4,008 research outputs found
Thermoelectric and thermal rectification properties of quantum dot junctions
The electrical conductance, thermal conductance, thermal power and figure of
merit (ZT) of semiconductor quantum dots (QDs) embedded into an insulator
matrix connected with metallic electrodes are theoretically investigated in the
Coulomb blockade regime. The multilevel Anderson model is used to simulate the
multiple QDs junction system. The charge and heat currents in the sequential
tunneling process are calculated by the Keldysh Green function technique. In
the linear response regime the ZT values are still very impressive in the small
tunneling rates case, although the effect of electron Coulomb interaction on ZT
is significant. In the nonlinear response regime, we have demonstrated that the
thermal rectification behavior can be observed for the coupled QDs system,
where the very strong asymmetrical coupling between the dots and electrodes,
large energy level separation between dots and strong interdot Coulomb
interactions are required.Comment: 8 page and 14 figure
High-dimensional glyph-based visualization and interactive techniques.
The advancement of modern technology and scientific measurements has led to datasets growing in both size and complexity, exposing the need for more efficient and effective ways of visualizing and analysing data. Despite the amount of progress in visualization methods, high-dimensional data still poses a number of significant challenges in terms of the technical ability of realising such a mapping, and how accurate they are actually interpreted. The different data sources and characteristics which arise from a wide range of scientific domains as well as specific design requirements constantly create new special challenges for visualization research. This thesis presents several contributions to the field of glyph-based visualization. Glyphs are parametrised objects which encode one or more data values to its appearance (also referred to as visual channels) such as their size, colour, shape, and position. They have been widely used to convey information visually, and are especially well suited for displaying complex, multi-faceted datasets. Its major strength is the ability to depict patterns of data in the context of a spatial relationship, where multi-dimensional trends can often be perceived more easily. Our research is set in the broad scope of multi-dimensional visualization, addressing several aspects of glyph-based techniques, including visual design, perception, placement, interaction, and applications. In particular, this thesis presents a comprehensive study on one interaction technique, namely sorting, for supporting various analytical tasks. We have outlined the concepts of glyph- based sorting, identified a set of design criteria for sorting interactions, designed and prototyped a user interface for sorting multivariate glyphs, developed a visual analytics technique to support sorting, conducted an empirical study on perceptual orderability of visual channels used in glyph design, and applied glyph-based sorting to event visualization in sports applications. The content of this thesis is organised into two parts. Part I provides an overview of the basic concepts of glyph-based visualization, before describing the state-of-the-art in this field. We then present a collection of novel glyph-based approaches to address challenges created from real-world applications. These are detailed in Part II. Our first approach involves designing glyphs to depict the composition of multiple error-sensitivity fields. This work addresses the problem of single camera positioning, using both 2D and 3D methods to support camera configuration based on various constraints in the context of a real-world environment. Our second approach present glyphs to visualize actions and events "at a glance". We discuss the relative merits of using metaphoric glyphs in comparison to other types of glyph designs to the particular problem of real-time sports analysis. As a result of this research, we delivered a visualization software, MatchPad, on a tablet computer. It successfully helped coaching staff and team analysts to examine actions and events in detail whilst maintaining a clear overview of the match, and assisted in their decision making during the matches. Abstract shortened by ProQuest
Creatinine, diet, micronutrients, and arsenic methylation in West Bengal, India.
