Drude model and Lifshitz formula

Since nearly 10 years, it is known that inserting the permittivity of the Drude model into the Lifshitz formula for free energy causes a violation of the third law of thermodynamics. In this paper we show that the standard Matsubara formulation for free energy contains a contribution that is non-perturbative in the relaxation parameter. We argue that the correct formula must have a perturbative expansion and conclude that the standard Matsubara formulation with the permittivity of the Drude model inserted is not correct. We trace the non-perturbative contribution in the complex frequency plane, where it shows up as a self-intersection or a bifurcation of the integration path.Comment: accepted for publication in EPJ

Human genetics and neuropathology suggest a link between miR-218 and amyotrophic lateral sclerosis pathophysiology

Motor neuron–specific microRNA-218 (miR-218) has recently received attention because of its roles in mouse development. However, miR-218 relevance to human motor neuron disease was not yet explored. Here, we demonstrate by neuropathology that miR-218 is abundant in healthy human motor neurons. However, in amyotrophic lateral sclerosis (ALS) motor neurons, miR-218 is down-regulated and its mRNA targets are reciprocally up-regulated (derepressed). We further identify the potassium channel Kv10.1 as a new miR-218 direct target that controls neuronal activity. In addition, we screened thousands of ALS genomes and identified six rare variants in the human miR-218-2 sequence. miR-218 gene variants fail to regulate neuron activity, suggesting the importance of this small endogenous RNA for neuronal robustness. The underlying mechanisms involve inhibition of miR-218 biogenesis and reduced processing by DICER. Therefore, miR-218 activity in motor neurons may be susceptible to failure in human ALS, suggesting that miR-218 may be a potential therapeutic target in motor neuron disease

Warming shortens flowering seasons of tundra plant communities

Advancing phenology is one of the most visible effects of climate change on plant communities, and has been especially pronounced in temperature-limited tundra ecosystems. However, phenological responses have been shown to differ greatly between species, with some species shifting phenology more than others. We analysed a database of 42,689 tundra plant phenological observations to show that warmer temperatures are leading to a contraction of community-level flowering seasons in tundra ecosystems due to a greater advancement in the flowering times of late-flowering species than early-flowering species. Shorter flowering seasons with a changing climate have the potential to alter trophic interactions in tundra ecosystems. Interestingly, these findings differ from those of warmer ecosystems, where early-flowering species have been found to be more sensitive to temperature change, suggesting that community-level phenological responses to warming can vary greatly between biomes

The numerical solution of the linearized and exponential hypervertex approximations for electrolytes

4 pags., 1 fig., 5 tabs.In this paper we present numerical solution of the linearized and exponential hypervertex approximations for the restricted primitive model for electrolytes. The method of solution is based on a Newton-Raphson scheme previously applied to simple fluids. Thermodynamic results computed from both approximations agree remarkably well with previously published Monte Carlo data even to a greater extent than well-known approximations such as the hypernetted-chain equation. © 1991 American Institute of Physics.E. L. wishes to thank The Royal Norwegian Council for Scientific and Industrial Research (NTNF) whose financial support made possible his stay at the Institutt for Fysikk in Trondheim. We would also like to thank the Norske Almenvitenskapelige Forsknigsnld (NA VF) which covered the expenses of computing time in the Cray XMP at Stiftelsen for Industriell og Teknisk Forskning (SINTEF) (Norway) where most of this work was performed. This work has been partially supported by the Direccion General de Investigacion Cientifica y Tecnica of Spain under Project No. PB8?- 0246-C02-0 1

Frequency spectra for fluids beyond the mean spherical approximation

10 pags., 1 app.In this paper, we investigate the frequency spectra of fluids (or fluid-like disordered materials) composed of particles with embedded harmonic oscillators. The general treatment is particularized at the low density limit, and a working scheme to add corrections to the mean spherical approximation for arbitrary density is introduced. A detailed comparison with an exactly solvable model in one dimension is also presented. © 1994 American Institute of Physics.E. L. acknowledges support from the Spanish Direccion General de Investigacion Cientifica y Tecnica (DGICYT) under Grant No. PB91-0110

Frequency spectra of two-band fluids and fluid mixtures: Mean spherical approximation and beyond

8 pags., 3 figs.In the framework of a recently proposed approximation, we investigate here the frequency spectra of two-band fluids (fluids composed of particles with two independent Drude oscillators embedded) as well as fluid mixtures of particles with one Drude oscillator. Both cases are analyzed in the low density regime where departures from the linear theories are more evident. Our theory, which goes beyond the mean spherical approximation (MSA), reproduces the correct low density spectra while retaining the proper qualitative behavior of the MSA at fluid densities. © 1995 American Institute of Physics.J.L.L. thanks the Spanish and Norwegian Ministries of Foreign Affairs which financially supported his stay in Trondheim by means of a Cultural Exchange Fellowship. This work has been partially financed by the Spanish Direccio´n General de Investigacio´n Cientıca y Tecnica ~DGICYT! under Grant No. PB91-0110. Norges Forskningsra˚d (NFR) is also acknowledged for the support provided to cover computer time expenses at the CRAY YMP at SINTEF ~Trondheim, Norway!

The uniform quantized electron gas revisited

In this article we continue and extend our recent work on the correlation energy of the quantized electron gas of uniform density at temperature T = 0. As before, we utilize the methods, properties, and results obtained by means of classical statistical mechanics. These were extended to quantized systems via the Feynman path integral formalism. The latter translates the quantum problem into a classical polymer problem in four dimensions. Again, the well known RPA (random phase approximation) is recovered as a basic result which we then modify and improve upon. Here we analyze the condition of thermodynamic selfconsistency. Our numerical calculations exhibit a remarkable agreement with well known results of a standard parameterization of Monte Carlo correlation energies.Peer Reviewe

A theoretical approach to the tight-binding band structure of liquid carbon and silicon beyond linear approximations

10 pags., 10 figs.,We present a study of the band structure of liquid Carbon and Silicon modelled in a Tight-Binding Hamiltonian approximation by means of an integral equation approximation that includes non-linear corrections. The theoretical predictions are contrasted with Tight Binding Molecular Dynamics simulations in which the energy bands are obtained by direct diagonalization of the Hamiltonian matrix. The results for Silicon are excellent, whereas in liquid Carbon only some of the qualitative features of the band structure are captured by the non-linear corrections. We find that this can largely be understood as an effect of missing three-body correlation functions in the theoretical treatment of the energy bands. This is particularly crucial in the case of strongly directional and short range bonding, as it occurs in Carbon. © 1997 American Institute of Physics.The authors wish to acknowledge support from the Austrian-Spanish Program of Acciones integradas under Grant HU1995-0015. We would like to thank Fernando Bresme for providing the code to perform the cluster analysis. This work has been supported in part by the Spanish Direccion General de Investigacion Cientıfica y Tecnica ~DGICYT! under Grant PB94-0112