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Biomedical subjects

A Loeb

Publications and source records attributed to A Loeb.

At least 19 recordsLinked to original sources
PubMed2001

TeV neutrinos and GeV photons from shock breakout in supernovae.

We show that as a Type II supernova shock breaks out of its progenitor star, it becomes collisionless and may accelerate protons to energies >10 TeV. Inelastic nuclear collisions of these protons produce an approximately 1 h long flash of TeV neutrinos and 10 GeV photons, about 10 h after the thermal (10 MeV) neutrino burst from the cooling neutron star. A Galactic supernova in a red supergiant star would produce a photon and neutrino flux of approximately 10(-4) erg cm(-2) s(-1). A km(2) neutrino detector will detect approximately 100 muons, thus allowing to constrain both supernova models and neutrino properties.

Journal Article↗
PubMed2001

A comparison of Hispanic and African-American sexually abused girls and their families.

OBJECTIVE: To study the differential effects of sexual abuse on Hispanic (HN) and African-American (AA) girls. METHOD: Sexually abused girls and their caretakers (N = 159), of which 52% (n = 82) were AA (mean age 9.8 years, SD = 3.4, R = 6-17) and 48% (n = 77) were HN (mean age 10.1 years, SD = 3.8, R = 6-18), were included in the study. The mother/caretaker was administered a demographic form, the Achenbach's Child Behavior Checklist (CBCL), and the Family Assessment Measure (FAM-P). The child completed the FAM-C and the Trauma Symptom Checklist for Children (TSCC). The clinician completed the Parental Reaction to Incest Disclosure Scale (PRIDS). RESULTS: HN girls were found to have a greater number of sexually abusive episodes and waited longer to disclose their abuse while AA girls were more likely to have experienced vaginal penetration. The perpetrators of HN girls were older and more likely to be fathers or stepfathers. The mothers/ caretakers of HN girls perceived their children as having significantly more aggressive behavior, anxiety/depression, somatic complaints, internalizing and externalizing behaviors, and had a higher total score on the CBCL than did AA girls. The HN girls were more likely to see their family as dysfunctional with confusion regarding family values and rules. HN mothers/caretakers perceived their families as more conflicted regarding adaptability and family controls. CONCLUSIONS: HN girls experienced more emotional and behavioral problems, and both HN girls and their mothers/caretakers perceived their families as more disturbed and dysfunctional.

Adolescent↗
PubMed2000

Cosmic gamma-ray background from structure formation in the intergalactic medium

The Universe is filled with a diffuse background of gamma-ray radiation, the origin of which remains one of the unsolved puzzles of cosmology. Less than one-quarter of the gamma-ray flux can be attributed to unresolved discrete sources, such as active galactic nuclei; the remainder appears to constitute a truly diffuse background. Here we show that the shock waves induced by gravity in the gas of the intergalactic medium, during the formation of large-scale structures like filaments and sheets of galaxies, produce a population of highly relativistic electrons. These electrons scatter a small fraction of the cosmic microwave background photons in the local Universe up to gamma-ray energies, thereby providing the gamma-ray background. The predicted diffuse flux agrees with the observed background across more than four orders of magnitude in photon energy, and the model predicts that the gamma-ray background, though generated locally, is isotropic to better than five per cent on angular scales larger than a degree. Moreover, the agreement between the predicted and observed background fluxes implies a mean cosmological density of baryons that is consistent with Big Bang nucleosynthesis.

Journal Article↗
PubMed2000

Child on child sexual abuse: psychological perspectives.

OBJECTIVE: This study describes the emotional and behavioral responses of children who have been sexually victimized by juveniles (CC) 17 years of age and younger compared to child victims of adults (CA) 18 years of age and older. METHOD: A total sample of N = 194 children and adolescents participated in the study, with 26% (n = 51) comprising CC and 74% (n = 143) encompassing CA. The mother/caretaker was administered a demographic form, Achenbach's Child Behavior Checklist (CBCL), and the Family Assessment Measure (FAM-P). The child was given the Family Assessment Measure (FAM-C) and the Trauma Symptom Checklist for Children (TSCC). The clinician completed the Parental Reaction to Incest Disclosure Scale (PRIDS). RESULTS: No differences were found between the two groups for the type of sexual abuse, penetration, or the use of force. CC were younger and more likely to be males who were abused in a school setting, home, or a relative's home by a sibling or a non-related male. CC endorsed clinically significant sexual preoccupations and manifested borderline clinically significant symptomatology. CONCLUSIONS: Children victimized by other children manifested elevated levels of emotional and behavioral problems and were not significantly different from those who had been sexually abused by adults.

Adolescent↗
PubMed1997

Cerebral blood flow regulation in neonatal rabbits is altered by chronic cocaine administration.

Maternal cocaine abuse has several deleterious effects in the newborn, including perinatal asphyxia, hypoxia, and hypercapnia. We hypothesized that chronic cocaine exposure during development may alter cerebral blood flow (CBF) regulation. We studied 16 neonatal rabbits that had received cocaine (20 mg/kg, i.p. b.i.d.) or saline since birth. Changes in CBF were measured by laser doppler flowmetry before (baseline), and during hypercapnia (FiCO2 = 7.5%), hypoxia (FiO2 = 12%), and asphyxia (apnea for 1 min). During hypercapnia, CBF increased less in cocaine than in control animals (28 +/- 3% vs. 69 +/- 10%, P < 0.05). During hypoxia, CBF increased similarly in both groups. During reventilation after asphyxia, CBF increased more in cocaine than in control animals (391 +/- 52% vs. 225 +/- 43%, P < 0.05). Chronic cocaine exposure during brain development appears to alter CBF regulation to hypercapnia and asphyxia, which may put the drug exposed newborn at risk for neurologic injury around birth.

