Crystalline ground states for classical particles

Pair interactions whose Fourier transform is non-negative and vanishes above a wave number K(0) are shown to give rise to periodic and aperiodic infinite volume ground state configurations (GSCs) in any dimension d. A typical three-dimensional example is an interaction of asymptotic form cosK(0)r/r(4). The result is obtained for densities rho > or = rho(d), where rho(1) = K(0)/2(pi), rho(2) = (sq.rt(3)/8)(K(0)/pi)(2), and rho(3) = (1/8sq.rt(2)) x (K(0)/pi)(3). At rho(d) there is a unique periodic GSC which is the uniform chain, the triangular lattice, and the bcc lattice for d = 1,2,3, respectively. For rho > rho(d), the GSC is nonunique and the degeneracy is continuous: Any periodic configuration of density rho with all reciprocal lattice vectors not smaller than K(0), and any union of such configurations, is a GSC. The fcc lattice is a GSC only for rho > or = (1/6 sq.rt(3)) x (K(0)/pi)(3).     

Stability of spikes in the shadow Gierer-Meinhardt system with Robin boundary conditions

We consider the shadow system of the Gierer-Meinhardt system in a smooth bounded domain Omega subset R(N),A(t)=epsilon(2)DeltaA-A+A(p)/xi(q),x is element of Omega, t>0, tau/Omega/xi(t)=-/Omega/xi+1/xi(s) integral(Omega)A(r)dx, t>0 with the Robin boundary condition epsilon partial differentialA/partial differentialnu+a(A)A=0, x is element of partial differentialOmega, where a(A)>0, the reaction rates (p,q,r,s) satisfy 10, r>0, s>or=0, 1or=0. We rigorously prove the following results on the stability of one-spike solutions: (i) If r=2 and 11 and tau sufficiently small the interior spike is stable. (ii) For N=1 if r=2 and 11 such that for a is element of (a(0),1) and mu=2q/(s+1)(p-1) is element of (1,mu(0)) the near-boundary spike solution is unstable. This instability is not present for the Neumann boundary condition but only arises for the Robin boundary condition. Furthermore, we show that the corresponding eigenvalue is of order O(1) as epsilon-->0.     

Bound states of the Klein－Gordon and Dirac equations for potential V0tanh2(r/d)

The exact bound state wavefunctions and energy equations of Klein－Gordon and Dirac equations are given with equal scalar and vector potential s(r)=v(r)=V(r)/2=V_0tanh^2(r/d). The relation between the energy equation and that of relativistic harmonic is discussed.     

Extracting weak phase information from B-->V1V2 decays

We describe a new method for extracting weak, CP-violating &Dmacr;phase information, with no hadronic uncertainties, from an angular analysis of B-->V1V2 decays, where V1 and V2 are vector mesons. The quantity sin (2)(2beta+gamma) can be cleanly obtained from the study of decays such as B(0)(d)(t)-->D*+/-rho(-/+), D(*+/-)a(-/+)(1), D(;) *0K(;) (*0), etc. Similarly, one can use B(0)(s)(t)-->D(*+/-)(s)K*-/+ to extract sin (2)gamma. There are no penguin contributions to these decays. It is possible that sin (2)(2beta+gamma) will be the second function of CP phases, after sin2beta, to be measured at B factories.     

Dynamics of fluctuations below a stationary bifurcation to electroconvection in the planar nematic liquid crystal N4

We fitted C(k,tau,epsilon) proportional to exp([-sigma(k,epsilon)tau] to time-correlation functions C(k,tau,epsilon) of structure factors S(k,t,epsilon) of shadowgraph images of fluctuations below a supercritical bifurcation at V(0)=V(c) to electroconvection of a planar nematic liquid crystal in the presence of a voltage V=sqrt[2]V(0)cos((2pift) [k=(p,q) is the wave vector and epsilon identical with V(2)(0)/V(2)(c)-1]. There were stationary oblique (normal) rolls at small (large) f. Fits of a modified Swift-Hohenberg form to sigma(k,epsilon) gave f-dependent critical behavior for the minimum decay rates sigma(0)(epsilon) and the correlation lengths xi(p,q)(epsilon).     

