3,756 research outputs found
Metal - non-metal transition and the second critical point in expanded metals
Based on the non-relativistic Coulomb model within which the matter is a
system of interacting electrons and nuclei, using the quantum field theory and
linear response theory methods, opportunity for the existence of the second
critical point in expanded metals, which is directly related to the
metal--nonmetal transition, predicted by Landau and Zeldovitch, is
theoretically justified. It is shown that the matter at the second critical
point is in the state of true dielectric with zero static conductivity. The
results obtained are in agreement with recent experiments for expanded metals.
The existence of the second critical point is caused by the initial
multi-component nature of the matter consisting of electrons and nuclei and the
long-range character of the Coulomb interaction. (Accepted in PTEP)Comment: 10 pages, Fig.4 (6
Anomalous Transport in Velocity Space, from Fokker-Planck to General Equation
The problem of anomalous diffusion in momentum (velocity) space is considered
based on the master equation and the appropriate probability transition
function (PTF). The approach recently developed by the author for coordinate
space, is applied with necessary modifications to velocity space. A new general
equation for the time evolution of the momentum distribution function in
momentum space is derived. This allows the solution of various problems of
anomalous transport when the probability transition function (PTF) has a long
tail in momentum space. For the opposite cases of the PTF rapidly decreasing as
a function of transfer momenta (when large transfer momenta are strongly
suppressed), the developed approach allows us to consider strongly
non-equilibrium cases of the system evolution. The stationary and
non-stationary solutions are studied. As an example, the particular case of the
Boltzmann-type PT-function for collisions of heavy and light particles with the
determined (prescribed) distribution function, which can be strongly
non-equilibrium, is considered within the proposed general approach. The
appropriate diffusion and friction coefficients are found. The Einstein
relation between the friction and diffusion coefficients is shown to be
violated in these cases.Comment: 23 pages, 0 figure
Kramers-Kronig Relations For The Dielectric Function And The Static Conductivity Of Coulomb Systems
The mutual influence of singularities of the dielectric permittivity e(q,w)
in a Coulomb system in two limiting cases w tends to zero, q tends to zero, and
opposite q tends to zero, w tends to zero is established. It is shown that the
dielectric permittivity e(q,w) satisfies the Kramers-Kronig relations, which
possesses the singularity due to a finite value of the static conductivity.
This singularity is associated with the long "tails" of the time correlation
functions.Comment: 9 pages, 0 figure
Diffusion in a Time-dependent External Field
The problem of diffusion in a time-dependent (and generally inhomogeneous)
external field is considered on the basis of a generalized master equation with
two times, introduced in [1,2]. We consider the case of the quasi Fokker-Planck
approximation, when the probability transition function for diffusion
(PTD-function) does not possess a long tail in coordinate space and can be
expanded as a function of instantaneous displacements. The more complicated
case of long tails in the PTD will be discussed separately. We also discuss
diffusion on the basis of hydrodynamic and kinetic equations and show the
validity of the phenomenological approach. A new type of "collision" integral
is introduced for the description of diffusion in a system of particles, which
can transfer from a moving state to the rest state (with some waiting time
distribution). The solution of the appropriate kinetic equation in the external
field also confirms the phenomenological approach of the generalized master
equation.Comment: 18 pages, no figure
Exploring Pompeii: discovering hospitality through research synergy
Hospitality research continues to broaden through an ever-increasing dialogue and alignment with a greater number of academic disciplines. This paper demonstrates how an enhanced understanding of hospitality can be achieved through synergy between archaeology, the classics and sociology. It focuses on classical Roman life, in particular Pompeii, to illustrate the potential for research synergy and collaboration, to advance the debate on hospitality research and to encourage divergence in research approaches. It demonstrates evidence of commercial hospitality activities through the excavation hotels, bars and taverns, restaurants and fast food sites. The paper also provides an example of the benefits to be gained from multidisciplinary analysis of hospitality and tourism
Tests of model of color reconnection and a search for glueballs using gluon jets with a rapidity gap
Gluon jets with a mean energy of 22 GeV and purity of 95% are selected from
hadronic Z0 decay events produced in e+e- annihilations. A subsample of these
jets is identified which exhibits a large gap in the rapidity distribution of
particles within the jet. After imposing the requirement of a rapidity gap, the
gluon jet purity is 86%. These jets are observed to demonstrate a high degree
of sensitivity to the presence of color reconnection, i.e. higher order QCD
processes affecting the underlying color structure. We use our data to test
three QCD models which include a simulation of color reconnection: one in the
Ariadne Monte Carlo, one in the Herwig Monte Carlo, and the other by Rathsman
in the Pythia Monte Carlo. We find the Rathsman and Ariadne color reconnection
models can describe our gluon jet measurements only if very large values are
used for the cutoff parameters which serve to terminate the parton showers, and
that the description of inclusive Z0 data is significantly degraded in this
case. We conclude that color reconnection as implemented by these two models is
disfavored. The signal from the Herwig color reconnection model is less clear
and we do not obtain a definite conclusion concerning this model. In a separate
study, we follow recent theoretical suggestions and search for glueball-like
objects in the leading part of the gluon jets. No clear evidence is observed
for these objects.Comment: 42 pages, 18 figure
Search for Yukawa Production of a Light Neutral Higgs Boson at LEP
Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs boson in
the mass range of 4-12 GeV has been performed in the Yukawa process e+e- -> b
bbar A/h -> b bbar tau+tau-, using the data collected by the OPAL detector at
LEP between 1992 and 1995 in e+e- collisions at about 91 GeV centre-of-mass
energy. A likelihood selection is applied to separate background and signal.
The number of observed events is in good agreement with the expected
background. Within a CP-conserving 2HDM type II model the cross-section for
Yukawa production depends on xiAd = |tan beta| and xihd = |sin alpha/cos beta|
for the production of the CP-odd A and the CP-even h, respectively, where tan
beta is the ratio of the vacuum expectation values of the Higgs doublets and
alpha is the mixing angle between the neutral CP-even Higgs bosons. From our
data 95% C.L. upper limits are derived for xiAd within the range of 8.5 to 13.6
and for xihd between 8.2 to 13.7, depending on the mass of the Higgs boson,
assuming a branching fraction into tau+tau- of 100%. An interpretation of the
limits within a 2HDM type II model with Standard Model particle content is
given. These results impose constraints on several models that have been
proposed to explain the recent BNL measurement of the muon anomalous magnetic
moment.Comment: 24 pages, 9 figures, Submitted to Euro. Phys. J.
Search for the Standard Model Higgs Boson with the OPAL Detector at LEP
This paper summarises the search for the Standard Model Higgs boson in e+e-
collisions at centre-of-mass energies up to 209 GeV performed by the OPAL
Collaboration at LEP. The consistency of the data with the background
hypothesis and various Higgs boson mass hypotheses is examined. No indication
of a signal is found in the data and a lower bound of 112.7GeV/C^2 is obtained
on the mass of the Standard Model Higgs boson at the 95% CL.Comment: 51 pages, 21 figure
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