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排序方式: 共有59条查询结果,搜索用时 15 毫秒
1.
2.
Arik M Aune S Barth K Belov A Borghi S Bräuninger H Cantatore G Carmona JM Cetin SA Collar JI Dafni T Davenport M Eleftheriadis C Elias N Ezer C Fanourakis G Ferrer-Ribas E Friedrich P Galán J García JA Gardikiotis A Gazis EN Geralis T Giomataris I Gninenko S Gómez H Gruber E Guthörl T Hartmann R Haug F Hasinoff MD Hoffmann DH Iguaz FJ Irastorza IG Jacoby J Jakovčić K Karuza M Königsmann K Kotthaus R Krčmar M Kuster M Lakić B Laurent JM Liolios A Ljubičić A Lozza V Lutz G Luzón G Morales J 《Physical review letters》2011,107(26):261302
The CERN Axion Solar Telescope (CAST) has extended its search for solar axions by using (3)He as a buffer gas. At T=1.8 K this allows for larger pressure settings and hence sensitivity to higher axion masses than our previous measurements with (4)He. With about 1 h of data taking at each of 252 different pressure settings we have scanned the axion mass range 0.39 eV?m(a)?0.64 eV. From the absence of excess x rays when the magnet was pointing to the Sun we set a typical upper limit on the axion-photon coupling of g(aγ)?2.3×10(-10) GeV(-1) at 95% C.L., the exact value depending on the pressure setting. Kim-Shifman-Vainshtein-Zakharov axions are excluded at the upper end of our mass range, the first time ever for any solar axion search. In the future we will extend our search to m(a)?1.15 eV, comfortably overlapping with cosmological hot dark matter bounds. 相似文献
3.
We investigate a special type of singularity in non-smooth solutions
of first-order partial differential equations, with emphasis on
Isaacs’ equation. This type, called focal manifold, is
characterized by the incoming trajectory fields on the two sides and a
discontinuous gradient. We provide a complete set of constructive
equations under various hypotheses on the singularity, culminating
with the case where no a priori hypothesis on its geometry is known,
and where the extremal trajectory fields need not be collinear. We
show two examples of differential games exhibiting non-collinear
fields of extremal trajectories on the focal manifold, one with a
transversal approach and one with a tangential approach. 相似文献
4.
Lanthanide‐Doped Nanocrystals: Strategies for Improving the Efficiency of Upconversion Emission and Their Physical Understanding 下载免费PDF全文
The fundamental understanding of lanthanide‐doped upconverted nanocrystals remains a frontier area of research because of potential applications in photonics and biophotonics. Recent studies have revealed that upconversion luminescence dynamics depend on host crystal structure, size of the nanocrystals, dopant concentration, and core–shell structures, which influence site symmetry and the distribution and energy migration of the dopant ions. In this review, we bring to light the influences of doping/co‐doping concentration, crystal phase, crystal size of the host, and core–shell structure on the efficiency of upconversion emission. Furthermore, the lattice strain, due to a change in the crystal phase and by the core–shell structure, strongly influences the upconversion emission intensity. Analysis suggests that the local environment of the ion plays the most significant role in modification of radiative and nonradiative relaxation mechanisms of overall upconversion emission properties. Finally, an outlook on the prospects of this research field is given. 相似文献
5.
Dr. Arik Kar Sumanta Sain Dr. Simanta Kundu Arka Bhattacharyya Dr. Swapan Kumar Pradhan Prof. Amitava Patra 《Chemphyschem》2015,16(5):1017-1025
Tuning the functional properties of nanocrystals is an important issue in nanoscience. Here, we are able to tune the photocatalytic properties of SnO2 nanocrystals by controlling their size and shape. A structural analysis was carried out by using X‐ray diffraction (XRD)/Rietveld and transmission electron microscopy (TEM). The results reveal that the number of oxygen‐related defects varies upon changing the size and shape of the nanocrystals, which eventually influences their photocatalytic properties. Time‐resolved spectroscopic studies of the carrier relaxation dynamics of the SnO2 nanocrystals further confirm that the electron–hole recombination process is controlled by oxygen/defect states, which can be tuned by changing the shape and size of the materials. The degradation of dyes (90 %) in the presence of SnO2 nanoparticles under UV light is comparable to that (88 %) in the presence of standard TiO2 Degussa P‐25 (P25) powders. The photocatalytic activity of the nanoparticles is significantly higher than those of nanorods and nanospheres because the effective charge separation in the SnO2 nanoparticles is controlled by defect states leading to enhanced photocatalytic properties. The size‐ and shape‐dependent photocatalytic properties of SnO2 nanocrystals make these materials interesting candidates for photocatalytic applications. 相似文献
6.
We discuss the parametrization of quantum groups in terms of independent operators. We find that this consideration leads to the parametrization ofSU q(2) in terms of aq-oscillator plus a commuting phase. The commuting phase is naturally identified with the subgroupU(1) and the remaining cosetSU q(2)/U(1)=CP q(1) consists of aq-oscillator. For unitary quantum groupsSU q (n), the analogous construction results in the quantum projective spaceSU q(n+1)/U q (n)=CP q (n) being identified with then-dimensionalq-oscillator. This yields a nonlinear action of the quantum groupSU q(n+1) on then-dimensionalq-oscillator. 相似文献
7.
We first investigate the high-temperature behavior of a two-parameter deformed quantum group fermionic gas with GLp,q(2) symmetry, where (p,q)C×C. We then discuss both the structural and thermodynamical differences between GLp,q(2)- and SUr(2)-fermions with r=p/q where (p,q)R×R. 相似文献
8.
K.G. Akdeniz M. Arik M. Durgut M. Hortaçsu S. Kaptanoǧlu N.K. Pak 《Physics letters. [Part B]》1982,116(1):34-36
The Gürsey model, a conformally invariant pure spinor model in four dimensions, is quantized to result in an asymptotically free theory. 相似文献
9.
M. Arik 《Physics letters. [Part B]》1976,63(3):312-314
It is pointed out that identifying the J-particle as a gauge boson gives a remarkable agreement between the psion spectrum observed at SPEAR and the spectrum of the resonances associated with the Reggeized gauge boson of spontaneously broken non-Abelian gauge theories. The consequences of this identification in relation to the χ and Pc resonances, the leptonic decay width of J and other properties of the J and ψ′ are then discussed. 相似文献
10.
Electronic structure calculations predict the existence of a novel type of a chemically bound noble gas compound. The predicted species is an extended linear and periodic polymer, made of the repeat unit -(XeCC)-, where CC is the acetylenic group. The polymer has a strong partly ionic nature, with positive partial charge on the xenon atoms and a negative one on the CC groups. High energy barriers are found for the removal of a Xe atom from the chain, indicating high stability. This is the first polymer with a noble-gas-containing building block. 相似文献