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At least 847 records · Page 47Linked to original sources
PubMed2006

Fitness conflicts and the costs of sociality in communal egg layers: a theoretical model and empirical tests.

Individuals within complex social groups often experience reduced reproduction owing to coercive or suppressive actions of other group members. However, the nature of social and ecological environments that favour individual acceptance of such costs of sociality is not well understood. Taxa with short periods of direct social interaction, such as some communal egg layers, are interesting models for study of the cost of social interaction because opportunities to control reproduction of others are limited to brief periods of reproduction. To understand the conditions under which communal egg layers are in fitness conflict and thus likely to influence each other's reproduction, we develop an optimality model involving a brood guarding 'host' and a nonguarding disperser, or 'egg dumper'. The model shows that when, where intermediate-sized broods have highest survival, lifetime inclusive fitnesses of hosts and dumpers are often optimized with different numbers of dumped eggs. We hypothesize that resolution of this conflict may involve attempts by one party to manipulate the other's reproduction. To test model predictions we used a lace bug (Heteroptera: Tingidae) that shows both hosts and egg dumpers as well as increased offspring survival in response to communal egg laying. We found that egg-dumping lace bugs oviposit a number of eggs that very closely matches predicted fitness optimum for hosts rather than predicted optimum of dumpers. This result suggests that dumpers pay a social cost for communal egg laying, a cost that may occur through host suppression of dumper reproduction. Although dumper allocation of eggs is thus sub-optimal for dumpers, previous models show that the decision to egg dump is nevertheless evolutionarily stable, possibly because hosts permit just enough dumper oviposition to encourage commitment to the behaviour.

Animals↗
PubMed1993

Comparison of X-ray powder-diffraction data of various bacterial lipopolysaccharide structures with theoretical model conformations.

X-ray powder-diffraction experiments have been performed on dry samples of lipid A and various rough-mutant lipopolysaccharides (LPS) of Salmonella minnesota, Salmonella typhimurium and Escherichia coli. The diffraction patterns obtained indicated exclusively lamellar, bilayered arrangements in all samples. The periodicities were found to be in the range 4.5 nm for lipid A to 8.8 nm for Ra-LPS. Upon treatment with water-saturated air, swelling of the lamellar structures was achieved, as indicated by shifts of reflections. The increase in bilayer dimensions normally was about 0.3 nm. X-ray intensities were used for the determination of the inner bilayer structure, i.e. for calculation of the one-dimensional electron-density distribution across the bilayer. For lipid A and several Re-LPS, Rd2-LPS, Rd1-LPS and Rc-LPS samples, a striking coincidence of the electron-density distributions in the lipid-A domain was found, suggesting that in all these structures the lipid-A portion is similarly arranged. For Rb1 and Ra-LPS the lipid-A domain could not be resolved due to the limited number of observed reflections. For other Re-mutant lipopolysaccharide samples, quite different X-ray patterns were obtained. Some samples yielded diffraction patterns indicating a very high state of order in the lipid-A domain, whereas, in others, a significantly reduced order in the lipid-A domain was inferred. Comparison of the X-ray data with features of a calculated three-dimensional molecular model of lipopolysaccharide revealed reasonable agreement in molecular dimensions and bilayer structure.

Escherichia coli↗
PubMed2006

Behavioral facilitation of medical treatment for headache--part II: Theoretical models and behavioral strategies for improving adherence.

This is the second of 2 articles addressing the problem of noncompliance in medical practice and, more specifically, compliance with headache treatment. The companion paper describes the problem of noncompliance in medical practice and reviews literature addressing compliance in headache care (Behavioral Facilitation of Medical Treatment for Headache--Part I: Review of Headache Treatment Compliance). The present paper first summarizes relevant health behavior theory to help account for the myriad biopsychosocial determinants of adherence, as well as patient's shifting responsiveness or "readiness for change" over time. Appreciation of health behavior models may assist in optimally tailoring interventions to patient needs through instructional, motivational, and behavioral treatment strategies. A wide range of specific cognitive and behavioral compliance-enhancing interventions are described, which may facilitate treatment adherence among headache patients. Strategies address patient education, patient/provider interaction, dosing regimens, psychiatric comorbidities, self-efficacy enhancement, and other behavioral interventions.

