1,472 research outputs found
Dual Band Electrodes in Generator-Collector Mode: Simultaneous Measurement of Two Species
A computational model for the simulation of a double band collector-generator
experiment is applied to the situation where two electrochemical reactions
occur concurrently. It is shown that chronoamperometric measurements can be
used to take advantage of differences in diffusion coefficients to measure the
concentrations of both electroactive species simultaneously, by measuring the
time at which the collection efficiency reaches a specific value. The
separation of the electrodes is shown to not affect the sensitivity of the
method (in terms of percentage changes in the measured time to reach the
specified collection efficiency), but wider gaps can provide a greater range of
(larger) absolute values of this characteristic time. It is also shown that
measuring the time taken to reach smaller collection efficiencies can allow for
the detection of smaller amounts of whichever species diffuses faster. The case
of a system containing both ascorbic acid and opamine in water is used to
exemplify the method, and it is shown that mole fractions of ascorbic acid
between 0.055 and 0.96 can, in principle, be accurately measured.Comment: 34 pages, 8 figure
Reconstructed human keloid models show heterogeneity within keloid scars
Keloid scars are often described as having an actively growing peripheral margin with a regressing centre. The aim of this study was to examine the possible heterogeneity within keloids and the involvement of different regions within and around keloid scars in the pathogenesis, using an in vitro keloid scar model. In vitro skin models were constructed from keratinocytes and fibroblasts from normal skin and different regions within and around keloid scars: periphery, centre, and (adjacent) surrounding-normal-skin regions. Additionally, fibroblasts were isolated from the superficial-central and deep-central regions of the keloid and combined with central keratinocytes. All keloid regions showed increased contraction compared to normal skin models, particularly in central regions. Myofibroblasts were present in all keloid regions but were more abundant in models containing central-deep keloid fibroblasts. Secretion of anti-fibrotic HGF and extracellular matrix collagen IV gene expression was reduced in the central deep keloid compared to normal skin. No significant differences between peripheral and central regions within keloids were observed for inflammatory cytokine CCL20, CCL27, CXCL8, IL-6 and IL-18 secretion. Parameters for surrounding-normal-skin showed similarities to both non-lesional normal skin and keloids. In conclusion, a simple but elegant method of culturing keloid-derived keratinocytes and fibroblasts in an organotypic 3D scar model was developed, for the dual purpose of studying the underlying pathology and ultimately testing new therapeutics. In this study, these tissue engineered scar models show that the central keloid region shows a more aggressive keloid scar phenotype than the periphery and that the surrounding-normal-skin also shares certain abnormalities characteristic for keloids
Interdigitated ring electrodes: Theory and experiment
The oxidation of potassium ferrocyanide, K_4Fe(CN)_6, in aqueous solution
under fully supported conditions is carried out at interdigitated band and ring
electrode arrays, and compared to theoretical models developed to simulate the
processes. Simulated data is found to fit well with experimental results using
literature values of diffusion coefficients for Fe(CN)_6^(4-) and
Fe(CN)_6^(3-). The theoretical models are used to compare responses from
interdigitated band and ring arrays, and the size of ring array required to
approximate the response to a linear band array is investigated. An equation is
developed for the radius of ring required for a pair of electrodes in a ring
array to give a result with 5% of a pair of electrodes in a band array. This
equation is found to be independent of the scan rate used over six orders of
magnitude
The medical student
The Medical Student was published from 1888-1921 by the students of Boston University School of Medicine
Top quark forward-backward asymmetry in R-parity violating supersymmetry
The interaction of bottom squark-mediated top quark pair production,
occurring in the R-parity violating minimal supersymmetric standard model
(MSSM), is proposed as an explanation of the anomalously large
forward-backward asymmetry (FBA) observed at the Tevatron. We find that this
model can give a good fit to top quark data, both the inclusive and invariant
mass-dependent asymmetries, while remaining consistent (at the 2-
level) with the total and differential production cross-sections. The scenario
is challenged by strong constraints from atomic parity violation (APV), but we
point out an extra diagram for the effective down quark-Z vertex, involving the
same coupling constant as required for the FBA, which tends to weaken the APV
constraint, and which can nullify it for reasonable values of the top squark
masses and mixing angle. Large contributions to flavor-changing neutral
currents can be avoided if only the third generation of sparticles is light.Comment: 24 pages, 7 figures. v3: included LHC top production cross section
data; model still consistent at 2 sigma leve
Recommended from our members
BioTIME: A database of biodiversity time series for the Anthropocene.
MotivationThe BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene.Main types of variables includedThe database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record.Spatial location and grainBioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2).Time period and grainBioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year.Major taxa and level of measurementBioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates.Software format.csv and .SQL
Meta-analysis of genome-wide association studies of asthma in ethnically diverse North American populations.
Asthma is a common disease with a complex risk architecture including both genetic and environmental factors. We performed a meta-analysis of North American genome-wide association studies of asthma in 5,416 individuals with asthma (cases) including individuals of European American, African American or African Caribbean, and Latino ancestry, with replication in an additional 12,649 individuals from the same ethnic groups. We identified five susceptibility loci. Four were at previously reported loci on 17q21, near IL1RL1, TSLP and IL33, but we report for the first time, to our knowledge, that these loci are associated with asthma risk in three ethnic groups. In addition, we identified a new asthma susceptibility locus at PYHIN1, with the association being specific to individuals of African descent (P = 3.9 × 10(-9)). These results suggest that some asthma susceptibility loci are robust to differences in ancestry when sufficiently large samples sizes are investigated, and that ancestry-specific associations also contribute to the complex genetic architecture of asthma
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
- …