1,687 research outputs found
Charged rotating dilaton black branes in AdS universe
We present the metric for the -dimensional charged rotating dilaton
black branes with cylindrical or toroidal horizons in the background of anti-de
Sitter spacetime. We find the suitable counterterm which removes the
divergences of the action in the presence of the dilaton potential in all
higher dimensions. We plot the Penrose diagrams of the spacetime and reveal
that the spacetime geometry crucially modifies in the presence of the dilaton
field. The conserved and thermodynamic quantities of the black branes are also
computed.Comment: 13 pages, 3 figures, to appear in Gen. Relat. Gravi
Experimental characterization and multi-physics simulation of a triple-junction cell in a novel hybrid III:V concentrator photovoltaic–thermoelectric receiver design with secondary optical element
A lattice-matched monolithic triple-junction Concentrator Photovoltaic cell (InGa(0.495)P/GaIn(0.012)As/Ge) was electrically and thermally interfaced to a Thermoelectric Peltier module. A single optical design secondary lens was bonded to the CPV-TE receiver. The hybrid SILO-CPV-TE solar energy harvesting device was electrically, thermally and theoretically investigated. The electrical performance data for the cell under variable irradiance and cell temperature conditions were measured using the integrated thermoelectric module as both a temperature sensor and as a solid-state heat pump. The cell was electrically characterised under standard test conditions (1000 W/m2 irradiance, 25°C temperature and AM1.5G spectrum) for comparison with literature data. Transient multiphysics simulations in ANSYS CFX 15.0 were carried out to calculate cell temperatures and to determine the short circuit current and temperature coefficient in a scaling law. The optimization was used to determine 15 model parameters for the component sub-cells within the triple-junction cell at STC with a MATLAB scaling law. The root-mean-square error in electrical currents between measurement and simulations was 0.66%
Thermodynamics of higher dimensional topological charged AdS black branes in dilaton gravity
In this paper, we study topological AdS black branes of -dimensional
Einstein-Maxwell-dilaton theory and investigate their properties. We use the
area law, surface gravity and Gauss law interpretations to find entropy,
temperature and electrical charge, respectively. We also employ the modified
Brown and York subtraction method to calculate the quasilocal mass of the
solutions. We obtain a Smarr-type formula for the mass as a function of the
entropy and the charge, compute the temperature and the electric potential
through the Smarr-type formula and show that these thermodynamic quantities
coincide with their values which are calculated through using the geometry.
Finally, we perform a stability analysis in the canonical ensemble and
investigate the effects of the dilaton field and the size of black brane on the
thermal stability of the solutions. We find that large black branes are stable
but for small black brane, depending on the value of dilaton field and type of
horizon, we encounter with some unstable phases.Comment: 21 pages, 21 figures, references updated, minor editing, accepted in
EPJC (DOI: 10.1140/epjc/s10052-010-1483-3
Onsager coefficients of a Brownian Carnot cycle
We study a Brownian Carnot cycle introduced by T. Schmiedl and U. Seifert
[Europhys. Lett. \textbf{81}, 20003 (2008)] from a viewpoint of the linear
irreversible thermodynamics. By considering the entropy production rate of this
cycle, we can determine thermodynamic forces and fluxes of the cycle and
calculate the Onsager coefficients for general protocols, that is, arbitrary
schedules to change the potential confining the Brownian particle. We show that
these Onsager coefficients contain the information of the protocol shape and
they satisfy the tight-coupling condition irrespective of whatever protocol
shape we choose. These properties may give an explanation why the
Curzon-Ahlborn efficiency often appears in the finite-time heat engines
Strategy and Long-term Outcomes of Endovascular Treatment for Budd–Chiari Syndrome Complicated by Inferior Vena Caval Thrombosis
