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Fourier time spectral method for subsonic and transonic flows

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Acta Mechanica Sinica 2016年第3期32卷 380-396页

作者： Lei Zhan Feng Liu dimitri Papamoschou School of Aeronautics Northwestern Polytechnical UniversityXi'an 710072China Department of Mechanical and Aerospace Engineering University of CaliforniaIrvineCA 92697USA

The time accuracy of the exponentially accurate Fourier time spectral method（TSM） is examined and compared with a conventional 2nd-order backward difference formula（BDF） method for periodic unsteady flows. In particular, detailed error analysis based on numerical computations is performed on the accuracy of resolving the local pressure coefficient and global integrated force coefficients for smooth subsonic and non-smooth transonic flows with moving shock waves on a pitching airfoil. For smooth subsonic flows, the Fourier TSM method offers a significant accuracy advantage over the BDF method for the prediction of both the local pressure coefficient and integrated force coefficients. For transonic flows where the motion of the discontinuous shock wave contributes significant higherorder harmonic contents to the local pressure fluctuations,a sufficient number of modes must be included before the Fourier TSM provides an advantage over the BDF *** Fourier TSM, however, still offers better accuracy than the BDF method for integrated force coefficients even for transonic flows. A problem of non-symmetric solutions for symmetric periodic flows due to the use of odd numbers of intervals is uncovered and analyzed. A frequency-searching method is proposed for problems where the frequency is not known a priori. The method is tested on the vortex shedding problem of the flow over a circular cylinder.

关键词： Fourier time spectral method(TSM) Pitching airfoil Transonic flow Non-symmetric solution Computational efficiency Vortex shedding flow Frequency search

Active gastrointestinal bleeding:Use of hemostatic forceps beyond endoscopic submucosal dissection

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World Journal of Gastroenterology 2010年第16期16卷 2061-2064页

作者： dimitri Coumaros Niki Tsesmeli Department of Hepatogastroenterology University Hospital of Strasbourg

To the best of our knowledge,this is the f irst report of the application of hemostatic forceps in active gastrointestinal(GI) bleeding that is not related to endoscopic submucosal *** 86-year-old woman with chronic intake of low-dose aspirin had a Dieulafoy's lesion of the third duodenal *** control with epinephrine injection was unsuccessful.A 60-year-old man presented with a bleeding ulcer in the duodenal *** days after combined endotherapy,he had recurrent bleeding from two minimal lesions in the same location.A 66-year-old woman under combined antithrombotic treatment was referred to us for chronic GI bleeding of unexplained *** revealed active diverticular bleeding in the second duodenal portion.A 61-year-old woman underwent endoscopic mucosal resection of superficial gastric adenocarcinoma,which was complicated with immediate *** all cases,the blood was washed out using a water-jet-equipped,single-channel gastroscope with a large working *** bleeding points were pinched and retracted with hemostatic *** electrocoagulation was performed using an electrosurgical current *** was *** complications *** conclusion,hemostatic forceps may be an effective as well as safe alternative approach for active GI bleeding of various origins.

关键词： Hemostasis Forceps Blood coagulation Hemorrhage Endoscopic submucosal dissection

Acute acalculous cholecystitis in children

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World Journal of Gastroenterology 2018年第43期24卷 4870-4879页

作者： dimitri Poddighe Vitaliy Sazonov Department of Medicine School of MedicineNazarbayev University Pediatric Intensive Care Unit UMC National Research Center for Mother and Child Health

Acute acalculous cholecystitis(AAC) is the inflammatory disease of the gallbladder in the absence of gallstones. AAC is estimated to represent at least 50% to 70% of all cases of acute cholecystitis during childhood. Although this pathology was originally described in critically ill or post-surgical patients, most pediatric cases have been observed during several infectious diseases. In addition to cases caused by bacterial and parasitic infections, most pediatric reports after 2000 described children developing AAC during viral illnesses(such as Epstein-Barr virus and hepatitis A virus infections). Moreover, some pediatric cases have been associated with several underlying chronic diseases and, in particular, with immune-mediated disorders. Here, we review the epidemiological aspects of pediatric AAC, and we discuss etiology, pathophysiology and clinical management, according to the cases reported in the medical literature.

关键词： Acute acalculous cholecystitis Children Viral biliary disorders

Prevalence and Factors Associated with Intestinal Metaplasia in Chronic Helicobacter pylori Gastritis in a Country with High Endemicity: Ivory Coast Case

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Open Journal of Gastroenterology 2023年第12期13卷 401-410页

作者： Hatrydt Guillaume dimitri kouam. Lisiane Mewetieh Kouassi Olivier Claver Koffi Bathaix Fulgence Mamert Yao Medical Sciences Training and Research Unit of Abidjan Félix Houphou&#235t-Boigny University Abidjan Ivory Coast Hepatology and Gastroenterology Unit Yopougon University Hospital Abidjan Ivory Coast

