate and early times. For Zimm dynamics,
our RG analysis indicates that the leading time dependence for the reaction rate is k(t) ∼ 1/t for very long chains. The leading term is again consistent with the expected relation between ring and equilibrium initial
conditions. We also find a logarithmic correction term which we “exponentiate” to a logarithmic form with a Landau pole. The
presence of the logarithm is particularly important for smaller chains and, in the Zimm case, large values of the reaction
rate. 相似文献
8.
We study a reaction-diffusion system of N equations with k nonzero and N − k zero diffusion coefficients. More exactly, the first k equations of the system contain the terms a
i
Δu
i
− f
j
(u, v), i = 1, …, k, with the diffusion coefficient a
i
> 0. The right-hand sides of the other N − k equations contain only nonlinear interaction functions −h
j
(u, v), j = k + 1, …, N, with zero diffusion. Here u = (u
1, …, u
k
) and v = (υ
k+1, …, υ
N
) are unknown concentration vectors. Under appropriate assumptions on the interaction functions f(·) and h(·), we construct the trajectory attractor of this reaction-diffusion system. We also find the trajectory attractors , δ = (δ
1, …, δ
k
), for the analogous reaction-diffusion systems having the terms δ
j
Δυ
j
− h
j
(u, v), j = k + 1, …, N, with small diffusion coefficients δ
j
⩾ 0 in the last N − k equations. We prove that the trajectory attractors converge to (in an appropriate topology) as δ → 0+.
Dedicated to the memory of Vladimir Borovikov
Partially supported by the Russian Foundation for Basic Research (projects nos. 08-01-00784 and 07-01-00500). 相似文献
9.
R. F. Polishchuk 《Bulletin of the Lebedev Physics Institute》2017,44(4):114-117
Hypothesis of friedmons as dark matter particles is proposed. Friedmons are stable particles with a mass of billion nucleon masses. These particles correspond to the not yet been discovered exact symmetry group dual to the SU(2) group: for the Standard model symmetries and dual symmetries, the roles of exact and broken symmetries and corresponding stable and unstable particles change places. The hypothesis of the decay of the primordial de Sitter vacuum of the Planck density to an asymptotic state of the expanding Universe with de Sitter vacuum of the observed critical density is proposed. The T -duality and S-duality hypotheses relating subgroups SU(3)×SU(2)×U(1) and dual subgroups S??(3)× S??(2) × ??(1) with decay of the primordial symmetry group E(8) × ??(8) are proposed. In particular, these dualities relate the minimum Planck length 10?13 cm to the primordial curvature radius 10?13 cmof theMetagalaxy of the Planck density and its modern curvature radius of 1028 cm. That is, the probable relation of the Planck mass to the Metagalaxy mass of 1061 Planck masses is indicated. 相似文献
10.
Lorenzo Iorio 《General Relativity and Gravitation》2011,43(6):1697-1706
The strategy followed so far in the performed or proposed tests of the general relativistic Lense-Thirring effect in the gravitational
field of the Earth with laser-ranged satellites of LAGEOS type relies upon the cancelation of the disturbing huge precessions
induced by the first even zonal harmonic coefficient J
2 of the multipolar expansion of the Newtonian part of the terrestrial gravitational potential by means of suitably designed
linear combinations of the nodes Ω of more than one spacecraft. Actually, such a removal does depend on the accuracy with
which the coefficients of the combinations adopted can be realistically known. Uncertainties of the order of 2 cm in the semimajor
axes a and 0.5 milliarcseconds in the inclinations I of LAGEOS and LAGEOS II, entering the expression of the coefficient c
1 of the combination of their nodes used so far, yield an uncertainty δc
1 = 1.30 × 10−8. It gives an imperfectly canceled J
2 signal of 10.8 milliarcseconds per year corresponding to 23% of the Lense-Thirring signature. Uncertainties of the order
of 10–30 microarcseconds in the inclinations yield δc
1 = 7.9 × 10−9 which corresponds to an uncanceled J
2 signature of 6.5 milliarcseconds per year, i.e. 14% of the Lense-Thirring signal. Concerning a future LAGEOS-LAGEOS II-LARES
combination with coefficients k
1 and k
2, the same uncertainties in a and the less accurate uncertainties in I as before yield δk
1 = 1.1 × 10−8, δk
2 = 2 × 10−9; they imply a residual J
2 combined precession of 14.7 milliarcseconds per year corresponding to 29% of the Lense-Thirring trend. Uncertainties in the
inclinations at ≈ 10 microarcseconds level give δk
1 = 5 × 10−9, δk
2 = 2 × 10−9; the uncanceled J
2 effect is 7.9 milliarcseconds per year, i.e. 16% of the relativistic effect. 相似文献
11.
