Light atom derivatives of structure-preserving sugars are unconventional negative stains

Although glucose and certain other sugars are known to greatly reduce distortion and denaturation of proteins during drying, use of this monosaccharide as an experimental negative stain does not permit imaging of lattice periodicities in test specimens of thin catalase crystals. However, the potassium and sodium salts of several forms of monophosphorylated glucose (200 mM), diphosphorylated glucose, monosulfated glucose, maltose-1-phosphate, and trehalose-6-phosphate, all dry into a glassy layer and scatter transmitted electrons sufficiently to show the 86 A major periods in catalase crystals. Glucose-6-phosphate provides sufficient image contrast at concentrations from 2 mM (=0.067%) to 500 mM (= 16.8%). Underfocusing increases visualization of the periodic lattice, indicating a large contribution of phase contrast to these images. Upon exposure to the electron beam, thicker regions of derivatized saccharides or pure glucose develop bubbling; this redistribution of dried stain largely can be precluded by imaging with low-dose exposures. Power spectra of images of catalase crystals contained within 200 mM disodium glucose-6-phosphate show that periodic information can be recorded to 21 A; some individual features of dipotassium glucose-6-phosphate distribution within the protein lattice have a measured width of around 5 A. The experimental results demonstrate that structure-preserving mono- and di-saccharides also serve successfully as negative stains after they are coupled to light atom scatterers.     

按照最严格的环境法规进行生产

中国、韩国以及美国的部分州都有类似于欧洲RoHS指令的环境法规,这些法规之间存在很小的差别但这些差别却又是不容忽视的。之所以说重要是因为这些差别集中在豁免、报告、合格证明等关键的地方。各国或地区依据不同的环境法规,产生了不同的新规定,这使国际贸易情况变得更加复杂     

Intraspecific Variation in Nutritional Composition Affects the Leaf Age Preferences of a Mammalian Herbivore

Ecologists have long been interested in how the nutritional composition of leaves changes as they age, and whether this affects herbivore feeding preferences. As a consequence, the literature abounds with reports that younger leaves contain higher concentrations of nitrogen and plant secondary metabolites (PSMs) than do older leaves. Most of these studies, however, base their conclusions on average values that often mean little to herbivores. We examined this issue in the well-studied marsupial-eucalypt system, using Eucalyptus melliodora and captive common brushtail possums (Trichosurus vulpecula) offered branches from individual trees containing both young and mature leaves. Like many plants, the concentrations of N and PSMs differed among individual E. melliodora. Although young leaves were, on average, “better defended” by the PSM sideroxylonal than were mature leaves, some trees produced leaves that were relatively undefended at both ages. In response, possums chose different proportions of young and mature leaves depending on the chemistry of the individual tree. Possums did not always prefer leaves with lower concentrations of sideroxylonal (mature leaves) or those with higher concentrations of available N (young leaves). Instead, the sideroxylonal concentration of young leaves dictated their choice: possums preferred young leaves with low sideroxylonal concentrations, but not with high concentrations. By skewing their feeding toward trees producing young leaves with low concentrations of PSMs, possums may influence plant fitness. Researchers will detect these potentially important interactions only if they are aware that measuring variation among plants discloses more information than do average relationships.     

Perceptual processes used by drivers during overtaking in a driving simulator

This study investigated the control strategies and decision making of drivers who were executing overtaking maneuvers in a fixed-base driving simulator. It was found that drivers were frequently inaccurate in deciding whether it was safe to overtake in front of an oncoming vehicle. One source of error in this situation was the control strategy adopted by the driver; in several instances our drivers initiated an overtaking maneuver when the oncoming car's distance was above a critical value, even though there was not sufficient time to complete a safe maneuver. Adaptation to closing speed (produced by driving on a straight open road) also had large effects on overtaking behavior. For all participants, closing speed adaptation resulted in decisions that were delayed, of higher risk, and more variable. Actual or potential applications of this research include improved training for younger drivers and the development of in-car interfaces that reduce closing speed adaptation.     

The new causal principle of cognitive learning theory: Perspectives on Bandura's "reciprocal determinism."

In conceptualizing person–environment interaction, A. Bandura (see record 1979-08427-001) contended that the traditional view of unidirectional causation had to be abandoned in favor of what he called "reciprocal determinism." It is argued that the unidirectional account can be made to work in the cases that Bandura cited and that the criticisms of the neo-Hegelian view of causation can also be applied to Bandura's arguments. In addition, in his Social Learning Theory (1977), Bandura stressed the history of the interaction between a person and the environment, and here "reciprocal determinism" is a misleading expression. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)