Testing the stability of fundamental constants with the 199Hg+ single-ion optical clock

Over a two-year duration, we have compared the frequency of the 199Hg+ 5d(10)6s (2)S(1/2)(F=0)<-->5d(9)6s(2) (2)D(5/2)(F=2) electric-quadrupole transition at 282 nm with the frequency of the ground-state hyperfine splitting in neutral 133Cs. These measurements show that any fractional time variation of the ratio nu(Cs)/nu(Hg) between the two frequencies is smaller than +/-7 x 10(-15) yr(-1) (1sigma uncertainty). According to recent atomic structure calculations, this sets an upper limit to a possible fractional time variation of g(Cs)(m(e)/m(p))alpha(6.0) at the same level.     

Gravitational Cherenkov losses in theories based on modified Newtonian dynamics

Survival of high-energy cosmic rays (HECRs) against gravitational Cherenkov losses is shown not to cast strong constraints on modified Newtonian dynamics (MOND) theories that are compatible with general relativity (GR): theories that coincide with GR for accelerations ?a(0) (a(0) is the MOND constant). The energy-loss rate, E, is many orders smaller than those derived in the literature for theories with no extra scale. Modification to GR, which underlies E, enters only beyond the MOND radius of the particle: r(M)=(Gp/ca(0))(1/2). The spectral cutoff, entering E quadratically, is thus r(M)(-1), not k(dB)=p/?. Thus, E is smaller than published rates, which use k(dB), by a factor ～(r(M)k(dB))(2)≈10(39)(cp/3×10(11) Gev)(3). Losses are important only beyond D(loss)≈q?(M), where q is a dimensionless factor, and ?(M)=c(2)/a(0) is the MOND length, which is ≈2π times the Hubble distance.     

Bright electrophosphorescent devices based on sterically hindered spacer-containing Cu(I) complex

A Cu(I) complex, [Cu(Dppp)(DPEphos)]BF₄ (Dppp=2,3-diphenyl-pyrazino[2,3-f][1,10]phenanthroline, DPEphos=Bis[2-(diphenylphosphino)phenyl]ether), is synthesized and used as the dopant in bright electrophosphorescent devices with the general structure ITO/m-MTDATA (30 nm)/NPB (20 nm)/CBP: ×wt% [Cu(Dppp)(DPEphos)]BF₄ (30 nm)/Bphen (20 nm)/Alq₃ (20 nm)/LiF (0.8 nm)/ Al (200 nm). These devices exhibit a maximum brightness of 4483 cd/m² and a peak efficiency of 3.4 cd/A. Compared with previously reported similar devices based on Cu(I) complexes, the brightness of the devices presented in this article is the best. Meanwhile, 2% [Cu(Dppp)(DPEphos)]BF₄-based devices exhibit white light-emitting properties with CIE coordinates of (0.32. 0.35) at 10 V.     

Limiting probability distribution for a random walk with topological constraints

The joint limiting probability distribution is studied for the two-dimensional random walk with topological constraints, omega(2ns), on Z(2) lattice, where 2n is its total length and (0相似文献   

Towards empirical EPR parameters for characterizing V(IV) complexes

Improved empirical techniques are described for determining the solution structures (coordination numbers and ligand donor groups) of oxoV(IV) complexes from isotropic EPR parameters. These methods will enable more detailed structural information to be obtained than was available previously from such empirical correlations. Assignments of the structures of the V(IV)/oxalate complexes were found to differ from those proposed in the literature and have been important in developing the empirical parameters reported here. In acidic solutions (pH≤1), V(V) oxalate complexes decay slowly to yield three V(IV) complexes, [V(O)(ox)₂]^2?, [V(O)(ox)(OH₂)₃]⁰ andcis-[V(O)(ox)₂(OH₂)]^2? (ox=oxalato(2-)), which have been characterized by EPR spectroscopy. These same three complexes are obtained from the direct reaction of V(IV) with oxalic acid. The structures of these complexes were assigned on the basis of the pH and [oxH₂] dependences of the EPR signals and differ significantly to those reported in the literature. The equilibria among the five- and six-coordinate complexes, and the protonation/deprotonation equilibrium of the six-coordinate species are consistent with the well-studied isoelectronic Cr(V) system.     

