1,549 research outputs found
Parton Model from Bi-local Solitonic Picture of the Baryon in two-dimensions
We study a previously introduced bi-local gauge invariant reformulation of
two dimensional QCD, called 2d HadronDynamics. The baryon arises as a
topological soliton in HadronDynamics. We derive an interacting parton model
from the soliton model, thus reconciling these two seemingly different points
of view. The valence quark model is obtained as a variational approximation to
HadronDynamics. A succession of better approximations to the soliton picture
are obtained. The next simplest case corresponds to a system of interacting
valence, `sea' and anti-quarks. We also obtain this `embellished' parton model
directly from the valence quark system through a unitary transformation. Using
the solitonic point of view, we estimate the quark and anti-quark distributions
of 2d QCD. Possible applications to Deep Inelastic Structure Functions are
pointed out.Comment: 12 page
A Model of Two Dimensional Turbulence Using Random Matrix Theory
We derive a formula for the entropy of two dimensional incompressible
inviscid flow, by determining the volume of the space of vorticity
distributions with fixed values for the moments Q_k= \int_w(x)^k d^2 x. This
space is approximated by a sequence of spaces of finite volume, by using a
regularization of the system that is geometrically natural and connected with
the theory of random matrices. In taking the limit we get a simple formula for
the entropy of a vortex field. We predict vorticity distributions of maximum
entropy with given mean vorticity and enstrophy; also we predict the
cylindrically symmetric vortex field with maximum entropy. This could be an
approximate description of a hurricane.Comment: latex, 12 pages, 2 figures, acknowledgement adde
Nuclear Waste and Native America: The MRS Siting Exercise
Drs. Gowda & Easterling provide cross-cultural perspectives on issues of risk perception, equity and policy as they affect nuclear waste storage on Native American sites
An Interacting Parton Model for Quark and Anti-quark distributions in the Baryon
In this paper we study a 1+1 dimensional relativistic parton model for the
structure of baryons. The quarks and anti-quarks interact through a linear
potential. We obtain an analytic formula for the isospin averaged valence quark
distribution in the chiral and large Nc limits. The leading 1/Nc and non-zero
current quark mass corrections are estimated. Then we extend this model to
include `sea' and anti-quarks. We find that the anti-quark content is small at
a low value of Q^2. Using these distributions as initial conditions for Q^2
evolution, we compare with experimental measurements of the structure function
xF_3(x,Q^2) and find reasonable agreement. The only parameters we can adjust
are the fraction of baryon momentum carried by valence quarks and the initial
scale Q_0^2.Comment: 14 page
Multispectral plasmon enhanced quantum dots in a well infrared photodetectors
Infrared detectors in 3-5 μm and 8-12 μm regions are extensively used for applications in remote sensing, target detection and medical diagnostics. Detectors using intersubband transitions in the quantum dots in a well (DWELL) system for infrared detection have gained prominence recently, owing to their ability to detect normally incident light, bicolor detection and use of mature III-V technology. In this dissertation, two aspects of DWELL detectors that make them suitable for third generation infrared systems are discussed: 1) High temperature operation, 2) Multispectral detection. There are two parts to this dissertation. In the first part, an alternate structure with an improved operating temperature and thicker active region is presented. Traditionally, DWELL detectors use InAs quantum dots embedded in In0.15Ga0.85As wells with GaAs barriers. Intersubband transitions in the conduction band of this system result in infrared detection. InAs quantum dots are grown using self assembly on a GaAs substrate for this system. The strain of the quantum dots and the In0.15Ga0.85As well limits the thickness of the active region. An improved design that minimizes the strain in growth of DWELL active region is discussed. By minimizing the amount of In0.15Ga0.85As in the quantum well, a lower strain per DWELL active region stack is achieved. This design consists of InAs dots in In0.15Ga0.85As/GaAs wells, forming dots-in-a-double-well (DDWELL) is presented. Optimization using PL and AFM is discussed. Detectors fabricated using DDWELL design show an operating temperature of 140 K and a background limited performance at 77 K. A peak detectivity of 6.7x1010 cm.Hz/W was observed for a wavelength of 8.7 μm. In the second part of this dissertation, multispectral and polarization detectors using DWELL absorbers are discussed. Integration of a subwavelength metallic pattern with the detector results in coupling of surface plasmons excited at the metal- semiconductor interface with DWELL active regions. Simulations indicate the presence of several modes of absorption, which can be tuned by changing the pitch of the pattern. Enhancement of absorption is predicted for the detector. Experimental demonstration show spectral tuning in MWIR and LWIR regions and a peak absorption enhancement of 4.9x. By breaking the symmetry of the fabricated pattern, we can extract a polarization dependent response, as shown from device measurements. The technique used is detector agnostic, simple and can easily be transferred to focal plane arrays (FPA). Integrating plasmonic structures on detectors using low noise DDWELL active regions can provide a higher operating temperature and high absorption. The origin of resonant peaks in multispectral DWELL detectors is examined. Use of surface patterns that selectively excite different types of modes, with absorbers of different thicknesses, show the presence of enhancement mechanisms in these devices. A 2.2x enhancement is measured from waveguide modes and 4.9x enhancement is observed from plasmon modes. Finally, a pathway of integration with FPA and integration with other infrared technologies is discussed
Fuzzy Fluid Mechanics in Three Dimensions
We introduce a rotation invariant short distance cut-off in the theory of an
ideal fluid in three space dimensions, by requiring momenta to take values in a
sphere. This leads to an algebra of functions in position space is
non-commutative. Nevertheless it is possible to find appropriate analogues of
the Euler equations of an ideal fluid. The system still has a hamiltonian
structure. It is hoped that this will be useful in the study of possible
singularities in the evolution of Euler (or Navier-Stokes) equations in three
dimensions.Comment: Additional reference
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