2,596 research outputs found

    Current distribution of collective thermal depinning of Josephson vortices in naturally stacked Josephson junctions

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    We investigated the thermal-depinning current (I(c)) distribution of Josephson vortices (JVs) in naturally stacked Bi(2)Sr(2)CaCu(2)O(8+delta) intrinsic Jospehson junctions in tesla-range magnetic fields and at different field tilt angles from the in-plane position. The I(c) distribution in the thermal-activation regime contains accurate information on the bias and magnetic-field dependence of the Josephson-vortex pinning potential. In a few-tesla-range magnetic field, JVs in a row in a junction, strongly coupled with each other, are pinned or depinned like a single physical entity at a single pinning center. In the best-aligned in-plane magnetic field, the edge pinning is most relevant and is insensitive to the field strength. In the presence of pancake vortices (PVs) in a slightly tilted field, however, the PV pinning deepens the JV pinning potential linearly with the number of PVs.open1122sciescopu

    The influence of clearance on friction, lubrication and squeaking in large diameter metal-on-metal hip replacements

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    Large diameter metal-on-metal bearings (MOM) are becoming increasingly popular, addressing the needs of young and more active patients. Clinical data has shown excellent short-to-mid-term results, though incidences of transient squeaking have been noted between implantation and up to 2 years post-operative. Geometric design features, such as clearance, have been significant in influencing the performance of the bearings. Sets of MOM bearings with different clearances were investigated in this study using a hip friction simulator to examine the influence of clearance on friction, lubrication and squeaking. The friction factor was found to be highest in the largest clearance bearings under all test conditions. The incidence of squeaking was also highest in the large clearance bearings, with all bearings in this group squeaking throughout the study. A very low incidence of squeaking was observed in the other two clearance groups. The measured lubricating film was found to be lowest in the large clearance bearings. This study suggests that increasing the bearing clearance results in reduced lubricant film thickness, increased friction and an increased incidence of squeaking

    Finite temperature calculations for the bulk properties of strange star using a many-body approach

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    We have considered a hot strange star matter, just after the collapse of a supernova, as a composition of strange, up and down quarks to calculate the bulk properties of this system at finite temperature with the density dependent bag constant. To parameterize the density dependent bag constant, we use our results for the lowest order constrained variational (LOCV) calculations of asymmetric nuclear matter. Our calculations for the structure properties of the strange star at different temperatures indicate that its maximum mass decreases by increasing the temperature. We have also compared our results with those of a fixed value of the bag constant. It can be seen that the density dependent bag constant leads to higher values of the maximum mass and radius for the strange star.Comment: 21 pages, 2 tables, 12 figures Astrophys. (2011) accepte

    Crystal Structures of the structure-selective nuclease Mus81-Eme1 bound to flap DNA substrates

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    The Mus81-Eme1 complex is a structure-selective endonuclease with a critical role in the resolution of recombination intermediates during DNA repair after interstrand cross-links, replication fork collapse, or double-strand breaks. To explain the molecular basis of 3 ' flap substrate recognition and cleavage mechanism by Mus81-Eme1, we determined crystal structures of human Mus81-Eme1 bound to various flap DNA substrates. Mus81-Eme1 undergoes gross substrate-induced conformational changes that reveal two key features: (i) a hydrophobic wedge of Mus81 that separates pre- and post-nick duplex DNA and (ii) a 5 ' end binding pocket that hosts the 5 ' nicked end of post-nick DNA. These features are crucial for comprehensive protein-DNA interaction, sharp bending of the 3 ' flap DNA substrate, and incision strand placement at the active site. While Mus81-Eme1 unexpectedly shares several common features with members of the 5 ' flap nuclease family, the combined structural, biochemical, and biophysical analyses explain why Mus81-Eme1 preferentially cleaves 3 ' flap DNA substrates with 5 ' nicked ends.X11119Ysciescopu

    Dynamics of a Bose-Einstein Condensate in an Anharmonic Trap

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    We present a theoretical model to describe the dynamics of Bose-Einstein condensates in anharmonic trapping potentials. To first approximation the center-of-mass motion is separated from the internal condensate dynamics and the problem is reduced to the well known scaling solutions for the Thomas-Fermi radii. We discuss the validity of this approach and analyze the model for an anharmonic waveguide geometry which was recently realized in an experiment \cite{Ott2002c}

    A comparison of friction in 28 mm conventional and 55 mm resurfacing metal-on-metal hip replacements

