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At least 757 records · Page 42Linked to original sources
PubMed1975

[Optimation of irradiation planning in deep therapy. Outline of the chance of survival of tumor patients].

Simple model conceptions are used for the demonstration of the chance of survival of tumor patients. The systematic judgement of therapy is possible after the adaptation to known survival curves for patients in different stages. The ascertainment of the tumor duplication period for primary tumor and--on principle--also for metastases, permits of conclusions on the recuperative capacity and radioresistance of the exposed normal tissue and of the tumor. It was seen that the values found can lie in the range of the data known from radiobiology. Vice versa, it is possible in principle by means of derived relation to optimate dose distribution, fractionation and total dose of the radiotherapy. Moreover, the systematic analysis of the known survival curves of tumor patients within the frame of model conception allows of the expectation that also influences of therapy on the tumor duplication time, and possibly the dissemination capacity of the tumor, can be analysed. These values reflect the tumor-host-relations and seem to be of decisive significance for future successful concepts of therapy.

Growth↗
PubMed1988

The effect of class and collection labels on cardinality, class-inclusion, and number conservation tasks.

3 experiments were carried out to assess Markman's hypothesis that the organizational principles underlying collection concepts facilitate children's performance on cognitive tasks requiring part-whole comparisons. In Experiment 1, the effect of class/collection labels on both cardinality and class-inclusion tasks was assessed. 32 3- and 4-year-olds from 2 populations (suburban middle class and inner-city working class) received both tasks. An additional 32 kindergarten and first-grade children from the 2 populations received the class-inclusion task. For cardinality, there was no difference in performance as a function of label. A facilitative effect of the collection label was found for class inclusion. Experiment 2 assessed the effect of class/collection labels on 28 nursery school children's demonstration of number conservation. Experiment 3 extended the age range and examined the effect of label on 56 kindergartners' and first graders' performance on number conservation. Both experiments failed to replicate Markman's findings. The results of the 3 experiments indicate that the facilitative effect of collection labels appears to be specific to the class-inclusion task. In light of these failures to replicate and the considerable variation in cognitive level among preschoolers, it is suggested that Markman's findings of a facilitative effect of collection labels on conservation and cardinality problems may have resulted from the use of small sample sizes and between-subject designs.

Attention↗
PubMed1988

Number-comparison learning by children classified as mentally retarded.

A training experiment was undertaken to determine whether children classified as mentally retarded could learn a general magnitude-comparison rule ("The number that comes after another in the number sequence is more than the preceding number"). After a pretest, 22 subjects were randomly assigned to an experimental or a control training group. On both immediate and delayed posttests, the experimental subjects significantly outperformed control children on trained number pairs. A modest amount of transfer was also evident. The results suggest that a counting-based approach that utilizes rule rehearsal can help children classified as mentally retarded to use their representation of the number sequence to make mental magnitude comparisons.

Adolescent↗
PubMed1987

Problem size and mentally retarded children's judgment of commutativity.

The effects of problem size on judgments of commutativity by 51 moderately and mildly mentally retarded students were investigated. The task required subjects to judge whether commuted addition problems (e.g., 5 + 2 and 2 + 5) and noncommuted problems (e.g., 5 + 3 and 5 + 0) would have the same or different sum. Small problems had addends of five or less; large problems had at least one addend greater than five. The subjects' responses to the commutativity task were highly consistent across the two problem sizes. Results indicated that many retarded students who are given computational practice recognize the general principle that addend order does not affect the sum.

Adolescent↗
PubMed1978

Perceptual and intellectual factors affecting number concept development in retarded and nonretarded children.

The role of MA and visual-perceptual ability in number concept development was examined with nonretarded and retarded children from regular school settings. Both groups were matched on MA and divided into high and low perceptual-ability levels. Using the Dodwell Number Concept Test, we tested each subject on various Piagetian tasks. Although retarded and nonretarded groups differed in IQ and CA, equivalence in MA resulted in equivalent number concept performance. For both groups, regardless of variation in IQ and CA, perceptual ability exerted a significant influence on number concept, with high perceptual ability resulting in superior number concept performance.

Child↗
PubMed2006

Systemic cancer progression and tumor dormancy: mathematical models meet single cell genomics.

Metastatic progression is thought to result from genetically advanced "fully-malignant" tumor cells. Within the concept the prevailing view holds that such cells disseminate mostly from large tumors and are capable of growing into metastases once they arrive at a distant site. Support for this scenario comes from numerous mouse models in which transplanted tumor cells grow into metastases within days or weeks. However, the assumption of such fully-malignant disseminating cells in human cancer is misleading and is neither supported by mathematical modeling of survival data from cancer patients nor by ex-vivo genomic data from disseminated cancer cells. For example, in breast cancer the growth of metastases is highly homogeneous and takes on average six years, the number of disseminated tumor cells before diagnosis of metastasis is similar for different tumor stages, and the genomic aberrations of disseminated cancer cells do rarely correspond to those in the primary tumor. Since these facts question conventional concepts of metastatic progression we provide a model of cancer progression in which time considerations and direct ex-vivo data form a starting point. In the proposed model tumor dormancy is a characteristic of almost all migrated tumor cells and metastatic growth is a rare, stochastic, evolutionary process of selection and mutation of cells that often disseminate shortly after transformation at the primary site.

