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Results for “Models, Theoretical”

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PubMed2004

Nonverbal learning disability: a tutorial for speech-language pathologists.

Nonverbal learning disability (NLD) is a diagnostic category that is unfamiliar to most speech-language pathologists. This brief tutorial describes NLD's characteristics, a theoretical model proposed to explain its source, and areas of overlap between NLD and similar diagnostic categories. The communicative profile, made up of difficulties in pragmatic and semantic language in the presence of relatively preserved syntactic skill, is also discussed. Empirical evidence relevant to NLD is also evaluated. Many questions remain unresolved, but until systematic research provides definitive answers, speech-language pathologists are encouraged to rely on careful description of the individual child's communicative strengths and weaknesses to identify appropriate targets and to focus intervention on improving the child's ability to communicate effectively in everyday contexts.

Asperger Syndrome↗

PubMed2001

Prevention: developing a framework for conceptualizing and evaluating outcomes of preventive services for older people.

There is growing preoccupation among policy makers and commissioners in developing preventive strategies and services. There is simultaneous concern with evidence-based purchasing and provision, within health and social care. In social care the evidence base regarding prevention is neither extensive nor robust. As the review of recent policy documents indicates, the concept of prevention is extremely slippery. What preventive services are and whether they are effective depends on the specific policy context, the overall service objectives and the perspective on outcomes adopted (user, carer, professional, service). Focusing on older people, the paper seeks a way through the confusion, locating prevention within a theoretical model of successful ageing. This conceptualizes ageing as involving adaptation to the changing balance between gains and losses over the life course. Successful ageing is perceived as the attainment of valued goals, the minimisation of losses and maximization of gains through the linked processes of selective compensation and optimisation. The paper then identifies necessary elaborations of the model to take into account the wider cultural and socio-economic context. This shapes and constrains the goals pursued and the resources available in adopting particular adaptation strategies. Within this model, preventive services may be conceived as resources to be drawn upon to support compensatory strategies. Similarly, outcomes and effectiveness of services may be evaluated in terms of whether they facilitate/allow older people to achieve valued goals. In developing and evaluating preventive services in social care the question of interest is reformulated: what contribution do specific services make in optimising gains and compensating for the losses that accompany ageing? This framework is explored in respect of two substantive areas ripe for secondary prevention services and strategies - bereavement and instrumental support in the home.

Adaptation, Psychological↗

PubMed1993

Ethical decision-making processes used by health care providers.

This paper reports the results of a study conducted with 18 health care providers (HCPs) in two Toronto hospitals. The study examined and assessed how these HCPs make clinical-ethical decisions in the light of a theoretical model of clinical-ethical decision making. Nine nurses and nine doctors were interviewed through two-phased, in-depth, semi-structured interviews. The results suggest that, in relation to the two major elements of the model, namely the ethical component and the decision theory component, the HCPs did not follow a consistent and systematic pattern of ethical decision making. Differences emerged between their actual self-reported behaviour and their potential more capability (i.e. their abstract thought process). The general picture that emerged was that decisions were made in a narrow, habitual manner, through the elimination of the most significant and demanding elements of the process. HCPs' ethical approaches affected the entire process of the decision making: their perception of the problem, their search for and selection of information and evidence, and their development of alternatives and resultant consequences. It is suggested to (a) further investigate and understand the subjective realities of the individuals involved in the decision making processes, their values and the meaning they ascribe to their choices, and (b) to establish extensive educational programmes to enhance HCPs' decision-making capacity and subsequently promote an effective and responsible professional practice.

Adult↗

PubMed2002

The meaning of models of nursing to practising nurses.

BACKGROUND: It is contended that models of nursing have lost the momentum and challenge that they promised the profession. Their use, value and purpose have been seriously questioned and new perspectives on their use and implementation in practice, education and research are required. In addition, limited evidence exists on the implementation of models into clinical areas. AIM: To explore the meaning of models of nursing to practising nurses. METHODS: Serial interviews with qualified nurses who were undertaking an educational programme or module that explored and examined models of nursing. FINDINGS: The outcome reveals that the use of the terms, models of nursing or nursing model, are limited and confusing as the terms can encompass a range of meanings. It is suggested that a three-model typology exists that clarifies more fully the present position of nursing models. The three models are Theoretical Model, Mental Model and Surrogate Model. LIMITATIONS: The focus on data collection through serial interviews with qualified practitioners could have been broadened to include a range of data sources such as teachers and clinical areas, which could have enriched the phenomenon of models of nursing. CONCLUSIONS: There is a greater need to understand nursing models within the framework of the three-model typology and to reconsider their introduction and use in this context.

