The electro-catalytic oxidation of CO and CO/H2 mixtures on polycrystalline Pt has been investigated on two electrodes with controllable degrees of coupling strength by means of experiments and numerical simulations. With strong positive coupling, large differences between the currents of the two almost-identical electrodes arise in a range of potential. Experiments on CO oxidation were carried out in three different electrolytes; all three electrolytes support pattern formation to an extent in the following order: 0.05 mol/L sulfuric acid with saturated sodium sulfate > 0.05 mol/L sulfuric acid > 0.1 mol/L perchloric acid. Experiments with 2% CO/H2 mixtures also exhibit nonuniform states with coupling. Numerical simulations on CO electro-oxidation confirmed the experimental findings: the current differences occur due to a symmetry breaking both with identical electrodes (through a pitchfork bifurcation) and with electrodes with inherent heterogeneities (due to a formation of an isola). The nonuniform reaction rates due to small inherent heterogeneities are greatly amplified by coupling. Simulations also show that the total coverage of CO and OH is always lower (and the number of total free active sites higher) in the nonuniform states; this suggests the possibility of increased total reaction rate not only in the CO oxidation system but also in systems in which the CO electro-oxidation occurs in parallel with other chemical and electrochemical reaction steps.
This center operates a number of sophisticated wind tunnels in order to fulfill the needs of its researchers. Compressed air, which is kept in steel storage vessels, is used to power many of these tunnels. Some of these vessels have been in use for many years, and Langley is currently recertifying these vessels to insure their continued structural integrity. One of the first facilities to be recertified under this program was the Langley 8-foot high-temperature structures tunnel. This recertification involved (1) modification, hydrotesting, and inspection of the vessels; (2) repair of all relevant defects; (3) comparison of the original design of the vessel with the current design criteria of Section 8, Division 2, of the 1974 ASME Boiler and Pressure Vessel Code; (4) fracture-mechanics, thermal, and wind-induced vibration analyses of the vessels; and (5) development of operating envelopes and a future inspection plan for the vessels. Following these modifications, analyses, and tests, the vessels were recertified for operation at full design pressure (41.4 MPa (6000 psi)) within the operating envelope developed.
A theoretical analysis is presented to show the general occurrence of phase clusters in weakly, globally coupled oscillators close to a Hopf bifurcation. Through a reductive perturbation method, we derive the amplitude equation with a higher-order correction term valid near a Hopf bifurcation point. This amplitude equation allows us to calculate analytically the phase coupling function from given limit-cycle oscillator models. Moreover, using the phase coupling function, the stability of phase clusters can be analyzed. We demonstrate our theory with the Brusselator model. Experiments are carried out to confirm the presence of phase clusters close to Hopf bifurcations with electrochemical oscillators.
Various stimulation desynchronization techniques are explored in a laboratory experiment on electrochemical oscillators, a system that exhibits transient dynamics, heterogeneities, and inherent noise. Stimulation with a short, single pulse applied at a vulnerable phase can effectively desynchronize a cluster. A double pulse method, that can be applied at any phase, can be improved either by adding an extra weak pulse between the original two pulses or by adding noise to the first pulse.
Background: Questions remain regarding both the safety and efficacy of bariatric surgery in patients with inflammatory bowel diseases (IBD), including the effects of bariatric surgery on the course of disease. We report a case series from a tertiary care IBD referral center and review the existing literature regarding the safety and efficacy of bariatric surgery in IBD patients. Objectives: Examine the safety and efficacy of bariatric surgery in IBD patients. Explore possible effects of weight loss on postoperative IBD course. Method: We performed a retrospective review of patients at our center undergoing bariatric surgery with a concurrent IBD diagnosis, collecting baseline characteristics, surgery type, and postoperative course (including IBD outcomes and weight loss). Data from these patients were combined with available data from the existing literature to calculate standardized means with standard error, variance, and confidence intervals (CI). Results: Data from 13 patients who had undergone bariatric surgery at our facility were combined with data from 8 other studies to create a study population of 101 patients. Of these, 61 had Crohn’s disease, 37 ulcerative colitis, and 3 IBD-unspecified, with a mean preoperative BMI of 44.2 (95% CI 42.9–45.7). Following surgery, a mean excess weight loss of 68.4% was demonstrated (95% CI, 65.7–71.2). Of the 101 patients, 22 experienced early and 20 experienced late postoperative complications. Postoperatively, 10 patients experienced a flare of IBD, 20 remained in remission, and 7 patients were able to discontinue immunosuppressive therapy. Conclusions: Based on available studies, bariatric surgery appears to be both an effective and safe option for weight loss in patients with IBD.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChaotic forcing generates a wrinkled boundaryOtto E. Rossler, John L. Hudson, and Michael KleinCite this: J. Phys. Chem. 1989, 93, 7, 2858–2860Publication Date (Print):April 1, 1989Publication History Published online1 May 2002Published inissue 1 April 1989https://pubs.acs.org/doi/10.1021/j100344a031https://doi.org/10.1021/j100344a031research-articleACS PublicationsRequest reuse permissionsArticle Views32Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts
Abstract The occurrence of instabilities in chemically reacting systems, resulting in unsteady and spatially inhomogeneous reaction rates, is a widespread phenomenon. In this article, we use nonlinear signal processing techniques to extract a simple, but accurate, dynamic model from experimental data of a system with spatiotemporal variations. The approach consists of a combination of two steps. The proper orthogonal decomposition [POD or Karhunen‐Loève (KL) expansion] allows us to determine active degrees of freedom (important spatial structures) of the system. Projection onto these “modes” reduces the data to a small number of time series. Processing these time series through an artificial neural network (ANN) results in a low‐dimensional, nonlinear dynamic model with almost quantitative predictive capabilities. This approach is demonstrated using spatiotemporal data from CO oxidation on a Pt (110) crystal surface. In this special case, the dynamics of the two‐dimensional reaction profile can be successfully described by four modes; the ANN‐based model not only correctly predicts the spatiotemporal short‐term behavior, but also accurately captures the long‐term dynamics (the attractor). While this approach does not substitute for fundamental modeling, it provides a systematic framework for processing experimental data from a wide variety of spatiotemporally varying reaction engineering processes.
