1,467 research outputs found

    Relativistic Kinetics of Phonon Gas in Superfluids

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    The relativistic kinetic theory of the phonon gas in superfluids is developed. The technique of the derivation of macroscopic balance equations from microscopic equations of motion for individual particles is applied to an ensemble of quasi-particles. The necessary expressions are constructed in terms of a Hamilton function of a (quasi-)particle. A phonon contribution into superfluid dynamic parameters is obtained from energy-momentum balance equations for the phonon gas together with the conservation law for superfluids as a whole. Relations between dynamic flows being in agreement with results of relativistic hydrodynamic consideration are found. Based on the kinetic approach a problem of relativistic variation of the speed of sound under phonon influence at low temperature is solved.Comment: 23 pages, Revtex fil

    A METHOD OF MOTION ANALYSIS FOR SELF-PROPELLED AQUATIC CRAFTS

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    Cimematography/videography has been the method of choice for the evaluation of self-propelled aquatic craft kinematics. However, direct measurements of acceleration of this type of craft has proved to be difficult. At Dalhousie the use of acceleration data in combination with video data has facilitated the analysis of rowing and canoeing kinematics. The aim of this study is to describe the method of motion analysis currently used at Dalhousie's Sport Science Lab. Description includes a custom software program developed to divide acceleration data into individual cycles and a cubic spline to normalize the data. In addition, impulse data was calculated integrating by acceleration data using Simpson's Rule as well as the Trapezoidal Rule. A multiple low pass 2nd order Butterworth digital filter has been used successfully to smooth the acceleration data. Video data has been used to confirm that the software correctly detects these variables

    Supersymmetric AdS5 black holes

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    The first examples of supersymmetric, asymptotically AdS5, black hole solutions are presented. They form a 1-parameter family of solutions of minimal five-dimensional gauged supergravity. Their angular momentum can never vanish. The solutions are obtained by a systematic analysis of supersymmetric solutions with Killing horizons. Other new examples of such solutions are obtained. These include solutions for which the horizon is a homogeneous Nil or SL(2,R) manifold.Comment: 31 pages. v2: References and calculation of holographic stress tensor added. v3: Solutions preserve 2 supersymmetries. Our original claim that they preserve 4 supersymmetries was based on Ref. [30], which contains a mistake (the general timelike solution preserves 2, not 4, supersymmetries). Nothing else affecte

    AN ANALYSIS OF SELECTED KINEMATIC VARIABLES IN SCULL ROWING USING MACON AND HATCHET OARS

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    The Hatchet oar is now used extensively in competitive rowing because it is believed to enhance performance. There has been little research to verify this. To determine possible differences between the scull kinematics using the Hatchet and Macon oar, a 24 year old male, lightweight rower, raced 2000 m on two separate days. An 8 mm video camera and a g.analyst accelerometer collected the data. A custom software program, divided the acceleration data into individual strokes and a cubic spline standardized the stroke length. Video data confirmed that the software correctly detected stroke cycles. The acceleration data was integrated using Simpson's Rule as well as the Trapezoidal Rule. First order derivatives where determined using first and second order finite differences and impulse. Velocity data was smoothed using a multiple low pass 2nd order Butterworth digital filter. Twelve discrete measures of percentage stroke length and the value at local vertices, as well as three measures of impulse where examined using one way ANOVAs. Most of the discrete measures examined were statistically significant (

    Equation of state of cosmic strings with fermionic current-carriers

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    The relevant characteristic features, including energy per unit length and tension, of a cosmic string carrying massless fermionic currents in the framework of the Witten model in the neutral limit are derived through quantization of the spinor fields along the string. The construction of a Fock space is performed by means of a separation between longitudinal modes and the so-called transverse zero energy solutions of the Dirac equation in the vortex. As a result, quantization leads to a set of naturally defined state parameters which are the number densities of particles and anti-particles trapped in the cosmic string. It is seen that the usual one-parameter formalism for describing the macroscopic dynamics of current-carrying vortices is not sufficient in the case of fermionic carriers.Comment: 30 pages, 15 figures, uses ReVTeX, equation of state corrected, comments and references added. Accepted for publication in Phys. Rev.

