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Multiagent Reinforcement Learning:Rollout and Policy Iteration

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IEEE/CAA Journal of Automatica Sinica 2021年第2期8卷 249-272页

作者： dimitri Bertsekas the Arizona State University(ASU) TempeAZ 85281 USAand also with Massachusetts Institute of Technology(MIT)CambridgeMA 02139

We discuss the solution of complex multistage decision problems using methods that are based on the idea of policy iteration(PI),i.e.,start from some base policy and generate an improved *** is the simplest method of this type,where just one improved policy is *** can view PI as repeated application of rollout,where the rollout policy at each iteration serves as the base policy for the next *** contrast with PI,rollout has a robustness property:it can be applied on-line and is suitable for on-line ***,rollout can use as base policy one of the policies produced by PI,thereby improving on that *** is the type of scheme underlying the prominently successful Alpha Zero chess *** this paper we focus on rollout and PI-like methods for problems where the control consists of multiple components each selected(conceptually)by a separate *** is the class of multiagent problems where the agents have a shared objective function,and a shared and perfect state *** on a problem reformulation that trades off control space complexity with state space complexity,we develop an approach,whereby at every stage,the agents sequentially(one-at-a-time)execute a local rollout algorithm that uses a base policy,together with some coordinating information from the other *** amount of total computation required at every stage grows linearly with the number of *** contrast,in the standard rollout algorithm,the amount of total computation grows exponentially with the number of *** the dramatic reduction in required computation,we show that our multiagent rollout algorithm has the fundamental cost improvement property of standard rollout:it guarantees an improved performance relative to the base *** also discuss autonomous multiagent rollout schemes that allow the agents to make decisions autonomously through the use of precomputed signaling information,which is sufficient to maintain the c

关键词： Dynamic programming multiagent problems neuro-dynamic programming policy iteration reinforcement learning rollout

Short-term nitisinone discontinuation of hereditary tyrosinemia type 1 mice causes metabolic alterations in glutathione metabolism/biosynthesis and multiple amino acid degradation pathways

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Genes & Diseases 2023年第5期10卷 1759-1762页

作者： Colemonts-Vroninks Haaike Norman P.Brendan Van Laere Sven Davison S.Andrew Marcélis Lionel Casimir Georges Goyens Philippe Claes Paul de bundel.dimitri Martens Geert Ranganath Lakshminarayan Rao Vanhaecke Tamara Gallagher James A de Kock Joery Vrije Universiteit Brussel Liver Therapy&Evolution TeamIn Vitro Toxicology and Dermato-Cosmetology(IVTD)Research GroupFaculty of Medicine and PharmacyLaarbeeklaan 103Brussels B-1090Belgium Vrije Universiteit Brussel Experimental Pharmacology(EFAR)Research GroupFaculty of Medicine and PharmacyLaarbeeklaan 103Brussels B-1090Belgium University of Liverpool Dept.of Musculoskeletal&Ageing ScienceInstitute of Life Course&Medical SciencesLiverpool L78TXUnited Kingdom Vrije Universiteit Brussel Interfaculty Center Data Processing and StatisticsFaculty of Medicine and PharmacyLaarbeeklaan 103Brussels B-1090Belgium Liverpool University Hospitals NHS Foundation Trust Clinical Biochemistry and Metabolic MedicineLiverpool L35PSUnited Kingdom UniversitéLibre de Bruxelles Laboratoire de PédiatrieBrussels B-1050Belgium Vrije Universiteit Brussel In Vitro Liver Disease Modelling TeamIn Vitro Toxicology and Dermato-Cosmetology(IVTD)Research GroupFaculty of Medicine and PharmacyLaarbeeklaan 103Brussels B-1090Belgium AZ delta General Hospital Department of Laboratory MedicineRoeselare 8800Belgium Ghent University Department of Biomolecular MedicineGhent 9052Belgium

