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1.
Pierre Gosselin Alain Bérard Hervé Mohrbach Subir Ghosh 《The European Physical Journal C - Particles and Fields》2009,59(4):883-889
In the present paper we have directly computed the Berry curvature terms relevant for graphene in the presence of an inhomogeneous lattice distortion. We have employed the generalized Foldy–Wouthuysen framework, developed by some of us. We show that a
non-constant lattice distortion leads to a valley–orbit coupling which is responsible for a valley–Hall effect. This is similar
to the valley–Hall effect induced by an electric field proposed in the literature and is the analogue of the spin–Hall effect
in semiconductors. Our general expressions for Berry curvature, for the special case of homogeneous distortion, reduce to
the previously obtained results. We also discuss the Berry phase in the quantization of cyclotron motion. 相似文献
2.
Keith Andrew Brett Bolen Chad A. Middleton 《General Relativity and Gravitation》2007,39(12):2061-2071
We examine the effect on cosmological evolution of adding a Gauss–Bonnet term to the standard Einstein–Hilbert action for
a (1 + 3) + d dimensional Friedman–Robertson–Walker (FRW) metric. By assuming that the additional dimensions compactify as a power law
as the usual 3 spatial dimensions expand, we solve the resulting dynamical equations and find that the solution may be of
either de Sitter or Kasner form depending upon whether the Gauss–Bonnet term or the Einstein term dominates. 相似文献
3.
Aspects of stochastic resonance in reaction–diffusion
systems: The nonequilibrium-potential approach
We analyze several aspects of the phenomenon of stochastic
resonance in reaction–diffusion systems, exploiting the
nonequilibrium potential's framework. The generalization of this
formalism (sketched in the appendix) to extended systems is
first carried out in the context of a simplified scalar model, for
which stationary patterns can be found analytically. We first show
how system-size stochastic resonance arises naturally in this
framework, and then how the phenomenon of array-enhanced
stochastic resonance can be further enhanced by letting the
diffusion coefficient depend on the field. A yet less trivial
generalization is exemplified by a stylized version of the
FitzHugh–Nagumo system, a paradigm of the
activator–inhibitor class. After discussing for this system
the second aspect enumerated above, we derive from it–through an
adiabatic-like elimination of the inhibitor field–an effective
scalar model that includes a nonlocal contribution. Studying
the role played by the range of the nonlocal kernel and its
effect on stochastic resonance, we find an optimal range that
maximizes the system's response. 相似文献
4.
It is shown that two-dimensional (2-D) T
1–T
2 relaxation spectra are sensitive to the changing microstructure in a model food system comprising water-in-water gelatin–agarose
gelled emulsions. This 2-D relaxation–microstructure relationship suggests that T
1–T
2 spectra have the potential of acting as “fingerprint” molecular biomarkers of microstructure in complex water-rich biological
systems and this has important future implications for in vivo magnetic resonance imaging studies of food digestion and of
the changing structure of cancerous tissue. 相似文献
5.
Soma Sanyal 《Pramana》2003,61(5):1033-1037
Baryon number inhomogeneities may be generated during the epoch when the baryon asymmetry of the universe is produced, e.g.
at the electroweak phase transition. These lumps will have a lower temperature than the background. Also the value ofT
c
will be different in these regions. Since a first-order quark-hadron (Q–H) transition is susceptible to small changes in
temperature, we investigate the effect of the presence of such baryonic lumps on the dynamics of the Q–H transition. We find
that the phase transition is delayed in these lumps for significant overdensities. Consequently, we argue that baryon concentration
in these regions grows by the end of the transition. We mention some models which may give rise to such high baryon overdensities
before the Q–H transition. 相似文献
6.
M. M. Asimov R. M. Asimov A. N. Rubinov S. A. Mamilov Yu. S. Plaksii 《Journal of Applied Spectroscopy》2006,73(1):99-102
We have studied the effect of temperature on laser-induced photodissociation of oxyhemoglobin in vivo by recording the change
in the oxygen saturation of arterial blood. We have established that on exposure to low-intensity laser radiation, the local
concentration of free oxygen in tissue significantly increases for a body temperature above 40°C, compared with the normal
temperature. We demonstrate a unique option for selectively and locally increasing the concentration of free molecular oxygen
in tissue, which promotes enhancement of cell metabolism. We consider the possibilities for biomedical use of this phenomenon.
The results obtained show that the temperature dependence of the quantum yield for photodissociation of oxyhemoglobin should
be considered in development of new therapeutic methods for laser medicine.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 90–93, January–February, 2006. 相似文献
7.
