10,300 research outputs found
Modelling electron distributions within ESA's Gaia satellite CCD pixels to mitigate radiation damage
The Gaia satellite is a high-precision astrometry, photometry and
spectroscopic ESA cornerstone mission, currently scheduled for launch in 2012.
Its primary science drivers are the composition, formation and evolution of the
Galaxy. Gaia will achieve its unprecedented positional accuracy requirements
with detailed calibration and correction for radiation damage. At L2, protons
cause displacement damage in the silicon of CCDs. The resulting traps capture
and emit electrons from passing charge packets in the CCD pixel, distorting the
image PSF and biasing its centroid. Microscopic models of Gaia's CCDs are being
developed to simulate this effect. The key to calculating the probability of an
electron being captured by a trap is the 3D electron density within each CCD
pixel. However, this has not been physically modelled for the Gaia CCD pixels.
In Seabroke, Holland & Cropper (2008), the first paper of this series, we
motivated the need for such specialised 3D device modelling and outlined how
its future results will fit into Gaia's overall radiation calibration strategy.
In this paper, the second of the series, we present our first results using
Silvaco's physics-based, engineering software: the ATLAS device simulation
framework. Inputting a doping profile, pixel geometry and materials into ATLAS
and comparing the results to other simulations reveals that ATLAS has a free
parameter, fixed oxide charge, that needs to be calibrated. ATLAS is
successfully benchmarked against other simulations and measurements of a test
device, identifying how to use it to model Gaia pixels and highlighting the
effect of different doping approximations.Comment: 12 pages, 6 figures, appearing in Proc. of SPIE Optics and Photonics
Conference (Focal Plane Arrays for Space telescopes IV), 2-6 August 2009, San
Diego, US
Erratum:A chromosome-based model for estimating the number of conserved segments between pairs of species from comparative genetic maps
The Minimum Wiener Connector
The Wiener index of a graph is the sum of all pairwise shortest-path
distances between its vertices. In this paper we study the novel problem of
finding a minimum Wiener connector: given a connected graph and a set
of query vertices, find a subgraph of that connects all
query vertices and has minimum Wiener index.
We show that The Minimum Wiener Connector admits a polynomial-time (albeit
impractical) exact algorithm for the special case where the number of query
vertices is bounded. We show that in general the problem is NP-hard, and has no
PTAS unless . Our main contribution is a
constant-factor approximation algorithm running in time
.
A thorough experimentation on a large variety of real-world graphs confirms
that our method returns smaller and denser solutions than other methods, and
does so by adding to the query set a small number of important vertices
(i.e., vertices with high centrality).Comment: Published in Proceedings of the 2015 ACM SIGMOD International
Conference on Management of Dat
The Heider balance - a continuous approach
The Heider balance (HB) is investigated in a fully connected graph of
nodes. The links are described by a real symmetric array r(i,j), i,j=1,...,N.
In a social group, nodes represent group members and links represent relations
between them, positive (friendly) or negative (hostile). At the balanced state,
r(i,j)r(j,k)r(k,i)>0 for all the triads (i,j,k). As follows from the structure
theorem of Cartwright and Harary, at this state the group is divided into two
subgroups, with friendly internal relations and hostile relations between the
subgroups. Here the system dynamics is proposed to be determined by a set of
differential equations. The form of equations guarantees that once HB is
reached, it persists. Also, for N=3 the dynamics reproduces properly the
tendency of the system to the balanced state. The equations are solved
numerically. Initially, r(i,j) are random numbers distributed around zero with
a symmetric uniform distribution of unit width. Calculations up to N=500 show
that HB is always reached. Time to get the balanced state varies with the
system size N as N^{-1/2}. The spectrum of relations, initially narrow, gets
very wide near HB. This means that the relations are strongly polarized. In our
calculations, the relations are limited to a given range around zero. With this
limitation, our results can be helpful in an interpretation of somestatistical
data.Comment: 9 pages, 4 figures. Int. J. Mod. Phys. C (2005), in prin
Many quantitative trait loci for feather growth in an F broiler × layer cross collocate with body weight loci
1. A genome-wide scan of 467 F progeny of a broiler x layer cross was conducted to identify quantitative trait loci (QTL) affecting the rate of growth of the tail, wing and back feathers, and the width of the breast feather tract, at three weeks of age. 2. Correlations between the traits ranged from 0·36 to 0·61. Males had longer tail and wing feathers and shorter back feathers than females. Breast feather tract width was greater in females than males. 3. QTL effects were generally additive and accounted for 11 to 45% of sex average feather lengths of the breeds, and 100% of the breast feather tract width. Positive and negative alleles were inherited from both lines, whereas the layer allele was larger than the broiler allele after adjusting for body weight. 4. A total of 4 genome-significant and 4 suggestive QTL were detected. At three or 6 weeks of age, 5 of the QTL were located in similar regions as QTL for body weight. 5. Analysis of a model with body weight at three weeks as a covariate identified 5 genome significant and 6 suggestive QTL, of which only two were coincident with body weight QTL. One QTL for feather length at 148 cM on GGA1 was identified at a similar location in the unadjusted analysis. 6. The results suggest that the rate of feather growth is largely controlled by body weight QTL, and that QTL specific for feather growth also exist
Social Cohesion, Structural Holes, and a Tale of Two Measures
EMBARGOED - author can archive pre-print or post-print on any open access repository after 12 months from publication. Publication date is May 2013 so embargoed until May 2014.This is an author’s accepted manuscript (deposited at arXiv arXiv:1211.0719v2 [physics.soc-ph] ), which was subsequently published in Journal of Statistical Physics May 2013, Volume 151, Issue 3-4, pp 745-764. The final publication is available at link.springer.com http://link.springer.com/article/10.1007/s10955-013-0722-
PARTAKE survey of public knowledge and perceptions of clinical research in India.
