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81.
This work reports a systematic study on the structural and superconducting properties in the Hg-Sm-In-Pb system. It is investigated how In and Sm dopings influence the superconducting properties of the HgPb2 phase which was recently reported. Results for the HgSm1 − xPb2 system show that Sm atoms substitute Hg vacancies in the tetragonal phase which do not affect the onset critical temperature of the HgPb2 compound. Simultaneous Sm and In doping effects on the properties of the HgPb2 phase are also studied. Experimental and simulations of X-ray powder diffractograms suggest that the HgSm1 − xInxPb2 system (0.2 ≤ x ≤ 0.7) has a pseudo-cubic structure with lattice parameters near 4.88 Å. Superconducting properties measurements show that this system has an optimum doping at x ∼ 0.5 with the onset critical temperature close to 6.9 K. This is the highest superconducting critical temperature for the AuCu prototype so far reported. 相似文献
82.
Steady-State Control Reference and Token Conservation Laws in Continuous Petri Net Systems 总被引:1,自引:0,他引:1
Mahulea C. Ramirez-Trevino A. Recalde L. Silva M. 《Automation Science and Engineering, IEEE Transactions on》2008,5(2):307-320
This paper addresses several questions related to the control of timed continuous Petri nets under infinite server semantics. First, some results regarding equilibrium states and control actions are given. In particular, it is shown that the considered systems are piecewise linear, and for every linear subsystem the possible steady states are characterized. Second, optimal steady-state control is studied, a problem that surprisingly can be computed in polynomial time, when all transitions are controllable and the objective function is linear. Third, an interpretation of some controllability aspects in the framework of linear dynamic systems is presented. An interesting finding is that noncontrollable poles are zero valued. 相似文献
83.
Herman Keith C.; Ostrander Rick; Walkup John T.; Silva Susan G.; March John S. 《Canadian Metallurgical Quarterly》2007,75(5):716
A latent profile analysis was conducted on the co-occurring symptoms of 423 adolescents diagnosed with major depressive disorder as part of the Treatment for Adolescents with Depression Study (TADS), a multisite, randomized treatment trial. The participants had a mean (SD) age of 14.6 (1.5) years; of the sample, 45.6% was male and 73.8% was white. Scores on the primary subscales of Conners' Parent Rating Scale-Revised were used as indicators in the analysis. Five classes of symptoms best described the clinical presentation of adolescents enrolled in the TADS. Of the adolescents in the sample, 80% were assigned to classes with clinically significant elevations on 1 or more subscales of the Children's Depression Rating Scale-Revised. The 5 classes met empirical criteria for distinctiveness and were validated against clinical diagnoses, child-rated symptoms, and clinician-rated functional impairment. The findings are consistent with prior studies that showed a high rate of co-occurring symptoms among depressed adolescents. The discussion focuses on understanding subtypes and comorbidity in adolescent depression as well as the implications for treatment and for prevention. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
84.
We describe the design and operation of a new high-pressure metal ebulliometer which can operate at pressures to at least 3 MPa in the range 220–400 K. Infinite-dilution activity coefficients are presented for the system CHF2Cl + CF3-CH, at 275 K and for the system CF3-CH2F + CH2F2, at 260, 230, and 300 K. The Wilson activity coellicient model and a virial coefficient model are applied to these systems, and the phase equilibrium conditions are calculated. The results are shown to agree well with predicted and with published measured values. The excess enthalpy is calculated and compared with results from a Peng Robinson equation of state. Vapor densities on the dew curves are given. 相似文献
85.
The solution behaviour of a new mesogenic side group polyacrylate in tetrahydrofuran and toluene has been investigated by static and dynamic light scattering. In the dilute regime the polymer behaves as typical polydisperse linear chains in good solvent and the dynamics is dominated by a single fast mode. Cluster formation was detected starting at a concentration around 50 g l−1. It seems to be independent of the solvent as well as of polymer molecular weight. In the semidilute regime, the behaviour of the reduced osmotic modulus leads to the conclusion that repulsion between the chains is stronger than in linear macromolecules. The appearance of larger clusters was revealed above a characteristic concentration and is slightly dependent on the polyacrylate molecular weight. The dynamics was generally characterised by a fast mode related to the cooperative diffusion and by a slow mode associated with large clusters. The existence of a network of multiconnected clusters is envisaged with increasing solution concentration. 相似文献
86.
