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141.
P. Krolak R. A. Briere E. Cheu D. A. Harris K. S. McFarland A. Roodman B. Schwingenheuer S. V. Somalwar Y. W. Wah B. Winstein R. WinstonK. Arisaka D. Roberts W. Slater M. WeaverA. R. BarkerE. C. Swallow G. J. Bock R. Coleman M. Crisler J. Enagonio R. Ford Y. B. Hsiung D. A. Jensen E. Ramberg R. TschirhartE. M. Collins G. D. GollinT. Nakaya T. YamanakaP. Gu P. Haas W. P. Hogan S. K. Kim J. N. Matthews S. S. Myung S. Schnetzer G. B. ThomsonY. Zou 《Physics letters. [Part B]》1994,320(3-4):407-410
A FNAL E799 Collaboration has carried out a search for the lepton-family number violating decay π0 → μ±e using π0's produced from KL → π0π0π0 decays in flight. No events were observed. Assuming that lepton-family number violation is charge independent, the 90% confidence level upper limit on was determined to be 8.6 × 10−9. 相似文献
142.
We prove that the ultimate fate of a bubble of negative energy density which forms in a metastable universe of zero energy density is gravitational collapse. We improve on previous treatments in that we allow for departures from O(3, 1) symmetry in the initial state, so long as they are not too great. 相似文献
143.
We apply the Schwinger boson scheme to the fully screened Kondo model and generalize the method to include antiferromagnetic interactions between ions. Our approach captures the Kondo crossover from local moment behavior to a Fermi liquid with a nontrivial Wilson ratio. When applied to the two-impurity model, the mean-field theory describes the "Varma-Jones" quantum phase transition between a valence bond state and a heavy Fermi liquid. 相似文献
144.
Ananchenko GS Pojarova M Udachin KA Leek DM Coleman AW Ripmeester JA 《Chemical communications (Cambridge, England)》2006,(4):386-388
In an ethanol/water mixture, the nitroxyl radical TEMPO abstracts a hydrogen atom from a phenolic OH group of the amphiphilic para-hexanoylcalix[4]arene, and the hydroxylamine TEMPOH formed yields a stable inclusion complex with another molecule of the calixarene. 相似文献
145.
Using a Luttinger-Ward scheme for interacting gauge particles, we present a conserving many body treatment of a family of fully screened infinite-U Anderson models that has a smooth crossover into the Fermi-liquid state, with a finite scattering phase shift at zero temperature and a Wilson ratio greater than 1. We illustrate our method, computing the temperature dependence of the thermodynamics, resistivity, and electron dephasing rate and discuss its future application to nonequilibrium quantum dots and quantum critical mixed valent systems. 相似文献
146.
R.V. Coleman B. Giambattista P.K. Hansma A. Johnson W.W. McNairy C.G. Slough 《物理学进展》2013,62(6):559-644
We have used scanning tunnelling microscopes (STMs) operating at liquid helium and liquid nitrogen temperatures to image the charge-density waves (CDWs) in transition metal chalcogenides. The layer structure dichalcogenides TaSe2, TaS2, NbSe2, VSe2, TiSe2 and TiS2 have been studied including representative polytype phases such as 1T, 2H and 4Hb. Experimental results are presented for the complete range of CDW amplitudes and structures observed in these materials. In most cases both the CDW and the surface atomic structure have been simultaneously imaged. Results on the trichalcogenide NbSe3 are also included. The formation of the CDW along with the associated periodic lattice distortion gaps the Fermi surface (FS) and modifies the local density-of-states (LDOS) detected by the tunnelling process. The tunnelling microscopes have been operated mostly in the constant current mode which maps the LDOS at the position of the tunnelling tip. The relative amplitudes and profiles of the CDW superlattice and the atomic lattice have been measured and confirm on an atomic scale the CDW structures predicted by X-ray, electron and neutron diffraction. The absolute STM deflections are larger than expected for the CDW induced modifications of the LDOS above the surface and possible enhancement mechanisms are reviewed. In the 2H trigonal prismatic coordination phases the CDWs involve a relatively small charge transfer and the atomic structure dominates the STM images. In the 1T octahedral coordination phases the charge transfer is large and the CDW structure dominates the STM image with an anomalously large enhancement of the STM profile. Systematic comparison of the STM profiles with band structure and FS information is included. In the case of the 4Hb mixed coordination phases at the lowest temperatures two nearly independent CDWs form in alternate sandwiches. STM studies on 4Hb crystals with both octahedral and trigonal prismatic surface sandwiches have been carried out. The STM scans detect the relative strengths of the two CDWs as well as the interactions between the two types of CDW structure. The STM scans are also able to detect defects and domain structure in the CDW image. Several examples will be given demonstrating the potential of the STM to detect these local variations in LDOS on an atomic scale. In contrast to the layer structure crystals the linear chain compound NbSe3 shows a complex surface atomic structure as well as the formation of two CDWs. The surface atomic structure is resolved in the STM scans and profiles have detected the presence of the CDW modulation at 77K and 4.2K. These results demonstrate the feasibility of detecting CDW structure in the presence of complex atomic structure and using materials where dynamical CDW effects can also be studied by STM. The range of STM results presented here show that the STM scans are extremely sensitive to the detail of the CDW structure and its effect on the LDOS. Although much of this structure has been deduced from diffraction studies, the ability to examine the CDW structure on an atomic scale with the STM is new. The sensitivity of the STM method suggests potential applications to a wide range of electronic structures in materials. 相似文献
147.
