Static dielectric constants of the binary mixtures of N-methylformamide with water,ethyl alcohol,ethylene glycol,dimethylsulphoxide, acetone and 1,4-dioxane

The static dielectric constants of binary mixtures of N-methylformamide (NMF), used as a solute with the solvents water (W), ethyl alcohol (EA), ethylene glycol (EG), dimethyl sulphoxide (DMSO), acetone (Ac) and 1,4-dioxane (Dx), have been measured over the entire concentration range at 30°C. The negative values of excess dielectric constant and less-than-unity values of the corrective Kirkwood correlation factor of these binary mixtures are used to analyse the formation of H-bond complexes and molar ratio of the stable adduct. In these systems, the unassociated mixture constituents, DMSO, Ac and Dx, act as structure-breakers for self-associated linear structures of NMF, whereas, both the self-associated mixture constituents (W, EA and EG mixtures with NMF) act as structure-breakers to each other during the complexations. It is found that the large variations in the strength of H-bond complexation and the effective number of parallel aligned dipoles in the mixtures are governed by the dielectric constant of the solvents.     

腹腔镜下胃转流术治疗2型糖尿病的疗效分析及可行性研究

胃转流术治疗重度肥胖由来已久.近年来,国内研究通过接受胃转流术的肥胖患者的长期随访后发现,胃转流术可长期、稳定的缓解2型糖尿病,并能减少糖尿病并发症,为2型糖尿病的外科治疗开辟了新途径.本文总结我院32例接受腹腔镜胃转流术的2型糖尿病患者术后随访情况,分析后认为腹腔镜下胃转流术治疗2型糖尿病疗效显著,具有微创、安全、有效的特点,是2型糖尿病治疗方法的一种补充和完善,值得临床推广.     

Income maximizing in concurrent interval-ratio schedules

Three mice chose between concurrent variable-ratio variable-interval schedules to produce a warm air stream while they were housed in a cold chamber. Across conditions, the duration of the warm air stream was varied between 10 and 80 s and was equal for both schedules. Preference for the VI schedule covaried with reinforcer duration as predicted by maximizing accounts of choice.     

Pigeons' choices in situations of diminishing returns: fixed- versus progressive-ratio schedules.

In two different discrete-trial procedures, pigeons were faced with choices between fixed-ratio and progressive-ratio schedules. The latter schedules entail diminishing returns, a feature analogous to foraging situations in the wild. In the first condition (no reset), subjects chose between a progressive-ratio schedule that increased in increments of 20 throughout a session and a fixed-ratio schedule that was constant across blocks of sessions. The size of the fixed ratio was varied parametrically through an ascending and then a descending series. In the reset condition, the same fixed-ratio values were used, but each selection (and completion) of the fixed ratio reset the progressive-ratio schedule back to its minimal value. In the no-reset procedure, the pigeons tended to cease selecting the progressive ratio when it equaled or slightly exceeded the fixed-ratio value, whereas in reset, they chose the fixed ratio well in advance of that equality point. These results indicate sensitivity to molar as well as to molecular reinforcement rates, and those molar relationships are similar to predictions based on the marginal value theorem of optimal foraging theory (e.g., Charnov, 1976). However, although previous results with monkeys (Hineline & Sodetz, 1987) appeared to minimize responses per reinforcement, the present results corresponded more closely to predictions based on sums-of-reciprocals of distance from point of choice to each of the next four reinforcers. Results obtained by Hodos and Trumbule (1967) with chimpanzees in a similar procedure were intermediate between these two relationships. Variability of choices, as well as median choice points, differed between the reset and no-reset conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Concurrent variable-ratio schedules: Implications for the generalized matching law

Rats' responses were reinforced on concurrent variable-ratio variable-ratio schedules in which responses on one lever incremented the ratio counter and responses on a second lever changed the schedule and correlated stimulus. The relative frequency of reinforcement was varied from .10 to .99. In one set of conditions, responding on the main lever incremented both ratio counters, but reinforcement required a response in the presence of the stimulus correlated with the ratio that had been completed. In a second set of conditions, responses on the main lever incremented only the ratio correlated with the stimulus that was currently present. When main-lever responses incremented both ratio counters, subjects distributed responding and time in a manner consistent with the generalized matching law. When responses on the main lever incremented only the schedule currently in effect, the rats responded almost exclusively on the schedule producing the higher frequency of reinforcement. These results extend the applicability of the generalized matching law to dependent ratio schedules.     

