310 research outputs found
Low-energy positron collisions with water: elastic and rotationally inelastic scattering
Differential, integral and momentum transfer cross sections for the vibrationally elastic and rotationally inelastic scattering of positrons from water at low collision energy ( E <= 10 eV) are reported. Several models within the R-matrix method are used to compute the body-fixed T-matrices, while the scattering calculations are performed within the fixed-nuclei approximation corrected with the standard Born-closure formula. These calculations are compared with experimental results for elastic scattering, and the best model gives reasonable agreement with the most recent measurements (Zecca et al 2006 J. Phys. B: At. Mol. Opt. Phys. 39 1597) but not with some earlier studies. The relative contribution of the rotationally inelastic processes is investigated and comparisons are made with the equivalent electron scattering cross sections
The experimental determination of reliable biodegradation rates for mono-aromatics towards evaluating QSBR models
Quantitative Structure Biodegradation Relationships (QSBRs) are a tool to predict the biodegradability of chemicals. The objective of this work was to generate reliable biodegradation data for mono-aromatic chemicals in order to evaluate and verify previously developed QSBRs models. A robust biodegradation test method was developed to estimate specific substrate utilization rates, which were used as a proxy for biodegradation rates of chemicals in pure culture. Five representative mono-aromatic chemicals were selected that spanned a wide range of biodegradability. Aerobic biodegradation experiments were performed for each chemical in batch reactors seeded with known degraders. Chemical removal, degrader growth and CO2 production were monitored over time. Experimental data were interpreted using a full carbon mass balance model, and Monod kinetic parameters (Y, Ks, qmax and μmax) for each chemical were determined. In addition, stoichiometric equations for aerobic mineralization of the test chemicals were developed. The theoretically estimated biomass and CO2 yields were similar to those experimentally observed; 35 (s.d ± 8) of the recovered substrate carbon was converted to biomass, and 65 (s.d ± 8) was mineralised to CO2. Significant correlations were observed between the experimentally determined specific substrate utilization rates, as represented by qmax and qmax/Ks, at high and low substrate concentrations, respectively, and the first order biodegradation rate constants predicted by a previous QSBR study. Similarly, the correlation between qmax and selected molecular descriptors characterizing the chemicals structure in a previous QSBR study was also significant. These results suggest that QSBR models can be reliable and robust in prioritising chemical half-lives for regulatory screening purposes
Explicit memory schemes for evolutionary algorithms in dynamic environments
Copyright @ 2007 Springer-VerlagProblem optimization in dynamic environments has atrracted a growing interest from the evolutionary computation community in reccent years due to its importance in real world optimization problems. Several approaches have been developed to enhance the performance of evolutionary algorithms for dynamic optimization problems, of which the memory scheme is a major one. This chapter investigates the application of explicit memory schemes for evolutionary algorithms in dynamic environments. Two kinds of explicit memory schemes: direct memory and associative memory, are studied within two classes of evolutionary algorithms: genetic algorithms and univariate marginal distribution algorithms for dynamic optimization problems. Based on a series of systematically constructed dynamic test environments, experiments are carried out to investigate these explicit memory schemes and the performance of direct and associative memory schemes are campared and analysed. The experimental results show the efficiency of the memory schemes for evolutionary algorithms in dynamic environments, especially when the environment changes cyclically. The experimental results also indicate that the effect of the memory schemes depends not only on the dynamic problems and dynamic environments but also on the evolutionary algorithm used
Pixel classification through Mahalanobis distance for identification of grapevine canopy elements on RGB images
Vine vigour and fruit-cluster exposure to sunlight in a grapevine canopy fruiting zone has been shown to strongly correlate with key fruit composition and diseases incidence. In this framework, the use of automated image analysis for the identification of plant elements is an important issue to be addressed for vineyard assessment (Dunn and Martin, 2004). In addition, optimum segmentation method is strongly application dependent and thus needs to be tested for each particular case (Cheng et al., 2001). The objective of the present work is to propose and test a simple, rapid and practical method for the identification of two relevant elements of grapevines canopy: clusters and green leaves
Low and intermediate energy electron collisions with the C molecular anion
Calculations are presented which use the molecular R-matrix with
