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81.
Dominik Rätz Kelly A. Jordan Gregory Perret Rakesh Chawla 《Annals of Nuclear Energy》2011,38(11):2319-2332
Two different types of perturbations of an SCWR-like fuel lattice have been investigated experimentally in the central test zone of the PROTEUS zero-power research reactor at the Paul Scherrer Institute in Switzerland. In each case, a campaign of high-resolution gamma-ray spectroscopy measurements was carried out on 34 fuel pins of the test lattice. In the first case, the test lattice was perturbed by inserting aluminum rods into the four central moderator regions, while in the second case, the perturbation was affected using steel absorber rods (instead of aluminum). The derived reaction rates are the capture rate in 238U (C8) and the total fission rate (Ftot), as also the reaction rate ratio C8/Ftot. Each of these has been mapped on the lattice and compared to calculated results from whole-reactor Monte Carlo simulations with MCNPX. Excellent agreement has been obtained, for both perturbed lattices, between the calculated and experimental distributions of C8, Ftot and C8/Ftot. Considering that control rods in an SCWR assembly are foreseen to be inserted into the central moderator regions, these results may be considered as generic validation of Monte Carlo simulations for the two different types of lattice perturbations which inserted control rods imply, viz. moderator displacement and strong neutron absorption.In a second step, calculated C8, Ftot and C8/Ftot distributions for the two perturbed lattices (as well as for the unperturbed lattice) have been compared, at assembly level, between MCNPX and the deterministic LWR lattice code CASMO-4E. In the case of the unperturbed lattice, as well as for the lattice with steel rods, the agreement between the codes is found to be within ~1% for all pins and each reaction rate. However, for the lattice with aluminum rods, i.e. the case with mainly just moderator displacement involved, CASMO overestimates the reaction rates in the vicinity of the perturbations by up to 2–3%, when employing the standard input options. The reason for this discrepancy has been found to be the leakage treatment, which uses the fundamental-mode buckling applied in a homogenized sense across the lattice. In this way, global leakage gradients get averaged out over the entire assembly. The optional input card BZ2 for CASMO resolves this problem, and the codes then agree within 1% even for the aluminum case. 相似文献
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OBJECTIVE: Higher than normal cellular levels of the phospholipid catabolic intermediate glycerophosphocholine have been found in postmortem brain tissue of persons with Alzheimer's disease. Proton magnetic resonance spectroscopy (1H-MRS) can detect a choline resonance that is largely due to glycerophosphocholine. The authors tested the hypothesis that treatment with xanomeline, an M1 selective muscarinic cholinergic agonist, would be associated with a decrease in the 1H-MRS choline resonance. METHOD: Patients with mild to moderate Alzheimer's disease received placebo or xanomeline for 6 months. 1H-MRS spectra were collected at baseline and after treatment discontinuation for 12 patients, two taking placebo and 10 taking xanomeline at a dose of 25 mg t.i.d. (N = 4), 50 mg t.i.d. (N = 3), or 75 mg t.i.d. (N = 3). RESULTS: For the combined group of patients taking xanomeline, there was a significant decrease in the choline/creatine ratio from baseline to endpoint. CONCLUSIONS: Treatment of Alzheimer's disease with a cholinergic agonist is associated with a decrease in the MRS choline resonance. Xanomeline may reduce breakdown of cholinergic neuron membranes by reducing the cellular requirement for free choline for acetylcholine synthesis. 相似文献
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The efficacy of γ-irradiation for the formation of Maillard reaction products (MRPs) from glucose and lysine/glycine and the antioxidant potential of MRPs thus formed were examined. Formation of MRPs was observed by monitoring absorbance at 284 nm and 420 nm. Upon irradiation, there was a dose-dependent increase in absorbance (r2 = 0.99) at both the wavelengths. Irradiation of glucose/lysine solution resulted in higher absorbance at 284 nm than did that of glucose/glycine solution. Similarly, increase in absorbance at 420 nm was observed upon irradiation in both the systems. No significant absorbance was observed with unirradiated solution of glucose and lysine/glycine. These findings thus clearly revealed the formation of intermediate products and brown complexes (of Maillard reaction) upon irradiation of glucose/amino acid solution. A fluorescence was also observed in irradiated glucose/amino acid solution, whereas, none was seen in non-irradiated solution. These observations further confirmed the formation of MRPs, as fluorescent compounds are known to be precursors of brown pigments formed during the Maillard reaction. These MRPs exhibited excellent antioxidant activity, as measured by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and β-carotene bleaching assays. MRPs, formed at a 40 kGy dose, scavenged up to 62% of DPPH radical and 82% of β-carotene was protected from bleaching. Reducing power of MRPs, estimated using the ferricyanide, method was also increased as compared to non-irradiated solutions. Further, these MRPs were able to scavenge hydroxyl radical and superoxide anion radical to the extents of 33% and 58%, respectively. These MRPs could chelate iron to an extent of 32% under in vitro conditions. Thus, these studies clearly demonstrated that radiation technology could be employed for obtaining novel antioxidants from sugar and amino acid combinations. 相似文献
86.
