1,321 research outputs found
String tension in gonihedric 3D Ising models
For the 3D gonihedric Ising models defined by Savvidy and Wegner the bare
string tension is zero and the energy of a spin interface depends only on the
number of bends and self-intersections, in antithesis to the standard
nearest-neighbour 3D Ising action. When the parameter kappa weighting the
self-intersections is small the model has a first order transition and when it
is larger the transition is continuous.
In this paper we investigate the scaling of the renormalized string tension,
which is entirely generated by fluctuations, using Monte Carlo simulations This
allows us to obtain an estimate for the critical exponents alpha and nu using
both finite-size-scaling and data collapse for the scaling function.Comment: Latex + postscript figures. 8 pages text plus 7 figures, spurious
extra figure now removed
Cold atoms in non-Abelian gauge potentials: From the Hofstadter "moth" to lattice gauge theory
We demonstrate how to create artificial external non-Abelian gauge potentials
acting on cold atoms in optical lattices. The method employs internal
states of atoms and laser assisted state sensitive tunneling. Thus, dynamics
are communicated by unitary -matrices. By experimental control of
the tunneling parameters, the system can be made truly non-Abelian. We show
that single particle dynamics in the case of intense U(2) vector potentials
lead to a generalized Hofstadter butterfly spectrum which shows a complex
``moth''-like structure. We discuss the possibility to employ non-Abelian
interferometry (Aharonov-Bohm effect) and address methods to realize matter
dynamics in specific classes of lattice gauge fields.Comment: 5 pages, 3 figure
On the Logarithmic Triviality of Scalar Quantum Electrodynamics
Using finite size scaling and histogram methods we obtain numerical results
from lattice simulations indicating the logarithmic triviality of scalar
quantum electrodynamics, even when the bare gauge coupling is chosen large.
Simulations of the non-compact formulation of the lattice abelian Higgs model
with fixed length scalar fields on lattices with ranging from
through indicate a line of second order critical points.
Fluctuation-induced first order transitions are ruled out. Runs of over ten
million sweeps for each produce specific heat peaks which grow
logarithmically with and whose critical couplings shift with picking
out a correlation length exponent of consistent with mean field
theory. This behavior is qualitatively similar to that found in pure
.Comment: 9 page
Bounds on Two Parametric New Generalized Fuzzy Entropy
In this paper we define a new two parametric generalized fuzzy average code-word length...Keywords Fuzzy set, Membership function, Shannon’s entropy, Fuzzy entropy, Code-word length, Kraft inequality, Coding theorem, Holder’s inequality and Optimal code length. More details can be found in the full paper.
Carotid Doppler ultrasonography in young stroke patients
Background: The present study focuses on the role of carotid doppler ultrasonography (CDUS) in the diagnosis and management of carotid stenosis in young stroke patients.
Methods: The findings of carotid doppler in 45 ischemic stroke patients between 15-45 years of age were reviewed retrospectively. The variables of interest for this study included risk factors for atherosclerotic disease, primary abnormality detected on carotid doppler ultrasonography (ulceration vs. stenosis), degree of stenosis and the type of plaque (soft vs. calcified).
Results: The prevalence of hypertension and diabetes was 50% and 35% respectively. The rate of carotid stenosis in the study population was found to be 31%. The degree of stenosis was mild in 35% and moderate in 21%. High-grade stenosis was found in 21% of patients. The plaque was soft in the majority of cases (43%).
CONCLUSION: The proportion of carotid stenosis in young stroke patients was relatively high compared with previous studies. This may be due to an increase in the risk factors for atherosclerotic disease in developing countries
R-Norm Information Measure with Applications in Multi Criteria Decision Making Technique under Intuitionistic Fuzzy Set Environment
The main aim of this research article is to define a new information measure for quantifying fuzziness in the intuitionistic fuzzy set environment. For this purpose, we present R-norm intuitionistic fuzzy measure that quantifies the amount of vagueness or fuzziness of a particular fuzzy set. We prove that this measure is a valid measure of intuitionistic fuzzy entropy by making it satisfy essential properties. Also, some mathematical properties are used to check the validation of the measure. In the end, a practical example of decision-making is illustrated in terms of Multi Criteria Decision Making problem that presents the application of the proposed measure
Scaling laws for the 2d 8-state Potts model with Fixed Boundary Conditions
We study the effects of frozen boundaries in a Monte Carlo simulation near a
first order phase transition. Recent theoretical analysis of the dynamics of
first order phase transitions has enabled to state the scaling laws governing
the critical regime of the transition. We check these new scaling laws
performing a Monte Carlo simulation of the 2d, 8-state spin Potts model. In
particular, our results support a pseudo-critical beta finite-size scaling of
the form beta(infinity) + a/L + b/L^2, instead of beta(infinity) + c/L^d +
d/L^{2d}. Moreover, our value for the latent heat is 0.294(11), which does not
coincide with the latent heat analytically derived for the same model if
periodic boundary conditions are assumed, which is 0.486358...Comment: 10 pages, 3 postscript figure
Evidence for a first order transition in a plaquette 3d Ising-like action
We investigate a 3d Ising action which corresponds to a a class of models
defined by Savvidy and Wegner, originally intended as discrete versions of
string theories on cubic lattices. These models have vanishing bare surface
tension and the couplings are tuned in such a way that the action depends only
on the angles of the discrete surface, i.e. on the way the surface is embedded
in . Hence the name gonihedric by which they are known. We show that
the model displays a rather clear first order phase transition in the limit
where self-avoidance is neglected and the action becomes a plaquette one. This
transition persists for small values of the self avoidance coupling, but it
turns to second order when this latter parameter is further increased. These
results exclude the use of this type of action as models of gonihedric random
surfaces, at least in the limit where self avoidance is neglected.Comment: 4 pages Latex text, 4 postscript figure
Oscillator strength measurements of the 5s6s 1S0→5snp 1P1 Rydberg transitions of strontium
We report the experimentally determined oscillator strengths for the 5s6s 1S0→5snp 1P1 Rydberg transitions of strontium using two-step excitation in conjunction with a thermionic diode ion detector. The absolute photoionization cross section from the 5s6s 1S0 excited state has been determined by adjusting the polarization vector of the ionizing laser beam parallel, perpendicular, and at the magic angle with respect to that of the exciting dye laser. The measured absolute value of the photoionization cross section 0.9±0.2 Mb at the 5s threshold is used to extract the f values of the 5s6s 1S0→5snp 1P1 (26≤n≤73) Rydberg transitions. The oscillator strength in the discrete region merges smoothly to the oscillator strength density at the ionization threshold
Chiral transition and monopole percolation in lattice scalar QED with quenched fermions
We study the interplay between topological observables and chiral and Higgs
transitions in lattice scalar QED with quenched fermions. Emphasis is put on
the chiral transition line and magnetic monopole percolation at strong gauge
coupling. We confirm that at infinite gauge coupling the chiral transition is
described by mean field exponents. We find a rich and complicated behaviour at
the endpoint of the Higgs transition line which hampers a satisfactory analysis
of the chiral transition. We study in detail an intermediate coupling, where
the data are consistent both with a trivial chiral transition clearly separated
from monopole percolation and with a chiral transition coincident with monopole
percolation, and characterized by the same critical exponent .
We discuss the relevance (or lack thereof) of these quenched results to our
understanding of the \chupiv\ model. We comment on the interplay of magnetic
monopoles and fermion dynamics in more general contexts.Comment: 29 pages, 13 figures included, LaTeX2e (elsart
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