pseudo-states (MRMPS) method to treat electron impact electron detachment and
electronic excitation of the carbon dimer anion. Resonances are found above the
ionisation threshold of C with , and
symmetry. These are shape resonances trapped by the effect of an attractive
polarisation potential competing with a repulsive Coulomb interaction. The
resonances are found to give structure in the detachment cross section
similar to that observed experimentally. Both excitation and detachment cross
sections are found to be dominated by large impact parameter collisions whose
contribution is modelled using the Born approximation.Comment: 18 pages, 5 figures constructed from 8 file
Stochastic Substitute Training: A Gray-box Approach to Craft Adversarial Examples Against Gradient Obfuscation Defenses
It has been shown that adversaries can craft example inputs to neural
networks which are similar to legitimate inputs but have been created to
purposely cause the neural network to misclassify the input. These adversarial
examples are crafted, for example, by calculating gradients of a carefully
defined loss function with respect to the input. As a countermeasure, some
researchers have tried to design robust models by blocking or obfuscating
gradients, even in white-box settings. Another line of research proposes
introducing a separate detector to attempt to detect adversarial examples. This
approach also makes use of gradient obfuscation techniques, for example, to
prevent the adversary from trying to fool the detector. In this paper, we
introduce stochastic substitute training, a gray-box approach that can craft
adversarial examples for defenses which obfuscate gradients. For those defenses
that have tried to make models more robust, with our technique, an adversary
can craft adversarial examples with no knowledge of the defense. For defenses
that attempt to detect the adversarial examples, with our technique, an
adversary only needs very limited information about the defense to craft
adversarial examples. We demonstrate our technique by applying it against two
defenses which make models more robust and two defenses which detect
adversarial examples.Comment: Accepted by AISec '18: 11th ACM Workshop on Artificial Intelligence
and Security. Source code at https://github.com/S-Mohammad-Hashemi/SS
Endotoxin-induced lung alveolar cell injury causes brain cell damage
Instituto de Salud Carlos III (ISCIII
Faint recombination lines in Galactic PNe with [WC] nucleus
We present spatially resolved high-resolution spectrophotometric data for the
planetary nebulae PB8, NGC2867, and PB6. We have analyzed two knots in NGC2867
and PB6 and one in PB8. The three nebulae are ionized by [WC] type nuclei:
early [WO] for PB6 and NGC2867 and [WC 5-6] in the case of PB8. Our aim is to
study the behavior of the abundance discrepancy problem (ADF) in this type of
PNe. We measured a large number of optical recombination (ORL) and
collisionally excited lines (CEL), from different ionization stages (many more
than in any previous work), thus, we were able to derive physical conditions
from many different diagnostic procedures. We determined ionic abundances from
the available collisionally excited lines and recombination lines. Based on
both sets of ionic abundances, we derived total chemical abundances in the
nebulae using suitable ionization correction factors. From CELs, we have found
abundances typical of Galactic disk planetary nebulae. Moderate ADF(O++) were
found for PB8 (2.57) and NGC2867 (1.63). For NGC2867, abundances from ORLs are
higher but still consistent with Galactic disk planetary nebulae. On the
contrary, PB8 presents a very high O/H ratio from ORLs. A high C/O was obtained
from ORLs for NGC2867; this ratio is similar to C/O obtained from CELs and with
the chemical composition of the wind of the central star, indicating that there
was no further C-enrichment in the star, relative to O, after the nebular
material ejection. On the contrary, we found C/O<1 in PB8. Interestingly, we
obtain (C/O)ORLs/(C/O)CELs < 1 in PB8 and NGC2867; this added to the similarity
between the heliocentric velocities measured in [OIII] and OII lines for our
three objects, argue against the presence of H-deficient metal-rich knots
coming from a late thermal pulse event.Comment: 25 pages, 13 Tables, 4 Figures Accepted for publication in A&A. First
page is blank for obscure latex reason
Feature selection and novelty in computational aesthetics
[Abstract] An approach for exploring novelty in expression-based evolutionary art systems is presented. The framework is composed of a feature extractor, a classifier, an evolutionary engine and a supervisor. The evolutionary engine exploits shortcomings of the classifier, generating misclassified instances. These instances update the training set and the classifier is re-trained. This iterative process forces the evolutionary algorithm to explore new paths leading to the creation of novel imagery. The experiments presented and analyzed herein explore different feature selection methods and indicate the validity of the approach.Portugal. Fundação para a Ciência e a Tecnologia; PTDC/EIA–EIA/115667/2009Galicia.Consellería de Innovación, Industria e Comercio ; PGIDIT10TIC105008P
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