6,197 research outputs found
Portable laser absolute gravimeter study Final report
Design and development of portable laser Doppler gravimeter mode
Hybrid Quantization: From Bianchi I to the Gowdy Model
The Gowdy cosmologies are vacuum solutions to the Einstein equations which
possess two space-like Killing vectors and whose spatial sections are compact.
We consider the simplest of these cosmological models: the case where the
spatial topology is that of a three-torus and the gravitational waves are
linearly polarized. The subset of homogeneous solutions to this Gowdy model are
vacuum Bianchi I spacetimes with a three-torus topology. We deepen the analysis
of the loop quantization of these Bianchi I universes adopting the improved
dynamics scheme put forward recently by Ashtekar and Wilson-Ewing. Then, we
revisit the hybrid quantization of the Gowdy cosmologies by combining
this loop quantum cosmology description with a Fock quantization of the
inhomogeneities over the homogeneous Bianchi I background. We show that, in
vacuo, the Hamiltonian constraint of both the Bianchi I and the Gowdy models
can be regarded as an evolution equation with respect to the volume of the
Bianchi I universe. This evolution variable turns out to be discrete, with a
strictly positive minimum. Furthermore, we argue that this evolution is
well-defined inasmuch as the associated initial value problem is well posed:
physical solutions are completely determined by the data on an initial section
of constant Bianchi I volume. This fact allows us to carry out to completion
the quantization of these two cosmological models.Comment: 20 pages, version accepted for publication in Physical Review
Loop quantum cosmology of Bianchi type IX models
The loop quantum cosmology "improved dynamics" of the Bianchi type IX model
are studied. The action of the Hamiltonian constraint operator is obtained via
techniques developed for the Bianchi type I and type II models, no new input is
required. It is shown that the big bang and big crunch singularities are
resolved by quantum gravity effects. We also present the effective equations
which provide modifications to the classical equations of motion due to quantum
geometry effects.Comment: 20 page
Investigation of prediction methods for the loads and stresses of Apollo type spacecraft parachutes. Volume 1: Loads
An analysis was conducted with the objective of upgrading and improving the loads, stress, and performance prediction methods for Apollo spacecraft parachutes. The subjects considered were: (1) methods for a new theoretical approach to the parachute opening process, (2) new experimental-analytical techniques to improve the measurement of pressures, stresses, and strains in inflight parachutes, and (3) a numerical method for analyzing the dynamical behavior of rapidly loaded pilot chute risers
Finite element analysis applied to redesign of submerged entry nozzles for steelmaking
The production of steel by continuous casting is facilitated by the use of refractory hollow-ware components. A critical component in this process is the submerged entry nozzle (SEN). The normal operating conditions of the SEN are arduous, involving large temperature gradients and exposure to mechanical forces arising from the flow of molten steel; experimental development of the components is challenging in so hazardous an environment. The effects of the thermal stress conditions in relation to a well-tried design were therefore simulated using a finite element analysis approach. It was concluded from analyses that failures of the type being experienced are caused by the large temperature gradient within the nozzle. The analyses pointed towards a supported shoulder area of the nozzle being most vulnerable to failure and practical in-service experience confirmed this. As a direct consequence of the investigation, design modifications, incorporating changes to both the internal geometry and to the nature of the intermediate support material, were implemented, thereby substantially reducing the stresses within the Al2O3/graphite ceramic liner. Industrial trials of this modified design established that the component reliability would be significantly improved and the design has now been implemented in series production
Partitioning of Adipose Lipid Metabolism by Altered Expression and Function of PPAR Isoforms After Bariatric Surgery
BACKGROUND:
Bariatric surgery remains the most effective treatment for reducing adiposity and eliminating type 2 diabetes; however, the mechanism(s) responsible have remained elusive. Peroxisome proliferator-activated receptors (PPAR) encompass a family of nuclear hormone receptors that upon activation exert control of lipid metabolism, glucose regulation and inflammation. Their role in adipose tissue following bariatric surgery remains undefined. RESULTS:
Within 7 days, bariatric surgery acutely drives a change in the activity and expression of PPARγ and PPARδ in subcutaneous adipose tissue thereby attenuating lipid storage, increasing lipolysis and potentiating lipid oxidation. This unique metabolic alteration leads to changes in downstream PPARγ/δ targets including decreased expression of fatty acid binding protein (FABP) 4 and stearoyl-CoA desaturase-1 (SCD1) with increased expression of carnitine palmitoyl transferase 1 (CPT1) and uncoupling protein 2 (UCP2). Increased expression of UCP2 not only facilitated fatty acid oxidation (increased 15-fold following surgery) but also regulated the subcutaneous adipose tissue redoxome by attenuating protein cysteine oxidation and reducing oxidative stress. The expression of UCP1, a mitochondrial protein responsible for the regulation of fatty acid oxidation and thermogenesis in beige and brown fat, was unaltered following surgery. CONCLUSIONS:
These results suggest that bariatric surgery initiates a novel metabolic shift in subcutaneous adipose tissue to oxidize fatty acids independently from the beiging process through regulation of PPAR isoforms. Further studies are required to understand the contribution of this shift in expression of PPAR isoforms to weight loss following bariatric surgery
Ethnicity predicts perceptions of smoking and smoking cessation among veterans
The objective of this study was to determine if race/ethnicity predicts motivation to quit smoking and preferences for cessation services among smokers serviced by a primarily psychiatric Veterans Affairs hospital. A selfâadministered survey was given to a convenience sample of smokers ( n = 146) at the Battle Creek Veterans Affairs Medical Center. Univariate, bivariate and multivariate regression analyses were calculated to determine the association between race/ethnicity and motivation to quit smoking. Fortyâtwo per cent of the sample was nonâWhite. NonâWhite patients smoked significantly less cigarettes per day as compared with White patients ( P = 0.002). In the multivariate analyses, compared with Whites, nonâWhites had 3.5 times greater odds of thinking that quitting smoking was extremely/very important to health ( P = 0.01), 4.0 times greater odds of thinking of quitting using tobacco products in the next 30 days ( P = 0.004) and 3.4 times greater odds of being interested in receiving smoking cessation services ( P = 0.007). Yet, nonâWhite patients were less likely to be interested in intensive nurse counselling and cessation medications. As the number of nonâWhites continues to increase in the military, novel strategies may be needed to capitalize on the high motivation to quit smoking and preference for nonâtraditional interventions among nonâWhite smokers treated in Veterans Affairs hospitals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90416/1/j.1365-2850.2011.01757.x.pd
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