Hypothesis: Cephalosporins are widely used and considered to be effective as prophylaxis in biliary surgery. Nevertheless, they lack activity against enterococci. We conducted a study to compare the efficacy of ampicillinsulbactam vs cefuroxime in preventing surgical site infections following elective cholecystectomy. Design: A prospective randomized controlled trial. Setting: A major tertiary care hospital. Patients: Four hundred eighteen randomized patients (of 549 total), who from July 2002 to August 2004 underwent elective open or laparoscopic cholecystectomy with prospective assessment for development of surgical site infections for 1 month postoperatively. Intervention: A single intravenous dose of 1.5 g of cefuroxime (group A, n = 207) or 3 g of ampicillinsulbactam (group B, n = 211) was administered during induction of anesthesia. Bile and gallbladder mucosal cultures were taken intraoperatively from all patients. Main Outcome Measure: Number of postoperative surgical site infections. Results: A postoperative surgical site infection was noted in 19 (4.5%) of 418 patients, 18 from group A and 1 from group B (PϽ.001). In the group that received cefuroxime, 15 (83.3%) of 18 surgical site infections were due to Enterococcus species. Intraoperative bactibilia as well as intraoperative gallbladder rupture were associated with surgical site infections (PϽ.001). Conclusions: A single dose of ampicillin-sulbactam favored better compared with cefuroxime for prevention of postoperative surgical site infections due to Enterococcus species after elective cholecystectomy. Ampicillinsulbactam may be a better agent for antimicrobial prophylaxis in high-risk patients undergoing elective cholecystectomy, especially in a setting where the incidence of enterococcal infections is higher.

Propeller performance is traditionally represented by a performance map that gives propeller efficiency as a function of the flight Mach number, the power coefficient C P , and the advance ratio J. This work aims to demonstrate how this map changes when the design C P and J change and to propose a novel map format that is able to capture the performance of different propeller designs. For this purpose, the propeller performance is simulated using a propeller lifting-line method validated for the SR3 propfan. Subsequently, the propeller model is used within a sequential quadratic programming framework to optimize the blade twist and chord distribution for different sets of design C P and J. A complete propeller performance map is then generated for each one of the optimized designs. The results demonstrate that all the investigated propellers can be modeled by a common map, which determines separately the ideal efficiency and the viscous losses. The ideal efficiency is given in the traditional format of η i fC P ;J, whereas the viscous losses are represented as a function of the relative variables C P ∕C Pdes and J∕J des .

The estimation of gas turbine engine weight during the preliminary or conceptual design phase is a key part of a Techno-economic Environmental Risk Analysis (TERA). Several methods that are available in the public domain are analysed and compared, in order to establish the physics driving them and their suitability for the weight estimation of modern gas turbine engines. Among the tested methods, only WATE managed to achieve acceptable accuracy for engine optimisation studies. This work demonstrates that the age and restrictions of existing 'whole engine based' methods, along with their dependency on old engine databases make them unsuitable for future and novel aero engines. A hybrid weight modelling approach is proposed as a solution permitting the creation of simple 'whole engine based' methods that do not depend on the availability of existing engine data, which are also subject to uncertainties and incoherencies.

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This paper outlines a novel meanline off-design model to predict the performance characteristics of a radial inflow turbine that operates with ideal and real working fluids. Experimental data available in open literature were used for validation, including radial turbines that operate with both ideal gas (air) and real working fluids (R123). Initially the differences in the expansion process between ideal and real fluids on a thermodynamic base are highlighted. Then, the proposed meanline off-design model is calibrated for a few selected points and validated against experimental data for both air and R123. The comparison between the predicted and measured results presented errors less than 10% for both ideal and real gas fluids. Finally, the predicted air turbine was simulated with a real gas fluid. Relative to air, operation with R123 revealed that the peak efficiency is 12% lower and occurs at 70% lower rotational speed. The proposed methodology gives insights for accurate model-based design of organic Rankine cycle (ORC) systems, as the radial turbo expander is the most crucial and expensive component of such heat recovery systems.