20,890 research outputs found
A mathematical morphology approach for a qualitative exploration of drought events in space and time
Drought events occur worldwide and possibly incur severe consequences. Trying to understand and characterize drought events is of considerable importance in order to improve the preparedness for coping with future events. In this paper, we present a methodology that allows for the delineation of drought events by exploiting their spatiotemporal nature. To that end, we apply operators borrowed from mathematical morphology to represent drought events as connected components in space and time. As an illustration, we identify drought events on the basis of a 35-year data set of daily soil moisture values covering mainland Australia. We then extract characteristics reflecting the affected area, duration and intensity from the proposed representation of a drought event in order to illustrate the impact of tuning parameters in the methodology presented. Yet, this paper we refrain from comparing with other drought delineation methods
Searching for the most powerful thermonuclear X-ray bursts with the Neil Gehrels Swift Observatory
We searched for thermonuclear X-ray bursts from Galactic neutron stars in all
event mode data of the Neil Gehrels Swift Observatory collected until March 31,
2018. In particular, we are interested in the intermediate-duration bursts
(shell flashes fueled by thick helium piles) with the ill-understood phenomenon
of strong flux fluctuations. Nine such bursts have been discussed in the
literature to date. Swift is particularly suitable for finding additional
examples. We find and list a total of 134 X-ray bursts; 44 are detected with
BAT only, 41 with XRT only, and 49 with both. Twenty-eight bursts involve
automatic slews. We find 12 intermediate-duration bursts, all detected in
observations involving automatic slews. Five show remarkably long
Eddington-limited phases in excess of 200 s. Five show fluctuations during the
decay phase; four of which are first discussed in the present study. We discuss
the general properties of the fluctuations, considering also 7 literature
cases. In general two types of fluctuations are observed: fast ones, with a
typical timescale of 1 s and up and downward fluctuations of up to 70%, and
slow ones, with a typical timescale of 1 min and only downward fluctuations of
up to 90%. The latter look like partial eclipses because the burst decay
remains visible in the residual emission. We revisit the interpretation of this
phenomenon in the context of the new data set and find that it has not changed
fundamentally despite the expanded data set. It is thought to be due to a
disturbance of the accretion disk by outflowing matter and photons, causing
obscuration and reflection due to Thompson scattering in an orbiting highly
ionized cloud or structure above or below the disk. We discuss in detail the
most pronounced burster SAX J1712.6-3739. One of the bursts from this source is
unusual in that it lasts longer than 5600 s, but does not appear to be a
superburst.Comment: Accepted for publication in Astronomy & Astrophysics, 29 pages, 12
figures. Version 2 has 3 bursts from IGR J17480-2446 re-identified to 2 from
Swift J174805.3-244637 and 1 from EXO 1745-24
Strongly-coupled quantum critical point in an all-in-all-out antiferromagnet
Dimensionality and symmetry play deterministic roles in the laws of Nature.
