共查询到20条相似文献,搜索用时 31 毫秒
1.
A. M. Balagurov V. V. Sikolenko I. S. Lyubutin G. Andre F. Bouree H. M. Duh 《JETP Letters》1997,66(9):647-652
Neutron diffraction investigations have shown that a 2% substitution Fe atoms for Pd radically alters the magnetic structure
of UPd2Ge2. If the magnetic structure in the undoped compound at T>50 K consists of a longitudinal spin density wave (LSDW) with “square” modulation, then in polycrystalline U(Pd0.98Fe0.02)2Ge2 a “simple” antiferromagnetic (AF) phase is observed below 65 K and a sinusoidally modulated LSDW-AF phase is observed between
65 K and the Neel temperature T
N
=135 K. In the interval 65> T>135 K the magnetic cell is incommensurate with the crystal cell, with the exception of the point T=93 K, where the wave vector of the magnetic structure passes through a “commensurate” value equal to 0.75. Below T
N
the magnetic moments of the uranium atoms are always parallel to the tetragonal axis c of the unit cell.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 9, 615–619 (10 November 1997) 相似文献
2.
A. M. M. Pruisken 《International Journal of Theoretical Physics》2009,48(6):1736-1765
It is shown that the “massless chiral edge excitations” are an integral and universal aspect of the low energy dynamics of
the ϑ vacuum that has historically gone unnoticed. Within the SU(M+N)/S(U(M)×U(N)) non-linear sigma model we introduce an effective theory of “edge excitations” that fundamentally explains the quantum Hall
effect. In sharp contrast to the common beliefs in the field our results indicate that this macroscopic quantization phenomenon
is, in fact, a super universal strong coupling feature of the ϑ angle with the replica limit M=N=0 only playing a role of secondary importance. To demonstrate super universality we revisit the large N expansion of the CP
N−1 model. We obtain, for the first time, explicit scaling results for the quantum Hall effect including quantum criticality
of the quantum Hall plateau transition. Consequently a scaling diagram is obtained describing the cross-over between the weak
coupling “instanton phase” and the strong coupling “quantum Hall phase” of the large N theory. Our results are in accordance with the “instanton picture” of the ϑ angle but fundamentally invalidate all the ideas, expectations and conjectures that are based on the historical “large N picture.” 相似文献
3.
The position and momentum space information entropies of weakly interacting trapped atomic Bose–Einstein condensates and spin-polarized
trapped atomic Fermi gases at absolute zero temperature are evaluated. We find that sum of the position and momentum space
information entropies of these quantum systems containing N atoms confined in a D( ≤ 3)-dimensional harmonic trap has a universal form as St(D) = N(a D - b lnN) S_\mathrm{t}^{(D)} = N(a D - b \ln N) , where a ≃ 2.332 and b = 2 for interacting bosonic systems and a ≃ 1.982 and b = 1 for ideal fermionic systems. These results obey the entropic uncertainty relation given by Beckner, Bialynicki-Birula
and Myceilski. 相似文献
4.
Michael K.-H. Kiessling 《Journal of statistical physics》2009,134(1):19-25
In 1969 Ruelle published his construction of the thermodynamic limit, in the sense of Fisher, for the quasi-microcanonical
entropy density of classical Hamiltonian N-body systems with stable and tempered pair interactions. Here, “quasi-microcanonical” refers to the fact that he discussed
the entropy defined with a regularized microcanonical measure as ln (N!−1
∫
χ
{ℰ−▵ℰ<H<ℰ}d6N
X) rather than defined with the proper microcanonical measure as ln (N!−1
∫
δ(ℰ−H) d6N
X). Replacing δ(ℰ−H) by χ
{ℰ−▵ℰ<H<ℰ} seems to have become the standard procedure for rigorous treatments of the microcanonical ensemble hence. In this note we
make a very elementary technical observation to the effect that Ruelle’s proof (still based on regularization) does establish
the thermodynamic limit also for the entropy density defined with the proper microcanonical measure. We also show that with
only minor changes in the proof the regularization of δ(ℰ−H) is actually not needed at all. 相似文献
5.
Joseph Ben Geloun Vincent Rivasseau 《The European Physical Journal C - Particles and Fields》2008,58(1):115-122
The β-functions of O(N) and U(N) invariant Grosse–Wulkenhaar models are computed at one loop using the matrix basis. In particular, for “parallel interactions”,
the model is proved to be asymptotically free in the UV limit for N>1, and it has a triviality problem or Landau ghost for N<1. The vanishing β-function is recovered solely at N=1. We discuss various possible consequences of these results.
Work supported by the ANR Program “GENOPHY” and by the Daniel Iagolnitzer Foundation, France. 相似文献
6.
