Conservative-variable average states for equilibrium gas multi-dimensional fluxes

Modern split component evaluations of the flux vector Jacobians are thoroughly analyzed for equilibrium-gas average-state determinations. It is shown that all such derivations satisfy a fundamental eigenvalue consistency theorem. A conservative-variable average state is then developed for arbitrary equilibrium-gas equations of state and curvilinear-coordinate fluxes. Original expressions for eigenvalues, sound speed, Mach number, and eigenvectors are then determined for a general average Jacobian, and it is shown that the average eigenvalues, Mach number, and eigenvectors may not coincide with their classical pointwise counterparts. A general equilibrium-gas equation of state is then discussed for conservative-variable computational fluid dynamics (CFD) Euler formulations. The associated derivations lead to unique compatibility relations that constrain the pressure Jacobian derivatives. Thereafter, alternative forms for the pressure variation and average sound speed are developed in terms of two average pressure Jacobian derivatives. Significantly, no additional degree of freedom exists in the determination of these two average partial derivatives of pressure. Therefore, they are simultaneously computed exactly without any auxiliary relation, hence without any geometric solution projection or arbitrary scale factors. Several alternative formulations are then compared and key differences highlighted with emphasis on the determination of the pressure variation and average sound speed. The relevant underlying assumptions are identified, including some subtle approximations that are inherently employed in published average-state procedures. Finally, a representative test case is discussed for which an intrinsically exact average state is determined. This exact state is then compared with the predictions of recent methods, and their inherent approximations are appropriately quantified

Endovascular Stent Grafts as a Safe Secondary Option for Paraanastomotic Abdominal Aortic Aneurysm

ObjectiveTo describe our experience of endovascular repair of paraanastomotic aortic aneurysm.Methods and resultsFrom March 2001 to December 2004 we identified 6 patients with a paraanastomotic aortic aneurysms following previous open repair of abdominal aortic aneurysm. All patients were treated with endovascular surgery under epidural anaesthesia. There were no major complications, surgical conversions or deaths. Four patients received a bifurcated aortic stent-graft, and two an aorto-uniliac stent-graft followed by a femoro-femoral bypass. At follow-up (mean 26.1±10.2 months) there were no deaths, endoleaks or graft migrations observed.ConclusionEndovascular surgery, avoiding general anesthesia and re-laparotomy, is the ideal technique for treatment of this complication resulting from failed primary conventional AAA repair

Endovascular Stent Grafts as a Safe Secondary Option for Paraanastomotic Abdominal Aortic Aneurysm

Objective: To describe our experience of endovascular repair of paraanastomotic aortic aneurysm. Methods and results: From March 2001 to December 2004 we identified 6 patients with a paraanastomotic aortic aneurysms following previous open repair of abdominal aortic aneurysm. All patients were treated with endovascular surgery under epidural anaesthesia. There were no major complications, surgical conversions or deaths. Four patients received a bifurcated aortic stent-graft, and two an aorto-uniliac stent-graft followed by a femoro-femoral bypass. At follow-up (mean 26.1 ± 10.2 months) there were no deaths, endoleaks or graft migrations observed. Conclusion: Endovascular surgery, avoiding general anesthesia and re-laparotomy, is the ideal technique for treatment of this complication resulting from failed primary conventional AAA repair. © 2006 Elsevier Ltd. All rights reserved

Cystic Dilation of Extrahepatic Bile Ducts in Adulthood: Diagnosis, Surgical Treatment and Long. Term Results

To evaluate the long-term results of surgery for choledohal cyst in adulthood, a series of 13 patients over the age of 16 operated on for choledochal cyst during a period of six years and followed-up for a minimum of 3 years was analyzed. Patients with type I and IVa cysts underwent extrahepatic cyst resection and Roux-en-Y hepatico-jejunostomy. Choledochoceles (type III) were managed endoscopically. No operative mortality or morbidity occurred. Type I and III cysts showed almost ideal follow-up with no sign of stricture on HIDA scan. One type IVa cyst patients developed recurrent cholangitis due to anastomotic stricture, managed percutaneously. Whenever possible, complete cyst resection and Roux-en-Y reconstruction is the treatment of choice for all extrahepatic biliary cysts. Intra- and extrahepatic dilatations are adequately treated by extrahepatic resection and careful endoscopic or radiologic surveillance. Small choledochoceles can be safely managed by endoscopic sphincterotomy

Kinetic theory of age-structured stochastic birth-death processes

Classical age-structured mass-action models such as the McKendrick-von Foerster equation have been extensively studied but are unable to describe stochastic fluctuations or population-size-dependent birth and death rates. Stochastic theories that treat semi-Markov age-dependent processes using, e.g., the Bellman-Harris equation do not resolve a population's age structure and are unable to quantify population-size dependencies. Conversely, current theories that include size-dependent population dynamics (e.g., mathematical models that include carrying capacity such as the logistic equation) cannot be easily extended to take into account age-dependent birth and death rates. In this paper, we present a systematic derivation of a new, fully stochastic kinetic theory for interacting age-structured populations. By defining multiparticle probability density functions, we derive a hierarchy of kinetic equations for the stochastic evolution of an aging population undergoing birth and death. We show that the fully stochastic age-dependent birth-death process precludes factorization of the corresponding probability densities, which then must be solved by using a Bogoliubov-–Born–-Green–-Kirkwood-–Yvon-like hierarchy. Explicit solutions are derived in three limits: no birth, no death, and steady state. These are then compared with their corresponding mean-field results. Our results generalize both deterministic models and existing master equation approaches by providing an intuitive and efficient way to simultaneously model age- and population-dependent stochastic dynamics applicable to the study of demography, stem cell dynamics, and disease evolution

Muscoloskeletal disorders and occupational stress of violinists

Although musculoskeletal disorders are the most frequent cause of occupational diseases in musicians, very few studies have focused attention on a single category of instruments, in particular on the violin. This involves, in its practice, almost all the areas of the body, besides being in the category of strings which is the most numerous in an orchestra. A specific protocol, investigating postural and clinical profiles of the muskoloskeletal apparatus as well as job stress, was utilized in a conservatory on graduates in the tenth year of violin study, who regularly participated in activities of orchestras or string quartets. The investigation revealed “target segments” of osteoarticular apparatus (jaw, vertebral spine, shoulders, elbows, hands and fingers, lower limbs) electively subjected to overuse, as well as muscle contracture of trapezoids and hyperkeratosis of fingers and clavicle. Although the work environment was comfortable, most violinists claimed to undergo intense rhythms and competitiveness. This study, highlighting sublinical occupational diseases in young musicians (violinists) suggests adequate prevention measures