Biomedical subjects
Publications and source records attributed to I Levin.
A portable signal generator that simulates the amplitude and frequency of neuronal signals for testing extracellular recording amplifiers is described. The signal generator is easy to construct and it is extremely useful in tracing signal processing stages in neurophysiological equipment.
Carbon-14 data on atmospheric CO2 as well as on plant material (tree leaves and wheat) from the vicinity of two German boiling water reactors (Philippsburg and Isar/Ohu) are reported. Atmospheric CO2 samples taken routinely with an integration time of one or two weeks 1.75 km downwind of the Philippsburg reactor (900 MW electrical power) show a maximum 14C excess concentration of delta 14C (excess) = 300 +/- 7%, corresponding to 12.7 mBq m-3 (STP air). The long-term average excess amounts to delta 14C (excess) = 47 +/- 3%, corresponding to 2.0 mBq m-3 (STP air). The concentrations observed with plant material at the same sampling site range between delta 14C (excess) = 0% and 120%, corresponding to 0 and 27 mBq (g carbon)-1. With the meteorological dispersion parameters actually measured at the nuclear power plants, the dispersion factors for the various sampling sites and for the individual periods of sampling were calculated on the basis of a one-dimensional Gaussian plume model. With the observed 14C excess concentrations and the dispersion factor, a "theoretical" (i.e. calculated) reactor 14C source strength is then determined. For the Philippsburg reactor, which is situated in the flat Rhine valley, the "theoretical" and the observed yearly mean 14C emissions compare rather well (within a factor of 2). A significant systematical deviation from the model was found in the concentration decrease with source distance: the decrease predicted between the 1.75-km and 3.25-km distances is steeper than actually observed. The 14C excess concentrations found in tree leaves around the Isar/Ohu reactor (907 MW electrical power) at 1-2 km distance fall into the same range as observed at Philippsburg. In the hilly terrain at this reactor site, the model calculations agree well with the observed values up to a distance of 1 km if the relative elevation of the sampling site is taken into account by introducing a "reduced stack height" in the model calculations. This method fails in predicting the concentrations at distances greater than 1 km from the source.
Primary neoplasms of the renal pelvis are rare. Most are malignant, and most of these are transitional cell carcinomas. We report the unusual occurrence of a squamous cell carcinoma with sarcomatoid stroma arising from the renal pelvic mucosa in a patient with renal lithiasis. Immunohistochemical stains for keratin intermediate filaments failed to demonstrate their presence in the spindle cell portion of the tumor. Transmission electron microscopic study did not reveal structures of an epithelial nature in these same cells. Our findings support the contention that the spindle cells of the stroma are not squamous in nature, but represent either a reactive or a neoplastic transformation of these underlying stromal elements.
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The purpose of the study was to determine the accuracy of measurements made of the mandible from panoramic radiographs. A comparison was made between measurements made directly from dry mandibles, and measurements made from panoramic radiographs of the same mandibles. The use of linear proportions reduced the errors of successive radiographic observations but failed to reveal left- and right-side differences. A method was developed to demarcate two areas of the radiograph, one of which was defined by the crest of the residual alveolar ridge and the other independent of the alveolar ridge. Both areas were measured and their proportions calculated for each mandible observed. This proportional value was referred to as the Area Index. The method was applied to panoramic radiographs of individuals with complete dentitions. The inter-observation error of the Area Index was found to be 4.9%. It was concluded that, in selected cases, panoramic radiographs can be used to provide information about resorption of the residual mandibular alveolar bone.
The effects of different food deprivation regimens on the thermogenic activity and capacity of brown adipose tissue in the golden hamster have been investigated. Thermogenesis in the tissue was assessed by measurements of tissue cytochrome-c oxidase activity, mitochondrial GDP binding, and the specific mitochondrial concentration of uncoupling protein. The thermogenic activity and capacity of brown adipose tissue were found to be markedly reduced in fasted or underweight hamsters. Measurements of cytochrome-c oxidase activity indicate that the reductions were caused exclusively by a loss in mitochondrial mass, uncoupling protein concentration and GDP binding to mitochondria remaining unchanged. The decrease in brown adipose tissue thermogenesis was associated with a reduction in the capacity for nonshivering thermogenesis in the whole animal. Hamsters recovered from weight losses without increasing their food intake, and the recovery was accompanied by a normalization in mitochondrial mass in brown adipose tissue. Mitochondrial mass was, however, restored only after 10 days of ad libitum refeeding. These results suggest that the reduction in energy expenditure in the fasted hamster could relate to a decrease in brown adipose tissue thermogenesis, in addition to the previously reported decreases in resting metabolic rate and locomotor activity. Reductions in thermogenesis may also represent a further mechanism by which energy stores recover in the golden hamster without postfast hyperphagia.
In two studies we examined gender differences in predicting loneliness from measures of social network structure and a measure of perceived social support. The results showed that social network characteristics, especially density, were consistently better predictors of perceived loneliness for men than for women. Study 1 used the traditional measure of network density in which the number of relationships among network members was determined. Study 2 used a newly developed index of density that assessed the extent of closeness of relationships between pairs of network members. Uniformly, male subjects with more highly interconnected, cohesive sets of friends reported themselves to be less lonely, whereas density had little relation to loneliness in female subjects. These results are discussed as possibly indicating that men and women use different standards in evaluating whether they are lonely. It is suggested that men may use more group-oriented criteria in evaluating loneliness, whereas women focus more on the qualities of dyadic relationships.