G. Tang Y. -L. Shen D. R. P. Singh N. Chawla 《International Journal of Mechanics and Materials in Design》2008,4(4):391-398
A numerical study was undertaken to study the elastic property of metal-ceramic multilayered composites derived from indentation
testing. The model system features alternating thin films of aluminum (Al) and silicon carbide (SiC), free from any effect
due to the underlying substrate. The anisotropic composite elastic response was obtained by simulating overall loading of
the multilayer structure. Finite element modeling of instrumented indentation was then employed to calculate the indentation-derived
modulus using the unloading portion of the load–displacement curve. The results from indenting the homogenized composite (with
the built-in multilayer property) and from indenting the real multilayers (with Al and SiC layers explicitly accounted for)
were compared. It was found that an indentation depth beyond approximately 8–10 initial layer thicknesses is sufficient to
yield a valid composite elastic response. The effective modulus thus obtained is representative of the out-of-plane modulus
of the multilayer composite. 相似文献
87.
Linepipe steels are susceptible to hydrogen-induced cracking (HIC) in wet, sour gas environments. Two commercially produced
linepipe steels were investigated with regard to HIC on cathodic charging. Both steels, B and C, showed a high banded microstructure
consisting of alternative layers of polygonal ferrite and a mixture of non-ferritic constituents (pearlite, bainite, and martensite-austenite).
The degree of banding was higher in Steel B than in Steel C. Also present were elongated inclusions in Steel B, while in Steel
C they were more or less equiaxed. On cathodically hydrogen-charging in the absence of external stress, microvoids formed
at low current densities at or around inclusions. On prolonged charging, these voids grew and propagated parallel to the bands,
running along the interface between ferrite/non-ferrite constituents, along inclusions lodged in the non-ferritic consitituents,
and at places through the non-ferritic constituents. Steel B, not unexpectedly, showed more severe permanent microstructural
damage than Steel C, leading to the conclusion that a high banded structure and/or the presence of elongated inclusions is
deleterious to resistance against HIC. 相似文献
88.
In order to evaluate hypotheses regarding production constraints on final consonants in babbling, 721 utterance-final consonants produced by 6 infants in consonant-vowel-consonant (CVC) syllables were examined and compared with the preceding consonant in the CVC. Consistent with earlier studies, major patterns were observed for each of the three main consonantal properties--place and manner of articulation and voicing. These patterns included a strong tendency for final consonants to repeat the place of articulation of nonfinal consonants and a tendency for relatively more fricative, nasal and voiceless consonants to occur in final position than in nonfinal position. The high frequency with which final consonants shared place of articulation with the preceding consonant was considered to reflect 'frame dominance' or the tendency of a relatively constant mandibular cycle (the frame) to determine the structure of utterances with very little contribution from other active articulators. The manner and voicing effects were attributed to an overall terminal energy decrease in the vocal production system. 相似文献
89.
The emission spectrum of TiCl has been investigated in the 3000-12 000 cm-1 region at high resolution using a Fourier transform spectrometer. The bands were excited in a microwave discharge through a flowing mixture of TiCl4 and helium. The observed bands have been classified into three electronic transitions, C4Delta-X4Phi, G4Phi-X4Phi, and G4Phi-C4Delta. In the 3000-3500 cm-1 region, four bands with R heads at 3368.7, 3331.8, 3291.9, and 3243.4 cm-1 have been assigned as the 0-0 bands of the 1/2-3/2, 3/2-5/2, 5/2-7/2, and 7/2-9/2 subbands, respectively, of the C4Delta-X4Phi transition. To higher wavenumbers, four transitions with 0-0 R heads at 10 930.7, 10 921.3, 10 906.5, and 10 886.9 cm-1 have been assigned as the 3/2-3/2, 5/2-5/2, 7/2-7/2, and 9/2-9/2 subbands, respectively, of the G4Phi-X4Phi system of TiCl. Four additional bands with 0-0 R heads at 7568.8, 7596.4, 7622.2, and 7651.7 cm-1 have been identified as the 1/2-3/2, 3/2-5/2, 5/2-7/2, and 7/2-9/2 subbands of the G4Phi-C4Delta transition, respectively. A rotational analysis of a number of vibrational bands of these transitions has been obtained and molecular constants have been extracted. The lowest 4Phi state has been assigned as the ground state of TiCl, by analogy with our recent work on TiF (R. S. Ram and P. F. Bernath, J. Mol. Spectrosc., in press). The correspondence between the electronic states of TiCl, TiF, TiH, and Ti+ is also discussed. Copyright 1997 Academic Press. Copyright 1997Academic Press 相似文献
90.