On the Excess Dispersion in the Polarization Position Angle of Pulsar Radio Emission

The polarization position angles (PA) of pulsar radio emission occupy a distribution that can be much wider than what is expected from the average linear polarization and the off-pulse instrumental noise. Contrary to our limited understanding of the emission mechanism, the excess dispersion in PA implies that pulsar PAs vary in a random fashion. An eigenvalue analysis of the measured Stokes parameters is developed to determine the origin of the excess PA dispersion. The analysis is applied to sensitive, well-calibrated polarization observations of PSR B1929+10 and PSR B2020+28. The analysis clarifies the origin of polarization fluctuations in the emission and reveals that the excess PA dispersion is caused by the isotropic inflation of the data point cluster formed by the measured Stokes parameters. The inflation of the cluster is not consistent with random fluctuations in PA, as might be expected from random changes in the orientation of the magnetic field lines in the emission region or from stochastic Faraday rotation in either the pulsar magnetosphere or the interstellar medium. The inflation of the cluster, and thus the excess PA dispersion, is attributed to randomly polarized radiation in the received pulsar signal. The analysis also indicates that orthogonal polarization modes (OPM) occur where the radio emission is heavily modulated. In fact, OPM may only occur where the modulation index exceeds a critical value of about 0.3.Comment: Accepted for publication in Ap

Comparative analysis of the secondary electron yield from carbon nanoparticles and pure water medium

The production of secondary electrons generated by carbon nanoparticles and pure water medium irradiated by fast protons is studied by means of model approaches and Monte Carlo simulations. It is demonstrated that due to a prominent collective response to an external field, the nanoparticles embedded in the medium enhance the yield of low-energy electrons. The maximal enhancement is observed for electrons in the energy range where plasmons, which are excited in the nanoparticles, play the dominant role. Electron yield from a solid carbon nanoparticle composed of fullerite, a crystalline form of C60 fullerene, is demonstrated to be several times higher than that from liquid water. Decay of plasmon excitations in carbon-based nanosystems thus represents a mechanism of increase of the low-energy electron yield, similar to the case of sensitizing metal nanoparticles. This observation gives a hint for investigation of novel types of sensitizers to be composed of metallic and organic parts.Comment: 9 pages, 5 figures; accepted for publication in the Topical Issue "COST Action Nano-IBCT: Nano-scale processes behind Ion-Beam Cancer Therapy" of Eur. Phys. J. D. arXiv admin note: text overlap with arXiv:1412.553

Lithium-induced phase transitions in lead-free Bi0. 5Na0. 5TiO3 based ceramics

Lithium-substituted 0.95[0.94(Bi0.5Na(0.5–x)Lix)TiO3–0.06BaTiO3]–0.05CaTiO3 materials include the polar rhombohedral R3c and the weakly polar tetragonal P4bm phases. On increasing lithium content, the (R3c/P4bm) phase ratio decreased, while the rhombohedral and tetragonal lattice distortions remained the same. The temperature corresponding to the shoulder in the dielectric permittivity shows no clear shift with respect to lithium substitution because of the rhombohedral distortion remaining constant. Electrical poling produced an increase of the rhombohedral phase fraction together with a rise of the rhombohedral and tetragonal distortion. This confirmed the occurrence of a phase transition from the weakly polar to the polar phase during electrical poling. Four peaks found in the current–electric field (I–E) loops are related to reversible electric field induced transitions. By studying the temperature dependence of the current peaks in the I–E loops, it was found that the minimum temperature where these electric field induced transitions take place decreases with increasing lithium substitution

Coherently Dedispersed Polarimetry of Millisecond Pulsars

We present a large sample of high-precision, coherently-dedispersed polarization profiles of millisecond pulsars (MSPs) at frequencies between 410 and 1414 MHz. These data include the first polarimetric observations of several of the pulsars, and the first low-frequency polarization profiles for others. Our observations support previous suggestions that the pulse shapes and polarimetry of MSPs are more complex than those of their slower relatives. An immediate conclusion is that polarimetry-based classification schemes proposed for young pulsars are of only limited use when applied to millisecond pulsars.Comment: 28 pages, 10 figures. Text matches version that appeared in ApJS. Full paper with high-resolution figures available at ftp://ftp.jb.man.ac.uk/pub/psr/papers/msppolpton.ps.g

