Analytical Hartree-Fock gradients for periodic systems

We present the theory of analytical Hartree-Fock gradients for periodic systems as implemented in the code CRYSTAL. We demonstrate how derivatives of the integrals can be computed with the McMurchie-Davidson algorithm. Highly accurate gradients with respect to nuclear coordinates are obtained for systems periodic in 0,1,2 or 3 dimensions.Comment: accepted by International Journal of Quantum Chemistr

Implications of Privacy Needs and Interpersonal Distancing Mechanisms for Space Station Design

The literature on privacy needs, personal space, interpersonal distancing, and crowding is reveiwed with special reference to spaceflight and spaceflight analogous conditions. A quantitative model is proposed for understanding privacy, interpersonal distancing, and performance. The implications for space station design is described

An approach to permutation symmetry for the electroweak theory

The form of the leptonic mixing matrix emerging from experiment has, in the last few years, generated a lot of interest in the so-called tribimaximal type. This form may be naturally associated with the possibility of a discrete permutation symmetry ($S_3$) among the three generations. However, trying to implement this attractive symmetry has resulted in some problems and it seems to have fallen out of favor. We suggest an approach in which the $S_3$ holds to first approximation, somewhat in the manner of the old SU(3) flavor symmetry of the three flavor quark model. It is shown that in the case of the neutrino sector, a presently large experimentally allowed region can be fairly well described in this first approximation. We briefly discuss the nature of the perturbations which are the analogs of the Gell-Mann Okubo perturbations but confine our attention for the most part to the $S_3$ invariant model. We postulate that the $S_3$ invariant mass spectrum consists of non zero masses for the $(\tau,b,t)$ and zero masses for the other charged fermions but approximately degenerate masses for the three neutrinos. The mixing matrices are assumed to be trivial for the charged fermions but of tribimaximal type for the neutrinos in the first approximation. It is shown that this can be implemented by allowing complex entries for the mass matrix and spontaneous breakdown of the $S_3$ invariance of the Lagrangian.Comment: 24 pages, 1 figure, minor corrections and acknowledgment added. To appear in IJM

Development of a human-structure dynamic interaction model for human sway for use in permanent grandstand design

This paper details a first attempt to develop a simple human-structure dynamic interaction (HSDI) model for vibration serviceability design of permanent grandstands subject to crowd sway. To date, extensive research has been conducted on vertical crowd-induced vibrations to understand interaction mechanisms and enable engineers to account for them. Similar mechanisms have not yet been fully understood or researched in the lateral plane. This, alongside the limited, verified measured response data has led to incomplete design assessment methods. In this work, an effective two-degree-of-freedom spring-mass-damper-actuator system is developed to represent co-ordinated spectators swaying laterally in the side-to-side direction on a real grandstand. The dynamic properties attributed in the constituents of the model are determined by curve fitting of laboratory-scale human sway data and the modal analysis of the grandstand’s finite element model. The comparison of the modelling output against existing serviceability criteria approaches illustrates potential conservatism in current practice. Namely, when the maximum responses and forces were examined as part of the integrated dynamic system a notable drop-out effect was observed. Although further research is required to validate and calibrate the proposed simple human-structure sway model for individuals and crowds, the observations qualitatively determine the significance of explicitly considering human-structure interaction in the design and assessment of permanent grandstands. Such effects may lead to construction cost savings in addition to unwanted limitations on architecture, hospitality areas and spectator circulation

Single reconstructed Fermi surface pocket in an underdoped single layer cuprate superconductor

The observation of a reconstructed Fermi surface via quantum oscillations in hole-doped cuprates opened a path towards identifying broken symmetry states in the pseudogap regime. However, such an identification has remained inconclusive due to the multi-frequency quantum oscillation spectra and complications accounting for bilayer effects in most studies. We overcome these impediments with high resolution measurements on the structurally simpler cuprate HgBa2CuO4+d (Hg1201), which features one CuO2 plane per unit cell. We find only a single oscillatory component with no signatures of magnetic breakdown tunneling to additional orbits. Therefore, the Fermi surface comprises a single quasi-two-dimensional pocket. Quantitative modeling of these results indicates that biaxial charge-density-wave within each CuO2 plane is responsible for the reconstruction, and rules out criss-crossed charge stripes between layers as a viable alternative in Hg1201. Lastly, we determine that the characteristic gap between reconstructed pockets is a significant fraction of the pseudogap energy

Spatial Relationship between Solar Flares and Coronal Mass Ejections

We report on the spatial relationship between solar flares and coronal mass ejections (CMEs) observed during 1996-2005 inclusive. We identified 496 flare-CME pairs considering limb flares (distance from central meridian > 45 deg) with soft X-ray flare size > C3 level. The CMEs were detected by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO). We investigated the flare positions with respect to the CME span for the events with X-class, M-class, and C-class flares separately. It is found that the most frequent flare site is at the center of the CME span for all the three classes, but that frequency is different for the different classes. Many X-class flares often lie at the center of the associated CME, while C-class flares widely spread to the outside of the CME span. The former is different from previous studies, which concluded that no preferred flare site exists. We compared our result with the previous studies and conclude that the long-term LASCO observation enabled us to obtain the detailed spatial relation between flares and CMEs. Our finding calls for a closer flare-CME relationship and supports eruption models typified by the CSHKP magnetic reconnection model.Comment: 7 pages; 4 figures; Accepted by the Astrophysical Journa

Competition and bistability of longitudinal modes in a Raman laser

A model for Raman lasers including several longitudinal modes is analyzed. Depending on the choice of the parameters the system can exhibit single-mode emission, wide bistability domains, and self-pulsing. The latter is often characterized by two frequencies, which are clearly related to single-mode and multimode instabilities, in agreement with the interpretation of earlier experimental results