The values of the insulator gap Δ in one-dimensional systems of interacting bosons described by the Hubbard Hamiltonian are
calculated at low temperatures by the quantum world-line Monte Carlo algorithm. The dependence of Δ on the size of the system,
the temperature, and the parameters of the model is investigated. It is shown that a chain with N
a=50 sites is already sufficient to estimate the thermodynamic value of the critical quantity (t/U)c for which a transition from the insulator into the superfluid state occurs in a commensurate system. To within the computational
error, this value, (t/U)c=0.300±0.005, agrees with the value (t/U)c=0.304±0.002 obtained previously by the combined “exact diagonalization + renormalization-group analysis” method. The characteristic
Kosterlitz-Thouless behavior of the insulator gap is demonstrated near the critical region: Δ∼exp[−b(1−t/t
c)−1/2].
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 2, 92–96 (25 July 1996) 相似文献
7.
P. Leifer 《Foundations of Physics》1997,27(2):261-285
The ordinary quantum theory points out that general relativity (GR) is negligible for spatial distances up to the Planck scale
lP=(hG/c3)1/2∼10−33cm. Consistency in the foundations of the quantum theory requires a “soft” spacetime structure of the GR at essentially longer
length. However, for some reasons this appears to be not enough. A new framework (“superrelativity”) for the desirable generalization
of the foundation of quantum theory is proposed. A generalized nonlinear Klein-Gordon equation has been derived in order to
shape a stable wave packet. 相似文献
8.
K. G. Shaynurova S. A. Bakhramov A. M. Kokhkharov U. K. Makhmanov E. A. Zakhidov 《Journal of Applied Spectroscopy》2012,78(6):802-810
Features of light pulse propagation and nonlinear optical transformation of the spectrum generated by titanium-sapphire laser
pulses (τ0.5 = 27 fs, λ0 = 790 nm) have been studied experimentally in a 50-cm cylindrical hollow waveguide (microcapillary with 280-μm diameter core)
filled with gaseous molecular nitrogen and helium. Stable guided propagation of light pulses with an intensity of ~1.5⋅1014 W/cm2 in the fundamental EH11 mode of the gas-filled capillary has been demonstrated. Exact focusing of the laser light made it possible to obtain rather
high relative (≥95%) and absolute (~60%) energy transmission efficiencies for the pulses at gas pressures equal to or lower
than 760 Torr. A method to determine the nonlinear phase shift of the pulses has been proposed. Values of the nonlinear refractive
index n2 ≈ 4.5⋅10–23 cm2/(W⋅Torr) (N2) and n2 ≈ 2.8⋅10–23 cm2/(W⋅Torr) (He) have been found. A short-wavelength shift in addition to the Kerr nonlinearity has been shown to be contributed
by the generated electron plasma at high pulse intensities (≥1014 W/cm2). 相似文献
9.
We consider a system of N non-relativistic spinless quantum particles (“electrons”) interacting with a quantized scalar Bose field (whose excitations
we call “photons”). We examine the case when the velocity v of the electrons is small with respect to the one of the photons, denoted by c (v/c = ε ≪ 1). We show that dressed particle states exist (particles surrounded by “virtual photons”), which, up to terms of order
(v/c)3, follow Hamiltonian dynamics. The effective N-particle Hamiltonian contains the kinetic energies of the particles and Coulomb-like pair potentials at order (v/c)0 and the velocity dependent Darwin interaction and a mass renormalization at order (v/c)2. Beyond that order the effective dynamics are expected to be dissipative.
The main mathematical tool we use is adiabatic perturbation theory. However, in the present case there is no eigenvalue which
is separated by a gap from the rest of the spectrum, but its role is taken by the bottom of the absolutely continuous spectrum,
which is not an eigenvalue. Nevertheless we construct approximate dressed electron subspaces, which are adiabatically invariant
for the dynamics up to order . We also give an explicit expression for the non-adiabatic transitions corresponding to emission of free photons. For the
radiated energy we obtain the quantum analogue of the Larmor formula of classical electrodynamics. 相似文献
10.
Microporous (TiO2)
x
–(SiO2)100 − x
(0 < x < 40) xerogels have been produced by sol–gel methods either by partial pre-hydrolysis or reflux of tetraethoxysilane and
titanium isopropoxide. These have been characterised by 29Si nuclear magnetic resonance, X-ray diffraction, EXAFS at the Ti–K edge, X-ray photoelectron spectroscopy, temperature-programmed
reduction, FT infrared, N2 adsorption at 78 K (BET), transmission electron microscopy and dynamic light scattering (DLS). These were dip coated onto
fused silica and characterised by atomic force microscopy and UV–visible absorption. Their photoactivity in removal of alkylphenol
ethoxylate TX100 from water was less than for less porous titania. The advantages of including thermally removable PEG or
PPG templates in terms of increasing surface, meso-porosity and photon absorbance at visible wavelengths to give nanoengineered
photocatalytic films are described. 相似文献
11.