Hereditary tyrosinemia type 1(HT1)is a life-threatening disease caused by the patient's inability to break down tyrosine due to loss-of-function mutations in the fumarylacetoacetate hydrolase(FAH)enzyme(Fig.S1).Currently,the only available life-saving treatment is nitisinone(NTBC).However,nitisinone therapy comes with debilitating side effects and requires a strict drug regime combined with a tyrosine-and phenylalanine-restricted ***,therapy adherence is often experienced as an additional *** this study,transcriptional profiling was conducted parallel to high-resolution metabolomics on,respectively,liver tissue and serum samples of Fah-deficient *** experimental workflow of our study is shown in Figure *** pathway analyses showed manifest activation of the NRF2-stress response,associated with hepatocellular damage and mainly driven by a markedly increased oxidative *** altered canonical pathways were primarily a downstream consequence of the ***,we observed an overall aminoacidemia and changes related to aminoacyl-tRNA biosynthesis,which postulates that short-term nitisinone discontinuation can already put the patient at risk for hepatocellular carcinoma ***,we did not only identify changes in numerous pathways,directly and indirectly,related to the metabolism of tyrosine and glutathione but also the presence of“side-chain”metabolites,such as y-glutamyl-and N-acetyl-coupled amino acids,indicating that non-directly related pathways like phase II biotransformation reactions are also affected.

关键词： continuation Figure hereditary

Carrier frequency of HLA-DQB1*02 allele in patients affected with celiac disease:A systematic review assessing the potential rationale of a targeted allelic genotyping as a first-line screening

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World Journal of Gastroenterology 2020年第12期26卷 1365-1381页

作者： dimitri Poddighe Chiara Rebuffi Annalisa de Silvestri Cristina Capittini department of Medicine School of MedicineNazarbayev UniversityNur-Sultan 010000Kazakhstan Grant Office and Scientific Documentation Center Fondazione IRCCS Policlinico San MatteoPavia 27100Italy Scientific Direction Clinical Epidemiology and Biometric UnitFondazione IRCCS Policlinico San MatteoPavia 27100Italy department of Biology and Biotechnology"Lazzaro Spallanzani" University of PaviaPavia 27100Italy

BACKGROUND Celiac Disease(CD)is an immune-mediated disorder,in which the HLA immunogenetic background(DQ2 and DQ8 heterodimers)and environmental trigger(gluten)are well ***,both factors are necessary–but not sufficient–to develop ***,it is very likely that CD is underdiagnosed in both developing and developed countries,due to several aspects,including the fact that a lot of patients present mild and/or atypical symptoms,without the presence of any recognized risk ***,the possibility and feasibility of widened screening strategies to identify CD patients are *** To provide further evidence of the main epidemiological importance of HLADQB1*02 allele in the population of CD *** We performed a systematic search in PubMed,EMBASE,Cochrane,Web of Science and Scopus databases,in order to produce a systematic review assessing the carrier frequency of HLA-DQB1*02 allele in the celiac *** the PRISMA guidelines,we retrieved all the original articles describing CD patients’HLA-DQB1 genotype in such a way that could allow to assess the HLADQB1*02 carrier frequency among CD patients,along with the evidence of the appropriate diagnostic work-up to achieve a correct and final diagnosis of *** The final output of this systematic search in the medical literature consisted of 38 studies providing the appropriate HLA-DQB1 genotype information of the respective CD *** to this systematic review,including a pool of 4945 HLA-DQ genotyped CD patients,the HLA-DQB1*02 carrier frequency was 94.94%,meaning that only 5.06%of CD patients were completely lacking this allelic ***,if we consider only the studies whereby the prevalence of CD patients affected with type 1 diabetes mellitus was supposed or clearly established to be very low,the frequency of non-HLA-DQB1*02 carriers among CD patients dropped to 3.65%.CONCLUSION Such a high carrier frequency of the HLA-DQB1*02 allelic varian

关键词： Celiac disease Children HLA-DQB1*02 DQ2 heterodimer Screening Systematic review

Feature-Based Aggregation and deep Reinforcement Learning:A Survey and Some New Implementations

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IEEE/CAA Journal of Automatica Sinica 2019年第1期6卷 1-31页

作者： dimitri P.Bertsekas the department of Electrical Engineering and Computer Science and the Laboratory for Information and Decision SystemsMassachusetts Institute of Technology

In this paper we discuss policy iteration methods for approximate solution of a finite-state discounted Markov decision problem, with a focus on feature-based aggregation methods and their connection with deep reinforcement learning schemes. We introduce features of the states of the original problem, and we formulate a smaller "aggregate" Markov decision problem, whose states relate to the features. We discuss properties and possible implementations of this type of aggregation, including a new approach to approximate policy iteration. In this approach the policy improvement operation combines feature-based aggregation with feature construction using deep neural networks or other calculations. We argue that the cost function of a policy may be approximated much more accurately by the nonlinear function of the features provided by aggregation, than by the linear function of the features provided by neural networkbased reinforcement learning, thereby potentially leading to more effective policy improvement.

