277 research outputs found
INTEGRAL/SPI γ -ray line spectroscopy : Response and background characteristics
© 2018 ESO. Reproduced with permission from Astronomy & Astrophysics. Content in the UH Research Archive is made available for personal research, educational, and non-commercial purposes only. Unless otherwise stated, all content is protected by copyright, and in the absence of an open license, permissions for further re-use should be sought from the publisher, the author, or other copyright holder.Context. The space based γ-ray observatory INTEGRAL of the European Space Agency (ESA) includes the spectrometer instrument "SPI". This is a coded mask telescope featuring a 19-element Germanium detector array for high-resolution γ-ray spectroscopy, encapsulated in a scintillation detector assembly that provides a veto for background from charged particles. In space, cosmic rays irradiate spacecraft and instruments, which, in spite of the vetoing detectors, results in a large instrumental background from activation of those materials, and leads to deterioration of the charge collection properties of the Ge detectors.Aim. We aim to determine the measurement characteristics of our detectors and their evolution with time, that is, their spectral response and instrumental background. These incur systematic variations in the SPI signal from celestial photons, hence their determination from a broad empirical database enables a reduction of underlying systematics in data analysis. For this, we explore compromises balancing temporal and spectral resolution within statistical limitations. Our goal is to enable modelling of background applicable to spectroscopic studies of the sky, accounting separately for changes of the spectral response and of instrumental background.Methods. We use 13.5 years of INTEGRAL/SPI data, which consist of spectra for each detector and for each pointing of the satellite. Spectral fits to each such spectrum, with independent but coherent treatment of continuum and line backgrounds, provides us with details about separated background components. From the strongest background lines, we first determine how the spectral response changes with time. Applying symmetry and long-term stability tests, we eliminate degeneracies and reduce statistical fluctuations of background parameters, with the aim of providing a self-consistent description of the spectral response for each individual detector. Accounting for this, we then determine how the instrumental background components change in intensities and other characteristics, most-importantly their relative distribution among detectors.Results. Spectral resolution of Ge detectors in space degrades with time, up to 15% within half a year, consistently for all detectors, and across the SPI energy range. Semi-annual annealing operations recover these losses, yet there is a small long-term degradation. The intensity of instrumental background varies anti-correlated to solar activity, in general. There are significant differences among different lines and with respect to continuum. Background lines are found to have a characteristic, well-defined and long-term consistent intensity ratio among detectors. We use this to categorise lines in groups of similar behaviour. The dataset of spectral-response and background parameters as fitted across the INTEGRAL mission allows studies of SPI spectral response and background behaviour in a broad perspective, and efficiently supports precision modelling of instrumental background.Peer reviewedFinal Published versio
Increasing Dominance - the Role of Advertising, Pricing and Product Design
Despite the empirical relevance of advertising strategies in concentrated markets, the economics literature is largely silent on the effect of persuasive advertising
strategies on pricing, market structure and increasing (or decreasing) dominance. In a simple model of persuasive advertising and pricing with differentiated goods,
we analyze the interdependencies between ex-ante asymmetries in consumer appeal, advertising and prices. Products with larger initial appeal to consumers will
be advertised more heavily but priced at a higher level - that is, advertising and price discounts are strategic substitutes for products with asymmetric initial appeal.
We find that the escalating effect of advertising dominates the moderating effect of pricing so that post-competition market shares are more asymmetric than pre-competition differences in consumer appeal. We further find that collusive advertising (but competitive pricing) generates the same market outcomes, and that network effects lead to even more extreme market outcomes, both directly and via
the effect on advertising
Trace Metals and Their Isotopes in the Tropical Atlantic Ocean - Cruise No. M81/1, February 04 – March 08, 2010, Las Palmas (Canary Islands, Spain) – Port of Spain (Trinidad & Tobago)
Summary
Meteor Cruise M81/1 was dedicated to the investigation of the distribution of dissolved and
particulate trace metals and their isotopic compositions (TEIs) in the full water column of the
tropical Atlantic Ocean and their driving factors including main external inputs and internal
cycling and ocean circulation. The research program is embedded in the international
GEOTRACES program (e.g. Henderson et al., 2007), which this cruise was an official part of
and thus corresponds to GEOTRACES cruise GA11. This cruise was completely dedicated to the
trace metal clean and contamination-free sampling of waters and particulates for subsequent
analyses of the TEIs in the home laboratories of the national and international participants.
