Measuring the principal Hugoniot of inertial-confinement-fusion-relevant TMPTA plastic foams.

Wetted-foam layers are of significant interest for inertial-confinement-fusion capsules, due to the control they provide over the convergence ratio of the implosion and the opportunity this affords to minimize hydrodynamic instability growth. However, the equation of state for fusion-relevant foams are not well characterized, and many simulations rely on modeling such foams as a homogeneous medium with the foam average density. To address this issue, an experiment was performed using the VULCAN Nd:glass laser at the Central Laser Facility. The aim was to measure the principal Hugoniot of TMPTA plastic foams at 260mg/cm^{3}, corresponding to the density of liquid DT-wetted-foam layers, and their "hydrodynamic equivalent" capsules. A VISAR was used to obtain the shock velocity of both the foam and an α-quartz reference layer, while streaked optical pyrometry provided the temperature of the shocked material. The measurements confirm that, for the 20-120 GPa pressure range accessed, this material can indeed be well described using the equation of state of the homogeneous medium at the foam density.

Controlling fast-electron-beam divergence using two laser pulses.

This Letter describes the first experimental demonstration of the guiding of a relativistic electron beam in a solid target using two colinear, relativistically intense, picosecond laser pulses. The first pulse creates a magnetic field that guides the higher-current, fast-electron beam generated by the second pulse. The effects of intensity ratio, delay, total energy, and intrinsic prepulse are examined. Thermal and Kα imaging show reduced emission size, increased peak emission, and increased total emission at delays of 4-6 ps, an intensity ratio of 10∶1 (second:first) and a total energy of 186 J. In comparison to a single, high-contrast shot, the inferred fast-electron divergence is reduced by 2.7 times, while the fast-electron current density is increased by a factor of 1.8. The enhancements are reproduced with modeling and are shown to be due to the self-generation of magnetic fields. Such a scheme could be of considerable benefit to fast-ignition inertial fusion.

Magnetically guided fast electrons in cylindrically compressed matter.

Fast electrons produced by a 10 ps, 160 J laser pulse through laser-compressed plastic cylinders are studied experimentally and numerically in the context of fast ignition. K(α)-emission images reveal a collimated or scattered electron beam depending on the initial density and the compression timing. A numerical transport model shows that implosion-driven electrical resistivity gradients induce strong magnetic fields able to guide the electrons. The good agreement with measured beam sizes provides the first experimental evidence for fast-electron magnetic collimation in laser-compressed matter.

Doppler spectrometry for ultrafast temporal mapping of density dynamics in laser-induced plasmas.

We present high resolution measurements of the ultrafast temporal dynamics of the critical surface in moderately overdense, hot plasma by using two-color, pump-probe Doppler spectrometry. Our measurements clearly capture the initial inward motion of the plasma inside the critical surface of the pump laser which is followed by outward expansion. The measured instantaneous velocity and acceleration profiles are very well reproduced by a hybrid simulation that uses a 1D electromagnetic particle-in-cell simulation for the initial evolution and a hydrodynamics simulation for the later times. The combination of high temporal resolution and dynamic range in our measurements clearly provides quantitative unraveling of the dynamics in this important region, enabling this as a powerful technique to obtain ultrafast snapshots of plasma density and temperature profiles for providing benchmarks for simulations.

Micron-scale mapping of megagauss magnetic fields using optical polarimetry to probe hot electron transport in petawatt-class laser-solid interactions.

The transport of hot, relativistic electrons produced by the interaction of an intense petawatt laser pulse with a solid has garnered interest due to its potential application in the development of innovative x-ray sources and ion-acceleration schemes. We report on spatially and temporally resolved measurements of megagauss magnetic fields at the rear of a 50-µm thick plastic target, irradiated by a multi-picosecond petawatt laser pulse at an incident intensity of ~1020 W/cm2. The pump-probe polarimetric measurements with micron-scale spatial resolution reveal the dynamics of the magnetic fields generated by the hot electron distribution at the target rear. An annular magnetic field profile was observed ~5 ps after the interaction, indicating a relatively smooth hot electron distribution at the rear-side of the plastic target. This is contrary to previous time-integrated measurements, which infer that such targets will produce highly structured hot electron transport. We measured large-scale filamentation of the hot electron distribution at the target rear only at later time-scales of ~10 ps, resulting in a commensurate large-scale filamentation of the magnetic field profile. Three-dimensional hybrid simulations corroborate our experimental observations and demonstrate a beam-like hot electron transport at initial time-scales that may be attributed to the local resistivity profile at the target rear.