J. D. Carey R. C. Smith S. R. P. Silva 《Journal of Materials Science: Materials in Electronics》2006,17(6):405-412
The influence of the different types of bonding present in a range of carbon based materials is discussed as a precursor to
describing the field emission characteristics of carbon cold cathode materials. Some of the controlling factors which govern
electron emission from carbon based cathodes are discussed. It is shown that from disordered carbon films the interplay between
the clustered sp2 phase and the insulating sp3 matrix is important. The transition from a ‘back contact’ to ‘front surface’ controlled emission mechanism is described in
terms of the sp2 content and field penetration. A possible reason for high field enhancement factors found in disordered films also is provided.
It is further shown that changes to the sp2 phase by current stressing can improve the field emission characteristics. Emission from carbon nanotubes is also discussed
and the prospects for new types of nanotube – polymer composite based cathodes are also considered. 相似文献
87.
Suely P. Freitas Fernando C. Da Silva Regina C. A. Lago & Raad Y. Qassim 《International Journal of Food Science & Technology》1996,31(4):319-325
Shear rate vs. shear stress data were obtained on avocado pulp in water emulsions using a concentric cylinder rheometer and fitted to a power law model. Dilution, as volume fraction of water, had a pronounced effect on the apparent viscosity of the pulp emulsions and the Richardson equation, (ηR = exp.( a φ) for the emulsion viscosity fitted the data well. A mean slope coefficient, a , of 4.57 can be used as a first approximation. Enzymatic treatment (40°C, 1 h), is slightly more effective than thermal treatment (65°C, 1 h), in reducing the initial apparent viscosity of the pulp-water emulsions 相似文献
88.
Christophe Nguyen-the Boris Halna-du-Frétay & Alexandra Abreu da Silva 《International Journal of Food Science & Technology》1996,31(6):481-487
Growth of aerobic mesophilic bacteria in mixed salad without dressing, containing cooked sweet corn and raw endive, was similar to that of raw endive alone. At 9°C, sweet corn permitted the growth of the lactic acid bacterium Leuconostoc mesenteroides , whenever the bacterium was present on raw endive, whereas no growth of lactic acid bacteria was recorded on raw endive alone. Listeria monocytogenes , artificially inoculated in the samples, grew more in the mixed salad than in the raw endive alone, for products stored at 6°C and 9°C. Acidification of sweet corn to pH 5.0 was proposed to reduce the development of L. monocytogenes in the mixed salad to a level similar to that recorded in the raw endive alone. Acidification with citric acid reduced spoilage of sweet corn, whereas acetic acid caused necrosis on the leaves of raw endive. 相似文献
89.
T De Brito CR Carneiro MC Nakhle DM Lima CP Abrantes-Lemos M Sandoval AM Silva 《Canadian Metallurgical Quarterly》1998,6(4):368-376
Gene therapy has the potential to provide cancer treatments based on novel mechanisms of action with potentially low toxicities. This therapy may provide more effective control of loco-regional recurrence in diseases such as non-small cell lung cancer (NSCLC), as well as systemic control of micrometastases. Despite current limitations, retroviral and adenoviral vectors can in certain circumstances provide an effective means of delivering therapeutic genes to tumour cells. Although multiple genes are involved in the process of carcinogenesis, mutations of the p53 gene are the most frequent abnormality identified in human tumours. Pre-clinical studies both in vitro and in vivo have shown that restoration of p53 function can induce apoptosis in cancer cells. Phase I clinical trials now show that p53 gene replacement therapy is feasible and safe using both retroviral and adenoviral vectors, and that it induces tumour regression in patients with advanced NSCLC and recurrent head and neck cancer. Other pre-clinical studies indicate that gene therapy may have useful synergy with cytotoxic and radiation therapy. This paper describes the different gene therapy strategies under investigation and the pre-clinical data that provides a rationale for the gene replacement approach, reviews clinical trial data and presents novel ideas for improving current vectors and gene delivery to tumours. 相似文献
90.