Dynamics and Scaling of Polymers in a Dilute Solution: Analytical Treatment in Two and Higher Dimensions

We consider the dynamical scaling of a single polymer chain in good solvent. In the case of two-dimensional systems, Shannon and Choy [Phys. Rev. Lett.79, 1455 (1997)] have suggested that the dynamical scaling for a dilute polymer solution breaks down. Using scaling arguments and analytical calculations based on the Zimm model, we show that the dynamical scaling of a dilute two-dimensional polymer system holds when the relevant dynamical quantities are properly extracted from finite systems. Most important, the polymerdiffusion coefficient in two dimensions scales logarithmically with system size, in excellent agreement with our extensive computer simulations. This scaling is the reason for the failure of the previous attempts to resolve the dynamical scaling of dilute two-dimensional polymer systems. In three and higher dimensions our analytic calculations are in agreement with previous results in the literature.Peer reviewe

Remarks on Screening in a Gauge-Invariant Formalism

In this paper we display a direct and physically attractive derivation of the screening contribution to the interaction potential in the Chiral Schwinger model and generalized Maxwell-Chern-Simons gauge theory. It is shown that these results emerge naturally when a correct separation between gauge-invariant and gauge degrees of freedom is made. Explicit expressions for gauge-invariant fields are found.Comment: 13 pages, 1 figure, to appear in PR

CP Violation in SUSY

Supersymmetry exhibts new sources of CP violation. We discuss the implications of these new contributions to CP violation both in the K and B physics. We show that CP violation puts severe constraints on low energy SUSY, but it represents also a promising ground to look for signals of new physics.Comment: 10 pages, 2 figures. Invited talk by A. Masiero at Ferrara 2000, CP violation physic

Reindeer lichen (Cladonia stellaris) from a Norwegian mountain region as a sustainable source of usnic acid

This is an open access article. You can find it online by following this link: http://www.ijarnp.org/index.php/ijarnp/article/view/302 The article is published under a Creative Commons Attribution 3.0 Unported licens (CC BY 3.0) : http://creativecommons.org/licenses/by/3.0/Summary. Usnic acid (UA) was extracted at 1.5-1.9 % dry weight from samples of Cladonia stellaris, a carpet-forming lichen growing abundantly in mountain areas in southeastern Norway. UA is known for its antibiotic activity as well as other bio-inhibitory functions, and is currently used in a number of formulations. Thus, the objective was to isolate and analyze UA to assess its availability. Preparations, made from lichen: acetone extraction (1:15) and from refining by recrystallization, were analyzed by one- and two-dimensional thin layer chromatography, gas chromatography, melting point, polarimetry and NMR. Only minor contaminants were observed, and both crude and refined preparations demonstrated properties (Rf-value, retention time, melting point and optical rotation) similar to the reference compound. However, polarimetry showed that C. stellaris contained the (-) enantiomer (>97 %) as opposed to Usnea-species where (+) UA is dominant. Both proton and 13C NMR confirmed structure identity to UA. Samples from four locations at different altitudes (250-650 m) around 62o north did not differ significantly (p< 0.05) in UA content. The study area has for a long time been carefully managed commercially for ornamental lichen harvesting to sustain regrowth. Thus applying the same practice, harvesting the lichen for recovering UA at high purity is highly feasible. Industrial relevance. Usnic acid has for a long time been subject to research for its biological activities, especially as a broad-sceptered antibiotic and more recently for its anti-cancerous effects in vitro. Considering the alarming spread of antibiotic resistance, UA can be a progressive alternative for those antibiotics, and to improve cancer treatment. Accumulating research data point to different biological effects of the two enantiomers. While the toxicity of the compound is still debated, UA is frequently used in health product formulations. The main commercial source Usnea barbata producing (+) UA is ubiquitous but limited to old-growth vegetation. C. stellaris remain a widespread, high-yielding producer of (-) UA in the boreal north, Fenno-scandinavia in particular. Under careful management, it can be efficiently harvested as already demonstrated in areas of Norway, and thereby become a valuable and sustainable source for large-scale production of UA

Dynamics and Scaling of 2D Polymers in a Dilute Solution

The breakdown of dynamical scaling for a dilute polymer solution in 2D has been suggested by Shannon and Choy [Phys. Rev. Lett. {\bf 79}, 1455 (1997)]. However, we show here both numerically and analytically that dynamical scaling holds when the finite-size dependence of the relevant dynamical quantities is properly taken into account. We carry out large-scale simulations in 2D for a polymer chain in a good solvent with full hydrodynamic interactions to verify dynamical scaling. This is achieved by novel mesoscopic simulation techniques