Context/Objective: Few studies have been carried out in a country with high endemicity for Helicobacter pylori (H. pylori) infection in Sub-Saharan Africa looking for the association of intestinal metaplasia (IM) with chronic gastritis. We hypothesize that IM is correlated with the intensity of H. pylori infection in a country with high endemicity, Ivory Coast. The objective of this study was to determine the prevalence of intestinal metaplasia in chronic H. pylori gastritis in Ivory Coast. Methods: This was a prospective, cross-sectional, multicenter study, carried out over a period of 5 months, in the reference hospital centers of Abidjan, specialized in Gastroenterology. All patients who had undergone Gastroscopy with biopsies according to the criteria of the Sydney System for the anatomopathological study, those with chronic gastritis and/or H. pylori intestinal metaplasia on histology and in whom all the parameters of the Sydney system classification had been well informed. The quantitative variables were expressed by their means accompanied by their standard deviations and the qualitative variables by their numbers and percentages. Chi-square and Fischer tests were used to look for associations between variables. The significance level was set at 5%. Results: 152 patients were retained. The mean age was 44.9 ± 12.9 years. The prevalence of intestinal metaplasia was 11.8%. In univariate analysis, no significant association was found between clinical and pathological sociodemographic factors (age, sex, ethnicity, educational level, profession) and intestinal metaplasia in chronic Helicobacter pylori gastric cases. In multivariate analysis we found that prolonged use of Proton Pump Inhibitors (PPIs) and a history of Gastroesophageal Reflux Disease (GERD) were significantly associated with the absence of IM. Conclusion: Chronic H. pylori gastritis is the main risk factor for intestinal metaplasia. Prolonged use of PPIs and a history of GERD were significantly iden

关键词： Helicobacter Pylori Chronic Gastritis Intestinal Metaplasia Ivory Coast

Carbon dioxide desorption behavior of potassium carbonate supported on gamma-alumina solid sorbent in wet fluidized bed under steam atmosphere

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Particuology 2023年第10期81卷 15-24页

作者： Sasitron Angkanawisan dimitri Gidaspow Pornpote Piumsomboon Benjapon Chalermsinsuwan Fuels Research Center Department of Chemical TechnologyFaculty of ScienceChulalongkorn University254 Phayathai RoadPathumwanBangkok10330Thailand Center of Excellence on Petrochemical and Materials Technology Chulalongkorn University254 Phayathai RoadPathumwanBangkok10330Thailand Department of Chemical and Biological Engineering Armour College of EngineeringIllinois Institute of Technology10 West 35th StreetChicagoIL60616United States Advanced Computational Fluid Dynamics Research Unit Chulalongkorn University254 Phayathai RoadPathumwanBangkok10330Thailand

Since the carbon dioxide(CO_(2))capture using solid sorbent is a reversible reaction,the solid sorbent can be regenerated by the desorption ***,the desorption process is one of the key important processes for the CO_(2)capture ***,most of the literature studies focus on the desorption of solid sorbent under an N_(2)***,the desorption process of the solid sorbent is inappropriate in the real system because the system will need another process to separate CO_(2)and nitrogen(N_(2))after the desorption *** study focused on the CO_(2)desorption of potassium carbonate supported on gamma-alumina(K2CO3/γ-Al_(2)O_(3))in a wet fluidized bed under a steam atmosphere by using the multiphase computational fluid dynamics(CFD)*** effects of water thickness and dry restitution coefficient on CO_(2)desorption rate were investigated to provide a realistic particle collision behavior and to explore their effects on CO_(2)desorption ***,the effect of steam velocity on the hydrodynamic behaviors of fluidization which on CO_(2)desorption rate was *** simulated results demonstrated that all the parameters,water thickness,dry restitution coefficient,and steam velocity had significantly affected system hydrodynamics and CO_(2)desorption rate in the wet fluidization desorption ***,the effect of desorption temperature on CO_(2)desorption rate was evaluated for finding the appropriate temperature for CO_(2)desorption process of K2CO3/γ-Al_(2)O_(3).The results showed that the appropriate desorption temperature for CO_(2)desorption under steam atmosphere was the temperature over 150℃.

关键词： CO_(2)desorption Fluidized bed K_(2)CO_(3)/Y-Al_(2)O_(3) Restitution coefficient Wet fluidization Computational fluid dynamics

EPR spectroscopy of whole blood and blood components:can we diagnose abnormalities?

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The Journal of Biomedical Research 2021年第4期35卷 294-300页

作者： dimitri A.Svistunenko School of Life Sciences University of EssexColchesterEssex CO43SQUK.

This mini-review gives a brief account of the emergence of the electron paramagnetic resonance(EPR)spectroscopy in the second half of the 20th century and reports the continuous wave EPR spectroscopy studies on human and animal *** question posed by this review is whether the EPR spectroscopy in the form it appeared 70 years ago is still able to provide useful information about different pathological conditions in humans,particularly in the area of diagnosis.

