Acoustic waves: should they be propagated forward in time, or forward in space?

The evolution of acoustic waves can be evaluated in two ways: either as a temporal, or a spatial propagation. Propagating in space provides the considerable advantage of being able to handle dispersion and propagation across interfaces with remarkable efficiency; but propagating in time is more physical and gives correctly behaved reflections and scattering without effort. Which should be chosen in a given situation, and what compromises might have to be made? Here the natural behaviors of each choice of propagation are compared and contrasted for an ordinary second order wave equation, the time-dependent diffusion wave equation, an elastic rod wave equation, and the Stokes'/ van Wijngaarden's equations, each case illuminating a characteristic feature of the technique. Either choice of propagation axis enables a partitioning the wave equation that gives rise to a directional factorization based on a natural "reference" dispersion relation. The resulting exact coupled bidirectional equations then reduce to a single unidirectional first-order wave equation using a simple "slow evolution" assumption that minimizes effect of subsequent approximations, while allowing a direct term-to-term comparison between exact and approximate theories.Comment: 12 pages, v2 correcte

Hot-hole lasers in III-V semiconductors

Following the success of p-Ge hot-hole lasers, there is also potential for using other semiconductor materials, notably III-V's such as GaAs and InSb. Previous analysis had suggested that a large effective mass ratio between the heavy and light holes is advantageous, which implies that InSb would make an excellent hot-hole laser. Using our Monte Carlo simulations of both GaAs and InSb hot-hole lasers in combination with a rate equation model, we see that previously accepted criteria used to predict performance are not always reliable, and we suggest suitable alternatives. The simulation results include gain and gain bandwidth as a function of field strength and laser frequency, and alternative field orientations and photon polarizations are considered. Comparisons are made with bulk p-Ge systems. The optimum conditions predicted by our simulations could then be used in the design of quantum-well hot-hole lasers.Comment: 7 pages, 4 figures (8 frames

The Perceived Impact of No Child Left Behind on Third- through Fifth-Grade Elementary Science Classrooms.

The purpose of this study was to describe the perceived impact of No Child Left Behind on elementary science classrooms in 3 Northeast Tennessee school districts. Quantitative descriptive methodology was used to document how No Child Left Behind impacts instructional methodology, professional development, administrative support, materials and resources, and assessment in 3rd through 5th grades. Data were collected using a survey developed by the researcher. The survey consisted of a demographic section, 28 statements, and 2 open-ended questions. The 51 participants included elementary-school science teachers in 8 schools in 3 upper East Tennessee school districts. Data analysis was based on the following demographics: differing levels of teaching experience, No Child Left Behind school status, and small and large schools. Findings included: The 3 greatest concerns of the impact of the No Child Left Behind Act were the pressures felt by teachers to increase test scores, the manner in which it impacted at-risk or disadvantaged students, and the lack of inservice, specifically for science. Findings also revealed that low- scoring schools or grades were receiving extra assistance and teachers reported they feel that their school or district fosters and supports change. An analysis of the open-ended questions emphasized the stress teachers reported feeling along with the loss of science instruction time to math and language arts

The biker-glove pattern of congenital melanocytic nevi

Congenital melanocytic nevi (CMN) are common birthmarks with 20% occurring on the limbs. We describe 4 patients with acral CMN with a “biker‐glove” distribution with sparing of the distal digits, as has previously been described in acral infantile hemangiomas (IH). The existence of the biker‐glove pattern suggests that CMN arise from early mutations in melanocyte precursors and supports the recently described Kinsler‐Larue hypothesis of mesenchymal distribution of melanocyte migration occurring in a circular field from a central point. Developmental errors in mesenchymal precursors with similar migration patterns may explain this shared pattern among CMN and IH

Epidermal choristoma: a case series and review of the literature

Epidermal choristoma is a rare, congenital lesion in which islands of ectopic skin are found within the oral cavity. They present as pigmented macules or papules on the tongue. Histologic appearances are characteristic and benign. We present three cases review the current literature and recommend observation of the lesion rather than complete excision should be considered as a reasonable management option

Dynamics of soap bubble bursting and its implications to volcano acoustics

In order to assess the physical mechanisms at stake when giant gas bubbles burst at the top of a magma conduit, laboratory experiments have been performed. An overpressurized gas cavity is initially closed by a thin liquid film, which suddenly bursts. The acoustic signal produced by the bursting is investigated. The key result is that the amplitude and energy of the acoustic signal strongly depend on the film rupture time. As the rupture time is uncontrolled in the experiments and in the field, the measurement of the acoustic excess pressure in the atmosphere, alone, cannot provide any information on the overpressure inside the bubble before explosion. This could explain the low energy partitioning between infrasound, seismic and explosive dynamics often observed on volcanoes

Differential expression of secreted factors SOSTDC1 and ADAMTS8 cause pro-fibrotic changes in linear morphoea fibroblasts

This is the peer reviewed version of the following article: Badshah, I. I., et al. "Differential expression of secreted factors SOSTDC1 and ADAMTS8 cause pro-fibrotic changes in linear morphoea fibroblasts." British Journal of Dermatology 0(ja)., which has been published in final form at https://doi.org/10.1111/bjd.17352. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived VersionsFunding: RO, IB and SB are funded by the Great Ormond Street Children's Charity. This research was supported by the NIHR Great Ormond Street Hospital Biomedical Research Centr

Magnetic phase transitions in Gd64Sc36 studied using non-contact ultrasonics

The speed and attenuation of ultrasound propagation can be used to determine material properties and identify phase transitions. Standard ultrasonic contact techniques are not always convenient due to the necessity of using couplant; however, recently reliable non-contact ultrasonic techniques involving electromagnetic generation and detection of ultrasound with electromagnetic acoustic transducers (EMATs) have been developed for use on electrically conducting and/or magnetic materials. We present a detailed study of magnetic phase transitions in a single crystal sample of Gd64Sc36 magnetic alloy using contact and non-contact ultrasonic techniques for two orientations of external magnetic field. Phase diagrams are constructed based on measurements of elastic constant C33, the attenuation and the efficiency of generation when using an EMAT. The EMATs are shown to provide additional information related to the magnetic phase transitions in the studied sample, and results identify a conical helix phase in Gd64Sc36 in the magnetic field orientation