909 research outputs found
Propellant tank pressurization system Patent
Method and apparatus for pressurizing propellant tanks used in propulsion motor feed syste
Hydrogen slush density reference system
A hydrogen slush density reference system was designed for calibration of field-type instruments and/or transfer standards. The device is based on the buoyancy principle of Archimedes. The solids are weighed in a low-mass container so arranged that solids and container are buoyed by triple-point liquid hydrogen during the weighing process. Several types of hydrogen slush density transducers were developed and tested for possible use as transfer standards. The most successful transducers found were those which depend on change in dielectric constant, after which the Clausius-Mossotti function is used to relate dielectric constant and density
Analyzing Transatlantic Network Traffic over Scientific Data Caches
Large scientific collaborations often share huge volumes of data around the
world. Consequently a significant amount of network bandwidth is needed for
data replication and data access. Users in the same region may possibly share
resources as well as data, especially when they are working on related topics
with similar datasets. In this work, we study the network traffic patterns and
resource utilization for scientific data caches connecting European networks to
the US. We explore the efficiency of resource utilization, especially for
network traffic which consists mostly of transatlantic data transfers, and the
potential for having more caching node deployments. Our study shows that these
data caches reduced network traffic volume by 97% during the study period. This
demonstrates that such caching nodes are effective in reducing wide-area
network traffic
Novel Nonreciprocal Acoustic Effects in Antiferromagnets
The possible occurrence of nonreciprocal acoustic effects in antiferromagnets
in the absence of an external magnetic field is investigated using both (i) a
microscopic formulation of the magnetoelastic interaction between spins and
phonons and (ii) symmetry arguments. We predict for certain antiferromagnets
the existence of two new nonreciprocal (non-time invariant) effects:
A boundary-condition induced nonreciprocal effect and the occurrence of
transversal phonon modes propagating in opposite directions having different
velocities. Estimates are given and possible materials for these effects to be
observed are suggested.Comment: Euro. Phys. Lett. (in press
FACT - Threshold prediction for higher duty cycle and improved scheduling
The First G-APD Cherenkov telescope (FACT) is the first telescope using
silicon photon detectors (G-APD aka. SiPM). The use of Silicon devices promise
a higher photon detection efficiency, more robustness and higher precision than
photo-multiplier tubes. Being operated during different light-conditions, the
threshold settings of a Cherenkov telescope have to be adapted to feature the
lowest possible threshold but also an efficient suppression of triggers from
night-sky background photons. Usually this threshold is set either by
experience or a mini-ratescan. Since the measured current through the sensors
is directly correlated with the noise level, the current can be used to set the
best threshold at any time. Due to the correlation between the physical
threshold and the final energy threshold, the current can also be used as a
measure for the energy threshold of any observation. This presentation
introduces a method which uses the properties of the moon and the source
position to predict the currents and the corresponding energy threshold for
every upcoming observation allowing to adapt the observation schedule
accordingly
FACT - Long-term Monitoring of Bright TeV-Blazars
Since October 2011, the First G-APD Cherenkov Telescope (FACT) is operated
successfully on the Canary Island of La Palma. Apart from the proof of
principle for the use of G-APDs in Cherenkov telescopes, the major goal of the
project is the dedicated long-term monitoring of a small sample of bright TeV
blazars. The unique properties of G-APDs permit stable observations also during
strong moon light. Thus a superior sampling density is provided on time scales
at which the blazar variability amplitudes are expected to be largest, as
exemplified by the spectacular variations of Mrk 501 observed in June 2012.
While still in commissioning, FACT monitored bright blazars like Mrk 421 and
Mrk 501 during the past 1.5 years so far. Preliminary results including the Mrk
501 flare from June 2012 will be presented.Comment: 4 pages, 4 figures, presented at the 33rd ICRC (2013
FACT - Long-term stability and observations during strong Moon light
The First G-APD Cherenkov Telescope (FACT) is the first Cherenkov telescope
equipped with a camera made of silicon photon detectors (G-APD aka. SiPM).