Animals↗
PubMed1987

Classroom factors and student characteristics predicting students' use of achievement standards during ability self-assessment.

The literature suggests that upper-elementary-school students have a strong inclination to conclude that they are competent in mathematics. How do students of widely varying abilities reach this conclusion? Do task structures, grading practices, and grouping patterns influence the achievement standards that students use in reaching a positive evaluation of their ability? Findings from analyses of 1,570 upper-elementary students who believe that they are good at math include the following. (1) The combination of differentiated task structures and infrequent grades is associated with students' low reliance on adults' assessments and across-domain comparisons as bases for their positive self-concepts, but the combination of differentiated task structures and frequent grades is associated with heavy reliance on these 2 standards. (2) Students' use of social comparison and task mastery is stratified according to students' talent levels when grades are frequent, but when grades are infrequent even untalented students decide on the basis of (selective?) social comparisons and (exaggerated?) estimates of task mastery that they are good at math.

Achievement↗
PubMed1997

A comparison of the geometric reasoning of students attending Israeli ultraorthodox and mainstream schools.

Effects of schooling on a geometric misconception were examined by comparing the performance of Israeli students attending ultraorthodox schools with that of peers attending mainstream schools. These groups were of special interest because both value education highly and send essentially all children to school, but I group receives extensive instruction in mathematics and science and the other receives almost none. Despite the ultraorthodox 12- to 14-year-olds' having received no instruction in geometry, they more often solved the geometric misconception problems than did mainstream peers who had received extensive instruction in the subject. Mainstream 16- to 18-year-olds did somewhat better on the misconception task than did orthodox age peers, but even there, the advantage of the mainstream students was limited to those exposed to the most advanced mathematics curriculum. How mainstream and orthodox schooling may have contributed to these findings is discussed.

Achievement↗
PubMedDate not supplied

Circular keratotomy for the correction of astigmatism.

BACKGROUND: Mathematical and physical considerations that are contained in Gauss' law lead to the concept of a circular cut for the correction of corneal astigmatism. METHODS: The method applied is the coupling of the aspheric corneal surface to the spherical obturator of the Guided Trephine System and cutting of 90% of the parenchyma. Nineteen human eyes were treated with this technique, using a double-running suture closure. RESULTS: Results of reduction of astigmatism can regularly be obtained but are of different amounts depending on the origin of astigmatism. Mean preoperative refractive astigmatism was 5.41 diopters and mean postoperative refractive astigmatism was 1.34 D. Six eyes required additional tranverse arcuate keratotomy. CONCLUSIONS: The procedure is effective, but the results are variable. It may be improved by the use of obturators that fit the radius of curvature of the cornea.

Astigmatism↗
PubMed1983

The probability that related individuals share some section of genome identical by descent.

A formal mathematical framework is presented for the study of linkage in man and the concept of chromosome pedigree is defined for both autosomes and X chromosomes. It is shown that, assuming no interference, all the crossover processes in the pedigree may be viewed jointly as a continuous-time Markov random walk on the vertices of a hypercube, the time parameter being map distance along the chromosome. The event that two individuals have a segment of chromosome in common, thus proving them to be related, corresponds to the random walk hitting a particular set of vertices. The probability of this happening is calculated for various types of relationship, making use of the symmetry of the situation to partition the vertices into a very much smaller number of orbits and render the computation manageable. The probability that an individual with n children passes on all his or her genes to them is also calculated in this way.

Chromosomes, Human↗
PubMed2003

Virtual and real brain tumors: using mathematical modeling to quantify glioma growth and invasion.

Over the last 10 years increasingly complex mathematical models of cancerous growths have been developed, especially on solid tumors, in which growth primarily comes from cellular proliferation. The invasiveness of gliomas, however, requires a change in the concept to include cellular motility in addition to proliferative growth. In this article we review some of the recent developments in mathematical modeling of gliomas. We begin with a model of untreated gliomas and continue with models of polyclonal gliomas following chemotherapy or surgical resection. From relatively simple assumptions involving homogeneous brain tissue bounded by a few gross anatomical landmarks (ventricles and skull) the models have recently been expanded to include heterogeneous brain tissue with different motilities of glioma cells in grey and white matter on a geometrically complex brain domain, including sulcal boundaries, with a resolution of 1 mm(3) voxels. We conclude that the velocity of expansion is linear with time and varies about 10-fold, from about 4 mm/year for low-grade gliomas to about 3 mm/month for high-grade ones.

Brain Neoplasms↗
PubMed1980

[Mathematical methods in clinical cardiology].

The use of mathematical methods along four interconnected directions in clinical cardiology is analysed: prognosis and diagnosis, elaboration of most accurate clinical concepts and classifications, rules of management of the patient, information-research systems.

Cardiology↗