Metamict mineral alteration: an implication for radioactive waste disposal

Pervasive alteration is a common feature of metamict minerals. Previous studies of metamict niobium-tantalum-titanium oxides and electron microprobe analyses of altered areas in metamict yttrialite document the leaching of uranium, thorium, and rare earth elements. These data suggest that glasses may not provide a stable medium for radioactive waste disposal.     

"Tactile" stimulus intensity: information transmission by relay neurons in different trigeminal nuclei

Comparison of the information transmitted about the intensity of a steady "tactile" stimulus applied to facial skin by single trigemino-thalamic neurons in nucleus oralis and nucleus caudalis indicates that little information loss occurs at the medial lemniscal synaptic relay (nucleus oralis), but that it is gross within the nucleus caudalis.     

Chick's response to an imprinting stimulus: heterosis and evolution

Tendencies of day-old chicks to respond toward, to approach, and to stay near a distant audiovisulal imprinting apparatus were shown to be inherited in a heterotic manner. High correlations found among the traits suggest that these behavioral responses are not independent but sequential. The fitness value of such a behavioral sequence is explained in terms of imprinting.     

Punishment by response-contingent withdrawal of an imprinted stimulus

Newly hatched ducklinigs were exposed to a moving, imprinted stiulullls; if they followed it, the stimnulus was withdrawn briefly. The tendency to follow gradually declined durinig punishment periods, but it returned to prepunishment amounts whlen punishmnent terminated. This finding attests to the efficacy of withdrawal of reinforcement as a techniquie for behavioral control.     

Evidence for an inter-organismic heme biosynthetic pathway in symbiotic soybean root nodules

The successful symbiosis of soybean with Bradyrhizobium japonicum depends on their complex interactions, culminating in the development and maintenance of root nodules. A B. japonicum mutant defective in heme synthesis in culture was able to produce heme as a result of its symbiotic association with the soybean host. The bacterial mutant was incapable of synthesizing the committed heme precursor delta-aminolevulinic acid (ALA), but nodule plant cells formed ALA from glutamate. In addition, exogenous ALA was taken up by isolated nodule bacteria of the parent strain and of the mutant. It is proposed that bacterial heme found in nodules can be synthesized from plant ALA, hence segments of a single metabolic pathway are spatially separated into two organisms.     

Ultraviolet light: a new stimulus for the induction of platelet aggregation

Exposure to ultraviolet light (253.7 nanometers) causes mammalian blood platelets to aggregate. Aggregation is markedly enhanced in the presence of extracellular fibrinogen and is followed by the grodual of relatively small amounts of nucleotide and serotonin. Aggregation is inhibited by ethylenediamine tetraacetic acid or a combination of 2-deoxy-D-glucose and antimycin A. Adenosine, apyrase, and prostaglandin E(1) produced slight inhibition. The effect of exposure to ultraviolet light is cumulative and lasting. This agent may be used to study the process of platelet aggregation after the removal of the stimulus, by delaying the addition of fibrinogen until after cessation of irradiation. Thus ultraviolet light is the first agent known which may be used to study platelet aggregation in a period following its removal.     

Control of behavior by presentation of an imprinted stimulus

When presentation of an imprinted stimulus is contingent upon an arbitrarily chosen response, the rate of emission of this response increases. This control of responding requires a moving imprinted stimulus and does not require a following response by the duck.     

Cat color vision: the effect of stimulus size

Adult cats were trained to discriminate blue from green and gray. Although the cats could discriminate the intensity of stimuli whose areas ranged from 33 to 0.36 square centimeters they could not discriminate color when the stimulus was 0.36 square centimeter (less than 20 degrees visual angle). This influence of stimulus size may account for both positive and negative results of previous studies.     

The application of ecological theory toward an understanding of the human microbiome

The human-microbial ecosystem plays a variety of important roles in human health and disease. Each person can be viewed as an island-like "patch" of habitat occupied by microbial assemblages formed by the fundamental processes of community ecology: dispersal, local diversification, environmental selection, and ecological drift. Community assembly theory, and metacommunity theory in particular, provides a framework for understanding the ecological dynamics of the human microbiome, such as compositional variability within and between hosts. We explore three core scenarios of human microbiome assembly: development in infants, representing assembly in previously unoccupied habitats; recovery from antibiotics, representing assembly after disturbance; and invasion by pathogens, representing assembly in the context of invasive species. Judicious application of ecological theory may lead to improved strategies for restoring and maintaining the microbiota and the crucial health-associated ecosystem services that it provides.     

