The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming tau neutrinos that interact in Earth's crust. Tau leptons from nu(tau) charged-current interactions can emerge and decay in the atmosphere to produce a nearly horizontal shower with a significant electromagnetic component. The data collected between 1 January 2004 and 31 August 2007 are used to place an upper limit on the diffuse flux of nu(tau) at EeV energies. Assuming an E(nu)(-2) differential energy spectrum the limit set at 90% C.L. is E(nu)(2)dN(nu)(tau)/dE(nu)<1.3 x 10(-7) GeV cm(-2) s(-1) sr(-1) in the energy range 2 x 10(17) eV< E(nu)< 2 x 10(19) eV. 相似文献
The energy spectrum of cosmic rays above 2.5 x 10;{18} eV, derived from 20,000 events recorded at the Pierre Auger Observatory, is described. The spectral index gamma of the particle flux, J proportional, variantE;{-gamma}, at energies between 4 x 10;{18} eV and 4 x 10;{19} eV is 2.69+/-0.02(stat)+/-0.06(syst), steepening to 4.2+/-0.4(stat)+/-0.06(syst) at higher energies. The hypothesis of a single power law is rejected with a significance greater than 6 standard deviations. The data are consistent with the prediction by Greisen and by Zatsepin and Kuz'min. 相似文献
Speakers may adapt the phonetic details of their productions when they anticipate perceptual difficulty or comprehension failure on the part of a listener. Previous research suggests that a speaking style known as clear speech is more intelligible overall than casual, conversational speech for a variety of listener populations. However, it is unknown whether clear speech improves the intelligibility of fricative consonants specifically, or how its effects on fricative perception might differ depending on listener population. The primary goal of this study was to determine whether clear speech enhances fricative intelligibility for normal-hearing listeners and listeners with simulated impairment. Two experiments measured babble signal-to-noise ratio thresholds for fricative minimal pair distinctions for 14 normal-hearing listeners and 14 listeners with simulated sloping, recruiting impairment. Results indicated that clear speech helped both groups overall. However, for impaired listeners, reliable clear speech intelligibility advantages were not found for non-sibilant pairs. Correlation analyses comparing acoustic and perceptual data indicated that a shift of energy concentration toward higher frequency regions and greater source strength contributed to the clear speech effect for normal-hearing listeners. Correlations between acoustic and perceptual data were less consistent for listeners with simulated impairment, and suggested that lower-frequency information may play a role. 相似文献
Titanium dioxide (TiO(2)) nanoparticles were synthesized by controlled hydrolysis of titanium alkoxide in reverse micelles in a hydrocarbon solvent. Upon annealing in situ in the presence of the micelles at temperatures considerably lower than those required for the traditional calcination treatment in the solid state, the TiO(2) nanoparticles became highly crystalline but still maintained the same physical parameters and remained in a stable suspension. Thus, the method has allowed the preparation of crystalline TiO(2) nanoparticles that are monodispersed in the same way as they are initially produced in the microemulsion. Effects of the fluid properties on the crystallization of nanoparticles are discussed. 相似文献
The partial current densities for the transfer of titanium(IV) and oxygen ions, and of electrons at the interface between the electrolyte and the titanium(IV) oxide layer on titanium were measured as functions of total current density and pH value. It is shown theoretically, how conclusions regarding the mechanisms of the transfer reactions of both ions can be drawn from various relations between the ionic partial current densities and their dependence on solution composition, even if the electric potential difference at the oxide interface cannot be measured. Mechanisms for the transfer reactions of titanium(IV) and oxygen ions are derived from the experiments. 相似文献
The propagation of plane waves in layered media including fluid, solid and porous layers is modelled with transfer matrices, the three Biot waves being taken into account in the porous layers. 相似文献
Five different poly(arylene‐diarylvinylene)s have been synthesized by reductive polyolefination starting from the corresponding bis(α,α‐dichlorobenzyl)‐substituted monomers and dicobaltoctacarbonyl as reducing agent. The resulting polymers all contain main chain tetraphenylethylene units. Thanks to the aggregation‐induced emission effect, the corresponding polymer films show remarkably high photoluminescence quantum yields (PLQYs) of 32%–73%. The polymer with the highest PLQY is tested as solid state sensing material for the PL‐quenching‐based detection of nitroaromatic analytes (1,3,5‐trinitrobenzene as prototypical analyte).
The stabilization of a bivalent oxidation state in cobalt complexes of phenolate-based asymmetric tridentate ligands with iodo and bromo substituents is studied. The complexes [CoII(LIA)2].2CH3OH (1) and [CoII(LBrA)2].CH3OH (2) were characterized by means of several spectroscopic and spectrometric techniques. The molecular structure of 1 was determined by diffractometric analysis and reveals the cobalt(II) ion in a distorted-octahedral geometry. The centrosymmetric metal ion adopts a local D2h symmetry and is surrounded by facially coordinated ligands. Equivalent donor sets in both ligands are trans to each other, and DFT calculations suggest that the fac-trans configuration is favored by a small margin when compared to the fac-cis isomers. Both DFT calculations and EPR spectroscopy agree with a high-spin S=3/2 electronic configuration given by [ag1, b1g1, ag1, b2g2, b3g2]. This oxidation state was indirectly observed by the lack of a ppiphenolate-->dsigma*cobalt(III) charge-transfer band, which is found between 430 and 470 nm for similar cobalt(III) species. On the basis of the geometrical preferences and the oxidation state of archetypical 1 and 2, two metallosurfactants [CoII(LI-ODA)2] (3) and [CoII(LI-NOBA)2].CH2Cl2 (4) were obtained. The redox chemistry of 1-4 is marked by metal- and ligand-centered activity with several follow up processes and film formation on the electrode. Both metallosurfactants exhibit amphiphilic properties and organization, as shown by compression isotherms and Brewster angle microscopy but exhibit dissimilar collapse mechanisms; whereas 3 collapses at constant pressure, 4 exhibits a constant-area collapse. Langmuir-Blodgett films are readily obtained and were characterized by equilibrium contact angle and atomic force microscopy. 相似文献