18,556 research outputs found
Static Potentials and the Magnetic Component of QCD Plasma near
Static quark-anti-quark potential encodes important information on the
chromodynamical interaction between color charges, and recent lattice results
show its very nontrivial behavior near the deconfinement temperature . In
this paper we study such potential in the framework of the ``magnetic
scenario'' for the near Tc QCD plasma, and particularly focus on the linear
part (as quantified by its slope, the tension) in the potential as well as the
strong splitting between the free energy and internal energy. By using an
analytic ``ellipsoidal bag'' model, we will quantitatively relate the free
energy tension to the magnetic condensate density and relate the internal
energy tension to the thermal monopole density. By converting the lattice
results for static potential into density for thermal monopoles we find the
density to be very large around Tc and indicate at quantum coherence, in good
agreement with direct lattice calculation of such density. A few important
consequences for heavy ion collisions phenomenology will also be discussed.Comment: 10 pages, 6 figure
Low-Complexity PAPR Minimization for Symbol Level Precoded Multi-User MISO-OFDM System
This paper proposes a method exploiting constructive interference (CI) to reduce the transmit signal’s peak-to-average power ratio (PAPR), while keeping the total transmission power as low as possible. An optimization problem that jointly performs power minimization and PAPR reduction is formulated, which is however difficult to solve directly due to the non-convex PAPR constraint. To obtain a feasible solution in low complexity, by using the vectorization method and introducing a regularization factor, we relax the PAPR constraint. The original optimization problem is transformed into a convex problem that can be solved with an improved fast iterative shrinkage-thresholding algorithm (FISTA). Numerical results are presented to show 1dB savings in terms of transmission power and 52% savings in terms of PAPR compared with state-of-the-art PAPR minimization techniques
The influence of structural defects on intra-granular critical currents of bulk MgB2
Bulk MgB2 samples were prepared under different synthesis conditions and
analyzed by scanning and transmission electron microscopy. The critical current
densities were determined from the magnetization versus magnetic field curves
of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow
cooling process, the oxygen dissolved in bulk MgB2 at high synthesis
temperatures can segregate and form nanometer-sized coherent precipitates of
Mg(B,O)2 in the MgB2 matrix. Magnetization measurements indicate that these
precipitates act as effective flux pinning centers and therefore significantly
improve the intra-grain critical current density and its field dependence.Comment: 4 pages, 4 figures, to be published in IEE Transactions in Applied
Superconductivit
Effect of Light Fermions on the Confinement Transition in QCD-like Theories
Dependence of the confinement transition parameters on the fermion content
provides information on the mechanism of confinement. Recent progress in
lattice gauge theories has allowed to study it for light flavor number and found this transition to shift toward significantly stronger
coupling. We propose an explanation for that: light fermions can occupy the
chromo-magnetic monopoles, via zero modes, making them "distinguishable" and
unsuitable for Bose-Einstein Condensation. Such dilution of unoccuplied
monopoles is compensated by stronger coupling that makes them lighter and more
numerous. We also suggest that flavor-carrying quark-monopole objects account
for the density beyond quark Fermi sphere seen in cold dense phase of
lattice QCD.Comment: 4 pages, 1 figure; few references added; close to the final published
versio
Microwave performance of high-density bulk MgB2
We have performed microwave measurements on superconducting
hot-isostatically- pressed (HIPed) bulk MgB2 using a parallel-plate resonator
technique. The high density and strength of the HIPed material allowed
preparation of samples with mirror-like surfaces for microwave measurements.
The microwave surface resistance decreased by about 40% at 20 K when the
root-mean-square surface roughness was reduced from 220 nm to 110 nm through
surface-polishing and ion-milling. The surface resistance was independent of
surface microwave magnetic field at least up to 4 Oe and below 30 K. We
attribute this behavior, and the overall low surface resistance (~0.8 mOhms at
10 GHz and 20 K), to the high density of our samples and the absence of weak
links between grains
Nuclear and cell membrane surface area alteration in hexamethylene bisacetamide (HMBA) induced human colonic carcinoma cell line (LoVo)
Synopses of Paperspostprin
Probabilistic Constructive Interference Precoding for Imperfect CSIT
This paper proposes a stochastic-robust constructive interference (CI) precoding scheme for downlink multi-user MISO systems, assuming that channel state information (CSI) at the transmitter side (CSIT) is contaminated by Gaussian-distributed uncertainties. Our objective is to minimize the total transmit power under users' quality-of-service constraints: formulating CI at each user with high probabilities for a given target signal-to-noise ratio (SINR). We first analyze the probability of CI under imperfect CSIT. A series of approximations are then developed, transforming the intractable stochastic CI constraints into determined convex constraints. The non-convex stochastic-robust CI power minimization (CIPM) problem is then converted into second-order cone programming. We show that we could create tightened or relaxed approximations by changing the parameters, enabling us to find upper-bounds and lower-bounds for the original stochastic CIPM problem. The best parameter values corresponding to the tightest upper and lower bounds are also discussed and obtained. Simulation results show that the proposed methods reasonably approximate the stochastic CIPM problem. Using the given parameter values, it can guarantee the required probability of CI for each user under acceptable channel uncertainties and outperform the existing robust CI precoding in terms of both transmit power and feasibility rate. The small gap between the upper and lower bounds also shows that the proposed method does not cause too much performance loss
Multiplexing More Data Streams in the MU-MISO Downlink by Interference Exploitation Precoding
In this paper, we focus on the constructive interference (CI) precoding for the scenario when the number of streams simultaneously transmitted by the base station (BS) is larger than that of transmit antennas at the BS, and derive the optimal precoding structure by employing the pseudo inverse. We show that the optimal pre-scaling vector in IE precoding is equal to a linear combination of the right singular vectors that correspond to zero singular values of the coefficient matrix. By formulating the dual problem, we further show that the optimal precoding matrix can be expressed as a function of the dual variables in a closed form, and an equivalent quadratic programming (QP) formulation is derived for computational complexity reduction. Numerical results validate our analysis and demonstrate significant performance improvements for interference exploitation precoding in the considered scenario
A Java Graphical User Interface for Large-Scale Scientific Computations in Distributed Systems
Large-scale scientific applications present great challenges to computational scientists in terms of obtaining high performance and in managing large datasets. These applications (most of which are simulations) may employ multiple techniques and resources in a heterogeneously distributed environment. Effective working in such an environment is crucial for modern large-scale simulations. In this paper, we present an integrated Java graphical user interface (IJ-GUI) that provides a control platform for managing complex programs and their large datasets easily. As far as performance is concerned, we present and evaluate our initial implementation of two optimization schemes: data replication and data prediction. Data replication can take advantage of \u27temporal locality\u27 by caching the remote datasets on local disks; data prediction, on the other hand, provides prefetch hints based on the datasets\u27 past activities that are kept in databases. We first introduce the data contiguity concept in such an environment that guides data prediction. The relationship between the two approaches is discussed
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