8,799 research outputs found
Symmetrized mean-field description of magnetic instabilities in k-(BEDT-TTF)_2Cu[N(CN)]_2 Y salts
We present a novel and convenient mean-field method, and apply it to study
the metallic/antiferromagnetic interface of k-(BEDT-TTF)_2Cu[N(CN)]_2 Y organic
superconductors (BEDT_TTF is bis-ethylen-dithio-tetrathiafulvalene, Y=Cl, Br).
The method, which fully exploits the crystal symmetry, allows one to obtain the
mean-field solution of the 2D Hubbard model for very large lattices, up to
6x10^5 sites, yielding a reliable description of the phase boundary in a wide
region of the parameter space. The metal/antiferromagnet transtion appears to
be second order, except for a narrow region of the parameter space, where the
transition is very sharp and possibly first order. The cohexistence of metallic
and antiferromagnetic properties is only observed for the transient state in
the case of smooth second order transitions. The relevance of the present
resaults to the complex experimental behavior of centrosymmetric k-phase
BEDT-TTF salts is discussed.Comment: 9 pages in PS format, 7 figures (included in PS), 1 tabl
Melting behavior of ultrathin titanium nanowires
The thermal stability and melting behavior of ultrathin titanium nanowires
with multi-shell cylindrical structures are studied using molecular dynamic
simulation. The melting temperatures of titanium nanowires show remarkable
dependence on wire sizes and structures. For the nanowire thinner than 1.2 nm,
there is no clear characteristic of first-order phase transition during the
melting, implying a coexistence of solid and liquid phases due to finite size
effect. An interesting structural transformation from helical multi-shell
cylindrical to bulk-like rectangular is observed in the melting process of a
thicker hexagonal nanowire with 1.7 nm diameter.Comment: 4 pages, 4 figure
Synchronisation of linear continuous multi-agent systems with switching topology and communication delay
A distributed dynamic output feedback control is designed by Scardovi and Sepulchre for the synchronization of a network of identical linear systems, known as agents in literature. The design is based on some mild conditions allowing switching topology. But it assumes that there is no time delay in signal transfer between the neighbouring agents. In this paper we extend their work to include known time delay in communications. Furthermore, our design has some special features: (a) the delay can be arbitrary and only need to be uniformly bounded by a constant, (b) the conditions that time delay should be the same and sufficiently small in some literature are not required here, and (c) no local buffer is required to store past data due to time-delay effect
Design and analysis of active power control strategies for distributed generation inverters under unbalanced grid faults
Distributed power generation systems are expected to deliver active power into the grid and support it without interruption during unbalanced grid faults. Aiming to provide grid-interfacing inverters the flexibility to adapt to the coming change of grid requirements, an optimised active power control strategy is proposed to operate under grid faults. Specifically, through an adjustable parameter it is possible to change the relative amplitudes of oscillating active and reactive power smoothly, while simultaneously eliminating the second-order active or reactive power ripple at the two extremes of the parameter range. The steering possibility of the proposed strategy enables distributed generation inverters to be optimally designed from the perspectives of both the power-electronic converters and the power system. The proposed strategy is proved through simulation and further validated by experimental results
Design and analysis of active power control strategies for distributed generation inverters under unbalanced grid faults
Distributed power generation systems are expected to deliver active power into the grid and support it without interruption during unbalanced grid faults. Aiming to provide grid-interfacing inverters the flexibility to adapt to the coming change of grid requirements, an optimised active power control strategy is proposed to operate under grid faults. Specifically, through an adjustable parameter it is possible to change the relative amplitudes of oscillating active and reactive power smoothly, while simultaneously eliminating the second-order active or reactive power ripple at the two extremes of the parameter range. The steering possibility of the proposed strategy enables distributed generation inverters to be optimally designed from the perspectives of both the power-electronic converters and the power system. The proposed strategy is proved through simulation and further validated by experimental results
Reconfiguring grid-interfacing converters for power quality improvement
