A. Medina

Feynman's ratchet optimization: maximum power and maximum efficiency regimes

The optimal performance of the Feynman ratchet-and-pawl engine is analysed by taking the power and the efficiency of the engine as objective functions. The power-efficiency curves are also obtained. These curves show a loop shape similar to those characteristic of some real heat engines. Explicit analytical expressions are reported in the so-called linear regime.

Optimization of heat engines including the saving of natural resources and the reduction of thermal pollution

The use of the new concept of a saving function as a measure of possible reductions of undesired side effects in heat engine operation is proposed. Two saving functions are introduced, one associated with fuel consumption and another associated with thermal pollution. Two optimization paths including the maximization of power output and these saving functions are presented. The first is based on a linear formalism and the second is based on a power-law formalism. When these optimization criteria are applied to a Curzon-Ahlborn heat engine, both criteria lead to a very similar optimum efficiency, opt = 1- 3/4 , where is the ratio between the temperatures of the cold and the hot external reservoirs. A numerical comparison with the efficiency of some modern nuclear power plants is reported.

Growth Factor and Th2 Cytokine Signaling Pathways Converge at STAT6 to Promote Arginase Expression in Progressive Experimental Visceral Leishmaniasis

Host arginase 1 (arg1) expression is a significant contributor to the pathogenesis of progressive visceral leishmaniasis (VL), a neglected tropical disease caused by the intracellular protozoan Leishmania donovani. Previously we found that parasite-induced arg1 expression in macrophages was dependent on STAT6 activation. Arg1 expression was amplified by, but did not require, IL-4, and required de novo synthesis of unknown protein(s). To further explore the mechanisms involved in arg1 regulation in VL, we screened a panel of kinase inhibitors and found that inhibitors of growth factor signaling reduced arg1 expression in splenic macrophages from hamsters with VL. Analysis of growth factors and their signaling pathways revealed that the Fibroblast Growth Factor Receptor 1 (FGFR-1) and Insulin-like Growth Factor 1 Receptor (IGF-1R) and a number of downstream signaling proteins were activated in splenic macrophages isolated from hamsters infected with L. donovani. Recombinant FGF-2 and IGF-1 increased the expression of arg1 in L. donovani infected hamster macrophages, and this induction was augmented by IL-4. Inhibition of FGFR-1 and IGF-1R decreased arg1 expression and restricted L. donovani replication in both in vitro and ex vivo models of infection. Inhibition of the downstream signaling molecules JAK and AKT also reduced the expression of arg1 in infected macrophages. STAT6 was activated in infected macrophages exposed to either FGF-2 or IGF-1, and STAT6 was critical to the FGFR-1- and IGF-1R-mediated expression of arg1. The converse was also true as inhibition of FGFR-1 and IGF-1R reduced the activation of STAT6 in infected macrophages. Collectively, these data indicate that the FGFR/IGF-1R and IL-4 signaling pathways converge at STAT6 to promote pathologic arg1 expression and intracellular parasite survival in VL. Targeted interruption of these pathological processes offers an approach to restrain this relentlessly progressive disease.

Estimation of the quadrupole and hexadecapole moments of N2 from the far-infrared spectrum of a N2–Xe gaseous mixture

A previously reported quantum spectral theory for evaluating the far-infrared absorption spectrum of diatomic molecules in rare-gas fluids [J. Chem. Phys. 103, 9161 (1995)] is applied to the case of a N2–Xe gaseous mixture at room temperature and a very low concentration of N2 (0.85%). The theoretical line shape is built by considering the two leading electric multipolar induced contributions. From comparison between theoretical and experimental spectra an estimation of the quadrupole and hexadecapole moments of N2 is given.

Many-body components in the integrated far-infrared absorption coefficient of diatomic molecules in spherical solvents

In this paper we present a quantitative study of the static cancellation effects between two- and three-body components of the total integrated absorption coefficient in the far-infrared spectra of several systems (diluted solutions of diatomic molecules in spherical solvents) with important electric multipolar induced contributions to absorption. This static cancellation decreases with an increasing order of the multipolar induced mechanism. Even more, for hexadecapole-induced dipole contributions, cancellation transforms into enhancement for all the systems considered (CO–Ar, N2–Ar, and N2–Xe at different densities and temperatures). These results are obtained first by computer simulations and second by means of the knowledge of the static structure of the fluid, that is two- and three-body static distribution functions. From both procedures results are similar.

