战前的科学

第二次世界大战深刻影响了人们对科学的看法,远超其他历史事件.特别是在广岛和长崎,科学展现了令人生畏的力量.科学与技术、政府之间的合作有可能会带来严重的风险.我们应该重点发展哪些技术?应该怎样规范科学研究,引导它向特定目标发展?政府又该扮演什么样的角色?二战以来,政府资助并组织了许多大规模研究,掌握了技术应用的方向,比如...     

Action mechanisms of a new erythrocyte-derived depressing factor

To investigate the action mechanisms of a new erythrocyte-derived depressing factor (EDDF), the focus is placed on the effect of EDDF on both cytosolic and nuclear free calcium (Ca²⁺) transportation in vascular smooth muscle cell (VSMC), as well as the apoptosis and cell cycle of VSMC of rats. EDDF has been extracted from human erythrocytes. The changes of Ca²⁺ levels in cytoplasm ([Ca²⁺]_i) and nucleus ([Ca²⁺]_n) have been observed using a laser scanning confocal microscope together with fluo-3/AM as a calcium indicator. Flow cytometric technique was used to study the effect of EDDF on cell cycle and apoptosis of VSMC. [Ca²⁺], and [Ca²⁺]_n were significantly decreased through several different pathways: ( i ) it reduced the Ca²⁺ influx by blocking L-type voltage-dependent calcium channel (L-VDC) and R-type voltage-dependent calcium channel (R-VDC); (ii) it inhibited the Ca²⁺ release from inositol 1, 4, 5-trisphosphate (IP₃) sensitive calcium store; and (iii) activated Ca²⁺-ATPase of sarcoplasmic reticulum (SR) and promoted the transportation of Ca²⁺ from cytoplasm to SR. However, EDDF seemed to have little inhibitory effect on the Ca²⁺ release from ryonodine sensitive calcium pool. It was also found that EDDF (10⁻⁴ g/mL) significantly decreased the proportion of S phase of human umbilical vein (HUV) and inhibited the proliferation of VSMC induced by angiotensin II (Angll, 10⁻⁵ mol/L). The apopotosis did not occur when VSMC was cultured under normal condition. While VSMC apoptosis was induced by Angll (10⁻⁵ mol/L) and EDDF (10⁻⁴ g/mL) seemed to have little effect on it. The inhibitory effect of EDDF on the elevation of [Ca²⁺]_i and [Ca²⁺]_n of VSMC might play an essential role in its action mechanisms and the ways it affects the Ca²⁺ handling of VSMC demonstrate that EDDF was different from other endogenous blood pressure regulators and some known antihypertensive drugs. EDDF could inhibit the proliferation of VSMC, which indicated that it might be beneficial to the prevention and treatment of hypertension and arteriosclerosis.     

奇妙的非晶态金属

在日常生活中,人们所接触的材料不外乎两类,即晶态材料和非晶态材料。形象地说,如果材料中的原子排列像被检阅的士兵方阵那样有序,该材料就是晶态材料;如果原子排列像集市的人群那样杂乱无章,那么这种材料就是非晶态材料。在我们接触的物质中,食盐、钻石等都属于晶态材料,而木材、纺     

Th-rich zircon from peralka line A-type granite： Mineralogical features and petrological implications

Zircon is one of the most common accessory minerals in igneous rocks, especially in granites. It exists through the crystallization and evolution of grantic magma be-cause of stable physicochemical properties. Trace element abundances (e.g. Hf, Th, U, Y) in zircon are very sensitive to the crystallization environments[1]. Therefore, zircon plays an important role in the granite research. However, although A-type granites are given more and more regards by the geologists owing to their charac…     

Comparison of distribution and habitat characteristics between an endemic and a wide-ranging cryptic species of Peromyscus on the Baja California Peninsula