关键词： Reinforcement learning dynamic programming Markovian decision problems aggregation feature-based architectures policy iteration deep neural networks rollout algorithms

Autoimmune pancreatitis and pancreatic cancer:Epidemiological aspects and immunological considerations

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World Journal of Gastroenterology 2021年第25期27卷 3825-3836页

作者： dimitri Poddighe department of Medicine School of MedicineNazarbayev UniversityNur-Sultan 010000Kazakhstan department of Pediatrics National Research Institute for Maternal and Child Health(NRCMCH)University Medical Center(UMC)Nur-Sultan 010000Kazakhstan

Ordinary chronic pancreatitis is a well-known risk factor for pancreatic cancer,whereas such an association with autoimmune pancreatitis(AIP)is widely *** to the rarity of the latter disorder,there are few specific clinical and epidemiological studies investigating the relation between AIP and pancreatic cancer,which do not seem to support ***,these studies are affected by several limitations and,therefore,a link between AIP(and,specifically,type 1 AIP)and pancreatic cancer cannot be ruled out definitively on this ***,several immunopathological aspects of type 1 AIP and,in general,immunoglobulin G4-related disease can create an immunological context that may impair the tumoral immunosurveillance and promote the pancreatic carcinogenesis and its *** detail,Th2 immunological dominance,type 2 macrophage polarization and basophil infiltration observed in type 1 AIP,may play a permissive role in creating a favorable immunological environment for pancreatic carcinogenesis,in addition to the immunosuppressive therapies that can be used in these patients.

关键词： Autoimmune pancreatitis Chronic pancreatitis Pancreatic cancer Immunoglobulin G4-related disease Epidemiology Immunology Basophils Macrophages Th2 cells Systemic lupus erythematosus

Compact fluidized bed sorber for CO_2 capture

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Particuology 2010年第6期8卷 531-535页

作者： Parinya Khongprom dimitri Gidaspow department of Chemical Engineering Faculty of EngineeringKasetsart UniversityBangkok 10900Thailand department of Chemical and Biological Engineering Illinois Institute of TechnologyChicagoIL 60616USA

Multiphase CFD is used to design a compact fluidized bed sorber for CO2 removal from flue gases using sodium or potassium carbonate pellets. The sorber sizes are much smaller than commercial amine absorbers and smaller than other proposed dry adsorbers. The size reduction is due to the elimination of dilute regions that cause bypassing. With proper solids feeding we eliminated the usual core-annular regime found in circulating fluidized beds.

关键词： Separation science Flue gas Carbon capture Multiphase flow Computational fluid dynamics

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

Measuring turbulence in a circulating fluidized bed using PIV techniques

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Particuology 2011年第6期9卷 572-588页

作者： Mayank Kashyap Benjapon Chalermsinsuwan dimitri Gidaspow department of Chemical and Biological Engineering Illinois Institute of Technology Fuel Research Center Department of Chemical Technology Faculty of Science Chulalongkorn University Center of Excellence for Petroleum Petrochemicals and Advanced Materials Chulalongkorn University

This study utilized the particle image velocimetry （P1V） technique, non-invasively near the wall, in the developing region, for the measurements of laminar and turbulent properties during circulation of Geldart B type particles in the U.S. department of Energy （DOE） National Energy Technology Laboratory （NETL） riser. A novel method was used to measure axial and radial laminar and turbulent solids dispersion coefficients using autocorrelation technique. The instantaneous and hydrodynamic velocities for the solid phase were measured simultaneously in the axial and radial directions using a CCD camera, with the help of a colored rotating transparency. The measured properties, such as laminar and Reynolds stresses, laminar and turbulent granular tempera- tures, laminar and turbulent dispersion coefficients and energy spectra exhibited anisotropy. The mixing in the riser was on the level of clusters. The total granular temperatures were in reasonable agreement with the literature values. However, the axial and radial solids dispersion coefficients measured near the wall were slightly lower than the radially averaged values in the literature.

关键词： Particle image velocimetry (PIV) Dispersion coefficient Autocorrelation Turbulence Anisotrnpy

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