Behavior Therapy↗
PubMedDate not supplied

Emotional development in infancy: theoretical models and nursing implications.

TOPIC: Theories of emotional development in infancy that are relevant to clinical practice. PURPOSE: A discussion of the complementary theories such as Emde's (1989) psychoanalytically based developmental model of early socioemotional reorganizations and Stern's (1985a) model of the developing self, with the goal of presenting an integrated view of key socioemotional processes and their developmental foundations during infancy. Concepts such as "emotional availability" and "affect attunement" are examined as vehicles for early socioemotional organization and adaptation. SOURCES: Relevant literature from nursing, child psychiatry, and developmental psychology. CONCLUSIONS: Implications are drawn from clinical assessment of high-risk caregiver-infant relationships and early causal pathways for later socioemotional dysfunction. Nurses should focus on the importance of assessing interpersonal variables and their ongoing contribution to internalizing patterns of dysfunctional behavior in children.

Child Development↗
PubMed2005

Membrane phospholipid redistribution in cytokinesis: a theoretical model.

In cell mitosis, cytokinesis is a major deformation process, during which the site of the contractile ring is determined by the biochemical stimulus from asters of the mitotic apparatus, actin and myosin assembly is related to the motion of membrane phospholipids, and local distribution and arrangement of the microfilament cytoskeleton are different at different cytokinesis stages. Based on the Zinemanas-Nir model, a new model is proposed in this study to simulate the entire process by coupling the biochemical stimulus with the mechanical actions. There were three assumptions in this model: the movements of phospholipid proteins are driven by gradients of biochemical stimulus on the membrane surface; the local assembly of actin and myosin filament depends on the amount of phospholipid proteins at the same location; and the surface tension includes membrane tensions due to both the passive deformation of the membrane and the active contraction of actin filament, which is determined by microfilament redistribution and rearrangement. This model could explain the dynamic movement of microfilaments during cytokinesis and predict cell deformation. The calculated results from this model demonstrated that the reorientation of phospholipid proteins and the redistribution and reorientation of microfilaments may play a crucial role in cell division. This model may better represent the cytokinesis process by the introduction of biochemical stimulus.

Actin Cytoskeleton↗
PubMed1983

Theoretical models of rouleau formation and disaggregation.

The formation of rouleaux of red blood cells is considered as an interaction of the surface adhesive energy and the elastic strain energy of the red blood cell membrane. A dynamic energy equation is written which applies to both the process of aggregation and the disaggregation by external forces. Any equilibrium state may be regarded as minimization of the appropriate energy potentials. The theory is illustrated by the computation of the shapes of two cell rouleaux under different surface adhesive energies. Disaggregation is studied in a model in which the red blood cells are idealized as cylindrical forms. It is shown that during disaggregation the strain energy stored in the cell contributes to the work done in overcoming the adhesive energy.

Cell Adhesion↗
PubMed2006

A theoretical model of enlarging intracranial fusiform aneurysms.

The mechanisms by which intracranial aneurysms develop, enlarge, and rupture are unknown, and it remains difficult to collect the longitudinal patient-based information needed to improve our understanding. We submit, therefore, that mathematical models hold promise by allowing us to propose and test competing hypotheses on potential mechanisms of aneurysmal enlargement and to compare predicted outcomes with limited clinical information--in this way, we may begin to narrow the possible mechanisms and thereby focus experimental studies. In this paper, we present a constrained mixture model of evolving thin-walled, fusiform aneurysms and compare multiple competing hypotheses with regard to the production, removal, and alignment of the collagen that provides the structural integrity of the wall. The results show that this type of approach has the capability to infer potential means by which lesions enlarge and whether such changes are likely to produce a stable or unstable process. Such information can better direct the requisite histopathological examinations, particularly on the need to quantify collagen orientations as a function of lesion geometry.

