Suppression of weak-localization (and enhancement of noise) by tunnelling in semiclassical chaotic transport

We add simple tunnelling effects and ray-splitting into the recent trajectory-based semiclassical theory of quantum chaotic transport. We use this to derive the weak-localization correction to conductance and the shot-noise for a quantum chaotic cavity (billiard) coupled to $n$ leads via tunnel-barriers. We derive results for arbitrary tunnelling rates and arbitrary (positive) Ehrenfest time, $\tau_{\rm E}$. For all Ehrenfest times, we show that the shot-noise is enhanced by the tunnelling, while the weak-localization is suppressed. In the opaque barrier limit (small tunnelling rates with large lead widths, such that Drude conductance remains finite), the weak-localization goes to zero linearly with the tunnelling rate, while the Fano factor of the shot-noise remains finite but becomes independent of the Ehrenfest time. The crossover from RMT behaviour ($\tau_{\rm E}=0$) to classical behaviour ($\tau_{\rm E}=\infty$) goes exponentially with the ratio of the Ehrenfest time to the paired-paths survival time. The paired-paths survival time varies between the dwell time (in the transparent barrier limit) and half the dwell time (in the opaque barrier limit). Finally our method enables us to see the physical origin of the suppression of weak-localization; it is due to the fact that tunnel-barriers ``smear'' the coherent-backscattering peak over reflection and transmission modes.Comment: 20 pages (version3: fixed error in sect. VC - results unchanged) - Contents: Tunnelling in semiclassics (3pages), Weak-localization (5pages), Shot-noise (5pages

How do metalloenzymes propagate and control chemical reactions?

Enzymes control and propagate a dizzying array of chemical reactions, including radical reactions and reactions cleaving carbon-carbon bonds. Metalloenzymes, which contain a metal cofactor, are particularly adept at propagating these reactions. This thesis focuses on several metalloenzymes; each an example of a different unique reaction control strategy. Both experimental and computational methodologies have been employed in order to identify specific residues or features which contribute to each enzyme\u27s ability to control the reaction. Emphasis is made on special properties of the metal Manganese. Controlling residues include not only first shell or active site residues, but also residues more distant from the active-site. Further, manipulation of such residues can be used to alter reactivity at non -active-sites, or to alter the apparent electrostatics of the protein (in the case of substitution of hydrogen with fluorine). Electron Paramagnetic Resonance (EPR) and other forms of magnetic spectroscopy can be used to evaluate subtle differences imposed by substitution for controlling residues to a metal center, which gives further insight into the electronic contributions of given residues, as well as the electronic properties of metal cofactors. In summary, the catalysis by Mn-dependent and other metal-dependent metalloenzymes can be investigated through multiple kinetic and spectroscopic avenues, unveiling suprising and novel themes in enzymatic catalysis, such as mechano-chemical switches and super long-distance metallo-interactions

Creating a Tobacco-Free Residential Substance Abuse Treatment Facility: A Toolkit for Designing an Effective Intervention

Individuals with a substance addiction and/or mental illness use tobacco at rates much higher than the general population. Approximately 21% of the U.S. population smokes, yet 40%-80% of substance abuse and mental health patients smoke and consume more than 44% of all the cigarettes sold in the United States each year. As a result, these individuals experience increased tobacco related morbidity and mortality. Tobacco use is common and accepted within this population, and has become a norm even within treatment programs. Only 30%-40% of treatment facilities offer smoking cessation resources, and many organizations are hesitant to address cessation or to adopt a tobacco-free campus policy. This toolkit addresses the unique barriers and challenges that a residential substance addiction facility will face when adopting a tobacco-free policy. A tobacco-free campus policy protects all individuals from dangerous secondhand smoke and promotes the health and recovery of clients from all addictions, including nicotine. This toolkit provides step-by-step information and resources to allow a facility to become tobacco-free and implement a full smoking cessation program over a six month time period. This project helps fill a need for specific resources related to concurrent smoking cessation and substance abuse/mental health treatment. This resource will be made available to residential substance abuse facilities in Georgia and will be provided to the Substance Abuse and Mental Health Service Administration’s Smoking Cessation Leadership Center

FTC Regulation of Endorsements in Advertising: In the Consumer\u27s Behalf?

