Hydrogen bonding effects on molecular structure: crystallographic studies of barbiturates

X-ray crystal structure determinations show systematic perturbations of the order of 0.01 Å in the oxopyrimidine rings of twelve barbiturate molecules. They appear to be related to the mode of intermolecular NHβO hydrogen bonding.     

Characteristics of inclusions in topaz from Serrinha pegmatite (Medina granite,Minas Gerais State,SE Brazil) studied by Raman spectroscopy

Eastern Brazilian Pegmatite Province includes many topaz-bearing pegmatitic bodies. Residual melts from the Fe–K-rich alkaline Medina granite (ca. 500 Ma) formed the Serrinha pegmatite—a system of branched thin pegmatite veins hosted by pink facies of the parent granite. The colourless topaz from Serrinha pegmatite contains both mineral and fluid inclusions. Microcline (513, 476, 456 cm⁻¹), albite (507, 479, 457 cm⁻¹), topaz (926, 858, 267, 239 cm⁻¹), quartz (463 cm⁻¹), rutile (610, 444 cm⁻¹), wolframite (884 cm⁻¹) and uranophane (968, 788 cm⁻¹) represent solid inclusions formed by fluid-induced processes from the pneumatolytic (∼600–400 °C) to hydrothermal (<400 °C) stages of pegmatite crystallization. Fluid inclusions are mainly liquid or liquid-gas, which contain CO₂ (marker bands ∼1388 cm⁻¹ and ∼1285 cm⁻¹) and traces of methane (2917 cm⁻¹). They are mainly of primary and pseudo-secondary origin, indicating tectonic quiescence during and after topaz crystallization (in agreement with the post-collisional nature of the parent granite). Topaz crystallized in high temperature conditions of the pneumatolytic stage at a depth around 8.5–10.0 km.     

巴西果仁致敏原的实时荧光PCR检测

针对巴西果仁2Salbumin mRNA基因设计引物、探针,在实时荧光PCR仪上进行扩增、检测和结果分析.结果显示:该组探针和引物对巴西果仁有很强的特异性,除巴西果仁外,其余8种对照树果材料均未检测到荧光信号,巴西果仁成分检测灵敏度达到0.1%.该方法具有灵敏度高、快速、简便的特点,可用于巴西果仁致敏原成分的定量检测.     

基于巴西劈裂法的饱水煤样能量耗散特征研究

为研究饱水煤样拉伸破坏过程中的能量耗散规律,利用RMT-150B岩石力学实验系统对赵固二矿二1煤层煤样在自然和饱水状态下进行巴西圆盘劈裂实验,探讨了自然与饱水状态下煤样的应力、强度及能量变化。结果表明:巴西劈裂实验时,加载过程应力-时间关系与实验控制方式有关。采用载荷控制方式时,峰值前拉应力与时间呈良好线性关系,达到峰值时应力瞬间跌落为零,表现出明显脆性破坏特征;采用变形控制方式时峰值前拉应力与时间呈非线性关系,峰值后出现分次破坏特征;采用两种控制方式在巴西圆盘劈裂实验破坏前没有本质区别;两种状态下不同层位煤样抗拉强度和峰值能率存在差异,自然状态下层位煤样抗拉强度较高(1.80MPa),中层位煤样抗拉强度较低(1.23MPa),上层位煤样抗拉强度介于两者之间(1.52MPa),饱水后上中下层位煤样的抗拉强度和峰值能率均有不同程度降低,抗拉强度平均软化系数分别为0.65,0.61和0.61,平均峰值能率降幅为36.0%,56.1%和40.6%;两种状态下煤样抗拉强度与峰值能率大致呈线性关系,表明抗拉强度越高的煤样,能量耗散越少,煤样抗拉强度越低,能量耗散越多。     

Hydrodynamic model for particle size segregation in granular media

We present a hydrodynamic theoretical model for “Brazil nut” size segregation in granular materials. We give analytical solutions for the rise velocity of a large intruder particle immersed in a medium of monodisperse fluidized small particles. We propose a new mechanism for this particle size-segregation due to buoyant forces caused by density variations which come from differences in the local “granular temperature”. The mobility of the particles is modified by the energy dissipation due to inelastic collisions and this leads to a different behavior from what one would expect for an elastic system. Using our model we can explain the size ratio dependence of the upward velocity.     

