2,314 research outputs found
Enhancing weak transient signals in SEVIRI false color imagery: application to dust source detection in southern Africa
A method is described to significantly enhance the signature of dust events using observations
from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI). The approach involves the derivation of a
composite clear-sky signal for selected channels on an individual time step and pixel basis. These composite
signals are subtracted from each observation in the relevant channels to enhance weak transient signals
associated with either (a) low levels of dust emission or (b) dust emissions with high salt or low quartz
content. Different channel combinations, of the differenced data from the steps above, are then rendered in
false color imagery for the purpose of improved identification of dust source locations and activity. We have
applied this clear-sky difference (CSD) algorithm over three (globally significant) source regions in southern
Africa: the Makgadikgadi Basin, Etosha Pan, and the Namibian and western South African coast. Case study
analyses indicate three notable advantages associated with the CSD approach over established image
rendering methods: (i) an improved ability to detect dust plumes, (ii) the observation of source activation
earlier in the diurnal cycle, and (iii) an improved ability to resolve and pinpoint dust plume source locations
The application of parameter sensitivity analysis methods to inverse simulation models
Knowledge of the sensitivity of inverse solutions to variation of parameters of a model can be very useful in making engineering design decisions. This paper describes how parameter sensitivity analysis can be carried out for
inverse simulations generated through approximate transfer function inversion methods and also by the use of feedback principles. Emphasis is placed on the use of sensitivity models and the paper includes examples and a case study involving a model of an underwater vehicle. It is shown that the use of sensitivity models can provide physical understanding of inverse simulation solutions that is not directly available using parameter sensitivity analysis methods that involve parameter perturbations and response
differencing
Chasing the identification of ASCA Galactic Objects (ChIcAGO): An X-ray survey of unidentified sources in the galactic plane. I : Source sample and initial results
We present the Chasing the Identification of ASCA Galactic Objects (ChIcAGO) survey, which is designed to identify the unknown X-ray sources discovered during the ASCA Galactic Plane Survey (AGPS). Little is known about most of the AGPS sources, especially those that emit primarily in hard X-rays (2-10 keV) within the Fx 10-13 to 10-11 erg cm -2 s-1 X-ray flux range. In ChIcAGO, the subarcsecond localization capabilities of Chandra have been combined with a detailed multiwavelength follow-up program, with the ultimate goal of classifying the >100 unidentified sources in the AGPS. Overall to date, 93 unidentified AGPS sources have been observed with Chandra as part of the ChIcAGO survey. A total of 253 X-ray point sources have been detected in these Chandra observations within 3′ of the original ASCA positions. We have identified infrared and optical counterparts to the majority of these sources, using both new observations and catalogs from existing Galactic plane surveys. X-ray and infrared population statistics for the X-ray point sources detected in the Chandra observations reveal that the primary populations of Galactic plane X-ray sources that emit in the Fx 10-13 to 10-11 erg cm -2 s-1 flux range are active stellar coronae, massive stars with strong stellar winds that are possibly in colliding wind binaries, X-ray binaries, and magnetars. There is also another primary population that is still unidentified but, on the basis of its X-ray and infrared properties, likely comprises partly Galactic sources and partly active galactic nuclei.Peer reviewedSubmitted Versio
Classification using distance nearest neighbours
This paper proposes a new probabilistic classification algorithm using a
Markov random field approach. The joint distribution of class labels is
explicitly modelled using the distances between feature vectors. Intuitively, a
class label should depend more on class labels which are closer in the feature
space, than those which are further away. Our approach builds on previous work
by Holmes and Adams (2002, 2003) and Cucala et al. (2008). Our work shares many
of the advantages of these approaches in providing a probabilistic basis for
the statistical inference. In comparison to previous work, we present a more
efficient computational algorithm to overcome the intractability of the Markov
random field model. The results of our algorithm are encouraging in comparison
