479 research outputs found
Fertigung laminarer optischer Gitter am HZB
Laminare optische Gitter stellen höchste Anforderungen an die mikrosystemtechnische Fertigung der Mikro und Nano strukturen in Hinsicht auf PrĂ€zision und HomogenitĂ€t. Im Rahmen des EU Projektes Aufbau eines Technologiezent rums fĂŒr hocheffiziente optische PrĂ€zisionsgitter am Helmholtz Zentrum Berlin HZB EFRE Vertrag Nr. 20072013 2 43 [1,2] wurden die fĂŒr die Herstellung von laminaren und geblazten Gittern notwendigen Anlagen in Betrieb ge nommen. Gleichzeitig wurde mit der Prozessentwicklung begonnen. In diesem Artikel werden die neuesten Prozessergebnisse von durch Laserinterferenzlithographie LIL in Photoresist erzeugter Gitterstrukturen und deren nur wenige Nanometer tiefe Ăbertragung in Siliziumsubstrate mittels Ionenstrahl Ă€tzen vorgestellt. english version Laminar optical gratings impose highest demands on microsystem technological manufacturing with regard to precision and uniformity. Within the project Installation of a technology centre for highly efficient precision gratings at Helm holtz Zentrum Berlin HZB EFRE Vertrag Nr. 20072013 2 43 [1,2] the necessary systems for the manufacturing of laminar and blazed gratings were taken into operation and process development has started. In this article we present the results of grating structures manufactured with laser interference lithography and subse quent ion beam etchin
Using NuRadioMC to study the performance of UHE radio neutrino detectors
NuRadioMC is an open-source, Python-based simulation and reconstruction framework for radio detectors of ultra-high energy neutrinos and cosmic rays. Its modular design makes NuRadioMC suitable for use with a range of past, current and future detectors. In addition, the recent deployment
of a complete documentation as well as a pip release make NuRadioMC relatively easy to learn and use. Here, we outline the features currently available and under development in NuRadioMC, with a focus on its usage to simulate and study in-ice radio neutrino detectors
Schooling for violence and peace : how does peace education differ from ânormalâ schooling?
This article reviews literature on the roles of schooling in both reproducing and actively perpetrating violence, and sets out an historical explanation of why schools are socially constructed in such a way as to make these roles possible. It then discusses notions of peace education in relation to one particular project in England before using empirical data from research on the project to examine contrasts between peace education approaches and ânormalâ schooling from the viewpoints of project workers, pupils and teachers. It concludes that such contrasts and tensions do indeed exist and that this raises serious questions about the compatibility of peace education and formal schooling
Interferometric imaging of intensely radiating negative leaders
The common phenomenon of lightning still harbors many secrets and only recently a new propagation mode was observed for negative leaders. While propagating in this "intensely radiating negative leader"(IRNL) mode a negative leader emits 100 times more very-high frequency (VHF) and broadband radiation than a more normal negative leader. We have reported that this mode occurs soon after initiation of all lightning flashes we have mapped as well as sometimes long thereafter. Because of the profuse emission of VHF the leader structure is very difficult to image. In this work we report on measurements made with the LOFAR radio telescope, an instrument primarily built for radio-astronomy observations. For this reason, as part of the present work, we have refined our time resolved interferometric 3-dimensional (TRI-D) imaging to take into account the antenna function. The images from the TRI-D imager show that during an IRNL there is an ionization front with a diameter in excess of 500 m where strong corona bursts occur. This is very different from what is seen for a normal negative leader where the corona bursts happen at the tip, an area of typically 10 m in diameter. The observed massive ionization wave supports the idea that this mode is indicative of a dense charge pocket
Interferometric imaging of intensely radiating negative leaders
