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71.
Kanishka Perera Elves A.B. Silva 《Journal of Mathematical Analysis and Applications》2006,323(2):1238-1252
In this work we combine perturbation arguments and variational methods to study the existence and multiplicity of positive solutions for a class of singular p-Laplacian problems. In the first two theorems we prove the existence of solutions in the sense of distributions. By strengthening the hypotheses, in the third and last result, we establish the existence of two ordered positive weak solutions. 相似文献
72.
G. Ariyawansa A.G.U. Perera X.H. Su S. Chakrabarti P. Bhattacharya 《Infrared Physics & Technology》2007,50(2-3):156-161
Quantum dot structures designed for multi-color infrared detection and high temperature (or room temperature) operation are demonstrated. A novel approach, tunneling quantum dot (T-QD), was successfully demonstrated with a detector that can be operated at room temperature due to the reduction of the dark current by blocking barriers incorporated into the structure. Photoexcited carriers are selectively collected from InGaAs quantum dots by resonant tunneling, while the dark current is blocked by AlGaAs/InGaAs tunneling barriers placed in the structure. A two-color tunneling-quantum dot infrared photodetector (T-QDIP) with photoresponse peaks at 6 μm and 17 μm operating at room temperature will be discussed. Furthermore, the idea can be used to develop terahertz T-QD detectors operating at high temperatures. Successful results obtained for a T-QDIP designed for THz operations are presented. Another approach, bi-layer quantum dot, uses two layers of InAs quantum dots (QDs) with different sizes separated by a thin GaAs layer. The detector response was observed at three distinct wavelengths in short-, mid-, and far-infrared regions (5.6, 8.0, and 23.0 μm). Based on theoretical calculations, photoluminescence and infrared spectral measurements, the 5.6 and 23.0 μm peaks are connected to the states in smaller QDs in the structure. The narrow peaks emphasize the uniform size distribution of QDs grown by molecular beam epitaxy. These detectors can be employed in numerous applications such as environmental monitoring, spectroscopy, medical diagnosis, battlefield-imaging, space astronomy applications, mine detection, and remote-sensing. 相似文献
73.
A.G.U. Perera G. Ariyawansa M.B.M. Rinzan M. Stevens M. Alevli N. Dietz S.G. Matsik A. Asghar I.T. Ferguson H. Luo A. Bezinger H.C. Liu 《Infrared Physics & Technology》2007,50(2-3):142-148
Results are reported on dual-band detectors based on a GaN/AlGaN structure operating in both the ultraviolet–midinfrared (UV–MIR) and ultraviolet–farinfrared (UV–FIR) regions. The UV detection is due to an interband process, while the MIR/FIR detection is from free carrier absorption in the emitter/contact followed by internal photoemission over the barrier at the GaN/AlGaN interface. The UV detection, which was observed from 300 K to 4.2 K, has a threshold of 360 nm with a peak responsivity of 0.6 mA/W at 300 K. The detector shows a free carrier IR response in the 3–7 μm range up to 120 K, and an impurity response around 54 μm up to 30 K. A response in the range 7–13 μm, which is tentatively assigned to transitions from C impurities and N vacancies in the barrier region, was also observed. It should also be possible to develop a detector operating in the UV–visible–IR regions by choosing the appropriate material system. A dual-band detector design, which allows not only to measure the two components of the photocurrent generated by UV and IR radiation simultaneously but also to optimize the UV and IR responses independently, is proposed. 相似文献
74.
Abbasi RU Abu-Zayyad T Amann JF Archbold G Bellido JA Belov K Belz JW Bergman DR Cao Z Clay RW Cooper MD Dai H Dawson BR Everett AA Fedorova YA Girard JH Gray RC Hanlon WF Hoffman CM Holzscheiter MH Hüntemeyer P Jones BF Jui CC Kieda DB Kim K Kirn MA Loh EC Manago N Marek LJ Martens K Martin G Matthews JA Matthews JN Meyer JR Moore SA Morrison P Moosman AN Mumford JR Munro MW Painter CA Perera L Reil K Riehle R Roberts M Sarracino JS Sasaki M Schnetzer SR Shen P Simpson KM Sinnis G Smith JD 《Physical review letters》2004,92(15):151101
We have measured the cosmic ray spectrum above 10(17.2) eV using the two air-fluorescence detectors of the High Resolution Fly's Eye observatory operating in monocular mode. We describe the detector, phototube, and atmospheric calibrations, as well as the analysis techniques for the two detectors. We fit the spectrum to a model consisting of galactic and extragalactic sources. 相似文献
75.
Davydov R Perera R Jin S Yang TC Bryson TA Sono M Dawson JH Hoffman BM 《Journal of the American Chemical Society》2005,127(5):1403-1413
EPR/ENDOR studies have been carried out on oxyferrous cytochrome P450cam one-electron cryoreduced by gamma-irradiation at 77 K in the absence of substrate and in the presence of a variety of substrates including its native hydroxylation substrate, camphor (a), and the alternate substrates, 5-methylenyl-camphor (b), 5,5-difluorocamphor (c), norcamphor (d), and adamantanone (e); the equivalent experiments have been performed on the T252A mutant complexed with a and b. The present study shows that the properties and reactivity of the oxyheme and of both the primary and the annealed intermediates are modulated by a bound substrate. This includes alterations in the properties of the heme center itself (g tensor; (14)N, (1)H, hyperfine couplings). It also includes dramatic changes in reactivity: the presence of any substrate increases the lifetime of hydroperoxoferri-P450cam (2) no less than ca. 20-fold. Among the substrates, b stands out as having an exceptionally strong influence on the properties and reactivity of the P450cam intermediates, especially in the T252A mutant. The intermediate, 2(T252A)-b, does not lose H(2)O(2), as occurs with 2(T252A)-a, but decays with formation of the epoxide of b. Thus, these observations show that substrate can modulate the properties of both the monoxygenase active-oxygen intermediates and the proton-delivery network that encompasses them. 相似文献
76.
