764 research outputs found
Constraining Radon Backgrounds in LZ
The LZ dark matter detector, like many other rare-event searches, will suffer
from backgrounds due to the radioactive decay of radon daughters. In order to
achieve its science goals, the concentration of radon within the xenon should
not exceed Bq/kg, or 20 mBq total within its 10 tonnes. The LZ
collaboration is in the midst of a program to screen all significant components
in contact with the xenon. The four institutions involved in this effort have
begun sharing two cross-calibration sources to ensure consistent measurement
results across multiple distinct devices. We present here five preliminary
screening results, some mitigation strategies that will reduce the amount of
radon produced by the most problematic components, and a summary of the current
estimate of radon emanation throughout the detector. This best estimate totals
mBq, sufficiently low to meet the detector's science goals.Comment: Low Radioactivity Techniques (LRT) 2017 Workshop Proceedings. 6
pages; 3 figure
Flight mechanics experiment onboard nasaâs zero gravity aircraft
This paper presents a method to promote STEM (Science, Technology, Engineering, and Mathematics) education through participation in a reduced gravity program with NASA (National Aeronautics and Space Administration). Microgravity programs with NASA provide students with a unique opportunity to conduct scientific research with innovative and creative solutions through hands-on experimental design and testing in reduced gravity conditions. A group of undergraduate students from California State Polytechnic University, Pomona, participated in the NASAâs SEED (Systems Engineering Educational Discovery) Reduced Gravity Program, which focuses on addressing systems engineering challenges in microgravity. The team worked with a NASA Principal Investigator on a project to build and fly a prototype test article to demonstrate emergency atmospheric reentry with single-axis control. Through this experience, the team was able to gain hands-on experience with spacecraft instrumentation and learn valuable lessons in teamwork and systems engineering that can be applied to real-world situations. As part of the SEED program, the team shared its experience with local high schools in order to spark interest in STEM-related fields in the next generation of scientists and engineers.Peer Reviewe
Solar wind interaction with comet 67P: impacts of corotating interaction regions
International audienceWe present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) to comet 67P from October to December 2014. When the comet is 3.1â2.7 AU from the Sun and the neutral outgassing rate âŒ1025â1026 sâ1, the CIRs significantly influence the cometary plasma environment at altitudes down to 10â30 km. The ionospheric low-energy (âŒ5 eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below â20 V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (âŒ10â100 eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2â5 as more interplanetary magnetic field piles up around the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events
Photometry of comet 9P/Tempel 1 during the 2004/2005 approach and the Deep Impact module impact
The results of the 9P/Tempel 1 CARA (Cometary Archive for Amateur
Astronomers) observing campaign is presented. The main goal was to perform an
extended survey of the comet as a support to the Deep Impact (DI) Mission. CCD
R, I and narrowband aperture photometries were used to monitor the
quantity. The observed behaviour showed a peak of 310 cm 83 days before
perihelion, but we argue that it could be distorted by the phase effect, too.
The phase effect is roughly estimated around 0.0275 mag/degree, but we had no
chance for direct determination because of the very similar geometry of the
observed apparitions. The log-slope of was around -0.5 between about
180--100 days before the impact but evolved near the steady-state like 0 value
by the impact time. The DI module impact caused an about 60%{} increase in the
value of and a cloud feature in the coma profile which was observed
just after the event. The expansion of the ejecta cloud was consistent with a
fountain model with initial projected velocity of 0.2 km/s and =0.73.
