12,348 research outputs found
Is it possible to Measure the Weak Phase of a Penguin Diagram?
The penguin amplitude receives contributions from internal ,
and -quarks. We show that it is impossible to measure the weak phase of any
of these penguin contributions without theoretical input. However, a single
assumption involving the hadronic parameters makes it possible to obtain the
weak phase and test for the presence of new physics in the
flavour-changing neutral current.Comment: 4 pages, latex, no figures, talk given by R. Sinha at the 3rd
International Conference on B Physics and CP Violation, Taipei, Taiwan,
December 3-7, 1999, to appear in the Proceeding
Probing New Physics via an Angular Analysis of B --> V1 V2 decays
We show that an angular analysis of B --> V1 V2 decays yields numerous tests
for new physics in the decay amplitudes. Unlike direct CP asymmetries, many of
these new-physics observables are nonzero even if the strong phase differences
vanish. For certain observables, neither time-dependent measurements nor
tagging is necessary. Should a signal for new physics be found, one can place a
lower limit on the size of the new-physics parameters, as well as on their
effect on the measurement of the phase of B0--Bbar0 mixing.Comment: 9 pages, plain latex, no figures. Title modified slightly. Paragraph
added about viability of method. Conclusions unchanged. To be published in
Europhysics Letter
Fully-coupled analysis of jet mixing problems. Three-dimensional PNS model, SCIP3D
Numerical procedures formulated for the analysis of 3D jet mixing problems, as incorporated in the computer model, SCIP3D, are described. The overall methodology closely parallels that developed in the earlier 2D axisymmetric jet mixing model, SCIPVIS. SCIP3D integrates the 3D parabolized Navier-Stokes (PNS) jet mixing equations, cast in mapped cartesian or cylindrical coordinates, employing the explicit MacCormack Algorithm. A pressure split variant of this algorithm is employed in subsonic regions with a sublayer approximation utilized for treating the streamwise pressure component. SCIP3D contains both the ks and kW turbulence models, and employs a two component mixture approach to treat jet exhausts of arbitrary composition. Specialized grid procedures are used to adjust the grid growth in accordance with the growth of the jet, including a hybrid cartesian/cylindrical grid procedure for rectangular jets which moves the hybrid coordinate origin towards the flow origin as the jet transitions from a rectangular to circular shape. Numerous calculations are presented for rectangular mixing problems, as well as for a variety of basic unit problems exhibiting overall capabilities of SCIP3D
Modeling the Field Emission Current Fluctuation in Carbon Nanotube Thin Films
Owing to their distinct properties, carbon nanotubes (CNTs) have emerged as
promising candidate for field emission devices. It has been found
experimentally that the results related to the field emission performance show
variability. The design of an efficient field emitting device requires the
analysis of the variabilities with a systematic and multiphysics based modeling
approach. In this paper, we develop a model of randomly oriented CNTs in a thin
film by coupling the field emission phenomena, the electron-phonon transport
and the mechanics of single isolated CNT. A computational scheme is developed
by which the states of CNTs are updated in time incremental manner. The device
current is calculated by using Fowler-Nordheim equation for field emission to
study the performance at the device scale.Comment: 4 pages, 5 figure
Cell growth rate dictates the onset of glass to fluid-like transition and long time super-diffusion in an evolving cell colony
Collective migration dominates many phenomena, from cell movement in living
systems to abiotic self-propelling particles. Focusing on the early stages of
tumor evolution, we enunciate the principles involved in cell dynamics and
highlight their implications in understanding similar behavior in seemingly
unrelated soft glassy materials and possibly chemokine-induced migration of
CD8 T cells. We performed simulations of tumor invasion using a minimal
three dimensional model, accounting for cell elasticity and adhesive cell-cell
interactions as well as cell birth and death to establish that cell growth
rate-dependent tumor expansion results in the emergence of distinct topological
niches. Cells at the periphery move with higher velocity perpendicular to the
tumor boundary, while motion of interior cells is slower and isotropic. The
mean square displacement, , of cells exhibits glassy behavior at
times comparable to the cell cycle time, while exhibiting super-diffusive
behavior, (), at longer times. We
derive the value of using a field theoretic approach
based on stochastic quantization. In the process we establish the universality
of super-diffusion in a class of seemingly unrelated non-equilibrium systems.
Super diffusion at long times arises only if there is an imbalance between cell
birth and death rates. Our findings for the collective migration, which also
suggests that tumor evolution occurs in a polarized manner, are in quantitative
agreement with {\it in vitro} experiments. Although set in the context of tumor
invasion the findings should also hold in describing collective motion in
growing cells and in active systems where creation and annihilation of
particles play a role.Comment: 56 pages, 19 figure
Hyperon bulk viscosity in strong magnetic fields
We study the bulk viscosity of neutron star matter including
hyperons in the presence of quantizing magnetic fields. Relaxation time and
bulk viscosity due to both the non-leptonic weak process involving
hyperons and direct Urca processes are calculated here. In the presence of a
strong magnetic field of G, the hyperon bulk viscosity coefficient is
reduced whereas bulk viscosity coefficients due to direct Urca processes are
enhanced compared with their field free cases when many Landau levels are
populated by protons, electrons and muons.Comment: LaTex, 28 pages including 9 figures; new results are discussed in
section I
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