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991.
A new 3D equilibrated residual method improving accuracy and efficiency of flux-free error estimates
Núria Parés Pedro Díez 《International journal for numerical methods in engineering》2019,120(4):391-432
The paper presents a novel strategy providing fully computable upper bounds for the energy norm of the error in the context of three-dimensional linear finite element approximations of the reaction-diffusion equation. The upper bounds are guaranteed regardless the size of the finite element mesh and the given data, and all the constants involved are fully computable. The upper bound property holds if the shape of the domain is polyhedral and the Dirichlet boundary conditions are piecewise-linear. The new approach is an extension of the flux-free methodology introduced by Parés and Díez in the paper “A new equilibrated residual method improving accuracy and efficiency of flux-free error estimates”, which introduces a guaranteed, low-cost, and efficient flux-free method substantially reducing the computational cost of obtaining guaranteed bounds using flux-free methods while retaining the good quality of the bounds. Besides extending the 2D methodology, specific new modifications are introduced to further reduce the computational cost in the three-dimensional setting. The presented methodology also provides a new strategy to obtain equilibrated boundary tractions, which improves the quality of standard techniques while having a similar computational cost. 相似文献
992.
Cintas P 《Chembiochem : a European journal of chemical biology》2004,5(7):917-920
For more than 150 years natural selection has been perceived to be the overwhelming force in evolution. Only in recent decades have we obtained new insights into environmental and physicochemical factors that participate with selection in a synergic way. Far from denying Darwin's theory, such neglected factors put order to the bewildering range of genotypes and morphologies found in living organisms and, more importantly, they place evolution in a planetary context where biology, geology, and chemistry can easily be integrated. 相似文献
993.
Naranjo J.E. Gonzalez C. Garcia R. de Pedro T. Haber R.E. 《Intelligent Transportation Systems, IEEE Transactions on》2005,6(4):406-415
The unmanned control of the steering wheel is, at present, one of the most important challenges facing researchers in autonomous vehicles within the field of intelligent transportation systems (ITSs). In this paper, we present a two-layer control architecture for automatically moving the steering wheel of a mass-produced vehicle. The first layer is designed to calculate the target position of the steering wheel at any time and is based on fuzzy logic. The second is a classic control layer that moves the steering bar by means of an actuator to achieve the position targeted by the first layer. Real-time kinematic differential global positioning system (RTK-DGPS) equipment is the main sensor input for positioning. It is accurate to about 1 cm and can finely locate the vehicle trajectory. The developed systems are installed on a Citroe/spl uml/n Berlingo van, which is used as a testbed vehicle. Once this control architecture has been implemented, installed, and tuned, the resulting steering maneuvering is very similar to human driving, and the trajectory errors from the reference route are reduced to a minimum. The experimental results show that the combination of GPS and artificial-intelligence-based techniques behaves outstandingly. We can also draw other important conclusions regarding the design of a control system derived from human driving experience, providing an alternative mathematical formalism for computation, human reasoning, and integration of qualitative and quantitative information. 相似文献
994.
Pedro Ado Paulo Mateus Tiago Reis Luca Vigan 《Electronic Notes in Theoretical Computer Science》2006,164(3):3
This paper contributes to further closing the gap between formal analysis and concrete implementations of security protocols by introducing a quantitative extension of the usual Dolev-Yao intruder model. This extended model provides a basis for considering protocol attacks that are possible when the intruder has a reasonable amount of computational power, in particular when he is able, with a certain probability, to guess encryption keys or other particular kind of data such as the body of a hashed message. We also show that these extensions do not augment the computational complexity of the protocol insecurity problem in the case of a finite number of interleaved protocol sessions. 相似文献
995.
Heat and mass transfer on a cylinder surface in cross flow under supersaturated frosting conditions 总被引:1,自引:0,他引:1
In this paper a semi-empirical model describing heat and mass transfer on a cylinder surface in humid air cross flow under supersaturated frosting conditions is presented. The lack of psychrometric data in the supersaturated zone of the psychrometric chart has historically impeded the ability of researchers to accurately predict heat and mass transfer in supersaturated air. The work described in this paper has been partially made possible by developing a systematic procedure to compute the properties of supersaturated moist air, especially in the low temperature zone of the psychrometric chart. Development of such a capability will allow us to predict the amount of frost collected on a coil, the frost deposition and coil heat transfer rates, frost thickness and frost surface temperature, and other important coil frost parameters under supersaturated conditions. 相似文献
996.
