T-Duality as a Duality of Loop Group Bundles

Representing the data of a string compactified on a circle in the background of H-flux in terms of the geometric data of a principal loop group bundle, we show that T-duality in type II string theory can be understood as the interchange of the momentum and winding homomorphisms of the principal loop group bundle, thus giving rise to a new interpretation of T-duality.Comment: 8 pages, latex 2e, new reference added, J.Phys.A: Fast Track Publications (to appear

Gastric stimulation: influence of electrical parameters on gastric emptying in control and diabetic rats

BACKGROUND: The aim of this study was to test the effect of different pulse frequencies and amplitudes during gastric stimulation (GS) on gastric emptying in the rat. METHODS: GS was performed in 2 groups of laparotomized rats: healthy control animals, and rats with acute diabetes. The effects of four pulse frequencies (0.5, 1, 10, 20 Hz) and three pulse amplitudes (5, 20, 40 mA) were tested. The volumes emptied from the stomach after the oro-gastric instillation of a nutrient solution were compared to those obtained in animals without GS. Intragastric pH values were assessed under basal conditions and after GS. RESULTS: In both groups, GS increased emptied volumes compared to conditions without stimulation (p < 0.05) for pulse frequencies above 0.5 Hz. Increases in pulse frequencies accelerated gastric emptying (p < 0.01) with a plateau at around 10 Hz. The increase in pulse amplitudes resulted in larger emptied volumes only when the pulse frequency was 1 Hz (p < 0.04) while the opposite effect was observed at 20 Hz (p < 0.04). The most effective combinations to enhance gastric emptying compared to baseline conditions were 10 Hz with 5 or 20 mA. The overall effect of GS on gastric emptying compared to baseline conditions without stimulation, was greater in diabetic than in controls rats (p < 0.05). During stimulation, intragastric pH values were not different from basal conditions during fasting or after a meal in control and diabetic rats. CONCLUSIONS: Although both pulse frequency and amplitude should be considered during GS, frequency appears to be the most critical point. The possibility of increasing gastric emptying by electrical stimulation in diabetic rats suggests potential clinical applications for this method

A systematic review on the effect of sweeteners on glycemic response and clinically relevant outcomes

<p>Abstract</p> <p>Background</p> <p>The major metabolic complications of obesity and type 2 diabetes may be prevented and managed with dietary modification. The use of sweeteners that provide little or no calories may help to achieve this objective.</p> <p>Methods</p> <p>We did a systematic review and network meta-analysis of the comparative effectiveness of sweetener additives using Bayesian techniques. MEDLINE, EMBASE, CENTRAL and CAB Global were searched to January 2011. Randomized trials comparing sweeteners in obese, diabetic, and healthy populations were selected. Outcomes of interest included weight change, energy intake, lipids, glycated hemoglobin, markers of insulin resistance and glycemic response. Evidence-based items potentially indicating risk of bias were assessed.</p> <p>Results</p> <p>Of 3,666 citations, we identified 53 eligible randomized controlled trials with 1,126 participants. In diabetic participants, fructose reduced 2-hour blood glucose concentrations by 4.81 mmol/L (95% CI 3.29, 6.34) compared to glucose. Two-hour blood glucose concentration data comparing hypocaloric sweeteners to sucrose or high fructose corn syrup were inconclusive. Based on two ≤10-week trials, we found that non-caloric sweeteners reduced energy intake compared to the sucrose groups by approximately 250-500 kcal/day (95% CI 153, 806). One trial found that participants in the non-caloric sweetener group had a decrease in body mass index compared to an increase in body mass index in the sucrose group (-0.40 vs 0.50 kg/m², and -1.00 vs 1.60 kg/m², respectively). No randomized controlled trials showed that high fructose corn syrup or fructose increased levels of cholesterol relative to other sweeteners.</p> <p>Conclusions</p> <p>Considering the public health importance of obesity and its consequences; the clearly relevant role of diet in the pathogenesis and maintenance of obesity; and the billions of dollars spent on non-caloric sweeteners, little high-quality clinical research has been done. Studies are needed to determine the role of hypocaloric sweeteners in a wider population health strategy to prevent, reduce and manage obesity and its consequences.</p

