2,859 research outputs found
Discrete Hubbard-Stratonovich transformations for systems with orbital degeneracy
A discrete Hubbard-Stratonovich transformation is presented for systems with
an orbital degeneracy and a Hubbard Coulomb interaction without multiplet
effects. An exact transformation is obtained by introducing an external field
which takes values. Alternative approximate transformations are
presented, where the field takes fewer values, for instance two values
corresponding to an Ising spin.Comment: 4 pages, revtex, 1 eps figure, additional material avalable at
http://librix.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene
Diffusive counter dispersion of mass in bubbly media
We consider a liquid bearing gas bubbles in a porous medium. When gas bubbles
are immovably trapped in a porous matrix by surface-tension forces, the
dominant mechanism of transfer of gas mass becomes the diffusion of gas
molecules through the liquid. Essentially, the gas solution is in local
thermodynamic equilibrium with vapor phase all over the system, i.e., the
solute concentration equals the solubility. When temperature and/or pressure
gradients are applied, diffusion fluxes appear and these fluxes are faithfully
determined by the temperature and pressure fields, not by the local solute
concentration, which is enslaved by the former. We derive the equations
governing such systems, accounting for thermodiffusion and gravitational
segregation effects which are shown not to be neglected for geological
systems---marine sediments, terrestrial aquifers, etc. The results are applied
for the treatment of non-high-pressure systems and real geological systems
bearing methane or carbon dioxide, where we find a potential possibility of the
formation of gaseous horizons deep below a porous medium surface. The reported
effects are of particular importance for natural methane hydrate deposits and
the problem of burial of industrial production of carbon dioxide in deep
aquifers.Comment: 10 pages, 5 figures, 1 table, Physical Review
Inferring Proteolytic Processes from Mass Spectrometry Time Series Data Using Degradation Graphs
Background: Proteases play an essential part in a variety of biological
processes. Besides their importance under healthy conditions they are also
known to have a crucial role in complex diseases like cancer. In recent years,
it has been shown that not only the fragments produced by proteases but also
their dynamics, especially ex vivo, can serve as biomarkers. But so far, only
a few approaches were taken to explicitly model the dynamics of proteolysis in
the context of mass spectrometry. Results: We introduce a new concept to model
proteolytic processes, the degradation graph. The degradation graph is an
extension of the cleavage graph, a data structure to reconstruct and visualize
the proteolytic process. In contrast to previous approaches we extended the
model to incorporate endoproteolytic processes and present a method to
construct a degradation graph from mass spectrometry time series data. Based
on a degradation graph and the intensities extracted from the mass spectra it
is possible to estimate reaction rates of the underlying processes. We further
suggest a score to rate different degradation graphs in their ability to
explain the observed data. This score is used in an iterative heuristic to
improve the structure of the initially constructed degradation graph.
Conclusion: We show that the proposed method is able to recover all degraded
and generated peptides, the underlying reactions, and the reaction rates of
proteolytic processes based on mass spectrometry time series data. We use
simulated and real data to demonstrate that a given process can be
reconstructed even in the presence of extensive noise, isobaric signals and
false identifications. While the model is currently only validated on peptide
data it is also applicable to proteins, as long as the necessary time series
data can be produced
4. The School Develops
Between 1947 and 1953, when M.P. Catherwood left the deanship to become New York’s industrial commissioner, the ILR School developed into a full fledged enterprise. These pages attempt to capture some of the excitement of this period of the school’s history, which was characterized by vigor, growth, and innovation. Includes: Alumni Recall Their Lives as Students; The Faculty Were Giants; Alice Cook: Lifelong Scholar, Consummate Teacher; Frances Perkins; Visits and Visitors; Tenth Anniversary: Reflection and Change; The Emergence of Departments at ILR; Development of International Programs and Outreach
Mining semantic relations between research areas
For a number of years now we have seen the emergence of repositories of research data specified using OWL/RDF as representation languages, and conceptualized according to a variety of ontologies. This class of solutions promises both to facilitate the integration of research data with other relevant sources of information and also to support more intelligent forms of querying and exploration. However, an issue which has only been partially addressed is that of generating and characterizing semantically the relations that exist between research areas. This problem has been traditionally addressed by manually creating taxonomies, such as the ACM classification of research topics. However, this manual approach is inadequate for a number of reasons: these taxonomies are very coarse-grained and they do not cater for the finegrained research topics, which define the level at which typically researchers (and even more so, PhD students) operate. Moreover, they evolve slowly, and therefore they tend not to cover the most recent research trends. In addition, as we move towards a semantic characterization of these relations, there is arguably a need for a more sophisticated characterization than a homogeneous taxonomy, to reflect the different ways in which research areas can be related. In this paper we propose Klink, a new approach to i) automatically generating relations between research areas and ii) populating a bibliographic ontology, which combines both machine learning methods and external knowledge, which is drawn from a number of resources, including Google Scholar and Wikipedia. We have tested a number of alternative algorithms and our evaluation shows that a method relying on both external knowledge and the ability to detect temporal relations between research areas performs best with respect to a manually constructed standard
A Millimeter-Wave Galactic Plane Survey With The BICEP Polarimeter
In addition to its potential to probe the Inflationary cosmological paradigm,
millimeter-wave polarimetry is a powerful tool for studying the Milky Way
galaxy's composition and magnetic field structure. Towards this end, presented
here are Stokes I, Q, and U maps of the Galactic plane from the millimeter-wave
polarimeter BICEP covering the Galactic longitude range 260 - 340 degrees in
three atmospheric transmission windows centered on 100, 150, and 220 GHz. The
maps sample an optical depth 1 < AV < 30, and are consistent with previous
characterizations of the Galactic millimeter-wave frequency spectrum and the
large-scale magnetic field structure permeating the interstellar medium.