A real-time polymerase chain reaction method for monitoring anaerobic,hydrocarbon-degrading bacteria based on a catabolic gene 总被引:1,自引:0,他引:1
We have developed a real-time polymerase chain reaction (PCR) method that can quantify hydrocarbon-degrading bacteria in sediment samples based on a catabolic gene associated with the first step of anaerobic toluene and xylene degradation. The target gene, bssA, codes for the alpha-subunit of benzylsuccinate synthase. The primer-probe set for real-time PCR was based on consensus regions of bssA from four denitrifying bacterial strains; bssA sequences for two of these strains were determined during this study. The method proved to be sensitive (detection limit ca. 5 gene copies) and had a linear range of >7 orders of magnitude. We used the method to investigate how gasohol releases from leaking underground storage tanks could affect indigenous toluene-degrading bacteria. Microcosms inoculated with aquifer sediments from four different sites were incubated anaerobically with BTEX (benzene, toluene, ethylbenzene, and xylenes) and nitrate in the presence and absence of ethanol. Overall, population trends were consistent with observed toluene degradation activity: the microcosms with the most rapid toluene degradation also had the largest numbers of bssA copies. In the microcosms with the most rapid toluene degradation, numbers of bssA copies increased 100-to 1000-fold over the first 4 days of incubation, during which time most of the toluene had been consumed. These results were supported by slot blot analyses with unamplified DNA and by cloning and sequencing of putative bssA amplicons, which confirmed the real-time PCR method's specificity for bssA. Use of a companion real-time PCR method for estimating total eubacterial populations (based on 16S rDNA) indicated that, in some cases, ethanol disproportionately supported the growth of bacteria that did not contain bssA. The real-time PCR method for bssA could be a powerful tool for monitored natural attenuation of BTEX in fuel-contaminated groundwater. To our knowledge, this is the first reported molecular method that targets anaerobic, hydrocarbon-degrading bacteria based on a catabolic gene. 相似文献
997.
We have engineered recombinant yeast to perform stereospecific hydroxylation of dehydroepiandrosterone (DHEA). This mammalian pro-hormone promotes brain and immune function; hydroxylation at the 7alpha position by P450 CYP7B is the major pathway of metabolic activation. We have sought to activate DHEA via yeast expression of rat CYP7B enzyme. Saccharomyces cerevisiae was found to metabolize DHEA by 3beta-acetylation; this was abolished by mutation at atf2. DHEA was also toxic, blocking tryptophan (trp) uptake: prototrophic strains were DHEA-resistant. In TRP(+) atf2 strains DHEA was then converted to androstene-3beta,17beta-diol (A/enediol) by an endogenous 17beta-hydroxysteroid dehydrogenase (17betaHSD). Seven yeast polypeptides similar to human 17betaHSDs were identified: when expressed in yeast, only AYR1 (1-acyl dihydroxyacetone phosphate reductase) increased A/enediol accumulation, while the hydroxyacyl-CoA dehydrogenase Fox2p, highly homologous to human 17betaHSD4, oxidized A/enediol to DHEA. The presence of endogenous yeast enzymes metabolizing steroids may relate to fungal pathogenesis. Disruption of AYR1 eliminated reductive 17betaHSD activity, and expression of CYP7B on the combination background (atf2, ayr1, TRP(+)) permitted efficient (>98%) bioconversion of DHEA to 7alpha-hydroxyDHEA, a product of potential medical utility. 相似文献
998.
Thermoreversible Self‐Assembly of Perfluorinated Core‐Coronas Cellulose‐Nanoparticles in Dry State
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Yonggui Wang Pedro B. Groszewicz Sabine Rosenfeldt Hendrik Schmidt Cynthia A. Volkert Philipp Vana Torsten Gutmann Gerd Buntkowsky Kai Zhang 《Advanced materials (Deerfield Beach, Fla.)》2017,29(43)
Self‐assembly of nanoparticles (NPs) forming unique structures has been investigated extensively over the past few years. However, many self‐assembled structures by NPs are irreversible, because they are generally constructed using their suspensions. It is still challenging for NPs to reversibly self‐assemble in dry state, let alone of polymeric NPs with general sizes of hundreds of nm. Herein, this study reports a new reversible self‐assembly phenomenon of NPs in dry state, forming thermoreversible strip‐like supermolecular structures. These novel NPs of around 150 nm are perfluorinated surface‐undecenoated cellulose nanoparticles (FSU‐CNPs) with a core‐coronas structure. The thermoreversible self‐assembled structure is formed after drying in the air at the interface between FSU‐CNP films and Teflon substrates. Remarkably, the formation and dissociation of this assembled structure are accompanied by a reversible conversion of the surface hydrophobicity, film transparency, and anisotropic properties. These findings show novel feasibility of reversible self‐assembly of NPs in dry state, and thereby expand our knowledge of self‐assembly phenomenon. 相似文献
999.
Optimization of gear ratio and power distribution for a multimotor powertrain of an electric vehicle
The architecture and design of the propulsion system of electric vehicles are highly important for the reduction of energy losses. This work presents a powertrain composed of four electric motors in which each motor is connected with a different gear ratio to the differential of the rear axle. A strategy to reduce energy losses is proposed, in which two phases are applied. Phase 1 uses a divide-and-conquer approach to increase the overall output efficiency by obtaining the optimal torque distribution for the electric motors. Phase 2 applies a genetic algorithm to find the optimal value of the gear ratios, in which each individual of each generation applies Phase 1. The results show an optimized efficiency map for the output torque and speed of the powertrain. The increase in efficiency and the reduction of energy losses are validated by the use of numerical experiments in various driving cycles. 相似文献
1000.
Jenő Gubicza Pedro Henrique R. Pereira Garima Kapoor Yi Huang Subramanya Sarma Vadlamani Terence G. Langdon 《Advanced Engineering Materials》2018,20(9)