Theory of correlations between ultra-cold bosons released from an optical lattice

In this paper we develop a theoretical description of the correlations between ultra-cold bosons after free expansion from confinement in an optical lattice. We consider the system evolution during expansion and give criteria for a far field regime. We develop expressions for first and second order two-point correlations based on a variety of commonly used approximations to the many-body state of the system including Bogoliubov, meanfield decoupling, and particle-hole perturbative solution about the perfect Mott-insulator state. Using these approaches we examine the effects of quantum depletion and pairing on the system correlations. Comparison with the directly calculated correlation functions is used to justify a Gaussian form of our theory from which we develop a general three-dimensional formalism for inhomogeneous lattice systems suitable for numerical calculations of realistic experimental regimes.Comment: 18 pages, 11 figures. To appear in Phys. Rev. A. (few minor changes made and typos fixed

Experience with fluorine and its safe use as a propellant

The industrial and the propulsion experience with fluorine and its derivatives is surveyed. The hazardous qualities of fluorine and safe handling procedures for the substance are emphasized. Procedures which fulfill the safety requirements during ground operations for handling fluorinated propulsion systems are discussed. Procedures to be implemented for use onboard the Space Transportation System are included

Synthetic Next Generation Very Large Array line observations of a massive star-forming cloud

Context. Studies of the interstellar medium and the pre-stellar cloud evolution require spectral line observations that have a high sensitivity and high angular and velocity resolution. Regions of high-mass star formation are particularly challenging because of line-of-sight confusion, inhomogeneous physical conditions, and potentially very high optical depths.Aims. We wish to quantify to what accuracy the physical conditions within a massive star-forming cloud can be determined from observations. We are particularly interested in the possibilities offered by the Next Generation Very Large Array (ngVLA) interferometer.Methods. We used data from a magnetohydrodynamic simulation of star formation in a high-density environment. We concentrated on the study of a filamentary structure that has physical properties similar to a small infrared-dark cloud. We produced synthetic observations for spectral lines observable with the ngVLA and analysed these to measure column density, gas temperature, and kinematics. Results were compared to ideal line observations and the actual 3D model.Results. For a nominal cloud distance of 4kpc, ngVLA provides a resolution of similar to 0.01 pc even in its most compact configuration. For abundant molecules, such as HCO+, NH3, N2H+, and CO isotopomers, cloud kinematics and structure can be mapped down to subarcsecond scales in just a few hours. For NH3, a reliable column density map could be obtained for the entire 15 '' x 40 '' cloud, even without the help of additional single-dish data, and kinetic temperatures are recovered to a precision of similar to 1 K. At higher frequencies, the loss of large-scale emission becomes noticeable. The line observations are seen to accurately trace the cloud kinematics, except for the largest scales, where some artefacts appear due to the filtering of low spatial frequencies. The line-of-sight confusion complicates the interpretation of the kinematics, and the usefulness of collapse indicators based on the expected blue asymmetry of optically thick lines is limited.Conclusions. The ngVLA will be able to provide accurate data on the small-scale structure and the physical and chemical state of star-forming clouds, even in high-mass star-forming regions at kiloparsec distances. Complementary single-dish data are still essential for estimates of the total column density and the large-scale kinematics.Peer reviewe

Ion-implantation induced anomalous surface amorphization in silicon

Spectroscopic ellipsometry (SE), high-depth-resolution Rutherford backscattering (RBS) and channeling have been used to examine the surface damage formed by room temperature N and B implantation into silicon. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fraction of the amorphous silicon component in the layers) by linear regression. The dependence of the thickness of the surface-damaged silicon layer (beneath the native oxide layer) on the implantation parameters was determined: the higher the dose, the thicker the disordered layer at the surface. The mechanism of the surface amorphization process is explained in relation to the ion beam induced layer-by-layer amorphization. The results demonstrate the applicability of Spectroscopic ellipsometry with a proper optical model. RBS, as an independent cross-checking method supported the constructed optical model

Biomechanical and Radiographic Evaluation of an Ovine Model for the Human Lumbar Spine

While various species of animal models have been used in preclinical investigations of spinal implant devices to assess their biological adaptation and biomechanical performance, few studies have made comprehensive comparisons to validate their suitability of modelling the human spine. The purpose of this study was to assess essential biomechanical behaviours and disc morphology of the ovine lumbar model. Flexibility testing was conducted on the spines (L3—L4 and L4—L5) of nine skeletally matured sheep. Segmental rotation and intradiscal pressure were measured and load sharing between the intervertebral disc and posterior elements were calculated on the basis of a simplified parallel spring model. Following the tests, the spinal segments were sectioned into a series of sagittal slabs, and transverse radiographs of these slabs were taken to evaluate the variation in the disc height and end-plate curvature. Comparing the biomechanical and radiographic results with published data on the human lumbar spine, good comparability between the ovine and cadaveric lumbar spines was found in terms of the general disc shape and in most of the biomechanical parameters including the range of motion, neutral zone, and load sharing between the intervertebral disc and posterior elements. A few distinctive differences were also found between the two, including flatter sagittal alignment, smaller disc dimensions, and greater lateral bending motion in the ovine model

Chronically Inadequate Sleep Results in Abnormal Bone Formation and Abnormal Bone Marrow in Rats

Insufficient sleep over long durations of the lifespan is believed to adversely affect proper development and healthful aging, although how this might become manifested is unknown. In the present study, rats were repeatedly sleep-restricted during 72 days to permit maladaptations to evolve, thereby permitting study. Densitometric and histomorphometric analyses were performed on harvested bone. In sleep-restricted rats, bone lined by osteoid was reduced 45-fold and osteoid thickness was decreased, compared with controls. This corresponded to a decrease in osteoblast number and activity. The percentage of bone lined by osteoclasts did not differ from that of controls. Plasma concentrations of an osteoclast marker (TRACP 5b) were increased in sleep-restricted rats, indicating increased bone resorption. The low amount of new bone formation without a reduction in bone resorption is diagnostic of osteopenia. Bone mineral density was decreased in femurs from sleep-restricted rats compared with controls, indicating osteoporosis. Red marrow in sleep-restricted rats contained only 37% of the fat and more than twice the number of megakaryocytes compared with that of the control rats. These findings in marrow suggest changed plasticity and increased hematopoiesis. Plasma concentrations of insulin-like growth factor-1, a known, major mediator of osteoblast differentiation and the proliferation of progenitor cells, was decreased by 30% in sleep-restricted rats. Taken together, these findings suggest that chronically inadequate sleep affects bone metabolism and bone marrow composition in ways that have implications for development, aging, bone healing and repair, and blood cell differentiation

Kids Don’t Float…and Their Parents Don’t Either: Using a Family-Centered Approach in Alaska’s Kids Don’t Float Program

The goal of this experiential report is to outline the adoption of a family-centered Kids Don’t Float approach. We conducted a critical synthesis of information to reflect the expansion of the Kids Don’t Float program into a more family-centered approach. The critical synthesis provided insights into why we should adopt this approach, how it was implemented, and how it influenced drowning incidents compared to the previously used child-centered approach. The adoption of a family-centered approach may contribute to reducing drowning incidents by targeting parents, providing safety information to families, and promoting parental modelling of life jackets. Program evaluators and water safety advocates may use these insights to strengthen injury prevention programs that target drowning incidents