A self-consistent Hartree-Fock approach for interacting bosons in optical lattices

A theoretical study of interacting bosons in a periodic optical lattice is presented. Instead of the commonly used tight-binding approach (applicable near the Mott insulating regime of the phase diagram), the present work starts from the exact single-particle states of bosons in a cubic optical lattice, satisfying the Mathieu equation, an approach that can be particularly useful at large boson fillings. The effects of short-range interactions are incorporated using a self-consistent Hartree-Fock approximation, and predictions for experimental observables such as the superfluid transition temperature, condensate fraction, and boson momentum distribution are presented.Comment: 12 pages, 15 figure file

Possible Role Of Breeding Phenology, Brood Size, And Male Parental Care On The Number Of Nesting Attempts By Female Eastern Bluebirds, A Facultatively Multibrooded Species

To maximize reproductive output, several species of songbirds attempt to raise two or more broods in a single breeding season. The results of previous studies have revealed much variation among species in the factors that influence the likelihood of female songbirds attempting to raise multiple broods during a breeding season. As such, additional studies are needed to better understand the roles of early breeding, brood sizes, and, especially, male parental care in determining the likelihood of having multiple broods. My objective, therefore, was to examine the possible effects of breeding initiation date, brood size, and male provisioning behavior on the number of nesting attempts by female Eastern Bluebirds (Sialia sialis) during a single breeding season. My study was conducted at the Blue Grass Army Depot in Madison County, Kentucky, from mid-March to mid-August 2018. I monitored the nests of 39 first broods, 34 second broods, and eight third broods during my study. Bluebirds were captured in mist-nets and banded with unique combinations of color bands. Adult provisioning behavior was monitored with video-recorders placed from 1.5 – 3 m from nest boxes, and each nest was recorded at least every other day until nestlings fledged. Recordings were subsequently reviewed to quantify the provisioning behavior of male and female Eastern Bluebirds. The combined provisioning rates of male and female Eastern Bluebirds were similar for first, second, and third broods. For first and second broods, males provisioned young at higher rates than females during the first 5-6 days post-hatching, likely because females brooded nestlings during this period. Males did not provision young at higher rates than females during the first 5-6 days post-hatching for third broods, possibly reducing their investment in young in broods late in the breeding season. For broods one and two, the combined provisioning rates of males and females were lower during the first four days post-hatching than for older nestlings, likely because the lower energy requirements of young during the first few days post-hatching. The number of young in broods did not affect the provisioning rates of male and female Eastern Bluebirds (in terms of feeding visits per nestling), with nestlings fed at similar rates regardless of the number of nestlings in a brood. One possible explanation for such results is that young in larger broods have, collectively, less exposed surface area, are better able to thermoregulate, and, therefore, require less food. I found that differences in initiation dates (laying of the first egg), clutch sizes, and brood sizes of first broods did not influence the likelihood of pairs having second and third broods during the breeding season. Rather, differences in individual quality among male and female Eastern Bluebirds may explain differences among pairs in the number of broods they attempt to raise in a breeding season

Induced p-wave superfluidity in strongly interacting imbalanced Fermi gases

The induced interaction among the majority spin species, due to the presence of the minority species, is computed for the case of a population-imbalanced resonantly-interacting Fermi gas. It is shown that this interaction leads to an instability, at low temperatures, of the recently observed polaron Fermi liquid phase of strongly imbalanced Fermi gases to a p-wave superfluid state. We find that the associated transition temperature, while quite small in the weakly interacting BCS regime, is experimentally accessible in the strongly interacting unitary regime.Comment: Published versio

Deployable Solar Array Structure: G1:3

This design project is in response to an AIAA RFP (Request-For-Proposal) to build a compact, durable, non-hinged solar array to be deployed from a spacecraft on its way from the Earth to Mars. The solar array structures are used to provide the continual supply of power to operate onboard equipment. A large array will be required but must fit within the fairing of the launch vehicle. Origami principles will be utilized to fit the given constrained stored volume of 10 cm3 while satisfying the power requirements and avoiding structural complications due to tight folds

Theory of Electron-Phonon Dynamics in Insulating Nanoparticles

We discuss the rich vibrational dynamics of nanometer-scale semiconducting and insulating crystals as probed by localized electronic impurity states, with an emphasis on nanoparticles that are only weakly coupled to their environment. Two principal regimes of electron-phonon dynamics are distinguished, and a brief survey of vibrational-mode broadening mechanisms is presented. Recent work on the effects of mechanical interaction with the environment is discussed.Comment: Revte

Induced superfluidity of imbalanced Fermi gases near unitarity

The induced intraspecies interactions among the majority species, mediated by the minority species, is computed for a population-imbalanced two-component Fermi gas. Although the Feshbach-resonance mediated interspecies interaction is dominant for equal populations, leading to singlet s-wave pairing, we find that in the strongly imbalanced regime the induced intraspecies interaction leads to p-wave pairing and superfluidity of the majority species. Thus, we predict that the observed spin-polaron Fermi liquid state in this regime is unstable to p-wave superfluidity, in accordance with the results of Kohn and Luttinger, below a temperature that, near unitarity, we find to be within current experimental capabilities. Possible experimental signatures of the p-wave state using radio-frequency spectroscopy as well as density-density correlations after free expansion are presented.Comment: 15 pages, 13 figures, submitted to Phys. Rev.

Full stress tensor measurement using colour centres in diamond

Stress and strain are important factors in determining the mechanical, electronic, and optical properties of materials, relating to each other by the material's elasticity or stiffness. Both are represented by second rank field tensors with, in general, six independent components. Measurements of these quantities are usually achieved by measuring a property that depends on the translational symmetry and periodicity of the crystal lattice, such as optical phonon energies using Raman spectroscopy, the electronic band gap using cathodoluminescence, photoelasticity via the optical birefringence, or Electron Back Scattering Diffraction (EBSD). A reciprocal relationship therefore exists between the maximum sensitivity of the measurements and the spatial resolution. Furthermore, of these techniques, only EBSD and off-axis Raman spectroscopy allow measurement of all six components of the stress tensor, but neither is able to provide full 3D maps. Here we demonstrate a method for measuring the full stress tensor in diamond, using the spectral and optical polarization properties of the photoluminescence from individual nitrogen vacancy (NV) colour centres. We demonstrate a sensitivity of order 10 MPa, limited by local fluctuations in the stress in the sample, and corresponding to a strain of about 10^-5, comparable with the best sensitivity provided by other techniques. By using the colour centres as built-in local sensors, the technique overcomes the reciprocal relationship between spatial resolution and sensitivity and offers the potential for measuring strains as small as 10^-9 at spatial resolution of order 10 nm. Furthermore it provides a straightforward route to volumetric stress mapping. Aside from its value in understanding strain distributions in diamond, this new approach to stress and strain measurement could be adapted for use in micro or nanoscale sensors.Comment: 12 pages, 5 figures - supplementary informations included in appendi

On the Verge of One Petabyte - the Story Behind the BaBar Database System

The BaBar database has pioneered the use of a commercial ODBMS within the HEP community. The unique object-oriented architecture of Objectivity/DB has made it possible to manage over 700 terabytes of production data generated since May'99, making the BaBar database the world's largest known database. The ongoing development includes new features, addressing the ever-increasing luminosity of the detector as well as other changing physics requirements. Significant efforts are focused on reducing space requirements and operational costs. The paper discusses our experience with developing a large scale database system, emphasizing universal aspects which may be applied to any large scale system, independently of underlying technology used.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, Ca, USA, March 2003, 6 pages. PSN MOKT01