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A step-by-step approach in the time-domain BEM formulation for the scalar wave equation
Carrer, J.A.M.,Mansur, W.J. Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.27 No.6
This article is concerned with the presentation of a time-domain BEM approach applied to the solution of the scalar wave equation for 2D problems. The basic idea is quite simple: the basic variables of the problem at time $t_n$ (potential and flux) are computed with the results related to the potential and to its time derivative at time $t_{n-1}$ playing the role of "initial conditions". This time-marching scheme needs the computation of the potential and its time derivative at all boundary nodes and internal points, as well as the entire discretization of the domain. The convolution integrals of the standard time-domain BEM formulation, however, are not computed; the matrices assembled, only at the initial time interval, are those related to the potential, flux and to the potential time derivative. Two examples are presented and discussed at the end of the article, in order to verify the accuracy and potentialities of the proposed formulation.
Carrer, J.A.M.,Mansur, W.J. Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.23 No.3
This work presents a time-truncation scheme, based on the Lagrange interpolation polynomial, for the solution of the two-dimensional scalar wave problem by the time-domain boundary element method. The aim is to reduce the number of stored matrices, due to the convolution integral performed from the initial time to the current time, and to keep a compromise between computational economy and efficiency and the numerical accuracy. In order to verify the accuracy of the proposed formulation, three examples are presented and discussed at the end of the article.
Gasdynamics of rapid and explosive decompressions of pressurized aircraft including active venting
Pagani, Alfonso,Carrer, Erasmo Techno-Press 2016 Advances in aircraft and spacecraft science Vol.3 No.1
In this paper, a zero-dimensional mathematical formulation for rapid and explosive decompression analyses of pressurized aircraft is developed. Air flows between two compartments and between the damaged compartment and external ambient are modeled by assuming an adiabatic, reversible transformation. Both supercritical and subcritical decompressions are considered, and the attention focuses on intercompartment venting systems. In particular, passive and active vents are addressed, and mathematical models of both swinging and translational blowout panels are provided. A numerical procedure based on an explicit Euler integration scheme is also discussed for multi-compartment aircraft analysis. Various numerical solutions are presented, which highlight the importance of considering the opening dynamics of blowout panels. The comparisons with the results from the literature demonstrate the validity of the proposed methodology, which can be also applied, with no lack of accuracy, to the decompression analysis of spacecraft.
Non-Tariff Measures: What Do We Know, What Might Be Done?
( Jaime De Melo ),( Celine Carrere ) 세종대학교 경제통합연구소(구 세종대학교 국제경제연구소) 2011 Journal of Economic Integration Vol.26 No.1
With the reduction in tariff barriers, Non-tariff and behind-the-border measures (NTM and BTB) have increased in importance. This paper surveys the state of knowledge with the view to drawing implications for policy suggestions to reduce those NTM barriers that are welfare reducing. Following a description of data bases and their shortcomings, the paper reviews the state of understanding on the effects of NTMs on trade flows. The more difficult issue of translating these effects into welfare implications are covered next. The paper concludes with different approaches at reducing NTMs.
Souza, L.A.,Carrer, J.A.M.,Martins, C.J. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.17 No.6
This work presents a direct integration scheme, based on a fourth order finite difference approach, for elastodynamics. The proposed scheme was chosen as an alternative for attenuating the errors due to the use of the central difference method, mainly when the time-step length approaches the critical time-step. In addition to eliminating the spurious numerical oscillations, the fourth order finite difference scheme keeps the advantages of the central difference method: reduced computer storage and no requirement of factorisation of the effective stiffness matrix in the step-by-step solution. A study concerning the stability of the fourth order finite difference scheme is presented. The Finite Element Method and the Boundary Element Method are employed to solve elastodynamic problems. In order to verify the accuracy of the proposed scheme, two examples are presented and discussed at the end of this work.
Notes on Detecting The Effects of Non Tariff Measures
( Jaime De Melo ),( Celine Carrere ) 세종대학교 경제통합연구소(구 세종대학교 국제경제연구소) 2011 Journal of Economic Integration Vol.26 No.1
Alternative approaches to estimating the effects of nontariff measures (NTMs) on trade flows are discussed and evaluated critically. Recent econometric studies point to three results: (i) NTM restrictiveness measures based on an aggregate of ‘core’ NTMs are more restrictive than existing tariffs and, because of export composition towards agricultural products, in the aggregate, these ‘core’ NTMs limit market access most for low-income countries; (ii) Proxies for individual NTMs have a negative effect on the volume of bilateral trade for the detailed product under scrutiny; (iii) harmonization of standards is trade enhancing. Case studies confirm several of these patterns, and also that perceived severity of NTMs varies across products and across destinations for a given product. Across broadly defined imports at the section level, NTMs are more restrictive than the corresponding tariffs with two-thirds of the ad-valorem equivalent estimates in the 25%-50% range. Technical regulations and non-automatic licensing are the most used single-NTM measures and the restrictiveness of technical regulations increases with income per capita.
Esther Nova,Blanca Viadel,Julia Wärnberg,Jose E. Carreres,Ascensión Marcos 한국식품영양과학회 2011 Journal of medicinal food Vol.14 No.1
The use of synbiotics as health promoters is still poorly defined, and human intervention studies are scarce. This study was designed to evaluate the effects of a commercialized synbiotic product containing Lactobacillus acidophilus La5, Bifidobacterium animalis ssp. lactis Bb-12, Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus paracasei ssp. paracasei, Streptococcus thermophilus, and fructooligosaccharides on the self-reported gastrointestinal well-being and the immunoinflammatory status of healthy human subjects. In this randomized, double-blind, placebo-controlled study, 20 women and 16 men (25–45 years old) received either three tablets per day of the synbiotic product (2.4×109 colony-forming units/day) or placebo during 6 weeks. Gastrointestinal symptoms and bowel habits were evaluated through a self-administered questionnaire. In those subjects suffering from any kind of digestive disturbance (mild dyspepsia, flatulence, postprandial bloating, constipation, etc.), improvements in symptoms after product consumption were also evaluated. Blood lymphocyte subsets, phagocytic activity, serum C-reactive protein, ceruloplasmin, and adhesion molecules concentrations were analyzed prior and after treatment. A significant improvement in overall self-reported gastrointestinal symptoms and bowel habit was found in the synbiotic group. A marginal effect of treatment (analysis of variance P=.050) was observed with L-selectin, which showed a significant decrease in the synbiotic group (P=.019). In addition, basal L-selectin levels correlated with final intercellular adhesion molecule (ICAM)-1 levels (r=0.468; P=.050), and basal ICAM-1 levels tended to correlate negatively with final L-selectin concentration (r=–0.457; P=.056). None of these correlations was found in the placebo group. The rest of the immunological parameters studied were not modified by the intervention. In conclusion, consumption of the synbiotic product improves self-perceived bowel habits and might facilitate a better profile of adhesion molecules in healthy adults.