They are important tools to characterize and understand quantum phase
transitions, especially in the limit of strong correlations between spin,
orbit, charge, and structural degrees of freedom. Using newly-developed,
high-pressure resonant x-ray magnetic and charge diffraction techniques, we
have discovered a quantum critical point in Cd2Os2O7 as the all-in-all-out
(AIAO) antiferromagnetic order is continuously suppressed to zero temperature
and, concomitantly, the cubic lattice structure continuously changes from space
group Fd-3m to F-43m. Surrounded by three phases of different time reversal and
spatial inversion symmetries, the quantum critical region anchors two phase
lines of opposite curvature, with striking departures from a mean-field form at
high pressure. As spin fluctuations, lattice breathing modes, and quasiparticle
excitations interact in the quantum critical region, we argue that they present
the necessary components for strongly-coupled quantum criticality in this
three-dimensional compound
Effect of Varying Dietary Selenium Levels on Tissue Composition, Blood Composition and Performance of Growing Swine Fed Seleniferous Grains
It is established that selenium is an essential micronutrient as well as a natural toxicant for domestic livestock. However, reports of selenium toxicosis in swine are limited and not well documented. The level at which selenium becomes toxic to swine is thought to be about 8 ppm. This value was derived from the initial selenium research of the 1930\u27s, with considerable extrapolation from other species used in this determination. Since that time, diet composition has become much more complex, nutrient level of diets has increased and feed additives are commonly used. It is not known what effect these factors or other nutritional interrelationships may have on the level at which selenium becomes toxic. Due to the variability of selenium content in feedstuffs and because selenium is now approved as a feed additive, it is important to better define the level at which selenium becomes toxic to swine. This research was conducted to determine the effect of varying dietary selenium levels on tissue and blood composition and performance of growing swine fed seleniferous grains
Interim report on the analysis of the microwave power module
The results of a traveling wave tube multistage depressed collector (TWT-MDC) design study in support of the DARPA/DoD Microwave Power Module (MPM) Program are described. The study stressed the MDC as a key element in obtaining the required high overall efficiencies in the MPM application. The results showed that an efficient MDC, utilizing conventional design and fabrication techniques can be designed for the first generation MPM TWT, which permits a package one wavelength thick (.66 in. at 18 GHz). The overall TWT efficiency goal of 40 percent for electronic countermeasure (ECM) applications appears to be readily achievable. However, the 50 percent goal for radar applications presents a considerable challenge
Mechanistic explanations of community structure: Introduction
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75364/1/j.1654-1103.1999.tb00597.x.pd
Partial suppression of the radial orbit instability in stellar systems
It is well known that the simple criterion proposed originally by Polyachenko
and Shukhman (1981) for the onset of the radial orbit instability, although
being generally a useful tool, faces significant exceptions both on the side of
mildly anisotropic systems (with some that can be proved to be unstable) and on
the side of strongly anisotropic models (with some that can be shown to be
stable). In this paper we address two issues: Are there processes of
collisionless collapse that can lead to equilibria of the exceptional type?
What is the intrinsic structural property that is responsible for the sometimes
noted exceptional stability behavior? To clarify these issues, we have
performed a series of simulations of collisionless collapse that start from
homogeneous, highly symmetrized, cold initial conditions and, because of such
special conditions, are characterized by very little mixing. For these runs,
the end-states can be associated with large values of the global pressure
anisotropy parameter up to 2K_r/K_T \approx 2.75. The highly anisotropic
equilibrium states thus constructed show no significant traces of radial
anisotropy in their central region, with a very sharp transition to a radially
anisotropic envelope occurring well inside the half-mass radius (around 0.2
r_M). To check whether the existence of such almost perfectly isotropic
"nucleus" might be responsible for the apparent suppression of the radial orbit
instability, we could not resort to equilibrium models with the above
characteristics and with analytically available distribution function; instead,
we studied and confirmed the stability of configurations with those
characteristics by initializing N-body approximate equilibria (with given
density and pressure anisotropy profiles) with the help of the Jeans equations.Comment: 26 pages, 9 figures, accepted for publication in The Astrophysical
Journa
Novel methods for spatial prediction of soil functions within landscapes (SP0531)
Previous studies showed that soil patterns could be predicted in agriculturally managed landscapes by modelling and extrapolating from extensive existing but related integrated datasets. Based on these results we proposed to develop and apply predictive models of the relationships between environmental data and known soil patterns to predict capacity for key soil functions within diverse
landscapes for which there is little detailed underpinning soil information available.
Objectives were:
To develop a high-level framework in which the non-specialist user-community could explore questions.
To generate digital soil maps for three selected catchments at a target resolution of 1:50000 to provide the base information for soil function prediction.
To use a modelling approach to predict the performance of key soil functions in catchments undergoing change but where only sparse or low resolution soil survey data are available.
To use a modelling approach to assess the impact of different management scenarios and/or environmental conditions on the delivery of multiple soil functions within a catchment.
To create a detailed outline of the requirements for ground-truthing to test the predicted model outputs at a catchment scale.
To contribute to the development of a high-level framework for decision makers
Blue Light Induces Phosphorylation at Seryl Residues on a Pea (Pisum sativum L.) Plasma Membrane Protein
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