A Statistical phonon transport model for thermal transport in cyrstalline materials from the diffuse to ballistic regime

Phonon transport in micro- nanoscale crystalline materials can be well modeled by the Boltzmann transport equation (BTE). The complexities associated with solving the BTE have led to the development of various numerical models to simulate phonon transport. These models have been applied to predict thermal transport from the di¤use to ballistic regime. While some success using techniques such as the Monte Carlo method has been achieved, there are still a significant number of approximations related to the intricacies of phonon transport that must be more accurately modeled for better predictions of thermal transport at reduced length scales. The objective of the present work is to introduce a Statistical Phonon Transport (SPT) model for simulating thermal transport in crystalline materials from the diffuse to ballistic regime. The SPT model provides a theoretically more realistic treatment of phonon transport physics by eliminating some of the common approximations utilized by other numerical modeling techniques. The SPT model employs full anisotropic dispersion. Phonon populations are modeled without the use of scaling factors or pseudo-random number generation. Three-phonon scattering is rigorously enforced following the selection rules of energy and pseudo-momentum. The SPT model provides a flexible framework for incorporating various phonon scattering mechanisms and models. Results related to the determination of allowable three-phonon interactions are presented along with several three-phonon scattering models. Steady-state and transient thermal transport results for silicon from the diffuse to ballistic regimes are presented and compared to analytical and experimental results. Recommendations for future work related to increasing the robustness of the SPT model as well as utilizing the SPT model to predict thermal transport in practical applications are given

NIRPS - Solutions Facilitator Status

No abstract availabl

The effects of changing chemistry on the shock response of basic polymers

The shock response of four common semicrystalline thermoplastic polymers—polyethylene (PE), polyvinylchloride (PVC), polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE)—have been studied in terms of their Hugoniots, release velocities and shear strengths. Through the variations in behaviour caused by changes to the attached atoms to the carbon backbone, it has been possible to suggest that there are two main factors in play. The first is an electrostatic repulsion between adjacent polymer chains. Where this force is large, for example in PTFE with highly electronegative fluorine atoms, this results in this force dominating the shock response, with low shock velocities, high release velocities and little if no hardening behind the shock front. In contrast, in materials such as PE, this force is now weaker, due to the lower electronegativity of hydrogen, and hence this force is easier to overcome by the applied shock stress. Now the main factor affecting shock behaviour is controlled by the shape of the polymer chain allowing inter chain tangling (tacticity). This results in higher shock velocities, lower release speeds and significant hardening behind the shock front as the chains are forced together. This is prevalent in materials with a relatively open structure such as PE and is enhanced with the presence of large side groups or atoms off the main polymer chain

Kepler-4B: A Hot Neptune-Like Planet of A G0 Star Near Main-Sequence Turnoff

Early time-series photometry from NASA's Kepler spacecraft has revealed a planet transiting the star we term Kepler-4, at R.A. = 19(h)02(m)27.(s)68, delta = +50 degrees 08'08 '' 7. The planet has an orbital period of 3.213 days and shows transits with a relative depth of 0.87 x 10(-3) and a duration of about 3.95 hr. Radial velocity (RV) measurements from the Keck High Resolution Echelle Spectrometer show a reflex Doppler signal of 9.3(-1.9)(+1.1) m s(-1), consistent with a low-eccentricity orbit with the phase expected from the transits. Various tests show no evidence for any companion star near enough to affect the light curve or the RVs for this system. From a transit-based estimate of the host star's mean density, combined with analysis of high-resolution spectra, we infer that the host star is near turnoff from the main sequence, with estimated mass and radius of 1.223(-0.091)(+0.053) M(circle dot) and 1.487(-0.084)(+0.071) R(circle dot).We estimate the planet mass and radius to be {M(P), R(P)} = {24.5 +/- 3.8 M(circle plus), 3.99 +/- 0.21 R(circle plus)}. The planet's density is near 1.9 g cm(-3); it is thus slightly denser and more massive than Neptune, but about the same size.W. M. Keck FoundationNASA's Science Mission DirectorateAstronom

Kepler Observations of Transiting Hot Compact Objects

Kepler photometry has revealed two unusual transiting companions orbiting an early A-star and a late B-star. In both cases the occultation of the companion is deeper than the transit. The occultation and transit with follow-up optical spectroscopy reveal a 9400 K early A-star, KOI-74 (KIC 6889235), with a companion in a 5.2 day orbit with a radius of 0.08 Rsun and a 10000 K late B-star KOI-81 (KIC 8823868) that has a companion in a 24 day orbit with a radius of 0.2 Rsun. We infer a temperature of 12250 K for KOI-74b and 13500 K for KOI-81b. We present 43 days of high duty cycle, 30 minute cadence photometry, with models demonstrating the intriguing properties of these object, and speculate on their nature.Comment: 12 pages, 3 figures, submitted to ApJL (updated to correct KOI74 lightcurve

Abnormal Ocular Pneumoplethysmographic Results in Unilateral Neovascular Glaucoma.

Little is known about the predictive value of ocular pneumoplethysmography in patients with ophthalmic disease. We evaluated eight patients with unilateral increased intraocular pressure due to neovascular glaucoma who did not have evidence of severe extracranial carotid stenosis by duplex scanning and continuous-wave Doppler ultrasound. The ophthalmic systolic pressure measured by ocular pneumoplethysmography was decreased in the affected eye of all eight patients, indicating that neovascular glaucoma may be a cause of abnormal ocular pneumoplethysmographic results. Patients with neovascular glaucoma tended to have larger interocular ophthalmic systolic pressure differences than other patients with false-positive ocular pneumoplethysmographic results by noninvasive criteria

Discovery of the Transiting Planet Kepler-5B

We present 44 days of high duty cycle, ultra precise photometry of the 13th magnitude star Kepler-5 (KIC 8191672, T(eff) = 6300 K, log g = 4.1), which exhibits periodic transits with a depth of 0.7%. Detailed modeling of the transit is consistent with a planetary companion with an orbital period of 3.548460 +/- 0.000032 days and a radius of 1.431(-0.052)(+0.041) R(J). Follow-up radial velocity measurements with the Keck HIRES spectrograph on nine separate nights demonstrate that the planet is more than twice as massive as Jupiter with a mass of 2.114(-0.059)(+0.056) M(J) and a mean density of 0.894 +/- 0.079 g cm(-3).NASA's Science Mission DirectorateAstronom