Besides a standard rosette for the less contaminant prone metals, trace metal clean sampling was
realized by using a dedicated and coated trace metal clean rosette equipped with Teflon-coated
GO-FLO bottles operated via a polyester coated cable from a mobile winch that was thankfully
made available by the U.S. partners of the GEOTRACES program for this cruise. The particulate
samples were also collected under trace metal clean conditions using established in-situ pump
systems. The cruise track led the cruise southward from the Canary Islands to 11°S and then
continued northwestward along the northern margin of South America until it reached Port of
Spain, Trinidad & Tobago. The track crossed areas of major external inputs including exchange
with the volcanic Canary Islands, the Saharan dust plume, as well as the plume of the Amazon
outflow. In terms of internal cycling the equatorial high biological productivity band, as well as
increased productivity associated with the Amazon Plume were covered. All major water masses
contributing the Atlantic Meridional Overturning Circulation, as well as the distinct narrow
equatorial surface and subsurface east-west current bands were sampled. A total of 17 deep
stations were sampled for the different dissolved TEIs, which were in most cases accompanied
by particulate sampling. In addition, surface waters were continuously sampled under trace metal
clean conditions using a towed fish
Collaboration in sensor network research: an in-depth longitudinal analysis of assortative mixing patterns
Many investigations of scientific collaboration are based on statistical
analyses of large networks constructed from bibliographic repositories. These
investigations often rely on a wealth of bibliographic data, but very little or
no other information about the individuals in the network, and thus, fail to
illustrate the broader social and academic landscape in which collaboration
takes place. In this article, we perform an in-depth longitudinal analysis of a
relatively small network of scientific collaboration (N = 291) constructed from
the bibliographic record of a research center involved in the development and
application of sensor network and wireless technologies. We perform a
preliminary analysis of selected structural properties of the network,
computing its range, configuration and topology. We then support our
preliminary statistical analysis with an in-depth temporal investigation of the
assortative mixing of selected node characteristics, unveiling the researchers'
propensity to collaborate preferentially with others with a similar academic
profile. Our qualitative analysis of mixing patterns offers clues as to the
nature of the scientific community being modeled in relation to its
organizational, disciplinary, institutional, and international arrangements of
collaboration.Comment: Scientometrics (In press
Spectral and intensity variations of Galactic 26^Al emission
Gamma-ray line emission from the radioactive decay of 26Al reflects
nucleosynthesis in massive stars and supernovae. We use INTEGRAL 26Al
measurements to characterize the distribution and characteristics of 26Al
source regions throughout the Galaxy. We detect the 26Al line from the inner
Galaxy at 28\sigma significance. The line appears narrow, and we constrain
broadening in the source regions to <1.3 keV (2\sigma). Different sky
distribution models do not significantly affect those large-scale results. The
26Al intensity for the inner Galaxy is derived as (2.9\pm 0.2)\times 10^{-4}ph\
cm^{-2} s^{-1} rad^{-1}, consistent with earlier results from COMPTEL and SPI
data. This can be translated to an 26Al mass of 2.7\pm 0.7 solar mass in the
Galaxy as a whole. The 26Al intensity is also confirmed to be somewhat brighter
in the 4th than in the 1st quadrant (ratio 1.3\pm 0.2). 26Al spectra separately
derived for regions along the Galactic plane show clear line centroid shifts,
attributed largely to the Galaxy's large-scale rotation. The 26Al line toward
the direction of the Aquila region (20deg < l < 40deg) appears somewhat
broadened. Latitudinal variations of 26Al emission towards the inner Galaxy are
studied, finding a latitudinal scale height of 130^{+120}_{-70} pc (1\sigma)
for 26Al in the inner Galaxy and a hint of peculiar 26Al emission towards the
region l5deg.Comment: 13 pages, 12 figures, accepted for the publication in A&
Attentive Learning of Sequential Handwriting Movements: A Neural Network Model
Defense Advanced research Projects Agency and the Office of Naval Research (N00014-95-1-0409, N00014-92-J-1309); National Science Foundation (IRI-97-20333); National Institutes of Health (I-R29-DC02952-01)
Arctic change and possible influence on mid-latitude climate and weather: a US CLIVAR White Paper
The Arctic has warmed more than twice as fast as the global average since the mid 20th century,
a phenomenon known as Arctic amplification (AA). These profound changes to the Arctic system
have coincided with a period of ostensibly more frequent events of extreme weather across the
Northern Hemisphere (NH) mid-latitudes, including extreme heat and rainfall events and recent
severe winters. Though winter temperatures have generally warmed since 1960 over mid-to-high
latitudes, the acceleration in the rate of warming at high-latitudes, relative to the rest of the NH,
started approximately in 1990. Trends since 1990 show cooling over the NH continents, especially
in Northern Eurasia.
The possible link between Arctic change and mid-latitude climate and weather has spurred a rush
of new observational and modeling studies. A number of workshops held during 2013-2014 have
helped frame the problem and have called for continuing and enhancing efforts for improving
our understanding of Arctic-mid-latitude linkages and its attribution to the occurrence of extreme
climate and weather events. Although these workshops have outlined some of the major challenges
and provided broad recommendations, further efforts are needed to synthesize the diversified
research results to identify where community consensus and gaps exist.
