147 research outputs found
The Rotationally Improved Skyrmion, or ``RISKY''
The perceived inability of the Skyrme model to reproduce pseudovector
pion-baryon coupling has come to be known as the ``Yukawa problem.'' In this
talk, we review the complete solution to this problem. The solution involves a
new configuration known as the rotationally improved Skyrmion, or ``RISKY,'' in
which the hedgehog structure is modified by a small quadrupole distortion. We
illustrate our ideas both in the Skyrme model and in a simpler model with a
global U(1) symmetry.Comment: Talk presented at the 1995 Int'l Workshop on Nuclear & Particle
Physics, Seoul, Kore
Modelling, simulation and optimisation of a piezoelectric energy harvester
The power generation efficiency of piezoelectric energy harvesters is dependent on the coupling of their resonant frequency with that of the source vibration. The mechanical design of the energy harvester plays an important role in defining the resonant frequency characteristics of the system and therefore in order to maximize power density it is important for a designer to be able to model, simulate and optimise designs to match new target applications. This paper investigates a strategy for the application of soft computing techniques from the field of evolutionary computation towards the design optimisation of piezoelectric energy harvesters that exhibit the targeted resonant frequency response chosen by the designer. The advantages of such evolutionary techniques are their ability to overcome challenges such as multi-modal and discontinuous search spaces which afflict more traditional gradient-based methods. A single case study is demonstrated in this paper, with the coupling of a multi-objective evolutionary algorithm NSGA-II to a multiphysics simulator COMSOL. Experimental results show successful implementation of the schema with all 5 experimental tests producing optimal piezoelectric energy harvester designs that matched the desired frequency response of 250 Hz
New Surgical Options in Glaucoma
The treatment of glaucoma is undergoing constant change. In the last decade, there has been a surge of novel surgical options that aim to lower intraocular pressure while providing improved safety profiles compared to traditional incisional glaucoma surgery. This article summarizes four such options— trabectome, iStent, canaloplasty and endocyclophotocoagulation— including descriptions of the procedures and evidence behind them
Boundary Entropy Can Increase Under Bulk RG Flow
The boundary entropy log(g) of a critical one-dimensional quantum system (or
two-dimensional conformal field theory) is known to decrease under
renormalization group (RG) flow of the boundary theory. We study instead the
behavior of the boundary entropy as the bulk theory flows between two nearby
critical points. We use conformal perturbation theory to calculate the change
in g due to a slightly relevant bulk perturbation and find that it has no
preferred sign. The boundary entropy log(g) can therefore increase during
appropriate bulk flows. This is demonstrated explicitly in flows between
minimal models. We discuss the applications of this result to D-branes in
string theory and to impurity problems in condensed matter.Comment: 20 page
Valley Bifurcation in an Model: Implications for High-Energy Baryon Number Violation
The valley method for computing the total high-energy anomalous cross section
is the extension of the optical theorem to the case of
instanton-antiinstanton backgrounds. As a toy model for baryon number violation
in Electroweak theory, we consider a version of the model in
which the conformal invariance is broken perturbatively. We show that at a
critical energy the saddle-point values of the instanton size and
instanton-antiinstanton separation bifurcate into complex conjugate pairs. This
nonanalytic behavior signals the breakdown of the valley method at an energy
where is still exponentially suppressed.
(Figures replaced 5/3/93).Comment: (14 pages, Los Alamos Preprint LA-UR-93-811). 3 uuencoded figures
include
D3-branes on the Coulomb branch and instantons
The relative coefficients of higher derivative interactions of the IIB
effective action of the form C^4, (D F_5)^4, F_5^8, ... (where C is the Weyl
tensor and F_5 is the five-form field strength) are motivated by supersymmetry
arguments. It is shown that the classical supergravity solution for N parallel
D3-branes is unaltered by this combination of terms. The non-vanishing of
\zeroC^2 in this background (where \zero C is the background value of the Weyl
tensor) leads to effective O(1/alpha') interactions, such as C^2 and Lambda^8
(where Lambda is the dilatino). These contain D-instanton contributions in
addition to tree and one-loop terms. The near horizon limit of the N D3-brane
system describes a multi-AdS_5xS^5 geometry that is dual to \calN=4 SU(N)
Yang-Mills theory spontaneously broken to S(U(M_1)x...xU(M_r)). Here, the N
D3-branes are grouped into r coincident bunches with M_r in each group, with
M_r/N = m_r fixed as N goes to infinity. The boundary correlation function of
eight Lambda's is constructed explicitly. The second part of the paper
considers effects of a constrained instanton in this large-N Yang-Mills theory
by an extension of the analysis of Dorey, Hollowood and Khoze of the
one-instanton measure at finite N. This makes precise the correspondence with
the supergravity D-instanton measure at leading order in the 1/N expansion.
However, the duality between instanton-induced correlation functions in
Yang-Mills theory and the dual supergravity is somewhat obscured by
complications relating to the structure of constrained instantons.Comment: 30 pages, JHEP style. Typos corrected and minor clarifications adde
Quantization of Sine-Gordon solitons on the circle: semiclassical vs. exact results
We consider the semiclassical quantization of sine-Gordon solitons on the
circle with periodic and anti-periodic boundary conditions. The 1-loop quantum
corrections to the mass of the solitons are determined using zeta function
regularization in the integral representation. We compare the semiclassical
results with exact numerical calculations in the literature and find excellent
agreement even outside the plain semiclassical regime.Comment: 20 pages, 5 figure
Conserved charges and soliton solutions in affine Toda theory
We study the conserved charges of affine Toda field theories by making use of
the conformally invariant extension of these theories. We compute the values of
all charges for the single soliton solutions, and show that these are related
to eigenvectors of the Cartan matrix of the finite-dimensional Lie algebra
underlying the theory.Comment: 18 pages, plain tex, minor changes, references adde
Heterotic/type I duality, D-instantons and an N=2 AdS/CFT correspondence
D-instanton effects are studied for the IIB orientifold T^2/I\Omega(-1)^{F_L}
of Sen using type I/heterotic duality. An exact one loop threshold calculation
of t_8 \tr F^4 and t_8(\tr F^2)^2 terms for the heterotic string on T^2 with
Wilson lines breaking SO(32) to SO(8)^4 is related to D-instanton induced terms
in the worldvolume of D7 branes in the orientifold. Introducing D3 branes and
using the AdS/CFT correspondence in this case, these terms are used to
calculate Yang-Mills instanton contributions to four point functions of the
large N_c limit of N=2 USp(2N_c) SYM with four fundamental and one
antisymmetric tensor hypermultiplets.Comment: 25 pages, harvmac(b), one figure, v2: minor changes, version to
appear in PR
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