检索结果-南通市图书馆

Slip-model Performance for Underexpanded micro-scale Rocket Nozzle Flows

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Thermal Science 2007年第3期16卷 223-230页

作者： joséA.morí■igo joséHermidaQuesada Francisco Caballero Requena Dept.of Space Programmes Dept.of

In aerospace micro-Electro mechanical Systems （mEmS）, the characteristic length scale of the flow approaches the molecular mean free path, thus invalidating the continuum description and enforcing the use of particle methods, like the Direct Simulation monte Carlo （DSmC）, to deal with the non-equilibrium regions. Within the slip-regime （0.01〈Kn〈-0.1） both approaches, continuum and particle-based, seem to behave well in terms of accuracy. The present study summarizes the implementation and results obtained with a 2nO-order slip boundary condition in a Navier-Stokes solver to address the rarefaction near the nozzle walls. Its assessment and application to a cold-gas micro-scale conical nozzle of 300μm throat diameter, discharging into the low-pressure freestream, constitutes the major aim of the work. The slip-model incorporates the velocity slip with thermal creep and temperature jump, thus permitting to deal with non-isothermal flows as well. Results show that the gas experiences an intense rarefaction in the lip vicinity, pointing to the limits of model validity. Furthermore, a strong mach deceleration is observed, attributed to the rather thick subsonic boundary layer and supersonic bulk heating caused by the viscous dissipation, in contrast with the expansion to occur in large rocket nozzles during underexpanded operation.

关键词： Slip flow mEmS micronozzles

A stable anthraquinone-derivative cathode to develop sodium metal batteries: The role of ammoniates as electrolytes

在线全文

学校读者我要写书评

暂无评论

Journal of Energy Chemistry 2023年第2期77卷 572-580,I0015页

作者： Débora Ruiz-martínez josé m.Orts Roberto Gómez Departament de Química Física i Institut Universitari d’Electroquímica Universitat d’AlacantApartat 99Alicante E-03080Spain

Rechargeable sodium metal batteries constitute a cost-effective option for energy storage although sodium shows some drawbacks in terms of reactivity with organic solvents and dendritic *** we demonstrate that an organic dye,indanthrone blue,behaves as an efficient cathode material for the development of secondary sodium metal batteries when combined with novel inorganic *** electrolytes are ammonia solvates,known as liquid ammoniates,which can be formulated as NaI·3.3NH_(3) and NaBF_(4)·2.5NH_(3).They impart excellent stability to sodium metal,and they favor sodium non-dendritic growth linked to their exceedingly high sodium ion *** advantage is complemented by a high specific *** battery described here can last hundreds of cycles at 10 C while keeping a Coulombic efficiency of 99%from the first *** of the high capacity of the cathode and the superior physicochemical properties of the electrolytes,the battery can reach a specific energy value as high as 210 W h kgIB^(-1),and a high specific power of 2.2 kW kgIB^(-1),even at below room temperature(4℃).Importantly,the battery is based on abundant and cost-effective materials,bearing promise for its application in large-scale energy storage.

关键词： Sodium metal batteries Anthraquinone-based cathode Vat dye Indanthrone blue Inorganic electrolytes Liquid ammoniates

Cost of postoperative complications:How to avoid calculation errors

在线全文

学校读者我要写书评

暂无评论

World Journal of Gastroenterology 2020年第21期26卷 2682-2690页

作者： Roberto De la Plaza Llamas josém Ramia Department of General and Digestive Surgery Hospital Universitario de GuadalajaraGuadalajara 19002Spain

Postoperative complications(PC)are a basic health outcome,but no surgery service in the world records and/or audits the PC associated with all the surgical procedures it *** studies that have assessed the cost of PC suffer from poor quality and a lack of transparency and *** payment system in place often rewards the volume of services provided rather than the quality of patients’clinical *** a thorough registration of PC,the economic costs involved cannot be *** accurate,reliable appraisal would help identify areas for investment in order to reduce the incidence of PC,improve surgical results,and bring down the economic *** article describes how to quantify and classify PC using the Clavien-Dindo classification and the comprehensive complication index,discusses the perspectives from which economic evaluations are performed and the minimum postoperative follow-up established,and makes various *** availability of accurate and impartially audited data on PC will help reduce their incidence and bring down ***,the health authorities,and society as a whole are sure to benefit.