Kohn-Sham exchange potential for a metallic surface

The behavior of the surface barrier that forms at the metal-vacuum interface is important for several fields of surface science. Within the density functional theory framework, this surface barrier has two nontrivial components: exchange and correlation. Exact results are provided for the exchange component, for a jellium metal-vacuum interface, in a slab geometry. The Kohn-Sham exact-exchange potential V(x)(z) has been generated by using the optimized effective potential method, through an accurate numerical solution, imposing the correct boundary condition. It has been proved analytically, and confirmed numerically, that V(x)(z--> infinity) --> -e(2)/z; this conclusion is not affected by the inclusion of correlation effects. Also, the exact-exchange potential develops a shoulderlike structure close to the interface, on the vacuum side. The issue of the classical image potential is discussed.     

Dynamical symmetry breaking as the origin of the zero-dc-resistance state in an ac-driven system

Under a strong ac drive the zero-frequency linear response dissipative resistivity rho(d)(j=0) of a homogeneous state is allowed to become negative. We show that such a state is absolutely unstable. The only time-independent state of a system with a rho(d)(j=0)<0 is characterized by a current which almost everywhere has a magnitude j(0) fixed by the condition that the nonlinear dissipative resistivity rho(d)(j(2)(0))=0. As a result, the dissipative component of the dc-electric field vanishes. The total current may be varied by rearranging the current pattern appropriately with the dissipative component of the dc-electric field remaining zero. This result, together with the calculation of Durst et al., indicating the existence of regimes of applied ac microwave field and dc magnetic field where rho(d)(j=0)<0, explains the zero-resistance state observed by Mani et al. and Zudov et al.     

Evidence of two dimensionality in quasi-one-dimensional cobalt oxides

The quasi-one-dimensional (Q1D) cobalt oxides A(N + 2)Co(n + 1)O(3n + 3) (A = Ca, Sr, and Ba, n = 1 - infinity) were investigated by muon-spin spectroscopy under applied pressures of up to 1.1 GPa. The relationship between the onset Néel temperature T(on)(N) and the interchain distance (d(ic)), which increases monotonically with n, is well fitted by the formula T(N)/T(N,0) = (1 - d(ic)/d(ic,o)(beta), here for T(on)(N) approximately 100 K for Ca(3)Co(2)O(6) (n = 1) and approximately 15 for BaCoCoO(3) (n = infinity at ambient P. The T(on)(N) - d(ic) curve also predicts a large dependence of Y(N) for the compounds with n > or = 5, i.e., in the vicinity of , while the compounds show only a very small effect. Indeed, our high-pressure mu(+) results show that of BaCoO(3) is enhanced by with a slope of 2.2 K(Gpa), whereas no detectable changes by P for both Ca(3)Co(2)O(6) and Sr(4)Co(3)O(9) (n = 2). This clearly confirms the role of the 2D-antiferromagnetic interaction on T(on)(N) in the Q1D cobalt oxides.     

Stochastic particle acceleration in multiple magnetic islands during reconnection

A nonthermal particle acceleration mechanism involving the interaction of a charged particle with multiple magnetic islands is proposed. The original Fermi acceleration model, which assumes randomly distributed magnetic clouds moving at random velocity V(c) in the interstellar medium, is known to be of second-order acceleration of O(V(c)/c)(2) owing to the combination of head-on and head-tail collisions. In this Letter, we reconsider the original Fermi model by introducing multiple magnetic islands during reconnection instead of magnetic clouds. We discuss that the energetic particles have a tendency to be distributed outside the magnetic islands, and they mainly interact with reconnection outflow jets. As a result, the acceleration efficiency becomes first order of O(V(A)/c), where V(A) and c are the Alfvén velocity and the speed of light, respectively.     

Measurement of Upsilon production for p + p and p + d interactions at 800 GeV/c

We report a high statistics measurement of Upsilon production with an 800 GeV/c proton beam on hydrogen and deuterium targets. The dominance of the gluon-gluon fusion process for Upsilon production at this energy implies that the cross section ratio, sigma(p+d-->Upsilon)/2sigma(p+p-->Upsilon), is sensitive to the gluon content in the neutron relative to that in the proton. Over the kinematic region 0相似文献   

Quasi-Gaussian statistics of hydrodynamic turbulence in 4 / 3 +epsilon dimensions

The statistics of two-dimensional turbulence exhibit a riddle: the scaling exponents in the regime of inverse energy cascade agree with the K41 theory of turbulence far from equilibrium, but the probability distribution functions are close to Gaussian-like in equilibrium. The skewness S identical with S3(R)/S(3/2)(2)(R) was measured as S (exp) approximately 0.03. This contradiction is lifted by understanding that two-dimensional turbulence is not far from a situation with equipartition of enstrophy, which exists as true thermodynamic equilibrium with K41 exponents in space dimension of d= 4 / 3. We evaluate the skewness S( d) for 4 / 3 < or =d< or =2, showing that S(d)=0 at d= 4 / 3, and that it remains as small as S (exp) in two dimensions.     

