Recent developments in the analysis of toxic elements

One may conclude that it is impractical to confine oneself to any one analytical method since ever more sensitive instrumentation continues to be produced. However, in certain methods such as anodic stripping voltammetry and flameless atomic absorption it may be background contamination from reagent impurities and surroundings rather than instrument sensitivity which controls the limits of element detection. The problem of contamination from dust or glassware is greatly magnified when the sample size becomes ever smaller. Air entering laboratories near highways may contain trace quantities of lead, cadmium, barium, antimony, and other elements from engine exhaust. Even plastic materials contacting the sample may be suspect as a source of contamination since specific metals may be used as catalysts in the synthesis of the plastic and traces may be retained in it. Certain elements may even be deliberately added to plastics during manufacture for identification purposes. Nondestructive methods such as neutron activation and x-ray techniques thus offer great advantages not only in time but in the elimination of impurities introduced during sample ashing. Future improvements in attainable limits of detection may arise largely from progress in the ultrapurification of reagents and "clean-room" techniques. Finally, the competence of the analyst is also vitally important in the skillful operation of modern complex analytical instrumentation and in the experienced evaluation of data.     

Reversible cryogenic blockade of neural function in the brain of unrestrained animals

Reversible cryogenic blockade of neural systems in the brain may be accomplished by local cooling. A small cryoprobe is described which may be implanted in the brain of an unrestrained, behaving animal. Cooling may be restricted to the tip of the cryoprobe and the temperature of the tip and the shaft may be regulated and monitored independently by miniature thermocouples and appropriate control and indicator devices. Electrophysiological results are presented which show that the cryogenic blocking effect may be localized to within a few millimeters of the tip of the cryoprobe and that the size of the region blocked is proportional to the tip temperature. The system described has been shown to be effective in both electrophysiological and behavioral studies.     

迦辽金法在管道不稳定流动分析中的应用

针对输油管道系统的组成特点，将系统划分成基本组成单元，建立了油品在单元中不稳定流动方程，并综合考虑它们的边界条件、连接条件和初始条件，通过引入线性化系数，采用迦辽金方法讨论了求解问题。该方法既具有解析解法的特点，又具有数值解法的特点。当所划分的管道单元较大时，可以得到直观的近似解析解；当所划分的管道单元较小时，可以得到更准确的数值解。与常用解析法相比，该方法可适用于各种管道结构，因其可在不同的管道单元和不同时间层上计算线性化系数，从而可以提高求解的准确性。与其它数值解法相比，由于管道单元和时间步长的选取可大可小，各管道单元的大小也可以不一样，这就提高了求解的灵活性。以此为基础，编制了计算机软件，对某输油管道进行了实际模拟分析，获得了满意结果。     

SOME REFLECTIONS CONCERNING VALENCE VARIATION AND ATOMIC STRUCTURE

In bringing to a conclusion these few scattered reflections concerning valence variation and atomic structure, may I be permitted to say this: He who is experimentally inclined may henceforth take heart and he need not be quite so timid in interpreting strange chemical reactions on the assumption of possible anomaly in the valence of the reactants. The physicist has no hesitation in speaking of the temporary existence, at the higher temperature employed in spectroscopic work, of such molecules as BaCl, AlO, (HO), CH(+), CH(2), MgF, etc. Is it not possible that under the influence of surface forces somewhat similar valence variation may not be excluded even at lower temperatures? That these strange compounds are thermodynamically unstable may be true. Nevertheless, they may function as the mysterious catalysts, or as initiators of chain reactions.     

Proteins from human cerebrospinal fluid: binding with nucleic acids

Cerebrospinal fluid (CSF) contains two groups of proteins that bind tightly to DNA and to polyriboguanylic acid, respectively. In certain diseases the amounts of a given nucleic acid bound by a constant volume of CSF may increase, while in others the amount of such proteins may be reduced. Binding of polyriboguanylic acid increased in CSF samples from patients with brain tumors, stroke, multiple sclerosis, and communicating hydrocephalus, but it significantly decreased in CSF samples from patients with obstructive hydrocephalus. These increases may or may not be proportional to the rise in total CSF proteins characteristic for these diseases. Elevated binding of DNA was observed in samples from patients with hydrocephalus, epilepsy, and cortical atrophy. The technique described may be applicable to the diagnosis of a variety of diseases of the central nervous system.     

