Maximizing phonon thermal conductance for ballistic membranes

At low temperatures, phonon scattering can become so weak that phonon transport becomes ballistic. We calculate the ballistic phonon conductance G for membranes using elasticity theory, considering the transition from three to two dimensions. We discuss the temperature and thickness dependence and especially concentrate on the issue of material parameters. For all membrane thicknesses, the best conductors have, counter-intuitively, the lowest speed of sound.Comment: 4 pages, 4 figures, proceedings to phonons 2007 conferenc

Scattering loss in electro-optic particulate composite materials

The effective permittivity dyadic of a composite material containing particulate constituent materials with one constituent having the ability to display the Pockels effect is computed, using an extended version of the strong-permittivity-fluctuation theory which takes account of both the distributional statistics of the constituent particles and their sizes. Scattering loss, thereby incorporated in the effective electromagnetic response of the homogenized composite material, is significantly affected by the application of a low-frequency (dc) electric field

Fall Migration of Ringed Seals (Phoca hispida) through the Beaufort and Chukchi Seas, 2001–02

In a study examining the range, distribution, and habitat use of the ringed seal, Phoca hispida, in Canada’s Western Arctic, eight ringed seals were live-captured, instrumented with satellite-linked (SLTDR-16) transmitters, and released at Cape Parry, Northwest Territories, Canada, on 17 – 19 September 2001 and 7 – 8 September 2002. Locations accepted by the filtering process were received from seven of the eight tagged seals (5 subadults, 1 adult female, 1 pup) over periods ranging from 35 to 207 days (mean 99 d, SD 66). Mean rates of travel were 0.91 m/s (SE 0.011, n = 7) in the Canadian Beaufort Sea, 0.92 m/s (SE 0.014, n = 7) offshore of Alaska’s North Slope, and 0.79 m/s (SE 0.008, n = 5) in the Chukchi Sea. On average, the seals took 32 days (range 19 – 56 d) to migrate between Cape Parry and Point Barrow, almost always remaining within 100 km of shore and over the continental shelf or slope, and covering an average migration distance of 2138 km. Dive depths for all groupings were mainly in the 4 – 80 m range (adult female: 63 – 73%; subadults: 54 – 73%; pup: 64 – 82%), with only the adult female diving deeper than 80 m on occasion, mainly in the Canadian Beaufort Sea (15.1% of her dives). The subadults and pup dove mainly for more than 1 to 5 min (60% and 55%, respectively), while a large proportion of the adult female’s dives were longer (34% for > 1 to 5 min; 31% for > 5 to 8 min; 5.4% for > 8 min). The tracks of the westward migrating seals revealed a routing through three political jurisdictions (including oil and gas industry lease areas in all three) over a period of about two months. This pattern highlights the importance of cooperation between the United States, Canada, and Russia in managing this species.Du 17 au 19 septembre 2001 et les 7 et 8 septembre 2002, dans le cadre d’une étude portant sur le parcours, la répartition et l’utilisation de l’habitat du phoque annelé, Phoca hispida, dans l’ouest de l’Arctique canadien, huit phoques annelés ont été capturés en vie, dotés de transmetteurs en liaison avec un satellite (SLTDR-16), puis relâchés au cap Parry, dans les Territoires du Nord-Ouest, au Canada. Des emplacements acceptés par filtrage ont été reçus de la part de sept des huit phoques marqués (5 préreproducteurs, 1 femelle adulte, 1 jeune) sur des périodes variant entre 35 et 207 jours (moyenne 99 d, SD 66). Les taux de déplacement moyens étaient de 0,91 m/s (SE 0,011; n = 7) dans la mer canadienne de Beaufort, de 0,92 m/s (SE 0,014; n = 7) au large du versant nord de l’Alaska et de 0,79 m/s (SE 0,008; n = 5) dans la mer des Tchouktches. En moyenne, la migration des phoques entre le cap Parry et la pointe Barrow durait 32 jours (écart de 19 à 56 d), et les phoques restaient presque toujours en-dedans de 100 km de la côte et au-dessus de la pente ou du plateau continental. Ils couvraient en moyenne une distance de migration de 2 138 km. La profondeur des plongées de tous les groupements variait entre 4 et 80 m (femelle adulte : 63 % à 73 %; préreproducteurs : 54 % à 73 %; jeune : 64 % à 82 %), et seulement la femelle adulte plongeait à plus de 80 m de profondeur à l’occasion, surtout dans la mer canadienne de Beaufort (15,1 % de ses plongées). Les prérepro­ducteurs et le jeune phoque étaient principalement en plongée pendant plus de 1 à 5 min (60 % et 55 %, respectivement), tandis qu’une grande proportion des plongées de la femelle adulte durait plus longtemps (34 % pour > 1 à 5 min; 31 % pour > 5 à 8 min; 5,4 % pour > 8 min). Les pistes des phoques en migration vers l’ouest révélaient des itinéraires passant par trois compétences politiques (comprenant des concessions de l’industrie pétrolière et gazière dans les trois cas) sur une période d’environ deux mois. Cette tendance fait ressortir l’importance d’une collaboration entre les États-Unis, le Canada et la Russie en matière de gestion de cette espèce

