共查询到20条相似文献,搜索用时 31 毫秒
1.
A. Yu. Gufan O. V. Kukin Yu. M. Gufan I. A. Osipenko 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(3):328-338
The third-order elastic modulus of α-Fe were calculated based on the computation of lattice sums. The lattice sums were determined
using an integer rational basis of invariants composed by vectors connecting equilibrium atomic positions in the crystal lattice.
Irreducible interactions within clusters consisting of atomic pairs and triplets were taken into account in performing the
calculations. Comparison with experimental data showed that the potential can be written in the form of e9 = - ?i,k A19 rik - 6 + ?i,k A29 rik - 12 + ?i,k,l Q9 I9 - 1\varepsilon _9 = - \sum\nolimits_{i,k} {A_{19} r_{ik}^{ - 6} } + \sum\nolimits_{i,k} {A_{29} r_{ik}^{ - 12} + \sum\nolimits_{i,k,l} {Q_9 I_9^{ - 1} } }, where I9 = [(r)\vec]ik2 [ ( [(r)\vec]ik [(r)\vec]kl )2 + ( [(r)\vec]li [(r)\vec]ik )2 ] + [(r)\vec]kl2 [ ( [(r)\vec]ik [(r)\vec]kl )2 + ( [(r)\vec]kl [(r)\vec]li )2 ] + [(r)\vec]li2 [ ( [(r)\vec]li [(r)\vec]ik )2 + ( [(r)\vec]kl [(r)\vec]li )2 ]I_9 = \vec r_{ik}^2 \left[ {\left( {\vec r_{ik} \vec r_{kl} } \right)^2 + \left( {\vec r_{li} \vec r_{ik} } \right)^2 } \right] + \vec r_{kl}^2 \left[ {\left( {\vec r_{ik} \vec r_{kl} } \right)^2 + \left( {\vec r_{kl} \vec r_{li} } \right)^2 } \right] + \vec r_{li}^2 \left[ {\left( {\vec r_{li} \vec r_{ik} } \right)^2 + \left( {\vec r_{kl} \vec r_{li} } \right)^2 } \right]. If the values of [(r)\vec]ik\vec r_{ik} are scaled in half-lattice constant units, then A19 = 1.22
ë t9
û GPa, A29 = 5.07 ×102
ë t15
û GPa, Q9 = 5.31
ë t9
û GPaA_{19} = 1.22\left\lfloor {\tau ^9 } \right\rfloor GPa, A_{29} = 5.07 \times 10^2 \left\lfloor {\tau ^{15} } \right\rfloor GPa, Q_9 = 5.31\left\lfloor {\tau ^9 } \right\rfloor GPa, and τ = 1.26 ?. It is shown that the condition of thermodynamic stability of a crystal requires that we allow for irreducible
interactions in atom triplets in at least four coordination spheres. The analytical expressions for the lattice sums determining
the contributions from irreducible interactions in the atom triplets to the second- and third-order elastic moduli of cubic
crystals in the case of interactions determined by I
9 are presented in the appendix. 相似文献
2.
Linsen Zhang Puxun Wu Hongwei Yu 《The European Physical Journal C - Particles and Fields》2011,71(3):1588
In this paper, two modified Ricci models are considered as the candidates of unified dark matter–dark energy. In model one,
the energy density is given by rMR=3Mpl(aH2+b[(H)\dot])\rho_{\mathrm{MR}}=3M_{\mathrm{pl}}(\alpha H^{2}+\beta\dot{H}), whereas, in model two, by
rMR=3Mpl(\fraca6 R+g[(H)\ddot]H-1)\rho_{\mathrm{MR}}=3M_{\mathrm{pl}}(\frac{\alpha}{6} R+\gamma\ddot{H}H^{-1}). We find that they can explain both dark matter and dark energy successfully. A constant equation of state of dark energy
is obtained in model one, which means that it gives the same background evolution as the wCDM model, while model two can give an evolutionary equation of state of dark energy with the phantom divide line crossing
in the near past. 相似文献
3.
In this paper, we consider the global wellposedness of the 3-D incompressible anisotropic Navier-Stokes equations with initial
data in the critical Besov-Sobolev type spaces B{\mathcal{B}} and
B-\frac12,\frac124{\mathcal{B}^{-\frac12,\frac12}_4} (see Definitions 1.1 and 1.2 below). In particular, we proved that there exists a positive constant C such that (ANS
ν
) has a unique global solution with initial data u0 = (u0h, u03){u_0 = (u_0^h, u_0^3)} which satisfies
||u0h||B exp(\fracCn4 ||u03||B4) £ c0n{\|u_0^h\|_{\mathcal{B}} \exp\bigl(\frac{C}{\nu^4} \|u_0^3\|_{\mathcal{B}}^4\bigr) \leq c_0\nu} or
||u0h||B-\frac12,\frac124 exp(\fracCn4 ||u03||B-\frac12,\frac1244) £ c0n{\|u_0^h\|_{\mathcal{B}^{-\frac12,\frac12}_{4}} \exp \bigl(\frac{C}{\nu^4} \|u_0^3\|_{\mathcal{B}^{-\frac12,\frac12}_{4}}^4\bigr)\leq c_0\nu} for some c
0 sufficiently small. To overcome the difficulty that Gronwall’s inequality can not be applied in the framework of Chemin-Lerner
type spaces, [(Lpt)\tilde](B){\widetilde{L^p_t}(\mathcal{B})}, we introduced here sort of weighted Chemin-Lerner type spaces, [(L2t, f)\tilde](B){\widetilde{L^2_{t, f}}(\mathcal{B})} for some apropriate L
1 function f(t). 相似文献
4.