Chuandong Jia Biao Wu Jianjun Liang Xiaojuan Huang Xiao-Juan Yang 《Journal of fluorescence》2010,20(1):291-297
N-Phenyl-N’-(3-quinolinyl)urea (1) has been developed as a highly selective colorimetric and ratiometric fluorescent chemosensor for fluoride ion based on a
proton transfer mechanism. Evidences for the mechanism were provided by UV-vis and fluorescence titration and especially 1H and 19F NMR experiments. The sensor gave the largest ratiometric fluorescent response reported so far (Rmax/Rmin = 2620) to fluoride. Taking H+ as the “recovering reagent”, the sensor can be reversibly “used” and “recovered” for several cycles with only a slight decay
of the response ability. 相似文献
12.
V. D. Lyakhovsky 《Czechoslovak Journal of Physics》2002,52(11):1269-1275
We study the twist deformations of algebras of motiong
H ⊂ sl(N) with the Cartan subalgebraH(gH) equal toH(sl(N)). The proposed deformations are maximal in the sense that their carrier algebrasg
c coincide withg
H. The algebraic properties are demonstrated forg
H ⊂ sl(5).
Presented at the 11th Colloquium “Quantum Groups and Integrable Systems”, Prague, 20–22 June 2002.
This work has been partially supported by the Russian Foundation for Fundamental Research under the grant N 00-01-00500. 相似文献
13.
The horizon (the surface) of a black hole is a null surface, defined by those hypothetical “outgoing” light rays that just
hover under the influence of the strong gravity at the surface. Because the light rays are orthogonal to the spatial two-dimensional
surface at one instant of time, the surface area of the black hole is the same for all observers (i.e. the same for all coordinate
definitions of “instant of time”). This value is 4π(2Gm/c
2)2 for nonspinning black holes, with G = Newton’s constant, c = speed of light, and m = mass of the black hole. The three-dimensional spatial volume inside a black hole, in contrast, depends explicitly on the
definition of time, and can even be time dependent, or zero. We give examples of the volume found inside a standard, nonspinning
spherical black hole, for several different standard time-coordinate definitions. Elucidating these results for the volume
provides a new pedagogical resource of facts already known in principle to the relativity community, but rarely worked out. 相似文献
14.
M. V. Tokarev I. Zborovský A. Kechechyan A. Alakhverdyants 《Physics of Particles and Nuclei Letters》2011,8(6):533-541
The general concepts in the critical phenomena related with the notions of “scaling” and “universality” are considered. Behavior
of various systems near a phase transition is displayed. Search for clear signatures of the phase transition of the nuclear
matter and location of the critical point in heavy-ion collisions (HIC) is discussed. The experimental data on inclusive spectra measured in HIC at RHIC and SPS over a wide range of energies s
N N
1/2 = 9–200 GeV are analyzed in the framework of z-scaling. A microscopic scenario of the constituent interactions is presented. Dependence of the energy loss on the momentum
of the produced hadron, energy and centrality of the collision is studied. Self-similarity of the constituent interactions
described in terms of momentum fractions is used to characterize the nuclear medium by “specific heat” and colliding nuclei
by fractal dimensions. Preferable kinematical regions to search for signatures of the phase transition of the nuclear matter
produced in HIC are discussed. Discontinuity of the “specific heat” is assumed to be a signature of the phase transition and the critical
point. 相似文献
15.
D. I. Diakonov 《JETP Letters》2009,90(6):407-411
We suggest to classify baryon resonances as single-quark states in a mean field, and/or as its collective excitations. Identifying
the Roper resonance N(1440, 1/2+), the nucleon resonance N(1535, 1/2−), and the singlet hyperon Λ(1405, 1/2−) as single-quark excitations, we find that there must be an exotic S = +1 baryon resonance Θ+ (the “pentaquark”) with a mass about 1440 + 1535 − 1405 = 1570 MeV and spin-parity 1/2+. We argue that Θ+ is an analog of the Gamov-Teller excitation long known in nuclear physics. 相似文献
16.
The saccharide binding and conformational characterization of a hemagglutinin, a low molecular weight protein from the seeds
of Moringa oleifera was studied using steady state and time resolved fluorescence. The lectin binds sugars LacNAc (K
a = 1380 M−1) and fructose (K
a = 975 M−1), as determined by the fluorescence spectroscopy. It has a single tryptophan per monomer which is exposed on the surface
and is in a strong electropositive environment as revealed by quenching with iodide. Quenching of the fluorescence by acrylamide
involved both static (K
s = 0.216 M−1) and collisional (K
sv = 8.19 M−1) components. The native protein showed two different lifetimes, τ
1 (1.6 ns) and τ
2 (4.36 ns) which decrease and get converted into a single one, (2.21 ns) after quenching with 0.15 M acrylamide. The bimolecular
quenching constant, k
q
was 7.55 × 1011 M−1 s−1. ANS binding studies showed that the native protein has exposed hydrophobic patches which get further exposed at extreme
acidic or alkaline pH. However, they get buried in the interior of the protein in presence of 1 M GdnHCl or urea. 相似文献
17.
