1,108 research outputs found
Autumn microhabitat breadth differs between family groups of Atlantic salmon parr (Salmo salar) in a small chalk stream
The effect of family traits on the microhabitat use by six genetically distinct groups (three in each year of study) of juvenile Atlantic salmon tagged with passive integrated transponder (PIT) tags was studied via PIT-tag detectors installed on the river bed in a small chalk stream of southern England, during Autumn in 2006 and 2007. Canonical correspondence analysis of the molecular and microhabitat data revealed considerable overlap in the microhabitat use of the family groups and notable differences in microhabitat breadth, which was partly influenced by sample size. The data suggest that microhabitat breadth and preferences of wild salmon are influenced by family of origin
Characterization of an antioxidant and antimicrobial extract from cool climate, white grape marc
Valorization of agricultural waste has become increasingly important. Wastes generated by wineries are high in phenolic compounds with antioxidant and antibacterial properties, which contribute to phytotoxicity, making their immediate use for agricultural means limited. Utilizing a water-based extraction method, the phenolic compounds from winery waste were extracted and purified. The resulting extract was characterized for phenolic composition using high-pressure liquid chromatography-ultraviolet/visible and electrochemical detectors (HPLC-UV/Vis, ECD) for monomers, and spectral assessment of the tannins present using attenuated total reflectance-Fourier transform infrared (ATR-FTIR), FT-Raman, and solid-state nuclear magnetic resonance (SSNMR) spectroscopies. The extract\u2019s antioxidant activity was assessed by the scavenging of the 2,2-diphenyl-1\u2013picrylhydrazyl (DPPH) radical and Folin-Ciocalteu total phenolic assay, and was found to be as effective as a commercially obtained grape extract. The extract\u2019s antimicrobial efficacy was tested for minimum bactericidal concentration using Candida albicans, Escherichia coli 25922, and Staphylococcus aureus 6538, which resulted in greater efficacy against gram-positive bacteria as shown over gram-negative bacteria, which can be linked to both monomeric and tannin polyphenols, which have multiple modes of bactericidal action
Glass transition of an epoxy resin induced by temperature, pressure and chemical conversion: a configurational entropy rationale
A comparative study is reported on the dynamics of a glass-forming epoxy
resin when the glass transition is approached through different paths: cooling,
compression, and polymerization. In particular, the influence of temperature,
pressure and chemical conversion on the dynamics has been investigated by
dielectric spectroscopy. Deep similarities are found in dynamic properties. A
unified reading of our experimental results for the structural relaxation time
is given in the framework of the Adam-Gibbs theory. The quantitative agreement
with the experimental data is remarkable, joined with physical values of the
fitting parameters. In particular, the fitting function of the isothermal
tau(P) data gives a well reasonable prediction for the molar thermal expansion
of the neat system, and the fitting function of the isobaric-isothermal tau(C)
data under step- polymerization conforms to the prediction of diverging tau at
complete conversion of the system.Comment: 16 pages, 8 figures, from the talk given at the 4th International
Discussion Meeting on Relaxations in Complex Systems (IDMRCS), Hersonissos,
Helaklion, Crete (Greece), 17-23 June 200
Recommended from our members
A simple method for integrating a complex model into an ensemble data assimilation system using MPI
This paper details a strategy for modifying the source code of a complex model so that the model may be used in a data assimilation context, {and gives the standards for implementing a data assimilation code to use such a model}. The strategy relies on keeping the model separate from any data assimilation code, and coupling the two through the use of Message Passing Interface (MPI) {functionality}. This strategy limits the changes necessary to the model and as such is rapid to program, at the expense of ultimate performance. The implementation technique is applied in different models with state dimension up to . The overheads added by using this implementation strategy in a coupled ocean-atmosphere climate model are shown to be an order of magnitude smaller than the addition of correlated stochastic random errors necessary for some nonlinear data assimilation techniques
Earth-as-an-exoplanet: comparing earthshine observations to models of an exo-Earth
Traditional methods of exoplanet characterization that only make use of emitted or reflected flux lack the ability to fully distinguish between different physical features of the target, such as cloud layers, hazes, or surface features. Polarimetry, however, is a powerful, more sensitive technique that has this ability, as it measures light as a vector (by the orientation of the electric field) rather than a scalar intensity. It is therefore extremely sensitive to the composition and structure of the planetary atmosphere and surface, being affected by properties such as the mixing ratios of atmospheric absorbing gases, cloud optical thickness, cloud top pressure, cloud particle size, and surface albedo. Various groups have theoretically studied the optical linear polarimetric signals of Earth-like exoplanets as functions of both orbital phase and wavelength. With this project we assess the accuracy of these theoretical models against observations of the Earthshine, the only known observations of an Earth-like planet thus far. Using data of the atmosphere and surface taken by the MODIS instrument aboard the Terra and Aqua satellites, as well as surface reflectance spectra from the JPL EcoStress Spectral Library, we created a gridded model of the Earth. Then, using this model data as input for three separate radiative transfer algorithms, we generate the flux and linear polarization spectra for the model exoplanet-Earth across the optical to near-infrared wavelengths. We compare the results from all three codes to each other and to the observational linear spectropolarimetric data of the Earthshine obtained by a member of our group. We identify similarities and potential pitfalls between the codes, and make necessary adjustments to them, in an effort to improve our future characterizations of terrestrial exoplanets.Stars and planetary system