Attitude of Health Personnel↗

PubMed2000

[Cerebral perfusion CT: theoretical aspects, methodical implementation and clinical experience in the diagnosis of ischemic cerebral infarction].

Cerebral perfusion CT using dynamic CT after bolus injection of contrast has recently been introduced in the clinical management of stroke patients. Based on the indicator dilution principle various theoretical models can be formulated which all aim at the quantitative determination of cerebral blood flow (CBF). Our Perfusion CT approach is based on the "maximum slope" model and allows in addition to the calculation of CBF parameter images the display of cerebral blood volume (CBV) and "time to peak" as diagnostically meaningful parameters. This approach allows the detection of acute ischemia of the supratentorial brain with a sensitivity of 91% and has proven its value as a routine diagnostic tool for acute stroke. The combination of various functional maps provides excellent information regarding the type of ischemia. Although the direct assessment of ischemia using absolute CBF values is severely restricted by patient dependent systematic errors, the severity of ischemia may reliably be assessed by using relative CBF perfusion indices.

Acute Disease↗

PubMed1992

Pathophysiology and epidemiology of chronic mountain sickness.

Chronic mountain sickness, which affects permanent residents of high altitudes, is the outcome of a progressive loss of ventilatory rate which naturally occurs with age and resulting in excessive hypoxemia and polycythemia. A theoretical model predicts the progressive failure of homeostatic control of the hemoglobin concentration when the values increase above those found at sea level. This is confirmed by lack of feedback mechanism between high altitude erythrocytosis and serum erythropoietin. The results of epidemiological studies are in agreement with the physiological findings. In a male population living at 4,300 m, an increase with age of the prevalences of excessive erythrocytosis (Hb > 213 g/l), blood oxygen saturation < 83%, headaches and a high score of symptoms of chronic mountain sickness has been found. The studies suggest the possibility that in addition to an accentuated hypoxemia, the excessive erythrocytosis may also result from an overreaction of the bone marrow to a fixed level of hypoxemia in ageing individuals.

Adult↗

PubMed1984

[Linearity of applanation tonometry].

A method has been developed for measuring intraocular pressure continuously. By comparing the results with theoretical models it has been established that only viscoelasticity of the sclera and cornea is able to compensate for rapid pressure fluctuations, whereas facility does this only to a minor degree.

Animals↗

PubMed2006

Multipole-multimode Floquet theory of rotational resonance width experiments: 13C-13C distance measurements in uniformly labeled solids.

A formal description of zero-quantum (ZQ) NMR processes using multipole-multimode Floquet theory is proposed for studying polarization transfer in magic angle spinning experiments. Specifically, we investigate the factors affecting the accuracy and precision of 13C-13C distance measurements that are based on ZQ-magnetization exchange processes in rotational resonance width experiments. With suitable examples drawn from measurements in N-acetyl-[U-13C,15N]-L-valine-L-leucine, we substantiate our approach and propose methods for improving the accuracy and reliability of such 13C-13C distance measurements in uniformly 13C, 15N-labeled solids. In addition, the theoretical model presented in this article provides a more general framework for describing relaxation phenomena involving multiple decay rate constants in zero-quantum processes.

Carbon Isotopes↗

PubMed2005

Prefrontal cortex and flexible cognitive control: rules without symbols.

Human cognitive control is uniquely flexible and has been shown to depend on prefrontal cortex (PFC). But exactly how the biological mechanisms of the PFC support flexible cognitive control remains a profound mystery. Existing theoretical models have posited powerful task-specific PFC representations, but not how these develop. We show how this can occur when a set of PFC-specific neural mechanisms interact with breadth of experience to self organize abstract rule-like PFC representations that support flexible generalization in novel tasks. The same model is shown to apply to benchmark PFC tasks (Stroop and Wisconsin card sorting), accurately simulating the behavior of neurologically intact and frontally damaged people.

Cognition↗

PubMed2006

Theory of the deuterium NMR of sterol-phospholipid membranes.

A general theoretical model is described for the NMR spectra of mixtures of sterols and deuterium-labeled phospholipids. In the case of homogeneous membranes, the average quadrupole splittings are determined by equilibria between lipids in cholesterol-phospholipid complexes and lipids not in complexes. Chemical exchange of lipids between those in the free state and those in the complex state affects the deuterium resonance line shapes. The lifetime of a phospholipid molecule in an ergosterol-dipalmitoylphosphatidylcholine complex is estimated to be of the order of 10(-5) s on the basis of the observed line broadenings. In the vicinity of a critical point of a cholesterol-phospholipid mixture, fluctuations in the concentration of complexes also can contribute to the deuterium nuclear resonance line broadening. At the critical point, the temperature derivative of the concentration of complexes is discontinuous. There is a corresponding jump in the calculated heat capacity as well as in the temperature derivative of the deuterium NMR first moment.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1972

Somatic mutational transients: models of response to acute and distributed doses of radiation applied to growing plants.

