Comparison of the bifurcation scenarios predicted by the single-mode and multimode semiconductor laser rate equations

We present a detailed comparison of the bifurcation scenarios predicted by single-mode and multimode semiconductor laser rate equation models under large amplitude injection current modulation. The influence of the gain model on the predicted dynamics is investigated. Calculations of the dependence of the time averaged longitudinal mode intensities on modulation frequency are compared with experiments performed on an AlxGa1-xAs Fabry-Pérot semiconductor laser.K. A. Corbett and M. W. Hamilto

Human gut Bacteroidetes can utilize yeast mannan through a selfish mechanism

Yeasts, which have been a component of the human diet for at least 7,000 years, possess an elaborate cell wall α-mannan. The influence of yeast mannan on the ecology of the human microbiota is unknown. Here we show that yeast α-mannan is a viable food source for the Gram-negative bacterium Bacteroides thetaiotaomicron, a dominant member of the microbiota. Detailed biochemical analysis and targeted gene disruption studies support a model whereby limited cleavage of α-mannan on the surface generates large oligosaccharides that are subsequently depolymerized to mannose by the action of periplasmic enzymes. Co-culturing studies showed that metabolism of yeast mannan by B. thetaiotaomicron presents a ‘selfish’ model for the catabolism of this difficult to breakdown polysaccharide. Genomic comparison with B. thetaiotaomicron in conjunction with cell culture studies show that a cohort of highly successful members of the microbiota has evolved to consume sterically-restricted yeast glycans, an adaptation that may reflect the incorporation of eukaryotic microorganisms into the human diet

Band structure of InGaP from pressure experiments

Positive identification of the Γ and X conduction‐band minima in InGaP has been made by performing hydrostatic‐pressure experiments on forward‐biased p‐n junction diodes. The Γ and X valleys are coincident in energy at a composition of In_0.37Ga_0.63P, and the corresponding bandgap is (2.17±0.02) eV at 300°K. The indirect bandgap E_X in InP is inferred from the measurements to be 2.0 eV at 300°K. In addition, the pressure coefficients of the direct and indirect bandgaps, ∂E_Γ∕∂P and ∂E_X∕∂P, respectively, have been measured at various In(1−x)GaxP compositions. For InP, ∂EΓ∕∂P is 8.7×10−3 eV∕kbar and this coefficient increases to 13×10⁻³ eV∕kbar for compositions close to In_0.5Ga_0.5P. On the other hand, ∂E_X∕∂P = −1.25×10⁻³ eV∕kbar for GaP and shows little change for compositions in the range 0.4<x<1. The deformation potential is 5.7 eV for the Γ valley in InP, and increases to about 9 eV for direct bandgap ternary compositions

Capsaicin-sensitive nerves mediate esophageal mucosal protection

The esophageal mucosa is exposed to damaging agents both by ingestion and reflux. Using our in vivo rabbit model of esophagitis, we have observed that acute luminal exposure (within 1 to 5 minutes) to potentially harmful agents, such as acid, bile, or ethanol, induces a rapid increase in mucosal blood flow; whereas prolonged exposure (10 to 60 minutes) results in mucosal injury and ablation of blood flow. We have also shown that capsaicin-sensitive mucosal afferent nerves can modulate esophageal blood flow. These findings led us to hypothesize that the reactive increase in blood flow induced by luminal agents represents a mechanism of protection mediated by capsaicin- sensitive nerves. The objective of these experiments was to determine if luminal capsaicin, a specific probe for visceral afferent nerves, could both preserve mucosal blood flow and protect against ethanol injury. Rabbits were subjected to luminal instillation of 50% ethanol with or without 1% capsaicin. Blood flow was measured with microspheres at baseline and after 2 and 10 minutes. Rabbits exposed only to ethanol developed severe mucosal injury coincident with near ablation of mucosal blood flow. In contrast, rabbits exposed to ethanol with capsaicin showed protection of the epithelium with a sixfold increase in mucosal blood flow. We conclude that capsaicin- sensitive nerves in the esophagus are local effectors of mucosal protection by virtue of preserving blood flow

Polytetrafluoroethylene and bovine mesenterial vein grafts for hemodialysis access: a comparative study

PURPOSE: This study aimed to evaluate the safety and patency rate of bovine mesenterial vein grafts (BMVG) for vascular access (VA) in hemodialysis patients (HDP), compared to expanded polytetrafluorethylene (ePTFE grafts) over a mid- to long-term period. METHODS: Patency and complication rate of 23 consecutive HDP with BMVG for VA were compared to a control group consisting of 23 similar HDP with ePTFE grafts. In both groups, the graft was placed preferably in a forearm loop configuration. The same surgeon performed all procedures. All patients were followed over a period of 4 yrs. RESULTS: Graft placement was successful in all patients. Patency rates did not differ significantly in both groups. However, there were less severe complications in the BMVG group. CONCLUSION: The BMVG is a viable alternative for HD access in patients where autologous construction is not possible, and should be given priority in patients with a failed ePTFE graft or high risk for infection