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At least 19 recordsLinked to original sources
PubMed1991

Modeling RNA secondary structures. I. Mathematical structural model for predicting RNA secondary structures.

A mathematical model for analyzing the secondary structures of RNA is developed that is based on the connection matrix associated with the planar p-h graph. The classification of the elementary structures allows the introduction of the basis of structural space from which to build the global secondary structure. All admissible solutions belong to the configuration space and can be obtained directly from its basis.

Algorithms↗
PubMed1991

Predicting postpartum depressive symptoms: a structural modelling analysis.

In this prospective, longitudinal study, 42 first-time mothers, recruited through prenatal classes, were assessed on variables predictive of postpartum depressive symptoms. Using a causal modelling structural analysis, it was found that prenatal depression, partners' support, and infant-related factors all contributed to the development of depression following childbirth.

Adult↗
PubMedDate not supplied

Enhanced antibody production at slowed growth rates: experimental demonstration and a simple structured model.

A simple structured model for monoclonal antibody (MAb) production kinetics was formulated by combining the cell cycle theory with the estimated number of MAb-coded messenger RNA (mRNA) molecules per cell: it is assumed that the rate-controlling step is first order in this mRNA and that the growth rate variation does not alter the MAb synthesis rate within any cycle phase but only changes the relative time length of the individual phases. The model predicted "negatively growth associated" MAb production kinetics and thus an enhanced MAb production rate to be achieved by slowing the cell growth. Experiments consistent with these assumptions provided support for the model. Hybridoma cultures where growth was slowed by either a DNA synthesis inhibitor (thymidine or hydroxyurea) or by a selective inhibitor of initiation of nonantibody protein (potassium acetate) exhibited 50-130% MAb production rate enhancement for growth slowed up to 50%; however, further decreases in the growth rate also decreased the MAb production rate. Experiments inconsistent with these assumptions showed other behavior: general inhibition of protein chain elongation (by cycloheximide) or inhibition of ribosomal RNA (rRNA) synthesis (by actinomycin D) each slowed both growth and the specific MAb production rate, leading to net "positive" growth associated MAb production rates. Thus, a need for models with greater structure is also demonstrated.

Animals↗
PubMed1991

Structural modeling of functional neural pathways mapped with 2-deoxyglucose: effects of acoustic startle habituation on the auditory system.

This paper describes the first application of structural modeling to neuroscience. Structural modeling (also known as path analysis) is a method to assess the relative impact of directional links in a system and how these interrelations may change under different conditions. The objective was to demonstrate how structural modeling can be used to determine the functional interrelationships between brain structures that form the auditory system. Using structural modeling, changes in auditory system 2-DG uptake were examined during long- and short-term habituation of the acoustic startle reflex. Models were based on the anatomical connections between central auditory system structures. Using functional 2-DG data, the correlations between these structures were calculated and numerical weights were computed for each anatomical link. The analysis revealed that the lemniscal path was dominant during short-term habituation, while during long-term habituation this influence was modified through extra-lemniscal pathways. The models are discussed in the context of previous findings to demonstrate how structural modeling can not only complement, but also extract more information from 2-DG mapping experiments.

Acoustic Stimulation↗
PubMed1992

Structural modeling of functional visual pathways mapped with 2-deoxyglucose: effects of patterned light and footshock.

This paper describes the first application of structural modeling to the visual system. Structural modeling, or path analysis, is a mathematical method that allows for the quantification of the functional strengths of anatomical connections between the structures that form a neural system. The objective was to demonstrate how structural modeling can be used to determine the functional interrelationships between brain structures that form the visual system and how these interrelationships change under different conditions. Data were obtained from measures of 2-deoxyglucose uptake in the visual system of rats presented with either patterned light or darkness. The effects of arousing footshock on visual system operations were also investigated. Models based on the anatomical connections and the interregional correlations between metabolic activity data were used to determine path coefficients representing the magnitude of the influence of each directional path. Statistical evaluation of the models revealed that the dominant positive influences on visual system activity in the darkness were the tectocortical subsystem and the descending connections from secondary visual cortex. In the patterned light model, the total influence of the geniculocortical subsystem was higher than in the dark, and the tectocortical pathways showed both a reduction and a shift in the direction of effects. The models also revealed that the effects of footshock-induced arousal on visual system operations depended upon the visual environment and on extra-visual influences. The footshock led to an increase in the interaction of the two main subsystems at the level of connections between primary visual cortex and the lateral posterior nucleus, and a descending negative influence from the secondary visual cortex became dominant. The models are discussed in the context of conventional analyses to show how structural modeling allows for the determination of much more information about the functional interactions within the visual system of subjects under different experimental conditions.