关键词： morbidity Postoperative complications Costs and cost analysis Economic evaluation Healthcare costs Opportunity cost Clavien-Dindo classification Comprehensive complication index

Postoperative complications in gastrointestinal surgery: A “hidden” basic quality indicator

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

World Journal of Gastroenterology 2019年第23期25卷 2833-2838页

作者： Roberto De la Plaza Llamas josém Ramia Department of General and Digestive Surgery Hospital Universitario de GuadalajaraGuadalajara 19002Spain

Postoperative complications represent a basic quality indicator for measuring outcomes at surgical units. At present, however, they are not systematically measured in all surgical procedures. A more accurate assessment of their impact could help to evaluate the real morbidity associated with different surgical interventions, establish measures for improvement, increase efficiency and identify benchmarking services. The Clavien-Dindo Classification is the most widely used system worldwide for assessing postoperative ***, the postoperative period is summarized by the most serious complication without taking into account others of lesser magnitude. Recently,two new scoring systems have emerged, the Comprehensive Complication Index and the Complication Severity Score, which include all postoperative complications and quantify them from 0(no complications) to 100(patient’s death), These allow the comparison of results. It is important to train surgical staff to report and classify complications and to record 90-d morbidity rates in all patients. Comparisons with other services must take into account patient comorbidities and the complexity of the particular surgical procedure. To avoid subjectivity and bias, external audits are necessary. In addition, ensuring transparency in the reporting of the results is an urgent obligation.

关键词： morbidity Postoperative complications Health policy Comprehensive Complication Index Clavien-Dindo Classification Complication Severity Score

Phasor-domain Dynamic model of Asymmetric Current Injection Controller for Converter-interfaced Generator

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of modern Power Systems and Clean Energy 2021年第6期9卷 1269-1278页

作者： Victor A.F.Almeida Glauco N.Taranto josé m.T.marinho Electrical Engineering Department of the Federal University of Rio de Janeiro(COPPE/UFRJ) Petrobras S.A.

This paper presents a controller model of asymmetric current injection for converter-interfaced generators suitable for root-mean-square(RmS)phasor-domain,fundamentalfrequency,three-phase,and dynamic simulation *** effectiveness of the proposed controller is assessed with simulations in test systems with high percentage of converter-interfaced *** simulations focus on the operation of protection relays that use negative-sequence quantities in their directional *** paper also presents and compares two strategies to limit reactive negative-sequence currents,and active and reactive positive-sequence currents.A tutorial test system and a regional system part of the actual Brazilian Interconnected Power System are used to assess the correctness of the proposed controller in three-phase fundamental-frequency RmS dynamic simulations.

关键词： Converter-interfaced generator three-phase model power system protection negative-sequence current injection negative-sequence current protection unbalanced fault three-phase root-mean-square(RmS)dynamic simulation

Deforestation and fragmentation trends of seasonal dry tropical forest in Ecuador: impact on conservation

在线全文

学校读者我要写书评

暂无评论

Forest Ecosystems 2021年第3期8卷 615-627页

作者： Carlos A.Rivas joséGuerrero-Casado Rafael m.Navarro-Cerillo Instituto de Ciencias Básicas Universidad Técnica de ManabíPortoviejoManabíEcuador Department of Forest Engineering Laboratory of DendrochronologySilviculture and Global Change–DendrodatLab–ERSAFUniversity of CordobaCampus de RabanalesCrta.IVkm.396E-14071 CordobaSpain Departamento de medicina Veterinaria Facultad de Ciencias VeterinariasUniversidad Técnica de ManabíPortoviejoManabíEcuador Department of Zoology University of CordobaCampus de Rabanales14071 CordobaSpain

