Reduced Density Matrix Approach to Phononic Dissipation in Friction

Understanding mechanisms for energy dissipation from nanoparticles in contact with large samples is a central problem in describing friction microscopically. Calculation of the reduced density matrix appears to be the most suitable metho to study such systems that are coupled to a large environment. In this paper the time evolution of the reduced density matrix has been evaluated for an arbitrary system coupled to a heat reservoir. The formalism is then applied to study the vibrational relaxation following the stick-slip motion of a small adsorbate on a surface. The frequency dependence of the relaxation time is also determined.Comment: 16 pages, 3 figures (included), revte

The pion wave function in covariant light-front dynamics

The structure of the pion wave function in the relativistic constituent quark model is investigated in the explicitly covariant formulation of light-front dynamics. We calculate the two relativistic components of the pion wave function in a simple one-gluon exchange model and investigate various physical observables: decay constant, charge radius, electromagnetic and transition form factors. We discuss the influence of the full relativistic structure of the pion wave function for an overall good description of all these observables, including both low and high momentum scales.Comment: 12 pages, 10 figure

QCD Factorization in BB Decays into ρπ\rho \pi

Based on the QCD factorization approach we analyse the branching ratios for the channel $B \to \rho \pi$. From the comparisons with experimental data provided by CLEO, BELLE and BABAR we constrain the form factor $F^{B \to \pi}(m_{\rho}^{2})$ and propose boundaries for this form factor depending on the CKM matrix element parameters $\rho$ and $\eta$.Comment: 11 pages, 9 figures. Talk presented at Fourth Tropical Workshop, Cairns, Australia, 9--13 June 2003. Proceedings to be published by AI

Introduction: Urban revolutions in the age of global urbanism

This special issue, papers presented at an Urban Studies Foundation-funded conference in Jakarta (March 2011), examines the current ‘urban century’ in terms of three revolutions. Revolutions from above index the logics and norms of mainstream global urbanism, particularly the form they have taken as policymakers work with municipal officials worldwide to organise urban development around neoliberal norms. Revolutions from below refer to the multifaceted contestations of global urbanism that take place in and around cities, ranging from urban street demonstrations and occupations (such as those riveting the world in early 2011 when these papers were written) to the quotidian actions of those pursuing politics and livelihoods that subvert the norms of mainstream global urbanism. It also highlights conceptual revolutions, referencing the ongoing challenge of reconceptualising urban theory from the South – not simply as a hemispheric location or geopolitical category but an epistemological stance, staged from many different locations but always fraught with the differentials of power and the weight of historical geographies. Drawing on the insights of scholars writing from, and not just about, such locations, a further iteration in this ‘southern’ turn of urban theorising is proposed. This spatio-temporal conjunctural approach emphasises how the specificity of cities – their existence as entities that are at once singular and universal – emerges from spatio-temporal dynamics, connectivities and horizontal and vertical relations. Practically, such scholarship entails taking the field seriously through collaborative work that is multi-sited, engages people along the spectrum of academics and activists, and is presented before and scrutinised by multiple publics

Alien plant species in Eastern Wisconsin Natural Areas

An expanded study of non-native plant species in eastern Wisconsin Natural Areas resulted in a total of 64 exotics being found. The most abundant were Rhamnus cathartica, Taraxacum officinale, and Berberis thunbergii. Sites suffering the greatest degrees of invasion were the oak openings, while the more mesic areas appeared relatively resistant

Dynamic NMR Study of Bond Rotational Activation Parameters in Micelles

The behavior of surfactants in solution has been and still is of scientific, technological, and industrial interest. The micelle forming compounds sodium N( octyloxycarbonyl)sarcosinate (NaOcSarc), and sodium N-(decyloxycarbonyl)sarcosinate (NaDecSarc) show in aqueous solution two lH NMR N-methyl peaks arising from a possible cis- or trans-conformation. The relative population of the N-methyl peaks depends mostly on the concentration of surfactant indicating micelle formation. Upon heating the two peaks start to coalesce and finally appear as one single peak . The temperature range in which this phenomenon occurs is from 25°C to 65°C. The primary interest of this study was to determine the activation parameters of rotation about the carbonyl-nitrogen (C-N) bond. Dynamic nuclear magnetic resonance spectroscopy was employed to approach this problem. A complete bandshape analysis was performed in order to calculate the free energy (G++), enthalpy (H++), and entropy (S++) of activation. The effect of a different counter ion (Li+) and sodium chloride salt addition were tested for possible changes of the activation parameters. Studies in nonaqeous solvents were conducted with the free acid form of the mentioned carbarnates. Dimethylsulfoxide and chloroform were chosen as organic solvents for these particular experiments. The critical micellar concentrations of all surfactants were determined, and the assignment of the individual N-methyl peaks to the correspondend conformation could be unambiguously shown by a two dimensional NMR experiment. The cmc\u27s show strong salt dependence. The effect of a lithium as an alternative counter ion has a less drastic effect. Micellization seems not to occur in the free acid cases. Interestingly, the surfactants show stronger salt dependence than micellization dependence upon the activation parameters, indicating that solvent exposure occurs at the C-N partial double bond and considerable deformation of the ideal spherical shape

A sub-product construction of Poincare-Einstein metrics

Given any two Einstein (pseudo-)metrics, with scalar curvatures suitably related, we give an explicit construction of a Poincar\'e-Einstein (pseudo-)metric with conformal infinity the conformal class of the product of the initial metrics. We show that these metrics are equivalent to ambient metrics for the given conformal structure. The ambient metrics have holonomy that agrees with the conformal holonomy. In the generic case the ambient metric arises directly as a product of the metric cones over the original Einstein spaces. In general the conformal infinity of the Poincare metrics we construct is not Einstein, and so this describes a class of non-conformally Einstein metrics for which the (Fefferman-Graham) obstruction tensor vanishes.Comment: 23 pages Minor correction to section 5. References update