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Raul Payri,F. J. Salvador,J. Gimeno,V. Soare 대한기계학회 2005 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.19 No.11
The present paper centers on the establishment of a quantified relationship between the macroscopic visual parameters of a Diesel spray and its most influential factors. The factors considered are the ambient gas density, as an external condition relative to the injection system, and nozzle hole diameter and injection pressure as internal ones. The main purpose of this work is to validate and extend the different correlations available in the literature to the present state of the Diesel engine, i.e. high injection pressure, small nozzle holes, severe cavitating conditions, etc. Five mono-orifice, axi-symmetrical nozzles with different diameters have been studied in two different test rigs from which one can reproduce solely the real engine in-cylinder air density, and the other, both the density and the pressure. A parametric study was carried out and it enabled the spray tip penetration to be expressed as a function of nozzle hole diameter, injection pressure and environment gas density. The temporal synchronization of the penetration and injection rate data revealed a possible explanation for the discontinuity observed as well by other authors in the spray’s penetration law. The experimental results obtained from both test rigs have shown good agreement with the theoretical analysis. There have been observed small but consistent differences between the two test rigs regarding the spray penetration and cone angle, and thus an analysis of the possible causes for these differences has also been included.
Raul Payri,S. Molina,F. J. Salvador,J. Gimeno 대한기계학회 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.7
This study examines the influence of geometry on the internal flow and macroscopic behavior of the spray in Diesel nozzles. For this investigation, two bi-orifice nozzles were employed: one cylindrical and one conical. The first step is to use a non-destructive characterization method which is based on the production of silicone moulds so that the precise internal geometry of the two nozzles can be measured. At this stage the nozzles have been characterized dimensionally and therefore the internal flow can be studied using CFD calculations. The results gained from this experiment make it possible also to ascertain the critical cavitation conditions. Once the critical cavitation conditions have been identified, the macroscopic parameters of the spray can be studied in both cavitating and non-cavitating conditions using a test rig pressurized with nitrogen and with the help of a image acquisition system and image processing software. Consequently, research can be carried out to determine the influence that cavitation has on macroscopic spray behavior. From the point of view of the spray macroscopic behavior, the main conclusion of the paper is that cavitation leads to an increment of the 'spray cone angle. On the other hand, from the point of view of the internal flow, the hole outlet velocity increases when cavitation appears. This phenomenon can be explained by the reduction in the cross section of the liquid phase in the outlet section of the hole.
Urinary Tract Infection in Postmenopausal Women
Raul Raz 대한비뇨의학회 2011 Investigative and Clinical Urology Vol.52 No.12
Urinary tract infection (UTI) is the most common bacterial infection in women in general and in postmenopausal women in particular. Two groups of elderly women with recurrent UTI should be differentiated regarding age and general status: healthy, young postmenopausal women aged 50 to 70 years who are neither institutionalized or catheterized and elderly institutionalized women with or without a catheter. Bacteriuria occurs more often in elderly functionally impaired women, but in general it is asymptomatic. However, the risk factors associated with recurrent UTI in elderly women are not widely described. In a multivariate analysis it was found that urinary incontinence, a history of UTI before menopause, and nonsecretor status were strongly associated with recurrent UTI in young postmenopausal women. Another study described the incidence and risk factors of acute cystitis among nondiabetic and diabetic postmenopausal women. Independent predictors of infection included insulin-treated patients and a lifetime history of urinary infection. Borderline associations included a history of vaginal estrogen cream use in the past month, kidney stones, and asymptomatic bacteriuria at baseline. Another important factor in postmenopausal women is the potential role that estrogen deficiency plays in the development of bacteriuria. There are at least two studies showing a beneficial effect of estrogen in the management of recurrent bacteriuria in elderly women. One of these studies showed that vaginal estrogen cream reduced vaginal pH from 5.5±0.7 to 3.6±1.0, restored lactobacillus, and decreased new episodes of UTI. Another study reported similar results using an estriol vaginal ring. However, contradictory results are found in the literature. For example, additional studies found that the use of estriol-containing vaginal pessaries was less effective than oral nitrofurantoin macrocrystals in preventing UTI in postmenopausal women. Two other studies also did not find any benefit in the reduction of UTI by oral estrogen therapy. Unfortunately, the use of estrogen in preventing UTI in postmenopausal women remains questionable. New strategies have been researched for reducing the use of antibiotics in the prevention and treatment of UTI. Two of them are probiotics and cranberry juice or capsules. Although several studies regarding probiotics and cranberry juice or capsules have reported a reduction of episodes of UTI, there is no conclusive evidence that they are useful in the prevention of UTI in postmenopausal women. As for the optimal drug, dosage, and length of treatment for UTI in the elderly, there are no studies comparing these data with the treatment for young women.