Loop versus end colostomy reversal: has anything changed?

PURPOSE: Though primary repair of colon injuries is preferred, certain injury patterns require colostomy creation. Colostomy reversal is associated with significant morbidity and healthcare cost. Complication rates may be influenced by technique of diversion (loop vs. end colostomy), though this remains ill-defined. We hypothesized that reversal of loop colostomies is associated with fewer complications than end colostomies. METHODS: This is a retrospective, multi-institutional study (four, level-1 trauma centers) of patients undergoing colostomy takedown for trauma during the time period 1/2006-12/2012. Data were collected from index trauma admission and subsequent admission for reversal and included demographics and complications of reversal. Student's t test was used to compare continuous variables against loop versus end colostomy. Discrete variables were compared against both groups using Chi-squared tests. RESULTS: Over the 6-year study period, 218 patients underwent colostomy takedown after trauma with a mean age of 30; 190 (87%) were male, 162 (74%) had penetrating injury as their indication for colostomy, and 98 (45%) experienced at least one complication. Patients in the end colostomy group (n = 160) were more likely to require midline laparotomy (145 vs. 18, p < 0.001), had greater intra-operative blood loss (260.7 vs. 99.4 mL, p < 0.001), had greater hospital length of stay (8.4 vs. 5.5 days, p < 0.001), and had more overall complications (81 vs. 17, p = 0.005) than patients managed with loop colostomy (n = 58). CONCLUSIONS: Local takedown of a loop colostomy is safe and leads to shorter hospital stays, less intra-operative blood loss, and fewer complications when compared to end colostomy.

Laboratory measurements of resistivity in warm dense plasmas relevant to the microphysics of brown dwarfs.

Since the observation of the first brown dwarf in 1995, numerous studies have led to a better understanding of the structures of these objects. Here we present a method for studying material resistivity in warm dense plasmas in the laboratory, which we relate to the microphysics of brown dwarfs through viscosity and electron collisions. Here we use X-ray polarimetry to determine the resistivity of a sulphur-doped plastic target heated to Brown Dwarf conditions by an ultra-intense laser. The resistivity is determined by matching the plasma physics model to the atomic physics calculations of the measured large, positive, polarization. The inferred resistivity is larger than predicted using standard resistivity models, suggesting that these commonly used models will not adequately describe the resistivity of warm dense plasma related to the viscosity of brown dwarfs.

Humoral factors that induce alterations of the pancreas in rats with obstructive jaundice.

This study was conducted to investigate the role of humoral factors in pancreatic alterations induced by obstructive jaundice (OJ) in rats. OJ in male Sprague-Dawley rats induced significant increases in pancreatic weight, DNA content, and RNA content of acinar cells. These changes were accompanied by enlargement of eosinophilic granules and compressed nuclei. Protein, amylase, and trypsinogen contents of pancreas were also increased in OJ rats. In addition, plasma levels of bilirubin, cholecystokinin (CCK), and estradiol increased in OJ rats and were correlated positively with each other and with pancreatic weights. Administration of a specific CCK receptor, L-364,718, to OJ rats partly attenuated the changes of the pancreas, indicating that CCK is involved in these changes. These findings suggest that estradiol may be involved in regulating the pancreatic changes induced by OJ in rats.

Absence of sodium appetite in cyclophosphamide and DOCA treated house mice.

Intraperitoneal administration of cyclophosphamide 100 mg/kg and 200 mg/kg significantly lowered plasma sodium and significantly increased plasma potassium but did not result in saline preference in a strain of wild-derived house mice given a choice between water and saline (0.15M) to drink. Deoxycorticosterone acetate treatment in dosages up to 1.5 mg for four days also failed to increase salt intake, The data suggest a possible absence of a sodium appetite mechanism in this species.

Circannual incidence of Giardia lamblia.

