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 $^{87}$Rb and fermionic $^{40}$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 $g$ 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 $\beta$ and the gauge-fixing parameter $\alpha$, 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 $20^4$ 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 $\alpha$ for sufficiently large $\alpha$.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