基于鲁米诺 高碘酸钾后化学发光测定肾上腺素

基于肾上腺素在高碘酸钾-鲁米诺碱性体系中的后化学发光反应,结合流动注射技术,建立了测定肾上腺素的流动注射-化学发光(FI(CL)方法.该方法简单、快速、灵敏,线性范围为3.0×10-5～1.2×10-4 g/L(r=0.996 9),检出限为3.0×10-7 g/L(3σ).对5.0×10-5 g/L的肾上腺素标准溶液进行11次平行测定,相对标准偏差为2.0%.将其应用于肾上腺素注射液中肾上腺素含量的测定,结果令人满意.同时,还初步探讨了该化学发光反应的发光机制.     

Thermodynamics of calcite growth: baseline for understanding biomineral formation

The complexity of biomineralized structures suggests the potential of organic constituents for controlling energetic factors during crystal synthesis. Atomic force microscopy was used to investigate the thermodynamic controls on carbonate growth and to measure the dependence of step speed on step length and the dependence of critical step length on supersaturation in precisely controlled solutions. These data were used to test the classic Gibbs-Thomson relationship and provided the step edge free energies and free energy barriers to one-dimension nucleation for calcite. Addition of aspartic acid, a common component in biomineralizing systems, dramatically affected growth morphology and altered the magnitude of the surface energy.     

Atrotoxin: a specific agonist for calcium currents in heart

A specific label for voltage-dependent calcium channels is essential for the isolation and purification of the membrane protein that constitutes the calcium channel and for a better understanding of its function. A fraction of Crotalus atrox that increases voltage-dependent calcium currents in single, dispersed guinea pig ventricular cells was isolated. In the doses used, neither sodium nor potassium currents were changed. The fraction was active in the absence of detectable phospholipase or protease activity, and the active component, designated atrotoxin, produced its effect rapidly and reversibly. The effect was produced by extracellular but not intracellular application of the agent. The increase in Ca2+ current was blocked by the Ca2+ channel blockers cobalt and nitrendipine. The active fraction completely blocked specific [3H]nitrendipine binding to guinea pig ventricular membrane preparations. The inhibition of nitrendipine binding by atrotoxin was apparently via an allosteric mechanism. Thus atrotoxin was shown to bind to the Ca2+ channel and to act as a specific Ca2+ channel agonist.     

Relationship between clinical signs and transmission of an infectious disease and the implications for control

Control of many infectious diseases relies on the detection of clinical cases and the isolation, removal, or treatment of cases and their contacts. The success of such "reactive" strategies is influenced by the fraction of transmission occurring before signs appear. We performed experimental studies of foot-and-mouth disease transmission in cattle and estimated this fraction at less than half the value expected from detecting virus in body fluids, the standard proxy measure of infectiousness. This is because the infectious period is shorter (mean 1.7 days) than currently realized, and animals are not infectious until, on average, 0.5 days after clinical signs appear. These results imply that controversial preemptive control measures may be unnecessary; instead, efforts should be directed at early detection of infection and rapid intervention.     

Significance of mitochondria for porphyrin and heme biosynthesis

It is concluded that mitochondria are involved in three steps of porphyrin and heme biosynthesis-first, in the formation of delta-aminolevulinic acid from glycine and active succinate; second, in the synthesis of protoporphyrin; third, in the incorporation of iron into the porphyrin ring-that is, in heme formation.     

V1 neurons signal acquisition of an internal representation of stimulus location

A fundamental aspect of visuomotor behavior is deciding where to look or move next. Under certain conditions, the brain constructs an internal representation of stimulus location on the basis of previous knowledge and uses it to move the eyes or to make other movements. Neuronal responses in primary visual cortex were modulated when such an internal representation was acquired: Responses to a stimulus were affected progressively by sequential presentation of the stimulus at one location but not when the location was varied randomly. Responses of individual neurons were spatially tuned for gaze direction and tracked the Bayesian probability of stimulus appearance. We propose that the representation arises in a distributed cortical network and is associated with systematic changes in response selectivity and dynamics at the earliest stages of cortical visual processing.     

Lattice effect of strong electron correlation: implication for ferroelectricity and superconductivity

Much theoretical work has been devoted to understanding the role of strong electron correlations in high-temperature superconductivity mainly through magnetic interactions, but the possible role of electron correlation in ferroelectricity of metal oxides has not received attention. Diagonalization of a simple many-body, tight-binding Hamiltonian shows that the electron-lattice interaction is dramatically enhanced in some cases by strong electron correlation because of deformation-induced charge transfer. This effect may be closely related to ferroelectricity and superconductivity in transition metal oxides.