The common phenomenon of lightning still harbors many secrets and only recently a new propagation mode was observed for negative leaders. While propagating in this `Intensely Radiating Negative Leader\u27 (IRNL) mode a negative leader emits 100 times more very-high frequency (VHF) and broadband radiation than a more normal negative leader. We have reported that this mode occurs soon after initiation of all lightning flashes we have mapped as well as sometimes long thereafter. Because of the profuse emission of VHF the leader structure is very difficult to image. In this work we report on measurements made with the LOFAR radio telescope, an instrument primarily built for radio-astronomy observations. For this reason, as part of the present work, we have refined our time resolved interferometric 3-Dimensional (TRI-D) imaging to take into account the antenna function. The images from the TRI-D imager show that during an IRNL there is an ionization front with a diameter in excess of 500~m where strong corona bursts occur. This is very different from what is seen for a normal negative leader where the corona bursts happen at the tip, an area of typically 10~m in diameter. The observed massive ionization wave supports the idea that this mode is indicative of a dense charge pocket
Imaging Jupiter's radiation belts down to 127 MHz with LOFAR
Context. Observing Jupiter's synchrotron emission from the Earth remains
today the sole method to scrutinize the distribution and dynamical behavior of
the ultra energetic electrons magnetically trapped around the planet (because
in-situ particle data are limited in the inner magnetosphere). Aims. We perform
the first resolved and low-frequency imaging of the synchrotron emission with
LOFAR at 127 MHz. The radiation comes from low energy electrons (~1-30 MeV)
which map a broad region of Jupiter's inner magnetosphere. Methods (see article
for complete abstract) Results. The first resolved images of Jupiter's
radiation belts at 127-172 MHz are obtained along with total integrated flux
densities. They are compared with previous observations at higher frequencies
and show a larger extent of the synchrotron emission source (>=4 ). The
asymmetry and the dynamic of east-west emission peaks are measured and the
presence of a hot spot at lambda_III=230 {\deg} 25 {\deg}. Spectral flux
density measurements are on the low side of previous (unresolved) ones,
suggesting a low-frequency turnover and/or time variations of the emission
spectrum. Conclusions. LOFAR is a powerful and flexible planetary imager. The
observations at 127 MHz depict an extended emission up to ~4-5 planetary radii.
The similarities with high frequency results reinforce the conclusion that: i)
the magnetic field morphology primarily shapes the brightness distribution of
the emission and ii) the radiating electrons are likely radially and
latitudinally distributed inside about 2 . Nonetheless, the larger extent
of the brightness combined with the overall lower flux density, yields new
information on Jupiter's electron distribution, that may shed light on the
origin and mode of transport of these particles.Comment: 10 pages, 12 figures, accepted for publication in A&A (27/11/2015) -
abstract edited because of limited character
Observation of classically `forbidden' electromagnetic wave propagation and implications for neutrino detection
Ongoing experimental efforts in Antarctica seek to detect ultra-high energy
neutrinos by measurement of radio-frequency (RF) Askaryan radiation generated
by the collision of a neutrino with an ice molecule. An array of RF antennas,
deployed either in-ice or in-air, is used to infer the properties of the
neutrino. To evaluate their experimental sensitivity, such experiments require
a refractive index model for ray tracing radio-wave trajectories from a
putative in-ice neutrino interaction point to the receiving antennas; this
gives the degree of signal absorption or ray bending from source to receiver.
The gradient in the density profile over the upper 200 meters of Antarctic ice,
coupled with Fermat's least-time principle, implies ray "bending" and the
existence of "forbidden" zones for predominantly horizontal signal propagation
at shallow depths. After re-deriving the formulas describing such shadowing, we
report on experimental results that, somewhat unexpectedly, demonstrate the
existence of electromagnetic wave transport modes from nominally shadowed
regions. The fact that this shadow-signal propagation is observed both at South
Pole and the Ross Ice Shelf in Antarctica suggests that the effect may be a
generic property of polar ice, with potentially important implications for
experiments seeking to detect neutrinos.Comment: 33 pages, 14 figures, accepted for publication in JCA
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