Logarithmic oscillators: ideal Hamiltonian thermostats

A logarithmic oscillator (in short, log-oscillator) behaves like an ideal thermostat because of its infinite heat capacity: when it weakly couples to another system, time averages of the system observables agree with ensemble averages from a Gibbs distribution with a temperature T that is given by the strength of the logarithmic potential. The resulting equations of motion are Hamiltonian and may be implemented not only in a computer but also with real-world experiments, e.g., with cold atoms.Comment: 5 pages, 3 figures. v4: version accepted in Phys. Rev. Let

Spacetime Properties of ZZ D-Branes

We study the tachyon and the RR field sourced by the $(m,n)$ ZZ D-branes in type 0 theories using three methods. We first use the mini-superspace approximation of the closed string wave functions of the tachyon and the RR scalar to probe these fields. These wave functions are then extended beyond the mini-superspace approximation using mild assumptions which are motivated by the properties of the corresponding wave functions in the mini-superspace limit. These are then used to probe the tachyon and the RR field sourced. Finally we study the space time fields sourced by the $(m,n)$ ZZ D-branes using the FZZT brane as a probe. In all the three methods we find that the tension of the $(m,n)$ ZZ brane is $mn$ times the tension of the $(1,1)$ ZZ brane. The RR charge of these branes is non-zero only for the case of both $m$ and $n$ odd, in which case it is identical to the charge of the $(1,1)$ brane. As a consistency check we also verify that the space time fields sourced by the branes satisfy the corresponding equations of motion.Comment: 32 pages, 4 figures. Clarifications on the principal characterization of ZZ branes added. Reference adde

Optical Phonons in Carbon Nanotubes: Kohn Anomalies, Peierls Distortions and Dynamic Effects

We present a detailed study of the vibrational properties of Single Wall Carbon Nanotubes (SWNTs). The phonon dispersions of SWNTs are strongly shaped by the effects of electron-phonon coupling. We analyze the separate contributions of curvature and confinement. Confinement plays a major role in modifying SWNT phonons and is often more relevant than curvature. Due to their one-dimensional character, metallic tubes are expected to undergo Peierls distortions (PD) at T=0K. At finite temperature, PD are no longer present, but phonons with atomic displacements similar to those of the PD are affected by strong Kohn anomalies (KA). We investigate by Density Functional Theory (DFT) KA and PD in metallic SWNTs with diameters up to 3 nm, in the electronic temperature range from 4K to 3000 K. We then derive a set of simple formulas accounting for all the DFT results. Finally, we prove that the static approach, commonly used for the evaluation of phonon frequencies in solids, fails because of the SWNTs reduced dimensionality. The correct description of KA in metallic SWNTs can be obtained only by using a dynamical approach, beyond the adiabatic Born-Oppenheimer approximation, by taking into account non-adiabatic contributions. Dynamic effects induce significant changes in the occurrence and shape of Kohn anomalies. We show that the SWNT Raman G peak can only be interpreted considering the combined dynamic, curvature and confinement effects. We assign the G+ and G- peaks of metallic SWNTs to TO (circumferential) and LO (axial) modes, respectively, the opposite of semiconducting SWNTs.Comment: 24 pages, 21 figures, submitted to Phys. Rev.

Numerical implementation of the exact dynamics of free rigid bodies

In this paper the exact analytical solution of the motion of a rigid body with arbitrary mass distribution is derived in the absence of forces or torques. The resulting expressions are cast into a form where the dependence of the motion on initial conditions is explicit and the equations governing the orientation of the body involve only real numbers. Based on these results, an efficient method to calculate the location and orientation of the rigid body at arbitrary times is presented. This implementation can be used to verify the accuracy of numerical integration schemes for rigid bodies, to serve as a building block for event-driven discontinuous molecular dynamics simulations of general rigid bodies, and for constructing symplectic integrators for rigid body dynamics.Comment: Shortened paper with updated references, 28 pages, 3 figure