Determination of heavy metals by inductively coupled plasma-optical emission spectrometry in fish from the Piracicaba River in Southern Brazil

A total of 202 fish, representing 16 species, were collected during 2008 (March–October) in the Tanquan region of the Piracicaba River using nets. Flesh samples were collected and analyzed, using inductively coupled plasma-optical emission spectroscopy for Al, As, Cd, Co Cr, Cu, Mn, Mo, Ni, Pb, Se, Sn, Sr, and Zn. The results showed that the flesh of these fish all contained extremely high levels of Al and Sr, and moderately high levels of Cr, As, Zn, Ni, Mn and Pb. The metals were higher in these fish during rainy season, with fish collected during the months of March and October being the highest. In addition, the accumulation of metals was species-dependent. Cascudos (Hypostomus punctatus) and piranhas (Serrasalmus spilopleura) exhibited high levels of almost all of the metals, while curimbata (Prochilodus lineatus) had moderate levels. A few species, including pacu (Piaractus mesopotamicus) and dourado (Salminus maxillosus), had very low levels of most metals. The results show that the Piracicaba River Basin is widely contaminated with high levels of many toxic heavy metals, and that human consumption of some fish species is a human health concern.     

Research on analytical chemistry in Brazil: an overview

An overview is presented of the beginnings, evolution and current status of research on analytical chemistry in Brazil. Among the various fields of chemistry two decades ago, Analytical Chemistry was considered one of the least developed in Brazil. In the last 15 years, however, research and development in this field have expanded considerably and today it is one of the most highly developed fields of Chemistry in Brazil. This paper offers a general overview of this evolution and some suggestions for possible routes for the future of analytical chemistry in Brazil.     

The Influence of Positivism on the Teaching of Mathematics in Brazil: 1870–1930

This article describes the strong influence of positivism on the teaching of mathematics in Brazil. The dissemination of positivism occurred in a very intensive way from 1870 to 1930, due mainly to the strong leadership of teachers at the military and engineering academies. From its firmly entrenched position in these institutions, the positivistic ideology affected the social, political, pedagogical, and ideological life in Brazil. Here, I identify the main representatives of positivism, who focused their research on Auguste Comte's concept of mathematics. They oriented curricula and programs according to Comte's principles as well as produced mathematics with a distinct positivist bent. Although a marked decline occurred after 1930, the positivistic phenomenon was not exhausted as a research topic, and, indeed, it still has not been entirely extinguished in Brazilian life. Copyright 1999 Academic Press.Este trabalho descreve a forte influência do positivismo no ensino da Matemática no Brasil. A difusão do positivismo aconteceu de forma muita intensa entre 1870 e 1930, devido principalmente a atuação dos docentes-militares, que mantinham uma liderança forte nas academias militares e de engenharia. Nestas instituições a ideologia positivista encontrou uma forte sustentação e pode, então, ter efeitos na vida social, polı́tica, pedagógica e ideológica brasileira. Identificamos os principais representantes do positivismo no cı́rculo acadêmico. Detectamos as primeiras manifestações da concepção de Matemática de Auguste Comte em livros-texto. Identificamos a orientação de currı́culos e programas segundo os preceitos de Comte e analisamos principalmente as obras de Matemática de autores positivistas. O declı́nio do positivismos depois de 1930 também é registrado. O fenômeno positivismo não foi esgotado como tema de pesquisa e tudo indica que ainda não se extinguiu completamente da vida brasileira. Copyright 1999 Academic Press.MSC 1991 subject classifications: 01A55, 01A70.     

On epidote fission track dating

The use of epidote in fission track dating was abandoned since the beginning of the 1980s due to difficulties like absence of a standard etching procedure, obtainment of different closure temperatures and the percentage of the datable samples. The results become much more reproducible when restricting fission track analysis to a peculiar kind of track. We are also studying confined track length, what makes possible to obtain information about fossil track annealing. Fission tracks in epidote were successfully etched with 48% HF at for 12.5 min. Dating samples by the external detector method was not possible due to problems in measuring the efficiency factor held between the number of fossil fission tracks and tracks induced in mica. Dating a sample from Brejuí, RN, Brazil with the population method gave a corrected age of , in agreement with published U/Th–Pb ages. From the fact that the fossil track length histogram was bimodal, we were able to infer that this sample registered a thermal episode during its history.

These preliminary results indicate that epidote deserves further studies to establish whether it can be employed as a thermochronological tool.