Design and simulation of thin-film silicon quantum well photovoltaic cell

A new thin-film silicon photovoltaic cell could be designed by inserting quantum well layers in the intrinsic region. Calculations show the improvement in spectral absorption due to the quantum well layer insertion. This article reports the design parameters and enhanced spectral absorption for a newly designed thin-film silicon quantum well photovoltaic cell. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/1057

A model for hedging load and price risk in the Texas electricity market

Energy companies with commitments to meet customers’ daily electricity demands face the problem of hedging load and price risk. We propose a joint model for load and price dynamics, which is motivated by the goal of facilitating optimal hedging decisions, while also intuitively capturing the key features of the electricity market. Driven by three stochastic factors including the load process, our power price model allows for the calculation of closed-form pricing formulas for forwards and some options, products often used for hedging purposes. Making use of these results, we illustrate in a simple example the hedging benefit of these instruments, while also evaluating the performance of the model when fitted to the Texas electricity market

Magnetic and structural properties of GeMn films: precipitation of intermetallic nanomagnets

We present a comprehensive study relating the nanostructure of Ge_0.95Mn_0.05 films to their magnetic properties. The formation of ferromagnetic nanometer sized inclusions in a defect free Ge matrix fabricated by low temperature molecular beam epitaxy is observed down to substrate temperatures T_S as low as 70 deg. Celsius. A combined transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) analysis of the films identifies the inclusions as precipitates of the ferromagnetic compound Mn_5Ge_3. The volume and amount of these precipitates decreases with decreasing T_S. Magnetometry of the films containing precipitates reveals distinct temperature ranges: Between the characteristic ferromagnetic transition temperature of Mn_5Ge_3 at approximately room temperature and a lower, T_S dependent blocking temperature T_B the magnetic properties are dominated by superparamagnetism of the Mn_5Ge_3 precipitates. Below T_B, the magnetic signature of ferromagnetic precipitates with blocked magnetic moments is observed. At the lowest temperatures, the films show features characteristic for a metastable state.Comment: accepted for publication in Phys. Rev. B 74 (01.12.2006). High resolution images ibide

Entangled Dilaton Dyons

Einstein-Maxwell theory coupled to a dilaton is known to give rise to extremal solutions with hyperscaling violation. We study the behaviour of these solutions in the presence of a small magnetic field. We find that in a region of parameter space the magnetic field is relevant in the infra-red and completely changes the behaviour of the solution which now flows to an $AdS_2\times R^2$ attractor. As a result there is an extensive ground state entropy and the entanglement entropy of a sufficiently big region on the boundary grows like the volume. In particular, this happens for values of parameters at which the purely electric theory has an entanglement entropy growing with the area, $A$, like $A \log(A)$ which is believed to be a characteristic feature of a Fermi surface. Some other thermodynamic properties are also analysed and a more detailed characterisation of the entanglement entropy is also carried out in the presence of a magnetic field. Other regions of parameter space not described by the $AdS_2\times R^2$ end point are also discussed.Comment: Some comments regarding comparison with weakly coupled Fermi liquid changed, typos corrected and caption of a figure modifie

Can the Hagedorn Phase Transition be explained from Matrix Model for Strings?

The partition function of BFSS matrix model is studied for two different classical backgrounds upto 1-loop level. One of the backgrounds correspond to a membrane wrapped around a compact direction and another to a localized cluster of $D0$-branes. It is shown there exist phase transitions between these two configurations - but only in presence of an IR cut-off. The low temperature phase corresponds to a string (wrapped membrane) phase and so we call this the Hagedorn phase transition. While the presence of an IR cut-off seemingly is only required for perturbative analysis to be valid, the physical necessity of such a cut-off can be seen in the dual supergravity side. It has been argued from entropy considerations that a finite size horizon must develop even in an extremal configuration of D0-branes, from higher derivative $O(g_s)$ corrections to supergravity. It can then be shown that the Hagedorn like transition exists in supergravity also. Interestingly the perturbative analysis also shows a second phase transition back to a string phase. This is also reminiscent of the Gregory-Laflamme instability.Comment: minor change

Non-relativistic metrics from back-reacting fermions

It has recently been pointed out that under certain circumstances the back-reaction of charged, massive Dirac fermions causes important modifications to AdS_2 spacetimes arising as the near horizon geometry of extremal black holes. In a WKB approximation, the modified geometry becomes a non-relativistic Lifshitz spacetime. In three dimensions, it is known that integrating out charged, massive fermions gives rise to gravitational and Maxwell Chern-Simons terms. We show that Schrodinger (warped AdS_3) spacetimes exist as solutions to a gravitational and Maxwell Chern-Simons theory with a cosmological constant. Motivated by this, we look for warped AdS_3 or Schrodinger metrics as exact solutions to a fully back-reacted theory containing Dirac fermions in three and four dimensions. We work out the dynamical exponent in terms of the fermion mass and generalize this result to arbitrary dimensions.Comment: 26 pages, v2: typos corrected, references added, minor change

Systemic Risk and Default Clustering for Large Financial Systems

As it is known in the finance risk and macroeconomics literature, risk-sharing in large portfolios may increase the probability of creation of default clusters and of systemic risk. We review recent developments on mathematical and computational tools for the quantification of such phenomena. Limiting analysis such as law of large numbers and central limit theorems allow to approximate the distribution in large systems and study quantities such as the loss distribution in large portfolios. Large deviations analysis allow us to study the tail of the loss distribution and to identify pathways to default clustering. Sensitivity analysis allows to understand the most likely ways in which different effects, such as contagion and systematic risks, combine to lead to large default rates. Such results could give useful insights into how to optimally safeguard against such events.Comment: in Large Deviations and Asymptotic Methods in Finance, (Editors: P. Friz, J. Gatheral, A. Gulisashvili, A. Jacqier, J. Teichmann) , Springer Proceedings in Mathematics and Statistics, Vol. 110 2015

Kinetics and Mechanism of Sulfation Reactions

Roasting of metallic sulfides have been studies by a large number of investigators in recent years. Wadsworth, McCabe in U.S.A. and Smirnov and his group have contrib-uted to our understanding of the roasting mechanism to a very considerable extent. On the basis of these works, two kinds of mechanisms have been proposed for the formation of metallic sulfate from metallic sulfide and oxygen. One of the theory suggests a direct formation of metallic sulfate, whereas the other theory assumes prior formation of metallic oxide of SO2 to SO3, which combines with metallic oxide to give sulfate. Present investigation is aimed at further clearing up the mechanism of sulfate formation and estabilishing the role of individuality of the system on a more generalised basis

Kinetics and Mechanism of Sulfation Reactions during roasting of Sulfides

ROASTING of sulphidic minerals is one of the very important steps in the extraction metallurgical practice of most of the non-ferrous metals from their concentrates. In recent times, the technique of roasting has undergone substantial changes leading to higher production and better products, more suitable for subsequent operations. Some of these processes have developed on the basis of our understanding of the kinetic limitations of the old proc-esses and elimination of such kinetic bottlenecks like diffusion in the roasting processes. These new processes like flash roasting or fluidized roasting are being increasingly utilised in production units. However, our present state of knowledge on the kinetics of roasting reaction lacks certain fundamental understanding of the process which is explained in the following paragraphs