15,995 research outputs found
Vector meson masses in hot nuclear matter : the effect of quantum corrections
The medium modification of vector meson masses is studied taking into account
the quantum correction effects for the hot and dense hadronic matter. In the
framework of Quantum Hadrodynamics, the quantum corrections from the baryon and
scalar meson sectors were earlier computed using a nonperturbative variational
approach through a realignment of the ground state with baryon-antibaryon and
sigma meson condensates. The effect of such corrections was seen to lead to a
softer equation of state giving rise to a lower value for the compressibility
and, an increase in the in-medium baryonic masses than would be reached when
such quantum effects are not taken into account. These quantum corrections
arising from the scalar meson sector result in an increase in the masses of the
vector mesons in the hot and dense matter, as compared to the situation when
only the vacuum polarisation effects from the baryonic sector are taken into
account.Comment: 13 pages revtex file, 6 figure
Force-induced desorption of a linear polymer chain adsorbed on an attractive surface
We consider a model of self-avoiding walk on a lattice with on-site repulsion
and an attraction for every vertex of the walk visited on the surface to study
force-induced desorption of a linear polymer chain adsorbed on an attractive
surface and use the exact enumeration technique for analyzing how the critical
force for desorption depends on the temperature. The curve
gives the boundary separating the adsorbed phase from the desorbed phase. Our
results show that in two dimensions where surface is a line the force
increases monotonically as temperature is lowered and becomes almost constant
at very low temperatures. In case of three-dimensions we, however, find
re-entrance, i. e. goes through a maximum as temperature is lowered.
The behaviour of the polymer chain at different values of temperature and force
is examined by calculating the probability distribution of the height from the
surface of the vertex at which external force is applied.Comment: Preprint 15 pages with 8figures and two tables. The file table-2d.ps
and table-3d.ps lists C_N(Ns,h) for given N with all possible Ns and h in two
and three dimension
Getting CICY high
Supervised machine learning can be used to predict properties of string geometries with previously unknown features. Using the complete intersection Calabi–Yau (CICY) threefold dataset as a theoretical laboratory for this investigation, we use low h1,1 geometries for training and validate on geometries with large h1,1. Neural networks and Support Vector Machines successfully predict trends in the number of Kähler parameters of CICY threefolds. The numerical accuracy of machine learning improves upon seeding the training set with a small number of samples at higher h1,1
Machine learning CICY threefolds
The latest techniques from Neural Networks and Support Vector Machines (SVM) are used to investigate geometric properties of Complete Intersection Calabi–Yau (CICY) threefolds, a class of manifolds that facilitate string model building. An advanced neural network classifier and SVM are employed to (1) learn Hodge numbers and report a remarkable improvement over previous efforts, (2) query for favourability, and (3) predict discrete symmetries, a highly imbalanced problem to which both Synthetic Minority Oversampling Technique (SMOTE) and permutations of the CICY matrix are used to decrease the class imbalance and improve performance. In each case study, we employ a genetic algorithm to optimise the hyperparameters of the neural network. We demonstrate that our approach provides quick diagnostic tools capable of shortlisting quasi-realistic string models based on compactification over smooth CICYs and further supports the paradigm that classes of problems in algebraic geometry can be machine learned
Coherent Change Detection with COSMO SkyMed Data-experimental Results
Change detection is a technique in which we try to find changes between two acquisitions. These acquisitions can be from different platforms and sensors. Acquisition from satellite using synthetic aperture radar (SAR) is of immense interest to military applications. Satellite has the ability to peep into the enemy territory while SAR has the capability of day and night operations, being an active sensor. Coherent change detection (CCD) can be used to detect minute changes between two images. This paper presents the coherent change detection experimental studies using COSMO SkyMed space borne data. It has been demonstrated that subtle changes caused by the vehicle movement can be detected using phase characteristic of the SAR data.Defence Science Journal, 2013, 63(1), pp.69-73, DOI:http://dx.doi.org/10.14429/dsj.63.376
Structure of the Vacuum in Nuclear Matter - A Nonperturbative Approach
We compute the vacuum polarisation correction to the binding energy of
nuclear matter in the Walecka model using a nonperturbative approach. We first
study such a contribution as arising from a ground state structure with
baryon-antibaryon condensates. This yields the same results as obtained through
the relativistic Hartree approximation of summing tadpole diagrams for the
baryon propagator. Such a vacuum is then generalized to include quantum effects
from meson fields through scalar-meson condensates. The method is applied to
study properties of nuclear matter and leads to a softer equation of state
giving a lower value of the incompressibility than would be reached without
quantum effects. The density dependent effective sigma mass is also calculated
including such vacuum polarisation effects.Comment: 26 pages including 5 eps files, uses revtex style; PACS number:
21.65.+f,21.30.+
Peristaltic Transport of a Physiological Fluid in an Asymmetric Porous Channel in the Presence of an External Magnetic Field
The paper deals with a theoretical investigation of the peristaltic transport
of a physiological fluid in a porous asymmetric channel under the action of a
magnetic field. The stream function, pressure gradient and axial velocity are
studied by using appropriate analytical and numerical techniques. Effects of
different physical parameters such as permeability, phase difference, wave
amplitude and magnetic parameter on the velocity, pumping characteristics,
streamline pattern and trapping are investigated with particular emphasis. The
computational results are presented in graphical form. The results are found to
be in perfect agreement with those of a previous study carried out for a
non-porous channel in the absence of a magnetic field
Fluctuation Induced Non-Fermi Liquid Behavior near a Quantum Phase Transition in Itinerant Electron Systems
The signature for a non-Fermi liquid behavior near a quantum phase transition
has been observed in thermal and transport properties of many metallic systems
at low temperatures. In the present work we consider specific examples of
itinerant ferromagnet as well as antiferromagnet in the limit of vanishing
transition temperature. The temperature variation of spin susceptibility,
electrical resistivity, specific heat, and NMR relaxation rates at low
temperatures is calculated in the limit of infinite exchange enhancement within
the frame work of a self consistent spin fluctuation theory. The resulting
non-Fermi liquid behavior is due to the presence of the low lying critically
damped spin fluctuations in these systems. The theory presented here gives the
leading low temperature behavior, as it turns out that the fluctuation
correlation term is always smaller than the mean fluctuation field term in
three as well as in two space dimensions. A comparison with illustrative
experimental results of these properties in some typical systems has been done.
Finally we make some remarks on the effect of disorder in these systems.Comment: File RevTex, 7 Figures available on request, Abstract and text
modified, To appear in Phys. Rev.
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