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A Multigrid Method for a Model of the Implicit Immersed Boundary Equations

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Communications in Computational Physics 2012年第7期12卷 378-400页

作者： robert d.Guy Bobby Philip department of Mathematics University of California DavisDavisCA 95616USA Oak Ridge National Laboratory Oak RidgeTN 37831USA

Explicit time stepping schemes for the immersed boundary method require very small time steps in order to maintain *** the equations that arise from an implicit discretization is ***,several different approaches have been proposed,but a complete understanding of this problem is still emerging.A multigrid method is developed and explored for solving the equations in an implicittime discretization of a model of the immersed boundary *** model problem consists of a scalar Poisson equation with conformation-dependent singular forces on an immersed *** model does not include the inertial terms or the incompressibility *** method is more efficient than an explicit method,but the efficiency gain is *** multigrid method alone may not be an effective solver,but when used as a preconditioner for Krylov methods,the speed-up over the explicit-time method is *** example,depending on the constitutive law for the boundary force,with a time step 100 times larger than the explicit method,the implicit method is about 15-100 times more efficient than the explicit method.A very attractive feature of this method is that the efficiency of the multigrid preconditioned Krylov solver is shown to be independent of the number of immersed boundary points.

关键词： Preconditioning implicit methods fluid-structure interaction

Epigenetic Repression of Male Gametophyte- Specific Genes in the Arabidopsis Sporophyte

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Molecular Plant 2013年第4期6卷 1176-1186页

作者： robert d. Hoffmann Michael G. Palmgren Centre for Membrane Pumps in Cells and disease--PUMPKIN Danish National Research Foundation Department of Plant and Environmental SciencesUniversity of Copenhagen Thorvaldsensvej 40 DK-1871 Frederiksberg Denmark

Tissue formation, the identity of cells, and the functions they fulfill, are results of gene regulation. The male gametophyte of plants, pollen, is outstanding in this respect as several hundred genes expressed in pollen are not expressed in the sporophyte. How pollen-specific genes are down-regulated in the sporophyte has yet to be established. In this study, we have performed a bioinformatics analysis of publicly available genome-wide epigenetics data of sev- eral sporophytic tissues. By combining this analysis with dNase ! footprinting data, we assessed means by which the repression of pollen-specific genes in the Arabidopsis sporophyte is conferred. Our findings show that, in seedlings, the majority of pollen-specific genes are associated with histone-3 marked by mono- or trimethylation of Lys-27 （H3K27me1/ H3K27me3）, both of which are repressive markers for gene expression in the sporophyte. Analysis of dNase footprint profiles of pollen-specific genes in the sporophyte displayed closed chromatin proximal to the start codon. We describe a model of two-staged gene regulation in which a lack of nucleosome-free regions in promoters and histone modifications in open reading frames repress pollen-specific genes in the sporophyte.

关键词： male gametophyte epigenetics gene repression dNase I footprinting transcription factors bioinformatics.

Fabrication and testing of polymer-based capacitive micromachined ultrasound transducers for medical imaging

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Microsystems & Nanoengineering 2018年第1期4卷 178-189页

作者： Carlos d.Gerardo Edmond Cretu robert Rohling department of Electrical and Computer Engineering University of British Columbia2332 Main MallVancouverBCCanada department of Mechanical Engineering University of British Columbia6250 Applied Science LnVancouverBCCanada

The ultrasonic transducer industry is dominated by piezoelectric *** an emerging alternative,capacitive micromachined ultrasound transducers(CMUTs)offer wider bandwidth,better integration with electronics,and ease of fabricating large *** have a sealed cavity between a fixed electrode and a suspended metalized *** cost and sensitivity are limiting factors in current CMUTs that depend on the fabrication equipment and,especially,on the materials *** widespread use of CMUTs,a much lower fabrication cost that uses inexpensive materials,which maintain or improve upon existing sensitivity,is ***,a new fabrication process is described for polymer-based CMUTs(polyCMUTs)using the photopolymer SU-8 and *** first ultrasound B-mode image of a wire phantom created with a 64-element linear array using synthetic aperture beamforming techniques is presented.A 12 VAC signal superimposed on a 10 VdC signal was used on the transmission side,and only a bias-tee,with no amplifiers,was used on the receiving *** low operational voltage and high sensitivity of this device can be partially attributed to a pre-biasing condition on the *** using a novel sacrificial layer combined with a top electrode embedded inside the membrane,we demonstrated that SU-8 can be used to manufacture CMUTs ***,the fabrication used relatively simple equipment,and the number of fabrication steps was reduced compared to traditional CMUT *** new fabrication process has the potential to increase the use of CMUTs in the ultrasound market,including the market for wearable transducers.

