Linear and angular momentum of electromagnetic fields generated by an arbitrary distribution of charge and current densities at rest

Starting from Stratton-Panofsky-Phillips-Jefimenko equations for the electric and magnetic fields generated by completely arbitrary charge and current density distributions at rest, we derive far-zone approximations for the fields, containing all components, dominant as well as sub-dominant. Using these approximate formulas, we derive general formulas for the total electromagnetic linear momentum and angular momentum, valid at large distances from arbitrary, non-moving charge and current sources.Comment: Six pages, one figure. Errors correcte

Wet chemical etching mechanism of silicon

We review what can be said on wet chemical etching of single crystals from the viewpoint of the science of crystal growth. Starting point is that there are smooth and rough crystal surfaces. The kinetics of smooth faces is controlled by a nucleation barrier that is absent on rough faces. The latter therefore etch faster by orders of magnitude. The analysis of the diamond crystal structure reveals that the {111} face is the only smooth face in this lattice-other faces might be smooth only because of surface reconstruction. In this way we explain the minimum of the etch rate in KOH:H2O in the <001> direction. Two critical predictions concerning the shape of the minimum of the etch rate close to <001> and the transition from isotropic to anisotropic etching in HF:HNO3 based solutions are tested experimentally. The results are in-agreement with the theor

Effect of ACASI on Reporting of Abortion and Other Pregnancy Outcomes in the US National Survey of Family Growth.

Abortion is a behavior that is stigmatized and difficult to measure. To improve reporting of abortion and other sensitive behaviors in the United States, the National Survey of Family Growth (NSFG) supplements the interviewer administered face-to-face (FTF) interview with audio computer-assisted self-interviewing (ACASI). This paper estimates differential reporting of abortion and other pregnancy outcomes (miscarriage, live birth) in the NSFG (2002, 2006-2010, 2011-2015) between women's ACASI and FTF interviews. Examining reporting of less stigmatized pregnancy outcomes can help understand the relative contributions of stigma and survey-level factors in reporting of abortions. More women reported abortions, miscarriages and births in the ACASI than the FTF interview. Differences in reporting were moderated by the length of recall. The ACASI elicited relatively more reporting of abortions and miscarriages among non-white and low-income women. Reporting ratios increased over time. ACASI is a tool that may work differently across time, for different measures, and with varying survey contexts

Home range and habitat use by Kemp's Ridley turtles in West-Central Florida

The Kemp's ridley turtle (Lepidochelys kempii) is an endangered species whose recovery depends in part on the identification and protection of required habitats. We used radio and sonic telemetry on subadult Kemp's ridley turtles to investigate home-range size and habitat use in the coastal waters of west-central Florida from 1994 to 1996. We tracked 9 turtles during May-August up to 70 days after release and fou.ld they occupied 5-30 km2 foraging ranges. Compositional analyses indicated that turtles used rock outcroppings in their foraging ranges at a significantly higher proportion than expected. based on availability within the study area. Additionally. turtles used live bottom (e.g .• sessile invertebrates) and green macroalgae habitats significantly more than seagrass habitat. Similar studies are needed through'mt the Kemp's ridley turtles' range to investigate regional and stage-specific differences in habitat use. which can then be used to conserve important foraging areas

Adolescent Sexual Activity, Contraceptive Use, and Pregnancy in Britain and the U.S.: A Multidecade Comparison.

PURPOSE: Pregnancy rates among adolescents have declined in the U.S. and Britain but remain high compared with other high-income countries. This comparison describes trends in pregnancy rates, recent sexual activity, and contraceptive use among women aged 16-19 years in the U.S. and Britain to consider the contribution of these two behavioral factors to the decline in pregnancy rates in the two countries and the differences between them. METHODS: We use data from two rounds of the U.S. National Survey of Family Growth, conducted 2002-2003 and 2011-2015, and the British National Survey of Sexual Attitudes and Lifestyles, conducted 2000-2001 and 2010-2012, to describe population-level differences between countries and over time in sexual activity and contraceptive use. We calculate pregnancy rates using national births and abortions data. RESULTS: Pregnancy rates declined in both countries; this began earlier in the U.S. and was steeper. There was no change in sexual activity in Britain, but in the U.S., the proportion reporting recent sex declined. In both countries, there was a shift toward more effective contraception. A higher proportion in Britain than the U.S. reported ever having had sex (65% vs. 49%) and sex in the last year (64% vs. 45%), 6 months (59% vs. 45%), and 4 weeks (48% vs. 45%). A higher proportion in Britain reported using more effective contraception (68% vs. 52%). CONCLUSIONS: In both countries, improvements in contraceptive use have contributed substantially to declines in pregnancy rates; however, the steeper decline in the U.S. likely also reflects declines in recent sex occurring only in that country

Inelastic scattering of light by a cold trapped atom: Effects of the quantum center-of-mass motion

The light scattered by a cold trapped ion, which is in the stationary state of laser cooling, presents features due to the mechanical effects of atom-photon interaction. These features appear as additional peaks (sidebands) in the spectrum of resonance fluorescence. Among these sidebands the literature has discussed the Stokes and anti-Stokes components, namely the sidebands of the elastic peak. In this manuscript we show that the motion also gives rise to sidebands of the inelastic peaks. These are not always visible, but, as we show, can be measured in parameter regimes which are experimentally accessible.Comment: 10 pages, 4 figures, submitted to Phys. Rev.