Discontinuous H∞ Control of Underactuated Mechanical Systems with Friction and Backlash
Raul Rascon,Joaquin Alvarez,Luis T. Aguilar 제어·로봇·시스템학회 2016 International Journal of Control, Automation, and Vol.14 No.5
Nonlinear H∞-control is extended to discontinuous mechanical systems with degree of underactuationone, where nonlinear phenomena such as Coulomb friction and backlash are considered. The problem in questionis to design a feedback controller via output measurements so as to obtain the closed-loop system in which alltrajectories are locally ultimate bounded, and the underactuated link is regulated to a desired position while alsoattenuating the influence of external perturbations and nonlinear phenomena. It is considered that positions are theonly measurements available for feedback in the system. Performance issues of the discontinuous H∞-regulationcontroller are illustrated in an experimental study made for a rectilinear plant with friction modified to have a gapin the point of contact between bodies.
Corrosion Behaviour of Type 316L Stainless Steel in Hot Caustic Aqueous Environments
Raul Davalos Monteiro,Nouryon Industrial Chemicals,Benjamin Krawczyk,Dirk L. Engelberg 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.5
The corrosion behaviour of type 316L stainless steel in aqueous 30–50 wt%. NaOH at temperatures up to 90 °C has been elucidated. Exposure to room temperature environment showed parabolic weight loss behaviour, with corrosion rates of up to 0.4 mm/year. Higher NaOH concentrations and exposure temperatures resulted in a reduced stability of the electrochemical passivity domain, associated with higher corrosion rates. Exposure to de-aerated 50 wt%. NaOH presented corrosion rates of up to 0.5 mm/year at open circuit potential, with maximum corrosion rates under polarisation of up to ≈18 mm/year. The formation of a dark iron-oxy-hydroxide and nickel-oxide was observed, with exposure to temperatures in excess of 50 °C. The behaviour of type 316L stainless steel in hot caustic environment is compared to types 204, 304, 2205 stainless steel, and nickel alloy 200.
Core Issues Facing Brazil’s Quest towards Sustainable Growth
Raul Gouvea 한국라틴아메리카학회 2013 라틴아메리카연구 Vol.26 No.4
The new global economic order is creating an inflection point in the global economy. BRIC countries have experienced a shift in global wealth, resulting in an increase in their economic and political clout on a global scale. Reflecting these recent trends and changes, the Brazilian economy was ranked 6th in the world in 2012. Companies doing business in Brazil need to understand the nature of its economy and design strategies and policies to maximize their earnings in the Brazilian market. Brazil’s booming oil & gas industries, agribusiness, services, and manufacturing industries offer a high potential for companies willing to face Brazil’s many challenges, such as shortages of qualified labor force, and high taxes. Brazil’s booming middle class also poses a number of challenges for companies that need to tailor their offerings to a young and evolving middle class. At the same time, Brazil is also building a sophisticated and vibrant middle class that will increasingly demand products and services that resemble offerings found in traditional developed markets. Still, market efficiency and productivity enhancers will have to be addressed in order to make the Brazilian economy more competitive. This paper addresses Brazil’s core issues permeating its quest towards sustainable growth. The paper addresses the different dimensions of Brazil’s economic and social environments, paying heed to recent developments and driving forces shaping Brazil’s economy and society.
A Study of Broline-Crowe-Isaacs Matrices of Polygon Dissections
Raul Felipe 경북대학교 자연과학대학 수학과 2022 Kyungpook mathematical journal Vol.62 No.2
The work realized by the authors of [4], [5] and [6] associates a non-negative matrix with positive integers entries to each dissection of a polygon. In the particular case of triangulations, these matrices called BCI-matrices here contain valuable information of their frieze patterns, a concept introduced by Coxeter and Conway. This paper is con cerned with the algebraic manipulation and properties of these matrices which are derived from operations acting on dissections.