Quantized charge transport through a static quantum dot using a surface acoustic wave
We present a detailed study of the surface acoustic wave mediated quantized
transport of electrons through a split gate device containing an impurity
potential defined quantum dot within the split gate channel. A new regime of
quantized transport is observed at low RF powers where the surface acoustic
wave amplitude is comparable to the quantum dot charging energy. In this regime
resonant transport through the single-electron dot state occurs which we
interpret as turnstile-like operation in which the traveling wave amplitude
modulates the entrance and exit barriers of the quantum dot in a cyclic fashion
at GHz frequencies. For high RF powers, where the amplitude of the surface
acoustic wave is much larger than the quantum dot energies, the quantized
acoustoelectric current transport shows behavior consistent with previously
reported results. However, in this regime, the number of quantized current
plateaus observed and the plateau widths are determined by the properties of
the quantum dot, demonstrating that the microscopic detail of the potential
landscape in the split gate channel has a profound influence on the quantized
acoustoelectric current transport.Comment: 9 page
Comparing models of an exoplanet-earth to earthshine observations
Polarimetry is widely becoming recognized as a powerful technique for enhancing the contrast between a star and an exoplanet, and thus improving upon the direct detection of exoplanets. The real power of polarimetry, however, is in its ability to characterize the physical properties of these worlds. This is because the state of the polarization of the light from the planet is very sensitive to the composition and structure of the planetary atmosphere and surface, being affected by properties such as the mixing ratios of atmospheric absorbing gases, cloud optical thickness, cloud top pressure, cloud particle size, and surface albedo. Various groups have theoretically studied the optical linear polarimetric signals of Earth-like exoplanets as functions of both orbital phase and wavelength. This project aims to validate the accuracy of these theoretical models against the only known observations of an Earth-like planet thus far: Earthshine. Using atmospheric and surface data taken by the MODIS instrument aboard the Terra and Aqua satellites, as well as surface albedo spectra from the EcoStress Spectral Library, we created a detailed model of the Earth. Then, using this model data as input for three separate radiative transfer algorithms, we generate the flux and linear polarization spectra for the model exoplanet-Earth from the optical to near-infrared wavelengths. We compare the results from all three codes to each other and to observational linear spectropolarimetric data of the Earthshine obtained by a member of our group. We identify similarities and potential pitfalls between these codes in an effort to improve our future characterizations of Earth-like exoplanets.Stars and planetary system
The embedding method beyond the single-channel case: Two-mode and Hubbard chains
We investigate the relationship between persistent currents in multi-channel
rings containing an embedded scatterer and the conductance through the same
scatterer attached to leads. The case of two uncoupled channels corresponds to
a Hubbard chain, for which the one-dimensional embedding method is readily
generalized. Various tests are carried out to validate this new procedure, and
the conductance of short one-dimensional Hubbard chains attached to perfect
leads is computed for different system sizes and interaction strengths. In the
case of two coupled channels the conductance can be obtained from a statistical
analysis of the persistent current or by reducing the multi-channel scattering
problem to several single-channel setups.Comment: 14 pages, 13 figures, submitted for publicatio
Limited Lifespan of Fragile Regions in Mammalian Evolution
An important question in genome evolution is whether there exist fragile
regions (rearrangement hotspots) where chromosomal rearrangements are happening
over and over again. Although nearly all recent studies supported the existence
of fragile regions in mammalian genomes, the most comprehensive phylogenomic
study of mammals (Ma et al. (2006) Genome Research 16, 1557-1565) raised some
doubts about their existence. We demonstrate that fragile regions are subject
to a "birth and death" process, implying that fragility has limited
evolutionary lifespan. This finding implies that fragile regions migrate to
different locations in different mammals, explaining why there exist only a few
chromosomal breakpoints shared between different lineages. The birth and death
of fragile regions phenomenon reinforces the hypothesis that rearrangements are
promoted by matching segmental duplications and suggests putative locations of
the currently active fragile regions in the human genome
Aharonov-Bohm Interferometry with Interacting Quantum Dots: Spin Configurations, Asymmetric Interference Patterns, Bias-Voltage-Induced Aharonov-Bohm Oscillations, and Symmetries of Transport Coefficients
We study electron transport through multiply-connected mesoscopic geometries
containing interacting quantum dots. Our formulation covers both equilibrium
and non-equilibrium physics. We discuss the relation of coherent transport
channels through the quantum dot to flux-sensitive Aharonov-Bohm oscillations
in the total conductance of the device. Contributions to transport in first and
second order in the intrinsic line width of the dot levels are addressed in
detail. We predict an interaction-induced asymmetry in the amplitude of the
interference signal around resonance peaks as a consequence of incoherence
associated with spin-flip processes. This asymmetry can be used to probe the
total spin of the quantum dot. Such a probe requires less stringent
experimental conditions than the Kondo effect, which provides the same
information. We show that first-order contributions can be partially or even
fully coherent. This contrasts with the sequential-tunneling picture, which
describes first-order transport as a sequence of incoherent tunneling
processes. We predict bias-voltage induced Aharonov-Bohm oscillations of
physical quantities which are independent of flux in the linear-response
regime. Going beyond the Onsager relations we analyze the relations between the
space symmetry group of the setup and the flux-dependent non-linear
conductance.Comment: 22 pages, 11 figure
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