Keto-aldehydes and cell division

Many problems are left open in this article. Its publication may be excused by the suffering cancer causes, which urges the researcher to publish as soon as he thinks he may have found a new trail, which also may be taken by others. What emerges clearly is that SH groups, with their specific reactivities, offer a hopeful target in the search for cancerostatic substances, among which the natural repressor of cell division may hold out the most promise. The glyoxal derivatives also have antiviral properties (7, 16) and may be in the center of a hitherto unknown system of equilibria which deserves a thorough study. The low molecular weight of the glyoxal derivative reported justifies the hope of an early clarification of its structure, as well as its synthesis (17).     

Continental accretion: from oceanic plateaus to allochthonous terranes

Some of the regions of the anomalously high sea-floor topography in today's oceans may be modern allochthonous terranes moving with their oceanic plates. Fated to collide with and be accreted to adjacent continents, they may create complex volcanism, cut off and trap oceanic crust, and cause orogenic deformaton. The accretion of plateaus during subduction of oceanic plates may be responsible for mountain building comparable to that produced by the collision of continents.     

不同处理对控制杏酶褐变的研究

试验表明，沸水烫漂杏４ｍｉｎ可基本控制多酚氧化酶（ＰＰＯ）引起的酶褐变。用１５ｇＬ－１（以有效ＳＯ２计）的亚硫酸盐溶液浸泡２ｈ，可使杏ＰＰＯ活性降至零，不产生ＰＰＯ褐变。抗坏血酸使杏ＰＰＯ活性降低，但成品褐变率显著提高。用１０ｇＬ－１半胱氨酸溶液浸泡１．５ｈ，可控制杏ＰＰＯ所致酶褐变。     

Chemistry and structure of nucleic acids of bacteriophages. Many forms of nucleic acids of bacteriophages show the ways that information is stored and reproduced

The nucleic acids of bacteriophages are characterized by a surprising multiformity. RNA and DNA may occur, the latter in single- or double-stranded form, circular or linear, with or without breaks or single-strand ends. Terminal redundancy may exist and the populations of linear phages may be uniform or randomly permuted. A double-stranded circular DNA does not occur in extracellular bacteriophage, but is often if not always formed after infection of the bacterial host. Phage DNA may be glucosylated or methylated to a certain extent, and the glucose and methyl residues may influence the stability of the DNA inside the host.     

重庆市林纸一体化工程林资源估算

依据重庆市森林资源二类调查和速生丰产林规划数据,对可供林纸一体化工程林资源进行了估算,结果表明：渝东南地区,可用于造纸的现有林年生长量158．3万m^3,规划速丰林12．6万hm^2,年生长量66万m^3;渝西地区,可用于造纸的现有竹林年产竹材60．8万t,规划小径竹2．6万hm^2,年产竹材33．2万t;其他地区的木材、竹材作为规避风险的补充。制浆规模：以木材为原料的化学浆应小于29万t/a,以竹材为原料的化学浆应小于23万t/a。     

Immunological Technique for Protein Isolation

Carefully coagulated antibody or antigen-antibody complexes may be used as specific adsorbents for antigen, and the antigen may be released subsequently by increasing the acidity. No cross adsorption appears to take place. The procedure may prove useful for the isolation of tissue-specific proteins (including those in disease states), toxins, or viruses.     

Gene order and dynamic domains

When considering the daunting complexity of eukaryotic genomes, some comfort can be found in the fact that the human genome may contain only 30,000 to 40,000 genes. Moreover, growing evidence suggests that genomes may be organized in such a way as to take advantage of space. A gene's location in the linear DNA sequence and its position in the three-dimensional nucleus can both be important in its regulation. Contrary to prevailing notions in this postgenomic era, the bacteriophage lambda, a paragon of simplicity, may still have a few things to teach us with respect to these facets of nonrandom genomes.     

Centrifugal homogenizer

Tissue can be homogenized in conventional ground-glass tissue grinders in conjunction with centrifugation. The method may be of special value for separating soluble from insoluble material during homogenization of tissue. As yet only yeast cells and spores of slime mold have been homogenized, but the method may be useful for many tissues.     

The brain connection: the corpus callosum is larger in left-handers

The size of the midsagittal area of the human corpus callosum obtained from postmortem measurement varied with tested hand preference. The corpus callosum, the main fiber tract connecting the two cerebral hemispheres, was larger by about 0.75 square centimeter, or 11 percent, in left-handed and ambidextrous people than in those with consistent right-hand preference. The difference was present in both the anterior and posterior halves, but not in the region of the splenium itself. This callosal morphology, which varied with hand preference, may also be related to individual differences in the pattern of hemispheric functional specialization. The greater bihemispheric representation of cognitive functions in left- and mixed-handers may be associated with greater anatomical connection between the hemispheres. The naturally occurring regressive events in neurogenesis, such as neuronal cell death and axonal elimination, may be factors in the individual differences in brain morphology and in functional lateralization. Specifically, right-handers may be those with more extensive early elimination of neural components.     

