Let T be a nonexpansive monotonic mapping from C to itself where C is a closed subset of a space of bounded real functions, with the supremum norm. We study asymptotic properties of several average iterates of T, related to the cycle time. 相似文献
Between July 1998 and June 1999, 93 lots of broiler chickens distributed on 57 farms were sampled in two abattoirs of the province of Quebec (Canada). A total of 2,325 samples of cecal material were analyzed to determine the prevalence of campylobacters. Biotyping and pulsed-field gel electrophoresis (PFGE) were done on 20% of the Campylobacter isolates to study the distribution within poultry production. Macrorestriction profiles were compared with profiles of 24 Campylobacter strains isolated from sporadic cases of human diarrheic patients in order to evaluate genetic relationships. Approximately 40% of the broiler chickens in 60% of the lots and 67% of the farms were colonized. Biotypes I and II of Campylobacter jejuni were the most prevalent biotypes in poultry and human isolates. The PFGE dendograms revealed a high genetic diversity among poultry isolates, with 49 different genotypes from the 56 positive lots. More than 75% of these lots were colonized by a unique genotype. All positive lots raised simultaneously on the same farm had common genotype(s). Different genotypes were isolated from lots raised at different grow-out periods on a farm. In some cases, identical genotypes were found at different grow-out periods on a farm and also from different farms. Macrorestriction profiles showed that approximately 20% of human Campylobacter isolates were genetically related to genotypes found in poultry. This genetic relationship and the high prevalence of C. jejuni biotypes I and II in poultry indicated that Campylobacter in broiler production of the province of Quebec could be a potential source of hazard for public health. 相似文献
A method that computes the quality of a digital microwave line-of-sight link affected by multipath propagation is presented. The use of a statistical propagation model and of the signature concept allows the propagation effects to be separated from the characteristics of the equipment. Since the variations of the statistical mode coefficients with respect to the characteristics of the link under consideration are not known, experimental results have been achieved using assumptions based on physical considerations. A single channel is considered and the same principles, although more speculative because of the lack of data, are applied to a diversity channel 相似文献
Here, we report on core–clad bioactive borosilicate fibers, that we have prepared both with round and rectangular cross-section profile. The exposed approach, which relies on the stacking and drawing of glass slabs, demonstrates our ability to develop bioactive-based glass fibers with tailored cross-section profiles. Tens-of-meters-long fibers were successfully drawn, although suffering from elevated losses in the case of the rectangular ones. The response of the fibers in simulated body fluid was studied for both geometries. We found that a round cladding can act as protective layer, tempering effects of the corrosion. We also noticed that rectangular fibers are more prone to degradation, the enhanced corrosion beginning from their sharp corners as they accumulated residual tensile stress during drawing. To the best of our knowledge, this is the first report on the effect of residual tensile stresses from surface tension deformations applied to the corrosion of rectangular fibers. As geometry plays a critical role on the biodegradation behavior of the fiberglass, we believe the enclosed results could lead to the design of fiber devices with tailored cross-section profile in order to tune their rate of degradation on solely based geometrical effects. 相似文献
With the development of free space optical links (FSO) for space-ground communications comes the need to mitigate the effects of the atmospheric turbulence to guarantee a lossless connection. By having a network of addressable ground stations, we want to guarantee to always target a point where the link is available. Assuming atmospheric transmission is managed thanks to site diversity, we focus only on the influence of atmospheric turbulence on the signal injected into a single mode fiber on the downlink. The use of adaptive optics (AO) is assumed to avoid turbulence-induced signal disruptions and enable a sufficiently high level of received signal for data transmission. Up to now, AO performance adequate assessment required the knowledge of high-resolution and wind profiles. With the advent of integrated atmospheric parameters measurement instruments, we investigate here the possibility to estimate AO-corrected performance from a limited number of integrated parameters. In this paper, we propose to use a Gaussian process metamodel to assess the statistics of the received optical power after an AO correction. Taking as input only four integrated parameters of the turbulence profile and associated wind profile, which can be measured with simple instruments, the estimation error on the value of the 1% quantile of the received optical power is inferior to . We also demonstrate the possibility to estimate the half correlation time of the received optical power using the same integrated parameters. 相似文献