Animals↗
PubMed1997

Use of Synthetic Serum Substitute and alpha-minimum essential medium for the extended culture of human embryos to the blastocyst stage.

This study was designed to provide further information on mouse and human embryo development in alpha-modified minimum essential medium (alphaMEM). First, we compared the development and implantation potential of murine in-vitro fertilized (IVF) embryos cultured in alphaMEM, in the presence and absence of co-culture cells. No significant difference was observed in blastocyst rate between alphaMEM alone (76.2%) and alphaMEM plus co-culture (79.9%). The percentage of hatched blastocysts was, however, higher with co-culture (47.5 versus 40%, P < 0.01). Transfer of blastocysts to pseudopregnant foster mothers resulted in similar live birth rates (14.9% alphaMEM alone versus 19.8% alphaMEM/co-culture). alphaMEM was also introduced into our clinical IVF programme for culture of human embryos beyond day 3. Spare human embryos were cultured under oil in microdrops of alphaMEM supplemented with 10% synthetic serum substitute. Blastocysts were evaluated for maturity and the presence and organization of the inner cell mass. A total of 206 embryos from 53 IVF patients underwent extended culture. The overall blastocyst rate was 45.1%. An inner cell mass was observed in 76 blastocysts (81.7%). With regard to developmental maturity, approximately 73% of blastocysts that had been frozen were expanding (cavity > 50% embryo volume) or fully expanded. These data suggest that alphaMEM in conjunction with a commercial protein preparation such as Synthetic Serum Substitute may be a good basal medium for culture of human embryos to the blastocyst stage.

Animals↗
PubMed1997

Regional vascular effects of rHb1.1, a hemoglobin-based oxygen carrier.

The goals of this study were to determine the effects of recombinant human hemoglobin (rHb1.1, 1 g/kg i.v.) on systemic hemodynamics, regional blood flows, and regional vascular resistances in rats. Cardiac output (CO) and regional blood flow in 13 tissues were determined by using the radiolabeled-microsphere method during halothane anesthesia. Microspheres were injected at three time points: before (control, t = 0), t = 30 [10 min after a 20-min infusion of vehicle (diluent) or rHb1.1], and at t = 120 min. Infusion of diluent did not alter CO, heart rate (HR), mean arterial pressure (MAP), or systemic vascular resistance (SVR) and had minimal effects on regional blood flows. Infusion of rHb1.1 did not alter CO or HR but did increase MAP and SVR compared with diluent. Infusion of rHb1.1 increased blood flow to the heart and decreased blood flow to the gastrointestinal tract (GIT) and liver. Compared with the corresponding values in the diluent-treated rats, resistance was increased after rHb1.1 in spleen, kidney, and hepatic artery. In conclusion, rHb1.1 administration increased MAP and SVR. The vasoconstriction was heterogeneous and was associated with increased coronary blood flow and with increased regional resistance in kidney, spleen, and hepatic artery, compared with diluent-infused controls.

Analysis of Variance↗
PubMed1986

Expression of smooth muscle-specific alpha-isoactin in cultured vascular smooth muscle cells: relationship between growth and cytodifferentiation.

The relationship between growth and cytodifferentiation was studied in cultured rat aortic smooth muscle cells (SMCs) using expression of the smooth muscle (SM)-specific isoactins (Vanderkerckhove, J., and K. Weber, 1979, Differentiation, 14:123-133) as a marker for differentiation in these cells. Isoactin expression was evaluated by: (a) measurements of fractional isoactin content and synthesis ([35S]methionine incorporation) by densitometric evaluation of two-dimensional isoelectric focusing sodium dodecyl sulfate gels, and (b) immunocytological examination using SM-specific isoactin antibodies. Results showed the following: (a) Loss of alpha-SM isoactin was not a prerequisite for initiation of cellular proliferation in primary cultures of rat aortic SMCs. (b) alpha-SM isoactin synthesis and content were low in subconfluent log phase growth cells but increased nearly threefold in density-arrested postconfluent cells. Conversely, beta-nonmuscle actin synthesis and content were higher in rapidly dividing subconfluent cultures than in quiescent postconfluent cultures. These changes were observed in primary and subpassaged cultures. (c) alpha-SM actin synthesis was increased by growth arrest of sparse cultures in serum-free medium (SFM; Libby, P., and K. V. O'Brien, 1983, J. Cell. Physiol., 115:217-223) but reached levels equivalent to density-arrested cells only after extended periods in SFM (i.e., greater than 5 d). (d) SFM did not further augment alpha-SM actin synthesis in postconfluent SMC cultures. (e) Serum stimulation of cells that had been growth-arrested in SFM resulted in a dramatic decrease in alpha-SM actin synthesis that preceded the onset of cellular proliferation. These findings demonstrate that cultured vascular SMCs undergo differential expression of isoactins in relation to their growth state and indicate that growth arrest promotes cytodifferentiation in these cells.

Actins↗