Eddy Current Signal Calculations for Surface Breaking Cracks

This paper contains a brief status report on analytical modeling of the probe-flaw interactions for surface breaking cracks and some data on comparisons of theory and experiment for EDM notches and true fatigue cracks. The goal of the work reported here and in companion papers by Rummel and Rathke (1984), Auld, et al. (1984), and Martinez and Bahr (1984) is to improve the quantitative character of eddy current testing. In this joint effort, the role of probe-flaw interaction modeling is to provide engineering tools not previously available for: (1) setting design guidelines to optimize sensitivity and spatial resolution, (2) permitting analytic extrapolation of measured flaw response data, (3) defining a test basis for monitoring probe calibration, and (4) establishing a rational inversion procedure based on multifrequency measurements and the shape signature of a scanned flaw signal as a function of position

Surface Flaw Detection with Ferromagnetic Resonance Probes

Small ferromagnetic resonators have been shown to provide effective electromagnetic detectors for surface flaws in magnetic and nonmagnetic metals. As such a resonator is moved along \u27the surface of a test piece it experiences a frequency shift when it passes over a flaw. lwo detection mechanisms are present: (1) an eddy current effect (2) a perturbation of the dc magnetic bias field used to tune the resonator. Results are given for experiments performed on machined slots in aluminum, titanium and steel and on tightly closed fatigue cracks in titanium. Results are also presented for some measurements on titanium aircraft fasteners

Quantum chaos in nanoelectromechanical systems

We present a theoretical study of the electron-phonon coupling in suspended nanoelectromechanical systems (NEMS) and investigate the resulting quantum chaotic behavior. The phonons are associated with the vibrational modes of a suspended rectangular dielectric plate, with free or clamped boundary conditions, whereas the electrons are confined to a large quantum dot (QD) on the plate's surface. The deformation potential and piezoelectric interactions are considered. By performing standard energy-level statistics we demonstrate that the spectral fluctuations exhibit the same distributions as those of the Gaussian Orthogonal Ensemble (GOE) or the Gaussian Unitary Ensemble (GUE), therefore evidencing the emergence of quantum chaos. That is verified for a large range of material and geometry parameters. In particular, the GUE statistics occurs only in the case of a circular QD. It represents an anomalous phenomenon, previously reported for just a small number of systems, since the problem is time-reversal invariant. The obtained results are explained through a detailed analysis of the Hamiltonian matrix structure.Comment: 14 pages, two column

Characteristics of phonon transmission across epitaxial interfaces: a lattice dynamic study

Phonon transmission across epitaxial interfaces is studied within the lattice dynamic approach. The transmission shows weak dependence on frequency for the lattice wave with a fixed angle of incidence. The dependence on azimuth angle is found to be related to the symmetry of the boundary interface. The transmission varies smoothly with the change of the incident angle. A critical angle of incidence exists when the phonon is incident from the side with large group velocities to the side with low ones. No significant mode conversion is observed among different acoustic wave branches at the interface, except when the incident angle is near the critical value. Our theoretical result of the Kapitza conductance $G_{K}$ across the Si-Ge (100) interface at temperature $T=200$K is 4.6\times10^{8} {\rm WK}^{-1}{\rmm}^{-2}. A scaling law $G_K \propto T^{2.87}$ at low temperature is also reported. Based on the features of transmission obtained within lattice dynamic approach, we propose a simplified formula for thermal conductanceacross the epitaxial interface. A reasonable consistency is found between the calculated values and the experimentally measured ones.Comment: 8 figure

