Molecular Cloud Structure in the Magellanic Clouds: Effect of Metallicity

The chemical structure of neutral clouds in low metallicity environments is examined with particular emphasis on the H to H_2 and C+ to CO transitions. We observed near-IR H_2 lines and the CO J=1-0 line from 30 Doradus and N159/N160 in the Large Magellanic Cloud and from DEM S 16, DEM S 37, and LI-SMC 36 in the Small Magellanic Cloud. We find that the H_2 emission is UV-excited and that (weak) CO emission always exists (in our surveyed regions) toward positions where H_2 and [CII] emission have been detected. Using a PDR code and a radiative transfer code, we simulate the emission of line radiation from spherical clouds and from large planar clouds. Because the [CII] emission and H_2 emission arise on the surface of the cloud and the lines are optically thin, these lines are not affected by changes in the relative sizes of the neutral cloud and the CO bearing core, while the optically thick CO emission can be strongly affected. The sizes of clouds are estimated by measuring the deviation of CO emission strength from that predicted by a planar cloud model of a given size. The average cloud column density and therefore size increases as the metallicity decreases. Our result agrees with the photoionization regulated star formation theory by Mc Kee (1989).Comment: 45 Pages including 15 figures. To be published in the ApJ May 10, 1998 issue, Vol. 49

Regulation of 5-HT Receptors and the Hypothalamic-Pituitary-Adrenal Axis

Disturbances in the serotonin (5-HT) system is the neurobiological abnormality most consistently associated with suicide. Hyperactivity of the hypothalmic-pituitary-adrenal (HPA) axis is also described in suicide victims. The HPA axis is the classical neuroendocrine system that responds to stress and whose final product, corticosteroids, targets components of the limbic system, particularly the hippocampus. We will review resulsts from animal studies that point to the possibility that many of the 5-HT receptor changes observed in suicide brains may be a result of, or may be worsened by, the HPA overactivity that may be present in some suicide victims. The results of these studies can be summarized as follows: (1) chronic unpredictable stress produces high corticosteroid levels in rats; (2) chronic stress also results in changes in specific 5-HT receptors (increases in cortical 5-HT2A and decreases in hipocampal 5-HT1A and 5-HT1B); (3) chronic antidepressant administration prevents many of the 5-HT receptor changes observed after stress; and (4) chronic antidepressant administration reverses the overactivity of the HPA axis. If indeed 5-HT receptors have a partial role in controlling affective states, then their modulation by corticosteroids provides a potential mechanism by which these hormones may regulate mood. These data may also provide a biological understanding of how stressful events may increase the risk for suicide in vulnerable individuals and may help us elucidate the neurobiological underpinnings of treatment resistance.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73437/1/j.1749-6632.1997.tb52357.x.pd

Transport Properties of the Quark-Gluon Plasma -- A Lattice QCD Perspective

Transport properties of a thermal medium determine how its conserved charge densities (for instance the electric charge, energy or momentum) evolve as a function of time and eventually relax back to their equilibrium values. Here the transport properties of the quark-gluon plasma are reviewed from a theoretical perspective. The latter play a key role in the description of heavy-ion collisions, and are an important ingredient in constraining particle production processes in the early universe. We place particular emphasis on lattice QCD calculations of conserved current correlators. These Euclidean correlators are related by an integral transform to spectral functions, whose small-frequency form determines the transport properties via Kubo formulae. The universal hydrodynamic predictions for the small-frequency pole structure of spectral functions are summarized. The viability of a quasiparticle description implies the presence of additional characteristic features in the spectral functions. These features are in stark contrast with the functional form that is found in strongly coupled plasmas via the gauge/gravity duality. A central goal is therefore to determine which of these dynamical regimes the quark-gluon plasma is qualitatively closer to as a function of temperature. We review the analysis of lattice correlators in relation to transport properties, and tentatively estimate what computational effort is required to make decisive progress in this field.Comment: 54 pages, 37 figures, review written for EPJA and APPN; one parag. added end of section 3.4, and one at the end of section 3.2.2; some Refs. added, and some other minor change

Prospective study of enhanced recovery after surgery protocol in children undergoing reconstructive operations

BACKGROUND: Enhanced recovery after surgery (ERAS) protocol is a set of peri-operative strategies to increase speed of recovery. ERAS is well established in adults but has not been well studied in children. OBJECTIVE: The purpose of the current study was to establish the safety and efficacy of an ERAS protocol in pediatric urology patients undergoing reconstructive operations. It was hypothesized that ERAS would reduce length of stay and decrease complications when compared with historical controls. STUDY DESIGN: Institutional Review Board approval was obtained to prospectively enroll patients agedpreparation, administration of pre-operative oral carbohydrate liquid, avoidance of opioids, regional anesthesia, laparoscopy when feasible, no postoperative nasogastric tube, early feeding, and early removal of intravenous fluids (IVF). Recent (2009-2014) historical controls were propensity matched in a 2:1 ratio on age, sex, ventriculoperitoneal shunt status and whether the patient was undergoing bladder augmentation. Outcomes were protocol adherence, length of stay (LOS), emergency department (ED) visits, re-admission within 30 days, re-operations and adverse events occurring within 90 days of surgery. RESULTS: A total of 26 historical and 13 ERAS patients were included. Median ages were 10.4 (IQR 8.0-12.4) and 9.9 years (IQR 9.1-11), respectively (P = 0.94) (see Summary Table). There were no significant between-group differences in prior abdominal surgery (38% vs 62%), rate of augmentation (88% vs 92%) or primary diagnosis of spina bifida (both 62%). ERAS significantly improved use of pre-operative liquid load (P \u3c 0.001), avoidance of opioids (P = 0.046), early discontinuation of IVF (P \u3c 0.001), and early feeding (P \u3c 0.001). Protocol adherence improved from 8/16 (IQR 4-9) historically to 12/16 (IQR 11-12) after implementation of ERAS. LOS decreased from 8 days to 5.7 days (P = 0.520). Complications of any grade per patient decreased from 2.1 to 1.3 (OR 0.71, 95% CI 0.51-0.97). There were fewer complications per patient across all grades with ERAS. No differences were seen in emergency department (ED) visits, re-admissions and re-operations. DISCUSSION: Implementation improved consistency of care delivered. Tenets of ERAS that appeared to drive improvements included maintenance of euvolemia through avoidance of excess fluids, multimodal analgesia, and early feeding. CONCLUSION: ERAS decreased length of stay and 90-day complications after pediatric reconstructive surgery without increased re-admissions, re-operations or ED visits. A multicenter study will be required to confirm the potential benefits of adopting ERAS