Animals↗
PubMed1987

A theoretical model for peripheral tissue heat transfer using the bioheat equation of Weinbaum and Jiji.

In this paper the new bioheat equation derived in Weinbaum and Jiji is applied to the three layer conceptual model of microvascular surface tissue organization proposed in. A simplified one-dimensional quantitative model of peripheral tissue energy exchange is then developed for application in limb and whole body heat transfer studies. A representative vasculature is constructed for each layer and the enhancement in the local tensor conductivity of the tissue as a function of vascular geometry and blood flow is examined. Numerical solutions for the boundary value problem coupling the three layers are presented and these results used to study the thermal behavior of peripheral tissue for a wide variety of physiological conditions from supine resting state to maximum exercise.

Animals↗
PubMedDate not supplied

Theoretical modeling and evaluation of the axial resolution of the adaptive optics scanning laser ophthalmoscope.

We present axial resolution calculated using a mathematical model of the adaptive optics scanning laser ophthalmoscope (AOSLO). The peak intensity and the width of the axial intensity response are computed with the residual Zernike coefficients after the aberrations are corrected using adaptive optics for eight subjects and compared with the axial resolution of a diffraction-limited eye. The AOSLO currently uses a confocal pinhole that is 80 microm, or 3.48 times the width of the Airy disk radius of the collection optics, and projects to 7.41 microm on the retina. For this pinhole, the axial resolution of a diffraction-limited system is 114 microm and the computed axial resolution varies between 120 and 146 microm for the human subjects included in this study. The results of this analysis indicate that to improve axial resolution, it is best to reduce the pinhole size. The resulting reduction in detected light may demand, however, a more sophisticated adaptive optics system. The study also shows that imaging systems with large pinholes are relatively insensitive to misalignment in the lateral positioning of the confocal pinhole. However, when small pinholes are used to maximize resolution, alignment becomes critical.

Computer Simulation↗
PubMedDate not supplied

Temperature distributions in hyperthermia by electromagnetic induction: a theoretical model for the thorax.

Steady-state temperature solutions to the bioheat equation are presented for magnetic induction heating of a thoracic model consisting of a spherical tumor embedded in lung tissue which is layered by muscle and fatty tissue. Analytical solutions are presented for each of the tissue regions along with their numerical evaluations over a range of physical characteristics, including surface cooling effects. A strong dependence of tumor temperature on size and blood perfusion rate is shown to exist and can be used to optimize treatment parameters. Tendencies of the chest muscles and overlaying fatty tissue to overheat, particularly in the case of an obese patient, are discussed along with the alleviating influence of surface cooling. Healthy lung tissue, on the other hand, is shown to be safe from any significant damage in such a heating situation. Transient times required for tumors to achieve thermal equilibrium are computed and shown to depend strongly on tumor size and, to a lesser extent, on blood perfusion rate. Finally, the overall results obtained from the model are compared with available clinical data and are found to be in line with those observations.

Hot Temperature↗
PubMedDate not supplied

Theoretical model of phase separation of erythrocytes, platelets, and plasma at branches.

Analytical expressions for the changes of the erythrocyte and platelet concentration are calculated as blood flows through a single bifurcation. The effect of the separation surface, which divides the blood into the two daughter vessels, upon the concentration changes is studied. Numerical fitting to the experimental data shows that both the erythrocyte and platelet distributions across the vessel are nonuniform. The maximum of the erythrocyte concentration is in the core, and of the platelet concentration, in the vicinity of the wall. A separation surface that is convex towards the axis of the vessel yields better fit to the experimental data than a concave one. Together with other studies, this suggests that flow-divider geometry depends on flow conditions and the vessel diameters. The results can be used for estimation of the distribution of erythrocytes and platelets in the microvasculature.

Blood Circulation↗