Anomalous quantum chaotic behavior in nanoelectromechanical structures

It is predicted that for sufficiently strong electron-phonon coupling an anomalous quantum chaotic behavior develops in certain types of suspended electro-mechanical nanostructures, here comprised by a thin cylindrical quantum dot (billiard) on a suspended rectangular dielectric plate. The deformation potential and piezoelectric interactions are considered. As a result of the electron-phonon coupling between the two systems the spectral statistics of the electro-mechanic eigenenergies exhibit an anomalous behavior. If the center of the quantum dot is located at one of the symmetry axes of the rectangular plate, the energy level distributions correspond to the Gaussian Orthogonal Ensemble (GOE), otherwise they belong to the Gaussian Unitary Ensemble (GUE), even though the system is time-reversal invariant.Comment: 4 pages, pdf forma

Improved Probe-Flaw Interaction Modeling, Inversion Processing, and Surface Roughness Clutter

In Reference 1 a first comparison was made of measured eddy current signals with calculations based on nonuniform probe-field interaction theory. These calculations followed the basic analysis developed in Reference 2. They used interrogating field distributions calculated by Dodd and Deeds theory for the air core coils of Reference 3. (Note that Fig. 6 in Reference 1 and Fig. 7 in Reference 3 should be interchanged). In Reference 1 theoretical and experimental plots of the flaw profile curve (a plot of △Z versus distance along the mouth of a surface breaking flaw) were found to be in good agreement, with regard to shape, for several selected EDM notch samples in aluminum. An iterative procedure was also developed for systematically varying the length, depth, and opening width to obtain a best fit to the experimental data.4 In the present paper a full inversion procedure is developed and illustrated for approximately rectangular-shaped EDM notches. The mathematical structure of the inversion problem is first examined and a solution is proposed. Physical reasoning, based on the form of the flaw profile curves, is then used to simplify the approach and to provide guidance in selection of the most suitable probe geometry. Other topics briefly addressed include, possible improvements in the theory for the region with a/§ close to unity and for more realistic flaw shapes (i.e., semi-elliptical, rather than rectangular), inaccuracies due to errors in the probe scan path, and background clutter due to surface roughness, machining marks, and micro-structure

Scaling Relations of Dwarf Galaxies without Supernova-Driven Winds

Nearby dwarf galaxies exhibit tight correlations between their global stellar and dynamical properties, such as circular velocity, mass-to-light ratio, stellar mass, surface brightness, and metallicity. Such correlations have often been attributed to gas or metal-rich outflows driven by supernova energy feedback to the interstellar medium. We use high-resolution cosmological simulations of high-redshift galaxies with and without energy feedback, as well as analytic modeling, to investigate whether the observed correlations can arise without supernova-driven outflows. We find that the simulated dwarf galaxies exhibit correlations similar to those observed as early as z~10, regardless of whether supernova feedback is included. We also show that the correlations can be well reproduced by our analytic model that accounts for realistic gas inflow but assumes no outflows, and star formation rate obeying the Kennicutt-Schmidt law with a critical density threshold. We argue that correlations in simulated galaxies arise due to the increasingly inefficient conversion of gas into stars in low-mass dwarf galaxies rather than supernova-driven outflows. We also show that the decrease of the observed effective yield in low-mass objects, often used as an indicator of gas and metal outflows, can be reasonably reproduced in our simulations without outflows. We show that this trend can arise if a significant fraction of metals in small galaxies is spread to the outer regions of the halo outside the stellar extent via mixing. In this case the effective yield can be significantly underestimated if only metals within the stellar radius are taken into account. Measurements of gas metallicity in the outskirts of gaseous disks of dwarfs would thus provide a key test of such explanation.Comment: accepted for publication in ApJ, 19 pages, 12 figures, uses emulateapj