Peromyscus eva and Peromyscus fraterculus are 2 morphologically similar species of the Peromyscus eremicus group occurring on the Baja California Peninsula. Due to the similarity between these 2 species, their ranges have been greatly confused; consequently, the specific habitat characteristics for each group are not well known. The goal of this study was to assess distribution ranges and characteristics of preferred habitats for P. eva and P. fraterculus in more detail. We identified taxonomy of individuals by evaluating genetic patterns produced by restriction fragment length polymorphisms (RFLPs). We evaluated the banding pattern generated by Alu I and Bam HI restriction enzymes in an 850-bp cytochrome b fragment. Consistent differences in number and size of fragments allowed for discrimination of individuals to species. The heterogeneity and evenness indexes showed that the microhabitat of P. fraterculus contained less-diverse soil types and is more homogeneous than the microhabitat of P. eva. In the state of Baja California Sur, P. eva occurs exclusively in the flat areas along the Pacific coast from the Vizcaino Desert to the south, including Margarita Island, with one small population in the Loreto area adjacent to Carmen Island. The habitats occupied by P. eva were heterogeneous (areas with friable, soft sandy soil and a low percentage of small stones). Peromyscus fraterculus occurs mostly in Baja California Norte, with some populations distributed in Baja California Sur, particularly in the western areas of the Vizcaino Desert along the mountain range, in the gulf side of the peninsula south of the city of La Paz, and in a small area on the eastern side of Sierra de Las Cruces. This species was mostly found on hard soil with high medium-size stone content.     

国外开发可食性包装

近几年来,世界许多国家和地区研制开发可以被人体消化吸收的可食性包装材料,对控制白色污染具有广阔前景。 美国农业部农业研究局南部地区研究中心,利用大豆提炼的蛋白质,制造成功类似塑料的化合物,作为新一代食品包装材料,替代过去以石油为原料合成的塑料。其制作技术是:将大豆用水浸泡,软化之后加工磨碎,使蛋白质从固体成分中分离出来,而后将其晾干浓缩;另一种是用机械除去其中的水     

环境温度对混凝土梁式桥频率的影响研究

现有关于环境温度影响桥梁自振频率特性的研究通常针对特定桥梁，其通用性受到了一定的限制.鉴于混凝土梁式桥是应用最广泛的桥梁类型，本文从自振频率解析解出发，推导了混凝土梁式桥自振频率和温度关系的通用迭代计算公式，并通过数值算例和环境耦合箱模型试验进行验证.结果表明：环境温度对桥梁自振频率的影响不可忽视，所提出的桥梁自振频率迭代计算公式能有效考虑环境温度的影响，可用于计算实际温度作用下的混凝土梁式桥的频率.     

Effect of homogenization process on the hardness of Zn–Al–Cu alloys

The effect of a homogenizing treatment on the hardness of as-cast Zn–Al–Cu alloys was investigated. Eight alloy compositions were prepared and homogenized at 350 ℃ for 180 h, and their Rockwell “B” hardness was subsequently measured. All the specimens were analyzed by X-ray diffraction and metallographically prepared for observation by optical microscopy and scanning electron microscopy. The results of the present work indicated that the hardness of both alloys (as-cast and homogenized) increased with increasing Al and Cu contents; this increased hardness is likely related to the presence of the θ and τ' phases. A regression equation was obtained to determine the hardness of the homogenized alloys as a function of their chemical composition and processing parameters, such as homogenization time and temperature, used in their preparation.     

Leaching of a copper flotation concentrate with ammonium persulfate in an autoclave system

The leaching behavior of a copper flotation concentrate was investigated using ammonium persulfate (APS) in an autoclave system. The decomposition products of APS, active oxygen, and acidic medium were used to extract metals from the concentrate. Leaching experiments were performed to compare the availability of APS as an oxidizing agent for leaching of the concentrate under atmospheric conditions and in an autoclave system. Leaching temperature and APS concentration were found to be important parameters in both leaching systems. Atmospheric leaching studies showed that the metal extractions increased with the increase in APS concentration and temperature (up to 333 K). A similar tendency was determined in the autoclave studies up to 423 K. It was also determined that the metal extractions decreased at temperatures above 423 K due to the passivation of the particle surface by molten elemental sulfur. The results showed that higher copper extractions could be achieved using an autoclave system.