31 research outputs found
Stratifications of Newton polygon strata and Traverso's conjectures for p-divisible groups
The isomorphism number (resp. isogeny cutoff) of a p-divisible group D over
an algebraically closed field is the least positive integer m such that D[p^m]
determines D up to isomorphism (resp. up to isogeny). We show that these
invariants are lower semicontinuous in families of p-divisible groups of
constant Newton polygon. Thus they allow refinements of Newton polygon strata.
In each isogeny class of p-divisible groups, we determine the maximal value of
isogeny cutoffs and give an upper bound for isomorphism numbers, which is shown
to be optimal in the isoclinic case. In particular, the latter disproves a
conjecture of Traverso. As an application, we answer a question of Zink on the
liftability of an endomorphism of D[p^m] to D.Comment: 50 pages, to appear in Annals of Mathematic
The Pointing System of the Herschel Space Observatory. Description, Calibration, Performance and Improvements
We present the activities carried out to calibrate and characterise the
performance of the elements of attitude control and measurement on board the
Herschel spacecraft. The main calibration parameters and the evolution of the
indicators of the pointing performance are described, from the initial values
derived from the observations carried out in the performance verification phase
to those attained in the last year and half of mission, an absolute pointing
error around or even below 1 arcsec, a spatial relative pointing error of some
1 arcsec and a pointing stability below 0.2 arsec. The actions carried out at
the ground segment to improve the spacecraft pointing measurements are
outlined. On-going and future developments towards a final refinement of the
Herschel astrometry are also summarised. A brief description of the different
components of the attitude control and measurement system (both in the space
and in the ground segments) is also given for reference. We stress the
importance of the cooperation between the different actors (scientists, flight
dynamics and systems engineers, attitude control and measurement hardware
designers, star-tracker manufacturers, etc.) to attain the final level of
performance.Comment: 28 pages, 8 figures, accepted for publication in Experimental
Astronom
Stellar Encounters with the Beta Pictoris Planetesimal System
We use data from the Hipparcos Catalog and the Barbier-Brossat & Figon (2000)
catalog of stellar radial velocities to test the hypothesis that the Beta Pic
planetesimal disk was disrupted by a close stellar encounter. We trace the
space motions of 21,497 stars and discover 18 that have passed within 5 pc of
Beta Pic in the past 1 Myr. Beta Pic's closest encounter is with the K2III star
HIP 27628 (0.6 pc), but dynamically the most important encounter is with the
F7V star HIP 23693 (0.9 pc). We calculate the velocity and eccentricity changes
induced by the 18 perturbations and conclude that they are dynamically
significant if planetesimals exist in a Beta Pic Oort cloud. We provide a
first-order estimate for the evolutionary state of a Beta Pic Oort cloud and
conclude that the primary role of these stellar perturbations would be to help
build a comet cloud rather than destroy a pre-existing structure. The stellar
sample is 20% complete and motivates future work to identify less common close
interactions that would significantly modify the observed circumstellar disk.
For future radial velocity study we identify six stars in the Hipparcos Catalog
that may have approached Beta Pic to within 0.1 pc and therefore remain as
candidate disk perturbers.Comment: 23 pages, 5 figures, Accepted for publication in Ap
Supersymmetric Dark Matter
There is almost universal agreement among astronomers that most of the mass
in the Universe and most of the mass in the Galactic halo is dark. Many lines
of reasoning suggest that the dark matter consists of some new, as yet
undiscovered, weakly-interacting massive particle (WIMP). There is now a vast
experimental effort being surmounted to detect WIMPS in the halo. The most
promising techniques involve direct detection in low-background laboratory
detectors and indirect detection through observation of energetic neutrinos
from annihilation of WIMPs that have accumulated in the Sun and/or the Earth.
Of the many WIMP candidates, perhaps the best motivated and certainly the most
theoretically developed is the neutralino, the lightest superpartner in many
supersymmetric theories. We review the minimal supersymmetric extension of the
Standard Model and discuss prospects for detection of neutralino dark matter.