关键词： polymer electrode testing

Pediatrician-friendly perspectives on cognitive behavioral therapy for anxious youth:Current status and clinical implications for the next normal

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World Journal of Clinical Pediatrics 2021年第6期10卷 112-123页

作者： robert d Friedberg Center for the Study and Treatment of Anxious Youth Palo Alto UniversitySan JoseCA 95136United States

Pediatric anxiety disorders are common and often debilitating *** is a psychosocial intervention that represents a potentially powerful antidote to these *** article reviews data from treatment outcome studies,meta-analyses,and systematic reviews as well as from moderation/mediational *** literature supports the efficacy,effectiveness,and durability of positive treatment outcomes for pediatric anxiety *** for clinical applications are suggested.

关键词： Pediatric anxiety Cognitive behavioral therapy Coping cat Exposure

Where physics meets chemistry： Thin film deposition from reactive plasmas

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Frontiers of Chemical Science and Engineering 2016年第4期10卷 441-458页

作者： Andrew Michelmore Jason d. Whittle James W. Bradley robert d. Short School of Engineering University of South Australia Mawson Lakes Australia SA 5095 Future Industries Institute University of South Australia Mawson Lakes Australia SA 5095 department of Electrical Engineering and Electronics University of Liverpool Liverpool L69 3GJ UK Material Science Institute Lancaster University Lancaster LA1 4YW UK

Functionalising surfaces using polymeric thin films is an industrially important field. One technique for achieving nanoscale, controlled surface functionalization is plasma deposition. Plasma deposition has advantages over other surface engineering processes, including that it is solvent free, substrate and geometry independent, and the surface properties of the film can be designed by judicious choice of precursor and plasma conditions. despite the utility of this method, the mechanisms of plasma polymer growth are generally unknown, and are usually described by chemical （i.e., radical） pathways. In this review, we aim to show that plasma physics drives the chemistry of the plasma phase, and surface-plasma interactions. For example, we show that ionic species can react in the plasma to form larger ions, and also arrive at surfaces with energies greater than 1000 kJ·mol^-1 （〉10 eV） and thus facilitate surface reactions that have not been taken into account previously. Thus, improving thin film deposition processes requires an understanding of both physical and chemical processes in plasma.

关键词： thin films plasma physics plasma chemistry,functionalization polymer

Management of inflammatory bowel disease with Clostridium difficile infection

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World Journal of Gastroenterology 2017年第27期23卷 4986-5003页

作者： Julie d’Aoust robert Battat Talat Bessissow division of Internal Medicine Jewish General Hospital division of Gastroenterology Jewish General Hospital division of Gastroenterology Mc Gill University Health Centre

To address the management of Clostridium difficile (C. difficile) infection (CdI) in the setting of suspected inflammatory bowel disease (IBd)-flare. METHOdSA systematic search of the Ovid MEdLINE and EMBASE databases by independent reviewers identified 70 articles including a total of 932141 IBd patients or IBd-related hospitalizations. RESULTSIn those with IBd, CdI is associated with increased morbidity, including subsequent escalation in IBd medical therapy, urgent colectomy and increased hospitalization, as well as excess mortality. Vancomycin-containing regimens are effective first-line therapies for CdI in IBd inpatients. No prospective data exists with regards to the safety or efficacy of initiating or maintaining corticosteroid, immunomodulator, or biologic therapy to treat IBd in the setting of CdI. Corticosteroid use is a risk factor for the development of CdI, while immunomodulators and biologics are not. CONCLUSIONStrong recommendations regarding when to initiate IBd specific therapy in those with CdI are precluded by a lack of evidence. However, based on expert opinion and observational data, initiation or resumption of immunosuppressive therapy after 48-72 h of targeted antibiotic treatment for CdI may be considered.