When planning a new wind farm, optimising the turbine layout to maximise power output is crucial. Traditional approaches based on analytical wake models often fail in complex terrain. In such areas, wake-to-wake interactions and terrain-induced effects need to be taken into account via high-fidelity optimisation. Building on our prior research on how best to maximise offshore wind farm power production by both micro-siting (layout optimisation) and wake steering (yaw angle optimisation), this study focuses on the optimisation of two onshore wind turbines located around a 2D hill. The proposed approach is based on high-fidelity simulations (LES) to account for the complexity of the flow and on Bayesian optimisation (BO) to systematically and efficiently find the optimal configuration for the two turbines given a set of parameters. The LES are performed with the high-order finite-difference wind farm simulator WInc3D, which has been modified for this study to deal with complex terrains and turbines with yaw and tilt. Following the validation of the immersed boundary method (IBM) and wall modelling used to model the complex terrain and of a modified actuator disc model (ADM) to account for tilted turbines, two BO campaigns are presented in this study, with different sets of parameters to optimise. The main flow features and some statistics for each optimum case are discussed using the flow fields with and without the optimised configuration of the upstream turbine to analyse its impact on the downstream turbine and on the overall power of the system. For the first optimisation, the design variables include the wind turbines' streamwise locations and their hub heights (4 parameters). This optimisation study benefits from an elevated upstream turbine hub, leading to a significant power increase in the downstream turbine, thanks to an acceleration of the flow in front of the hill. For the second optimisation, the design space is modified based on the data from the first optimisation, by replacing the turbine's hub height with the possibility of changing the tilt angle of the upstream turbine (4 parameters). It is found that considerable power gains can be obtained while maintaining a modest upstream turbine hub height, by introducing a positive tilt angle in the upstream turbine. Overall, it is found that by setting up the turbines in ways that exploit the speed-up of the flow around the hill, both optimised layouts achieve considerable enhancements in power density over a reference configuration. 相似文献
1,3‐Butadiene is involved in a photocatalyzed amidoarylation reaction that allows the synthesis of N‐allyl amides. The reaction was evaluated on a wide range of aryl diazonium salts and nitriles as co‐reactants. Selectivity issues were studied from the help of a computational approach.
Here, it is demonstrated that the stack-and-draw approach can be expanded to unusual materials association and profile geometries to generate fiber assemblies with unprecedented functionalities. This approach relies on the stacking of flat oxide glass slides into a preform, which is then thermally elongated into tens-of-meters-long ribbon fibers with preserved cross-section ratio. Fabrication methodology is introduced. In order to illustrate the versatility of the method, a panel of fibers with diverse geometries and functions is exposed, including glass-only exposed-core fibers for chemical sensing and, upon the insertion of metal electrodes, H-shaped multi-cavity structures and compact, glass-metal fiber optical detectors applied to a gas analysis by means of fiber-tip plasma spectroscopy. It is believed this new approach will offer an attractive, straightforward solution for designing innovative, complex multimaterial fiber platforms with enhanced functionalities. 相似文献
The morphology of hybrid organic–inorganic perovskite films is known to strongly affect the performance of perovskite‐based solar cells. CH3NH3PbI3‐xClx (MAPbI3‐xClx) films have been previously fabricated with 100% surface coverage in glove boxes. In ambient air, fabrication generally relies on solvent engineering to obtain compact films. In contrast, this work explores the potential of altering the perovskites microstructure for solar cell engineering. This work starts with CH3NH3PbI3‐xClx, films with grain morphology carefully controlled by varying the deposition speed during the spin‐coating process to fabricate efficient and partially transparent solar cells. Devices produced with a CH3NH3PbI3‐xClx film and a compact thick top gold electrode reach a maximum efficiency of 10.2% but display a large photocurrent hysteresis. As it is demonstrated, the introduction of different concentrations of bromide in the precursor solution addresses the hysteresis issues and turns the film morphology into a partially transparent interconnected network of 1D microstructures. This approach leads to semitransparent solar cells with negligible hysteresis and efficiencies up to 7.2%, while allowing average transmission of 17% across the visible spectrum. This work demonstrates that the optimization of the perovskites composition can mitigate the hysteresis effects commonly attributed to the charge trapping within the perovskite film. 相似文献
The charge compensation mechanisms that occur when Li+ substitutes a 2+ element in superionic conductor (MgCoNiCuZn)O high-entropy oxide have been studied using a combination of thermogravimetric analysis and X-ray photoemission spectroscopy. Depending on the concentration of Li+ in the compound, the charge compensation involves first partial oxidation of Co2+ into Co3+ for low fraction of Li+, and then a combination of both the oxidation of cobalt and the formation of oxygen vacancies for large fraction of Li+. 相似文献