Since October 2011, it is regularly taking data on the Canary Island of La
Palma. G-APDs are ideal detectors for Cherenkov telescopes as they are robust
and stable. Furthermore, the insensitivity of G-APDs towards strong ambient
light allows to conduct observations during bright Moon and twilight. This gain
in observation time is essential for the long-term monitoring of bright TeV
blazars. During the commissioning phase, hundreds of hours of data (including
data from the the Crab Nebula) were taken in order to understand the
performance and sensitivity of the instrument. The data cover a wide range of
observation conditions including different weather conditions, different zenith
angles and different light conditions (ranging from dark night to direct full
Moon). We use a new parmetrisation of the Moon light background to enhance our
scheduling and to monitor the atmosphere. With the data from 1.5 years, the
long-term stability and the performance of the camera during Moon light is
studied and compared to that achieved with photomultiplier tubes so far.Comment: 3 pages, 3 figures, FACT Contribution to the 33rd International
Cosmic Ray Conference (ICRC), Rio de Janeir
FACT - How stable are the silicon photon detectors?
The First G-APD Cherenkov telescope (FACT) is the first telescope using
silicon photon detectors (G-APD aka. SiPM). The use of Silicon devices promise
a higher photon detection efficiency, more robustness and higher precision than
photo-multiplier tubes. Since the properties of G-APDs depend on auxiliary
parameters like temperature, a feedback system adapting the applied voltage
accordingly is mandatory.
In this presentation, the feedback system, developed and in operation for
FACT, is presented. Using the extraction of a single photon-equivalent (pe)
spectrum as a reference, it can be proven that the sensors can be operated with
very high precision. The extraction of the single-pe, its spectrum up to
10\,pe, its properties and their precision, as well as their long-term behavior
during operation are discussed. As a by product a single pulse template is
obtained. It is shown that with the presented method, an additional external
calibration device can be omitted. The presented method is essential for the
application of G-APDs in future projects in Cherenkov astronomy and is supposed
to result in a more stable and precise operation than possible with
photo-multiplier tubes
A Halomethane thermochemical network from iPEPICO experiments and quantum chemical calculations
Internal energy selected halomethane cations CH3Cl+, CH2Cl2+, CHCl3+, CH3F+, CH2F2+, CHClF2+ and CBrClF2+ were prepared by vacuum ultraviolet photoionization, and their lowest energy dissociation channel studied using imaging photoelectron photoion coincidence spectroscopy (iPEPICO). This channel involves hydrogen atom loss for CH3F+, CH2F2+ and CH3Cl+, chlorine atom loss for CH2Cl2+, CHCl3+ and CHClF2+, and bromine atom loss for CBrClF2+. Accurate 0 K appearance energies, in conjunction with ab initio isodesmic and halogen exchange reaction energies, establish a thermochemical network, which is optimized to update and confirm the enthalpies of formation of the sample molecules and their dissociative photoionization products. The ground electronic states of CHCl3+, CHClF2+ and CBrClF2+ do not confirm to the deep well assumption, and the experimental breakdown curve deviates from the deep well model at low energies. Breakdown curve analysis of such shallow well systems supplies a satisfactorily succinct route to the adiabatic ionization energy of the parent molecule, particularly if the threshold photoelectron spectrum is not resolved and a purely computational route is unfeasible. The ionization energies have been found to be 11.47 ± 0.01 eV, 12.30 ± 0.02 eV and 11.23 ± 0.03 eV for CHCl3, CHClF2 and CBrClF2, respectively. The updated 0 K enthalpies of formation, âfHo0K(g) for the ions CH2F+, CHF2+, CHCl2+, CCl3+, CCl2F+ and CClF2+ have been derived to be 844.4 ± 2.1, 601.6 ± 2.7, 890.3 ± 2.2, 849.8 ± 3.2, 701.2 ± 3.3 and 552.2 ± 3.4 kJ molâ1, respectively. The âfHo0K(g) values for the neutrals CCl4, CBrClF2, CClF3, CCl2F2 and CCl3F and have been determined to be â94.0 ± 3.2, â446.6 ± 2.7, â702.1 ± 3.5, â487.8 ± 3.4 and â285.2 ± 3.2 kJ molâ1, respectively
FlashCam: a fully-digital camera for the medium-sized telescopes of the Cherenkov Telescope Array
The FlashCam group is currently preparing photomultiplier-tube based cameras
proposed for the medium-sized telescopes (MST) of the Cherenkov Telescope Array
(CTA). The cameras are designed around the FlashCam readout concept which is
the first fully-digital readout system for Cherenkov cameras, based on
commercial FADCs and FPGAs as key components for the front-end electronics
modules and a high performance camera server as back-end. This contribution
describes the progress of the full-scale FlashCam camera prototype currently
under construction, as well as performance results also obtained with earlier
demonstrator setups. Plans towards the production and implementation of
FlashCams on site are also briefly presented.Comment: 8 pages, 6 figures. In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions
at arXiv:1508.0589
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