V. Bernard N. Kaiser Ulf-G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》1999,4(3):259-275
We evaluate the threshold matrix–element for the reaction pp→ppπ0 in a fully relativistic Feynman diagrammatic approach. We employ a simple effective range approximation to take care of the
S–wave pp final–state interaction. The experimental value for the threshold amplitude A = (2.7 −i0.3) fm4 can be reproduced by contributions from tree level chiral (long–range) pion exchange and short–range effects related to vector
meson exchanges, with ω-exchange giving the largest individual contribution. Pion loop effects appear to be small. We stress
that the commonly used heavy baryon formalism is not applicable in the NN–system above the pion production threshold due to
the large external momentum, |p|≃ (Mm
π)−1/2, with M and m
π the nucleon and the pion mass, respectively. We furthermore investigate the reaction pp→pnπ+ near threshold within the same approach. We extract from the data the triplet threshold amplitude as B = (2.8 −i1.5) fm4. Its real part can be well understood from (relativistic) tree level meson–exchange diagrams. In addition, we investigate
the process pp→ppη near threshold. We use a simple factorization ansatz for the ppη final–state interaction and extract from the data the modulus of the threshold amplitude, |C|= 1.32 fm4. With g
ηN= 5.3, this value can be reproduced by (relativistic) tree level meson–exchange diagrams and η–rescattering, whose strength
is fixed by the ηN scattering length. We also comment on the recent near threshold data for η′–production.
Received: 27 November 1998 相似文献
8.
Sarira Sahu W.-Y. P. Hwang 《The European Physical Journal C - Particles and Fields》2008,58(4):609-615
We have calculated the effective potential experienced by highly relativistic neutrinos in a weakly magnetized electron–positron
plasma, where a momentum-dependent finite-width correction to the propagator of W is considered to account for the threshold effect. Magnetars are believed to be sources of TeV–PeV neutrinos which are produced
due to photomeson and proton–proton interactions in their atmosphere. We have studied the resonant-oscillation process ν
e
↔
ν
μ,τ
of the highly relativistic neutrinos in the atmosphere of SGR 1806-20, which is a magnetar. It is shown that, for high-energy
neutrinos propagating within the magnetar atmosphere, the resonance condition can never be satisfied. On the other hand, if
GeV neutrinos are produced deep inside the magnetar atmosphere, where the temperature is about 50 keV or more, then these
neutrinos can undergo resonant oscillation. 相似文献
9.
Chengfu Mu Pengfei Zhuang 《The European Physical Journal C - Particles and Fields》2008,58(2):271-279
We investigate the effect of the restoration of chiral symmetry on the quark potential in a quark–meson plasma by considering
meson exchanges in the two flavor Nambu–Jona-Lasinio model at finite temperature and density. There are two possible oscillations
in the chiral restoration phase; one is the Friedel oscillation due to the sharp quark Fermi surface at high density, and
the other is the Yukawa oscillation driven by the complex meson poles at high temperature. The quark–meson plasma is strongly
coupled in the temperature region 1≤T/T
c≤3, with T
c being the critical temperature of the chiral phase transition. The maximum coupling in this region is located at the phase
transition point. 相似文献
10.
Zhiyuan Tian Yazhou Zhang Yanli Zhang Aidong Peng Ying Ma Yu Chen Wensheng Yang Yalin Tang Jiannian Yao 《Journal of nanoparticle research》2006,8(1):65-77
Nanostructures with well-defined shape and highly monodisperse size were fabricated from model stilbazolium-like dyes with specific molecular structural and conformational characteristics. With the help of absorption and fluorescence optical spectroscopy, the correlated spectroscopy (COSY) and two- dimensional nuclear Overhauser effect spectroscopy (2D NOESY) techniques, along with X-ray diffraction (XRD) measurement, distinctively different aggregation processes of the model molecules are demonstrated. For model dye molecule with linear donor–π system–acceptor (D–π–A) structure, strong D–A pair, and planar conformation, specific intermolecular interaction was identified and special crystal structures as well as spectral properties were observed. For model dye molecules bearing nonlinear D–π–A–π–D structure, weak D–A pair but actual amphiphilic characteristics, a special aggregation process was confirmed and a focused size distribution of the produced nanostructures was obtained. 相似文献
11.
