Biomedical subjects

R Akers

Publications and source records attributed to R Akers.

12 recordsLinked to original sources

PubMed2004

Spatial and temporal structure of edge-localized modes.

This Letter provides information on the spatial and temporal structure of periodic eruptions observed in magnetically confined laboratory fusion plasmas, called edge-localized modes (ELMs), and highlights similarities with solar eruptions. Taken together, the observations presented in this Letter provide strong evidence for ELMs being associated with a filamentlike structure. These filaments are extended along a field line, are generated on a 100 micros time scale, erupt from the outboard side, and connect back into the plasma. Such structures are predicted by a theoretical model based on the "ballooning" instability, developed for both solar and tokamak applications.

Journal Article↗

PubMed2002

Neoclassical tearing physics in the spherical tokamak MAST.

Results from MAST provide a first test of neoclassical tearing mode physics in the spherical tokamak (ST). The mode accounts for the main performance limit in conventional tokamaks. Its behavior in the ST is remarkably well described by existing theoretical models, although it is more readily seeded by sawtooth events in these scenarios. Modeling confirms the significance of stabilizing field-curvature effects. This provides good grounds for optimism that with suitable control of profiles, it may be possible to avoid these modes in the ST.

Journal Article↗

PubMed2000

Birth control method choice and use of barrier methods for sexually transmitted disease prevention among low-income African-American women.

In a prospective study of 1122 women attending a sexually transmitted disease (STD) clinic in Alabama, consistent use of the male condom and vaginal microbicide/spermicides was promoted to reduce STD risk. This analysis evaluated: 1) baseline characteristics that may influence birth control method choice; and 2) the association of birth control method and other baseline characteristics with consistency of barrier use during follow up. Birth control method was associated with sociodemographic variables, sexual, and reproductive history. Women who adopted user-independent methods (tubal ligation, implants, injectable hormones) appear to have completed their family plan. Oral contraceptive users were of higher socioeconomic status and at lower STD risk. Barrier method users and women who used no method were young and at higher STD risk. Consistency of condom/spermicide use increased in all groups. Barrier method users were more likely than other women to use condoms and spermicides during the study. Women who used no birth control method at baseline experienced the largest increase in barrier use during follow up, although their barrier use rates were lower than in other groups. The synergism between the intention to prevent pregnancy and the intention to prevent STD should be considered in the design of interventions promoting condom use.

Adolescent↗

PubMed2000

Uterine effects of 3-year raloxifene therapy in postmenopausal women younger than age 60.

OBJECTIVE: To assess the uterine effects of 3 years of therapy with raloxifene in healthy, postmenopausal women under age 60. METHODS: Integrated data from two identically designed, randomized, double-masked, placebo-controlled clinical trials were analyzed. Nine hundred sixty-nine healthy women with uteri (ages 45 through 60, 2 to 8 years postmenopausal) were assigned randomly to raloxifene 30, 60, or 150 mg per day, or an identical placebo for 3 years. Endometrial thickness was evaluated with transvaginal ultrasonography every 6 months for 2 years and again after 3 years. Further uterine evaluation, including endometrial sampling if necessary, was initiated for vaginal bleeding or findings of endometrial thickness greater than 5 mm. RESULTS: Endometrial thickness was unchanged by raloxifene and not significantly different from placebo at any time. One hundred seventy-two women had at least one episode of endometrial thickness greater than 5 mm or vaginal bleeding distributed equally among all groups. A total of 102 (10.5%) women underwent endometrial sampling at least once: 15 (1.5%) for vaginal bleeding, 78 (8.0%) for endometrial thickness greater than 5 mm, and nine (0.9%) for other reasons. There were no significant treatment differences in the proportion of women sampled, in the clinical findings, or in the histologic diagnoses. CONCLUSION: Raloxifene given to healthy postmenopausal women at doses from 30 to 150 mg per day does not stimulate uterine growth and does not cause vaginal bleeding, spotting, or discharge through 3 years of therapy. Thus, any bleeding during therapy should be deemed unexpected and prompt a clinical evaluation.

Endometrium↗

PubMed1999

Prostate-specific antigen in vaginal fluid as a biologic marker of condom failure.

Forty women participated in three clinic visits during which they were exposed to their partner's semen (10 microL, 100 microL, and 1 mL). At each visit they took vaginal fluid samples before exposure to their partner's semen, immediately after, and at 1, 24, and 48 h after exposure. PSA was measured with an enzyme-linked immunoassay. The mean PSA level for preexposure swabs ranged between 0.43 and 0.88 ng/mL. The mean PSA levels were 193 immediately after exposure to 10 microL, 472 after 100 microL, and 19,098 after 1 mL. The PSA levels declined within 1 h, and returned to background at 48 h. The findings confirm that our procedure is a sensitive and specific method for detecting recent semen exposure, and indicate that PSA levels depend on exposure intensity and time since exposure. Application of this method in condom efficacy studies provides objective evidence of condom failure that enhances the interpretation of self-report.

Adult↗

PubMed1988

Expression of Epi 1, an epidermis-specific marker in Xenopus laevis embryos, is specified prior to gastrulation.

The induction of morphologically observable neural structures occurs as the result of tissue interactions between chordamesoderm and overlying ectoderm beginning at gastrulation. Since the future dorsal, and hence neural, side of the embryo is determined around the time of fertilization, we questioned whether the presumptive neural epithelium might have received some developmental instructions prior to contact with the migrating chordamesoderm. Epi 1, a cell surface antigen present only on epidermal epithelium was used as a marker to determine when epithelial cells have been programmed to express (or not express) this epidermal-specific molecule. We find that ligated animal halves of precleavage embryos already contain all the information necessary for expression of Epi 1 at the appropriate developmental time (early neurula). By at least the eight-celled stage, the epithelial cells derived from ventral animal blastomeres are much better at expressing the Epi 1 antigen than their dorsal counterparts. We suggest that the mechanisms responsible for expression of the Epi 1 antigen are localized within the animal hemisphere prior to the onset of cleavage. By the third cleavage division, dorsal animal cells appear to have received information which inhibits the subsequent expression of this epidermal antigen.

Animals↗

PubMed1986