Light Collimation and Focussing by a Thin Flat Metallic Slab

We present experimental and theoretical work showing that a flat metallic slab can collimate and focus light impinging on the slab from a punctual source. The effect is optimised when the radiation is around the bulk, not at the surface, plasma frequency. And the smaller the imaginary part of the permittivity is, the better the collimation. Experiments for Ag in the visible as well as calculations are presented. We also discuss the interesting case of the Aluminium whose imaginary part of the permittivity is very small at the plasma frequency in UV radiation. Generalization to other materials and radiations are also discussed.Comment: 6 pages, 3 figures. To be published on Optics Lette

Full-length prepro-alpha-factor can be translocated across the mammalian microsomal membrane only if translation has not terminated.

We have previously shown that fully synthesized prepro-alpha-factor (pp alpha F), the precursor for the yeast pheromone alpha-factor, can be translocated posttranslationally across yeast rough microsomal (RM) membranes from a soluble, ribosome-free pool. We show here that this is not the case for translocation of pp alpha F across mammalian RM. Rather we found that a small amount of translocation of full-length pp alpha F is observed, but is solely due to polypeptide chains that were still ribosome bound and covalently attached to tRNA, i.e., not terminated. In addition, both signal recognition particle (SRP) and SRP receptor are required, i.e., the same targeting machinery that is normally responsible for the coupling between protein synthesis and translocation. Thus, the molecular requirements for targeting are distinct from posttranslational translocation across yeast RM. As termination is generally regarded as part of translation, the translocation of full-length pp alpha F across mammalian RM does not occur "posttranslationally," albeit independent of elongation. Most other proteins for which posttranslational translocation across mammalian RM was previously claimed fall into the same category in that ribosome attachment as peptidyl-tRNA is required. To clearly separate these two distinct processes, we suggest that the term posttranslational be reserved for those processes that occur in the complete absence of the translational machinery. We propose the term "ribosome-coupled translocation" for the events described here

Magnetic behavior of lamellar mnps3 and cdps3 composites with a paramagnetic manganese(iii) macrocyclic guest

Indexación: ScieloSix new composites derived from the intercalation of the MPS3 phases (M = MnII, CdIII) with the macrocyclic manganese(III) complex [MnL(H2O)2].NO3(H2O) (LH2 = Schiff base macrocyclic ligand derived from the condensation of 2-hydroxy-5-methy1-1,3-benzene-dicarbaldehyde and 1,2-diamine-benzene) were obtained by two different synthetic procedures: a conventional and a microwave assisted method. The composites [MnL]0.25K0.15Mn0.80 PS3(H2O)~1.0 (1), and [MnL]0.25K0.15Cd 0. 80PS3(H2O)~0.5 (2) were obtained by the conventional method, after stirring a suspension of the corresponding potassium precursor and the macrocyclic complex for two weeks, while [MnL]0.35K0.15Mn0.80 PS3(H2O)~1.0 (3) and [MnL]0.25K0.15Cd 0. 80PS3(H2O)~0.5 (4) after stirring for four weeks at room temperature. Using a microwave assisted reaction permitted to obtain in a shorter period of time as compared with the conventional method, composites [MnL]0.20K0.15Mn0.80 PS3(H2O)~1.0 (5) and [MnL]0.15K0.15Cd 0. 80PS3(H2O)~0.5 (6). All the M = MnII, MnIII composites show a bulk antiferromagnetic behavior. However, the spontaneous magnetization present at low temperature in the potassium precursor K0.40Mn0.80 PS3(H2O)~1.0 is observable in composite [MnL]0.20K0.15Mn0.80 PS3(H2O)~1.0 (5), while it is completely absent in composites [MnL]0.25K0.15Mn0.80 PS3(H2O)~1.0 (1) and [MnL]0.35K0.15Mn0.80 PS3(H2O)~1.0 (3). Keywords: Intercalation; MPS3 phases; MnIII macrocyclic complex; microwave assisted synthesis; magnetic properties

Brazil in the 21st century: How to escape the high real interest trap?

The hope that lower real interest rates and higher growth would follow the floatation of the currency was in large measure frustrated. Two international liquidity crises, caused by the reversal of capital flows, hit in 2001 and 2002. These crises were associated with higher interest rates, lower economic activity and higher inflation. Therefore, the name exchange-rate stagflation seems to characterize the essence of the phenomenon. A stylized model, due to Caballero and Krishnamurthy [2002], was used to explain the events. The main characteristic of the model is that domestic investment depends on the aggregate international liquidity of the economy, which is a limiting factor. During a liquidity crisis, the amount of liquidity is reduced, and the economy falls in recession. Neither the fiscal authority nor the monetary authority can reflate the economy by increasing government expenditures or the money supply. The bulk of the difficulties Brazil is currently facing derives from the uncertainty associated with the course of the future economic policy to be followed by the new administration, and to the sustainability of the public debt. To avert a painful default, real interest rates must fall and sustained growth must resume. To increase the chances of success, several policy measures are suggested: · To increase the exportability of the economy; · To increase the fiscal effort, in order to help dispel the doubts over the sustainability of the public debt; · To increase the credibility of the monetary authority, by conferring instrument independence to the Brazilian Central Bank; and · To resume the debt management efforts to lengthen the debt profile while reducing the indexation to the exchange rate and to the Selic short term rate, by making larger user of inflation-linked bonds. When and if the current international liquidity crisis is overcome, the above measures will help Brazil to lower the real interest rates and achieve sustained growth.