4,856 research outputs found
On the applicability of Taylor's hypothesis in streaming magnetohydrodynamic turbulence
We examine the range of applicability of Taylor's hypothesis used in
observations of magnetic turbulence in the solar wind. We do not refer to
turbulence theory. We simply ask whether in a turbulent magnetohydrodynamic
flow the observed magnetic frequency spectrum can be interpreted as mapping of
the wavenumber turbulence into the stationary spacecraft frame. In addition to
the known restrictions on the angle of propagation with respect to the
fluctuation spectrum and the question on the wavenumber dependence of the
frequency in turbulence which we briefly review, we show that another
restriction concerns the inclusion or exclusion of turbulent fluctuations in
the velocity field. Taylor's hypothesis in application to magnetic (MHD)
turbulence encounters its strongest barriers here. It is applicable to magnetic
turbulence only when the turbulent velocity fluctuations can practically be
completely neglected against the bulk flow speed. For low flow speeds the
transformation becomes rather involved. This account makes even no use of the
additional scale dependence of the turbulent frequency, viz. the existence of a
"turbulent dispersion relation".Comment: 31 pages, 3 figures, submitted to Earth, Planets & Spac
On the ion-inertial range density power spectra in solar wind turbulence
A model-independent first-principle first-order investigation of the shape of
turbulent density-power spectra in the ion-inertial range of the solar wind at
1 AU is presented. De-magnetised ions in the ion-inertial range of
quasi-neutral plasmas respond to Kolmogorov (K) or Iroshnikov-Kraichnan (IK)
inertial-range velocity turbulence power spectra via the spectrum of the
velocity-turbulence-related random-mean-square induction-electric field.
Maintenance of electrical quasi-neutrality by the ions causes deformations in
the power spectral density of the turbulent density fluctuations. Kolmogorov
inertial range spectra in solar wind velocity turbulence and observations of
density power spectra suggest that the occasionally observed scale-limited
bumps in the density-power spectrum may be traced back to the electric ion
response. Magnetic power spectra react passively to the density spectrum by
warranting pressure balance. This approach still neglects contribution of Hall
currents and is restricted to the ion-inertial range scale. While both density
and magnetic turbulence spectra in the affected range of ion-inertial scales
deviate from Kolmogorov or Iroshnikov-Kraichnan, the velocity turbulence
preserves its inertial range shape in this process to which spectral advection
turns out to be secondary but may become observable under special external
conditions. One such case observed by WIND is analysed. We discuss various
aspects of this effect including the affected wavenumber scale range,
dependence on angle between mean flow velocity and wavenumber and, for a
radially expanding solar wind flow when assuming adiabatic expansion at fast
solar wind speeds and a Parker dependence of the solar wind magnetic field on
radius, also the presumable limitations on the radial location of the turbulent
source region.Comment: Pages 18, Figures 5, Discussion paper submitte
Detailed Studies of Pixelated CZT Detectors Grown with the Modified Horizontal Bridgman Method
The detector material Cadmium Zinc Telluride (CZT), known for its high
resolution over a broad energy range, is produced mainly by two methods: the
Modified High-Pressure Bridgman (MHB) and the High-Pressure Bridgman (HPB)
process. This study is based on MHB CZT substrates from the company Orbotech
Medical Solutions Ltd. with a detector size of 2.0x2.0x0.5 cm^3, 8x8 pixels and
a pitch of 2.46 mm. Former studies have emphasized only on the cathode material
showing that high-work-function improve the energy resolution at lower
energies. Therfore, we studied the influence of the anode material while
keeping the cathode material constant. We used four different materials:
Indium, Titanium, Chromium and Gold with work-functions between 4.1 eV and 5.1
eV. The low work-function materials Indium and Titanium achieved the best
performance with energy resolutions: 2.0 keV (at 59 keV) and 1.9 keV (at 122
keV) for Titanium; 2.1 keV (at 59 keV) and 2.9 keV (at 122 keV) for Indium.
These detectors are very competitive compared with the more expensive ones
based on HPB material if one takes the large pixel pitch of 2.46 mm into
account. We present a detailed comparison of our detector response with 3-D
simulations, from which we determined the mobility-lifetime-products for
electrons and holes. Finally, we evaluated the temperature dependency of the
detector performance and mobility-lifetime-products, which is important for
many applications. With decreasing temperature down to -30C the breakdown
voltage increases and the electron mobility-lifetime-product decreases by about
30% over a range from 20C to -30C. This causes the energy resolution to
deteriorate, but the concomitantly increasing breakdown voltage makes it
possible to increase the applied bias voltage and restore the full performance.Comment: Accepted for publication in Astroparticle Physics, 25 pages, 13
figure
The Prograde Orbit of Exoplanet TrES-2b
We monitored the Doppler shift of the G0V star TrES-2 throughout a transit of
its giant planet. The anomalous Doppler shift due to stellar rotation (the
Rossiter-McLaughlin effect) is discernible in the data, with a signal-to-noise
ratio of 2.9, even though the star is a slow rotator. By modeling this effect
we find that the planet's trajectory across the face of the star is tilted by
-9 +/- 12 degrees relative to the projected stellar equator. With 98%
confidence, the orbit is prograde.Comment: ApJ, in press [15 pages
THE ROLE OF SOCIAL SERVICES AND COMMUNITY EMPOWERMENT IN HANDLING CHILDREN OF STREET VENDORS ON M. YAMIN STREET AND JUANDA STREET, SAMARINDA CITY: PERAN DINAS SOSIAL DAN PEMBERDAYAAN MASYARAKAT DALAM PENANGANAN ANAK-ANAK PEDAGANG ASONGAN DI JALAN M. YAMIN DAN JALAN JUANDA KOTA SAMARINDA
Penelitian ini bertujuan untuk mengidentifikasi dan menggambarkan peran Dinas Sosial dan Pemberdayaan Masyarakat dalam menangani anak-anak pedagang asongan di Jalan M. Yamin dan Jalan Juanda Kota Samarinda. Penelitian ini menggunakan teori peran Jim Ife, yang mencakup peran fasilitasi, edukasi, representasi, dan teknis. Penelitian menggunakan deskriptif kualitatif. Untuk mengidentifikasi informan penelitian menggunakan metode purposive dan accidental sampling. Data primer dan sekunder adalah bagian dari sumber data. Pengumpulan data dilakukan melalui observasi, wawancara, dokumentasi, dan studi kepustakaan. Kemudian, data dievaluasi melalui teknik reduksi, penyajian, dan penarikan kesimpulan. Hasil penelitian menunjukkan bahwa Dinas Sosial berfungsi sebagai fasilitator dan bekerja sama dengan panti asuhan untuk menyediakan fasilitas setiap tahun. Edukasi mereka menawarkan pendidikan formal dan nonformal. Perwakilan Dinas Sosial bekerja sama dengan lembaga masyarakat seperti satpol PP, kepolisian, dan masyarakat. Selain itu, pendataan teknis dilakukan sesuai dengan standar operasional prosedur (SOP)
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