The Hamiltonian structure of a two-dimensional rigid circular cylinder interacting dynamically with N point vortices

This paper studies the dynamical fluid plus rigid-body system consisting of a two-dimensional rigid cylinder of general cross-sectional shape interacting with N point vortices. We derive the equations of motion for this system and show that, in particular, if the vortex strengths sum to zero and the rigid-body has a circular shape, the equations are Hamiltonian with respect to a Poisson bracket structure that is the sum of the rigid body Lie–Poisson bracket on Se(2)*, the dual of the Lie algebra of the Euclidean group on the plane, and the canonical Poisson bracket for the dynamics of N point vortices in an unbounded plane. We then use this Hamiltonian structure to study the linear and nonlinear stability of the moving Föppl equilibrium solutions using the energy-Casimir method

Three Dimensional Constraint Effects on the Estimated (Delta)CTOD during the Numerical Simulation of Different Fatigue Threshold Testing Techniques

Variation in constraint through the thickness of a specimen effects the cyclic crack-tip-opening displacement (DELTA CTOD). DELTA CTOD is a valuable measure of crack growth behavior, indicating closure development, constraint variations and load history effects. Fatigue loading with a continual load reduction was used to simulate the load history associated with fatigue crack growth threshold measurements. The constraint effect on the estimated DELTA CTOD is studied by carrying out three-dimensional elastic-plastic finite element simulations. The analysis involves numerical simulation of different standard fatigue threshold test schemes to determine how each test scheme affects DELTA CTOD. The American Society for Testing and Materials (ASTM) prescribes standard load reduction procedures for threshold testing using either the constant stress ratio (R) or constant maximum stress intensity (K(sub max)) methods. Different specimen types defined in the standard, namely the compact tension, C(T), and middle cracked tension, M(T), specimens were used in this simulation. The threshold simulations were conducted with different initial K(sub max) values to study its effect on estimated DELTA CTOD. During each simulation, the DELTA CTOD was estimated at every load increment during the load reduction procedure. Previous numerical simulation results indicate that the constant R load reduction method generates a plastic wake resulting in remote crack closure during unloading. Upon reloading, this remote contact location was observed to remain in contact well after the crack tip was fully open. The final region to open is located at the point at which the load reduction was initiated and at the free surface of the specimen. However, simulations carried out using the constant Kmax load reduction procedure did not indicate remote crack closure. Previous analysis results using various starting K(sub max) values and different load reduction rates have indicated DELTA CTOD is independent of specimen size. A study of the effect of specimen thickness and geometry on the measured DELTA CTOD for various load reduction procedures and its implication in the estimation of fatigue crack growth threshold values is discussed

Role of staging laparoscopy in upstaging CT findings and influencing treatment decisions in gastric cancers

Background: It is estimated that 990000 new gastric cancer (GC) cases occur in the world annually. The aim of this study was to examine the accuracy of laparoscopy in staging patients with gastric cancer in comparison with preoperative computed tomography (CT) examination and to determine the influence of staging laparoscopy on treatment decisions in gastric cancers.Methods: This was a prospective study conducted in a tertiary care hospital between August 2014 and February 2016. Thirty patients out of a series of 60 patients with gastric adenocarcinoma underwent a preoperative staging CT followed by a staging laparoscopy. The strengths of the agreement between the CT stage, the laparoscopic stage, and the final histopathological stage were determined by the weighted Kappa statistic (Kw). The number of patients with treatment decision-changes was counted.Results: The strengths of agreement between the CT stage and the final histopathological stage were Kw- 0.314 (95% confidence interval [CI]; 0.03-0.66; P≥0.0001) for T stage and 0.00 (95% CI; 0.0-0.00) for M stage, compared with 0.668 (95% CI; 0.39-0.98; P≥0.0001) and 1.00 (95% CI; 1.0-1.0; P≥0.0001) for the laparoscopic T and M stages, respectively. Unsuspected metastases that were not detected by CT, were found in 12 patients at laparoscopy, all of whom had T3 or T4 locally advanced tumors evident on CT.Conclusions: Preoperative laparoscopic staging of gastric cancer is indicated for potential surgical candidates with locally advanced disease in the absence of metastases on CT and influences treatment decision making apart from preventing unnecessary laparotomies

Performance Enhancement Using Selective Reinforcement for Metallic Single- and Multi-Pin Loaded Holes

An analysis based investigation of aluminum with metal matrix composite selectively reinforced single- and multi-hole specimens was performed and their results compared with results from geometrically comparable non-reinforced specimens. All reinforced specimens exhibited a significant increase in performance. Performance increase of up to 170 percent was achieved. Specimen failure modes were consistent with results from reinforced polymeric matrix composite specimens. Localized reinforcement application (circular) proved as effective as a broader area (strip) reinforcement. Also, selective reinforcement is an excellent method of increasing the performance of multi-hole specimens

Evaluation of buprenorphine as an adjuvant to 2% lidocaine during intravenous regional anaesthesia