BackgroundIngested inorganic arsenic (InAs) is methylated to monomethylated (MMA) and dimethylated metabolites (DMA). Methylation may have an important role in arsenic toxicity, because the monomethylated trivalent metabolite [MMA(III)] is highly toxic.ObjectivesWe assessed the relationship of creatinine and nutrition--using dietary intake and blood concentrations of micronutrients--with arsenic metabolism, as reflected in the proportions of InAS, MMA, and DMA in urine, in the first study that incorporated both dietary and micronutrient data.MethodsWe studied methylation patterns and nutritional factors in 405 persons who were selected from a cross-sectional survey of 7,638 people in an arsenic-exposed population in West Bengal, India. We assessed associations of urine creatinine and nutritional factors (19 dietary intake variables and 16 blood micronutrients) with arsenic metabolites in urine.ResultsUrinary creatinine had the strongest relationship with overall arsenic methylation to DMA. Those with the highest urinary creatinine concentrations had 7.2% more arsenic as DMA compared with those with low creatinine (p < 0.001). Animal fat intake had the strongest relationship with MMA% (highest tertile animal fat intake had 2.3% more arsenic as MMA, p < 0.001). Low serum selenium and low folate were also associated with increased MMA%.ConclusionsUrine creatinine concentration was the strongest biological marker of arsenic methylation efficiency, and therefore should not be used to adjust for urine concentration in arsenic studies. The new finding that animal fat intake has a positive relationship with MMA% warrants further assessment in other studies. Increased MMA% was also associated, to a lesser extent, with low serum selenium and folate
Amyloid seeding of transthyretin by ex vivo cardiac fibrils and its inhibition
Each of the 30 human amyloid diseases is associated with the aggregation of a particular precursor protein into amyloid fibrils. In transthyretin amyloidosis (ATTR), mutant or wild-type forms of the serum carrier protein transthyretin (TTR), synthesized and secreted by the liver, convert to amyloid fibrils deposited in the heart and other organs. The current standard of care for hereditary ATTR is liver transplantation, which replaces the mutant TTR gene with the wild-type gene. However, the procedure is often followed by cardiac deposition of wild-type TTR secreted by the new liver. Here we find that amyloid fibrils extracted from autopsied and explanted hearts of ATTR patients robustly seed wild-type TTR into amyloid fibrils in vitro. Cardiac-derived ATTR seeds can accelerate fibril formation of wild-type and monomeric TTR at acidic pH and under physiological conditions, respectively. We show that this seeding is inhibited by peptides designed to complement structures of TTR fibrils. These inhibitors cap fibril growth, suggesting an approach for halting progression of ATTR
Fast matrix computations for pair-wise and column-wise commute times and Katz scores
We first explore methods for approximating the commute time and Katz score
between a pair of nodes. These methods are based on the approach of matrices,
moments, and quadrature developed in the numerical linear algebra community.
They rely on the Lanczos process and provide upper and lower bounds on an
estimate of the pair-wise scores. We also explore methods to approximate the
commute times and Katz scores from a node to all other nodes in the graph.
Here, our approach for the commute times is based on a variation of the
conjugate gradient algorithm, and it provides an estimate of all the diagonals
of the inverse of a matrix. Our technique for the Katz scores is based on
exploiting an empirical localization property of the Katz matrix. We adopt
algorithms used for personalized PageRank computing to these Katz scores and
theoretically show that this approach is convergent. We evaluate these methods
on 17 real world graphs ranging in size from 1000 to 1,000,000 nodes. Our
results show that our pair-wise commute time method and column-wise Katz
algorithm both have attractive theoretical properties and empirical
performance.Comment: 35 pages, journal version of
http://dx.doi.org/10.1007/978-3-642-18009-5_13 which has been submitted for
publication. Please see
http://www.cs.purdue.edu/homes/dgleich/publications/2011/codes/fast-katz/ for
supplemental code
Spatial correlation between submillimetre and Lyman-alpha galaxies in the SSA 22 protocluster
Lyman-alpha emitters are thought to be young, low-mass galaxies with ages of
~10^8 yr. An overdensity of them in one region of the sky (the SSA 22 field)
traces out a filamentary structure in the early Universe at a redshift of z =
3.1 (equivalent to 15 per cent of the age of the Universe) and is believed to
mark a forming protocluster. Galaxies that are bright at (sub)millimetre
wavelengths are undergoing violent episodes of star formation, and there is
evidence that they are preferentially associated with high-redshift radio
galaxies, so the question of whether they are also associated with the most
significant large-scale structure growing at high redshift (as outlined by
Lyman-alpha emitters) naturally arises. Here we report an imaging survey of
1,100-um emission in the SSA 22 region. We find an enhancement of submillimetre