After limited exposures of whole plants to gamma radiation, the induced-mutation frequency, measured in somatic tissue of successively blooming flowers, is a transient function of time. Quantitative interpretation of the data is aided by construction of a cell-generation model. Seven theoretical models are designed to represent interaction between the cell-generation model and seven different modes of application of the radiation treatment. The models provide a structure for integration of the mutational contributions from different floral primordia. These different contributions are distributed over the array of mature flowers by the quantitative relationships of each model. A mathematical expression for the average response of a model can be equated to the average observed response and solved for the implied mutation rate per cell per roentgen.

Journal Article↗

PubMed1991

Micromotion of mammalian cells measured electrically.

Motility is a fundamental property of mammalian cells that normally is observed in tissue culture by time lapse microscopy where resolution is limited by the wavelength of light. This paper examines a powerful electrical technique by which cell motion is quantitatively measured at the nanometer level. In this method, the cells are cultured on small evaporated gold electrodes carrying weak ac currents. A large change in the measured electrical impedance of the electrodes is observed when cells attach and spread on these electrodes. When the impedance is tracked as a function of time, fluctuations are observed that are a direct measure of cell motion. Surprisingly, these fluctuations continue even when the cell layer becomes confluent. By comparing the measured impedance with a theoretical model, it is clear that under these circumstances the average motions of the cell layer of 1 nm can be inferred from the measurements. We refer to this aspect of cell motility as micromotion.

Cell Line↗

PubMed1996

The evolution of begging: signaling and sibling competition.

In many species, young solicit food from their parents, which respond by feeding them. Because of the difference in genetic make-up between parents and their offspring and the consequent conflict, this interaction is often studied as a paradigm for the evolution of communication. Existent theoretical models demonstrate that chick signaling and parent responding can be stable if solicitation is a costly signal. The marginal cost of producing stronger signals allows the system to converge to an equilibrium: young beg with intensity that reflects their need, and parents use this information to maximize their own inclusive fitness. However, we show that there is another equilibrium where chicks do not beg and parents' provisioning effort is optimal with respect to the statistically probable distribution of chicks' states. Expected fitness for parents and offspring at the nonsignaling equilibrium is higher than at the signaling equilibrium. Because nonsignaling is stable and it is likely to be the ancestral condition, we would like to know how natural systems evolved from nonsignaling to signaling. We suggest that begging may have evolved through direct sibling fighting before the establishment of a parental response, that is, that nonsignaling squabbling leads to signaling. In multiple-offspring broods, young following a condition-dependent strategy in the contest for resources provide information about their condition. Parents can use this information even though it is not an adaptation for communication, and evolution will lead the system to the signaling equilibrium. This interpretation implies that signaling evolved in multiple-offspring broods, but given that signaling is evolutionarily stable, it would also be favored in species which secondarily evolved single-chick broods.

Animal Communication↗

PubMed1997

Strong balancing selection at HLA loci: evidence from segregation in South Amerindian families.

The genotypic proportions for major histocompatibility complex loci, HLA-A and HLA-B, of progeny in families in 23 South Amerindian tribes in which segregation for homozygotes and heterozygotes could occur are examined. Overall, there is a large deficiency of homozygotes compared with Mendelian expectations (for HLA-A, 114 observed and 155.50 expected and for HLA-B 110 observed and 144.75 expected), consistent with strong balancing selection favoring heterozygotes. There is no evidence that these deficiencies were associated with particular alleles or with the age of the individuals sampled. When these families were divided into four mating types, there was strong selection against homozygotes, averaging 0.462 for three of the mating types over the two loci. For the other mating type in which the female parent is homozygous and shares one allele with the heterozygous male parent, there was no evidence of selection against homozygotes. A theoretical model incorporating these findings surprisingly does not result in a stable polymorphism for two alleles but does result in an excess of heterozygotes and a minimum fitness at intermediate allele frequencies. However, for more than two alleles, balancing selection does occur and the model approaches the qualities of the symmetrical heterozygote advantage model as the number of alleles increases.

Alleles↗

PubMed1997

Effect of protein dynamics on biological electron transfer.

