Biomedical subjects

J D Baldwin

Publications and source records attributed to J D Baldwin.

16 recordsLinked to original sources

PubMed2000

Heterosexual anal intercourse: an understudied, high-risk sexual behavior.

Differences between heterosexuals who have or have not engaged in anal intercourse were analyzed. Though anal intercourse is widely recognized as an activity that greatly increases the risks for HIV transmission, it has received little attention in heterosexual populations. A questionnaire was mailed to a random sample of university students, a population in which many people engage in vaginal intercourse with several partners each year. The three largest minorities were randomly oversampled in order that all four major ethnic/racial groups could be statistically evaluated for possible differences. Almost 23% of nonvirgin students had engaged in anal intercourse. Regression analysis indicated that people who had participated in anal intercourse were more likely than people without anal experience to have been younger at first vaginal intercourse, to be older when the data were collected, to have engaged in vaginal intercourse in the last three months before data collection, to be more erotophilic, to use less effective contraceptive methods, and to have used no condom at last coitus. Overall, people who engage in anal intercourse take more sexual risks when engaging in vaginal intercourse than do people without anal experience. No major ethnic/racial differences were detected. Sexologists have not explored anal sex in much detail, hence we have been weak in educating those 20 to 25% of young adults who are not reluctant or (inhibited about) exploring anal intercourse. As young adults use condoms less for anal than vaginal intercourse, they have not learned enough about the risk of anal sex.

Adult↗

PubMed1998

Molecular phylogeny and biogeography of the marine shrimp Penaeus.

The evolutionary relationships among 13 species representing all six subgenera of the shrimp genus Penaeus were examined using 558 bp of mitochondrial (mt) DNA from the cytochrome oxidase subunit I gene. Analyses of this sequence revealed high genetic divergence between species (d = 8-24%), a finding which contrasts with previous work, which indicated that genetic diversity, based on electrophoretic analysis of allozymes, was extremely low in Penaeus. Three tree-building methods (maximum parsimony, neighbor joining, and maximum likelihood) were concordant in indicating that current subgenera assignments do not reflect evolutionary partitions within the genus Penaeus. While the molecular phylogenies cast doubt on the validity of subgenera, the observed relationships are concordant with biogeographic boundaries across the tropical range of Penaeus. Both the western Atlantic and eastern Pacific contain monophyletic species pairs which cluster together in all analyses. The Indo-Pacific contains a putative basal taxa (P. indicus), the deepest mtDNA lineages, and the highest diversity, including representatives of all three primary lineages observed in Penaeus. These data are consistent with the suggestion by Dall et al. (1990) that Penaeus arose in the Indo-Pacific and radiated eastward and westward to account for the current circumtropical distribution of the genus. This phylogenetic framework for Penaeus will enhance the scientific foundations for wildlife resource management and breeding experiments (hybridization and related manipulations) designed to improve the commercial value of captive strains.

Animals↗

PubMed1998

Immunological characterisation of the acrosomal filament in the marine shrimp Sicyonia ingentis.

During sperm/egg interaction, the sperm of Sicyonia ingentis undergoes a unique biphasic acrosome reaction. After acrosomal vesicle exocytosis, the sperm generates an acrosomal filament, over a period of 4-6 min, that is approximately 10 microns in length. Neither actin filaments nor normal microtubules have been demonstrated at the ultrastructural level of this unusual filament. Using a battery of cytoskeleton-directed antibodies the biochemical nature of this filament has been investigated. Antibodies to actin and tubulin do not label the subacrosome or acrosomal filament, but do recognise actin and tubulin in other shrimp tissues. Antibodies to tau, MAP2, and neurofilament medium and heavy subunits were all localised to the subacrosomal region of the sperm. It is interesting, however, that only the two clones of neurofilament monoclonal antibodies recognised the acrosomal filament. Electrophoretic and Western blot analysis in conjunction with amino acid sequencing revealed that the proteins localised to the acrosomal filament are of a unique sequence and may represent a new type of protein of centrosomal origin.

Acrosome↗

PubMed1997

Gender differences in sexual interest.

A common gender stereotype is that males are more interested than females in sex for purely physical reasons. Sociobiologists claim that this difference is biologically determined. In contrast, many sociologists and anthropologists claim that the difference is cultural. The debate about nature versus nurture regarding sexual interest has been long-standing without resolution. We propose a biosocial model that integrates data about nature and nurture to show (i) how several biological factors tilt males and females in different directions related to sexual interest, and (ii) how numerous social factors influence the way the biological tilts can be redirected in countless different ways as individuals grow up in subsets of their culture and subculture. This interactionist approach does not down-play the importance of either biological or social factors: It avoids nature-nurture debates that pit nature against nurture by showing how biological and social factors act in concert, combining their influences. The resulting work contributes to both the theoretical and practical literature, not only showing how sexology can deal with issues of nature and nurture but also providing information useful to people who are troubled about common gender differences in sexual interest.

Culture↗

PubMed1995

Strain-based fatigue analysis of wheelchairs on a double roller fatigue machine.

