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Biomedical subjects

I Levin

Publications and source records attributed to I Levin.

53 records · Page 3Linked to original sources
PubMed1984

Development of time quantification: integration and nonintegration of beginnings and endings in comparing durations.

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.

Adolescent↗
PubMed1983

A developmental analysis of early time concepts: the equivalence and additivity of the effect of interfering cues on duration comparisons of young children.

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.

Child, Preschool↗
PubMed1979

Interference of time-related and unrelated cues with duration comparisons of young children: analysis of Piaget's formulation of the relation of time and speed.

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.

Age Factors↗
PubMed1978

The development of time concepts in young children: the relations between duration and succession.

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.

Child↗
PubMedDate not supplied

Crystallography of ribosomes: attempts at decorating the ribosomal surface.

Crystals of various ribosomal particles, diffracting best to 2.9 A resolution were grown. Crystallographic data were collected from shock frozen crystals with intense synchrotron radiation at cryo temperature. For obtaining phase information, monofunctional reagents were prepared from an undecagold and a tetrairidium cluster, by attaching to them chemically reactive handles, specific for sulfhydryl moieties. Heavy-atom derivatives were prepared by a specific and quantitative binding of the undecagold cluster to an exposed sulfhydryl prior to the crystallization. To create potential binding sites on the halophilic and thermophilic ribosomal particles, which yield our best and most interesting crystals, exposed reactive moieties were inserted, using genetic and chemical procedures. In order to choose the appropriate locations for these insertions, the surfaces of the ribosomal particles were mapped by direct chemical determination of exposed amino and sulfhydryl groups.

Bacteria↗
PubMedDate not supplied

Mapping DNA polymorphisms using PCR primers derived from the sequence of an avian CR1 element.

Primers complementary to the chicken middle repetitive sequence element CR1 were used to generate and simultaneously map polymorphic polymerase chain reaction products (CR1-PCR) with various chicken DNAs as templates. Ten primers were prepared using the sequence of a single CR1 element as a guide. These 10 primers generated 23 polymorphic CR1-PCR products. The average number of polymorphic CR1-PCR products generated using single primers (1.1 per primer) was significantly higher than the average number observed using combinations of two primers (0.3 per primer combination). The polymorphic CR1-PCR products were mapped in a subset of a reference backcross population designed for the genetic linkage analysis of the chicken. Nineteen of the polymorphic CR1-PCR products identified were assigned to 13 of 19 linkage groups characterized thus far in this population; three have yet to be linked to a specific map location. One of the CR1-PCR markers mapped to the chicken Z chromosome. There was no evidence for a significant clustering of CR1-PCR markers within the map, even at the site of the CR1 element whose sequence was used for primer design.

Animals↗
PubMedDate not supplied

An autosomal genetic linkage map of the chicken.

We have developed an autosomal genetic linkage map of the chicken genome using a subpanel of 52 DNAs from a previously described reference backcross mapping population. The population derived from a cross of an inbred Red Jungle Fowl male and a highly inbred White Leghorn female. The backcross subpanel used was made up of offspring of a single F1 male with four White Leghorn females. Ninety-eight markers consisting of classical and erythrocyte antigen genes, restriction fragment length polymorphisms, random amplified polymorphic DNA, and chicken CR1 repeat-element polymorphisms were typed. Seventy-two of these markers were resolved into 19 linkage groups. Four of the linkage groups were assigned to chromosomes 1, 4, and 17. Four linkage groups were associated with linkage groups published earlier. Linkages within approximately 27 cM can be detected with a lod score of 3 with the panel used. The preliminary map contains approximately 590 cM within the linkage groups, and approximately 70% of the randomly selected markers fell in one of the groups; however, a considerable portion of the genome may remain outside of the existing linkage groups. These markers greatly expand the existing linkage map of the chicken genome.

Animals↗
PubMedDate not supplied

A milestone in ribosomal crystallography: the construction of preliminary electron density maps at intermediate resolution.

