Biomedical subjects

W J Greenleaf

Publications and source records attributed to W J Greenleaf.

8 recordsLinked to original sources

PubMed2000

Atomic force microscopy captures quantized plastic deformation in gold nanowires.

Scanning probe microscopy has become a powerful tool to detect structural changes in small clusters of atoms. Herein, we use an atomic force microscope to measure the length of gold nanowire structures during extension and compression cycles. We have found that nanowires elongate under force in quantized steps of up to three integer multiples of 1.76 A and that they shorten spontaneously in steps of 1.52 A. Our results can be explained by the sliding of crystal planes within the gold nanowires creating stacking faults that change the local structure from face-centered cubic to hexagonal close packed. Our data also show that there can be up to three simultaneous slip events, in good agreement with the tetrahedral arrangement of slip planes in a gold crystal. These experiments provide direct evidence for the mechanism underlying the plastic deformation of a nanowire. A similar approach can be used to examine the atomic events underlying the plastic failure of other metals and their alloys.

Journal Article↗

PubMed2000

Telerehabilitation services using web-based telecommunication.

A World Wide Wide-based telerehabilitation platform has been demonstrated in a laboratory environment. This platform allows a rehabilitation provider to thoroughly evaluate the progress of a patient remotely with the same care and measurement precision that would be possible if the provider and the patient were in the same room. The platform was designed to be Web-based so that the service could be offered at the same price without regard to long distance telecommunication facility charges. The Web-based implementation allows enough bandwidth for a simultaneous video teleconference and a precision data acquisition mode even when the Web connection is a low cost analog modem computer interface at both ends of the connection.

Ambulatory Care↗

PubMed1998

Artificial cavitation nuclei significantly enhance acoustically induced cell transfection.

The efficiency of ultrasound-mediated gene transfection was enhanced three- to fourfold, compared to previous results, through the use of green fluorescent protein reporter gene, cultured immortalized human chondrocytes and artificial cavitation nuclei in the form of Albunex. Cells were exposed to 1.0-MHz ultrasound transmitted through the bottom of six-well culture plates containing immortalized chondrocytes, media, DNA at a concentration of 40 micrograms/mL and Albunex at 50 x 10(6) bubbles/mL. Transfection efficiency increased linearly with ultrasound exposure pressure with a transfection threshold observed at a spatial average peak positive pressure (SAPP) of 0.12 MPa and reaching about 50% of the living cells when exposed to 0.41 MPa SAPP for 20 s. Adding fresh Albunex at 50 x 10(6) bubbles/mL prior to sequential 1-s, 0.32- or 0.41-MPa exposures increased transfection with each exposure, reaching 43% transfection after four exposures. Efficient in vitro and in vivo transfection now appear possible with these enhancements.

Albumins↗

PubMed1994

Augmenting reality in rehabilitation medicine.

Virtual reality comprises the computer-based generation of realistic three-dimensional visual, auditory, and tactile environments in which a user can explore and interact with virtual objects. Although traditionally used for input devices to virtual worlds, the instrumented glove and sensor technologies of virtual reality may provide a dramatic new method for the measurement and amplification of human motion. This paper discusses some potential uses of virtual reality technology to support and augment routine activities for people who have physical disabilities. We present two different but related applications of this technology.

Computer Graphics↗

PubMed1993

Aging and sexual function in men.

Sexual function, and in particular erectile capacity, declines with age in men. The present study attempted to identify possible sensory/neural and autonomic factors related to this decline. Data on self-reported sexual activity and functioning, as well as erectile response to visual erotic stimulation, were gathered from 39 healthy, sexually functional men ranging in age from 21 to 82. In addition, four parameters of putative significance to sexual functioning were measured: penile electrical and vibrotactile thresholds, pudendal somatosensory evoked potentials, penile autonomic response to ischemia, and blood testosterone. Results indicated significant age-related decreases in self-reported frequency of sexual activity and in erectile response to erotica. Furthermore, penile sensitivity, response to penile ischemia, and somatosensory evoked potentials showed age-related changes. In contrast, self-reported erectile capacity, ratings of overall sex life, and levels of testosterone did not change over age groups. These findings suggest that decreasing erectile capacity in aging men may be related to decreasing sensory/neural and autonomic functioning, but they also indicate that factors other than the frequency of and potency for sexual response are important to the overall rating of sex life.