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    Total hip replacement has been a common, successful surgical intervention for many years. However, it has long been considered unsatisfactory for younger, more active patients due to the limited survivorship of conventional implants employing polyethylene. Larger resurfacing implants were developed to preserve bone stock and improve stability, however, early metal-on-polyethylene implants failed due to high wear. More recent developments, utilizing a metal-on-metal bearing, have encouraging short- to medium-term clinical performance. Concerns exist regarding the increased sliding distance and frictional torque generated within a larger diameter bearing. A large diameter metal-on-metal surface replacement was contrasted with a conventional 28 mm diameter implant with the same bearing material combination using a pendulum friction simulator. Studies were performed under different swing-phase load and lubrication conditions. The larger diameter bearing exhibited the lower friction factor under all test conditions, although the measured frictional torque was higher. Increasing swing-phase load was shown to cause an increase in friction factor in all tests. Increased serum concentration resulted in a reduction in friction factor for both bearings. Variation of the friction factor with the head diameter suggested that fluid-film lubrication contributed to the reduction of friction

    A comprehensive comparison of computational methods on propeller modelling of an AUV

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    The propeller of a self-propelled marine vehicle isthe key to understanding the hull-propeller interactions. Thepresence of a propeller not only provides the necessary propulsionforce, but also significantly modifies the flow field around themarine vehicle. This modification made to flow field influences thehydrodynamic loading experienced by the marine vehicle and thushas an impact on its maneuvering characteristics. There arevarious methods to represent the actions of a propeller for a rangeof marine applications within CFD. Actuator disc or virtual disc isone of the earliest and most commonly used approach. Thisapproach solves the body force generated as an equally distributedforce over a cylindrical disc while ignoring the geometry of thepropeller. Another method to evaluate the force of a propeller isdirect simulations, which replicate a propeller based on its truegeometry within CFD. This method utilizes the overset meshtechnology within CFD that enables the propeller to rotateindependently with respect to the background mesh. The presentpaper primarily used commercially available CFD softwarepackage, Star-CCM+ to investigate the accuracy and feasibility ofrepresenting the propeller of an Explorer Class AUV using theearlier mentioned methods. The solved advance ratio, and forwardvelocity from the two methods was benchmarked against openwatertrial data

    Utilise Higher Modulation Formats with Heterogeneous Mobile Networks Increases Wireless Channel Transmission

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    In this paper, a higher modulation format with a heterogeneous mobile network (small cells, Macrocells) is proposed, explored and evaluated at a wireless transmission system. As such, study the effect of utilising developed schemes of modulation like the 256 Quadrature Amplitude Modulation (QAM) on the modulation/de-modulation level of the currently applied Orthogonal Frequency Division Multiplexing (OFDM). Since the higher bit-rate of transmission is one of the important topics for the forthcoming generation of mobile, the introduced system aims to regulate the trade-off relationship between the maximum achieved bit-rate and the minimum required level of the Signal-to-Noise Ratio (SNR). Hence, involve the small cell technology as a supportive tool for the higher schemes of modulation to increase the capacity of the channel at the accepted limit of error. Consequently, the presented system that combines both the higher modulation formats and the small cells can expand the transmission coverage with a higher bit-rate yet keeping a similar level of the received power. Moreover, the system performance in terms of the maximum bit-rate and the Bit Error Rate (BER) is investigated in the presence of the Additive White Gaussian Noise (AWGN) channel model. Also, the OFDM waveform is considered herein as an accommodating environment to examine the activity of the intended modulation techniques due to its’ efficiency in using the available Bandwidth (BW). Furthermore, a MATLAB simulation is used to implement the promoted system and clarify the advantages and disadvantages of it in comparison with the currently applied 64 QAM

    Linear, Deterministic, and Order-Invariant Initialization Methods for the K-Means Clustering Algorithm

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    Over the past five decades, k-means has become the clustering algorithm of choice in many application domains primarily due to its simplicity, time/space efficiency, and invariance to the ordering of the data points. Unfortunately, the algorithm's sensitivity to the initial selection of the cluster centers remains to be its most serious drawback. Numerous initialization methods have been proposed to address this drawback. Many of these methods, however, have time complexity superlinear in the number of data points, which makes them impractical for large data sets. On the other hand, linear methods are often random and/or sensitive to the ordering of the data points. These methods are generally unreliable in that the quality of their results is unpredictable. Therefore, it is common practice to perform multiple runs of such methods and take the output of the run that produces the best results. Such a practice, however, greatly increases the computational requirements of the otherwise highly efficient k-means algorithm. In this chapter, we investigate the empirical performance of six linear, deterministic (non-random), and order-invariant k-means initialization methods on a large and diverse collection of data sets from the UCI Machine Learning Repository. The results demonstrate that two relatively unknown hierarchical initialization methods due to Su and Dy outperform the remaining four methods with respect to two objective effectiveness criteria. In addition, a recent method due to Erisoglu et al. performs surprisingly poorly.Comment: 21 pages, 2 figures, 5 tables, Partitional Clustering Algorithms (Springer, 2014). arXiv admin note: substantial text overlap with arXiv:1304.7465, arXiv:1209.196
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