1,514 research outputs found
Handling Resource Oscillations Through Selective Misinformation
When resource consumers select among competing providers based on delayed
information, inefficient oscillations in resource utilization can emerge. This paper
describes an approach, based on selective stochastic resource request rejection, for
dealing with this emergent dysfunction.This work was supported by the NSF Computational and Social Systems program as well as the DARPA Control of Agent-Based Systems program
A mixture of feature experts approach for protein-protein interaction prediction
High-throughput methods can directly detect the set of interacting proteins in yeast but the results are often incomplete and exhibit high false positive and false negative rates. A number of researchers have recently presented methods for integrating direct and indirect data for predicting interactions. However, due to missing data and the high redundancy among the features used, different samples may benefit from different features based on the set of attributes available. In addition, in many cases it is hard to directly determine which of the datasets led to the prediction, which is an important issue for the biologists using these predications to design new experiments. To address these challenges we use a Mixture-of-Experts method. We split the data into four (roughly) homogeneous sets. The individual experts use logistic regression and their scores are combined using another logistic regression. However, when combining the scores the weighting of each expert depends on the set of input attributes. Thus different experts will have different influence on the prediction depending on the available features. We applied our method to predict the set of interacting proteins in yeast. Our method improved upon the best previous methods for this task. In addition, using the weighting of the experts the prediction can be easily evaluated by biologists based on the features that they feel are the most reliable.
Structure factor and dynamics of the helix-coil transition
Thermodynamical properties of the helix-coil transition were successfully
described in the past by the model of Lifson, Poland and Sheraga. Here we
compute the corresponding structure factor and show that it possesses a
universal scaling behavior near the transition point, even when the transition
is of first order. Moreover, we introduce a dynamical version of this model,
that we solve numerically. A Langevin equation is also proposed to describe the
dynamics of the density of hydrogen bonds. Analytical solution of this equation
shows dynamical scaling near the critical temperature and predicts a gelation
phenomenon above the critical temperature. In the case when comparison of the
two dynamical approaches is possible, the predictions of our phenomenological
theory agree with the results of the Monte Carlo simulations.Comment: 11 pages, 7 figure
An atom fiber for guiding cold neutral atoms
We present an omnidirectional matter wave guide on an atom chip. The
rotational symmetry of the guide is maintained by a combination of two current
carrying wires and a bias field pointing perpendicular to the chip surface. We
demonstrate guiding of thermal atoms around more than two complete turns along
a spiral shaped 25mm long curved path (curve radii down to 200m) at
various atom--surface distances (35-450m). An extension of the scheme for
the guiding of Bose-Einstein condensates is outlined
Development of one-part geopolymers based on industrial waste
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Trapping and manipulating neutral atoms with electrostatic fields
We report on experiments with cold thermal Li atoms confined in combined
magnetic and electric potentials. A novel type of three-dimensional trap was
formed by modulating a magnetic guide using electrostatic fields. We observed
atoms trapped in a string of up to six individual such traps, a controlled
transport of an atomic cloud over a distance of 400m, and a dynamic
splitting of a single trap into a double well potential. Applications for
quantum information processing are discussed.Comment: 4 pages, 4 figure
Retention of Re in metakaolin based geopolymer in the presence of an organic reductant – an experimental study
The goal of this research was to examine the change in redox sensitive contaminant retention and leaching behavior from a model geopolymer system, during oxidation and carbonation, in the presence of an organic reductant. The behavior of redox sensitive elements under variable environmental conditions is specifically important for understanding the leaching of radionuclides retained in geopolymeric materials (e.g. Tc) that are soluble when oxidized and insoluble under reducing conditions.
An alkali-activated metakaolin geopolymer with high silica/alumina ratio was selected as a model material. Rhenium was selected as the model redox sensitive element, which exhibits a large valence (-3 to +7) and solubility range. Rhenium was introduced in its most oxidized form (VII) as Re2S7. Ascorbic acid was used as a reducing agent during geopolymer casting due to its high solubility and homogeneous distribution within the matrix. Cylindrical monoliths were cured for 90 days under an inert atmosphere (N2) and then aged for 60 days under 98% N2 + 2% CO2 or CO2 deficient air, at a constant relative humidity (68%). The samples were then subjected to EPA 1313 pH dependent leaching test and EPA 1315 monolith leaching test. Leachates were analyzed using DOC and ICP techniques. XRD and SEM – EDS imaging and analyses were used to characterizes the solids
Results show that Re has precipitated as ReS2 (IV) in the matrix. The pH dependent leaching test show that Re was released homogenously throughout most of the pH range (3-12). However, the retention of the material aged under CO2 deficient air was three times lower, indicating that the main effect on leaching from this material is of the oxidation process. The natural pH values were 11.3 and 12 for the material aged under 2% CO2 and for material aged under CO2 deficient air respectively, indicating minor carbonation in the former, however, no carbonate minerals were detected in the matrix.
Monolith leaching results show that the geopolymers aged under CO2 deficient air have retained significantly less Re (0.24% leaching) relative to the sample aged under 2% CO2 (0.07wt % leaching). -log(diffusivity) values were in the order of 15 and 16 for CO2 deficient air and 2% CO2 respectively. There is a clear positive correlation between the amount of Re and DOC released from the samples, where their amounts are significantly larger for the samples aged under CO2 deficient air, indicating that the main Re-release mechanism from these samples is related to chelation to organic species under oxidizing conditions
Inference on the Nature and the Mass of Earth's Late Veneer from Noble Metals and Gases
Noble metals and gases are very sensitive to the late accretion to the Earth
of asteroids and comets. We present mass balance arguments based on these
elements that indicate that 0.7E22-2.7E22 kg of extraterrestrial bodies struck
the Earth after core formation and that comets comprised less than 1E-5 by mass
of the impacting population. These results imply that the dynamics of asteroids
and comets changed drastically with time and that biogenic elements and
prebiotic molecules were not delivered to the Earth by comets but rather by
carbonaceous asteroids.Comment: 10 pages, 2 figures, 1 table, submitted to JG
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