Electromagnetic cascades in pulsars

The development of pair photon cascades initiated by high energy electrons above a pulsar polar cap is simulated numerically. The calculation uses the energy of the primary electron, the magnetic field strength, and the period of rotation as parameters and follows the curvature radiation emitted by the primary, the conversion of this radiation e(+) - e(-) pairs in the intense fields, and the quantized synchrotron radiation by the secondary pairs. A recursive technique allows the tracing of an indefinite number of generations using a Monte Carlo method. Gamma ray and pair spectra are calculated for cascades in different parts of the polar cap and with different acceleration models. It is found that synchrotron radiation from secondary pairs makes an important contribution to the gamma ray spectrum above 25 MeV, and that the final gamma ray and pair spectra are insensitive to the height of the accelerating region, as long as the acceleration of the primary electrons is not limited by radiation reaction

Pair production in superstrong magnetic fields

The production of electron-positron pairs by single photons in magnetic fields 10 to the twelth power G was investigated in detail for photon energies near threshold as well as for the asymptotic limit of high photon energy. The exact attenuation coefficient, which is derived and then evaluated numerically, is strongly influenced by the discrete energy states of the electron and positron. Near threshold, it exhibits a sawtooth pattern as a function of photon energy, and its value is significantly below that predicted by the asymptotic expression for the attenuation coefficient. The energy distributions of the created pair are computed numerically near threshold and analytic expressions are derived in the asymptotic limit. These results indicate that as field strength and photon energy increase, it becomes increasingly probable for the pair to divide the photon energy unequally. This effect, as well as the threshold behavior of the attenuation coefficient, could have important consequences for pulsar models

Cascade model of gamma-ray bursts: Power-law and annihilation-line components

If, in a neutron star magnetosphere, an electron is accelerated to an energy of 10 to the 11th or 12th power eV by an electric field parallel to the magnetic field, motion of the electron along the curved field line leads to a cascade of gamma rays and electron-positron pairs. This process is believed to occur in radio pulsars and gamma ray burst sources. Results are presented from numerical simulations of the radiation and photon annihilation pair production processes, using a computer code previously developed for the study of radio pulsars. A range of values of initial energy of a primary electron was considered along with initial injection position, and magnetic dipole moment of the neutron star. The resulting spectra was found to exhibit complex forms that are typically power law over a substantial range of photon energy, and typically include a dip in the spectrum near the electron gyro-frequency at the injection point. The results of a number of models are compared with data for the 5 Mar., 1979 gamma ray burst. A good fit was found to the gamma ray part of the spectrum, including the equivalent width of the annihilation line

Development of core pharmacy roles with competency/EPA alignment and levels of entrustment.

The purpose of this two-phase embedded mixed-method project was to investigate the extent to which a consensus exists among pharmacy professionals regarding core practice-ready roles for graduates that align with current pharmacy competencies/EPA statements with entrustment levels. Current competencies/EPAs were perceived as mapping to the core roles developed during this study, with some missing competencies. Some of the EPA levels of entrustment varied depending on the role to which it was mapped. Some levels were different than the current recommended EPA entrustment level recommended to be used by schools/colleges. The development of a set of core roles with the mapping of pharmacy competencies and EPAs is the first step in pharmacy developing an education model like medicine

A Changing Role for Technology Teacher Education

Is it time for a major redesign in technology teacher education? The field of technology education has gone through considerable introspection and revision in recent years. Welty (2003) suggested that over the last twenty years, the recommended curriculum for the study of technology has evolved dramatically in response to a new emphasis on teaching design, the development of standards, and other new initiatives. Welty further stated that, In light of these advancements, technology teacher educators are being challenged to evaluate their technical curricula, to look beyond traditions in teacher education, to reflect on the nature of knowledge, and to update both technical and professional courses for undergraduate technology teacher education (p. 74). The convergence of new standards, accreditation requirements, research on teaching and learning, as well as new state certification policies have forced many technology teacher education programs to consider changes. In addition to these challenges, technology teacher education programs are facing unparalleled external problems. Some of these problems include shortages of entering pre-service teachers, program closures, and shortages of funding to support substantial programmatic adaptations. Pressure also comes from school administrators to maintain or reinstate traditional programs for students with limited abilities, from business and industry to focus on trade-specific courses, from community colleges to prepare students for post-secondary technical programs (Welty, 2003), and from professional associations to include courses related to pre-engineering, design, and technological literacy

The \u3ci\u3eSciedad por Acciones Simplificada\u3c/i\u3e: Suggestions for Further Reform of Mexico\u27s First Unipersonal Limited Liability Entity