A circannual rhythm of Giardia lamblia positive stools was found by examination of records from three clinical laboratories in central Arkansas for the period 1980-1986. Cosinor analysis of monthly Giardia incidence based on stool specimen records from approximately 12,000 patients over the 7-year period revealed a circannual rhythm (P less than 0.001) on the basis of percent positive patients/month, with a computive acrophase occurring in late summer and minimum values in the winter. Patients involved in the study were primarily from the central Arkansas metropolitan areas, southern delta regions and northern mountainous regions of the state. Analysis of the data on the basis of total positive Giardia patients/month also revealed a circannual rhythm with the acrophase again occurring in late summer. The overall mean for percent positive stool specimens for the 7-year period was 5.3%, compared with the national average of 3.8% for G. lamblia positive stools. The data indicate that there may be a "Giardia season" in Arkansas since they could not be explained on the basis of day-care age distribution, or geographic origin. Awareness by epidemiologists, public health officials and other health care professionals of this circannual incidence of giardiasis is important for the prevention, diagnosis and treatment of this infectious disorder.

Alteration in gastrointestinal peptides after thermal injury in humans.

Alterations in gastrointestinal function are common after thermal injury in humans. The peptide hormones gastrin and cholecystokinin are known to exert effects on gastric and biliary motility and on secretory function and to induce trophic changes in gut mucosa. The effect of injury on these hormones has received little attention. Six patients with burns were studied while receiving a combination of regular diet and continuous enteral feeding. Four healthy members of the nursing staff served as the control group. Blood was drawn every 4 hours for 24 hours. Gastrin and cholecystokinin were analyzed by radioimmunoassay. Patients with burns demonstrated significantly higher levels of gastrin and lower levels of cholecystokinin when compared with the control group. Patients with burns also failed to demonstrate the normal circadian variation in these peptides.

Distribution of 3H-nicotine in rat tissues under the influence of simulated microgravity.

Rat tail suspension offers a useful model to reproduce physiologic responses to weightlessness. The present study was conducted in the head-down-tilt (HDT) rat model to assess changes in metabolism of body tissues employing 3H-nicotine. Twelve male rats were used in the study. Half of the rats were tail suspended at 30 degrees for two weeks on a 12/12 light/dark cycle. During this period, body weight, food and fluid intakes were measured. At term, animals were anesthetized and injected i.v. with a solution containing 4 microcuries of nicotine. After 90 min the animals were sacrificed, exsanguinated and tissues (brain, blood, trachea, salivary gland, lung, heart, esophagus, spleen, kidneys and testes) were harvested. The distribution of 3H-nicotine per gram of each tissue was determined and calculated as percent of total injected radioactivity. Final body weights of suspended animals were significantly (P < 0.05) lower than those of controls (309 +/- 21 vs 350 +/- 11 g). 3H-Nicotine was retained in greatest amounts by the kidneys, followed in order by salivary glands, spleen, and gastrointestinal tissues. Compared to non-suspended control, the tissue retention of nicotine in suspended animals was decreased in the following tissues: esophagus (25%), aorta (25%), fundus (25%), trachea (22%), adrenals (18%), spleen (17%), and pancreas (12%). The decreased retention of nicotine in tissues from suspended animals may be indicative of the fluid shifts and changes in blood flow to those tissue beds. The lack of differences in nicotine retention in liver and kidney between control and suspended groups may implicate a normal metabolic function of these organs even under simulated weightlessness.

Energy transport in short-pulse-laser-heated targets measured using extreme ultraviolet laser backlighting.

The accurate characterization of thermal electron transport and the determination of heating by suprathermal electrons in laser driven solid targets are both issues of great importance to the current experiments being performed at the National Ignition Facility, which aims to achieve thermonuclear fusion ignition using lasers. Ionization, induced by electronic heat conduction, can cause the opacity of a material to drop significantly once bound-free photoionization is no longer energetically possible. We show that this drop in opacity enables measurements of the transmission of extreme ultraviolet (EUV) laser pulses at 13.9 nm to act as a signature of the heating of thin (50 nm) iron layers with a 50-nm thick parylene-N (CH) overlay irradiated by 35-fs pulses at irradiance 3×10(16) Wcm(-2). Comparing EUV transmission measurements at different times after irradiation to fluid code simulations shows that the target is instantaneously heated by hot electrons (with approximately 10% of the laser energy), followed by thermal conduction with a flux limiter of ≈0.05.