Preliminary electron density maps of the large and the small ribosomal particles from halophilic and thermophilic sources, phased by the isomorphous replacement method, have been constructed at intermediate resolution. These maps contain features comparable in size with what is expected for the corresponding particles, and their packing arrangements are in accord with the schemes obtained by ab-initio procedures as well as with the motifs observed in thin sections of the crystals by electron microscopy. To phase higher resolution data, procedures are being developed for derivatization by specific labeling of the ribosomal particles at selected locations with rather small and dense clusters. Potential binding sites are being inserted either by site directed mutagenesis or by chemical modifications to facilitate cluster binding on the surface of the halophilic large and the thermophilic small ribosomal particles, which yield the crystals diffracting to highest resolution (2.9 and 7.3 A (1 A = 0.1 nm), respectively). For this purpose, the surface of these ribosomal particles is being characterized and procedures are being developed for quantitative detachment of selected ribosomal proteins and for their incorporation into core particles. The genes of these proteins are being cloned, sequenced, mutated to introduce reactive side groups, mainly cysteines, and overexpressed. In parallel, two in situ small and stable complexes were isolated from the halophilic ribosome. Procedures for their crystal production in large quantities are currently being developed. Models, reconstructed at low resolution from crystalline arrays of ribosomes and their large subunits, are being used for initial low-resolution phasing of the X-ray amplitudes. The interpretation of these models stimulated the design and the crystallization of complexes mimicking defined functional states of a higher quality than those obtained for isolated ribosomes. These models also inspired modelling experiments according to results of functional studies, performed elsewhere, focusing on the progression of nascent proteins.

Base Sequence↗
PubMedDate not supplied

Lymph node revealing solution: a new method for lymph node sampling: results in gastric adenocarcinoma.

Staging of gastric carcinoma depends on exact lymph node status. However, very small nodes are not easily found as they are obscured by the surrounding adipose tissue. The purpose of the present study was to demonstrate the usefulness of a Olymph node revealing solutionO (LNRS) in gastric cancer. The perigastric adipose tissue of ten OproblematicO cases of gastric carcinoma, in which <10 lymph nodes were found using the traditional method, was immersed in LNRS for 6-12 h. Subsequently, the lymph nodes stood out as white chalky nodules. They were excised and processed routinely. The traditional method yielded a total of 30 lymph nodes with a mean size of 6.69 +/- 3.43 mm. The LNRS revealed 89 additional nodes with a mean size of 3.03 +/- 3.43 mm, which was significantly smaller. The Node (N) stage was changed in four cases from Nx to N0, in one case from N1 to N2, and in one case from N0 to N2. LNRS seems to be the technique of choice for staging of patients with gastric adenocarcinoma in whom <10 lymph nodes were found with the traditional method and accurate staging was not possible.

Adenocarcinoma↗
PubMedDate not supplied

[Resection of the kidney in nephrolithiasis].

The results of 155 partial nephrectomies performed in 149 patients during the years 1962-1981 are discussed. Indications, surgical technique, complications and results are presented. The results show that partial nephrectomy has an acceptably low risk and late results show lower recurrence of stone formation as compared with pyelolithotomy or nephrolithotomy. The rate of true ipsilateral recurrences was 18.69 per cent in 123 followed kidneys.

Adolescent↗
PubMedDate not supplied

Initial TPS serum level as an indicator of relapse and survival in colorectal cancer.

BACKGROUND: Tissue polypeptide specific antigen (TPS) measures a soluble fragment of cytokeratine 18 and may be regarded as a proliferative marker. MATERIALS AND METHODS: TPS was measured in 173 consecutive patients with colorectal cancer. Median follow up time was 36 months. Of 137 evaluable patients 39 developed metastases (P.D.) and 98 remained with no evidence of disease (N.E.D.). RESULTS: Initial TPS levels were elevated in 75% of P.D. patients compared to 32% of N.E.D. patients (p < 0.001), CEA levels were elevated in 26% of P.D. patients had elevated initial TPS compared to 35.5% of N.E.D. patients (p < 0.001), CEA was elevated in 33.3% of the P.D. patients compared to 1.3% of N.E.D. patients (p < 0.001). Survival and disease free survival were significantly shorter for patients with initial high TPS level. TPS was more sensitive than CEA in predicting relapse. CONCLUSIONS: These preliminary data suggest that TPS may be a prognostic factor for relapse and may help to allocate Dukes'B2 patients for adjuvant chemotherapy.

Adult↗