Dipole-dipole interaction between orthogonal dipole moments in time-dependent geometries

In two nearby atoms, the dipole-dipole interaction can couple transitions with orthogonal dipole moments. This orthogonal coupling accounts for a number of interesting effects, but strongly depends on the geometry of the setup. Here, we discuss several setups of interest where the geometry is not fixed, such as particles in a trap or gases, by averaging over different sets of geometries. Two averaging methods are compared. In the first method, it is assumed that the internal electronic evolution is much faster than the change of geometry, whereas in the second, it is vice versa. We find that the orthogonal coupling typically survives even extensive averaging over different geometries, albeit with qualitatively different results for the two averaging methods. Typically, one- and two-dimensional averaging ranges modelling, e.g., low-dimensional gases, turn out to be the most promising model systems.Comment: 11 pages, 14 figure

Simplified SIMPs and the LHC

The existence of Dark Matter (DM) in the form of Strongly Interacting Massive Particles (SIMPs) may be motivated by astrophysical observations that challenge the classical Cold DM scenario. Other observations greatly constrain, but do not completely exclude, the SIMP alternative. The signature of SIMPs at the LHC may consist of neutral, hadron-like, trackless jets produced in pairs. We show that the absence of charged content can provide a very efficient tool to suppress dijet backgrounds at the LHC, thus enhancing the sensitivity to a potential SIMP signal. We illustrate this using a simplified SIMP model and present a detailed feasibility study based on simulations, including a dedicated detector response parametrization. We evaluate the expected sensitivity to various signal scenarios and tentatively consider the exclusion limits on the SIMP elastic cross section with nucleons.Comment: 18 pages, 7 figure

The Cytology of Developing Muscle

Development of myofibrils in myotome muscle of chick embryos may be divided into two phases. During the first, with which the present observations are concerned, primary fibrils arise in the cytoplasm of the presumptive muscle cells. During the second period the number of myofibrils increases apparently by splitting of the primary fibrils

Radio to Gamma-Ray Emission from Shell-type Supernova Remnants: Predictions from Non-linear Shock Acceleration Models

Supernova remnants (SNRs) are widely believed to be the principal source of galactic cosmic rays. Such energetic particles can produce gamma-rays and lower energy photons via interactions with the ambient plasma. In this paper, we present results from a Monte Carlo simulation of non-linear shock structure and acceleration coupled with photon emission in shell-like SNRs. These non-linearities are a by-product of the dynamical influence of the accelerated cosmic rays on the shocked plasma and result in distributions of cosmic rays which deviate from pure power-laws. Such deviations are crucial to acceleration efficiency and spectral considerations, producing GeV/TeV intensity ratios that are quite different from test particle predictions. The Sedov scaling solution for SNR expansions is used to estimate important shock parameters for input into the Monte Carlo simulation. We calculate ion and electron distributions that spawn neutral pion decay, bremsstrahlung, inverse Compton, and synchrotron emission, yielding complete photon spectra from radio frequencies to gamma-ray energies. The cessation of acceleration caused by the spatial and temporal limitations of the expanding SNR shell in moderately dense interstellar regions can yield spectral cutoffs in the TeV energy range; these are consistent with Whipple's TeV upper limits on unidentified EGRET sources. Supernova remnants in lower density environments generate higher energy cosmic rays that produce predominantly inverse Compton emission at super-TeV energies; such sources will generally be gamma-ray dim at GeV energies.Comment: 62 pages, AASTeX format, including 1 table and 11 figures, accepted for publication in The Astrophysical Journal (Vol 513, March 1, 1999

Personality and team performance: a meta-analysis

Using a meta-analytical procedure, the relationship between team composition in terms of the Big-Five personality traits (trait elevation and variability) and team performance were researched. The number of teams upon which analyses were performed ranged from 106 to 527. For the total sample, significant effects were found for elevation in agreeableness ( = 0.24) and conscientiousness ( = 0.20), and for variability in agreeableness ( = -0.12) and conscientiousness ( = -0.24). Moderation by type of team was tested for professional teams versus student teams. Moderation results for agreeableness and conscientiousness were in line with the total sample results. However, student and professional teams differed in effects for emotional stability and openness to experience. Based on these results, suggestions for future team composition research are presented

Spatiotemporal chaos induces extreme events in an extended microcavity laser

Extreme events such as rogue wave in optics and fluids are often associated with the merging dynamics of coherent structures. We present experimental and numerical results on the physics of extreme events appearance in a spatially extended semiconductor microcavity laser with intracavity saturable absorber. This system can display deterministic irregular dynamics only thanks to spatial coupling through diffraction of light. We have identified parameter regions where extreme events are encountered and established the origin of this dynamics in the emergence of deterministic spatiotemporal chaos, through the correspondence between the proportion of extreme events and the dimension of the strange attractor

Spin dynamics in the ordered spin ice Tb2_2Sn2_2O7_7

Geometrical frustration is a central challenge in contemporary condensed matter physics, a crucible favourable to the emergence of novel physics. The pyrochlore magnets, with rare earth magnetic moments localized at the vertices of corner-sharing tetrahedra, play a prominent role in this field, with a rich variety of exotic ground states ranging from the "spin ices" \hoti\ and \dyti\ to the "spin liquid" and "ordered spin ice" ground states in \tbti\ and \tbsn. Inelastic neutron scattering provides valuable information for understanding the nature of these ground states, shedding light on the crystal electric field (CEF) level scheme and on the interactions between magnetic moments. We have performed such measurements with unprecedented neutron flux and energy resolution, in the "ordered spin ice" \tbsn. We argue that a new interaction, which involves the spin lattice coupling through a low temperature distortion of the trigonal crystal field, is necessary to account for the data