ObjectivesThe aim of this study was to evaluate the strategy and long-term outcomes of endovascular treatment of Budd–Chiari syndrome (BCS) complicated by inferior vena cava (IVC) thrombosis.MethodsThe treatment strategy and outcomes of BCS complicated by IVC thrombosis were retrospectively evaluated in a single-center study. The treatment was aimed at the IVC thrombus, not hepatic vein occlusion. All 133 patients with BCS complicated by IVC thrombosis from February 2003 to March 2013 underwent endovascular treatment. For the fresh thrombus group (n = 75) recanalization was performed after transcatheter thrombolysis with urokinase. For the mixed thrombus group (n = 19) a small balloon pre-dilation of the IVC was performed first, followed by transcatheter thrombolysis using urokinase and a large balloon dilation of the IVC. For the old thrombus group (n = 39) a large balloon dilation or/and stent placement was performed directly. Pre- and post-treatment follow-ups were recorded.ResultsThe endovascular treatment was successful in 131 out of 133 patients (98.5%). Thirty seven patients had synchronous hepatic vein occlusion. The incidence of serious complications was 4.5% (6/133). Symptomatic pulmonary embolism occurred in three cases, cerebral hemorrhage in two, and cardiac tamponade in one. The cumulative 1-, 5-, and 10-year primary patency rate was 96.3%, 84.0%, and 64.6%, respectively. The cumulative 1-, 5-, and 10-year secondary patency rate was 99.0%, 96.1% and 91.3%, respectively. Segmental occlusion of the IVC and duration of anticoagulant therapy less than 6 months were independent risk factors for reocclusion.ConclusionsFor patients with BCS complicated by IVC thrombosis, an individualized treatment strategy based on the property of the thrombus can result in excellent long-term patency
Simulations of the Static Friction Due to Adsorbed Molecules
The static friction between crystalline surfaces separated by a molecularly
thin layer of adsorbed molecules is calculated using molecular dynamics
simulations. These molecules naturally lead to a finite static friction that is
consistent with macroscopic friction laws. Crystalline alignment, sliding
direction, and the number of adsorbed molecules are not controlled in most
experiments and are shown to have little effect on the friction. Temperature,
molecular geometry and interaction potentials can have larger effects on
friction. The observed trends in friction can be understood in terms of a
simple hard sphere model.Comment: 13 pages, 13 figure
Treatment of backscattering in a gas of interacting fermions confined to a one-dimensional harmonic atom trap
An asymptotically exact many body theory for spin polarized interacting
fermions in a one-dimensional harmonic atom trap is developed using the
bosonization method and including backward scattering. In contrast to the
Luttinger model, backscattering in the trap generates one-particle potentials
which must be diagonalized simultaneously with the two-body interactions.
Inclusion of backscattering becomes necessary because backscattering is the
dominant interaction process between confined identical one-dimensional
fermions. The bosonization method is applied to the calculation of one-particle
matrix elements at zero temperature. A detailed discussion of the validity of
the results from bosonization is given, including a comparison with direct
numerical diagonalization in fermionic Hilbert space. A model for the
interaction coefficients is developed along the lines of the Luttinger model
with only one coupling constant . With these results, particle densities,
the Wigner function, and the central pair correlation function are calculated
and displayed for large fermion numbers. It is shown how interactions modify
these quantities. The anomalous dimension of the pair correlation function in
the center of the trap is also discussed and found to be in accord with the
Luttinger model.Comment: 19 pages, 5 figures, journal-ref adde
Conceptual design and performance evaluation of a hybrid concentrating photovoltaic system in preparation for energy
Concentrating sunlight and focussing it on smaller sized solar cells increases the device's power output per unit active area. However, this process tends to increase the solar cell temperature considerably and has the potential to compromise system reliability. Adding a heat exchanger system to regulate this temperature rise, can improve the electrical performance whilst simultaneously providing an additional source of low temperature heat. In this study the performance of a low concentrator photovoltaic system with thermal (LCPV/T) extraction was conceptualised and evaluated in depth. An experimental analysis was performed using a first-generation prototype consisting of 5 units of Cross Compound Parabolic Concentrators (CCPC) connected to a heat extraction unit. A bespoke rotating table was used as experimental apparatus to effectively evaluate the optical performance of the system, as a function of its angular positions to replicate the motion of actual sun. Key design performance parameters for the LCPV/T collector are presented and discussed. This work also provides a useful technique to effectively calculate system performance, as a function of the orientation-dependant electrical characterisation parameters