Polarized emission is detected over the entire region within two degrees of the
Galactic plane and indicates that the large-scale magnetic field is oriented
parallel to the plane of the Galaxy. An observed trend of decreasing
polarization fraction with increasing total intensity rules out the simplest
model of a constant Galactic magnetic field throughout the Galaxy. Including
WMAP data in the analysis, the degree-scale frequency spectrum of Galactic
polarization fraction is plotted between 23 and 220 GHz for the first time. A
generally increasing trend of polarization fraction with electromagnetic
frequency is found, which varies from 0.5%-1.5%at frequencies below 50 GHz to
2.5%-3.5%above 90 GHz. The BICEP and WMAP data are fit to a two-component
(synchrotron and dust) model showing that the higher frequency BICEP data are
necessary to tightly constrain the amplitude and spectral index of Galactic
dust. Furthermore, the dust amplitude predicted by this two-component fit is
consistent with model predictions of dust emission in the BICEP bands
From high-mass starless cores to high-mass protostellar objects
Aims: Our aim is to understand the evolutionary sequence of high-mass star
formation from the earliest evolutionary stage of high-mass starless cores, via
high-mass cores with embedded low- to intermediate-mass objects, to finally
high-mass protostellar objects. Methods: Herschel far-infrared PACS and SPIRE
observations are combined with existing data at longer and shorter wavelengths
to characterize the spectral and physical evolution of massive star-forming
regions. Results: The new Herschel images spectacularly show the evolution of
the youngest and cold high-mass star-forming regions from mid-infrared shadows
on the Wien-side of the spectral energy distribution (SED), via structures
almost lost in the background emission around 100mum, to strong emission
sources at the Rayleigh-Jeans tail. Fits of the SEDs for four exemplary regions
covering evolutionary stages from high-mass starless cores to high-mass
protostellar objects reveal that the youngest regions can be fitted by
single-component black-bodies with temperatures on the order of 17K. More
evolved regions show mid-infrared excess emission from an additional warmer
component, which however barely contributes to the total luminosities for the
youngest regions. Exceptionally low values of the ratio between bolometric and
submm luminosity additionally support the youth of the infrared-dark sources.
Conclusions: The Herschel observations reveal the spectral and physical
properties of young high-mass star-forming regions in detail. The data clearly
outline the evolutionary sequence in the images and SEDs. Future work on larger
samples as well as incorporating full radiative transfer calculations will
characterize the physical nature at the onset of massive star formation in even
more depth.Comment: 4 pages, A&A Herschel special issu
Helicobacter pylori Colonization in Infants and Young Children is Not Necessarily Associated with Diarrhoea
A cohort of 151 infants and young children aged 1-23 months from a poor peri-urban community of Bangladesh was studied to determine the relationship between Helicobacter pylori colonization and morbidity due to diarrhoea. A 13C urea breath test was performed to detect the presence of H. pylori.Children were followed up at home every alternate day for 6 months and diarrhoeal morbidity datawere collected. Diarrhoeal morbidity was compared between H. pylori-positive and H. pylori-negative children. Sixty-eight (45 per cent) children were H. pylori positive and 83 (55 per cent) were H. pylori negative. During the first 1-month period following the breath test, three (4.4 per cent) H. pylori-positive and four (4.8 per cent) H. pylori-negative children had diarrhoea. Thirty-two (47 per cent) of the children in the positive group and 43 (52 per cent) in the negative group had one or more episodesof diarrhoea during the 6-month follow-up period. Median number of diarrhoeal episodes was 1.0(range 1.0-4.0) in the H. pylori-positive children and 2.0 (range 1.0-5.0) in the H. pylori-negativechildren (p = 0.19). No significant difference was observed in the cumulative days with diarrhoea.The results of this study suggest that H. pylori colonization is not associated with diarrhoealmorbidity in infants and young childre
A Schwarz lemma for K\"ahler affine metrics and the canonical potential of a proper convex cone
This is an account of some aspects of the geometry of K\"ahler affine metrics
based on considering them as smooth metric measure spaces and applying the
comparison geometry of Bakry-Emery Ricci tensors. Such techniques yield a
version for K\"ahler affine metrics of Yau's Schwarz lemma for volume forms. By
a theorem of Cheng and Yau there is a canonical K\"ahler affine Einstein metric
on a proper convex domain, and the Schwarz lemma gives a direct proof of its
uniqueness up to homothety. The potential for this metric is a function
canonically associated to the cone, characterized by the property that its
level sets are hyperbolic affine spheres foliating the cone. It is shown that
for an -dimensional cone a rescaling of the canonical potential is an
-normal barrier function in the sense of interior point methods for conic
programming. It is explained also how to construct from the canonical potential
Monge-Amp\`ere metrics of both Riemannian and Lorentzian signatures, and a mean
curvature zero conical Lagrangian submanifold of the flat para-K\"ahler space.Comment: Minor corrections. References adde
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