Martin Gaume 《Mathematical Physics, Analysis and Geometry》2010,13(3):205-217
In this paper, we consider a class of two-particle tight-binding Hamiltonians, describing pairs of interacting quantum particles
on the lattice ℤ
d
, d ≥ 1, subject to a common external potential V(x) which we assume quasi-periodic and depending on auxiliary parameters. Such parametric families of ergodic deterministic
potentials (“grands ensembles”) have been introduced earlier in Chulaevsky (2007), in the framework of single-particle lattice systems, where it was proved that a non-uniform analog of the Wegner bound
holds true for a class of quasi-periodic grands ensembles. Using the approach proposed in Chulaevsky and Suhov (Commun Math
Phys 283(2):479–489, 2008), we establish volume-dependent Wegner-type bounds for a class of quasi-periodic two-particle lattice systems with a non-random
short-range interaction. 相似文献
18.
S. V. Meriakri 《Technical Physics》1999,44(12):1472-1476
The propagation of a microwave pulse in a ferrite thin film-substrate structure in a regime of rereflections (“ringing”) of
the acoustic component of the substrate is studied theoretically. It is shown that as a result of the interaction of microwave
pulses with the boundaries of the substrate, propagation of a microwave excitation in this system can be regarded as a propagation
of a wave packet in a periodic nonuniform medium. The basic characteristics of a propagating wave packet are obtained.
Zh. Tekh. Fiz. 69, 82–86 (December 1999) 相似文献
19.
The energy excitation functions of directed flow (v1) and elliptic flow (v2) from Ebeam=90 A MeV to Ecm=200 A GeV are explored within the UrQMD framework and discussed in the context of the available data. The radial and the elliptic
flow of the particles produced in a relativistic heavy-ion collision are intimately connected to the pressure and its gradients
in the early stage of the reaction. Therefore, these observables should also be sensitive to changes in the equation of state.
To prove this connection, the temporal evolution of the pressure, pressure gradients and elliptic flow are shown. For the
flow excitation functions it is found that, in the energy regime below Ebeam≤10 A GeV, the inclusion of nuclear potentials is necessary to describe the data. Above 40 A GeV beam energy, the UrQMD model starts to underestimate the elliptic flow. Around the same energy the slope of the rapidity
spectra of the proton directed flow develops negative values. This effect is known as the third flow component (“antiflow”)
and cannot be reproduced by the transport model. The difference between the data and the UrQMD model can possibly be explained
by assuming a phase transition from hadron gas to quark–gluon plasma around Elab=40 A GeV. This would be consistent with the model calculations, indicating a transition from hadronic matter to “string matter”
in this energy range. Thus, we speculate that the missing pressure might be generated by strong interactions in the early
pre-hadronic/partonic phase of central Au + Au (Pb + Pb) collisions already at lower SPS energies.
PACS 25.75.-q; 25.75.Ld; 25.75.Dw; 25.75.Gz; 24.10.Lx 相似文献
20.
The interaction between a classic uncoupler (2,4-dinitrophenol, DNP) and bovine serum albumin (BSA) was investigated by fluorescence
spectroscopy under the physiological conditions. The fluorescence quenching constants were calculated by the Stern-Volmer
equation, and based upon the temperature dependence of quenching constants, it was proved that DNP caused a static quenching
of the intrinsic fluorescence of BSA. Owing to the static quenching mechanism, different associative binding constants at
various temperatures were determined and thus the thermodynamic parameters, namely enthalpy (ΔH = −21.12 kJ mol−1) and entropy changes (ΔS = 23.51 J mol−1 K−1) could be calculated based on the binding constants. Moreover, the enthalpy and entropy changes are consistent with the “Enthalpy-Entropy
Compensation” equation obtained from our previous work. The negative enthalpy and positive entropy indicated that the electrostatic
interactions played a major role in DNP-BSA binding process. Site marker competitive displacement experiments were carried
out by using fluorescence and isothermal titration calorimetry (ITC) methods. These results showed that DNP bound with high
affinity to Sudlow’s site I (subdomain IIA) of BSA. The distance (r = 3.78 nm) between donor (BSA) and acceptor (DNP) was obtained according to the mechanism of fluorescence resonance energy
transfer (FRET). Furthermore, the results of synchronous fluorescence and circular dichroism (CD) spectroscopic studies indicated
that the microenvironment and the secondary conformation of BSA were altered. The above results were supported by theoretical
molecular modeling methods. 相似文献