Mexico introduced its first unipersonal limited liability entity in 2016, the Sociedad por Acciones Simplificada (“SAS”). The introduction of Mexico’s SAS is in line with legal development in Latin America as a whole, where there has been a recent trend towards introducing new unipersonal limited liability entities that are specially designed to reduce barriers to entry for burgeoning business owners and ease the requirements of owning a business entity. However, the Mexican SAS as it currently exists is uniquely overly restrictive. To remedy this, some of the current restrictions on the entity should be lifted to facilitate the functionality of the entity. Particularly considered for further reform are the five-million-peso total annual income cap, bar on SAS entities having juridical person shareholders, and bar on SAS entities having shareholders who are controlling shareholders in another Mexican entity. The excessive restrictiveness of the Mexican SAS entity is illustrated from three perspectives: legislative intent, rule of law, and comparative law

Measurement of cosmic ray positron and negatron spectra between 50 and 800 MeV

A balloon-borne magnetic spectrometer was used to measure the spectra of cosmic ray positrons and negatrons at energies between 50 and 800 MeV. Comparisons of the separate positron and negatron spectra observed near the earth with their expected intensities in interstellar space can be used to investigate the complex (and variable) interaction of galactic cosmic rays with the expanding solar wind. The present measurements, which have established finite values or upper limits for the positron and negatron spectral between 50 and 800 MeV, have confirmed earlier evidence for the existence of a dominant component of negatrons from primary sources in the galaxy. The present results are shown to be consistent with the hypothesis that the positron component is in fact mainly attributable to collisions between cosmic ray nuclei and the interstellar gas. The estimate of the absolute intensities confirm the indications from neutron monitors that in 1972 the interplanetary cosmic ray intensities were already recovering toward their high levels observed in 1965

Gamma Ray Pulsars: Emission from Extended Polar Cap Cascades

We have used a Monte Carlo simulation of a Polar Cap (PC) model of gamma-ray pulsars to estimate light curves and phase-resolved spectra for sources whose rotational and magnetic axes are oriented so that only one of the magnetic poles produces emission directed at the Earth. In this Single Polar Cap (SPC) scenario, even sources whose light curves have two distinct peaks (Crab, Vela, Geminga, PSR B1951+32) are due to emission concentrated near the rim of a single PC. If the inclination alpha is comparable to the half-width of the PC gamma-beam, alpha ~ theta_{b}, the peak-to-peak phase separation can have the large values (0.4 - 0.5) observed from these sources. In the model presented here we attribute the observed interpeak emission to pair cascades above the PC interior. Our simulation assumes the physics of conventional PC models, in which the gamma rays are due to photon-pair cascades initiated by curvature radiation from the acceleration of electrons above the PCs. In this work we assume that the acceleration occurs over a finite region which may extend up to several radii above the neutron star surface. We find that the combined effects of moderately enlarged PC dimensions and extended acceleration zones resolve a major difficulty with earlier PC models, namely their small beam widths (and hence small detection probabilities). Our best fits to the observed light curves are obtained from models in which the accelerated electrons have a uniform surface density over the PC interior and a sharp density increase of 3 - 5 near the rim.Comment: 31 pages (AASTEX) + 9 figures (uuencoded, compressed ps), to be published in ApJ, Feb. 10 199

Teaching Students Personal and Social Responsibility With Measurable Learning Outcomes

In 2005 the Association of American Colleges and Universities launched a national initiative that championed the importance of a 21st-century liberal education. What was unique about this initiative was the underlying assumption that educating for personal and social responsibility was “core” for an educated citizenry and should be taught. So the question became “How does higher education teach responsibility?” Student affairs divisions atWinthrop University and Rollins College approached this question by focusing on collaborative programs and student learning experiences in the curriculum and cocurriculum with the ability to measure outcomes

Disinfection Byproduct Formation Resulting from Settled, Filtered, and Finished Water Treated by Titanium Dioxide Photocatalysis

This study evaluated strategies targeting disinfection byproduct (DBP) mitigation using TiO2 photocatalysis with varying influent water quality. A Purifics Photo-CAT Lab reactor was used to assess total trihalomethane (TTHM) and haloacetic acid (HAA) formation as a function of photocatalytic treatment using water from a conventional coagulation/flocculation/sedimentation process, granular activated carbon filtration, and a DBP hot spot in the water distribution system. Regardless of influent water quality, photocatalysis reduced DBP precursors; however, low-energy limited photocatalysis (m−3), exacerbated the production of TTHMs and HAA5s beyond initial levels. Accordingly, limited photocatalysis is not a suitable option when TTHMs and HAA5s are a concern, regardless of the level of pretreatment. Limited photocatalysis yields incomplete oxidation, wherein larger, more aromatic, humic organic compounds are broken into smaller molecular weight, less aromatic, and less humic moieties, which have considerable potential to produce DBPs. More complete mineralization of DBP precursors is obtained using extended photocatalysis (80–160 kW h m−3), which substantially decreases DBP precursors as well as TTHM and HAA5 concentrations. In order to balance DBP mitigation, energy, and chemical usage, targeted use of TiO2 photocatalysis is necessary in a water treatment train (e.g., extended photocatalysis at a distribution system hot spot, where the volumetrically high energy requirements may be justifiable)