Mass spectrum ofP-wave mesons

Mass splittings of mesons withL≧1 are discussed on the basis of a general spin-dependent potential consisting of a vector (V(r)) and a scalar (S(r)) part. For arbitraryV(r) andS(r), the four masses, for the three³ L _J and the one¹ L _J=L levels, are given in terms of only three unknown expectation values 〈(1/r)(dV/dr)〉, 〈d ² V/dr ²〉 and 〈(1/r)(dS/dr)〉. These expectations values are extracted for theP-wave \(u\bar s\) (or \(d\bar s\) ) mesons which are discussed in detail. It is argued that the 0⁺⁺ mass should be around 1150 to 1230 MeV, rather than at 1350 MeV. On comparing the expectation values for the \(u\bar s\) , \(c\bar c\) , \(b\bar b\) and the \(I = 1u\bar u\) systems, we find that they all scale asa+bμ, wherea andb are constants and μ is the reduced mass. Remarkably enough, we also find that theP-wave meson masses for these systems satisfy mass formulae of the formA+B(m₁+m₂), with constantA andB. It is shown that similar linear mass formulae also work forS-wave mesons. These facts seem to reveal a rather general property of \(q\bar q\) states.     

The role of N dopant in inducing ferromagnetism in (ZnO)n clusters (n = 1-16)

The effect of nitrogen doping on the magnetic properties of (ZnO)(n) clusters (n = 1-16) has been investigated using spin polarized density functional theory. The total energy calculations suggest that N is more stable at the O site than at the Zn site in (ZnO)(n) clusters and induces a magnetic moment of 1 μ(B)/N atom. The N-Zn-N configuration is more stable than isolated N for 3D structures. The N dopants do not show any tendency for clustering. The binding energy is found to decrease with the increase in the number of N dopants. The magnetic moment increases gradually with the increase in the number of atoms with 1 μ(B)/N atom for n ≤ 4 and less than 1 μ(B)/N for n > 4. The local magnetic moment is mainly localized at the N site with a small magnetic moment induced at the O site. The presence of a Zn vacancy (V(Zn)) induced an additional magnetic moment of 2 μ(B) on the nearest O atoms. The N dopant prefers to form a N-V(Zn) pair. The combination of N and V(Zn) in 3D structures leads to a total magnetic moment of 3 μB. The Mulliken charge transfers from Zn to N and O in all N doped (ZnO)(n) clusters. The calculated results are consistent with existing experimental and theoretical results.     

Impact of a global quadratic potential on galactic rotation curves

We present a conformal gravity fit to the 20 largest of a sample of 110 spiral galaxies. We identify the presence of a universal quadratic potential V(κ)(r)=-κc2r2/2 with κ=9.54×10??? cm?2 induced by cosmic inhomogeneities. When V(κ)(r) is taken in conjunction with both a universal linear potential V(γ?)(r)=γ?c2r/2 with γ?=3.06×10?3? cm?1 generated by the homogeneous cosmic background and the contribution generated by the local luminous matter in galaxies, the theory then accounts for the rotation curve systematics observed in the entire 110 galaxies, without the need for any dark matter whatsoever. Our study suggests that using dark matter may be nothing more than an attempt to describe global effects in purely local galactic terms. With V(κ)(r) being negative, galaxies can only support bound orbits up to distances of order γ?/κ=100kpc, with global physics imposing a limit on the size of galaxies.     

电力系统非线性振荡过程的图析

【摘　要】在本论文里,作者对一个由下列形式的三阶非线性微分方程A(d³δ)/(dt³)+(d²δ)/(dt²)-Acotδ(dδ)/(dt)(d²δ)/(dt²)+((P_iA)/M)cotδ+Csin²δ)(dδ)/(dt)+ +Bsinδ-(P_i)/M=0。所表征的电力机械振荡问题,进行了透彻的拓扑形象分析,并提出了一简易图解法来计算这振荡系统的性能。文中还举出一实例来说明这种分析方法。