BRST Structures and Symplectic Geometry on a Class of Supermanifolds

By investigating the symplectic geometry and geometric quantization on a class of supermanifolds, we exhibit BRST structures for a certain kind of algebras. We discuss the undeformed and q-deformed cases in the classical as well as in the quantum cases.Comment: 14 pages, Late

Computer simulation of multiple pilots flying a modern high performance helicopter

A computer simulation of a human response pilot mechanism within the flight control loop of a high-performance modern helicopter is presented. A human response mechanism, implemented by a low order, linear transfer function, is used in a decoupled single variable configuration that exploits the dominant vehicle characteristics by associating cockpit controls and instrumentation with specific vehicle dynamics. Low order helicopter models obtained from evaluations of the time and frequency domain responses of a nonlinear simulation model, provided by NASA Lewis Research Center, are presented and considered in the discussion of the pilot development. Pilot responses and reactions to test maneuvers are presented and discussed. Higher level implementation, using the pilot mechanisms, are discussed and considered for their use in a comprehensive control structure

A complex environment around Cir X-1

We present the results of an archival 54 ks long Chandra observation of the peculiar source Cir X--1 during the phase passage 0.223-0.261. A comparative analysis of X-ray spectra, selected at different flux levels of the source, allows us to distinguish between a very hard state, at a low countrate, and a brighter, softer, highly absorbed spectrum during episodes of flaring activity, when the unabsorbed source luminosity is about three times the value in the hard state. The spectrum of the hard state clearly shows emission lines of highly ionized elements, while, during the flaring state, the spectrum also shows strong resonant absorption lines. The most intense and interesting feature in this latter state is present in the Fe K alpha region: a very broadened absorption line at energies ~ 6.5 keV that could result from a smeared blending of resonant absorption lines of moderately ionized iron ions (Fe XX - Fe XXIV). We also observe strong resonant absorption lines of Fe XXV and Fe XXVI, together with a smeared absorption edge above 7 keV. We argue that the emitting region during the quiescent/hard state is constituted of a purely photo-ionized medium, possibly present above an accretion disk, or of a photo-ionized plasma present in a beamed outflow. During the flaring states the source undergoes enhanced turbulent accretion that modifies both the accretion geometry and the optical depth of the gas surrounding the primary X-ray source.Comment: Accepted for publication in Ap

Constraining Alternate Models of Black Holes: Type I X-ray Bursts on Accreting Fermion-Fermion and Boson-Fermion Stars

The existence of black holes remains open to doubt until other conceivable options are excluded. With this motivation, we consider a model of a compact star in which most of the mass consists of dark particles of some kind, and a small fraction of the mass is in the form of ordinary nucleonic gas. The gas does not interact with the dark matter other than via gravity, but collects at the center as a separate fermionic fluid component. Depending on whether the dark mass is made of fermions or bosons, the objects may be called fermion-fermion stars or boson-fermion stars, respectively. For appropriate choices of the mass of the dark matter particles, these objects are viable models of black hole candidates in X-ray binaries. We consider models with a dark mass of 10 solar masses and a range of gas mass from 10^{-6} to nearly one solar mass, and analyse the bursting properties of the models when they accrete gas. We show that all the models would experience thermonuclear Type I X-ray bursts at appropriate mass accretion rates. Since no Type I bursts have been reported from black hole candidates, the models are ruled out. The case for identifying black hole candidates in X-ray binaries as true black holes is thus strengthened.Comment: 29 pages, 7 figures, to appear in The Astrophysical Journa

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

On the existence of internal modes of sine-Gordon kinks

We study whether or not sine-Gordon kinks exhibit internal modes or ``quasimodes.'' By considering the response of the kinks to ac forces and initial distortions, we show that neither intrinsic internal modes nor ``quasimodes'' exist in contrast to previous reports. However, we do identify a different kind of internal mode bifurcating from the bottom edge of the phonon band which arises from the discretization of the system in the numerical simulations, thus confirming recent predictions.Comment: 4 pages, 2 figures, REVTeX, to appear as a Rapid Communication in Phys Rev E (July 1st

Detecting Singleton Review Spammers Using Semantic Similarity

Online reviews have increasingly become a very important resource for consumers when making purchases. Though it is becoming more and more difficult for people to make well-informed buying decisions without being deceived by fake reviews. Prior works on the opinion spam problem mostly considered classifying fake reviews using behavioral user patterns. They focused on prolific users who write more than a couple of reviews, discarding one-time reviewers. The number of singleton reviewers however is expected to be high for many review websites. While behavioral patterns are effective when dealing with elite users, for one-time reviewers, the review text needs to be exploited. In this paper we tackle the problem of detecting fake reviews written by the same person using multiple names, posting each review under a different name. We propose two methods to detect similar reviews and show the results generally outperform the vectorial similarity measures used in prior works. The first method extends the semantic similarity between words to the reviews level. The second method is based on topic modeling and exploits the similarity of the reviews topic distributions using two models: bag-of-words and bag-of-opinion-phrases. The experiments were conducted on reviews from three different datasets: Yelp (57K reviews), Trustpilot (9K reviews) and Ott dataset (800 reviews).Comment: 6 pages, WWW 201

Dynamic disorder in receptor-ligand forced dissociation experiments

Recently experiments showed that some biological noncovalent bonds increase their lifetimes when they are stretched by an external force, and their lifetimes will decrease when the force increases further. Several specific quantitative models have been proposed to explain the intriguing transitions from the "catch-bond" to the "slip-bond". Different from the previous efforts, in this work we propose that the dynamic disorder of the force-dependent dissociation rate can account for the counterintuitive behaviors of the bonds. A Gaussian stochastic rate model is used to quantitatively describe the transitions observed recently in the single bond P-selctin glycoprotein ligand 1(PSGL-1)$-$P-selectin force rupture experiment [Marshall, {\it et al.}, (2003) Nature {\bf 423}, 190-193]. Our model agrees well to the experimental data. We conclude that the catch bonds could arise from the stronger positive correlation between the height of the intrinsic energy barrier and the distance from the bound state to the barrier; classical pathway scenario or {\it a priori} catch bond assumption is not essential.Comment: 4 pages, 2 figure

Hadronic Annihilation Decay Rates of P-wave Heavy Quarkonia with Both Relativistic and QCD Radiative Corrections

Hadronic annihilation decay rates of P-wave heavy quarkonia are given to next-to-leading order in both $\alpha_s$ and $v^2$. They include ten nonperturbative parameters, which can be rigorously defined as the matrix elements of color-singlet and color-octet operators in NRQCD. We expect these papameters will be determined from lattice calculations in future.Comment: 5 Pages RevTex. The paper is withdraw