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Biomedical subjects

W J Bell

Publications and source records attributed to W J Bell.

At least 19 recordsLinked to original sources
PubMed1996

Transport characterization of membranes for immunoisolation.

This study relates to the diffusive transport characterization of hollow fibre membranes used in implantable bio-hybrid organs and other immunoisolatory devices. Techniques were developed to accurately determine the mass transfer coefficients for diffusing species in the 10(2)-10(5) MW range, validated and then used to study one membrane type known to effectively immunoisolate both allografts and xenografts in vivo. Low-molecular-weight diffusing markers included glucose, vitamin B12 and cytochrome C; higher-molecular-weight molecules were bovine serum albumin, immunoglobulin G, apoferritin and a range of fluorescein-tagged dextrans. Overall and fractional mass transfer coefficients through the hollow fibres were determined using a resistance-in-series model for transport. A flowing dialysis-type apparatus was used for the small-molecular-weight diffusants, whereas a static diffusion chamber was used for large-molecular-weight markers. For diffusion measurements of small-molecular-weight solutes, convective artefacts were minimized and the effect of boundary layers on both sides of the membrane were accounted for in the model. In measuring diffusion coefficients of large-molecular-weight species, boundary layer effects were shown to be negligible. Results showed that for small-molecular-weight species (< 13,000 MW) the diffusion coefficient in the membrane was reduced relative to diffusion in water by two to four times. The diffusion rate of large-molecular-weight species was hindered by several thousand-fold over their rate of diffusion in water.

Animals↗
PubMed1995

Defining stops in search pathways.

The alternation of stationary periods and periods of movement may be an important feature of an animal's search tactic. Unambiguously differentiating stops and moves may be difficult, especially from highly resolved digitized pathways, but their identification may be essential for understanding an animal's searching behavior. In this paper, we describe a method for defining stops in search pathways. A computer program that identifies the stop-and-go movement patterns from digitized pathway data is available upon request from the authors.

Animals↗
PubMed1991

The problem of movelength and turn definition in analysis of orientation data.

This study examines the analysis of arthropod orientation data. Three problems are discussed: (1) dealing with time as it applies to spatial data, (2) determining the appropriate movelength to be used in collecting and in analyzing data, and (3) defining a turn, to discriminate between "gait noise" and course changes. The main objective is to determine the solution to defining the most appropriate movelength for comparisons between variables and between species. The technique described here for selecting the appropriate movelength that has relevance to both the locomotory rate of the animal and its body length, reduces variation resulting from lateral translational movements, prevents the use of movelengths that lead to artifactual or unrealistic turning values per move, and permits comparisons of species and individuals under various stimulus conditions.

Animals↗
PubMed1991

The use of visual information by house flies, Musca domestica (Diptera: muscidae), foraging in resource patches.

House flies, Musca domestica, respond to visual contrasts on the substrate if a resource is associated with the contrasting patterns. Visible resource patch boundaries serve as a signal to flies that they are about to leave a rewarding patch. Searching flies respond to such visual information by walking along the resource patch boundary and turning back into the patch at its edge. This edge detection and response serve as a mechanism for flies with visual cues to stay in a rewarding patch and locate more resources within it. The intensity of their response correlates with the quality of the resource. In the absence of visual cues, patch shape affects foraging success; flies find more resources in circular than in linear resource distributions. The effects of visual cues, however, render patch shape unimportant. Various substrate contrasts are effective as resource information for flies: dark (e.g., green) figures on bright (e.g., white) backgrounds or bright figures on dark backgrounds. Responses to substrate contrasts measured in this study indicate that, over the short term, house flies can learn a visual cue associated with a food source.

Animals↗
PubMed1991

A simple video position-digitizer for studying animal movement patterns.

A simple video position-digitizer has been developed for studying the movement patterns of small animals. This report provides a complete procedure for constructing the circuit, which when used in conjunction with a conventional video camera and an IBM PC compatible computer, automatically digitizes and records the path of a dark animal against a light colored background for relatively long periods of time.

Animals↗
PubMed1984

Radon-222 in the gastrointestinal tract: a proposed modification of the ICRP Publication 30 model.

The New England states have a long involved history of radon in individual well water supplies. As a result of these previous findings on the abundance of radon, coupled with its potential health impact, the New England Radiological Health Committee (NERHC) formulated a technical working group in 1980 which was charged with evaluating the possibility of developing uniform concentration guidelines for radon in individual domestic water supplies. This working group determined that the current ICRP Publication 30 metabolic model for the gastrointestinal (GI) tract was inadequate to address the empirically observed rates of 222Rn removal from the body. A modification to the ICRP Publication 30 GI tract model is proposed which attempts to resolve these differences. Calculations are presented, using both the original and modified ICRP Publication 30 models, which indicate that individual potable water supplies containing 222Rn concentrations as high as 400,000 pCi/l. do not significantly increase the probability of stomach or intestinal cancer, as defined by the BEIR III risk estimates. Since this paper deals exclusively with the GI tract, no attempt is made to address the lung burden imposed by the contribution of radon released into the household air by aeration at the tap or other fixtures. Only when the contribution of the radon water source term to both the respiratory and ingestion pathways is evaluated as a whole can any meaningful standard for 222Rn in individual domestic water supplies be established.

Digestive System↗
PubMed1982

Cell-mediated immune-type response of the American cockroach.

Cell-mediated immunity in the American cockroach, Periplaneta americana, was measured by counting nuclei in a transect through the mass of host hemocytes reacting against transplanted xenograft or autograft integument. Responses to xenografts (Leucophaea maderae) were significantly higher than control responses to autograft integument. Responses to Leucophaea xenografts increased with longer durations of xenograft exposure to hosts for up to eight days, then decreased by day sixteen. Responses to cockroach species from a phylogenetically graded series of donors were stronger and correlated with increasing phylogenetic distance between various donors and hosts (Periplaneta americana).

Animals↗
PubMed1980

Vitellogenin: its structure, synthesis and processing in the cockroach Periplaneta americana.

The vitellogenin in the oocyte of the American cockroach contains three different polypeptides with approximate molecular weights of 123 000, 118 000 and 57 000. These are present in a molar ratio of 2 : 2 : 2; all three contain carbohydrate. The same subunit structure is observed in vitellogenin isolated from hemolymph and in that secreted by fat body in organ culture. The only protein found within fat body by precipitation with female-specific antiserum is a large polypeptide, with a molecular weight of approx. 250 000. No mature vitellogenin subunits are found in fat body, even after pulsing with labeled amino acids and chasing with unlabeled substrates for up to 4 h. These data suggest that vitellogenin is synthesized in the fat body as a large precursor, which is processed to smaller polypeptides upon secretion into the hemolymph.

Animals↗