Transcriptional profiling of the spleen in progressive visceral leishmaniasis reveals mixed expression of type 1 and type 2 cytokine-responsive genes

BackgroundThe Syrian golden hamster (Mesocricetus aureus) has been used as a model to study infections caused by a number of human pathogens. Studies of immunopathogenesis in hamster infection models are challenging because of the limited availability of reagents needed to define cellular and molecular determinants.ResultsWe sequenced a hamster cDNA library and developed a first-generation custom cDNA microarray that included 5131 unique cDNAs enriched for immune response genes. We used this microarray to interrogate the hamster spleen response to Leishmania donovani, an intracellular protozoan that causes visceral leishmaniasis. The hamster model of visceral leishmaniasis is of particular interest because it recapitulates clinical and immunopathological features of human disease, including cachexia, massive splenomegaly, pancytopenia, immunosuppression, and ultimately death. In the microarray a differentially expressed transcript was identified as having at least a 2-fold change in expression between uninfected and infected groups and a False Discovery Rate of <5%. Following a relatively silent early phase of infection (at 7 and 14 days post-infection only 8 and 24 genes, respectively, were differentially expressed), there was dramatic upregulation of inflammatory and immune-related genes in the spleen (708 differentially expressed genes were evident at 28 days post-infection). The differentially expressed transcripts included genes involved in inflammation, immunity, and immune cell trafficking. Of particular interest there was concomitant upregulation of the IFN-γ and interleukin (IL)-4 signaling pathways, with increased expression of a battery of IFN-γ- and IL-4-responsive genes. The latter included genes characteristic of alternatively activated macrophages.ConclusionsTranscriptional profiling was accomplished in the Syrian golden hamster, for which a fully annotated genome is not available. In the hamster model of visceral leishmaniasis, a robust and functional IFN-γ response did not restrain parasite load and progression of disease. This supports the accumulating evidence that macrophages are ineffectively activated to kill the parasite. The concomitant expression of IL-4/IL-13 and their downstream target genes, some of which were characteristic of alternative macrophage activation, are likely to contribute to this. Further dissection of mechanisms that lead to polarization of macrophages toward a permissive state is needed to fully understand the pathogenesis of visceral leishmaniasis.

Electric multipolar induction in the far-infrared spectra of CO in liquid Ar: Translational/rotational contributions and static cancellation effects

We have analyzed by means of molecular dynamics simulations the temperature and density dependence of the different pure induced components of the far-infrared integrated absorption coefficient of CO in liquid Ar (an interesting example for which experimental far-infrared spectra show the existence of high order electric multipolar induction). The main contribution to these components (for all the thermodynamic conditions we elected) comes from the rotation of the diatomic except for dipole induced-dipole absorption, where quantitatively rotation and translation are similar. By studying static cancellation effects separately in rotation and translation, we can assert an interesting result: All those contributions to the integrated absorption coefficient with radial decay equal or faster than the first repulsive decay of the solute–solvent interaction present enhancement effects and all those decaying slower present cancellation effects.

Parametric analysis of thermal losses on hybrid solar gas-turbine power plants

In this paper a parametric analysis of thermal and pressure losses for a hybrid Brayton thermosolar plant is carried out. A serial hybridization is modelled with the purpose of delivering an stable power output. A purely thermodynamic model describing this sort of facilities is presented. The model is general and flexible, so it is easily applicable to different plant configurations (hybrid or pure combustion modes). The overall system is considered as formed by three subsystems linked by heat exchangers: solar collector, combustion chamber, and recuperative Brayton gas-turbine. All the main irreversibility sources existing in real installations are assumed by the subsystem models. For numerical calculations, particular parameters from a real installation and actual meteorological data are taken (solar irradiance and ambient temperature are yearly averaged). Later, a sensitivity analysis is accomplished, in which both solar and turbine subsystems are examined, being the optical efficiency of the heliostat field and the turbine efficiency, respectively, the most influential variables. This kind of studies could be a guideline for the design of future hybrid gas-turbine thermosolar facilities.