Stephen Coleman 《The Journal of mathematical sociology》2013,37(2):95-130
This paper investigates aggregate voting behavior in American presidential elections from 1904 to 1980; the state is unit of analysis. We abandon the traditional assumption that voting is a rational process and instead construct a model to test the power of social conformity over voting decisions. The model, which uses the entropy measure of statistical information theory, allows specific numerical tests of its validity and, additionally, reveals unexpected dynamic patterns in voting behavior. We find four distinct processes related to social conformity that affect voter turnout and the distribution of votes among presidential candidates. A mathematical model for each process is identified and parameters are estimated from election data. 相似文献
148.
Calix[4]arene forms elongated nanoporous microcrystals. The pores are linear nano-channels (1.7 nm diameter) arranged in a honeycomb network. The crystals luminesce at room temperature according to a variety of processes that include monomer fluorescence (lifetime of ca. 1.1 ns), dimer fluorescence (lifetime of ca. 5.4 ns), and monomer phosphorescence (lifetime of ca. 2 s). The dimers result from pi-orbital overlap of adjacent phenol groups from neighboring nano-channels, with C-C distances of ca. 4 A. 相似文献
149.
Abouzaid E Arenton M Barker AR Bellantoni L Bellavance A Blucher E Bock GJ Cheu E Coleman R Corcoran MD Cox B Erwin AR Escobar CO Glazov A Golossanov A Gomes RA Gouffon P Hsiung YB Jensen DA Kessler R Kotera K Ledovskoy A McBride PL Monnier E Nguyen H Niclasen R Ii DG Ping H Ramberg EJ Ray RE Ronquest M Santos E Slater W Smith D Solomey N Swallow EC Toale PA Tschirhart R Wah YW Wang J White HB Whitmore J Wilking MJ Winstein B Winston R Wolfe C Worcester ET Worcester M Yamanaka T Zimmerman ED 《Physical review letters》2008,100(13):131803
The Fermilab KTeV experiment has searched for lepton-flavor-violating decays of the K(L) meson in three decay modes. We observe no events in the signal region for any of the modes studied, and we set the following upper limits for their branching ratios at the 90% C.L.: BR(K(L) --> pi(0) micro(+/-) e(-/+)) <7.6 x 10(-11); BR(K(L) --> pi(0)pi(0) micro(+/-) e(-/+)) <1.7 x 10(-10); BR(pi(0) --> micro(+/-) e(-/+)) <3.6 x 10(-10). This result represents a factor of 82 improvement in the branching ratio limit for K(L) --> pi(0) micro(+/-) e(-/+) and is the first reported limit for K(L) --> pi(0)pi(0) micro(+/-) e(-/+). 相似文献
150.
Adamson P Andreopoulos C Arms KE Armstrong R Auty DJ Ayres DS Baller B Barr G Barrett WL Becker BR Belias A Bernstein RH Bhattacharya D Bishai M Blake A Bock GJ Boehm J Boehnlein DJ Bogert D Bower C Buckley-Geer E Cavanaugh S Chapman JD Cherdack D Childress S Choudhary BC Coleman SJ Culling AJ de Jong JK Diwan MV Dorman M Dytman SA Escobar CO Evans JJ Falk Harris E Feldman GJ Frohne MV Gallagher HR Goodman MC Gouffon P Gran R Grashorn EW Grossman N Grzelak K Habig A Harris D Harris PG 《Physical review letters》2008,101(15):151601
A search for a sidereal modulation in the MINOS near detector neutrino data was performed. If present, this signature could be a consequence of Lorentz and CPT violation as predicted by the effective field theory called the standard-model extension. No evidence for a sidereal signal in the data set was found, implying that there is no significant change in neutrino propagation that depends on the direction of the neutrino beam in a sun-centered inertial frame. Upper limits on the magnitudes of the Lorentz and CPT violating terms in the standard-model extension lie between 10(-4) and 10(-2) of the maximum expected, assuming a suppression of these signatures by a factor of 10(-17). 相似文献