Referring to a 25~000 km radius area centered on the nucleus, the total cross
section of the ejected dust was 8.2/ km 0.06 days after the impact, and
1.2/ km 1.93 days after the impact ( is the dust albedo). 5 days
after the event no signs of the impact were detected nor deviations from the
expected activity referring both to the average pre-impact behaviour and to the
previous apparitions ones.Comment: 25 pages (including cover pages), 9 figures, 1 table, accepted by
Icarus DI Special Issu
A virtual seed file: the use of multispectral image analysis in the management of genebank seed accessions
We present a method for multispectral seed phenotyping as a fast and robust tool for managing genebank accessions. A multispectral vision system was used to take images of the seeds of 20 diverse varieties of rice (approximately 30 seeds for each variety). This was followed by extraction of feature information from the images. Multivariate analysis of the feature data was used to classify seed phenotypes according to accession. The proportion of correctly classified rice seeds was 93%. We conclude that the multispectral image analysis could play a role in comparing incoming seeds against existing accessions, identifying different seed types within a sample of seeds and/or in checking whether regenerated seeds match the original seeds.</jats:p
Spatial distribution of low-energy plasma around 2 comet 67P/CG from Rosetta measurements
International audienceWe use measurements from the Rosetta plasma consortium (RPC) Langmuir probe (LAP) and mutual impedance probe (MIP) to study the spatial distribution of low-energy plasma in the near-nucleus coma of comet 67P/Churyumov-Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e. the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be âŒ1-2·10 â6 , at a cometocentric distance of 10 km and at 3.1 AU from the sun. A clear 6.2 h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisonless plasma within 260 km from the nucleus falls of with radial distance as âŒ1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet
Rosetta and Mars Express observations of the influence of high solar wind pressure on the Martian plasma environment
International audienceWe report on new simultaneous in-situ observations at Mars from Rosetta and Mars Express (MEX) on how the Martian plasma environment is affected by high pressure solar wind. A significant sharp increase in solar wind density, magnetic field strength and turbulence followed by a gradual increase in solar wind velocity is observed during ~24 h in the combined data set from both spacecraft after Rosetta's closest approach to Mars on 25 February 2007. The bow shock and magnetic pileup boundary are coincidently observed by MEX to become asymmetric in their shapes. The fortunate orbit of MEX at this time allows a study of the inbound boundary crossings on one side of the planet and the outbound crossings on almost the opposite side, both very close to the terminator plane. The solar wind and interplanetary magnetic field (IMF) downstream of Mars are monitored through simultaneous measurements provided by Rosetta. Possible explanations for the asymmetries are discussed, such as crustal magnetic fields and IMF direction. In the same interval, during the high solar wind pressure pulse, MEX observations show an increased amount of escaping planetary ions from the polar region of Mars. We link the high pressure solar wind with the observed simultaneous ion outflow and discuss how the pressure pulse could also be associated with the observed boundary shape asymmetry
Isomorphs in model molecular liquids
Isomorphs are curves in the phase diagram along which a number of static and
dynamic quantities are invariant in reduced units. A liquid has good isomorphs
if and only if it is strongly correlating, i.e., the equilibrium
virial/potential energy fluctuations are more than 90% correlated in the NVT
ensemble. This paper generalizes isomorphs to liquids composed of rigid
molecules and study the isomorphs of two systems of small rigid molecules, the
asymmetric dumbbell model and the Lewis-Wahnstrom OTP model. In particular, for
both systems we find that the isochoric heat capacity, the excess entropy, the
reduced molecular center-of-mass self part of the intermediate scattering
function, the reduced molecular center-of-mass radial distribution function to
a good approximation are invariant along an isomorph. In agreement with theory,
we also find that an instantaneous change of temperature and density from an
equilibrated state point to another isomorphic state point leads to no
relaxation. The isomorphs of the Lewis-Wahnstrom OTP model were found to be
more approximative than those of the asymmetric dumbbell model, which is
consistent with the OTP model being less strongly correlating. For both models
we find "master isomorphs", i.e., isomorphs have identical shape in the
virial/potential energy phase diagram.Comment: 20 page
High Precision Astrometry with MICADO at the European Extremely Large Telescope
In this article we identify and discuss various statistical and systematic
effects influencing the astrometric accuracy achievable with MICADO, the
near-infrared imaging camera proposed for the 42-metre European Extremely Large
Telescope (E-ELT). These effects are instrumental (e.g. geometric distortion),
atmospheric (e.g. chromatic differential refraction), and astronomical
(reference source selection). We find that there are several phenomena having
impact on ~100 micro-arcsec scales, meaning they can be substantially larger
than the theoretical statistical astrometric accuracy of an optical/NIR
42m-telescope. Depending on type, these effects need to be controlled via
dedicated instrumental design properties or via dedicated calibration
procedures. We conclude that if this is done properly, astrometric accuracies
of 40 micro-arcsec or better - with 40 micro-arcsec/year in proper motions
corresponding to ~20 km/s at 100 kpc distance - can be achieved in one epoch of
actual observationsComment: 15 pages, 9 figures, 3 tables. Accepted by MNRA
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