Optimizing Expression of the Common Human Genome for Child Development

Molecular biology has moved the gene-environment issue in behavior genetics to how and when expression of the human genome is triggered and maintained. How does environment influence gene expression? How many genes are expressed in producing a given behavior? The genome is a data bank and does not automatically create a working brain. The body and brain grow well when (a) endocrine hormones initiate and promote the expression of genes, (b) nutrition is sufficient to sustain the production of proteins, and (c) stress does not suppress gene expression. The growth of brain synapses also requires appropriate neural stimulation. To study gene expression, it is essential to view the complex biology of the cell from a system context that includes the entire genome plus the biological and psychological environments. Optimizing geneexpression for child growth can be achieved by a balance of medicine, nutrition, and appropriate physical, educational, and psychological environments.     

Matching, delay-reduction, and maximizing models for choice in concurrent-chains schedules.

Models of choice in concurrent-chains schedules are derived from melioration, generalized matching, and optimization. The resulting models are compared with those based on Fantino's (1969, 1981) delay-reduction hypothesis. It is found that all models involve the delay reduction factors (T - t2L) and (T - t2R), where T is the expected time to primary reinforcement and t2L, t2R are the durations of the terminal links. In particular, in the case of equal initial links, the model derived from melioration coincides with Fantino's original model for full (reliable) reinforcement and with the model proposed by Spetch and Dunn (1987) for percentage (unreliable) reinforcement. In the general case of unequal initial links, the model derived from melioration differs from the revised model advanced by Squires and Fantino (1971) only in the factors affecting the delay-reduction terms (T - t2L) and (T - t2R). The models of choice obtained by minimizing the expected time to reinforcement depend on the type of feedback functions used. In particular, if power feedback functions are used, the optimization model coincides with that obtained from melioration.     

Income maximizing on concurrent ratio-interval schedules of reinforcement

Three experiments examined the effect of food availability on pigeons' choice behavior under concurrent schedules of reinforcement. In Experiment 1, 3 pigeons earned their daily food ration by choosing, in 30-min sessions, between concurrent variable-ratio 30 variable-interval 40-s schedules. Food presentations during both schedules lasted 2 or 12 s, depending upon the condition. Relative variable-ratio response rate was inversely related to hopper duration. In Experiment 2, 4 pigeons received their daily feeding by responding on the same schedule pair as in Experiment 1 (with 4-s food presentations) in sessions that varied in length from 10 to 30 min, depending on the condition. The length of a vertical slit projected on a response key increased with time so that “passage of time” might be more easily discriminable. As session duration decreased, relative variable-ratio response rate increased. In Experiment 3, 4 pigeons chose between two variable-interval 40-s schedules. One schedule operated without regard to the schedule selected, whereas the other operated only when the subject responded in its presence (dependent). Although these schedules had the same feedback function, preference for the dependent variable interval increased as session duration decreased from 30 to 10 min. The preference changes in these studies reveal the operation of an income-maximizing process in choice.     

Discrete-trial choice in pigeons: Effects of reinforcer magnitude

The preference of pigeons for large reinforcers which occasionally followed a response versus small reinforcers which invariably followed a response was studied in a discrete-trial situation. Two differently colored keys were associated with the two reinforcement alternatives, and preference was measured as the proportion of choice trials on which the key associated with uncertain reinforcement was pecked. A combination of choice and guidance trials insured that received distributions of reinforcement equalled the scheduled distributions. For five of six subjects, preference for the uncertain reinforcer appeared to be a linear function of the magnitude of the certain reinforcer. In addition, there was greater preference for the response alternative associated with uncertain reinforcement than would be expected on the basis of net reinforcer value.