Thermoelectric properties of Pb0.75-xMnxSn0.25Te alloys with variable manganese content

Lead tin telluride is one of the well-established thermoelectric materials in the temperature range 350-750 K. In the present study, Pb0.75-xMnxSn0.25Te1.00 alloys with variable manganese (Mn) content were prepared by solid state synthesis and the thermoelectric properties were studied. X-ray diffraction, (XRD) showed that the samples followed Vegard's law, indicating solid solution formation and substitution of Mn at the Pb site. Scanning Electron Microscopy (SEM) showed that the grain sizes varied from <1 mu m to more than 10 mu m and MnTe rich phase was present for higher Mn content. Seebeck coefficient, electrical resistivity and thermal conductivity were measured from room temperature to 720 K. At 300 K, large Seebeck values were obtained, possibly due to increased effective mass on Mn substitution and low carrier concentration of the samples. At higher temperatures, transition from n-type to p-type indicated the presence of thermally generated carriers. Temperature dependent electrical resistivity showed the transition from degenerate to non-degenerate behavior. For thermal conductivity, low values (similar to 1 W/m-K at 300 K) were obtained. At higher temperatures bipolar conduction was observed, in agreement with the Seebeck and resistivity data. Due to low power factor, the maximum thermoelectric figure of merit (zT) was limited to 0.23 at 329 K for the sample with lowest Mn content (x=0.03). (C) 2015 Elsevier Ltd. All rights reserved.

Probing the role of highly conserved residues in triosephosphate isomerase-analysis of site specific mutants at positions 64 and 75 in the Plasmodial enzyme

Highly conserved residues in enzymes are often found to be clustered close to active sites, suggesting that functional constraints dictate the nature of amino acid residues accommodated at these sites. Using the Plasmodiumfalciparum triosephosphate isomerase (PfTIM) enzyme () as a template, we have examined the effects of mutations at positions 64 and 75, which are not directly involved in the proton transfer cycle. Thr (T) occurring at position 75 is completely conserved, whereas only Gln (Q) and Glu (E) are accommodated at position 64. Biophysical and kinetic data are reported for four T75 (T75S/V/C/N) and two Q64 (Q64N/E) mutants. The dimeric structure is weakened in the Q64E and Q64N mutants, whereas dimer integrity is unimpaired in all four T75 mutants. Measurement of the concentration dependence of enzyme activity permits an estimate of K-d values for dimer dissociation (Q64N=73.79.2nm and Q64E=44.6 +/- 8.4nm). The T75S/V/C mutants have activities comparable to the wild-type enzyme, whereas a fourfold drop is observed for T75N. All four T75 mutants show a dramatic fall in activity between 35 degrees C and 45 degrees C. Crystal structure determination of the T75S/V/N mutants provides insights into the variations in local interactions, with the T75N mutant showing the largest changes. Hydrogen-bond interactions determine dimer stability restricting the choice of residues at position 64 to Gln (Q) and Glu (E). At position 75, the overwhelming preference for Thr (T) may be dictated by the imperative of maintaining temperature stability of enzyme activity.

Sapientia, 1965, Vol. XX, nº 75 (número completo)

Contenido: Técnica y espíritu / Octavio N. Derisi – Fundamento y esencia del bien / Agustín Basave Fernández del Valle – Blaise Pascal, ¿filósofo o apologista? / Carmen Balzer – El porvenir del hombre / Alberto Caturelli – Notas y comentarios -- Bibliografía

东方红-75拖拉机车架在垂直非对称载荷作用下的内力分布和翘曲变形

本文采用结构矩阵分析力法,对东方红-75拖拉机车架在受到翘曲变形时的内力进行了计算与分析,系统的研究了当结构参数改变时车架内力分布的变化规律。以及该种车架强度和刚度不足的主要原因。提出了改进车架强度和刚度的实施办法。

Mixed-mode fracture mechanisms near the fatigue threshold of aisi-316 stainless-steel

Near threshold, mixed mode (I and II), fatigue crack growth occurs mainly by two mechanisms, coplanar (or shear) mode and branch (or tensile) mode. For a constant ratio of ΔK_I/ΔK_II the shear mode growth shows a self-arrest character and it would only start again when ΔK_I and ΔK_II are increased. Both shear crack growth and the early stages of tensile crack growth, are of a crystallographic nature; the fatigue crack proceeds along slip planes or grain boundaries. The appearance of the fracture surfaces suggest that the mechanism of crack extension is by developing slip band microcracks which join up to form a macrocrack. This process is thought to be assisted by the nature of the plastic deformation within the reversed plastic zone where high back stresses are set up by dislocation pile-ups against grain boundaries. The interaction of the crack tip stress field with that of the dislocation pile-ups leads to the formation of slip band microcracks and subsequent crack extension. The change from shear mode to tensile mode growth probably occurs when the maximum tensile stress and the microcrack density in the maximum tensile plane direction attain critical values.