BACKGROUND: A public that is an informed partner in clinical research is important for ethical, methodological, and operational reasons. There are indications that the public is unaware or misinformed, and not sufficiently engaged in clinical research but studies on the topic are lacking. PARTAKE - Public Awareness of Research for Therapeutic Advancements through Knowledge and Empowerment is a program aimed at increasing public awareness and partnership in clinical research. The PARTAKE Survey is a component of the program. OBJECTIVE: To study public knowledge and perceptions of clinical research. METHODS: A 40-item questionnaire combining multiple-choice and open-ended questions was administered to 175 English- or Hindi-speaking individuals in 8 public locations representing various socioeconomic strata in New Delhi, India. RESULTS: Interviewees were 18-84 old (mean: 39.6, SD ± 16.6), 23.6% female, 68.6% employed, 7.3% illiterate, 26.3% had heard of research, 2.9% had participated and 58.9% expressed willingness to participate in clinical research. The following perceptions were reported (% true/% false/% not aware): 'research benefits society' (94.1%/3.5%/2.3%), 'the government protects against unethical clinical research' (56.7%/26.3%/16.9%), 'research hospitals provide better care' (67.2%/8.7%/23.9%), 'confidentiality is adequately protected' (54.1%/12.3%/33.5%), 'participation in research is voluntary' (85.3%/5.8%/8.7%); 'participants treated like 'guinea pigs'' (20.7%/53.2%/26.0%), and 'compensation for participation is adequate' (24.7%/12.9%/62.3%). CONCLUSIONS: Results suggest the Indian public is aware of some key features of clinical research (e.g., purpose, value, voluntary nature of participation), and supports clinical research in general but is unaware of other key features (e.g., compensation, confidentiality, protection of human participants) and exhibits some distrust in the conduct and reporting of clinical trials. Larger, cross-cultural surveys are required to inform educational programs addressing these issues
Innovation as a Nonlinear Process, the Scientometric Perspective, and the Specification of an "Innovation Opportunities Explorer"
The process of innovation follows non-linear patterns across the domains of
science, technology, and the economy. Novel bibliometric mapping techniques can
be used to investigate and represent distinctive, but complementary
perspectives on the innovation process (e.g., "demand" and "supply") as well as
the interactions among these perspectives. The perspectives can be represented
as "continents" of data related to varying extents over time. For example, the
different branches of Medical Subject Headings (MeSH) in the Medline database
provide sources of such perspectives (e.g., "Diseases" versus "Drugs and
Chemicals"). The multiple-perspective approach enables us to reconstruct facets
of the dynamics of innovation, in terms of selection mechanisms shaping
localizable trajectories and/or resulting in more globalized regimes. By
expanding the data with patents and scholarly publications, we demonstrate the
use of this multi-perspective approach in the case of RNA Interference (RNAi).
The possibility to develop an "Innovation Opportunities Explorer" is specified.Comment: Technology Analysis and Strategic Management (forthcoming in 2013
Modelling methods for determining fault management requirements in future MEA and MEE platforms
This paper presents a modular transient modelling tool which provides model-based support for the design and technology selection within future MEE and MEA electrical systems. The developed tool is a Matlab/Simulink library consisting of functional sub-system units, which can be rapidly integrated to build complex system architecture models. The paper focusses on the ability of the tool to assess the thermally-defined fault withstand capability of power electronic converters in order to inform on technology trades and derive the operating requirements of the associated power system protection/fault management devices
- …