关键词： EPR spectroscopy biological tissues paramagnetic metals protein free radicals human blood animal blood

Celiac Disease in Asia beyond the Middle East and Indian subcontinent:Epidemiological burden and diagnostic barriers

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World Journal of Gastroenterology 2021年第19期27卷 2251-2256页

作者： dimitri Poddighe Diyora Abdukhakimova Department of Medicine School of MedicineNazarbayev UniversityNur-Sultan 010000Kazakhstan Clinical Academic Department of Pediatrics Research Center for Maternal and Child HealthUniversity Medical CenterNur-Sultan 010000Kazakhstan

Celiac Disease(CD)had been considered uncommon in Asia for a long ***,several studies suggested that,in the Indian subcontinent and Middle East countries,CD is present and as prevalent as in Western *** these Asian regions,the information about the epidemiology of CD is still lacking or largely incomplete for different and variable ***,we discuss the epidemiological aspects and the diagnostic barriers in several Asian regions including China,Japan,Southeast Asia and Russia/Central *** some of those regions,especially Russia and Central Asia,the prevalence of CD is very likely to be *** factors may,to a different extent,contribute to CD underdiagnosis(and,thus,underestimation of its epidemiological burden),including the poor disease awareness among physicians and/or patients,limited access to diagnostic resources,inappropriate use or interpretation of the serological tests,absence of standardized diagnostic and endoscopic protocols,and insufficient expertise in histopathological interpretation.

关键词： Celiac disease Epidemiology Prevalence Asia China Japan Russia Central Asia HLA-DQB1 Diagnostic barriers

Static Analysis of Doubly-Curved Shell Structures of Smart Materials and Arbitrary Shape Subjected to General Loads Employing Higher Order Theories and Generalized Differential Quadrature Method

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Computer Modeling in Engineering & Sciences 2022年第12期133卷 719-798页

作者： Francesco Tornabene Matteo Viscoti Rossana dimitri Department of Innovation Engineering School of EngineeringUniversity of SalentoLecce73100Italy

The article proposes an Equivalent Single Layer(ESL)formulation for the linear static analysis of arbitrarily-shaped shell structures subjected to general surface loads and boundary conditions.A parametrization of the physical domain is provided by employing a set of curvilinear principal *** generalized blendingmethodology accounts for a distortion of the structure so that disparate geometries can be *** layer of the stacking sequence has an arbitrary orientation and is modelled as a generally anisotropic *** addition,re-entrant auxetic three-dimensional honeycomb cells with soft-core behaviour are considered in the *** unknown variables are described employing a generalized displacement field and pre-determined through-the-thickness functions assessed in a unified ***,a weak assessment of the structural problem accounts for shape functions defined with an isogeometric approach starting fromthe computational *** has been proposed to define two-dimensional distributions of static surface *** the same way,boundary conditions with three-dimensional features are implemented along the shell edges employing linear *** fundamental relations are obtained from the stationary configuration of the total potential energy,and they are numerically tackled by employing the Generalized Differential Quadrature(GDQ)method,accounting for nonuniform computational *** the post-processing stage,an equilibrium-based recovery procedure allows the determination of the three-dimensional dispersion of the kinematic and static *** case studies have been presented,and a successful benchmark of different structural responses has been performed with respect to various refined theories.

关键词： 3D honeycomb anisotropic materials differential quadrature method general loads and constraints higher order theories linear static analysis weak formulation

Approximate policy iteration:a survey and somenew methods

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控制理论与应用（英文版） 2011年第3期9卷 310-335页

作者： dimitri P.BERTSEKAS Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology

We consider the classical policy iteration method of dynamic programming(DP),where approximations and simulation are used to deal with the curse of *** survey a number of issues:convergence and rate of convergence of approximate policy evaluation methods,singularity and susceptibility to simulation noise of policy evaluation,exploration issues,constrained and enhanced policy iteration,policy oscillation and chattering,and optimistic and distributed policy *** discussion of policy evaluation is couched in general terms and aims to unify the available methods in the light of recent research developments and to compare the two main policy evaluation approaches:projected equations and temporal differences(TD),and *** the context of these approaches,we survey two different types of simulation-based algorithms:matrix inversion methods,such as least-squares temporal difference(LSTD),and iterative methods,such as least-squares policy evaluation(LSPE) and TD(λ),and their scaled *** discuss a recent method,based on regression and regularization,which recti?es the unreliability of LSTD for nearly singular projected Bellman *** iterative version of this method belongs to the LSPE class of methods and provides the connecting link between LSTD and *** discussion of policy improvement focuses on the role of policy oscillation and its effect on performance *** illustrate that policy evaluation when done by the projected equation/TD approach may lead to policy oscillation,but when done by aggregation it does *** implies better error bounds and more regular performance for aggregation,at the expense of some loss of generality in cost function representation *** aggregation provides the connecting link between projected equation/TD-based and aggregation-based policy evaluation,and is characterized by favorable error bounds.

关键词： Dynamic programming Policy iteration Projected equation Aggregation Chattering Regularization