Social Organization of the Eastern Rock Elephant-Shrew (\u3cem\u3eElephantulus myurus\u3c/em\u3e): The Evidence for Mate Guarding

Understanding the costs and benefits of defending solitary females, or mate guarding, may be the key to understanding the evolution of monogamy in most mammals. Elephant-shrews, or sengis, are a unique clade of small mammals that are particularly attractive for studies of mate guarding. We studied the spatial organization of Eastern Rock Sengis (Elephantulus myurus) in KwaZulu-Natal, South Africa, from August – December 2000. Our objectives were to describe the home ranges of males and females using radiotelemetry, noting the sizes and overlap of adjacent ranges and how the spatial organization changes through time. Males and females were spatially associated in monogamous pairs despite the fact that males contributed no obvious direct care to offspring. These monogamous associations persisted despite the fact that some males had home ranges large enough to encompass multiple females. Males also had more variable ranges, perhaps because they spent more time at the periphery of their ranges exploring for the presence of additional females. There was likely competition for females, as range shifts were observed when male territory holders died or disappeared. It seems likely that this species is a model study organism to investigate the costs and benefits of mate guarding

Hanbury Brown Twiss effect for ultracold quantum gases

We have studied 2-body correlations of atoms in an expanding cloud above and below the Bose-Einstein condensation threshold. The observed correlation function for a thermal cloud shows a bunching behavior, while the correlation is flat for a coherent sample. These quantum correlations are the atomic analogue of the Hanbury Brown Twiss effect. We observe the effect in three dimensions and study its dependence on cloud size.Comment: Figure 1 availabl

Dirac neutrino mass from the beta decay end-point modified by the dynamics of a Lorentz-violating equation of motion

Using a generalized procedure for obtaining the equation of motion of a propagating fermionic particle, we examine previous claims for a lightlike preferred axis embedded in the framework of Lorentz-invariance violation with preserved algebra. In a high energy scale, the corresponding equation of motion is reduced to a conserving lepton number chiral (VSR) equation, and in a low energy scale, the Dirac equation for a free is recovered. The new dynamics introduces some novel ingredients (modified cross section) to the phenomenology of the tritium beta decay end-point.Comment: 11 pages, 4 figure

The sediment of mixtures of charged colloids: segregation and inhomogeneous electric fields

We theoretically study sedimentation-diffusion equilibrium of dilute binary, ternary, and polydisperse mixtures of colloidal particles with different buoyant masses and/or charges. We focus on the low-salt regime, where the entropy of the screening ions drives spontaneous charge separation and the formation of an inhomogeneous macroscopic electric field. The resulting electric force lifts the colloids against gravity, yielding highly nonbarometric and even nonmonotonic colloidal density profiles. The most profound effect is the phenomenon of segregation into layers of colloids with equal mass-per-charge, including the possibility that heavy colloidal species float onto lighter ones

The Structure of High Strehl Ratio Point-Spread Functions

We describe the symmetries present in the point-spread function (PSF) of an optical system either located in space or corrected by an adaptive o to Strehl ratios of about 70% and higher. We present a formalism for expanding the PSF to arbitrary order in terms of powers of the Fourier transform of the residual phase error, over an arbitrarily shaped and apodized entrance aperture. For traditional unapodized apertures at high Strehl ratios, bright speckles pinned to the bright Airy rings are part of an antisymmetric perturbation of the perfect PSF, arising from the term that is first order in the residual phase error. There are two symmetric second degree terms. One is negative at the center, and, like the first order term, is modulated by the perfect image's field strength -- it reduces to the Marechal approximation at the center of the PSF. The other is non-negative everywhere, zero at the image center, and can be responsible for an extended halo -- which limits the dynamic range of faint companion detection in the darkest portions of the image. In regimes where one or the other term dominates the speckles in an image, the symmetry of the dominant term can be exploited to reduce the effect of those speckles, potentially by an order of magnitude or more. We demonstrate the effects of both secondary obscuration and pupil apodization on the structure of residual speckles, and discuss how these symmetries can be exploited by appropriate telescope and instrument design, observing strategies, and filter bandwidths to improve the dynamic range of high dynamic range AO and space-based observations. Finally, we show that our analysis is relevant to high dynamic range coronagraphy.Comment: Accepted for publication in ApJ; 20 pages, 4 figure

A ring trap for ultracold atoms

We propose a new kind of toroidal trap, designed for ultracold atoms. It relies on a combination of a magnetic trap for rf-dressed atoms, which creates a bubble-like trap, and a standing wave of light. This new trap is well suited for investigating questions of low dimensionality in a ring potential. We study the trap characteristics for a set of experimentally accessible parameters. A loading procedure from a conventional magnetic trap is also proposed. The flexible nature of this new ring trap, including an adjustable radius and adjustable transverse oscillation frequencies, will allow the study of superfluidity in variable geometries and dimensionalities.Comment: 4 figures, 10 pages ; the order of the sections has been changed ; to appear in Phys. Rev.

Evaporative cooling in a radio-frequency trap

A theoretical investigation for implementing a scheme of forced evaporative cooling in radio-frequency (rf) adiabatic potentials is presented. Supposing the atoms to be trapped by a rf field RF1, the cooling procedure is facilitated using a second rf source RF2. This second rf field produces a controlled coupling between the spin states dressed by RF1. The evaporation is then possible in a pulsed or continuous mode. In the pulsed case, atoms with a given energy are transferred into untrapped dressed states by abruptly switching off the interaction. In the continuous case, it is possible for energetic atoms to adiabatically follow the doubly-dressed states and escape out of the trap. Our results also show that when the frequencies of the fields RF1 and RF2 are separated by at least the Rabi frequency associated with RF1, additional evaporation zones appear which can make this process more efficient.Comment: 12 pages, 11 figure