    Fermionic massive modes along cosmic strings

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    The influence on cosmic string dynamics of fermionic massive bound states propagating in the vortex, and getting their mass only from coupling to the string forming Higgs field, is studied. Such massive fermionic currents are numerically found to exist for a wide range of model parameters and seen to modify drastically the usual string dynamics coming from the zero mode currents alone. In particular, by means of a quantization procedure, a new equation of state describing cosmic strings with any kind of fermionic current, massive or massless, is derived and found to involve, at least, one state parameter per trapped fermion species. This equation of state exhibits transitions from subsonic to supersonic regimes while the massive modes are filled.Comment: 27 pages, 15 figures, uses ReVTeX. Shortened version, accepted for publication in Phys. Rev.

    Quicksort, Largest Bucket, and Min-Wise Hashing with Limited Independence

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    Randomized algorithms and data structures are often analyzed under the assumption of access to a perfect source of randomness. The most fundamental metric used to measure how "random" a hash function or a random number generator is, is its independence: a sequence of random variables is said to be kk-independent if every variable is uniform and every size kk subset is independent. In this paper we consider three classic algorithms under limited independence. We provide new bounds for randomized quicksort, min-wise hashing and largest bucket size under limited independence. Our results can be summarized as follows. -Randomized quicksort. When pivot elements are computed using a 55-independent hash function, Karloff and Raghavan, J.ACM'93 showed O(nlogn)O ( n \log n) expected worst-case running time for a special version of quicksort. We improve upon this, showing that the same running time is achieved with only 44-independence. -Min-wise hashing. For a set AA, consider the probability of a particular element being mapped to the smallest hash value. It is known that 55-independence implies the optimal probability O(1/n)O (1 /n). Broder et al., STOC'98 showed that 22-independence implies it is O(1/A)O(1 / \sqrt{|A|}). We show a matching lower bound as well as new tight bounds for 33- and 44-independent hash functions. -Largest bucket. We consider the case where nn balls are distributed to nn buckets using a kk-independent hash function and analyze the largest bucket size. Alon et. al, STOC'97 showed that there exists a 22-independent hash function implying a bucket of size Ω(n1/2)\Omega ( n^{1/2}). We generalize the bound, providing a kk-independent family of functions that imply size Ω(n1/k)\Omega ( n^{1/k}).Comment: Submitted to ICALP 201

    Identification of a novel benzimidazole pyrazolone scaffold that inhibits KDM4 lysine demethylases and reduces proliferation of prostate cancer cells

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    Human lysine demethylase (KDM) enzymes (KDM1-7) constitute an emerging class of therapeutic targets, with activities that support growth and development of metastatic disease. By interacting with and co-activating the androgen receptor, the KDM4 subfamily (KDM4A-E) promotes aggressive phenotypes of prostate cancer (PCa). Knockdown of KDM4 expression or inhibition of KDM4 enzyme activity reduces the proliferation of PCa cell lines and highlights inhibition of lysine demethylation as a possible therapeutic method for PCa treatment. To address this possibility, we screened the ChemBioNet small molecule library for inhibitors of the human KDM4E isoform and identified several compounds with IC50 values in the low micromolar range. Two hits, validated as active by an orthogonal enzyme-linked immunosorbent assay, displayed moderate selectivity toward the KDM4 subfamily and exhibited antiproliferative effects in cellular models of PCa. These compounds were further characterized by their ability to maintain the transcriptionally silent histone H3 tri-methyl K9 epigenetic mark at subcytotoxic concentrations. Taken together, these efforts identify and validate a hydroxyquinoline scaffold and a novel benzimidazole pyrazolone scaffold as tractable for entry into hit-to-lead chemical optimization campaigns
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