Animals↗
PubMed1992

A structural model for sequence-specific proflavin-DNA interactions during in vitro frameshift mutagenesis.

Molecular models describing intermediates that may lead to proflavin-induced 1 bp deletions during in vitro polymerization by E. coli DNA polymerase I Klenow fragment are proposed. The models provide structural explanations for the fact that the induced frameshifts always occur opposite template bases that are adjacent to 5' pyrimidines and are based on the underlying hypothesis that the deletions arise because the polymerase passes by a template base without copying it. Because the most frequent mutations are opposite Pu in the template sequence 5' Py Pu 3', a single-strand loop-out model was constructed for this sequence and proflavin was added, using structures found in crystalline oligonucleotides and their complexes with proflavin. The model seeks to rationalize the roles of the 5' pyrimidine and proflavin in facilitating the bypass. Four potential roles for proflavin in mutagenesis are described: 1) stacking on the looped-out base; 2) stacking on the base pair immediately preceding the site of mutation; 3) hydrogen bonding with the 5' pyrimidine; 4) hydrogen bonding with the phosphate backbone. These models point to the possibility that a number of proflavin-DNA interactions may be involved. In contrast, modeling does not suggest a role for classically intercalated proflavin in frameshift mutagenesis arising during in vitro DNA polymerization.

Base Sequence↗
PubMed1979

A structural model of functional capacity in the aged.

The core problem in geriatrics is the continuous loss of adaptive capacity by bones, joints, brain, heart and lungs. Thus many old persons cannot take care of themselves any longer in matters of food, safety, body temperature and hygiene, the basic functions for human independence. Geriatricians agree about the basic functions that an elderly person should be able to perform. Only with such criteria can goals be defined more accurately and comparisons made of therapeutic efforts, leading to a higher level of efficiency in therapy, prognosis and care. A theoretical framework is proposed which may serve as a model for assessment of functional capacity in the aged patient. The model (hierarchic structure) has four components: household activities, mobility, activities of daily living, and function of the autonomic nervous system. No component covers more than five items. There is great need for studies on an international level so that assessments and treatments of elderly patients can be compared.

Activities of Daily Living↗
PubMed1991

A new structural model for the thyrotropin (TSH) receptor, as determined by covalent cross-linking of TSH to the recombinant receptor in intact cells: evidence for a single polypeptide chain.

The most widely held model for the human TSH receptor is of holoreceptor of 80 kDa with two subunits of approximately 50 and 30 kDa linked by disulfide bridges, with the former subunit containing the major hormone-binding site. We reexamined this model by covalently cross-linking radiolabeled TSH to the recombinant human TSH receptor stably expressed in Chinese hamster ovary (CHO) cells. When cross-linking was performed after the preparation of CHO membranes, analysis of hormone-receptor complexes under reducing and nonreducing conditions provided results supporting the two-subunit TSH receptor model. In contrast, however, cross-linking of TSH to the TSH receptor in intact CHO cells before membrane preparation revealed, even under reducing conditions, an approximately 100-kDa receptor as well as an approximately 54-kDa hormone-binding subunit. The approximately 100-kDa holoreceptor size is consistent with the size of the TSH receptor, as predicted from its derived amino acid sequence. The proportions of the approximately 100-kDa TSH receptor and the 54-kDa fragment varied in different experiments, suggesting the occurrence of proteolytic cleavage. Cross-linking of radiolabeled TSH to intact cells expressing a mutant TSH receptor (TSHR-D1) lacking amino acids 317-366 localized the proteolytic cleavage site to just up-stream of amino acid residue 317. In summary, the present data obtained by cross-linking TSH to recombinant human TSH receptors in intact cells provides evidence that the receptor exists in vivo as an approximately 100-kDa glycoprotein with a single polypeptide chain with intramolecular disulfide bridges.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[Possibility of internal organization of RNA and proteins in ribosomal subparticles. A structural model of Escherichia coli 30S ribosomal subparticle].