Synthetic Lethality of Chk1 Inhibition Combined with p53 and/or p21 Loss During a DNA Damage Response in Normal and Tumor Cells

Cell cycle checkpoints ensure genome integrity and are frequently compromised in human cancers. A therapeutic strategy being explored takes advantage of checkpoint defects in p53-deficient tumors in order to sensitize them to DNA-damaging agents by eliminating Chk1-mediated checkpoint responses. Using mouse models, we demonstrated that p21 is a key determinant of how cells respond to the combination of DNA damage and Chk1 inhibition (combination therapy) in normal cells as well as in tumors. Loss of p21 sensitized normal cells to the combination therapy much more than did p53 loss and the enhanced lethality was partially blocked by CDK inhibition. In addition, basal pools of p21 (p53 independent) provided p53 null cells with protection from the combination therapy. Our results uncover a novel p53-independent function for p21 in protecting cells from the lethal effects of DNA damage followed by Chk1 inhibition. As p21 levels are low in a significant fraction of colorectal tumors, they are predicted to be particularly sensitive to the combination therapy. Results reported in this study support this prediction

Spectral properties of the t-J model in the presence of hole-phonon interaction

We examine the effects of electron-phonon interaction on the dynamics of the charge carriers doped in two-dimensional (2D) Heisenberg antiferromagnet. The $t$-$J$ model Hamiltonian with a Fr\"ohlich term which couples the holes to a dispersionless (optical) phonon mode is considered for low doping concentration. The evolution of the spectral density function, the density of states, and the momentum distribution function of the holes with an increase of the hole-phonon coupling constant $g$ is studied numerically. As the coupling to a phonon mode increases the quasiparticle spectral weight decreases and a ``phonon satellite'' feature close to the quasi-particle peak becomes more pronounced. Furthermore, strong electron-phonon coupling smears the multi-magnon resonances (``string states'') in the incoherent part of the spectral function. The jump in the momentum distribution function at the Fermi surface is reduced without changing the hole pocket volume, thereby providing a numerical verification of Luttinger theorem for this strongly interacting system. The vertex corrections due to electron- phonon interaction are negligible in spite of the fact that the ratio of the phonon frequency to the effective bandwidth is not small.Comment: REVTeX, 20 pages, 9 figures, to be published in Phys. Rev. B (Nov. 1, 1996

How much time does a tunneling particle spend in the barrier region?

The question in the title may be answered by considering the outcome of a ``weak measurement'' in the sense of Aharonov et al. Various properties of the resulting time are discussed, including its close relation to the Larmor times. It is a universal description of a broad class of measurement interactions, and its physical implications are unambiguous.Comment: 5 pages; no figure

Sex Differences in Social Attention in Infants at Risk for Autism

We studied visual attention to emotional faces in 10-month-old infant siblings of children with ASD (ASD-sibs; N = 70) and a siblings of typically developing children (N = 29) using static stimuli. Contrary to our predictions, we found no evidence for atypical gaze behavior in ASD-sibs when boys and girls were analyzed together. However, a sex difference was found in ASD-sibs' visual attention to the mouth. Male ASD-sibs looked more at the mouth across emotions compared to male controls and female ASD-sibs. In contrast, female ASD-sibs looked less at the mouth compared to female controls. These findings suggest that some aspects of early emerging atypical social attention in ASD-sibs may be sex specific

A Hybrid Higgs

We construct composite Higgs models admitting a weakly coupled Seiberg dual description. We focus on the possibility that only the up-type Higgs is an elementary field, while the down-type Higgs arises as a composite hadron. The model, based on a confining SQCD theory, breaks supersymmetry and electroweak symmetry dynamically and calculably. This simultaneously solves the \mu/B_\mu problem and explains the smallness of the bottom and tau masses compared to the top mass. The proposal is then applied to a class of models where the same confining dynamics is used to generate the Standard Model flavor hierarchy by quark and lepton compositeness. This provides a unified framework for flavor, supersymmetry breaking and electroweak physics. The weakly coupled dual is used to explicitly compute the MSSM parameters in terms of a few microscopic couplings, giving interesting relations between the electroweak and soft parameters. The RG evolution down to the TeV scale is obtained and salient phenomenological predictions of this class of "single-sector" models are discussed.Comment: 56 pages, 7 figures, v2: discussion on FCNCs and references added, v3: JHEP versio