The Federal Trade Commission, as recently as 1980, has issued Guides designed to prevent deception of consumers due to misleading product endorsement advertising by celebrities and others. The new Guides indicate that the FTC intends to continue its recent trend offending advertisers and even endorsers liable for deceptive endorsement practices. However, a critical analysis of the Guides, in light of marketplace realities and consumer needs, raises serious question as to whether they are likely to promote accurate endorsement advertising. This comment will explore pre-1980 regulations and trace the progression of controls through the advent of the FTC Guides. The Guides will be analyzed in light of past and present case law and alternative controls will be surveyed. Recommendations concerning the Guides will be suggested. The most important of these is a change from the present narrow and restrictive interpretive rules, which lack the force of law, to more general, substantive rules, which could be strictly enforced. The prospects for their implementation, however, appear dismal due to inertia within the FTC and federal budgetary reductions proposed by the current Administration

Allosteric Activation of the Par-6 PDZ Via a Partial Unfolding Transition

Proteins exist in a delicate balance between the native and unfolded states, where thermodynamic stability may be sacrificed to attain the flexibility required for efficient catalysis, binding, or allosteric control. Partition-defective 6 (Par-6) regulates the Par polarity complex by transmitting a GTPase signal through the Cdc42/Rac interaction binding PSD-95/Dlg/ZO-1 (CRIB-PDZ) module that alters PDZ ligand binding. Allosteric activation of the PDZ is achieved by local rearrangement of the L164 and K165 side chains to stabilize the interdomain CRIB:PDZ interface and reposition a conserved element of the ligand binding pocket. However, microsecond to millisecond dynamics measurements revealed that L164/K165 exchange requires a larger rearrangement than expected. The margin of thermodynamic stability for the PDZ domain is modest (∼3 kcal/mol) and further reduced by transient interactions with the disordered CRIB domain. Measurements of local structural stability revealed that tertiary contacts within the PDZ are disrupted by a partial unfolding transition that enables interconversion of the L/K switch. The unexpected participation of partial PDZ unfolding in the allosteric mechanism of Par-6 suggests that native-state unfolding may be essential for the function of other marginally stable proteins

Classification of Stellar Spectra with LLE

We investigate the use of dimensionality reduction techniques for the classification of stellar spectra selected from the SDSS. Using local linear embedding (LLE), a technique that preserves the local (and possibly non-linear) structure within high dimensional data sets, we show that the majority of stellar spectra can be represented as a one dimensional sequence within a three dimensional space. The position along this sequence is highly correlated with spectral temperature. Deviations from this "stellar locus" are indicative of spectra with strong emission lines (including misclassified galaxies) or broad absorption lines (e.g. Carbon stars). Based on this analysis, we propose a hierarchical classification scheme using LLE that progressively identifies and classifies stellar spectra in a manner that requires no feature extraction and that can reproduce the classic MK classifications to an accuracy of one type.Comment: 15 pages, 13 figures; accepted for publication in The Astronomical Journa

Visuomotor Crowding: The Resolution of Grasping in Cluttered Scenes

Reaching toward a cup of coffee while reading the newspaper becomes exceedingly difficult when other objects are nearby. Although much is known about the precision of visual perception in cluttered scenes, relatively little is understood about acting within these environments – the spatial resolution of visuomotor behavior. When the number and density of objects overwhelm visual processing, crowding results, which serves as a bottleneck for object recognition. Despite crowding, featural information of the ensemble persists, thereby supporting texture perception. While texture is beneficial for visual perception, it is relatively uninformative for guiding the metrics of grasping. Therefore, it would be adaptive if the visual and visuomotor systems utilized the clutter differently. Using an orientation task, we measured the effect of crowding on vision and visually guided grasping and found that the density of clutter similarly limited discrimination performance. However, while vision integrates the surround to compute a texture, action discounts this global information. We propose that this dissociation reflects an optimal use of information by each system

Scout motor performance analysis and prediction study /PAPS/

Scout motor performance analysis and predictio