Results are presented from an experimental program that recorded the outputs of strain gages mounted on two wheelchair frames (one manual, one power) as the wheelchairs were run on a double roller fatigue machine. Rectangular strain gage rosettes were attached to the frames near the cross tube center pin and on the side frame behind a front caster. Thirty data sets were recorded from each rosette on each wheelchair frame. The fatigue test machine and test protocol were in substantial conformance with the recently published ANSI/RESNA Standard for wheelchair fatigue testing. Two analyses have been performed on the recorded strain data. The von Mises stress histories were computed from the strain data and show that peak stresses are frequently twice the mean value. Also, estimates of the number of fatigue machine cycles to failure have been made using a strain-based fatigue analysis. These data will provide wheelchair designers with useful data to incorporate into their design process.

Mathematics↗

PubMed1993

Characterization of the dynamic stress response of manual and powered wheelchair frames.

Two wheelchairs, one manual, one electrically powered, were instrumented with strain gages and operated over various laboratory terrains. Both wheelchairs were folding models with cross tubes pinned together at the center. The wheelchairs were operated on a constant speed treadmill with no bump, and with 0.953 cm (0.375 in) and 1.6 cm (0.625 in) dowels simulating bumps. The wheelchairs were also rolled off a 10.8 cm (4.25 in) platform to simulate a curb drop. The von Mises stresses were computed from the recorded strains, and statistical hypothesis tests were performed to determine whether the stresses were consistent with a stationary, narrow-band Gaussian random process. Such a stress history has been used in random fatigue analyses. Summary data for two strain gage locations on each wheelchair, for the four different test terrains, suggest that the von Mises stress can be considered stationary, but neither narrow-banded, nor Gaussian distributed.

Humans↗

PubMed1992

Preservation and visualization of the sea urchin embryo blastocoelic extracellular matrix.

Several methods were utilized to visualize the structure and orientation of the blastocoelic extracellular matrix (ECM) in Strongylocentrotus purpuratus embryos at the mesenchyme blastula stage. Rapid freezing in liquid propane cooled to LN2 temperatures followed by freeze substitution was used to preserve the ECM without shrinkage due to dehydration. Scanning, transmission, and light microscopy were employed to elucidate the ECMs' structure. The blastocoelic ECM consisted of parallel fibrillar sheets that were interconnected by finer filaments and oriented along the animal-vegetal axis. The ECM completely filled the blastocoelic cavity as viewed by scanning electron microscopy. The basal lamina could be distinguished from the blastocoelic ECM as a thin coat on the plasma membrane of epithelial cells; the ECM was in contact with this coat. In contrast, the blastocoelic ECM attached directly to the plasma membrane of primary mesenchyme cells (PMC) which did not possess a basal lamina. The blastocoelic ECM was isolated as an intact "bag" and probed in a hydrated state with Con A and alcian blue. Confocal microscopy confirmed that the entire blastocoel was filled with a fibrillar ECM. These approaches offer advantages for future studies of the ECMs of sea urchin embryos and their roles in gastrulation.

Animals↗

PubMed1989

The socialization of homosexuality and heterosexuality in a non-Western society.

Data on the Sambia--a tribe living in Papua New Guinea--are presented to demonstrate how Sambia males develop a homosexual orientation in boyhood and adolescence, then switch to become heterosexuals in adulthood. Social learning theory is used to explain how sexual orientation in the Sambia change from homo- to heterosexual during the transition to adulthood. Whereas most learning analyses of sexual orientation are based on data from Western cultures, this manuscript extends that literature to deal with a non-Western culture. While including Pavlovian and operant conditioning, which is stressed in many learning analyses of sexual learning, the present analysis also includes detail on the social and cognitive learning principles that are important in understanding the learning of sexual orientation and behavior.

Adolescent↗

PubMed1976

Effects of food ecology on social play: a laboratory simulation.

A laboratory group of 8 squirrel monkeys was exposed to two experimental conditions in which food was made moderately and extremely difficult to obtain, compared with the free access conditions of baseline. Both experiments produced sharp decreased in the frequency of social play within 4 to 6 days. The stronger manipulation produced the more dramatic effect, reducing play to 1% of the baseline level (P less than .001). Neither experiment produced a total absence of play as was observed in a previous field study in southwestern Panama (Baldwin and Baldwin 1973, 1974) which suggests that the field study sampled conditions of even more severe and/or prolonged food deprivation. No pathological or dysfunctional consequences were observed in any of the circumstances where play was reduced to zero or near zero. The question is raised whether certain theories of play have overstated the case for the necessity of play experience in producing normal socialization in primates. Alternative hypotheses are presented concerning the factors that determine the frequency of play and the consequences of play versus no-play for socialization. After both experiments, the frequency of play rose to a level 50% higher than the average baseline levels of play. This "rebound" reached a peak 5 to 6 days after the termination of each experiment; and during the subsequent days the frequency of play declined to more normal levels. A reinforcement theory is presented as a possible explanation of the rebound effect.

Animals↗

PubMed1976

Vocalizations of howler monkeys (Alouatta palliata) in southwestern Panama.

This report presents an analysis of the vocal repertoire of howler monkeys (Alouatta palliata) observed during a field study in southwestern Panama. 26 types of vocalizations were identified and described, and sonagrams are presented for 21 of them. The vocal repertoire contained many nondiscrete calls that graded continuously into each other, and all of the calls appeared to fit into 5 or 6 broad families. A tape recording of the vocalizations described in this study is available.

Alouatta↗

PubMed1974