This study investigated the relation of five individual difference variables (extroversion, depression, self-esteem, neuroticism, and attitude toward others) to loneliness. The relative contributions of two different models that might explain these relations were examined. One model suggests that individual difference variables are related to loneliness through the mediation of social network variables; that is, individual difference variables may reduce people's motivation and/or ability to build and maintain social relationships, which in turn leads to loneliness. The second model, the cognitive bias model, states that both the individual difference variables and loneliness are influenced by the same intrapersonal, cognitive processes. Some people are prone to negative affect and tend to evaluate themselves and their relationships negatively. The relations of self-esteem, neuroticism, and depression to loneliness were hypothesized to reflect the cognitive bias model, while extroversion and attitudes toward others were hypothesized to be related to loneliness through the mediation of social network variables. Eighty-two female and 42 male adults completed measures of loneliness and the five individual difference variables, as well as an instrument assessing their social networks. The results indicated partial support for both models for each of the individual difference variables. Together, the two models did a good job of explaining the correlations of the individual difference variables and loneliness. The implications of these findings, as well as their relation to previous research, are discussed.
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The nature of 5- to 8-year-old childrens ' time concepts was examined by analyzing two possible explanations for the greater difficulty children demonstrate in comparing durations that differ in beginning times as compared to those that differ in ending times. The explanations were (a) poor recall of beginnings as compared to endings due to their lower salience, (b) difficulty in integrating information from both points and reliance on endings only due to their greater salience. The subjects were 630 boys and girls from kindergarten to second grade. The children were presented with a series of two lights in different orders and combinations and were asked to compare order of beginnings and endings, and duration of the two lights. Results contradicted the memory explanation. In addition, repetitious questioning about order of one point (beginning or ending) appeared to have shifted children's attention from that point to the complementary point. Possible sources of children's failure to integrate beginning and end points when comparing durations were discussed.
The development of the concept of time in third, fifth, and seventh graders of two Israeli social groups--advantaged Westerners (n = 144) and disadvantaged Easterners (n = 120)--was compared. Contrary to expectations, no difference in performance was found between the social groups throughout the entire age range. In both groups performance, while far from reaching perfection, increased with age. In addition, disparity between our findings and those of Siegler and Richards cast doubts on the generalizability of the rules they extracted through the rule-assessment method.
This study investigated how children handle time information when deducing durations of events. In an elaboration of the commonly used choice paradigm to study children's time concepts, pairs of durations were presented in a 4 beginning lags X 4 ending lags design in 2 different problem series. Children's task was to equalize the durations of the 2 events by restarting 1 event for a certain time. The normative rule, quantification of duration differences in beginnings and endings and their integration by addition or subtraction, began to predominate at the age of 10 years and was the only rule employed by 13-year-olds. In contrast, almost all 7-year-olds simplified the task to an ordinal level. 4 different nonalgebraic rules were identified, each placing more importance on endings than on beginnings. Neither young children's tendency to simplify nor older children's capacity to quantify could be detected in previous studies, because they investigated time concepts on an ordinal level only. In light of the present findings, previous notions on the development of time concepts in children have to be reevaluated.
Young children compare durations correctly and explain their conclusions logically only when no interfering cues such as distance and speed are introduced. We investigated whether type of cue and additivity of interfering cues affect children's duration comparisons. 4- and 5-year-old children were asked to compare the burning times of pairs of partially synchronous lights differing in intensity, bulb size, or both. Those who erred tended to attribute longer duration to the brighter or larger bulb, brightness having a stronger interfering effect than size. Since brightness might qualify as "work" more than bulb size might, the finding that the former interferes more than the latter supports Piaget's basic claim of children's confusion of time with "work." The fact that bulb size interferes at all, which does not fit into Piaget's framework, may be explained in terms of children's inability to distinguish clearly between time-related and time-unrelated cues and their assumption of direct relations between dimensions. Additivity of interference did not emerge, indicating that the previous finding which suggested its existence--distance plus speed interfering with duration comparisons more than speed alone--should be reassessed in terms of type of interfering cues, that is, distance interferes more than speed with time.
The analysis of the relation of time and speed led Piaget to conclude that the time-speed confusion characterizing the intuitive stage undergoes development. He claimed that in the first stage, a child comparing the duration of two moving bodies attributes longer duration to the faster body, whereas in the second stage, he attributes longer duration to the slower body. It is proposed here that time-speed confusion is mediated simply by "more is more," and hence, as long as the child continues to confuse time with speed, he believes "faster" implies longer duration. Moreover, this confusion should not differ either in form or extent from the confusion of time and many other arbitrary quantitative dimensions (e.g., intensity of light). 72 children, 4-7 years old, compared duration differing either on speed or on intensity of light. As predicted, the tasks did not differ on performance level or on error types. Moreover, the performance on both tasks was consistent with the predictions of a facet model pertaining to analysis of time problems. Confusion dissipated with age and was similar for boys and girls.
108 children from nursery school, first grade, and third grade were given 5 problems measuring the concept of time, in which they were required to judge and explain which of 2 partially overlapping events started first, which ended first, and which lasted for a longer time. 2 types of problems were used which presented time with and without the interference of movement: "still time" (the duration of 2 lights) and "linear time" (the traveling time of 2 toy cars). In both types of problems, judging the succession of both beginnings and endings was equally difficult and was easier than judging duration. Duration judgments were explaned predominantly by succession, whereas succession judgments were explained tautologically or by mere "seeing." Overall, performance increased with age and decreased with interference. A recent model of the development of time concepts is further elaborated and compared with Piaget's framework.
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