Fractal surfaces of proteins

Fractal surfaces can be used to characterize the roughness or irregularity of protein surfaces. The degree of irregularity of a surface may be described by the fractal dimension D. For protein surfaces defined with probes in the range of 1.0 to 3.5 angstroms in radius, D is approximately 2.4 or intermediate between the value for a completely smooth surface (D = 2) and that for a completely space-filling surface (D = 3). Individual regions of proteins show considerable variation in D. These variations may be related to structural features such as active sites and subunit interfaces, suggesting that surface texture may be a factor influencing molecular interactions.     

“五元三法”教学体系初探—谈经济管理类本科专业理论课程教学法

人类认识事物运动并对其运动施控的过程有三次“质”的飞跃阶段。理，工科本科教育基本定位于人类认识的第三次“质”的飞跃阶段，而经济管理类本科教育则横跨人类认识的全过程，即定位于第一，二，三次“质”的飞跃阶段，因而其教育教学的特性与理，工科不同，更注重应付不确定性因素与风险因素以及由此导致的知识综合性，交叉性，初中性与多变性，这些特性决定了经济管理类本科教育理论课教学的多元化特色，笔称之为“二元三法”体系，即针对经济管理类本科教育五类理论课程的划分或设置以及不同课程特性的差异，对不同程程可分别或复合式采取传统讲授，专题讲座和案例分析三种方法。     

From force fields to dynamics: classical and quantal paths

Reaction path methods provide a powerful tool for bridging the gap between electronic structure and chemical dynamics. Classical mechanical reaction paths may usually be understood in terms of the force field in the vicinity of a minimum energy path (MEP). When there is a significant component of hydrogenic motion along the MEP and a barrier much higher than the average energy of reactants, quantal tunneling paths must be considered, and these tend to be located on the corner-cutting side of the MEP. As the curvature of the MEP in mass-scaled coordinates is increased, the quantal reaction paths may deviate considerably from the classical ones, and the force field must be mapped out over a wider region, called the reaction swath. The required force fields may be represented by global or semiglobal analytic functions, or the dynamics may be computed "directly" from the electronic structure results without the intermediacy of potential energy functions. Applications to atom and diatom reactions in the gas phase and at gas-solid interfaces and to reactions of polyatomic molecules in the gas phase, in clusters, and in aqueous solution are discussed as examples.     

杀虫剂在木本植物体内传导理论研究进展

杀虫剂通过在植物体内输导而使其通体带药来控制害虫。药剂进入植物体内 ,通过植物蒸腾作用产生的拉力随液流到达作用部位 ,在植物体内呈不均匀分布 ,从而达到控制害虫的目的 ;性质不同的杀虫剂在不同植物体内传导机理不同 ;传导速度与植物生理状态、气候因子、药剂的理化性质等诸因素有关 ;杀虫剂在植物体内的代谢不同于常规施药方法 ,一般在植物代谢旺盛的部位残留量较大 ;通过该技术控制害虫的大量试验表明 ,植物体内注药的方法是行之有效的 ,且对环境的污染显著小于常规施药方法     

Scanning electron microscopes: is high resolution possible?

Experiments with this scanning microscope have produced extremely encouraging results so that we feel Confident in predicting high resolution and high contrast after some obvious modifications are made in the system, such as providing a good objective lens. Experience with conventional lenses indicates that the instrument behaves in a predictable manner and there is no reason to doubt that the resolution can be as good as that of a conventional microscope. The use of quadrupole lenses will depend on calculations now being performed. There is cause for optimism; high resolution may also be possible with this kind of lens. Experience with field emission shows that the technology is not difficult and that there is more than enough current available for any conceivable use. Energy-loss measurements have been made on a variety of materials. It is attractive to consider the possibility of chemical analysis of selected areas of a specimen. We believe that a very crude form of analysis may indeed be possible. The principal advantage of the use of energy-loss techniques, however, may be in the availability of another contrast mechanism. The ability to "see" small details may be considerably enhanced. Finally, we are experimenting with the possibility of using transmitted electrons of different energy losses to produce different colors on a color television display. This should add an extra element to the picture contrast which may be of some value.