Background: Intravenous regional anaesthesia (IVRA) is a simple, effective method of anaesthesia for surgical procedures on the extremities. Major limitations are tourniquet pain, short duration of block and absence of post-operative analgesia. Buprenorphine is known to improve the quality of anaesthesia. Aim of this study is to evaluate the efficacy of buprenorphine as an adjuvant to lignocaine in IVRA. Methods: Sixty patients between 18-60 years age, belonging to the ASA grade 1, 2 undergoing upper limb surgeries were enrolled into the study. Patients belonging to group BL patients received 10 ml of preservative free lidocaine 2% diluted to 40 ml. Group BB-patients received 10 ml of preservative free lidocaine 2% mixed with 60 mcg of buprenorphine diluted to 40 ml. Onset of sensory and motor block; recovery time and postoperative analgesia were noted. Data were analyzed using chi-square test, independent ‘t’ test. Results: The onset time of both sensory and motor block were significantly shortened, the recovery of sensory and motor block was prolonged, the incidence of tourniquet pain was comparatively lesser and there was significantly increased duration of post-operative analgesia in the buprenorphine group. Haemo-dynamic parameters were similar in both groups Conclusions: Sixty mcg buprenorphine as an adjuvant to lidocaine in IVRA effectively enhances the anaesthesia and post-operative analgesia.

Experimental and Finite Element Modeling of Near-Threshold Fatigue Crack Growth for the K-Decreasing Test Method

The experimental methods to determine near-threshold fatigue crack growth rate data are prescribed in ASTM standard E647. To produce near-threshold data at a constant stress ratio (R), the applied stress-intensity factor (K) is decreased as the crack grows based on a specified K-gradient. Consequently, as the fatigue crack growth rate threshold is approached and the crack tip opening displacement decreases, remote crack wake contact may occur due to the plastically deformed crack wake surfaces and shield the growing crack tip resulting in a reduced crack tip driving force and non-representative crack growth rate data. If such data are used to life a component, the evaluation could yield highly non-conservative predictions. Although this anomalous behavior has been shown to be affected by K-gradient, starting K level, residual stresses, environmental assisted cracking, specimen geometry, and material type, the specifications within the standard to avoid this effect are limited to a maximum fatigue crack growth rate and a suggestion for the K-gradient value. This paper provides parallel experimental and computational simulations for the K-decreasing method for two materials (an aluminum alloy, AA 2024-T3 and a titanium alloy, Ti 6-2-2-2-2) to aid in establishing clear understanding of appropriate testing requirements. These simulations investigate the effect of K-gradient, the maximum value of stress-intensity factor applied, and material type. A material independent term is developed to guide in the selection of appropriate test conditions for most engineering alloys. With the use of such a term, near-threshold fatigue crack growth rate tests can be performed at accelerated rates, near-threshold data can be acquired in days instead of weeks without having to establish testing criteria through trial and error, and these data can be acquired for most engineering materials, even those that are produced in relatively small product forms

Role of staging laparoscopy to evaluate feasibility of performing optimal cytoreductive surgery in epithelial ovarian cancers

Background: The main stay of treatment for epithelial ovarian cancers is surgical cytoreduction. CT scan and staging laparotomy are methods used to assess feasibility to carry out optimal cytoreduction. We evaluated the role of staging laparoscopy in assessing operability for optimal cytoreduction as well as avoidance of unnecessary laparotomies.Methods: Between September 2014-2016, 23 patients of epithelial ovarian cancer underwent staging laparoscopy as part of evaluation method to check feasibility to carry out optimal cytoreductive surgery. The findings were correlated with clinical findings as well as CT scan findings. The impact of laparoscopy to predict operability was studied as well as its use to avoid unnecessary laparotomies.Results: Laparoscopy could correctly evaluate the nature of abdominal mass in 91.3% patients. It picked up omental and peritoneal deposits in 87% and 95.7% patients respectively as compared to 60.9% and 39% picked up on CT scan. More importantly laparoscopy could diagnose mesenteric and small bowel deposits in 34.8% of patients which were never reported on CT scan. The overall impact was reduction in unnecessary laparotomies.Conclusions: Laparoscopic evaluation is a useful adjunct prior to performing a formal laparotomy in epithelial ovarian cancer cytoreductive surgery

Three Dimensional Numerical Simulation and Characterization of Crack Growth in the Weld Region of a Friction Stir Welded Structure

Friction stir welding (FSW) fabrication technology is being adopted in aerospace applications. The use of this technology can reduce production cost, lead-times, reduce structural weight and need for fasteners and lap joints, which are typically the primary locations of crack initiation and multi-site fatigue damage in aerospace structures. FSW is a solid state welding process that is well-suited for joining aluminum alloy components; however, the process introduces residual stresses (both tensile and compressive) in joined components. The propagation of fatigue cracks in a residual stress field and the resulting redistribution of the residual stress field and its effect on crack closure have to be estimated. To insure the safe insertion of complex integral structures, an accurate understanding of the fatigue crack growth behavior and the complex crack path process must be understood. A life prediction methodology for fatigue crack growth through the weld under the influence of residual stresses in aluminum alloy structures fabricated using FSW will be detailed. The effects and significance of the magnitude of residual stress at a crack tip on the estimated crack tip driving force are highlighted. The location of the crack tip relative to the FSW and the effect of microstructure on fatigue crack growth are considered. A damage tolerant life prediction methodology accounting for microstructural variation in the weld zone and residual stress field will lead to the design of lighter and more reliable aerospace structure