1,841 research outputs found
Incremental Sampling-based Algorithm for Minimum-violation Motion Planning
This paper studies the problem of control strategy synthesis for dynamical
systems with differential constraints to fulfill a given reachability goal
while satisfying a set of safety rules. Particular attention is devoted to
goals that become feasible only if a subset of the safety rules are violated.
The proposed algorithm computes a control law, that minimizes the level of
unsafety while the desired goal is guaranteed to be reached. This problem is
motivated by an autonomous car navigating an urban environment while following
rules of the road such as "always travel in right lane'' and "do not change
lanes frequently''. Ideas behind sampling based motion-planning algorithms,
such as Probabilistic Road Maps (PRMs) and Rapidly-exploring Random Trees
(RRTs), are employed to incrementally construct a finite concretization of the
dynamics as a durational Kripke structure. In conjunction with this, a weighted
finite automaton that captures the safety rules is used in order to find an
optimal trajectory that minimizes the violation of safety rules. We prove that
the proposed algorithm guarantees asymptotic optimality, i.e., almost-sure
convergence to optimal solutions. We present results of simulation experiments
and an implementation on an autonomous urban mobility-on-demand system.Comment: 8 pages, final version submitted to CDC '1
Evaluation of bacteria for biological control of early blightdisease of tomato
Twenty three bacterial isolate out of 190, exhibiting inhibitory affects against Alternaria solani in preliminary tests, were screened for their activity towards A. solani Ell. and G. Martin) Sor. by a dualculture in vitro assay on nutrient agar (NA) medium and in vivo (whole plant) test. In vitro studies indicated that all the 23 bacterial isolates inhibited the mycelial growth of A. solani by forming inhibition zone ranging from 9.35 to 31.3 mm. The most effective isolate was Serratia plymuthica (IK- 139) (31.3 mm) based on the in vitro test results. Twenty three bacterial isolates were subjected to a whole plant test to investigate their ability to protect the tomato plant against early blight disease. In whole plant tests, 0.5 x 108 cfu/ml bacterial suspension was sprayed and one day later, A. solani spores suspension were applied on tomato seedlings and plants were incubated in moist chamber at 20°C with 95% relative humidity (RH) and 12 h photoperiods for 21 days. Based on the whole plant tests, Paenibacillus macerans-GC subgroup A (1.82), Serratia plymuthica (1.78), Bacillus coagulans (1.75), Serratia marcescens-GC subgroup A (1.50), Bacillus pumilis –GC subgroup B (1.50) and Pantoea agglomerans (1.32) bacterial isolates reduced the disease severity of early blight significantly when compared with control. These results suggest that the bacterial isolates studied have a good potential to be used as biocontrol agents of A. solani in tomato.Key words: Alternaria solani, early blight, biological control, bacterial isolate
Antioxidant and antimutagenic activities of Viscum album fruit ethanolic extract in human lymphocytes
Polyphenolic compounds are widely distributed in plants and known to be excellent antioxidants in vitro. They have the capacity to reduce free-radical formation by scavenging free-radicals. In this studywe have evaluated the antioxidant and antimutagenic potencies of polyphenolic compounds of Viscum album against trichloroethylene (TCE)-induced oxidative and genotoxic damage. V. album extract (VAE0.5 g/ml) protected human lymphocytes against TCE. In chromosomal aberration (CA) analysis, no significant increase in total aberrations were found after treatment with TCE and all VAE concentrations. The mitotic index (MI) showed significant increase in 0.5 ìg/ml VAE samples whencompared with TCE-treated (2 ìM) group. VAE (0.5 ìg/ml) reduced the levels of malondialdehyde (MDA) significantly wherease VAE (1.0 and 2.0 ìg/ml) samples increased MDA concentrations significantly. We have also shown that the various DNA effects of TCE treatment seem to be DNA damages, but not mutations as TCE treated profiles were reverted back to the control like profiles by most probably DNA repair mechanisms in VAE 0.5 g/ml treated group
Role of thermally-stable deformation twins on the high-temperature mechanical response of an austenitic stainless steel
In the present study, a two-step thermo-mechanical processing consisting of cold work and heat treatment steps was performed to increase the operating temperature of 316 austenitic stainless steels. A hierarchical microstructure of thermally-stable, nano twin bands was achieved forming into bundles in elongated grains. The mechanical response of the samples with this microstructure was evaluated through uniaxial tension tests at temperatures ranging from 20 °C to 500 °C and compared with those from the fully annealed samples. The results demonstrate that such hierarchical microstructure leads to a significant increase in the elevated temperature yield strengths due to the presence of nano-twin boundaries and resulting decrease in dislocation mean free path and increase in dislocation storage capacity. In fact, the yield strength ratio of the twinned and annealed samples increases with increasing temperature up to 500 °C, indicating the effectiveness of pre-existing thermally-stable twin boundaries as the strengthening source at temperatures as high as 0.46 homologous temperature. The hierarchical microstructure also led to irregular serrations through dynamic strain aging in the stress-strain response at 500 °C, which is attributed to the bi-modal microstructural length-scales present in the structure affecting the diffusion distances during dynamic strain aging. This structure also increases the tensile strength, and without a total loss in ductility, even though the flow stress of the twinned samples surpasses the tensile strength of the annealed samples, especially at elevated temperatures. Total hardening rate is consistently higher in the twinned samples as compared to the annealed samples, indicating the positive role of nano-twin boundaries in the dislocation storage capacity at elevated temperatures. Overall, the present study clearly demonstrate the positive role of thermally stable nano-twins on the elevated temperature mechanical response of austenitic stainless steels
From Uncertainty Data to Robust Policies for Temporal Logic Planning
We consider the problem of synthesizing robust disturbance feedback policies
for systems performing complex tasks. We formulate the tasks as linear temporal