The quantum effects for a physical system can be described by the set E(H)\mathcal{E(H)} of positive operators on a complex Hilbert space H\mathcal{H} that are bounded above by the identity operator I. We denote the set of sharp effects by P(H){\mathcal{P(H) }}. For A,B ? E(H)A,B\in\mathcal{E(H)}, the operation of sequential product
A°B=A\frac12BA\frac12A\circ B=A^{\frac{1}{2}}BA^{\frac{1}{2}} was proposed as a model for sequential quantum measurements. Denote by
A*B=\fracAB+BA2A\ast B=\frac{AB+BA}{2} the Jordan product of A,B ? E(H)A,B\in\mathcal{E(H)}. The main purpose of this note is to study some of the algebraic properties of the Jordan product of effects. Many of our
results show that algebraic conditions on A∗B imply that A and B commute for the usual operator product. And there are many common properties between Jordan product and sequential product
of effects. For example, if A∗B satisfies certain associative laws, then AB=BA. Moreover, A*B ? P(H)A\ast B\in{\mathcal{P(H) }} if and only if A°B ? P(H)A\circ B\in{\mathcal{P(H)}}. 相似文献
5.
Lorenzo Iorio 《General Relativity and Gravitation》2010,42(1):199-208
Analytical and numerical calculations show that a putative temporal variation of the speed of light c, with the meaning of space-time structure constant c
ST, assumed to be linear over timescales of about one century, would induce a secular precession of the longitude of the pericenter
v{\varpi} of a test particle orbiting a spherically symmetric body. By comparing such a predicted effect to the corrections D[(v)\dot]{\Delta\dot\varpi} to the usual Newtonian/Einsteinian perihelion precessions of the inner planets of the Solar System, recently estimated by
E.V. Pitjeva by fitting about one century of modern astronomical observations with the standard classical/relativistic dynamical
force models of the EPM epehemerides, we obtained [(c)\dot]/c = (0.5±2)×10-7 yr-1{\dot c/c =(0.5\pm 2)\times 10^{-7} {\rm yr}^{-1}} . Moreover, the possibility that [(c)\dot]/c 1 0{\dot c/c\neq 0} over the last century is ruled out at 3−12σ level by taking the ratios of the perihelia for different pairs of planets. Our results are independent of any measurement
of the variations of other fundamental constants which may be explained by a variation of c itself (with the meaning of electromagnetic constant c
EM). It will be important to repeat such tests if and when other teams of astronomers will estimate their own corrections to
the standard Newtonian/Einsteinian planetary perihelion precessions with different ephemerides. 相似文献
6.
H.?W.?Grie?hammer M.?R.?Schindler 《The European Physical Journal A - Hadrons and Nuclei》2010,46(1):73-83
We address the typical strengths of hadronic parity-violating three-nucleon interactions in “pion-less” Effective Field Theory
(EFT) in the nucleon-deuteron (iso-doublet) system. By analysing the superficial degree of divergence of loop diagrams, we
conclude that no such interactions are needed at leading order, O(eQ-1)\ensuremath {O}(\epsilon Q^{-1}) . The only two distinct parity-violating three-nucleon structures with one derivative mix
2S\frac12\ensuremath ^2S_{\frac{1}{2}} and
2P\frac12\ensuremath ^2P_{\frac{1}{2}} waves with iso-spin transitions D \Delta
I = 0 or 1. Due to their structure, they cannot absorb any divergence ostensibly appearing at next-to-leading order, O(eQ0)\ensuremath {O}(\epsilon Q^0) . This observation is based on the approximate realisation of Wigner’s combined SU(4) spin-isospin symmetry in the two-nucleon system, even when effective-range corrections are included. Parity-violating
three-nucleon interactions thus only appear beyond next-to-leading order. This guarantees renormalisability of the theory
to that order without introducing new, unknown coupling constants and allows the direct extraction of parity-violating two-nucleon
interactions from three-nucleon experiments. 相似文献
7.