We study hypoelliptic operators with polynomially bounded coefficients that are of the form K=∑
i=1
m
X
i
T
X
i
+X
0+f, where the X
j
denote first order differential operators, f is a function with at most polynomial growth, and X
i
T
denotes the formal adjoint of X
i
in L
2. For any ɛ>0 we show that an inequality of the form ||u||δ,δ≤C(||u||0,ɛ+||(K+iy)u||0,0) holds for suitable δ and C which are independent of yR, in weighted Sobolev spaces (the first index is the derivative, and the second the growth). We apply this result to the Fokker-Planck
operator for an anharmonic chain of oscillators coupled to two heat baths. Using a method of Hérau and Nier [HN02], we conclude
that its spectrum lies in a cusp {x+iy|x≥|y|τ−c,τ(0,1],cR}.
Received: 30 July 2002 / Accepted: 18 October 2002 Published online: 25 February 2003
RID="*"
ID="*" Present address: Mathematics Research Centre of the University of Warwick
Communicated by A. Kupiainen 相似文献
12.
13.
We establish a connection between conformally related Einstein spaces and conformai killing vectors (CKV). We begin with the conformal map and prove that (a) under the conformal mapping¯g
ik=–2gik, the necessary and sufficient condition for the tracefree part of the Ricci tensor (S
ik=Rik–(R/4)g
ik) to remain invariant is that
i is a CKV ofg
ik, and (b) the most general form for for conformally flat Einstein space, which is the de Sitter space, is composed of three terms each of which alone represents a flat space. The existence of gradient CKV (GCKV) is examined in relation to vacuum and perfect fluid spacetimes. 相似文献
14.
Viorel Chiritoiu Gheorghe Zet 《The European Physical Journal C - Particles and Fields》2008,57(4):809-815
A formulation of the de Sitter symmetry as a purely inner symmetry defined on a fixed Minkowski space-time is presented. We
define the generators of the de Sitter group and write the structure equations using a constant deformation parameter λ. The conserved gauge currents are calculated, and their physical meaning is given. Local gauge transformations and the corresponding
covariant derivative depending on the gauge fields are also obtained. We study the behavior of gauge fields, the torsion and
curvature tensors and give a regularization technique in terms of the ζ function. 相似文献
15.
V. G. Krechet 《Russian Physics Journal》2007,50(10):1021-1025
Interrelations of the intrinsic momentum (spin), rotation of material distributions, and intrinsic momentum of the gravitational
field are investigated in the context of the general relativistic theory of gravitation involving the general relativity theory
(GRT) and the Einstein-Cartan theory. It is demonstrated that the spin density vector of the gravitational field s
g
i
is equal to the rotor of the tetrad reference point ωi=ɛiklm e
k
(a)
e(a)l,m/2 to within the factor 1/κ (s
g
i
=ω/κc). It is demonstrated that the vector s
g
i
is proportional to the spin density vector of the gravitating field si (ω)=jc(Ψγiγ5Ψ)/2 as well as the pseudovector of space-time torsion Qi in the Einstein-Cartan theory, which in both cases induces a cubic nonlinearity of the spinor field. An expression for the
energy-momentum density tensor of the eddy gravitational field is derived. It is also demonstrated that the free eddy gravitational
field with polarized spin can form “mole holes.” An ideal fast-rotating self-gravitating fluid can cause a similar effect.
The corresponding exact solutions of joint systems of the Einstein and rotating ideal fluid equations are presented.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 57–60, October, 2007. 相似文献
16.