Engaging adolescent Kyrgyzstani EFL students in digital storytelling projects about astronomy

This research is based on the Journey through Space and Time (JTST) educational astronomy project for primary and junior high school science curricula in Australia, which seeks to improve students\u27 astronomy content knowledge through science inquiry. The focus of the current project is on the learning needs of students for whom the language of instruction is a foreign or second language (EFL/ESL). This article reports the results of a pilot case study conducted in Bishkek, Kyrgyzstan in December 2017. The research employed a Type II Case Study design. Data were collected through video and audio recordings of classroom interactions. The Astronomy Diagnostic Test measured changes in content knowledge and written feedback at the end of the course and helped to understand students\u27 overall impression from the course. The study revealed that engaging Kyrgyzstani EFL students aged between 12 and 15 years in making videos about their learning of astronomy significantly facilitated their content knowledge acquisition. This research contributes to the existing knowledge about the use of technology in students\u27 science education, and specifically as a tool to enhance EFL students\u27 understanding of the integrated science, technology engineering and mathematics (STEM) curriculum. The results of the shared knowledge construction stimulated by the collaboration in video production create a case for further research in EFL students\u27 disciplinary literacy development

Screening for HIV-Associated Neurocognitive Impairment

Neurocognitive impairment (NCI) is common in people aging with HIV and can adversely affect health-related quality of life. However, early NCI may be largely asymptomatic and neurocognitive function is rarely assessed in the context of routine clinical care. In this study, we considered the utility of two assessment tools as screens for NCI in patients attending a community-based clinic (N=58; mean age=57 years): the Montreal Cognitive Assessment (MoCA) and a 3-item cognitive concerns questionnaire derived from the HIV Dementia Scale. Health-related quality of life and depression/anxiety were also measured. Indication of NCI using the MoCA was more prevalent compared to the 3-item questionnaire and was associated with the patients’ initial antiretroviral therapy commencing between the years of 1997 and 2001, independently of age. Findings of the MoCA were not confounded by existing mood disorders, unlike the 3-item questionnaire. Therefore, we suggest implementing the MoCA as an initial screen for NCI

Licensing Support Network: An Electronic Discovery System

The necessary authorization for the U. S. Department of Energy's (DOE) Office of Civilian Radioactive Waste Management (OCRWM) to submit a License Application (LA) is contingent upon the policy process defined in the Nuclear Waste Policy Act, as amended (NWPA), with some steps yet to occur. In spite of this uncertainty, the DOE must take prudent and appropriate action now, and over the next several years, to prepare for submittal of an application and to facilitate the U. S. Nuclear Regulatory Commission (NRC) review of this application, if the Yucca Mountain site is recommended and approved for repository development. One of these steps the DOE has taken involves working with the NRC's Advisory Review Panel to develop Licensing Support Network (LSN) requirements and guidelines. The NRC has made a prototype of the LSN web page available at www.LSNNET.gov. The OCRWM part of the LSN currently has an indefinite life cycle and may need to remain in existence until the repository is closed, which could be as long as 325 years

Bohmian arrival time without trajectories

The computation of detection probabilities and arrival time distributions within Bohmian mechanics in general needs the explicit knowledge of a relevant sample of trajectories. Here it is shown how for one-dimensional systems and rigid inertial detectors these quantities can be computed without calculating any trajectories. An expression in terms of the wave function and its spatial derivative, both restricted to the boundary of the detector's spacetime volume, is derived for the general case, where the probability current at the detector's boundary may vary its sign.Comment: 20 pages, 12 figures; v2: reference added, extended introduction, published versio