In this paper reconfiguration of grid-interfacing converters is proposed for power quality improvement. In addition to the traditional function of delivering energy between distributed sources and the utility grid, more flexible ancillary functions can be integrated into the control of grid-interfacing converters to both improve the power quality at the user side and the utility side. The potential for solving or improving various problems on different system levels is described in detail. Two three-phase four-leg inverters, together with DC microsources and loads, are employed to construct a general gridinterfacing system module. Through the redefinition of system functions, it is possible to achieve voltage unbalance correction, harmonic current compensation at the point of connection with the utility grid, protection of distributed generation systems from grid disturbances, and high quality voltage for sensitive loads under various utility grid situations. While the effect on helping the utility grid is small for a single module, a number of the modules put together could be pronounced. The Control scheme and validation results are presented in the paper
New Properties and Applications of Polyvinylidene-Based Ferroelectric Polymer
There are different kinds of novel properties and applications of polyvinylidene difluoride (PVDF)-based ferroelectric polymer films. Several issues associated with the structure, properties, and applications of PVDF-based ferroelectric polymer films are discussed. The main achievements of the research include high electric tunability of relaxor ferroelectric Langmuir–Blodgett (LB) terpolymer films, the creep process of the domain switching in poly(vinylidene fluoride-trifluoroethylene) ferroelectric thin films, transition from relaxor to ferroelectric-like phase in poly(vinylidene fluoride-trifluoroethylene -chlorofluoroethylene) terpolymer ultrathin films, abnormal polarization switching of relaxor terpolymer films at low temperatures, huge electrocaloric effect in LB ferroelectric polymer thin films, self-polarization in ultrathin LB polymer films, enhanced dielectric and ferroelectric properties in artificial polymer multilayers, and transition of polarization switching from extrinsic to intrinsic in ultrathin PVDF homopolymer films
Jet measurements in the ALICE experiment at the LHC
Jet tomography probes provide a means to explore the properties of highly
compressed and excited nuclear matter created in heavy ion collisions. The
capabilities of the ALICE experiment, with its electromagnetic calorimeter
(EMCal) upgrade, to trigger on and reconstruct jets in p+p and Pb+Pb collisions
at =5.5 TeV are presented.Comment: 8 pages, 6 figures. Presented at the IX International Conference on
Nucleus-Nucleus Collisions, Rio de Janeiro, Brazil, August 28 - September 1,
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Anomalous magnetophotoluminescence as a result of level repulsion in arrays of quantum dots
Selectively excited photoluminescence (SPL) of an array of self-organized
InGaAs quantum dots has been measured in a magnetic field up to
11T. Anomalous magnetic field sensitivity of the SPL spectra has been observed
under conditions for which the regular photoluminescence spectra is insensitive
to the magnetic field due to large inhomogeneous broadening. The anomalous
sensitivity is interpreted in terms of the repulsion of excited levels of the
dots in a random potential. A theory presented to describe this phenomena is in
excellent agreement with the experimental data. The data estimated the
correlation in the positions of excited levels of the dots to be 94%. The
magnetic field dependence allows the determination of the reduced cyclotron
effective mass in a dot. For our sample we have obtained
.Comment: 12 revtex preprint pages + 4 ps figures, uuencode
Prokaryotic expression, purification and immunogenicity analysis of CpsD protein from Streptococcus iniae
Streptococcus iniae is a major cause of serious bacterial infections in both fish and human beings. Capsular polysaccharide (CPS) of S. iniae is vital to evade phagocytic clearance of the host and serves as an important protective antigen of S. iniae infection in aquatic animals. The CpsD gene was determined to be highly conservative in capsule polysaccharide operon. Prokaryotic expression of the CpsD gene of a clinical isolate of S. iniae from channel catfish and immunogenic examination of the recombinant protein were first described in this essay. The recombinant protein was expressed in the form of inclusion bodies (IBs). Induction conditions in Escherichia coli were optimized with 0.6mM Isopropyl β-D-1-Thiogalactopyranoside at 37°C for 5h after the culture mid-log phase in Luria Bertani (LB) medium. The recombinant protein CpsD was thus expressed and purified by immobilized metal affinity chromatography (IMAC), yielding approximate 582.47 mg the protein per liter culture. Western blot analysis showed that the purified CpsD had reactogenicity. It will possibly reveal more details of capsule synthesis and capsule regulation during various stages of the S. iniae infectious process
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