The hypothetic model of reciprocal spatial arrangement of 18 from 21 proteins in the E. coli 30S ribosomal subparticle is suggested. The model is based on conception of the 16S R-A molecule macrostrand which is the right superhelix in the subparticle composition. Macrohelix's biopolarity against single-stranded sites of RNA and its small width result in that proteins binding with single-stranded RNA organized in chain, one-number sequence. The double helixes uniting the corresponding one single-stranded sites of RNA play the role of rigid transmission between them. So, in the course of subparticles reconstruction from RNA and proteins the spatially uncoupled proteins can interact without its direct contact. The model takes into consideration the vast amount of information.

Binding Sites↗
PubMedDate not supplied

Modeling incomplete longitudinal and cross-sectional data using latent growth structural models.

In this paper we describe some mathematical and statistical models for identifying and dealing with changes over age. We concentrate specifically on the use of a latent growth structural equation model approach to deal with issues of: (1) latent growth models of change, (2) differences in longitudinal and cross-sectional results, and (3) differences due to longitudinal attrition. This is a methodological paper using simulated data, but we base our models on practical and conceptual principles of modeling change in developmental psychology. Our results illustrate both benefits and limitations using structural models to analyze incomplete longitudinal data.

Aging↗
PubMed1992

[Latent structure model of physicians' opinions on National Health Insurance].

The purpose of this study is to construct the latent structure models of physicians' opinions on National Health Insurance (NHI). The data for the analysis came from a mail survey of 1619 physicians in January of 1990. Five latent structure models were established as follows: Structure 1. Physicians' viewpoint on NHI. Hospital physicians: Steady, 69%; Turn-Over, 26%; Career-change, 5%. Clinic physicians: Steady-with Insurance Contract, 55%; Steady-without Insurance Contract, 41%; Career-Change, 4%. Structure 2. Physicians' expected impact of NHI. Hospital physicians: Pessimistic, 45%; Disadvantaged, 38%; Constant, 17%. Clinic physicians: Pessimistic, 72%; Constant, 12%; Ambitious, 16%. Structure 3. Physicians' expected workload change due to the implement of NHI. Hospital physicians: Decreasing, 30%; No-Change, 18%; Increasing, 52%. Clinic physicians: Decreasing, 30%; Non-Change, 23%; Increasing, 48%. Structure 4. Ideal practice pattern. Hospital physicians: Traditional, 47%; Transitional, 42%; Practice Abandoned, 12%. Clinic physicians: Traditional, 20%; Transitional, 21%; Rural-Orientated 59%. Structure 5. Expected payment methods for physicians. Hospital physicians: Credentiality-Specialty-based, 44%; Specialty-Equal Pay-based, 11%; Equal Pay-Specialty-based, 42%; Equal Pay-Credentiality-based, 4%. Clinic physicians: Credentiality-based, 24%; Mixed, 11%; Equal Service-Equal Pay-based, 60%; Urbanization Level-based, 5%.

Attitude of Health Personnel↗
PubMed1991

A three-dimensional motion model of loads on the lumbar spine: I. Model structure.

Traditionally most biomechanical models that are used to estimate the loading experienced by the spine during work focus on static, two-dimensional representations of the work. However, most work tasks impose loads on the lumbar spine under dynamic, three-dimensional conditions. The objective of this study was to describe the structure and logic of a model that is capable of producing estimates of spine loading under three-dimensional motion conditions. This model is intended for use primarily under laboratory conditions. The model was designed initially for workplace simulation in which the trunk is moving under symmetric and asymmetric constant velocity lifting conditions. Future embellishments may enable the model to be used under free dynamic conditions. The model predicts lumbar spine compression, shear, and torsional forces as well as trunk torque production continuously throughout the exertion. This information may be compared with spine tolerance limits so that the risk of causing a vertebral end-plate microfracture by workplace requirements could be determined.

Biomechanical Phenomena↗