galaxies near the core of the protocluster, and a large-scale correlation
between the submillimetre galaxies and the low-mass Lyman-alpha emitters,
suggesting synchronous formation of the two very different types of
star-forming galaxy within the same structure at high redshift. These results
are in general agreement with our understanding of the formation of cosmic
structure.Comment: Published in Nature (7th May 2009 issue). The astro-ph paper includes
the main text (10 pages, 2 figures, 1 table) and supplementary material (6
pages, 4 figures, 1 table
Shape from Sound: Toward New Tools for Quantum Gravity
To unify general relativity and quantum theory is hard in part because they are formulated in two very different mathematical languages, differential geometry and functional analysis. A natural candidate for bridging this language gap, at least in the case of the Euclidean signature, is the discipline of spectral geometry. It aims at describing curved manifolds in terms of the spectra of their canonical differential operators. As an immediate benefit, this would offer a clean gauge-independent identification of the metric’s degrees of freedom in terms of invariants that should be ready to quantize. However, spectral geometry is itself hard and has been plagued by ambiguities. Here, we regularize and break up spectral geometry into small, finite-dimensional and therefore manageable steps. We constructively demonstrate that this strategy works at least in two dimensions. We can now calculate the shapes of two-dimensional objects from their vibrational spectra
Early Science with the Large Millimeter Telescope: COOL BUDHIES I - a pilot study of molecular and atomic gas at z~0.2
An understanding of the mass build-up in galaxies over time necessitates
tracing the evolution of cold gas (molecular and atomic) in galaxies. To that
end, we have conducted a pilot study called CO Observations with the LMT of the
Blind Ultra-Deep H I Environment Survey (COOL BUDHIES). We have observed 23
galaxies in and around the two clusters Abell 2192 (z = 0.188) and Abell 963 (z
= 0.206), where 12 are cluster members and 11 are slightly in the foreground or
background, using about 28 total hours on the Redshift Search Receiver (RSR) on
the Large Millimeter Telescope (LMT) to measure the CO J = 1 --> 0
emission line and obtain molecular gas masses. These new observations provide a
unique opportunity to probe both the molecular and atomic components of
galaxies as a function of environment beyond the local Universe. For our sample
of 23 galaxies, nine have reliable detections (S/N3.6) of the CO
line, and another six have marginal detections (2.0 < S/N < 3.6). For the
remaining eight targets we can place upper limits on molecular gas masses
roughly between and . Comparing our results to other
studies of molecular gas, we find that our sample is significantly more
abundant in molecular gas overall, when compared to the stellar and the atomic
gas component, and our median molecular gas fraction lies about above
the upper limits of proposed redshift evolution in earlier studies. We discuss
possible reasons for this discrepancy, with the most likely conclusion being
target selection and Eddington bias.Comment: MNRAS, submitte
Statistical Mechanics Analysis of LDPC Coding in MIMO Gaussian Channels
Using analytical methods of statistical mechanics, we analyse the typical
behaviour of a multiple-input multiple-output (MIMO) Gaussian channel with
binary inputs under LDPC network coding and joint decoding. The saddle point
equations for the replica symmetric solution are found in particular
realizations of this channel, including a small and large number of
transmitters and receivers. In particular, we examine the cases of a single
transmitter, a single receiver and the symmetric and asymmetric interference
channels. Both dynamical and thermodynamical transitions from the ferromagnetic
solution of perfect decoding to a non-ferromagnetic solution are identified for
the cases considered, marking the practical and theoretical limits of the
system under the current coding scheme. Numerical results are provided, showing
the typical level of improvement/deterioration achieved with respect to the
single transmitter/receiver result, for the various cases.Comment: 25 pages, 7 figure
Polyimide hollow fiber membranes for CO2 separation from wet gas mixtures
Matrimid®5218 hollow fiber membranes were prepared using the dry-wet spinning process. The transport properties were measured with pure gases (H2, CO2, N2, CH4 and O2) and with a mixture (30% CO2 and 70% N2) in dry and wet conditions at 25 ºC, 50 ºC, 60 ºC and 75 ºC and up to 600 kPa. Interesting values of single gas selectivity up to 60 ºC (between 31 and 28 for CO2/N2 and between 33 and 30 for CO2/CH4) in dry condition were obtained. The separation factor measured for the mixture was 20% lower compared to the single gas selectivity, in the whole temperature range analyzed. In saturation conditions the data showed that water influences the performance of the membranes, inducing a reduction of the permeance of all gases. Moreover, the presence of water caused a decrease of single gas selectivity and separation factor, although not so significant, highlighting the very high water resistance of hollow fiber membrane modules
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