logic specifications and encode them into an optimization framework via
mixed-integer constraints. Both the system dynamics and the specifications are
known but affected by uncertainty. The distribution of the uncertainty is
unknown, however realizations can be obtained. We introduce a data-driven
approach where the constraints are fulfilled for a set of realizations and
provide probabilistic generalization guarantees as a function of the number of
considered realizations. We use separate chance constraints for the
satisfaction of the specification and operational constraints. This allows us
to quantify their violation probabilities independently. We compute disturbance
feedback policies as solutions of mixed-integer linear or quadratic
optimization problems. By using feedback we can exploit information of past
realizations and provide feasibility for a wider range of situations compared
to static input sequences. We demonstrate the proposed method on two robust
motion-planning case studies for autonomous driving
An inverse optimization strategy to determine single crystal mechanical behavior from polycrystal tests: Application to AZ31 Mg alloy
An inverse optimization strategy was developed to determine the single crystal properties from experimental results of the mechanical behavior of polycrystals. The polycrystal behavior was obtained by means of the finite element simulation of a representative volume element of the microstructure in which the dominant slip and twinning systems were included in the constitutive equation of each grain. The inverse problem was solved by means of the Levenberg-Marquardt method, which provided an excellent fit to the experimental results. The iterative optimization process followed a hierarchical scheme in which simple representative volume elements were initially used, followed by more realistic ones to reach the final optimum solution, leading to important reductions in computer time. The new strategy was applied to identify the initial and saturation critical resolved shear stresses and the hardening modulus of the active slip systems and extension twinning in a textured AZ31 Mg alloy. The results were in general agreement with the data in the literature but also showed some differences. They were partially explained because of the higher accuracy of the new optimization strategy but it was also shown that the number of independent experimental stress-strain curves used as input is critical to reach an accurate solution to the inverse optimization problem. It was concluded that at least three independent stress-strain curves are necessary to determine the single crystal behavior from polycrystal tests in the case of highly textured Mg alloys
The effect of subsequent stress‐induced martensite aging on the viscoelastic properties of aged NiTiHf polycrystals
This study investigated the effect of stress‐induced martensite aging under tensile and compressive stresses on the functional and viscoelastic properties in Ni50.3Ti32.2Hf17.5 polycrystals containing dispersed H‐phase particles up to 70 nm in size obtained by preliminary austenite aging at 873 K for 3 h. It was found that stress‐induced martensite aging at 428 K for 12 h results in the appearance of a two‐way shape memory effect of −0.5% in compression and +1.8% in tension. Moreover, a significant change in viscoelastic properties can be observed: an increase in internal friction (by 25%) and a change in elastic modulus in tensile samples. The increase in internal friction during martensitic transformation after stress‐induced martensite aging is associated with the oriented growth of thermal‐induced martensite. After stress‐induced martensite aging, the elastic modulus of martensite (EM) increased by 8 GPa, and the elastic modulus of austenite (EA) decreased by 8 GPa. It was shown that stress‐induced martensite aging strongly affects the functional and viscoelastic properties of material and can be used to control them
The effect of stress-induced martensite aging in tension and compression on B2–B19′ martensitic transformation in Ni50.3Ti32.2Hf17.5 high-temperature shape memory alloy
The present study investigates the high-temperature shape memory effect (SME) in heterophase Ni50.3Ti32.2Hf17.5 polycrystals with nanosized H-phase particles after stress-induced martensite (SIM) aging in tension and compression. SIM aging created the conditions for fully reversible two-way SME with a strain of up to 50% of the one-way shape memory strain. SIM aging altered the viscoelastic properties of material, in particular, the elastic moduli of austenite and martensite increased, as did internal friction. Increased interface mobility is suggested as the reason for internal friction growth
Removal of imidacloprid from polluted water using adsorption and membrane separation technologies
In this work, the stability of imidacloprid in fresh water and sludge was studied. The results
revealed that the pesticide is unstable in both media. In freshwater, it underwent hydrolysis
whereas a degradation to several metabolites has been observed in sludge. The rate constants for
the hydrolysis and degradation at 25°C were 0.0.0067 and 0.0.0099 d–1, respectively. Monitoring
the degradation of imidacloprid in sludge by high-pressure liquid chromatography-mass spectrometry
(HPLC-MS) revealed that five metabolites have emerged during the study. These metabolites
include imidacloprid urea, imidacloprid-guanidine, 6-hydroxynicotinic acid, an olefin, and
5-hydroxy, 1-(6-chloro-3-pyridylmethyl)-2-(nitroimino)-imidazolidin-5-ol. The efficiency of Al-Quds
University Wastewater Treatment Plant towards the removal of imidacloprid indicates that the
ultrafiltration-hollow fiber unit was insufficient, whereas the ultrafiltration-spiral wound, activated
carbon, and reverse osmosis units were efficient for complete removal of the pesticide. Adsorption
experiments of imidacloprid using either activated charcoal or micelle-clay complex were found to
fit Langmuir isotherms better than Freundlich isotherm. The data demonstrate a higher Langmuir
Qmax value for the activated charcoal (126.6 mg g–1) when compared to the micelle-clay complex
(11.76 mg g–1). Filtration column experiments, conducted with mixed micelle-clay complex and sand
(using a ratio of 1/50 by mass) at a flow rate of 2 mL min–1 and influent concentration of 50 mg L–1,
revealed that a sufficient removal of imidacloprid was achieved in the first fraction of 100 mL
elution. These findings indicate that the adsorption technology using the micelle-clay complex
provides efficient removal of imidacloprid in continuous flow mode
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