Computer simulations of the effect of protein dynamics on the long distance tunneling mediated by the protein matrix have been carried out for a Ru-modified (His 126) azurin molecule. We find that the tunneling matrix element is a sensitive function of the atomic configuration of the part of the protein matrix in which tunneling currents (pathways) are localized. Molecular dynamics simulations show that fluctuations of the matrix element can occur on a time scale as short as 10 fs. These short time fluctuations are an indication of a strong dynamic coupling of a tunneling electron to vibrational motions of the protein nuclear coordinates. The latter results in a modification of the conventional Marcus picture of electron transfer in proteins. The new element in the modified theory is that the tunneling electron is capable of emitting or absorbing vibrational energy (phonons) from the medium. As a result, some biological reactions may occur in an activationless fashion. An analytical theoretical model is proposed to account for thermal fluctuations of the medium in long distance electron transfer reactions. The model shows that, at long distances, the phonon-modified inelastic tunneling always dominates over the conventional elastic tunneling.

Computer Simulation↗

PubMed1999

Biophysical characterization of lithostathine. Evidences for a polymeric structure at physiological pH and a proteolysis mechanism leading to the formation of fibrils.

Lithostathine is a calcium carbonate crystal habit modifier. It is found precipitated under the form of fibrils in chronic calcifying pancreatitis or Alzheimer's disease. In order to gain better insight into the nature and the formation of fibrils, we have expressed and purified recombinant lithostathine. Analytical ultracentrifugation and quasi-elastic light scattering techniques were used to demonstrate that lithostathine remains essentially monomeric at acidic pH while it aggregates at physiological pH. Analysis of these aggregates by electron microscopy showed an apparently unorganized structure of numerous monomers which tend to precipitate forming regular unbranched fibrils. Aggregated forms seem to occur prior to the apparition of fibrils. In addition, we have demonstrated that these fibrils resulted from a proteolysis mechanism due to a specific cleavage of the Arg(11)-Ile(12) peptide bond. It is deduced that the NH(2)-terminal undecapeptide of lithostathine normally impedes fiber formation but not aggregation. A theoretical model explaining the formation of amyloid plaques in neurodegenerative diseases or stones in lithiasis starting from lithostathine is described. Therefore we propose that lithostathine, whose major function is unknown, defines a new class of molecules which is activated by proteolysis and is not involved in cytoskeleton nor intermediate filament functions.

Alzheimer Disease↗

PubMed2004

A new intrinsic thermal parameter for enzymes reveals true temperature optima.

Two established thermal properties of enzymes are the Arrhenius activation energy and thermal stability. Arising from anomalies found in the variation of enzyme activity with temperature, a comparison has been made of experimental data for the activity and stability properties of five different enzymes with theoretical models. The results provide evidence for a new and fundamental third thermal parameter of enzymes, T(eq), arising from a subsecond timescale-reversible temperature-dependent equilibrium between the active enzyme and an inactive (or less active) form. Thus, at temperatures above its optimum, the decrease in enzyme activity arising from the temperature-dependent shift in this equilibrium is up to two orders of magnitude greater than what occurs through thermal denaturation. This parameter has important implications for our understanding of the connection between catalytic activity and thermostability and of the effect of temperature on enzyme reactions within the cell. Unlike the Arrhenius activation energy, which is unaffected by the source ("evolved") temperature of the enzyme, and enzyme stability, which is not necessarily related to activity, T(eq) is central to the physiological adaptation of an enzyme to its environmental temperature and links the molecular, physiological, and environmental aspects of the adaptation of life to temperature in a way that has not been described previously. We may therefore expect the effect of evolution on T(eq) with respect to enzyme temperature/activity effects to be more important than on thermal stability. T(eq) is also an important parameter to consider when engineering enzymes to modify their thermal properties by both rational design and by directed enzyme evolution.

Acid Phosphatase↗

PubMed1998

Correlates of recency of eye examination among elderly African-Americans.

This study uses a theoretical model of health services utilization to assess the effects of predisposing, enabling, and need-for-care characteristics on recency of eye examinations among a sample of 998 elderly African-American persons. More than 64% of participants reported that they had had eye examinations within the last 12 months. Multiple logistics regression analysis explains 13.3% of the variance of eye examinations. This data indicates that recency of eye examination is related to health locus of control, private insurance, Medicare, insulin-dependent diabetes, and presence of eye disease. No significant relationship between recency of eye examination and self-rated health status, social support, vision impairment, and non-insulin-dependent diabetes were detected. The lack of association between non-insulin-dependent diabetes and the recency of eye examination suggests that the amount of preventive care in place may not be adequate. This data shows that the unique contributions of need characteristics account for a major variance of recency of eye examination. However, enabling characteristics play a significant role in sending the participants of this study to eye-specialists, even after need-for-care factors are held constant.

Black or African American↗