Using Brownian hydrodynamic simulation techniques, we study single polymers in shear. We investigate the effects of hydrodynamic
interactions, excluded volume, chain extensibility, chain length and semiflexibility. The well-known stretching behavior with
increasing shear rate [(g)\dot] \dot{{\gamma}} is only observed for low shear [(g)\dot] \dot{{\gamma}} < [(g)\dot]max \dot{{\gamma}}^{{\max}}_{} , where [(g)\dot]max \dot{{\gamma}}^{{\max}}_{} is the shear rate at maximum polymer extension. For intermediate shear rates [(g)\dot]max \dot{{\gamma}}^{{\max}}_{} < [(g)\dot] \dot{{\gamma}} < [(g)\dot]min \dot{{\gamma}}^{{\min}}_{} the radius of gyration decreases with increasing shear with minimum chain extension at [(g)\dot]min \dot{{\gamma}}^{{\min}}_{} . For even higher shear [(g)\dot]min \dot{{\gamma}}^{{\min}}_{} < [(g)\dot] \dot{{\gamma}} the chain exhibits again shear stretching. This non-monotonic stretching behavior is obtained in the presence of excluded-volume
and hydrodynamic interactions for sufficiently long and inextensible flexible polymers, while it is completely absent for
Gaussian extensible chains. We establish the heuristic scaling laws [(g)\dot]max \dot{{\gamma}}^{{\max}}_{} ∼ N
-1.4 and [(g)\dot]min \dot{{\gamma}}^{{\min}}_{} ∼ N
0.7 as a function of chain length N , which implies that the regime of shear-induced chain compression widens with increasing chain length. These scaling laws
also imply that the chain response at high shear rates is not a universal function of the Weissenberg number Wi = [(g)\dot] \dot{{\gamma}}
t \tau anymore, where t \tau is the equilibrium relaxation time. For semiflexible polymers a similar non-monotonic stretching response is obtained. By
extrapolating the simulation results to lengths corresponding to experimentally studied DNA molecules, we find that the shear
rate [(g)\dot]max \dot{{\gamma}}^{{\max}}_{} to reach the compression regime is experimentally realizable. 相似文献
8.
Siegfried Bethke 《The European Physical Journal C - Particles and Fields》2009,64(4):689-703
Measurements of α
s, the coupling strength of the Strong Interaction between quarks and gluons, are summarised and an updated value of the world
average of as(MZ0)\alpha_{\mathrm{s}}(M_{\mathrm{Z}^{0}}) is derived. Special emphasis is laid on the most recent determinations of α
s. These are obtained from τ-decays, from global fits of electroweak precision data and from measurements of the proton structure function F2, which are based on perturbative QCD calculations up to O(as4)\mathcal{O}(\alpha_{\mathrm{s}}^{4}); from hadronic event shapes and jet production in e+e− annihilation, based on O(as3)\mathcal{O}(\alpha_{\mathrm{s}}^{3}) QCD; from jet production in deep inelastic scattering and from ϒ decays, based on O(as2)\mathcal{O}(\alpha_{\mathrm{s}}^{2}) QCD; and from heavy quarkonia based on unquenched QCD lattice calculations. A pragmatic method is chosen to obtain the world
average and an estimate of its overall uncertainty, resulting in
as(MZ0)=0.1184±0.0007.\alpha_\mathrm{s}(M_{\mathrm{Z}^0})=0.1184\pm 0.0007. 相似文献
9.
N. Kaiser 《The European Physical Journal A - Hadrons and Nuclei》2010,45(1):61-68
We extend a recent calculation of the nuclear energy density functional in the framework of chiral perturbation theory by
computing the isovector surface and spin-orbit terms: ([(?)\vec] rp - [(?)\vec] rn\vec \nabla \rho _p - \vec \nabla \rho _n )2
G
d(r \rho) + ([(?)\vec] rp - [(?)\vec] rn\vec \nabla \rho _p - \vec \nabla \rho _n ·([(J)\vec]p - [(J)\vec]n\vec J_p - \vec J_n )G
so(r \rho) + ([(J)\vec]p - [(J)\vec]n\vec J_p - \vec J_n )2
G
J(r \rho) pertaining to different proton and neutron densities. Our calculation treats systematically the effects from 1p \pi -exchange, iterated 1p \pi -exchange, and irreducible 2p \pi -exchange with intermediate D \Delta -isobar excitations, including Pauli-blocking corrections up to three-loop order. Using an improved density-matrix expansion,
we obtain results for the strength functions G
d(r \rho) , G
so(r \rho) and G
J(r \rho) which are considerably larger than those of phenomenological Skyrme forces. These (parameter-free) predictions for the strength
of the isovector surface and spin-orbit terms as provided by the long-range pion-exchange dynamics in the nuclear medium should
be examined in nuclear structure calculations at large neutron excess. 相似文献
10.
In this paper we consider a simplified two-dimensional scalar model for the formation of mesoscopic domain patterns in martensitic
shape-memory alloys at the interface between a region occupied by the parent (austenite) phase and a region occupied by the
product (martensite) phase, which can occur in two variants (twins). The model, first proposed by Kohn and Müller (Philos
Mag A 66(5):697–715, 1992), is defined by the following functional:
|