Tunneling-induced restoration of classical degeneracy in quantum kagome ice

Quantum effect is expected to dictate the behavior of physical systems at low temperature. For quantum magnets with geometrical frustration, quantum fluctuation usually lifts the macroscopic classical degeneracy, and exotic quantum states emerge. However, how different types of quantum processes entangle wave functions in a constrained Hilbert space is not well understood. Here, we study the topological entanglement entropy and the thermal entropy of a quantum ice model on a geometrically frustrated kagome lattice. We find that the system does not show a Z(2) topological order down to extremely low temperature, yet continues to behave like a classical kagome ice with finite residual entropy. Our theoretical analysis indicates an intricate competition of off-diagonal and diagonal quantum processes leading to the quasidegeneracy of states and effectively, the classical degeneracy is restored

Frequency Evolution of Neutron Peaks Below Tc: Commensurate and Incommensurate Structure in LaSrCuO and YBaCuO

We study the evolution of the neutron cross-section with variable frequency $\omega$ and fixed $T$ below $T_c$ in two different cuprate families. Our calculations, which predominantly probe the role of d-wave pairing, lead to generic features, independent of Fermi surface shapes. Among our findings, reasonably consistent with experiment, are (i) for $\omega$ near the gap energy $\Delta$, both optimal {LaSrCuO} and slightly underdoped YBCO exhibit (comparably) incommensurate peaks (ii) peak sharpening below $T_c$ is seen in {LaSrCuO}, (iii) quite generically, a frequency evolution from incommensurate to commensurate and then back to incommensurate structure is found with increasing $\omega$. Due to their narrow $\omega$ regime of stability, commensurate peaks in {LaSrCuO} should be extremely difficult to observe.Comment: RevTex 5pages, 4figures; Manuscript rewritten, figures revised, and direct comparisons with experiments adde

Comment on "Interface state recombination in organic solar cells"

In a recent paper, Street et al. [Phys. Rev. B 81, 205307 (2010)] propose first order recombination due to interface states to be the dominant loss mechanism in organic bulk heterojunction solar cells, based on steady-state current--voltage characteristics. By applying macroscopic simulations, we found that under typical solar cell conditions, monomolecular or bimolecular recombination cannot be inferred from the slope of the light intensity dependent photocurrent. In addition, we discuss the validity of calculating a mobility--lifetime product from steady-state measurements. We conclude that the experimental technique applied by Street et al. is not sufficient to unambiguously determine the loss mechanism.Comment: 4 pages, 2 figures. Corrected Eqns. (2) and (4): 1/... was missin

Development of modified vibration test criteria for qualifying space vehicle components

Simplified methods are described to estimate the test criteria of primary structures at component attachment points subjected to broadband random acoustic excitations. The current method utilizes a constant smeared component mass attenuation factor across the frequency range of interest. The developed method indicates that the attenuation factor is based on a frequency dependent ratio of the mechanical impedances of both the component and primary structures. The procedures used to predict the structural responses are considered as the present state-of-the-art and provide satisfactory prediction results. Example problems are used to illustrate the application procedures of the two methods and to compare the significant difference. It was found that the lower test criteria obtained by the impedance ratio method is due to the results of considering the effects of component/primary structure interaction

Analyses of mean and turbulent motion in the tropics with the use of unequally spaced data

Wind velocities from 25 km to 60 km over Ascension Island, Fort Sherman and Kwajalein for the period January 1970 to December 1971 are analyzed in order to achieve a better understanding of the mean flow, the eddy kinetic energy and the Eulerian time spectra of the eddy kinetic energy. Since the data are unequally spaced in time, techniques of one-dimensional covariance theory were utilized and an unequally spaced time series analysis was accomplished. The theoretical equations for two-dimensional analysis or wavenumber frequency analysis of unequally spaced data were developed. Analysis of the turbulent winds and the average seasonal variance and eddy kinetic energy of the turbulent winds indicated that maximum total variance and energy is associated with the east-west velocity component. This is particularly true for long period seasonal waves which dominate the total energy spectrum. Additionally, there is an energy shift for the east-west component into the longer period waves with altitude increasing from 30 km to 50 km

Characteristics of the motions, turbulence intensity, diffusivity, flux of momentum and sensible heat in the upper atmosphere

Analyses of the meteorological rocket data obtained from an experiment conducted at 3-hour intervals at 8 western meridional rocket stations are presented. Large variations in the meridional wind contribute substantially to overall turbulence in the tropical stratosphere. The solar semidiurnal component of wind oscillations in the tropics was observed to be much higher than predicted by theory, often exceeding the magnitude of the diurnal amplitude throughout the stratosphere. The observed value of the solar diurnal amplitude in the stratosphere was in line with theoretical prediction. The solar terdiurnal amplitudes for temperature, meridional and zonal winds were non-negligible and must be considered in any harmonic analysis. Phase angle variation with height was rapid for all harmonics; however, there was general agreement between predicted and observed phase angles. Because of large changes in the mean winds in the mesosphere with season, harmonic determinations are difficult. There appear to be large zonal wind changes even within the same season as mentioned previously. Turbulence diffusivity in the upper stratosphere is greater near the equator than in the mid-latitudes

Development of modified vibration test criteria for qualifying space vehicle components

The results of the evaluation of two response prediction methods relating to the prediction of structural responses of stiffened shell structures with or without attached components, and subjected to broadband acoustic excitations are presented. The methods under evaluation were the constant mass attenuation method and the impedance ratio method. Example problems were used to illustrate the application procedures of these two methods and to compare their predicted results with the experimentally measured data. It is found that more realistic estimates of the structural response can be obtained by the impedance ratio method