4,702 research outputs found
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
OH species, U ions, and CO/CO2 in thermally annealed metamict zircon (ZrSiO4)
Metamict zircon crystals have been thermally annealed between 500 and 1800 K and analyzed\ud
using infrared and optical spectroscopy in the spectral region of 1400ā7000 cmā1. Recrystallization\ud
and dehydroxylation via complex proton/OH diffusion, redistribution, and incorporations of additional\ud
hydrogen-related species within the crystal structure of zircon occur at temperatures above 700 K\ud
in partially metamict zircon and above 1200 K in heavily amorphized material. Thermally induced\ud
changes in O-H stretching spectra are different between E || c and E ā„ c in weakly metamict zircon. The\ud
O-H stretching band near 3342 cmā1 (with E ā„ c) in an untreated sample shifts to 3277 cmā1 at 1200 K,\ud
where the frequency of O-H stretching bands with E || c increases. Conversions of hydrogen-related\ud
species were observed and extra OH bands were found at temperatures between 1200 and 1600 K. A\ud
dramatic change of OH spectra was recorded between 1600 and 1800 K in partially metamict crystals,\ud
resulting in additional absorption features (near 3098 and 2998 cmā1 along E ā„ c). U4+ and U5+ related\ud
spectra are also affected by high-temperature annealing. For highly metamict zircon, the U4+ band\ud
near 4830 cmā1 shows an increase in intensity above 1200 K. Additional IR bands at 2146 and 2344\ud
cmā1 appear in the spectra of metamict zircon annealed at high temperatures. Their frequencies are\ud
consistent with stretching vibrations of CO and CO2
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 PPARĪ³ and PPARĪ“ in subcutaneous adipose tissue thereby attenuating lipid storage, increasing lipolysis and potentiating lipid oxidation. This unique metabolic alteration leads to changes in downstream PPARĪ³/Ī“ 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
Design of Strongly Modulating Pulses to Implement Precise Effective Hamiltonians for Quantum Information Processing
We describe a method for improving coherent control through the use of
detailed knowledge of the system's Hamiltonian. Precise unitary transformations
were obtained by strongly modulating the system's dynamics to average out
unwanted evolution. With the aid of numerical search methods, pulsed
irradiation schemes are obtained that perform accurate, arbitrary, selective
gates on multi-qubit systems. Compared to low power selective pulses, which
cannot average out all unwanted evolution, these pulses are substantially
shorter in time, thereby reducing the effects of relaxation. Liquid-state NMR
techniques on homonuclear spin systems are used to demonstrate the accuracy of
these gates both in simulation and experiment. Simulations of the coherent
evolution of a 3-qubit system show that the control sequences faithfully
implement the unitary operations, typically yielding gate fidelities on the
order of 0.999 and, for some sequences, up to 0.9997. The experimentally
determined density matrices resulting from the application of different control
sequences on a 3-spin system have overlaps of up to 0.99 with the expected
states, confirming the quality of the experimental implementation.Comment: RevTeX3, 11 pages including 2 tables and 5 figures; Journal of
Chemical Physics, in pres
Multi-time delay, multi-point Linear Stochastic Estimation of a cavity shear layer velocity from wall-pressure measurements
Multi-time-delay Linear Stochastic Estimation (MTD-LSE) technique is thoroughly described, focusing on its fundamental properties and potentialities. In the multi-time-delay ap- proach, the estimate of the temporal evolution of the velocity at a given location in the flow field is obtained from multiple past samples of the unconditional sources. The technique is applied to estimate the velocity in a cavity shear layer flow, based on wall-pressure measurements from multiple sensor
Theoretical investigation of structural, energetic and electronic properties of titanate pyrochlores
Ab initio total energy calculations using the plane-wave pseudopotential method based on density functional theory were carried out to investigate the structural, energetic and electronic properties of A2Ti2O7 (A = Ā La, Gd and Yb) pyrochlores. It turned out that the formation energies of antisite defects are not linearly dependent on the ratio of the cation radii, and, for the three compositions, the cation antisite formation energy is largest for Gd2Ti2O7 pyrochlore. It was indicated that Gd2Ti2O7 compound is the least likely to form defect fluorite structure, which gives rise to the least resistance to radiation-induced amorphization. DOS analysis showed that stronger interaction exists in the Gd2Ti2O7 compound, and its electronic structure is very different from that of La2Ti2O7 and Yb2Ti2O7. Our calculations suggested that the electronic structure of the A cation and bond type should be taken into account when explaining the response behavior of A2Ti2O7 (A = Ā La, Gd, Yb) pyrochlores to ion irradiation-induced amorphization.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58124/2/cm7_34_346203.pd
SEQuel: improving the accuracy of genome assemblies
Motivation: Assemblies of next-generation sequencing (NGS) data, although accurate, still contain a substantial number of errors that need to be corrected after the assembly process. We develop SEQuel, a tool that corrects errors (i.e. insertions, deletions and substitution errors) in the assembled contigs. Fundamental to the algorithm behind SEQuel is the positional de Bruijn graph, a graph structure that models k-mers within reads while incorporating the approximate positions of reads into the model
Heavy-Light Mesons with Quenched Lattice NRQCD: Results on Decay Constants
We present a quenched lattice calculation of heavy-light meson decay
constants, using non-relativistic (NRQCD) heavy quarks in the mass region of
the quark and heavier, and clover-improved light quarks. The NRQCD
Hamiltonian and the heavy-light current include the corrections at first order
in the expansion in the inverse heavy quark mass. We study the dependence of
the decay constants on the heavy meson mass , for light quarks with the tree
level ( = 1), as well as the tadpole improved clover coefficient. We
compare decay constants from NRQCD with results from clover () heavy
quarks.
Having calculated the current renormalisation constant in one-loop
perturbation theory, we demonstrate how the heavy mass dependence of the
pseudoscalar decay constants changes after renormalisation. For the first time,
we quote a result for from NRQCD including the full one-loop matching
factors at .Comment: 45 pages, latex, 24 postscript figure
Detailed study of dissipative quantum dynamics of K-2 attached to helium nanodroplets
We thoroughly investigate vibrational quantum dynamics of dimers attached to
He droplets motivated by recent measurements with K-2 [1]. For those
femtosecond pump-probe experiments, crucial observed features are not
reproduced by gas phase calculations but agreement is found using a description
based on dissipative quantum dynamics, as briefly shown in [2]. Here we present
a detailed study of the influence of possible effects induced by the droplet.
The helium droplet causes electronic decoherence, shifts of potential surfaces,
and relaxation of wave packets in attached dimers. Moreover, a realistic
description of (stochastic) desorption of dimers off the droplet needs to be
taken into account. Step by step we include and study the importance of these
effects in our full quantum calculation. This allows us to reproduce and
explain all major experimental findings. We find that desorption is fast and
occurs already within 2-10 ps after electronic excitation. A further finding is
that slow vibrational motion in the ground state can be considered
frictionless.Comment: 17 pages, 5 figure
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