Adult↗

PubMed1983

Hormonal changes and sexual function in aging men.

A cross-sectional study on 220 men, aged 41-93 yr, was conducted to determine whether age-related changes in circulating pituitary and gonadal hormone levels are related to quantitatively assessed changes in sexuality over this age span. The conclusion of most previous studies, that total and free plasma testosterone (T) levels decline with advancing age as gonadotropins increase, was corroborated. These changes were found to roughly parallel a decline in sexual function affecting the level of sexual activity, libido, and potency measures. PRL and estradiol did not change with age, and the age-related decline in free T was greater than that in total T. Decreases in free T and increases in LH manifested significant, but small, correlations with sexual hypofunction. Behavioral variables were also clearly related to LH and to the ratio of free T to LH and estradiol. The data also suggested that aging and hormonal changes were more strongly related to sexual activity and nocturnal erections that to libido (enjoyment, drive, and thoughts). Partial correlation procedures demonstrated that diseases and drugs were not responsible for the hormone-behavior relationships. Declining androgen levels, reduced sexual activity, and decreased sexual interest thus appear to be related sequelae of the aging process in men. Hormonal factors do not completely account for age-related changes in sexuality, although the full explanation of these changes must include a consideration of hormonal factors.

Adult↗

PubMed1983

The nature of androgen action on male sexuality: a combined laboratory-self-report study on hypogonadal men.

Sexual function and the effects thereon of testosterone enanthate were studied in six hypogonadal men with the objective of delineating the specific components of male sexuality affected by androgen. To obtain a detailed picture of these components, prospective self-report data (from daily logs) of sexual activity and feelings, recordings of all night penile tumescence, and laboratory psychophysiological data were assessed. Double blind placebo experiments with cross-over design were used to compare the effects of placebo and 200- and 400-mg doses of testosterone enanthate. Erectile responses to erotic film and fantasy were not lower in the hypogonadal patients than in normal men and, in fact, were higher on some parameters, especially prolongation of detumescence time after exposure to film or fantasy. Three subjects who kept consistent daily logs had increased frequencies of sexual acts and feelings, orgasms, and spontaneous erections after testosterone administration. Nocturnal penile tumescence and spontaneous daytime erections were reduced in untreated hypogonadal men and were significantly increased after testosterone treatment, but the laboratory-tested erectile responses to film and fantasy were not affected by testosterone. These data and previous findings lead to the conclusion that the major androgen action on male sexuality involves libido factors (i.e. sexual motivation/interest). Though stimulus-bound erections elicited in the laboratory were not reduced in hypogonadal men, spontaneous (sleep or waking) erections were clearly testosterone dependent.

Adult↗

PubMed1982

Hormonal replacement and sexuality in men.

Only in the last few years has the scientific study of hormonal replacement therapy for hyposexuality begun in earnest with the advent of appropriately controlled experiment studies. Dose-response relationships can be demonstrated between testosterone (T) and sexual measures, but these have not yet been investigated in detail. Some aspects of sexual function are maintained in the presence of androgen levels well below the normal range, but preliminary evidence suggests that within a normal population high levels of T are correlated with more vigorous responses to visual erotic stimuli. Though T (and to a greater extent free T) declines with aging in parallel with the decline of sexual function, these hormonal changes contribute only to a minor extent to the behavioural change. Some non-aromatizable androgens may be less effective in stimulating sexual behaviour than T, but initial data on effects of dihydrotestosterone suggests that the capacity of an androgen to be aromatized (converted to oestrogen) is not a requirement for its sexual action. While T apparently increases the incidence of all types of male sexual activity, recent data contradict the belief that it directly facilitates the erectile mechanism in men, even though erection frequency is greatly reduced in untreated hypogonadal men. At the present juncture, it appears that the initial action of T may be on libido factors which lead in turn to the stimulation of other aspects of sexuality. Specifically, we propose that androgen acts through stimulating genital sensations and/or other pleasurable awareness of sexual response rather than directly through cognitive processes such as sexual imagery.

Adult↗