5,434 research outputs found
Particle dislodgement and entrainment by a low density airstream flowing over a surface
Dislodgement and entrainment of solid particles by low density airstream flowing over particulate surface, for aerodynamic surface erosion stud
Network Lasso: Clustering and Optimization in Large Graphs
Convex optimization is an essential tool for modern data analysis, as it
provides a framework to formulate and solve many problems in machine learning
and data mining. However, general convex optimization solvers do not scale
well, and scalable solvers are often specialized to only work on a narrow class
of problems. Therefore, there is a need for simple, scalable algorithms that
can solve many common optimization problems. In this paper, we introduce the
\emph{network lasso}, a generalization of the group lasso to a network setting
that allows for simultaneous clustering and optimization on graphs. We develop
an algorithm based on the Alternating Direction Method of Multipliers (ADMM) to
solve this problem in a distributed and scalable manner, which allows for
guaranteed global convergence even on large graphs. We also examine a
non-convex extension of this approach. We then demonstrate that many types of
problems can be expressed in our framework. We focus on three in particular -
binary classification, predicting housing prices, and event detection in time
series data - comparing the network lasso to baseline approaches and showing
that it is both a fast and accurate method of solving large optimization
problems
Planetary environment simulation - Martian sand and dust storm simulation and evaluation, volume 2
Particle behavior in simulated Martian sand and dust stor
African vegetable diversity in the limelight: project activities by ProNIVA.
Poster presented at Botanical Congress. Hamburg (Germany), 3-7 Sep 200
Cosmic-ray induced background intercomparison with actively shielded HPGe detectors at underground locations
The main background above 3\,MeV for in-beam nuclear astrophysics studies
with -ray detectors is caused by cosmic-ray induced secondaries. The
two commonly used suppression methods, active and passive shielding, against
this kind of background were formerly considered only as alternatives in
nuclear astrophysics experiments. In this work the study of the effects of
active shielding against cosmic-ray induced events at a medium deep location is
performed. Background spectra were recorded with two actively shielded HPGe
detectors. The experiment was located at 148\,m below the surface of the Earth
in the Reiche Zeche mine in Freiberg, Germany. The results are compared to data
with the same detectors at the Earth's surface, and at depths of 45\,m and
1400\,m, respectively.Comment: Minor errors corrected; final versio
Network Inference via the Time-Varying Graphical Lasso
Many important problems can be modeled as a system of interconnected
entities, where each entity is recording time-dependent observations or
measurements. In order to spot trends, detect anomalies, and interpret the
temporal dynamics of such data, it is essential to understand the relationships
between the different entities and how these relationships evolve over time. In
this paper, we introduce the time-varying graphical lasso (TVGL), a method of
inferring time-varying networks from raw time series data. We cast the problem
in terms of estimating a sparse time-varying inverse covariance matrix, which
reveals a dynamic network of interdependencies between the entities. Since
dynamic network inference is a computationally expensive task, we derive a
scalable message-passing algorithm based on the Alternating Direction Method of
Multipliers (ADMM) to solve this problem in an efficient way. We also discuss
several extensions, including a streaming algorithm to update the model and
incorporate new observations in real time. Finally, we evaluate our TVGL
algorithm on both real and synthetic datasets, obtaining interpretable results
and outperforming state-of-the-art baselines in terms of both accuracy and
scalability
Electrical transport properties of bulk NiFe alloys and related spin-valve systems
Within the Kubo-Greenwood formalism we use the fully relativistic,
spin-polarized, screened Korringa-Kohn-Rostoker method together with the
coherent-potential approximation for layered systems to calculate the
resistivity for the permalloy series NiFe. We are able to
reproduce the variation of the resistivity across the entire series; notably
the discontinuous behavior in the vicinity of the structural phase transition
from bcc to fcc. The absolute values for the resistivity are within a factor of
two of the experimental data. Also the giant magnetoresistance of a series of
permalloy-based spin-valve structures is estimated; we are able to reproduce
the trends and values observed on prototypical spin-valve structures.Comment: 6 pages, ReVTeX + 4 figures (Encapsulated Postscript), submitted to
PR
Near Infrared Imaging of the Hubble Deep Field with The Keck Telescope
Two deep K-band () images, with point-source detection limits of
mag (one sigma), taken with the Keck Telescope in subfields of the
Hubble Deep Field, are presented and analyzed. A sample of objects to K=24 mag
is constructed and and colors are measured. By
stacking visually selected objects, mean colors can be measured to
very faint levels; the mean color is constant with apparent
magnitude down to mag.Comment: Replaced with slightly revised source positions and corrected V-I
magnitudes (which were incorrect in the Tables and Figure 5). 18 pages. The
data are publicly available at http://www.cco.caltech.edu/~btsoifer/hdf.html
along with a high-resolution version of Fig.
Microbial âgardeningâ by a seaweed holobiont: Surface metabolites attract protective and deter pathogenic epibacterial settlement
Epimicrobial communities on seaweed surfaces usually contain not only potentially pathogenic but also potentially beneficial microâorganisms. Capacity of terrestrial plants for chemically mediated recruitment, that is, âgardeningâ of bacterial communities in the rhizosphere was recently demonstrated. Empirical evidence directly linking such chemical âgardeningâ with the beneficial role of gardened microbes in terrestrial plants is rare and largely missing for aquatic macrophytes.
Here, we demonstrate that our model invasive seaweed holobiont Agarophyton vermiculophyllum possesses beneficial microbiota on its surface that provide protection from bacterial pathogens. Metabolites from the algal holobiontâs surface reduced settlement of opportunistic pathogens but attracted protective epibacterial settlement.
We tested 58 different bacterial species (isolated from the surface of A. vermiculophyllum ) individually in tip bleaching assays. Kordia algicida was identified as a âsignificant pathogenâ inducing a bleaching disease. In addition, nine other species significantly reduced the risk of algal bleaching and were thus âsignificantly protectiveâ. Additionally, two âpotential pathogensâ and 10 âpotential protectorsâ were identified. When 19 significant and potential protectors and 3 significant and potential pathogens were tested together, the protective strains fully prevented bleaching, suggesting that a component of A. vermiculophyllumâs epimicrobiome provides an associational defence against pathogens. Chemically mediated selective recruitment of microbes was demonstrated in bioassays, where A. vermiculophyllum surface metabolites attracted the settlement of protective strains, but reduced settlement of pathogens.
Synthesis . The capacity of an aquatic macrophyte to chemically âgardenâ protective microâorganisms to the benefit of strengthened disease resistance is demonstrated for the first time. Such a role of surface chemistry in âgardeningâ of microbes as found in the current study could also be applicable to other host plantâmicrobe interactions. Our results may open new avenues towards manipulation of the surface microbiome of seaweeds via chemical âgardening,â enhancing sustainable production of healthy seaweeds
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