We review in detail how to calculate the cosmological abundance of the
neutralino and the event rates for both direct- and indirect-detection schemes,
and we discuss astrophysical and laboratory constraints on supersymmetric
models. We isolate and clarify the uncertainties from particle physics, nuclear
physics, and astrophysics that enter at each step in the calculation. We
briefly review other related dark-matter candidates and detection techniques.Comment: The complete postscript file is available at
ftp://ftp.npac.syr.edu/pub/users/jungman/susyreview/susyreview.ps.Z The TeX
source and figures (plain TeX; macros included) are at
ftp://ftp.npac.syr.edu/pub/users/jungman/susyreview/susyreview.tar.Z Full
paper NOT submitted to lanl archive: table of contents only. To appear in
Physics Report
Letter to the editor - round table unites to tackle culture change in an effort to improve animal research reporting
A round table discussion was held during the LAVA-ESLAV-ECLAM conference on Reproducibility of Animal Studies on the 25th of September 2017 in Edinburgh. The aim of the round table was to discuss how to enhance the rate at which the quality of reporting animal research can be improved. This signed statement acknowledges the efforts that participant organizations have made towards improving the reporting of animal studies and confirms an ongoing commitment to drive further improvements, calling upon both academics and laboratory animal veterinarians to help make this cultural change
New genetic loci link adipose and insulin biology to body fat distribution.
Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms
PHYSICO-CHEMICAL AND PHYSICAL PROPERTIES OF HALLOYSITE RICH SOILS IN GUADELOUPE
In Guadeloupe, under moderate humid climatic conditions (1800 - 3000mm.), hydrolysis of young andesitic parent rock lead to the pedogenesis of 1:1 lattice clay (halloysite) rich soils (Rusty brown soils). But in the old, highly weathered north-eastern part of the island, covered by ferrallitic soils, halloysite equally appears to be the major mineral soil constituent. For the latter soils, in addition to the dominant 1:1 lattice clay, the presence of accessory 2:1 clay minerals has been noted. In these highly impoverished soils, the presence of such 2:1 minerals causes an important variability of physico-chemical properties, in particular the cation exchange properties and the occurence of exchangeable aluminium. Soil water properties of halloysite rich soils show remarkable differences with regard to water retention, total porosity and shrinkage. In addition to their minera1ogica1 nature, the morphology and size of the halloysite particles, as well as their spatial arrangement seem to play a leading part with regard to the soil's physical behaviour
Is the operationally defined fraction of soil organic matter, “GRSP” (glomalin-related soil protein), stable in soils? Evidence from trends in long-term bare fallow soil
International audienceThe operationally defined fraction of soil organic matter (SOM), glomalin-related soil protein (GRSP), has been reported to be particularly stable. This is the first study to test this hypothesis. Archived soil has been used from the long-term bare fallow trial, known as the 42-Plots, in Versailles, France. With no input from plants for 80 years, changes in GRSP must result from either turnover of SOM or net mineralization. Intrinsically, stability of protein would lead to progressive enrichment in GRSP. Soils from treatments that influenced pH, soil C:N ratio and physical stability were studied. Soil having received manure amendment was also studied to give contrasting microbial activity. Both GRSP and soil organic carbon (SOC) contents declined over the 80-year period, with the exception of the manure treatment. GRSP and SOC contents were positively correlated. SOC was continuously enriched in GRSP in the control treatment, suggesting greater stability of GRSP. The SOC in manure-amended soil was also progressively enriched in GRSP, but this can be attributed to the GRSP content of added manure. For the other treatments, the ratio GRSP:SOC fell continuously (CaCO3 amendment) or fell to a minimum value after 45 years (KCl amendment) or levelled off after a progressive increase ((NH4)2SO4 amendment). Trends are compared with measured soil properties and changes in microbial activity inferred from soil pH. No reliable independent assessment of microbial composition of these archived soils is possible. The results cannot be explained by inherent chemical or physicochemical stability of GRSP. We conclude that recycling of SOM continually produces soil protein. The net change in GRSP content is a complex function of SOM cycling and protein mineralization. These findings add to the increasing body of evidence that the operationally defined fraction of SOM known as GRSP does not predominantly originate from arbuscular mycorrhizal fungal activity. Highlights: Processes determining SOM enrichment in GRSP in C-depleted soils are not understood. GRSP decreased along with SOC, but relative rates of decline varied with amendments. Levels of GRSP appear to be due to organic matter turnover as well as mineralization. GRSP does not appear to originate from arbuscular mycorrhizal fungal activity