225 research outputs found
In situ observations of waves in Venus’s polar lower thermosphere with Venus Express aerobraking
Waves are ubiquitous phenomena found in oceans and atmospheres alike. From the earliest formal studies of waves in the Earth’s atmosphere to more recent studies on other planets, waves have been shown to play a key role in shaping atmospheric bulk structure, dynamics and variability1, 2, 3, 4. Yet, waves are difficult to characterize as they ideally require in situ measurements of atmospheric properties that are difficult to obtain away from Earth. Thus, we have incomplete knowledge of atmospheric waves on planets other than our own, and we are thereby limited in our ability to understand and predict planetary atmospheres. Here we report the first ever in situ observations of atmospheric waves in Venus’s thermosphere (130–140 km) at high latitudes (71.5°–79.0°). These measurements were made by the Venus Express Atmospheric Drag Experiment (VExADE)5 during aerobraking from 24 June to 11 July 2014. As the spacecraft flew through Venus’s atmosphere, deceleration by atmospheric drag was sufficient to obtain from accelerometer readings a total of 18 vertical density profiles. We infer an average temperature of T = 114 ± 23 K and find horizontal wave-like density perturbations and mean temperatures being modulated at a quasi-5-day period
GEO debris and interplanetary dust: fluxes and charging behavior
In September 1996, a dust/debris detector: GORID was launched into the
geostationary (GEO) region as a piggyback instrument on the Russian Express-2
telecommunications spacecraft. The instrument began its normal operation in
April 1997 and ended its mission in July 2002. The goal of this work was to use
GORID's particle data to identify and separate the space debris to
interplanetary dust particles (IDPs) in GEO, to more finely determine the
instrument's measurement characteristics and to derive impact fluxes. While the
physical characteristics of the GORID impacts alone are insufficient for a
reliable distinction between debris and interplanetary dust, the temporal
behavior of the impacts are strong enough indicators to separate the
populations based on clustering. Non-cluster events are predominantly
interplanetary, while cluster events are debris. The GORID mean flux
distributions (at mass thresholds which are impact speed dependent) for IDPs,
corrected for dead time, are 1.35x10^{-4} m^{-2} s^{-1} using a mean detection
rate: 0.54 d^{-1}, and for space debris are 6.1x10^{-4} m^{-2} s^{-1} using a
mean detection rate: 2.5 d^{-1}. Beta-meteoroids were not detected. Clusters
could be a closely-packed debris cloud or a particle breaking up due to
electrostatic fragmentation after high charging.Comment: * Comments: 6 pages, 4 postscript figures, in Dust in Planetary
Systems 2005, Krueger, H. and Graps, A. eds., ESA Publications, SP in press
(2006). For high resolution version, see:
http://www.mpi-hd.mpg.de/dustgroup/~graps/dips2005/GrapsetalDIPS2005.pd
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A comparative analysis of Simplified General Circulation Models of the atmosphere of Venus
Within the context of a working group supported by ISSI (Bern, Switzerland), we have made an intercomparison work between Global Circulation Models using simpli?ed parameterizations for radiative forcing and other physical processes. Even with similar schemes and parameters, the different GCMs produce different circulations, illustrating interesting differences between dynamical model cores
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Differential item functioning for items in Berger's HIV Stigma Scale: an analysis of cohorts from the Indian, Swedish, and US contexts
PURPOSE: To examine whether items in Berger's HIV Stigma Scale function differently with persons of different age, gender, and cultural backgrounds.
METHODS: Secondary data from cohorts, collected in South India (n = 250), Sweden (n = 193), and the US (n = 603) were reanalyzed to evaluate DIF within, between, and across these cohorts. All participants had answered the revised version of the HIV stigma scale consisting of 32 items forming the subscales Personalized stigma, Disclosure concerns, Concerns about public attitudes, and Negative self-image. Differential Item Functioning (DIF) for these items was assessed using hybrid ordinal regression-IRT technique. When DIF was detected, the cumulative impact of DIF on individual subscale scores was evaluated.
RESULTS: DIF was detected for 9 items within, between, or across cohorts, but the DIF was negligible in general. Detected DIF between the Swedish and Indian cohorts had a cumulative salient impact on individual scores for the subscale Disclosure Concerns; Disclosure concerns were overestimated in the Swedish cohort and both over- and underestimated in the Indian cohort.
CONCLUSIONS: The items in the 32-item version of the HIV stigma scale did not seem to be particularly prone to present DIF. The DIF between the Indian and Swedish cohort for items in the subscale Disclosure Concerns could, however, result in both type I and type II errors if scores should be compared between the Indian and Swedish cohort
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Differential item functioning for items in Berger's HIV Stigma Scale: an analysis of cohorts from the Indian, Swedish, and US contexts
PURPOSE: To examine whether items in Berger's HIV Stigma Scale function differently with persons of different age, gender, and cultural backgrounds. METHODS: Secondary data from cohorts, collected in South India (n = 250), Sweden (n = 193), and the US (n = 603) were reanalyzed to evaluate DIF within, between, and across these cohorts. All participants had answered the revised version of the HIV stigma scale consisting of 32 items forming the subscales Personalized stigma, Disclosure concerns, Concerns about public attitudes, and Negative self-image. Differential Item Functioning (DIF) for these items was assessed using hybrid ordinal regression-IRT technique. When DIF was detected, the cumulative impact of DIF on individual subscale scores was evaluated. RESULTS: DIF was detected for 9 items within, between, or across cohorts, but the DIF was negligible in general. Detected DIF between the Swedish and Indian cohorts had a cumulative salient impact on individual scores for the subscale Disclosure Concerns; Disclosure concerns were overestimated in the Swedish cohort and both over- and underestimated in the Indian cohort. CONCLUSIONS: The items in the 32-item version of the HIV stigma scale did not seem to be particularly prone to present DIF. The DIF between the Indian and Swedish cohort for items in the subscale Disclosure Concerns could, however, result in both type I and type II errors if scores should be compared between the Indian and Swedish cohort
An ATP-binding cassette-type cysteine transporter in Campylobacter jejuni inferred from the structure of an extracytoplasmic solute receptor protein
Campylobacter jejuni is a Gram-negative food-borne pathogen associated with gastroenteritis in humans as well as cases of the autoimmune disease Guillain Barre syndrome. C. jejuni is asaccharolytic because it lacks an active glycolytic pathway for the use of sugars as a carbon source. This suggests an increased reliance on amino acids as nutrients and indeed the genome sequence of this organism indicates the presence of a number of amino acid uptake systems. Cj0982, also known as CjaA, is a putative extracytoplasmic solute receptor for one such uptake system as well as a major surface antigen and vaccine candidate. The crystal structure of Cj0982 reveals a two-domain protein with density in the enclosed cavity between the domains that clearly defines the presence of a bound cysteine ligand. Fluorescence titration experiments were used to demonstrate that Cj0982 binds cysteine tightly and specifically with a K-d of similar to 10(-7) M consistent with a role as a receptor for a high- affinity transporter. These data imply that Cj0982 is the binding protein component of an ABC-type cysteine transporter system and that cysteine uptake is important in the physiology of C. jejuni
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SMART-1 Impact Ground-based campaign
Based on predictions of impact magnitude and cloud ejecta dynamics, we organized a SMART-1 ground-based observation campaign to perform coordinated measurements of the impact. Results from the coordinated multi-site campaign will be discussed
Hot flow anomalies at Venus
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95474/1/jgra21752.pd
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