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1612.02986
|
in this paper we study the resonance graphs of benzenoid systems , tubulenes , and fullerenes . the resonance graph reflects the interactions between the kekul ' e structures of a molecule . the equivalence of the zhang - zhang polynomial ( which counts clar covers ) of the molecular graph and the cube polynomial ( which counts hypercubes ) of its resonance graph is known for all three families of molecular graphs . instead of considering only interactions between 6-cycles ( clar covers ) , we also consider 10-cycles , which contribute to the resonance energy of a molecule as well . therefore , we generalize the concepts of the zhang - zhang polynomial and the cube polynomial and prove the equality of these two polynomials .
| 128
|
hep-ph0005099
|
recently , barger _ et al . _ computed energy losses into kaluza klein modes from astrophysical plasmas in the approximation of zero density for the plasmas . we extend their work by considering the effects of finite density for two plasmon processes . our results show that , for fixed temperature , the energy loss rate per @xmath0 is constant up to some critical density and then falls exponentially . this is true for transverse and longitudinal plasmons in both the direct and crossed channels over a wide range of temperature and density . a difficulty in deriving the appropriate covariant interaction energy at finite density and temperature is addressed . we find that , for the cases considered by barger _ et al . _ , the zero density approximation and the neglect of other plasmon processes is justified to better than an order of magnitude .
| 149
|
cond-mat0102008
|
monte carlo simulations were performed in order to determine the excess number of clusters @xmath0 and the average density of clusters @xmath1 for the two - dimensional `` swiss cheese '' continuum percolation model on a planar @xmath2 system and on the surface of a sphere . the excess number of clusters for the @xmath3 system was confirmed to be a universal quantity with a value @xmath4 as previously predicted and verified only for lattice percolation . the excess number of clusters on the surface of a sphere was found to have the value @xmath5 for discs with the same coverage as the flat critical system . finally , the average critical density of clusters was calculated for continuum systems @xmath6 . #
| 123
|
0804.2134
|
let @xmath0 be an elementary closed semi - algebraic set in @xmath1 , i.e. , there exist real polynomials @xmath2 ( @xmath3 ) such that @xmath4 ; in this case @xmath2 are said to represent @xmath0 . denote by @xmath5 the maximal number of the polynomials from @xmath6 that vanish in a point of @xmath7 if @xmath0 is non - empty and bounded , we show that it is possible to construct @xmath8 polynomials representing @xmath7 furthermore , the number @xmath8 can be reduced to @xmath5 in the case when the set of points of @xmath0 in which @xmath5 polynomials from @xmath6 vanish is finite . analogous statements are also obtained for elementary open semi - algebraic sets . primary : 14p10 , secondary : 14q99 , 03c10 , 90c26 approximation , elementary symmetric function , ojasiewicz s inequality , polynomial optimization , semi - algebraic set , theorem of brcker and scheiderer
| 153
|
hep-ph0303151
|
feynman s path amplitude formulation of quantum mechanics is used to analyse the production of charged leptons from charged current weak interaction processes . for neutrino induced reactions the interference effects predicted are usually called ` neutrino oscillations ' . similar effects in the detection of muons from pion decay are here termed ` muon oscillations ' . processes considered include pion decay ( at rest and in flight ) , and muon decay and nuclear @xmath0-decay at rest . in all cases studied , a neutrino oscillation phase different from the conventionally used one is found . a concise critical review is made of previous treatments of the quantum mechanics of neutrino and muon oscillations . 24.5 cm -5pt -5pt -50pt addtoresetequationsection * j.h.field * dpartement de physique nuclaire et corpusculaire universit de genve . 24 , quai ernest - ansermet ch-1211 genve 4 . pacs 03.65.bz , 14.60.pq , 14.60.lm , 13.20.cz quantum mechanics , neutrino oscillations .
| 160
|
1110.1272
|
we report xmm-_newton _ observations of the galactic supernova remnant g296.8@xmath00.3 , together with complementary radio and infrared data . the spatial and spectral properties of the x - ray emission , detected towards g296.8@xmath00.3 , was investigated in order to explore the possible evolutionary scenarios and the physical connexion with its unusual morphology detected at radio frequencies . g296.8@xmath00.3 displays diffuse x - ray emission correlated with the peculiar radio morphology detected in the interior of the remnant and with the shell - like radio structure observed to the northwest side of the object . the x - ray emission peaks in the soft / medium energy range ( 0.5 - 3.0 kev ) . the x - ray spectral analysis confirms that the column density is high ( @xmath1@xmath20.64@xmath310@xmath4 @xmath5 ) which supports a distant location ( d@xmath69 kpc ) for the snr . its x - ray spectrum can be well represented by a thermal ( pshock ) model , with @xmath7 @xmath2 0.86 kev , an ionization timescale of 6.1@xmath310@xmath8 @xmath9 s , and low abundance ( @xmath2 0.12 @xmath10 ) . the 24 @xmath11 m observations show shell - like emission correlated with part of the northwest and southeast boundaries of the snr . in addition a point - like x - ray source is also detected close to the geometrical center of the radio snr . the object presents some characteristics of the so - called compact central objects ( cco ) . its x - ray spectrum is consistent with those found at other ccos and the value of @xmath1 is consistent with that of g296.8@xmath00.3 , which suggests a physical connexion with the snr .
