Hyperbolic surface subgroups of one-ended doubles of free groups

Gromov asked whether every one-ended word-hyperbolic group contains a hyperbolic surface group. We prove that every one-ended double of a free group has a hyperbolic surface subgroup if (1) the free group has rank two, or (2) every generator is used the same number of times in the amalgamating words. To prove this, we formulate a stronger statement on Whitehead graphs and prove its specialization by combinatorial induction for (1) and the characterization of perfect matching polytopes by Edmonds for (2).Comment: 30 pages, 8 figures. This version has been accepted for publication by the Journal of Topolog

Slot error rate performance of DH-PIM with symbol retransmission for optical wireless links

In this paper we introduce the dual-header pulse interval modulation (DH-PIM) technique employing a simple retransmission coupled with a majority decision detection scheme at the receiver. We analytically investigate the slot error rate (SER) performance and compare results with simulated data for the symbol retransmissions rates of three, four and five, showing a good agreement. We demonstrate that the proposed scheme significantly reduces the SER compared with the standard single symbol transmission system, with retransmission rate of five offering the highest code gain of 5 dB

On Radiation Pressure in Static, Dusty HII Regions

Radiation pressure acting on gas and dust causes HII regions to have central densities that are lower than the density near the ionized boundary. HII regions in static equilibrium comprise a family of similarity solutions, parametrized by 3 parameters: beta, gamma, and the product (Q_0 n_rms); beta characterizes the stellar spectrum, gamma characterizes the dust/gas ratio, Q_0 is the ionizing output from the star (photons/s), and n_rms is the rms density within the ionized region. Adopting standard values for beta and gamma, varying (Q_0 n_rms) generates a one-parameter family of density profiles, ranging from nearly uniform density (small Q_0 n_rms), to hollow-sphere HII regions (large Q_0 n_rms). When (Q_0 n_rms) exceeds 10^{52} cm^{-3} s^{-1}, dusty HII regions have conspicuous central cavities, even if no stellar wind is present. For given beta, gamma and (Q_0 n_rms), a fourth quantity, which can be Q_0, determines the overall size and density of the HII region. Examples of density and emissivity profiles are given. We show how quantities of interest -- such as the peak-to-center emissivity ratio, the rms-to-mean density ratio, the edge-to-rms density ratio, and the fraction of the ionizing photons absorbed by the gas -- depend on the 3 parameters beta, gamma, and (Q_0 n_rms). For dusty HII regions, compression of the gas and dust into an ionized shell results in a substantial increase in the fraction of the >13.6 eV photons that actually ionize H (relative to a uniform density HII region with the same dust/gas ratio and density n=n_rms). We discuss the extent to which radial drift of dust grains in HII regions can alter the dust-to-gas ratio. The applicability of these solutions to real HII regions is discussed.Comment: New material and figures that were not in version 1. To appear in Ap

FK 506 ameliorates the hepatic injury associated with ischemia and reperfusion in rats

The effect of FK 506 on regeneration of the liver was studied in rats after a two‐thirds partial hepatectomy after 60 min of ischemia of the unresected liver. The animals were divided into three distinct groups of 10 rats each. Group 1 (controls) received 0.5 ml saline solution intravenously 30 min after the induction of ischemia. Groups 2 and 3 were injected with FK 506 (0.3 mg/kg) intravenously 30 min after and 24 min before the induction of hepatic ischemia, respectively. The hepatic content of ATP and serum levels of ALT and lactate dehydrogenase were determined on each animal. In addition, the histological appearance and mitotic activity of the remnant liver was determined at regular 24‐hr intervals after hepatic ischemia. All 10 control animals died within 72 hr. Treatment with FK 506 resulted in improved survival in groups 2 and 3 (30% and 80%, respectively). The improved survival seen in the FK 506–treated animals was reflected by a restoration of hepatic ATP content, a reduction in the serum levels of ALT and lactate dehydrogenase, an amelioration of hepatic necrosis and neutrophilic infiltration and an increase in the mitotic activity of the liver. These results suggest that FK 506 ameliorates the hepatic injury associated with ischemia/reperfusion and has a potent stimulatory effect on liver cell regeneration that may make it valuable as a hepatoprotective agent when administered to organ donors before graft harvesting. (HEPATOLOGY 1991;13:947–951.) Copyright © 1991 American Association for the Study of Liver Disease

