Mathematical model for predicting human vertebral fracture

Mathematical model has been constructed to predict dynamic response of tapered, curved beam columns in as much as human spine closely resembles this form. Model takes into consideration effects of impact force, mass distribution, and material properties. Solutions were verified by dynamic tests on curved, tapered, elastic polyethylene beam

Canonical Equivalence of a Generic 2D Dilaton Gravity Model and a Bosonic String Theory

We show that a canonical tranformation converts, up to a boundary term, a generic 2d dilaton gravity model into a bosonic string theory with a Minkowskian target space.Comment: LaTeX file, 9 pages, no figure

The investigation of vertebral injury sustained during aircrew ejection

A series of tests were performed on excised human vertebral segments to determine the static and dynamic response of the thoraco-lumbar spine when loaded in flexion. A total of fifteen tests were performed on eleven specimens. Specimens were obtained from male donors ranging in age from 34 to 60 years. Demographic data pertinent to each specimen and the elapsed time between death of the donor and testing of each corresponding specimen are presented. Only spinal segments comprised of lower thoracic and upper lumbar vertebrae were tested because in aircraft ejection injuries clinical complications in this anatomical region predominate. A complex continuum mathematical model describing the dynamic response of the human spine was formulated, solved, and verified experimentally. Detailed results are presented in figures, tables, and equations

Study of physiological tolerance to centrifugation Final report

Physiological effects and acceleration tolerances after weightlessness based on space environment simulation with human centrifuges and bed res

Probing the quantum phase transition in the Dicke model through mechanical vibrations

This paper is concerned with quantum dynamics of a system coupled to a critical reservoir. In this context, we employ the Dicke model which is known to exhibit a super radiant quantum phase transition (QPT) and we allow one of the mirrors to move under a linear restoring force. The electromagnetic field couples to the movable mirror though radiation pressure just like in typical optomechanical setups. We show that, in the thermodynamical limit, the super-radiant phase induces a classical driving force on the mirror without causing decoherence.Comment: 6 pages, 3 figures, final versio

Starspot Jitter in Photometry, Astrometry and Radial Velocity Measurements

Analytical relations are derived for the amplitude of astrometric, photometric and radial velocity perturbations caused by a single rotating spot. The relative power of the star spot jitter is estimated and compared with the available data for $\kappa^1$ Ceti and HD 166435, as well as with numerical simulations for $\kappa^1$ Ceti and the Sun. A Sun-like star inclined at i=90\degr at 10 pc is predicted to have a RMS jitter of 0.087 \uas in its astrometric position along the equator, and 0.38 m s$^{-1}$ in radial velocities. If the presence of spots due to stellar activity is the ultimate limiting factor for planet detection, the sensitivity of SIM Lite to Earth-like planets in habitable zones is about an order of magnitude higher that the sensitivity of prospective ultra-precise radial velocity observations of nearby stars.Comment: accepted in ApJ Letters, Nov. 200

Microwave emission from a crystal of molecular magnets -- The role of a resonant cavity

We discuss the effects caused by a resonant cavity around a sample of a magnetic molecular crystal (such as Mn${}_{12}$-Ac), when a time dependent external magnetic field is applied parallel to the easy axis of the crystal. We show that the back action of the cavity field on the sample significantly increases the possibility of microwave emission. This radiation process can be supperradiance or a maser-like effect, depending on the strength of the dephasing. Our model provides further insight to the theoretical understanding of the bursts of electromagnetic radiation observed in recent experiments accompanying the resonant quantum tunneling of magnetization. The experimental findings up to now can all be explained as being a maser effect rather than superradiance. The results of our theory scale similarly to the experimental findings, i.e., with increasing sweep rate of the external magnetic field, the emission peaks are shifted towards higher field values.Comment: 12 pages, 6 figures. To appear in Phys. Rev.

Free fields via canonical transformations of matter-coupled 2D dilaton gravity models

It is shown that the 1+1-dimensional matter-coupled Jackiw-Teitelboim model and the model with an exponential potential can be converted by means of appropriate canonical transformations into a bosonic string theory propagating on a flat target space with an indefinite signature. This makes it possible to consistently quantize these models in the functional Schroedinger representation thus generalizing recent results on CGHS theory.Comment: 15 pages, Late

Localized states in strong magnetic field: resonant scattering and the Dicke effect

We study the energy spectrum of a system of localized states coupled to a 2D electron gas in strong magnetic field. If the energy levels of localized states are close to the electron energy in the plane, the system exhibits a kind of collective behavior analogous to the Dicke effect in optics. The latter manifests itself in ``trapping'' of electronic states by localized states. At the same time, the electronic density of states develops a gap near the resonance. The gap and the trapping of states appear to be complementary and reflect an intimate relation between the resonant scattering and the Dicke effect. We reveal this relation by presenting the exact solution of the problem for the lowest Landau level. In particular, we show that in the absence of disorder the system undergoes a phase transition at some critical concentration of localized states.Comment: 28 pages + 9 fig