Background:Fragmentation and deforestation are one of the greatest threats to forests,and these processes are of even more concern in the tropics,where the seasonal dry forest is possibly one of the most threatened ecosystems with the least remaining surface ***:The deforestation and fragmentation patterns that had occurred in Ecuadorian seasonal dry forests between 1990 and 2018 were verified,while geographic information systems and land cover shapes provided by the Ecuadorian ministry of the Environment were employed to classify and evaluate three types of seasonal dry forests:deciduous,semi-deciduous,and *** study area was tessellated into 10 km2 hexagons,in which six fragmentation parameters were measured:number of patches,mean patch size,median patch size,total edge,edge density and reticular fragmentation index(RFI).The RFI was also measured both outside and inside protected natural areas(unprotected,national protected areas and protected forest).moreover,the areas with the best and worst conservation status,connectivity and risk of disappearance values were identified by means of a Getis-Ord Gi*statistical ***:The deforestation of seasonal dry forests affected 27.04%of the original surface area still remaining in 1990,with an annual deforestation rate of−1.12%between 1990 and *** RFI has increased by 11.61%as a result of the fact that small fragments of forest have tended to disappear,while the large fragments have been fragmented into smaller *** semi-deciduous forest had the highest levels of fragmentation in *** three categories of protection had significantly different levels of fragmentation,with lower RFI values in national protected areas and greater values in protected ***:The seasonal dry forest is fragmenting,deforesting and disappearing in some *** increased protection and conservation of the Ecuadorian seasonal dry forest is,therefore,necessary owing to the fact that not all prot

关键词： Deciduous forest Semi-deciduous forest Remnant forest Patch isolation Habitat loss Protected areas

Universal Deformation Rings of modules over Self-injective Cluster-Tilted Algebras Are Trivial

在线全文

学校读者我要写书评

暂无评论

Algebra Colloquium 2021年第2期28卷 269-280页

作者： I.D.m.Gaviria joséA.Vélez-marulanda Peng Shan Universidad Nacional de Colombia Bogota D.C.Colombia Department of mathematics Valdosta State UniversityValdostaGAUSA 不详

Let k be a fixed algebraically closed field of arbitrary characteristic,let Λ be a finite dimensional self-injective k-algebra,and let ∨ be an indecomposable non-projective left Λ-module with finite dimension over *** prove that if τΛ∨ is the Auslander-Reiten translation of ∨,then the versal deformation rings R(Λ,∨)and R(Λ,τΛ∨)(in the sense of *** and the second author)are *** use this to prove that if Λ is further a cluster-tilted k-algebra,then R(Λ,∨)is universal and isomorphic to k.

关键词： self-injective cluster tilted algebras Frobenius algebras (uni)versal deformation rings

On a Variant of Giuga Numbers

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta mathematica Sinica,English Series 2012年第4期28卷 653-660页

作者： jos maría GRAU Florian LUCA Antonio m. OLLER-mARCN Departmento de matemáticas Universidad de Oviedo Avda. Calvo Sotelo s/n Instituto de matemáticas Universidad Nacional Autnoma de México The John Knopfmacher Centre for Applicable Analysis and Number Theory University of the Witwatersrand Centro Universitario de la Defensa Academia General Militar Ctra. Huesca s/n

In this paper, we characterize the odd positive integers n satisfying the congruence ∑j=1^n-1 j n-1/2 We show that the set of such positive integers has an asymptotic densitywhich turns out to be slightly larger than... 详细信息

关键词： Congruence Giuga numbers asymptotic density

Simulation of Needle-Type Corona Electrodes by the Finite Element method

在线全文

学校读者我要写书评

暂无评论

Plasma Science and Technology 2007年第6期9卷 698-701页

作者：杨仕友 josé márcio mACHADO Nancy mieko ABE Angelo PASSARO College of Electrical Engineering Zhejiang UniversityHangzhou 310027China So Institute

This paper describes a software tool, called LEVSOFT, suitable for the electric field simulations of corona electrodes by the Finite Element method （FEm）. Special attention was paid to the user friendly construction of geometries with corners and sharp points, and to the fast generation of highly refined triangular meshes and field maps. The execution of selfadaptive meshes was also implemented. These customized features make the code attractive for the simulation of needle-type corona electrodes. Some case examples involving needle type electrodes are presented.

关键词： corona electrodes finite element methods numerical analysis