Effect of cyclosporine on hepatic energy status and on fructose metabolism after portacaval shunt in dog as monitored by phosphorus‐31 nuclear magnetic resonance spectroscopy in vivo

The effect of cyclosporin A on the hepatic energy status and intracellular pH of the liver and its response to a fructose challenge has been investigated using in vivo phosphorus‐31 nuclear magnetic resonance spectroscopy in dogs. Three experimental groups were studied: (a) control dogs (n = 5), (b) dogs 4 days after the creation of an end‐to‐side portacaval shunt (n = 5), and (c) dogs 4 days after portacaval shunt and continuous infusion of cyclosporin A (4 mg/kg/day) by way of the left portal vein (portacaval shunt plus cyclosporin A, n = 5). The phosphorus‐31 nuclear magnetic resonance spectra were obtained at 81 MHz using a Bruker BIOSPEC II 4.7‐tesla nuclear magnetic resonance system equipped with a 40‐cm horizontal bore superconducting solenoid. The phosphomonoesters (p < 0.01), inorganic phosphate and ATP levels (p < 0.05) were decreased significantly in portacaval shunt–treated and in portacaval shunt‐pluscyclosporin A–treated dogs compared with unshunted control dogs. After a fructose challenge (750 mg/kg body wt, intravenously), fructose‐1‐phosphate metabolism was reduced in portacaval shunt–treated dogs compared with either the normal or portacaval shuntplus‐cyclosporin A–treated dogs (p < 0.05). Both portacaval shunt– and portacaval shunt‐plus‐cyclosporin A–treated dogs demonstrated a reduced decline in ATP levels after fructose infusion when compared with the controls (p < 0.05). Immediately after the fructose challenge, the intracellular pH decreased from 7.30 ± 0.03 to 7.00 ± 0.05 in all animals (p < 0.01) and then gradually returned to normal over 60 min. These data, obtained in vivo using phosphorus‐31 nuclear magnetic resonance spectroscopy of the liver after a portacaval shunt, suggest that: (a) the energy status of the liver is reduced in dogs with a portacaval shunt compared with that of normal controls and (b) cyclosporin A treatment ameliorates the reduction in hepatic metabolism normally observed after a fructose challenge to the liver with a portacaval shunt. (HEPATOLOGY 1991;13:780–785.) Copyright © 1991 American Association for the Study of Liver Disease

The assessment of usability of electronic shopping: A heuristic evaluation

Today there are thousands of electronic shops accessible via the Web. Some provide user-friendly features whilst others seem not to consider usability factors at all. Yet, it is critical that the electronic shopping interface is user-friendly so as to help users to obtain their desired results. This study applied heuristic evaluation to examine the usability of current electronic shopping. In particular, it focused on four UK-based supermarkets offering electronic services: including ASDA, Iceland, Sainsbury, and Tesco. The evaluation consists of two stages: a free-flow inspection and a task-based inspection. The results indicate that the most significant and common usability problems have been found to lie within the areas of ‘User Control and Freedom’ and ‘Help and Documentation’. The findings of this study are applied to develop a set of usability guidelines to support the future design of effective interfaces for electronic shopping

MoS2-HgTe Quantum Dot Hybrid Photodetectors beyond 2 μm

Mercury telluride (HgTe) colloidal quantum dots (CQDs) have been developed as promising materials for the short and mid-wave infrared photodetection applications because of their low cost, solution processing and size tunable absorption in the short wave- and mid- infrared spectrum. However, the lowmobility and poor photo-gain have limited the responsivity of HgTe CQDs-based photodetectors to only tens of mA/W. Here, we integrated HgTe CQDs on a TiO2 encapsulated MoS2 transistor channel to form hybrid phototransistors with high responsivity of ~106 A/W, the highest reported to date for HgTe QDs. By operating the phototransistor in the depletion regime enabled by the gate modulated current of MoS2, the noise current is significantly suppressed leading to an experimentally measured specific detectivity D* of ~1012 Jones at a wavelength of 2 μm. This work demonstrates for the first time the potential of the hybrid 2D/QD detector technology in reaching out to wavelengths beyond 2 μm with compelling sensitivity.Peer ReviewedPostprint (author's final draft