| 283
|
hep-ph9802232
|
we discuss the constraints from rare b and k decays on the electroweak symmetry breaking ( ewsb ) sector , as well as on theories of fermion masses . we focus on models involving new strong dynamics and show that transitions involving flavor changing neutral currents ( fcnc ) play an important role in disentangling the physics in these scenarios . in a model - independent approach to the ewsb sector , the information from rare decays is complementary to precision electroweak observables in bounding the contributions to the effective lagrangian . we compare the pattern of deviations from the standard model ( sm ) that results from these sources , with the deviations associated with the mechanism for generating fermion masses . madph-98 - 1039 +
| 127
|
1004.2740
|
we study the hole binding energy and pairing correlations in the three - band hubbard model coupled to an apical oxygen phonon , by exact diagonalization and constrained - path monte carlo simulations . in the physically relevant charge - transfer regime , we find that the hole binding energy is strongly enhanced by the electron - phonon interaction , which is due to a novel potential - energy - driven pairing mechanism involving reduction of both electronic potential energy and phonon related energy . the enhancement of hole binding energy , in combination with a phonon - induced increase of quasiparticle weight , leads to a dramatic enhancement of the long - range part of d - wave pairing correlations . our results indicate that the apical oxygen phonon plays a significant role in the superconductivity of high-@xmath0 cuprates .
| 141
|
1408.6985
|
the process of neutrino production of electron positron pairs in a magnetic field of arbitrary strength , where electrons and positrons can be created in the states corresponding to excited landau levels , is analysed . the mean value of the neutrino energy loss due to the process @xmath0 is calculated . the result can be applied for calculating the efficiency of the electron - positron plasma production by neutrinos in the conditions of the kerr black hole accretion disc considered by experts as the most possible source of a short cosmological gamma burst . the presented research can be also useful for further development of the calculation technic for an analysis of quantum processes in external active medium , and in part in the conditions of moderately strong magnetic field , when taking account of the ground landau level appears to be insufficient .
| 145
|
cond-mat9910264
|
a density functional theory for many - body lattice models is considered in which the single - particle density matrix @xmath0 is the basic variable . eigenvalue equations are derived for solving levy s constrained search of the interaction energy functional @xmath1 $ ] . @xmath1 $ ] is expressed as the sum of hartree - fock energy @xmath2 $ ] and the correlation energy @xmath3 $ ] . exact results are obtained for @xmath4 of the hubbard model on various periodic lattices , where @xmath5 for all nearest neighbors @xmath6 and @xmath7 . the functional dependence of @xmath4 is analyzed by varying the number of sites @xmath8 , band filling @xmath9 and lattice structure . the infinite one - dimensional chain and one- , two- , or three - dimensional finite clusters with periodic boundary conditions are considered . the properties of @xmath4 are discussed in the limits of weak ( @xmath10 ) and strong ( @xmath11 ) electronic correlations , and in the crossover region ( @xmath12 ) . using an appropriate scaling we observe that @xmath13 has a pseudo - universal behavior as a function of @xmath14 . the fact that @xmath15 depends weakly on @xmath8 , @xmath9 and lattice structure suggests that the correlation energy of extended systems could be obtained quite accurately from finite cluster calculations . finally , the behavior of @xmath4 for repulsive ( @xmath16 ) and attractive ( @xmath17 ) interactions are contrasted . 2
| 243
|
0907.3736
|
we compute the entropy of antiferromagnetic quantum spin-@xmath0 chains in an external magnetic field using exact diagonalization and quantum monte carlo simulations . the magnetocaloric effect , _ i.e. _ , temperature variations during adiabatic field changes , can be derived from the isentropes . first , we focus on the example of the spin-@xmath1 chain and show that one can cool by closing the haldane gap with a magnetic field . we then move to quantum spin-@xmath0 chains and demonstrate linear scaling with @xmath0 close to the saturation field . in passing , we propose a new method to compute many low - lying excited states using the lanczos recursion . quantum spin chains , magnetocaloric effect , entropy , exact diagonalization , quantum monte carlo 75.10.pq ; 75.30.sg ; 75.50.ee ; 02.70.-c
| 134
|
1506.04688
|
as a generalization of orbit - polynomial and distance - regular graphs , we introduce the concept of a quotient - polynomial graph . in these graphs every vertex @xmath0 induces the same regular partition around @xmath0 , where all vertices of each cell are equidistant from @xmath0 . some properties and characterizations of such graphs are studied . for instance , all quotient - polynomial graphs are walk - regular and distance - polynomial . also , we show that every quotient - polynomial graph generates a ( symmetric ) association scheme . _ mathematics subject classifications : _ 05e30 , 05c50 . _ keywords : _ graph quotient ; distance - faithful partition ; walk - regular partition ; quotient - polynomial graph ; distance - regular graph ; eigenvalues ; orthogonal polynomials ; intersection numbers .
| 139
|
0801.2228
|
conducting submicron particles are well - suited as filler particles in non - conducting polymer matrices to obtain a conducting composite with a low percolation threshold . going to nanometer - sized filler particles imposes a restriction to the conductivity of the composite , due to the reduction of the density of states involved in the hopping process between the particles , compared to its value within the crystallites . we show how those microscopic parameters that govern the charge - transport processes across many decades of length scales , can accurately and consistently be determined by a range of dielectric - spectroscopy techniques from a few hz to infrared frequencies . the method , which is suited for a variety of systems with restricted geometries , is applied to densely packed 7-nm - sized tin - oxide crystalline particles with various degree of antimony doping and the quantitative results unambiguously show the role of the nanocrystal charging energy in limiting the hopping process .
| 165
|
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