Alejandro?Guarnizo Leonardo?Casta?eda Juan?M.?Tejeiro 《General Relativity and Gravitation》2010,42(11):2713-2728
The main goal of this paper is to get in a straightforward form the field equations in metric f (R) gravity, using elementary variational principles and adding a boundary term in the action, instead of the usual treatment
in an equivalent scalar–tensor approach. We start with a brief review of the Einstein–Hilbert action, together with the Gibbons–York–Hawking
boundary term, which is mentioned in some literature, but is generally missing. Next we present in detail the field equations
in metric f (R) gravity, including the discussion about boundaries, and we compare with the Gibbons–York–Hawking term in General Relativity.
We notice that this boundary term is necessary in order to have a well defined extremal action principle under metric variation. 相似文献
12.
Nonlinear optical properties of photonic crystal heterostructures with embedded n–i–p–i superlattices are investigated. Self-consistent calculations of the transmission and reflection spectra near the defect mode
are performed using the transfer-matrix method and taking into account the gain saturation. Analysis of features and output
characteristics is carried out for one-dimensional photonic crystal heterostructure amplifiers in the GaAs–GaInP system having
at the central part an active “defect” from doubled GaAs n–i–p–i crystal layers. The gain saturation in the active layers in the vicinity of the defect changes the index contrast of the
photonic structure and makes worse the emission at the defect mode. Spectral bistability effect, which can be exhibited in
photonic crystal heterostructure amplifiers, is predicted and the hysteresis loop and other attending phenomena are described.
The bistability behavior and modulation response efficiency demonstrate the potential possibilities of the photonic crystal
heterostructures with n–i–p–i layers as high-speed optical amplifiers and switches.
相似文献
13.
Using first principles density functional theory calculations, we investigated the X and X–N–X (X = Al and Ga) doped 3C–SiC
nanowires grown along the [111] crystal direction with diameter of 1.00 and 1.33 nm. We found that the ionization energy of
acceptor state is much larger in nanowires than that in the bulk SiC as a result of quantum confinement effect. Simulation
results show that the reduced dimensionality in p-type SiC nanowires strongly reduces the capability of the materials to generate free carriers. It is also found that X–N–X
(X = Al and Ga) complexes are energetically favored to form in the materials and have lower ionization energy than single
doping. It is confirm that codoping is more suitable method for achieving low-resistivity semiconductors either in nano materials
or bulk material. 相似文献
14.
We consider weighted traces of products of intertwining operators for quantum groups U
q
(?), suitably twisted by a “generalized Belavin–Drinfeld triple”. We derive two commuting sets of difference equations – the
(twisted) Macdonald–Ruijsenaars system and the (twisted) quantum Knizhnik–Zamolodchikov–Bernard (qKZB) system. These systems
involve the nonstandard quantum R-matrices defined in a previous joint work with T. Schedler ([ESS]). When the generalized
Belavin–Drinfeld triple comes from an automorphism of the Lie algebra ?, we also derive two additional sets of difference
equations, the dual Macdonald–Ruijsenaars system and the \textit{dual} qKZB equations.
Received: 20 March 2000 / Accepted: 11 December 2000 相似文献
15.
S. Habib Mazharimousavi M. Halilsoy Z. Amirabi 《General Relativity and Gravitation》2010,42(2):261-280
We find large classes of non-asymptotically flat Einstein–Yang–Mills–Dilaton and Einstein–Yang–Mills–Born–Infeld–Dilaton black
holes in N-dimensional spherically symmetric spacetime expressed in terms of the quasilocal mass. Extension of the dilatonic
YM solution to N-dimensions has been possible by employing the generalized Wu-Yang ansatz. Another metric ansatz, which aided
in finding exact solutions is the functional dependence of the radius function on the dilaton field. These classes of black
holes are stable against linear radial perturbations. In the limit of vanishing dilaton we obtain Bertotti–Robinson type metrics
with the topology of AdS
2×S
N–2. Since connection can be established between dilaton and a scalar field of Brans–Dicke type we obtain black hole solutions
also in the Brans–Dicke–Yang–Mills theory as well. 相似文献
16.
Pearson and Bellissard recently built a spectral triple – the data of Riemannian noncommutative geometry – for ultrametric Cantor sets. They derived a family of Laplace–Beltrami
like operators on those sets. Motivated by the applications to specific examples, we revisit their work for the transversals
of tiling spaces, which are particular self-similar Cantor sets. We use Bratteli diagrams to encode the self-similarity, and Cuntz–Krieger algebras to implement it. We show that the abscissa of convergence of the ζ-function of the spectral triple gives indications on the exponent of complexity of the tiling. We determine completely the
spectrum of the Laplace–Beltrami operators, give an explicit method of calculation for their eigenvalues, compute their Weyl
asymptotics, and a Seeley equivalent for their heat kernels. 相似文献
17.