data. Finally, a Computational Fluid Dynamics (CFD) model was also applied to investigate the efficacy of the heat exchanger and hence estimate the overall co-generation benefit of using such optimisation techniques on realistic CPV systems. It was highlighted through these simulations that the water flow rate had the potential to be a critical power-generation optimisation criterion for LCPV-T systems. The maximum power output at normal incidence with concentrators and no water flow was found to be 78.4 mW. The system was found to perform with an average electrical efficiency ranging between 10 and 16% when evaluated at five different geographic locations. Experimental analysis of the data obtained showed an increase in power of 141% (power ratio 2.41) compared to the analogous non-concentrating counterpart. For example, in the case of London which receives an annual solar radiation of 1300 kWh/m2 the system is expected to generate 210 kWh/m2. This may reduce further to include losses due to temperature, reflectance/glazing losses, and electrical losses in cabling and inverter by up to 36% leading to an annual power output of 134 kWh/m2 of module
Microfluidic-assisted ZIF-silk-polydopamine nanoparticles as promising drug carriers for breast cancer therapy
Metal–organic frameworks (MOFs) are heralded as potential nanoplatforms for biomedical applications. Zeolitic imidazolate framework-8 (ZIF-8), as one of the most well known MOFs, has been widely applied as a drug delivery carrier for cancer therapy. However, the application of ZIF-8 nanoparticles as a therapeutic agent has been hindered by the challenge of how to control the release behaviour of anti-cancer zinc ions to cancer cells. In this paper, we designed microfluidic-assisted core-shell ZIF-8 nanoparticles modified with silk fibroin (SF) and polydopamine (PDA) for sustained release of zinc ions and curcumin (CUR) and tested these in vitro in various human breast cancer cells. We report that microfluidic rapid mixing is an efficient method to precisely control the proportion of ZIF-8, SF, PDA, and CUR in the nanoparticles by simply adjusting total flow rates (from 1 to 50 mL/min) and flow rate ratios. Owing to sufficient and rapid mixing during microfluidic-assisted nanoprecipitation, our designer CUR@ZIF-SF-PDA nanoparticles had a desired particle size of 170 nm with a narrow size distribution (PDI: 0.08), which is much smaller than nanoparticles produced using traditional magnetic stirrer mixing method (over 1000 nm). Moreover, a properly coated SF layer successfully enhanced the capability of ZIF-8 as a reservoir of zinc ions. Meanwhile, the self-etching reaction between ZIF-8 and PDA naturally induced a pH-responsive release of zinc ions and CUR to a therapeutic level in the MDA-MB-231, SK-BR-3, and MCF-7 breast cancer cell lines, resulting in a high cellular uptake efficiency, cytotoxicity, and cell cycle arrest. More importantly, the high biocompatibility of designed CUR@ZIF-SF-PDA nanoparticles remained low in cytotoxicity on AD-293 non-cancer cells. We demonstrate the potential of prepared CUR@ZIF-SF-PDA nanoparticles as promising carriers for the controlled release of CUR and zinc ions in breast cancer therapy
De Sitter Gravity and Liouville Theory
We show that the spectrum of conical defects in three-dimensional de Sitter
space is in one-to-one correspondence with the spectrum of vertex operators in
Liouville conformal field theory. The classical conformal dimensions of vertex
operators are equal to the masses of the classical point particles in dS_3 that
cause the conical defect. The quantum dimensions instead are shown to coincide
with the mass of the Kerr-dS_3 solution computed with the Brown-York stress
tensor. Therefore classical de Sitter gravity encodes the quantum properties of
Liouville theory. The equality of the gravitational and the Liouville stress
tensor provides a further check of this correspondence. The Seiberg bound for
vertex operators translates on the bulk side into an upper mass bound for
classical point particles. Bulk solutions with cosmological event horizons
correspond to microscopic Liouville states, whereas those without horizons
correspond to macroscopic (normalizable) states. We also comment on recent
criticism by Dyson, Lindesay and Susskind, and point out that the
contradictions found by these authors may be resolved if the dual CFT is not
able to capture the thermal nature of de Sitter space. Indeed we find that on
the CFT side, de Sitter entropy is merely Liouville momentum, and thus has no
statistical interpretation in this approach.Comment: 22 pages, LateX2e; added references for section 1 and section 2;
corrected typos; improved discussion in section
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