3,567 research outputs found
A new approach for Delta form factors
We discuss a new approach to reducing excited state contributions from two-
and three-point correlation functions in lattice simulations. For the purposes
of this talk, we focus on the Delta(1232) resonance and discuss how this new
method reduces excited state contamination from two-point functions and mention
how this will be applied to three-point functions to extract hadronic form
factors.Comment: 4 pages, 3 figures, talk given at MENU 2010, Williambsurg, V
Quantum Pumping with Ultracold Atoms on Microchips: Fermions versus Bosons
We present a design for simulating quantum pumping of electrons in a
mesoscopic circuit with ultra-cold atoms in a micro-magnetic chip trap. We
calculate theoretical results for quantum pumping of both bosons and fermions,
identifying differences and common features, including geometric behavior and
resonance transmission. We analyze the feasibility of experiments with bosonic
Rb and fermionic K atoms with an emphasis on reliable atomic
current measurements.Comment: 4 pages; 4 figure
Order of the Chiral and Continuum Limits in Staggered Chiral Perturbation Theory
Durr and Hoelbling recently observed that the continuum and chiral limits do
not commute in the two dimensional, one flavor, Schwinger model with staggered
fermions. I point out that such lack of commutativity can also be seen in
four-dimensional staggered chiral perturbation theory (SChPT) in quenched or
partially quenched quantities constructed to be particularly sensitive to the
chiral limit. Although the physics involved in the SChPT examples is quite
different from that in the Schwinger model, neither singularity seems to be
connected to the trick of taking the nth root of the fermion determinant to
remove unwanted degrees of freedom ("tastes"). Further, I argue that the
singularities in SChPT are absent in most commonly-computed quantities in the
unquenched (full) QCD case and do not imply any unexpected systematic errors in
recent MILC calculations with staggered fermions.Comment: 14 pages, 1 figure. v3: Spurious symbol, introduced by conflicting
tex macros, removed. Clarification of discussion in several place
Bacterially Grown Cellulose/Graphene Oxide Composites Infused with γ-Poly (Glutamic Acid) as Biodegradable Structural Materials with Enhanced Toughness
Bioinspired bacterial cellulose (BC) composites are next-generation renewable materials that exhibit promising industrial applications. However, large-scale production of inorganic/organic BC composites by in situ fermentation remains difficult. The methods based on BC mechanical disintegration impair the mechanical property of dried BC films, while the static in situ fermentation methods fail to incorporate inorganic particles within the BC network because of the limited diffusion ability. Furthermore, the addition of other components in the fermentation medium significantly interferes with the production of BC. Here, a tough BC composite with a layered structure reminiscent of the tough materials found in nature (e.g., nacre, dentin, and bone) is prepared using a semistatic in situ fermentation method. The bacterially produced biopolymer γ-poly(glutamic acid) (PGA), together with graphene oxide (GO), is introduced into the BC fermentation medium. The resulting dried BC-GO-PGA composite film shows high toughness (36 MJ m-3), which makes it one of the toughest BC composite film reported. In traditional in situ fermentation methods, the addition of a second component significantly reduces the wet thickness of the final composites. However, in this report, we show that addition of both PGA and GO to the fermentation medium shows a synergistic effect in increasing the wet thickness of the final BC composites. By gently agitating the solution, GO particles get entrapped into the BC network, as the formed pellicles can move below the liquid level and the GO particles suspended in the liquid can be entrapped into the BC network. Compared to other methods, this method achieves high toughness while using a mild and easily scalable fabrication procedure. These bacterially produced composites could be employed in the next generation of biodegradable structural high-performance materials, construction materials, and tissue engineering scaffolds (tendon, ligament, and skin) that require high toughness. BN/Marie-Eve Aubin-Tam La
Lattice Gauge Fixing as Quenching and the Violation of Spectral Positivity
Lattice Landau gauge and other related lattice gauge fixing schemes are known
to violate spectral positivity. The most direct sign of the violation is the
rise of the effective mass as a function of distance. The origin of this
phenomenon lies in the quenched character of the auxiliary field used to
implement lattice gauge fixing, and is similar to quenched QCD in this respect.
This is best studied using the PJLZ formalism, leading to a class of covariant
gauges similar to the one-parameter class of covariant gauges commonly used in
continuum gauge theories. Soluble models are used to illustrate the origin of
the violation of spectral positivity. The phase diagram of the lattice theory,
as a function of the gauge coupling and the gauge-fixing parameter
, is similar to that of the unquenched theory, a Higgs model of a type
first studied by Fradkin and Shenker. The gluon propagator is interpreted as
yielding bound states in the confined phase, and a mixture of fundamental
particles in the Higgs phase, but lattice simulation shows the two phases are
connected. Gauge field propagators from the simulation of an SU(2) lattice
gauge theory on a lattice are well described by a quenched mass-mixing
model. The mass of the lightest state, which we interpret as the gluon mass,
appears to be independent of for sufficiently large .Comment: 28 pages, 14 figures, RevTeX
Approach of a class of discontinuous dynamical systems of fractional order: existence of the solutions
In this letter we are concerned with the possibility to approach the
existence of solutions to a class of discontinuous dynamical systems of
fractional order. In this purpose, the underlying initial value problem is
transformed into a fractional set-valued problem. Next, the Cellina's Theorem
is applied leading to a single-valued continuous initial value problem of
fractional order. The existence of solutions is assured by a P\'{e}ano like
theorem for ordinary differential equations of fractional order.Comment: accepted IJBC, 5 pages, 1 figur
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