结构弛豫对Zr_(64.13)Cu_(15.75)Ni_(10.12)Al_(10)块体非晶合金硬度和剪切带特征的影响

通过接近玻璃转变温度的等温退火获得不同弛豫状态的Zr64.13Cu15.75Ni10.12Al10块体非晶合金样品。利用维氏显微硬度计和洛氏硬度计研究结构弛豫对合金硬度和压痕周围剪切带特征的影响规律。结果表明:在590K等温退火处理使Zr64.13Cu15.75Ni10.12Al10块体非晶合金发生焓弛豫行为,其维氏显微硬度随退火时间的延长较快增加后趋于稳定,而大载荷洛氏硬度对结构弛豫不敏感。通过洛氏压痕周围剪切带特征的研究,定量比较了结构弛豫对剪切带间距、数量的影响规律。

Diário da Constituinte [gravação de vídeo] : [programa n. 316]

Conclusão das votações na Comissão de Sistematização. Na discussão sobre Anisitia, foram rejeitadas as propostas que previam o pagamento de atrasados aos anistiados. Uma delas foi a emenda do Deputado Brandão Monteiro (PDT-RJ), que estendia os benefícios da Anistia aos membros da Marinha e Aeronáutica. Aprovada emenda do Deputado José Maria Eymael (PDC-SP) estabelecendo que a lei ordinária irá criar uma compesação financeira para os pilotos da Força Aérea Brasileira (FAB) cassados depois de março de 1964. Aprovado destaque do Deputado José Costa (PMDB-AL), que possibilita às vítimas cassadas após 1964, recorrerem à justiça para terem seus direitos revistos. A Anistia foi também estendida aos trabalhadores do setor privado com a emenda do Deputado João Paulo Vasconcellos (PT-MG). Aprovada a emenda de Nelson Carneiro (PMDB-RJ), que regula a aplicação do parlamentarismo nos Estados. A Deputada Raquel Cândido (PFL-RO) tem a sua emenda aprovada, que cria o Código de Defesa do Consumidor. A duração do mandato do Presidente José Sarney gera polêmica entre os constituintes. Opinam os Deputados: Elizer Moreira (PFL-MA), João Carlos Barcelar (PMDB-BA) e João Hermann Neto (PMDB-SP).

The Freshwater Biological Association at 75

The year 2004 marked the 75th anniversary of the Freshwater Biological Association. The author reflects the history of the Association focusing on the main events of the last 25 years since 1979.

Bird migration and the spread of Crustacea. [Translation from: Verhandlungen der Deutschen Zoologischen Gesellschaft 27, 311-316, 1963.]

The passive spread of a high percentage of freshwater organisms is one of the most important requirements in short-lived and insular communities for species to attai n and survive - and consequently to balance the lack of a topographical continuity of most inland waters. Unfortunately hardly anything is known about the amounts of seed material typical for any lake into which it is carried. The causes of passive dissemination - wind, water and animals as well as man - are confirmed by many examples. It has been assumed now for at least a hundered years that , among animals, birds play a prominent role, although also disappointingly few facts are at hand. The passage and spread through birds' intestines has up to now been supported only by some limited data. This paper reports on experimental research where the eggs of Daphnia magna, Triops cancriformis, Artemia salina, Diaptomus spinosus and Cypris pubera were introduced by means of gelatine capsules into the oesophagus of a drake. The bird's excrements were inspected under a microscope for eggs and resting stages, and these were transferred into corresponding cultures.

The effect of oxygen concentration in water on the growth and nitrogen metabolism in the fry of rainbow trout [Translation from: Rybnoe Khoziaistvo,V.33, 74-75, 1957]

To ascertain the effect of various concentrations of oxygen in water on the fry of rainbow trout experiments were made with aquaria at various concentrations of oxygen. The food supplied was chironomid larvae (Chironomus plumosus). A surplus of food was supplied to the fry. Indices are given of the reaction of the fry to different temperatures.

75 mW robust single frequency Yb-doped DFB fiber Bragg grating laser

Incorporating the shielded method and post-processing method, a 75 mW single frequency Yb-doped DFB fiber laser was obtained with a 250 mW laser diode pump source at 978 nm. The threshold of the laser is 2 mW. The laser is single-polarization operation and the output power fluctuation is less than 0.2 mW in one hour when the pump power is 250 mW.