Quantitative Analysis of LISA Pathfinder Test Mass Noise

In this paper we discuss two main problems associated with the analysis of the data from LISA Pathfinder (LPF): i) Excess noise detection and ii) Noise parameter identification. The mission is focused on the low frequency region ([0.1; 10] mHz) of the available signal spectrum. In such a region the signal is dominated by the force noise acting on test masses. Noise analysis is expected to deal with a limited amount of non-Gaussian data, since the spectrum statistics will be far from Gaussian and the lowest available frequency is limited by the data length. In this paper we analyze the details of the expected statistics for spectral data and develop two suitable excess noise estimators. One is based on the statistical properties of the integrated spectrum, the other is based on Kolmogorov-Smirnov test. The sensitivity of the estimators is discussed theoretically for independent data, then the algorithms are tested on LPF synthetic data. The test on realistic LPF data allows the effect of spectral data correlations on the efficiency of the different noise excess estimators to be highlighted. It also reveals the versatility of the Kolmogorov-Smirnov approach, which can be adapted to provide reasonable results on correlated data from a modified version of the standard equations for the inversion of the test statistic. Closely related to excess noise detection, the problem of noise parameter identification in non-Gaussian data is approached in two ways. One procedure is based on maximum likelihood estimator and another is based on the Kolmogorov-Smirnov goodness of fit estimator. Both approaches provide unbiased and accurate results for noise parameter estimation and demonstrate superior performance with respect to standard weighted least-squares and Huber's norm.Comment: Accepted for publication in Phys Rev

East Bay Coalition for the Homeless: Branding Study and Marketing Strategy

There are a number of potential positioning strategies. The two which make the most sense for the EBCH are to “position the EBCH away from others in the category” and to “position the EBCH as unique.” These strategies have the advantage of setting the EBCH apart from the other organizations that address homelessness. Occupying its own “position” in the minds of potential and current donors is not only an effective communications/marketing strategy but also a less costly one because it avoids head-to-head competition and comparisons

The Sensory and Perceptual Scaffolding of Absorption, Inner Speech, and Self in Psychosis

This study examines the interconnectedness between absorption, inner speech, self, and psychopathology. Absorption involves an intense focus and immersion in mental imagery, sensory/perceptual stimuli, or vivid imagination that involves decreased self-awareness and alterations in consciousness. In psychosis, the dissolution and permeability in the demarcation between self and one's sensory experiences and perceptions, and also between self-other and/or inter-object boundaries alter one's sense of self. Thus, as the individual integrates these changes new "meaning making" or understanding evolves as part of an ongoing inner dialogue and dialogue with others. This study consisted of 117 participants: 81 participants with psychosis and 36 controls. We first conducted a bivariate correlation to elucidate the relationship between absorption and inner speech. We next conducted hierarchical multiple regressions to examine the effect of absorption and inner speech to predict psychopathology. Lastly, we conducted a network analysis and applied extended Bayesian Information Criterion to select the best model. We showed that in both the control and psychosis group dialogic and emotional/motivational types of inner speech were strongly associated with absorption subscales, apart from the aesthetic subscale in the control group which was not significant, while in psychosis, condensed inner speech was uniquely associated with increased imaginative involvement. In psychosis, we also demonstrated that altered consciousness, dialogic, and emotional/motivational inner speech all predicted positive symptoms. In terms of network associations, imaginative involvement was the most central, influential, and most highly predictive node in the model from which all other nodes related to inner speech and psychopathology are connected. This study shows a strong interrelatedness between absorption, inner speech and psychosis thus identifying potentially fertile ground for future research and directions, particularly in the exploration into the underlying construct of imaginative involvement in psychotic symptoms

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

First two years of TanDEM-X mission: interferometric performance overview

The TerraSAR-X add-on for Digital Elevation Measurement (TanDEM-X) mission comprises two nearly identical satellites: TerraSAR-X (TSX, launched in June 2007), and TanDEM-X (TDX, launched in June 2010), which form an innovative and flexible single-pass radar interferometer. The primary objective of the mission is to generate a worldwide and consistent digital elevation model (DEM) with an unprecedented accuracy. After a calibration phase of the TDX satellite, which was performed during the first 3 months after its launch, the two satellites were brought into close formation to begin the bistatic commissioning phase. Then, in December 2010, TanDEM-X started the operational global DEM acquisition in bistatic configuration. During the last 2 years, dedicated analyses on test acquisitions as well as persistent monitoring of the interferometric performance have been carried out, which are the subject of this paper. Key quantities in estimating interferometric performance such as coherence, relative height error, and phase-unwrapping indicators are investigated, showing the outstanding capabilities of TanDEM-X. Then, the main focus is shifted to those critical areas which, for various reasons, have shown unsatisfactory data quality and therefore must be reacquired with optimized imaging geometries in order to fulfill the DEM accuracy requirements. Promising results have been obtained so far, and future strategies to handle the critical data are discussed. This paper will present an overview of the interferometric performance of TanDEM-X, based on investigations performed in the first 2 years of mission operation, and will include results from the bistatic commissioning phase until the end of the first global DEM acquisition