6,252 research outputs found
Mocarts: a lightweight radiation transport simulator for easy handling of complex sensing geometries
In functional neuroimaging (fNIRS), elaborated sensing geometries pairing multiple light sources and detectors arranged over the tissue surface are needed. A variety of software tools for probing forward models of radiation transport in tissue exist, but their handling of sensing geometries and specification of complex tissue architectures is, most times, cumbersome. In this work, we introduce a lightweight simulator, Monte Carlo Radiation Transport Simulator (MOCARTS) that attends these demands for simplifying specification of tissue architectures and complex sensing geometries. An object-oriented architecture facilitates such goal. The simulator core is evolved from the Monte Carlo Multi-Layer (mcml) tool but extended to support multi-channel simulations. Verification against mcml yields negligible error (RMSE~4-10e-9) over a photon trajectory. Full simulations show concurrent validity of the proposed tool. Finally, the ability of the new software to simulate multi-channel sensing geometries and to define biological tissue models in an intuitive nested-hierarchy way are exemplified
Maceration Enzymes and Mannoproteins: A Possible Strategy To Increase Colloidal Stability and Color Extraction in Red Wines
Different strategies were adopted to achieve increases in color stability in Tempranillo wines: (i) addition of maceration enzymes directly to the must, (ii) addition of commercial mannoproteins to the must, and (iii) inoculation of must with yeast overexpressed of mannoproteins. The addition of enzymes favored color extraction, and the wines obtained presented higher values of wine color, color intensity, bisulfite-stable color, and visually enhanced color intensity. The enzyme hydrolytic activity produced an increase in the acid polysaccharide content and polyphenol index and yielded to wines with more astringency, tannin, and length. Added mannoproteins had clearer effects on the analyzed parameters than yeast. Contrary to what may be thought, mannoproteins did not maintain the extracted polyphenols in colloidal dispersion and neither ensured color stability. These compounds clearly modified the gustative structure of the wines, enhancing the sweetness and roundness. © 2007 American Chemical Society
Temperature dependent magnetization dynamics of magnetic nanoparticles
Recent experimental and theoretical studies show that the switching behavior
of magnetic nanoparticles can be well controlled by external time-dependent
magnetic fields. In this work, we inspect theoretically the influence of the
temperature and the magnetic anisotropy on the spin-dynamics and the switching
properties of single domain magnetic nanoparticles (Stoner-particles). Our
theoretical tools are the Landau-Lifshitz-Gilbert equation extended as to deal
with finite temperatures within a Langevine framework. Physical quantities of
interest are the minimum field amplitudes required for switching and the
corresponding reversal times of the nanoparticle's magnetic moment. In
particular, we contrast the cases of static and time-dependent external fields
and analyze the influence of damping for a uniaxial and a cubic anisotropy.Comment: accepted by Journal of Physics: Condensed Matte
OVRO N2H+ Observations of Class 0 Protostars: Constraints on the Formation of Binary Stars
We present the results of an interferometric study of the N2H+(1--0) emission
from nine nearby, isolated, low-mass protostellar cores, using the OVRO
millimeter array. The main goal of this study is the kinematic characterization
of the cores in terms of rotation, turbulence, and fragmentation. Eight of the
nine objects have compact N2H+ cores with FWHM radii of 1200 -- 3500 AU,
spatially coinciding with the thermal dust continuum emission. The only more
evolved (Class I) object in the sample (CB 188) shows only faint and extended
N2H+ emission. The mean N2H+ line width was found to be 0.37 km/s. Estimated
virial masses range from 0.3 to 1.2 M_sun. We find that thermal and turbulent
energy support are about equally important in these cores, while rotational
support is negligible. The measured velocity gradients across the cores range
from 6 to 24 km/s/pc. Assuming these gradients are produced by bulk rotation,
we find that the specific angular momenta of the observed Class 0 protostellar
cores are intermediate between those of dense (prestellar) molecular cloud
cores and the orbital angular momenta of wide PMS binary systems. There appears
to be no evolution (decrease) of angular momentum from the smallest prestellar
cores via protostellar cores to wide PMS binary systems. In the context that
most protostellar cores are assumed to fragment and form binary stars, this
means that most of the angular momentum contained in the collapse region is
transformed into orbital angular momentum of the resulting stellar binary
systems.Comment: 35 pages, 9 figures (one in color), 6 tables. Accepted by ApJ (to
appear in Nov. 2007
Horseshoe-based Bayesian nonparametric estimation of effective population size trajectories
Phylodynamics is an area of population genetics that uses genetic sequence
data to estimate past population dynamics. Modern state-of-the-art Bayesian
nonparametric methods for recovering population size trajectories of unknown
form use either change-point models or Gaussian process priors. Change-point
models suffer from computational issues when the number of change-points is
unknown and needs to be estimated. Gaussian process-based methods lack local
adaptivity and cannot accurately recover trajectories that exhibit features
such as abrupt changes in trend or varying levels of smoothness. We propose a
novel, locally-adaptive approach to Bayesian nonparametric phylodynamic
inference that has the flexibility to accommodate a large class of functional
behaviors. Local adaptivity results from modeling the log-transformed effective
population size a priori as a horseshoe Markov random field, a recently
proposed statistical model that blends together the best properties of the
change-point and Gaussian process modeling paradigms. We use simulated data to
assess model performance, and find that our proposed method results in reduced
bias and increased precision when compared to contemporary methods. We also use
our models to reconstruct past changes in genetic diversity of human hepatitis
C virus in Egypt and to estimate population size changes of ancient and modern
steppe bison. These analyses show that our new method captures features of the
population size trajectories that were missed by the state-of-the-art methods.Comment: 36 pages, including supplementary informatio
TEMPORAL AND SPATIAL DISTRIBUTION OF POACEAE POLLEN IN AREAS OF SOUTHERN UNITED KINGDOM, SPAIN AND PORTUGAL
Overall, longer Poaceae pollen seasons coincided with earlier pollen season start dates. Winter rainfall noticeably affects
the intensity of Poaceae pollen seasons in Mediterranean areas, but this was not as important in Worcester. Weekly data
from Worcester followed a similar pattern to that of Badajoz and Évora but at a distance of more than 1500 km and 4-5
weeks later
Phonon runaway in nanotube quantum dots
We explore electronic transport in a nanotube quantum dot strongly coupled
with vibrations and weakly with leads and the thermal environment. We show that
the recent observation of anomalous conductance signatures in single-walled
carbon nanotube (SWCNT) quantum dots can be understood quantitatively in terms
of current driven `hot phonons' that are strongly correlated with electrons.
Using rate equations in the many-body configuration space for the joint
electron-phonon distribution, we argue that the variations are indicative of
strong electron-phonon coupling requiring an analysis beyond the traditional
uncorrelated phonon-assisted transport (Tien-Gordon) approach.Comment: 8 pages, 6 figure
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