Parongama Sen 《Pramana》2008,71(2):313-317
We consider navigation or search schemes on networks which have a degree distribution of the form P(k) ∝ exp(−k
γ). In addition, the linking probability is taken to be dependent on social distances and is governed by a parameter λ. The searches are realistic in the sense that not all search chains can be completed. An estimate of μ = ρ/s
d, where ρ is the success rate and s
d the dynamic path length, shows that for a network of N nodes, μ ∝ N
−δ
in general. Dynamic small world effect, i.e., δ ≃ 0 is shown to exist in a restricted region of the λ−γ plane.
相似文献
17.
Yuji Kajiyama Hiroshi Okada Takashi Toma 《The European Physical Journal C - Particles and Fields》2011,71(8):1688
We study fermionic dark matter in a non-supersymmetric extension of the standard model with a family symmetry based on D6 ×[^(Z)]2×Z2D_{6} \times\hat{Z}_{2}\times Z_{2}. In our model, the final state of the dark matter annihilation is determined to be e
+
e
− by the flavor symmetry, which is consistent with the PAMELA result. At first, we show that our dark matter mass should be
within the range of 230 GeV–750 GeV in the WMAP analysis combined with μ→eγ constraint. Moreover, we simultaneously explain the experiments of direct and indirect detection, by simply adding a gauge
and D
6 singlet real scalar field. In the direct detection experiments, we show that the lighter dark matter mass ≃230 GeV and the
lighter standard model Higgs boson ≃115 GeV are in favor of the observed bounds reported by CDMS II and XENON100. In the indirect
detection experiments, we explain the positron excess reported by PAMELA through the Breit–Wigner enhancement mechanism. We
also show that our model is consistent with there being no antiproton excess, as suggested by PAMELA. 相似文献
18.
Bianchi Type-I cosmological models containing perfect fluid with time varying G and Λ have been presented. The solutions obtained represent an expansion scalar θ bearing a constant ratio to the anisotropy in the direction of space-like unit vector λ
i
. Of the two models obtained, one has negative vacuum energy density, which decays numerically. In this model, we obtain Λ
∼ H
2, Λ ∼ R
44/R and Λ ∼ T
−2 (T is the cosmic time) which is in accordance with the main dynamical laws for the decay of Λ. The second model reduces to a
static solution with repulsive gravity.
相似文献
19.
B. M. Forster J. M. Bailey G. A. Beer J. L. Beveridge J. H. Brewer W. N. Hardy T. M. Huber K. R. Kendall A. R. Kunselman J. A. Macdonald G. M. Marshall G. R. Mason A. Olin M. Senba J. B. Warren 《Hyperfine Interactions》1991,65(1-4):1007-1013
Muonic hydrogen isotopes (μ− p, μ− d, and μ−t) are simple quantum mechanical systems ideally suited for studies of numerous fundamental phenomena in electroweak and strong
interactions as well as in applied areas such as muon chemistry or muon catalyzed fusion.
Emission of muonic hydrogen isotopes into vacuum helps to overcome the limitations which are normally imposed on conventional
investigations with gaseous and liquid targets. A proof of principle experiment for this new technique was performed at TRIUMF
last year. Negative muons with 30 MeV/c momentum were stopped in a thin film of solid hydrogen and produced very low energy μ−d in vacuum. The distribution center of the normal velocity components of emitted μ−d atoms was measured to be ∼1 cm/μs. The yield of μ−d in vacuum is an increasing function of H2 film thickness δ up to a value of δ≥1 mm. 相似文献
20.
R. N. Garifullin B. I. Suleimanov 《Journal of Experimental and Theoretical Physics》2010,110(1):133-146
An analysis is presented of the effect of weak dispersion on transitions from weak to strong discontinuities in inviscid fluid
dynamics. In the neighborhoods of transition points, this effect is described by simultaneous solutions to the Korteweg—de
Vries equation u
t
′ + uu
x
″ + u
xxx
‴ = 0 and fifth-order nonautonomous ordinary differential equations. As x2 + t
2 →∞, the asymptotic behavior of these simultaneous solutions in the zone of undamped oscillations is given by quasi-simple
wave solutions to Whitham equations of the form r
i(t, x) = tli x/t2. 相似文献