79 research outputs found
Localization properties of lattice fermions with plaquette and improved gauge actions
We determine the location of the mobility edge in the spectrum of
the hermitian Wilson operator in pure-gauge ensembles with plaquette, Iwasaki,
and DBW2 gauge actions. The results allow mapping a portion of the (quenched)
Aoki phase diagram. We use Green function techniques to study the localized and
extended modes. Where we characterize the localized modes in
terms of an average support length and an average localization length, the
latter determined from the asymptotic decay rate of the mode density. We argue
that, since the overlap operator is commonly constructed from the Wilson
operator, its range is set by the value of for the Wilson
operator. It follows from our numerical results that overlap simulations
carried out with a cutoff of 1 GeV, even with improved gauge actions, could be
afflicted by unphysical degrees of freedom as light as 250 MeV.Comment: RevTeX, 37 pages, 10 figures. Some textual changes. Final for
Classification of Minimally Doubled Fermions
We propose a method to control the number of species of lattice fermions
which yields new classes of minimally doubled lattice fermions. We show it is
possible to control the number of species by handling Wilson-term-like
corrections in fermion actions, which we will term ``Twisted-ordering Method".
Using this method we obtain new minimally doubled actions with one exact chiral
symmetry and exact locality. We classify the known minimally doubled fermions
into two types based on the locations of the propagator poles in the Brillouin
zone.Comment: 23 pages, 6 figures; version accepted in Phys.Rev.
Quark mass dependence of the vacuum electric conductivity induced by the magnetic field in SU(2) lattice gluodynamics
We study the electric conductivity of the vacuum of quenched SU(2) lattice
gauge theory induced by the magnetic field B as a function of the bare quark
mass m. The conductivity grows as the quark mass decreases. Simplest power-like
fit indicates that the conductivity behaves as B/sqrt(m). We discuss the
implications of this result for dilepton angular distributions in heavy ion
collisions.Comment: 5 pages RevTeX, 4 figure
Broken Symmetries from Minimally Doubled Fermions
Novel chirally symmetric fermion actions containing the minimum amount of
fermion doubling have been recently proposed in the literature. We study the
symmetries and renormalization of these actions and find that in each case,
discrete symmetries, such as parity and time-reversal, are explicitly broken.
Consequently, when the gauge interactions are included, these theories
radiatively generate relevant and marginal operators. Thus the restoration of
these symmetries and the approach to the continuum limit require the
fine-tuning of several parameters. With some assumptions, we show that this
behavior is unavoidable for actions displaying minimal fermion doubling.Comment: 13 pages, 3 figures, published version, analysis reorganized and
condense
Optimizations of sub-100 nm Si/SiGe MODFETs for high linearity RF applications
Based on careful calibration in respect of 70 nm n-type strained Si channel S/SiGe modulation doped FETs (MODFETs) fabricated by Daimler Chrysler, numerical simulations have been used to study the impact of the device geometry and various doping strategies on device performance and linearity. The device geometry is sensitive to both RF performance and device linearity. Doped channel devices are found to be promising for high linearity applications. Trade-off design strategies are required for reconciling the demands of high device performance and high linearity simultaneously. The simulations also suggest that gate length scaling helps to achieve higher RF performance, but decreases the linearity
Reducing Residual-Mass Effects for Domain-Wall Fermions
It has been suggested to project out a number of low-lying eigenvalues of the
four-dimensional Wilson--Dirac operator that generates the transfer matrix of
domain-wall fermions in order to improve simulations with domain-wall fermions.
We investigate how this projection method reduces the residual chiral
symmetry-breaking effects for a finite extent of the extra dimension. We use
the standard Wilson as well as the renormalization--group--improved gauge
action. In both cases we find a substantially reduced residual mass when the
projection method is employed. In addition, the large fluctuations in this
quantity disappear.Comment: 18 pages, 10 figures, references updated, comments adde
DRESS with delayed onset acute interstitial nephritis and profound refractory eosinophilia secondary to Vancomycin
<p>Abstract</p> <p>Background</p> <p>Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) is a relatively rare clinical entity; even more so in response to vancomycin.</p> <p>Methods</p> <p>Case report.</p> <p>Results</p> <p>We present a severe case of vancomycin-induced DRESS syndrome, which on presentation included only skin, hematological and mild liver involvement. The patient further developed severe acute interstitial nephritis, eosinophilic pneumonitis, central nervous system (CNS) involvement and worsening hematological abnormalities despite immediate discontinuation of vancomycin and parenteral corticosteroids. High-dose corticosteroids for a prolonged period were necessary and tapering of steroids a challenge due to rebound-eosinophilia and skin involvement.</p> <p>Conclusion</p> <p>Patients with DRESS who are relatively resistant to corticosteroids with delayed onset of certain organ involvement should be treated with a more prolonged corticosteroid tapering schedule. Vancomycin is increasingly being recognized as a culprit agent in this syndrome.</p
A note on Neuberger's double pass algorithm
We analyze Neuberger's double pass algorithm for the matrix-vector
multiplication R(H).Y (where R(H) is (n-1,n)-th degree rational polynomial of
positive definite operator H), and show that the number of floating point
operations is independent of the degree n, provided that the number of sites is
much larger than the number of iterations in the conjugate gradient. This
implies that the matrix-vector product can be approximated to very high precision with sufficiently large n,
without noticeably extra costs. Further, we show that there exists a threshold
such that the double pass is faster than the single pass for , where for most platforms.Comment: 18 pages, v3: CPU time formulas are obtained, to appear in Physical
Review
Numerical Methods for the QCD Overlap Operator: I. Sign-Function and Error Bounds
The numerical and computational aspects of the overlap formalism in lattice
quantum chromodynamics are extremely demanding due to a matrix-vector product
that involves the sign function of the hermitian Wilson matrix. In this paper
we investigate several methods to compute the product of the matrix
sign-function with a vector, in particular Lanczos based methods and partial
fraction expansion methods. Our goal is two-fold: we give realistic comparisons
between known methods together with novel approaches and we present error
bounds which allow to guarantee a given accuracy when terminating the Lanczos
method and the multishift-CG solver, applied within the partial fraction
expansion methods.Comment: 30 pages, 2 figure
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