The smooth Hom-stack of an orbifold

For a compact manifold M and a differentiable stack X presented by a Lie groupoid X, we show the Hom-stack Hom.M;X/ is presented by a Frechet- Lie groupoid Map.M; X/ and so is an infinite-dimensional differentiable stack. We further show that if X is an orbifold, presented by a proper etale Lie groupoid, then Map.M; X/ is proper etale and so presents an infinite-dimensional orbifold.David Michael Roberts and Raymond F. Vozz

Smooth loop stacks of differentiable stacks and gerbes

Abstract published in French and English.Nous d´efinissons un groupo¨ıde de Fr´echet-Lie Map(S 1 ,X) d’anafoncteurs du cercle vers un groupo¨ıde de LieX. Ceci fournit une pr´esentation du Hom-champ Hom(S 1 ,X), o`u X est le champ diff´erentiable associ´e `a X. Nous appliquons cette construction au groupo¨ıde de Lie sous-jacent au ‘fibr´egerbe’ (= ”bundle gerbe”) d’une vari´et´e diff´erentiable M; le r´esultat est un fibr´e-gerbe au-dessus de l’espace des lacets LM de M. = We define a Fr´echet–Lie groupoid Map(S 1 ,X) of anafunctors from the circle into a Lie groupoid X. This provides a presentation of the Hom-stack Hom(S 1 ,X), where X is the differentiable stack associated to X. We apply this construction to the Lie groupoid underlying a bundle gerbe on a manifold M; the result is a bundle gerbe on the loop space LM of M.David Michael Roberts and Raymond F. Vozz

Equivariant bundle gerbes

We develop the theory of simplicial extensions for bundle gerbes and their characteristic classes with a view towards studying descent problems and equivariance for bundle gerbes. Equivariant bundle gerbes are important in the study of orbifold sigma models. We consider in detail two examples: the basic bundle gerbe on a unitary group and a string structure for a principal bundle. We show that the basic bundle gerbe is equivariant for the conjugation action and calculate its characteristic class; we show also that a string structure gives rise to a bundle gerbe which is equivariant for a natural action of the String 2-group.Michael K. Murray, David Michael Roberts, Danny Stevenson, and Raymond F. Vozz

Effect of nitric oxide synthase inhibitors on short-term appetite and food intake in humans

Animal studies suggest that nitric oxide (NO) may be a physiological regulator of appetite; NO synthase (NOS) inhibition suppresses food intake in rats, mice, and chickens. It is not known whether NO has any effect on appetite in humans. We have usedN G-monomethyl-l-arginine (l-NMMA) andN G-nitro-l-arginine methyl ester (l-NAME), both competitive, nonselective inhibitors of NOS, in two separate studies to evaluate the role of NO in the short-term regulation of appetite in humans. Instudy I, 13 men (18–25 yr) underwent paired studies, in randomized, double-blind fashion, after an overnight fast. l-NMMA (4 mg ⋅ kg−1 ⋅ h−1) or saline (0.9%) was infused intravenously at a rate of 40 ml/h for 1.5 h. In study II, eight men (18–26 yr) underwent three randomized, double-blind studies after an overnight fast. l-NAME (75 or 180 μg ⋅ kg−1 ⋅ h−1) or saline (0.9%) was infused intravenously at a rate of 20 ml/h for 120 min. Hunger and fullness were measured using visual analog scales; blood pressure and heart rate were monitored, and 30 min before the end of the infusion, subjects were offered a cold buffet meal. Total caloric intake and the macronutrient composition of the meal were determined. Both l-NMMA (P = 0.052) andl-NAME (P < 0.05; both doses) decreased heart rate, l-NMMA increased diastolic blood pressure (P < 0.01), and l-NAME increased systolic blood pressure (P = 0.052). Neither drug had any effect on caloric intake or sensations of hunger or fullness. Despite having significant effects on cardiovascular function in the doses used, neitherl-NMMA norl-NAME had any effect on feeding, suggesting that NO does not affect short-term appetite or food intake in humans.Rosalie Vozzo, Gary A. Wittert, Michael Horowitz, John E. Morley, and Ian M. Chapma