关键词： Biologic therapy Clostridium difficile Inflammatory bowel disease Ulcerative colitis Crohn’s disease Corticosteroids

Feed supplementation with arginine and zinc on antioxidant status and inflammatory response in challenged weanling piglets

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Animal Nutrition 2017年第3期3卷 236-246页

作者： Nadia Bergeron Claude robert Frédéric Guay département des sciences animales Université Laval

Although supplementing the diet with zinc oxide and arginine is known to improve growth in weanling piglets, the mechanism of action is not well understood. We measured the antioxidant status and inflammatory response in 48 weanling castrated male piglets fed diets supplemented with or without zinc oxide(2,500 mg Zn oxide per kg) and arginine(1%) starting at the age of 20 days. The animals were injected with lipopolysaccharide(100 μg/kg) on day 5. Half of them received another injection on day *** samples were taken just before and 6, 24 and 48 h after injection and the mucosa lining the ileum was recovered following euthanizing on days 7 and 14. Zinc supplementation increased reduced and total glutathione(GSH)(reduced and total) during days 5 to 7 and arginine decreased oxidized GSH measured on days 5 and 12 and the ratio of total antioxidant capacity to total oxidative status during days12 to 14. Zinc decreased plasma malondialdehyde measured on days 5 and 12 and serum haptoglobin measured on day 12 and increased both metallothionein-1 expression and total antioxidant capacity measured in the ileal mucosa on day 14. Tumour necrosis factor a concentration decreased from days 5 to12(all effects were significant at P dy shows that the zinc supplement reduced lipid oxidation and lipopolysaccharide-induced inflammation during the post-weaning period, while the arginine supplementation had only a limited effect.

关键词： Antioxidant Inflammation Zinc Arginine Piglet Weanling

Fractal and Multifractal Propertiesof the Spatial distribution of Natural Fractures——Analyses and Applications

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Acta Geologica Sinica(English Edition) 1999年第4期73卷 477-487页

作者： XU Jiandong QU Guosheng robert d. JACOBI Institute of Geology China Seismological Bureau Beijing 100029 PRC department of Geology State University of New York at Buffalo USA

The Cantor's dust theory is applied to investigate the scaling properites of the spatial distribution of natural fractures obtained from detailed scanline surveys of 27 field sites in the Appalachian Plateau of western New York, USA. The results obtained in this study indicate: 1) fracture spacing is characterized by fractal and multifractal properties. On small scales analyses yield an average fractal dimension of 0.15, which suggests a very high degree of clustering. In contrast, on large scales, fractures tend to be more regular and evenly distributed with an average fracture dimension of 0.52; 2) fractal dimension varies with different sets in different orientations, which can be attributed to interactions between pre-existing fractures and younger ones, as well as variations of the intensity of the stresses under which the fractures were formed; 3) a time sequence of fracture set formation can be proposed based on fractal and multifractal analyses, which consists of (from old to young): N-S, NW, ENE, and NE-striking sets. This time sequence is confirmed by the study of the abutting relationships of different fracture sets observed in the field.

关键词： fractal multifractal fracture

Projection Preconditioner for Solving the Implicit Immersed Boundary Equations

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Numerical Mathematics(Theory,Methods and Applications) 2014年第4期7卷 473-498页

作者： Qinghai Zhang robert d.Guy Bobby Philip department of Mathematics University of UtahSalt Lake CityUT 84112USA department ofMathematics University of California DavisDavisCA 95616USA Oak Ridge National Laboratory Oak RidgeTN 37831USA

This paper presents a method for solving the linear semi-implicit immersed boundary equations which avoids the severe time step restriction presented by explicit-time *** Lagrangian variables are eliminated via a Schur complement to form a purely Eulerian saddle point system,which is preconditioned by a projection operator and then solved by a Krylov subspace *** the viewpoint of projection methods,we derive an ideal preconditioner for the saddle point problem and compare the efficiency of a number of simpler preconditioners that approximate this perfect *** low Reynolds number and high stiffness,one particular projection preconditioner yields an efficiency improvement of the explicit IB method by a factor around *** speed-ups over explicit-time method are achieved for Reynolds number below *** speedup increases as the Eulerian grid size and/or the Reynolds number are further reduced.

关键词： Fluid-structure interaction immersed boundary method projection method preconditioning