10,219 research outputs found
Mesons and Flavor on the Conifold
We explore the addition of fundamental matter to the Klebanov-Witten field
theory. We add probe D7-branes to the theory obtained from placing
D3-branes at the tip of the conifold and compute the meson spectrum for the
scalar mesons. In the UV limit of massless quarks we find the exact dimensions
of the associated operators, which exhibit a simple scaling in the large-charge
limit. For the case of massive quarks we compute the spectrum of scalar mesons
numerically.Comment: 19 pages, 3 figures, v2: typos fixe
Defect turbulence in inclined layer convection
We report experimental results on the defect turbulent state of undulation
chaos in inclined layer convection of a fluid withPrandtl number .
By measuring defect density and undulation wavenumber, we find that the onset
of undulation chaos coincides with the theoretically predicted onset for
stable, stationary undulations. At stronger driving, we observe a competition
between ordered undulations and undulation chaos, suggesting bistability
between a fixed-point attractor and spatiotemporal chaos. In the defect
turbulent regime, we measured the defect creation, annihilation, entering,
leaving, and rates. We show that entering and leaving rates through boundaries
must be considered in order to describe the observed statistics. We derive a
universal probability distribution function which agrees with the experimental
findings.Comment: 4 pages, 5 figure
Merger & Acquisition and Capital Expenditure in Health Care: Information Gleaned From Stock Price Variation
Investment, especially through merger and acquisition (M&A), is a leading topic of concern among health care managers. In addition, the implications of this activity for organization and market concentration are of great interest to policy makers. Using a sample of 2256 firm-year observations in the health care industry during the period from 1985 to 2011, this article provides novel evidence that managers learn from financial markets in making capital expenditure (CAPEX) and M&A investment decisions. Within the industry, managers in the Drugs subsector are most likely to do so, whereas managers in the Medical Equipment and Supplies are least likely to do so. We find informative stock prices improve firm financial performance. This article highlights the importance of financial markets for real economic activity in the health care industry
Elastic Convection in Vibrated Viscoplastic Fluids
We observe a new type of behavior in a shear thinning yield stress fluid:
freestanding convection rolls driven by vertical oscillation. The convection
occurs without the constraint of container boundaries yet the diameter of the
rolls is spontaneously selected for a wide range of parameters. The transition
to the convecting state occurs without hysteresis when the amplitude of the
plate acceleration exceeds a critical value. We find that a non-dimensional
stress, the stress due to the inertia of the fluid normalized by the yield
stress, governs the onset of the convective motion.Comment: 4 pages, 6 figure
Penta-Hepta Defect Motion in Hexagonal Patterns
Structure and dynamics of penta-hepta defects in hexagonal patterns is
studied in the framework of coupled amplitude equations for underlying plane
waves. Analytical solution for phase field of moving PHD is found in the far
field, which generalizes the static solution due to Pismen and Nepomnyashchy
(1993). The mobility tensor of PHD is calculated using combined analytical and
numerical approach. The results for the velocity of PHD climbing in slightly
non-optimal hexagonal patterns are compared with numerical simulations of
amplitude equations. Interaction of penta-hepta defects in optimal hexagonal
patterns is also considered.Comment: 4 pages, Postscript (submitted to PRL
Rhombic Patterns: Broken Hexagonal Symmetry
Landau-Ginzburg equations derived to conserve two-dimensional spatial symmetries lead to the prediction that rhombic arrays with characteristic angles slightly differ from 60 degrees should form in many systems. Beyond the bifurcation from the uniform state to patterns, rhombic patterns are linearly stable for a band of angles near the 60 degrees angle of regular hexagons. Experiments conducted on a reaction-diffusion system involving a chlorite-iodide-malonic acid reaction yield rhombic patterns in good accord with the theory.Energy Laboratory of the University of HoustonOffice of Naval ResearchU.S. Department of Energy Office of Basic Energy SciencesRobert A. Welch FoundationCenter for Nonlinear Dynamic
Electron properties of carbon nanotubes in a periodic potential
A periodic potential applied to a nanotube is shown to lock electrons into
incompressible states that can form a devil's staircase. Electron interactions
result in spectral gaps when the electron density (relative to a half-filled
Carbon pi-band) is a rational number per potential period, in contrast to the
single-particle case where only the integer-density gaps are allowed. When
electrons are weakly bound to the potential, incompressible states arise due to
Bragg diffraction in the Luttinger liquid. Charge gaps are enhanced due to
quantum fluctuations, whereas neutral excitations are governed by an effective
SU(4)~O(6) Gross-Neveu Lagrangian. In the opposite limit of the tightly bound
electrons, effects of exchange are unimportant, and the system behaves as a
single fermion mode that represents a Wigner crystal pinned by the external
potential, with the gaps dominated by the Coulomb repulsion. The phase diagram
is drawn using the effective spinless Dirac Hamiltonian derived in this limit.
Incompressible states can be detected in the adiabatic transport setup realized
by a slowly moving potential wave, with electron interactions providing the
possibility of pumping of a fraction of an electron per cycle (equivalently, in
pumping at a fraction of the base frequency).Comment: 21 pgs, 8 fig
N=1 gauge superpotentials from supergravity
We review the supergravity derivation of some non-perturbatively generated
effective superpotentials for N=1 gauge theories. Specifically, we derive the
Veneziano-Yankielowicz superpotential for pure N=1 Super Yang-Mills theory from
the warped deformed conifold solution, and the Affleck-Dine-Seiberg
superpotential for N=1 SQCD from a solution describing fractional D3-branes on
a C^3 / Z_2 x Z_2 orbifold.Comment: LaTeX, iopart class, 8 pages, 3 figures. Contribution to the
proceedings of the workshop of the RTN Network "The quantum structure of
space-time and the geometric nature of fundamental interactions", Copenhagen,
September 2003; v2: published version with minor clarification
Turing Instability in a Boundary-fed System
The formation of localized structures in the chlorine dioxide-idodine-malonic
acid (CDIMA) reaction-diffusion system is investigated numerically using a
realistic model of this system. We analyze the one-dimensional patterns formed
along the gradients imposed by boundary feeds, and study their linear stability
to symmetry-breaking perturbations (Turing instability) in the plane transverse
to these gradients. We establish that an often-invoked simple local linear
analysis which neglects longitudinal diffusion is inappropriate for predicting
the linear stability of these patterns. Using a fully nonuniform analysis, we
investigate the structure of the patterns formed along the gradients and their
stability to transverse Turing pattern formation as a function of the values of
two control parameters: the malonic acid feed concentration and the size of the
reactor in the dimension along the gradients. The results from this
investigation are compared with existing experiments.Comment: 41 pages, 18 figures, to be published in Physical Review
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