Building upon findings and recommendations of the previous workshops, the US CLIVAR Working
Group on Arctic Change and Possible Influence on Mid-latitude Climate and Weather convened an
international workshop at Georgetown University in Washington, DC, on February 1-3, 2017. Experts
in the fields of atmosphere, ocean, and cryosphere sciences assembled to assess the rapidly evolving
state of understanding, identify consensus on knowledge and gaps in research, and develop specific
actions to accelerate progress within the research community. With more than 100 participants,
the workshop was the largest and most comprehensive gathering of climate scientists to address
the topic to date. In this white paper, we synthesize and discuss outcomes from this workshop and
activities involving many of the working group members
Functional Amyloids Composed of Phenol Soluble Modulins Stabilize Staphylococcus aureus Biofilms
Staphylococcus aureus is an opportunistic pathogen that colonizes the skin and mucosal surfaces of mammals. Persistent staphylococcal infections often involve surface-associated communities called biofilms. Here we report the discovery of a novel extracellular fibril structure that promotes S. aureus biofilm integrity. Biochemical and genetic analysis has revealed that these fibers have amyloid-like properties and consist of small peptides called phenol soluble modulins (PSMs). Mutants unable to produce PSMs were susceptible to biofilm disassembly by matrix degrading enzymes and mechanical stress. Previous work has associated PSMs with biofilm disassembly, and we present data showing that soluble PSM peptides disperse biofilms while polymerized peptides do not. This work suggests the PSMs' aggregation into amyloid fibers modulates their biological activity and role in biofilms
Unresponsive wakefulness syndrome: a new name for the vegetative state or apallic syndrome
BACKGROUND: Some patients awaken from coma (that is, open the eyes) but remain unresponsive (that is, only showing reflex movements without response to command). This syndrome has been coined vegetative state. We here present a new name for this challenging neurological condition: unresponsive wakefulness syndrome (abbreviated UWS). DISCUSSION: Many clinicians feel uncomfortable when referring to patients as vegetative. Indeed, to most of the lay public and media vegetative state has a pejorative connotation and seems inappropriately to refer to these patients as being vegetable-like. Some political and religious groups have hence felt the need to emphasize these vulnerable patients' rights as human beings. Moreover, since its first description over 35 years ago, an increasing number of functional neuroimaging and cognitive evoked potential studies have shown that physicians should be cautious to make strong claims about awareness in some patients without behavioral responses to command. Given these concerns regarding the negative associations intrinsic to the term vegetative state as well as the diagnostic errors and their potential effect on the treatment and care for these patients (who sometimes never recover behavioral signs of consciousness but often recover to what was recently coined a minimally conscious state) we here propose to replace the name. CONCLUSION: Since after 35 years the medical community has been unsuccessful in changing the pejorative image associated with the words vegetative state, we think it would be better to change the term itself. We here offer physicians the possibility to refer to this condition as unresponsive wakefulness syndrome or UWS. As this neutral descriptive term indicates, it refers to patients showing a number of clinical signs (hence syndrome) of unresponsiveness (that is, without response to commands) in the presence of wakefulness (that is, eye opening)
Contribution of CgPDR1-Regulated Genes in Enhanced Virulence of Azole-Resistant Candida glabrata
In Candida glabrata, the transcription factor CgPdr1 is involved
in resistance to azole antifungals via upregulation of ATP binding cassette
(ABC)-transporter genes including at least CgCDR1,
CgCDR2 and CgSNQ2. A high diversity of GOF
(gain-of-function) mutations in CgPDR1 exists for the
upregulation of ABC-transporters. These mutations enhance C.
glabrata virulence in animal models, thus indicating that
CgPDR1 might regulate the expression of yet unidentified
virulence factors. We hypothesized that CgPdr1-dependent virulence factor(s)
should be commonly regulated by all GOF mutations in CgPDR1. As
deduced from transcript profiling with microarrays, a high number of genes (up
to 385) were differentially regulated by a selected number (7) of GOF mutations
expressed in the same genetic background. Surprisingly, the transcriptional
profiles resulting from expression of GOF mutations showed minimal overlap in
co-regulated genes. Only two genes, CgCDR1 and
PUP1 (for PDR1
upregulated and encoding a mitochondrial protein), were
commonly upregulated by all tested GOFs. While both genes mediated azole
resistance, although to different extents, their deletions in an azole-resistant
isolate led to a reduction of virulence and decreased tissue burden as compared
to clinical parents. As expected from their role in C. glabrata
virulence, the two genes were expressed as well in vitro and
in vivo. The individual overexpression of these two genes
in a CgPDR1-independent manner could partially restore
phenotypes obtained in clinical isolates. These data therefore demonstrate that
at least these two CgPDR1-dependent and -upregulated genes
contribute to the enhanced virulence of C. glabrata that
acquired azole resistance
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