Irreversible and reversible modes of operation of deterministic ratchets

We discuss a problem of optimization of the energetic efficiency of a simple rocked ratchet. We concentrate on a low-temperature case in which the particle's motion in a ratchet potential is deterministic. We show that the energetic efficiency of a ratchet working adiabatically is bounded from above by a value depending on the form of ratchet potential. The ratchets with strongly asymmetric potentials can achieve ideal efficiency of unity without approaching reversibility. On the other hand we show that for any form of the ratchet potential a set of time-protocols of the outer force exist under which the operation is reversible and the ideal value of efficiency is also achieved. The mode of operation of the ratchet is still quasistatic but not adiabatic. The high values of efficiency can be preserved even under elevated temperatures

Mechanical coupling in flashing ratchets

We consider the transport of rigid objects with internal structure in a flashing ratchet potential by investigating the overdamped behavior of a rod-like chain of evenly spaced point particles. In 1D, analytical arguments show that the velocity can reverse direction multiple times in response to changing the size of the chain or the temperature of the heat bath. The physical reason is that the effective potential experienced by the mechanically coupled objects can have a different symmetry than that of individual objects. All analytical predictions are confirmed by Brownian dynamics simulations. These results may provide a route to simple, coarse-grained models of molecular motor transport that incorporate an object's size and rotational degrees of freedom into the mechanism of transport.Comment: 9 pages, 10 figure

Chromobacterium violaceum ATCC12472: Multi-drug and ethidium bromide resistant

_Chromobacterium violaceum_ is an opportunistic human pathogen causing a range of gastric infections and occasionally septicemia. This Gram-negative bacillus is a common inhabitant of soil and water in tropical and subtropical areas of the world. Infection occurs after contamination of damaged skin exposed to soil or environmental water. Alternatively, systemic infection can follow the aspiration or ingestion of contaminated water. The major features of infections by _C. violaceum_ are, in generally, rapid clinical course, multiple visceral abscesses, and high mortality. Genomic data on the type strain ATCC 12472 has provided a comprehensive basis for detailed studies of pathogenicity, virulence and drug resistance genes. In this study, the susceptibility of this organism was tested on a variety of drugs at different concentrations, in solid and liquid media. _C. violaceum_ shown to be resistance to ampicilin, penicillin, rifampicin, erythromycin, vancomycin and also to ethidium bromide. The bacteria was susceptible to gentamicin, tetracycline, chloramphenicol, cotrimoxazole, kanamycin, streptomycin and nalidixic acid, at the tested concentrations

Alguns aspectos importantes da erva sal (Atriplex nummularia) quando irrigada com o rejeito da dessalinizacao de agua salobra no semi-arido brasileiro.

Com o objetivo de adequar a técnica da osmose inversa às águas salinas oriundas dos aqüíferos do cristalino, e de avaliar técnicas de manejo eficiente dos rejeitos, a fim de reduzir problemas ambientais, este projeto se propõe a dessalinizar água por osmose inversa e estudas alternativas para uso e acondicionamento adequado dos rejeitos. Os estudos estão sendo realizados no Campo Experimental de Manejo da Caatinga da Embrapa Semi-Árido. O sistema proposto para acondicionamento dos rejeitos é: utilização como água de irrigação para cultivos da erva sal (Atriplex nummularia)

Fontes energéticas e protéicas em suplementos múltiplos para torinhos na fase de recria em pastagens, durante o periodo de transição seca-águas: digestabilidade.

Projeto 03.08.06.010.00.0

EU enlargement and the portuguese economy

Ten states, primarily from Central and Eastern Europe, will be admitted to the EU in 2004. The present paper assesses the competitiveness implications of this enlargement for Portugal. Four specific topics are considered: the trade and industry effects, the implications for Portugal's ability to attract FDI, the likely levels and consequences of immigration from Central and Eastern Europe and the implications for Portugal's budgetary relations with the rest of the EU.Financial support of the Fundação para a Ciência e a Tecnologia /MCT under SFRH/BD/6412/2001 (supported by the European Social Fund)