Cronin-Hennessey D Kwon Y Lyon AL Thorndike EH Jessop CP Mariske H Perl ML Savinov V Ugolini D Zhou X Coan TE Fadeyez V Maravin Y Narsky I Stroynowski R Ye J Wlodek T Artuso M Ayad R Boulahouache C Bukin K Dambasuren E Karamnov S Kopp S Majumder G Moneti GC Mountain R Schuh S Skwarnicki T Stone S Viehauser G Wang JC Wolf A Wu J Csorna SE Danko I McLean KW Márka S Xu Z Godang R Kinoshita K Lai IC Schrenk S Bonvicini G Cinabro D Perera LP Zhou GJ Eigen G Lipeles E Sharma V 《Physical review letters》2000,85(3):515-519
We have studied charmless hadronic decays of B mesons into two-body final states with kaons and pions and observe three new processes with the following branching fractions: beta(B-->pi(+)pi(-)) = (4.3(+1. 6)(-1.4)+/-0.5)x10(-6), beta(B-->K(0)pi(0)) = (14.6(+5.9+2.4)(-5.1-3. 3))x10(-6), and beta(B-->K(+)/-pi(0)) = (11.6(+3.0+1.4)(-2.7-1.3))x10(-6). We also update our previous measurements for the decays B-->K(+)/-pi(-/+) and B+/--->K(0)pi(+/-). 相似文献
77.
Jean Pierre Simonin Reginald Mills Aurelien Perera Pierre Turq F. Tallet 《Journal of solution chemistry》1986,15(12):1015-1030
The closed capillary method for the determination of self-diffusion coefficients of trace species in liquids has been further developed for use with biological macromolecules. In this development, a new correction to permit its use with -emitting radioisotopes has been introduced. The improved method has been applied to the case of a human blood lipoprotein. 相似文献
78.
This is a theoretical paper which attempts to study for the first time the effect of high elasticity in flow situations involving elastico-viscous liquids and abrupt changes in geometry. It is argued that implicit rheological models are essential in this exercise and, accordingly, the numerical method of solution is forced to recognise the equations of continuity, the stress equations of motion and the rheological equations as separate equations involving velocity, pressure and stress variables with appropriate boundary conditions on these variables.The present paper is concerned with L-shaped and T-shaped geometries, and the effect of elasticity is assessed by comparing the numerical predictions for an elastic liquid with those for an inelastic liquid with the same “viscosity” behaviour. This comparison is facilitated by a simple limiting procedure outlined in Section 2.The main conclusions from the work are that, in general terms, elasticity works against inertia, reducing the pressure drop caused by the abrupt change in geometry and reducing the area of influence of the bend (for finite Reynolds numbers). So far as the stress fields are concerned most interest centres on the corner region, as one would expect, but there is also a region of normal-stress activity, which is generated by “stretching” rather than “shearing”.In an appendix, some consideration is given to the entry-length and exit-length problems. It is concluded that the overall problem is a complex one, since it depends to a large measure on the criterion one uses for “fully-developed” flow. If a fairly crude criterion is used, fluid elasticity is found to decrease the entry-length and increase the exit-length. 相似文献
79.
The pulse train evolution in an injection mode locked TECO2 laser has been investigated for a wide range of input pulse widths e.g., ranging from the cavity round-trip time to near
the bandwidth-limited value for the system. Regimes in which pulse narrowing and pulse broadening occur have been identified
and are discussed. The combined use of injection and saturable-absorber mode-locking techniques has produced reliable subnanosecond
pulse trains from a large aperture TEACO2 laser. 相似文献
80.
Akerib DS Alvaro-Dean J Armel-Funkhouser MS Attisha MJ Baudis L Bauer DA Beaty J Brink PL Bunker R Burke SP Cabrera B Caldwell DO Callahan D Castle JP Chang CL Choate R Crisler MB Cushman P Dixon R Dragowsky MR Driscoll DD Duong L Emes J Ferril R Filippini J Gaitskell RJ Haldeman M Hale D Holmgren D Huber ME Johnson B Johnson W Kamat S Kozlovsky M Kula L Kyre S Lambin B Lu A Mahapatra R Manalaysay AG Mandic V May J McDonald R Merkel B Meunier P Mirabolfathi N Morrison S Nelson H Nelson R 《Physical review letters》2004,93(21):211301
We report the first results from a search for weakly interacting massive particles (WIMPs) in the Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory. Four Ge and two Si detectors were operated for 52.6 live days, providing 19.4 kg d of Ge net exposure after cuts for recoil energies between 10 and 100 keV. A blind analysis was performed using only calibration data to define the energy threshold and selection criteria for nuclear-recoil candidates. Using the standard dark-matter halo and nuclear-physics WIMP model, these data set the world's lowest exclusion limits on the coherent WIMP-nucleon scalar cross section for all WIMP masses above 15 GeV/c2, ruling out a significant range of neutralino supersymmetric models. The minimum of this limit curve at the 90% C.L. is 4 x 10(-43) cm2 at a WIMP mass of 60 GeV/c2. 相似文献