to the k-nearest neighbour algorithm.Comment: 12 pages, 2 figures. To appear in Statistics and Computin
Enhancement factor for the electron electric dipole moment in francium and gold atoms
If electrons had an electric dipole moment (EDM) they would induce EDMs of
atoms. The ratio of the atomic EDM to the electron EDM for a particular atom is
called the enhancement factor, R. We calculate the enhancement factor for the
francium and gold atoms, with the results 910 plus/minus 5% for Fr and 260
plus/minus 15% for Au. The large values of these enhancement factors make these
atoms attractive for electron EDM measurements, and hence the search for
time-reversal invariance violation.Comment: 6 pages, no figures, uses RevTex, reference adde
An extrapolation of Foucault's Technologies of the Self to effect positive transformation in the intensivist as teacher and mentor
In critical care medicine, teaching and mentoring practices are extremely important in regard to attracting and retaining young trainees and faculty in this important subspecialty that has a scarcity of needed personnel in the USA. To this end, we argue that Foucault’s Technologies of the Self is critical background reading when endeavoring to effect the positive transformation of faculty into effective teachers and mentors
An Overview of the 13:8 Mean Motion Resonance between Venus and Earth
It is known since the seminal study of Laskar (1989) that the inner planetary
system is chaotic with respect to its orbits and even escapes are not
impossible, although in time scales of billions of years. The aim of this
investigation is to locate the orbits of Venus and Earth in phase space,
respectively to see how close their orbits are to chaotic motion which would
lead to unstable orbits for the inner planets on much shorter time scales.
Therefore we did numerical experiments in different dynamical models with
different initial conditions -- on one hand the couple Venus-Earth was set
close to different mean motion resonances (MMR), and on the other hand Venus'
orbital eccentricity (or inclination) was set to values as large as e = 0.36 (i
= 40deg). The couple Venus-Earth is almost exactly in the 13:8 mean motion
resonance. The stronger acting 8:5 MMR inside, and the 5:3 MMR outside the 13:8
resonance are within a small shift in the Earth's semimajor axis (only 1.5
percent). Especially Mercury is strongly affected by relatively small changes
in eccentricity and/or inclination of Venus in these resonances. Even escapes
for the innermost planet are possible which may happen quite rapidly.Comment: 14 pages, 11 figures, submitted to CMD
Intermediate inflation in Gauss-Bonnet braneworld
In this article we study an intermediate inflationary universe models using
the Gauss-Bonnet brane. General conditions required for these models to be
realizable are derived and discussed. We use recent astronomical observations
to constraint the parameters appearing in the model.Comment: 16 pages, 2 figures, accepted for publication in European Physical
Journal
Immortalized mouse caput epididymal epithelial (mECap18) cell line recapitulates the in-vivo environment
OnlinePublResiding between the testes and the vas deferens, the epididymis is a highly convoluted tubule whose unique luminal microenvironment is crucial for the functional maturation of spermatozoa. This microenvironment is created by the combined secretory and resorptive activity of the lining epididymal epithelium, including the release of extracellular vesicles (epididymosomes), which encapsulate fertility modulating proteins and a myriad of small non-coding RNAs (sncRNAs) that are destined for delivery to recipient sperm cells. To enable investigation of this intercellular communication nexus, we have previously developed an immortalized mouse caput epididymal epithelial cell line (mECap18). Here, we describe the application of label-free mass spectrometry to characterize the mECap18 cell proteome and compare this to the proteome of native mouse caput epididymal epithelial cells. We report the identification of 5,313 mECap18 proteins, as many as 75.8% of which were also identified in caput epithelial cells wherein they mapped to broadly similar protein classification groupings. Furthermore, key pathways associated with protein synthesis (e.g., EIF2 signaling) and cellular protection in the male reproductive tract (e.g., sirtuin signaling) were enriched in both proteomes. This comparison supports the utility of the mECap18 cell line as a tractable in-vitro model for studying caput epididymal epithelial cell function.Jess E. Mulhall, Natalie A. Trigg, Ilana R. Bernstein, Amanda L. Anderson, Heather C. Murray, Petra Sipilä, Tessa Lord, John E. Schjenken, Brett Nixon, David A. Skerrett-Byrn
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