Timothy M. Garoni Giovanni Ossola Marco Polin Alan D. Sokal 《Journal of statistical physics》2011,144(3):459-518
We study, via Monte Carlo simulation, the dynamic critical behavior of the Chayes–Machta dynamics for the Fortuin–Kasteleyn
random-cluster model, which generalizes the Swendsen–Wang dynamics for the q-state Potts ferromagnet to non-integer q≥1. We consider spatial dimension d=2 and 1.25≤q≤4 in steps of 0.25, on lattices up to 10242, and obtain estimates for the dynamic critical exponent z
CM. We present evidence that when 1≤q≲1.95 the Ossola–Sokal conjecture z
CM≥β/ν is violated, though we also present plausible fits compatible with this conjecture. We show that the Li–Sokal bound z
CM≥α/ν is close to being sharp over the entire range 1≤q≤4, but is probably non-sharp by a power. As a byproduct of our work, we also obtain evidence concerning the corrections to
scaling in static observables. 相似文献
18.
E. Basso M. B. Gay Ducati E. G. de Oliveira J. T. de Santana Amaral 《The European Physical Journal C - Particles and Fields》2008,58(1):9-15
Among the dipole models of deep inelastic scattering at small values of the Bjorken variable x, one has been recently proposed which relates the virtual photon–proton cross section to the dipole–proton forward scattering
amplitude in momentum space. The latter is parametrized by an expression which interpolates between its behavior at saturation
and the travelling wave, ultraviolet, amplitudes predicted by perturbative QCD from the Balitsky–Kovchegov equation. Inspired
by recent developments in coordinate space, we use this model to parametrize the structure function of the proton and confront
it with HERA data on ep deep inelastic scattering. Both event-by-event and physical amplitudes are considered, the latter being used to investigate
the effect of gluon number fluctuations, beyond the mean-field approximation. We conclude that fluctuations are not present
in DIS at HERA energies. 相似文献
19.
H.-Ch. Schröder A. Badertscher P.F.A. Goudsmit M. Janousch H.J. Leisi E. Matsinos D. Sigg Z.G. Zhao D. Chatellard J.-P. Egger K. Gabathuler P. Hauser L.M. Simons A.J. Rusi El Hassani 《The European Physical Journal C - Particles and Fields》2001,21(3):473-488
This is the final publication of the ETH Zurich–Neuchatel–PSI collaboration on the pionic hydrogen and deuterium precision
X-ray experiments. We describe the recent hydrogen 3p–1s measurement, report on the determination of the Doppler effect correction to the transition line width, analyze the deuterium
shift measurement and discuss implications of the combined hydrogen and deuterium results. From the pionic hydrogen 3p–1s transition experiments we obtain the strong-interaction energy level shift eV and the total decay width eV of the state. Taking into account the electromagnetic corrections we find the hadronic
s-wave scattering amplitude for elastic scattering and for single charge exchange, respectively. We then combine the pionic hydrogen results with the 1s level shift measurement on pionic deuterium and test isospin symmetry of the strong interaction: our data are still compatible
with isospin symmetry. The isoscalar and isovector scattering lengths (within the framework of isospin symmetry) are found to be and , respectively. Using the GMO sum rule, we obtain from a new value of the coupling constant () from which follows the Goldberger–Treiman discrepancy . The new values of and imply an increase of the nucleon sigma term by at least 9 MeV.
Received: 20 April 2001 / Revised version: 6 July 2001 / Published online: 24 August 2001 相似文献
20.
Using twistor methods, we explicitly construct all local forms of four–dimensional real analytic neutral signature anti–self–dual
conformal structures (M, [g]) with a null conformal Killing vector. We show that M is foliated by anti-self-dual null surfaces, and the two-dimensional leaf space inherits a natural projective structure.
The twistor space of this projective structure is the quotient of the twistor space of (M, [g]) by the group action induced by the conformal Killing vector.
We obtain a local classification which branches according to whether or not the conformal Killing vector is hyper-surface
orthogonal in (M, [g]). We give examples of conformal classes which contain Ricci–flat metrics on compact complex surfaces and discuss other conformal
classes with no Ricci–flat metrics.
Dedicated to the memory of Jerzy Plebański 相似文献