Preconditioning complex symmetric linear systems

A new polynomial preconditioner for symmetric complex linear systems based on Hermitian and skew-Hermitian splitting (HSS) for complex symmetric linear systems is herein presented. It applies to Conjugate Orthogonal Conjugate Gradient (COCG) or Conjugate Orthogonal Conjugate Residual (COCR) iterative solvers and does not require any estimation of the spectrum of the coefficient matrix. An upper bound of the condition number of the preconditioned linear system is provided. Moreover, to reduce the computational cost, an inexact variant based on incomplete Cholesky decomposition or orthogonal polynomials is proposed. Numerical results show that the present preconditioner and its inexact variant are efficient and robust solvers for this class of linear systems. A stability analysis of the method completes the description of the preconditioner.Comment: 26 pages, 4 figures, 4 table

CLIO: a Novel Robotic Solution for Exploration and Rescue Missions in Hostile Mountain Environments

Rescue missions in mountain environments are hardly achievable by standard legged robots - because of the high slopes - or by flying robots - because of limited payload capacity. We present a novel concept for a rope-aided climbing robot, which can negotiate up-to-vertical slopes and carry heavy payloads. The robot is attached to the mountain through a rope, and is equipped with a leg to push against the mountain and initiate jumping maneuvers. Between jumps, a hoist is used to wind/unwind the rope to move vertically and affect the lateral motion. This simple (yet effective) two-fold actuation allows the system to achieve high safety and energy efficiency. Indeed, the rope prevents the robot from falling, while compensating for most of its weight, drastically reducing the effort required by the leg actuator. We also present an optimal control strategy to generate point-to-point trajectories overcoming an obstacle. We achieve fast computation time ($<$1 s) thanks to the use of a custom simplified robot model. We validated the generated optimal movements in Gazebo simulations with a complete robot model, showing the effectiveness of the proposed approach, and confirming the interest of our concept. Finally, we performed a reachability analysis showing that the region of achievable targets is strongly affected by the friction properties of the foot-wall contact.Comment: 6 page

Numerical Methods for Optimal Control Problems with Application to Autonomous Vehicles

In the present PhD thesis an optimal problem suite is proposed as benchmark for the test of numerical solvers. The problems are divided in four categories, classic, singular, constrained and hard problems. Apart from the hard problems, where it is not possible to give the analytical solution but only some details, all other problems are supplied with the derivation of the solution. The exact solution allows a precise comparison of the performance of the considered software. All of the proposed problems were taken from published papers or books, but it turned out that an analytic exact solution was only rarely provided, thus a true and reliable comparison among numerical solvers could not be done before. A typical wrong conclusion when a solver obtains a lower value of the target functional with respect to other solvers is to claim it better than the others, but it is not recognized that it has only underestimated the true value. In this thesis, a cutting edge application of optimal control to vehicles is showed: the optimization of the lap time in a race circuit track considering a number of realistic constraints. A new algorithm for path planning is completely described for the construction of a quasi G2 fitting of the GPS data with a clothoid spline in terms of the G1 Hermite interpolation problem. In particular the present algorithm is proved to work better than state of the art algorithms in terms of both efficiency and precision

Accuracy of magnetic resonance cholangiography compared to operative endoscopy in detecting biliary stones, a single center experience and review of literature

none6noAbstract AIM: To compare diagnostic sensitivity, specificity and accuracy of magnetic resonance cholangiopancreatography (MRCP) without contrast medium and endoscopic ultrasound (EUS)/endoscopic retrograde cholangiopancreatography (ERCP) for biliary calculi. METHODS: From January 2012 to December 2013, two-hundred-sixty-three patients underwent MRCP at our institution, all MRCP procedure were performed with the same machinery. In two-hundred MRCP was done for pure hepatobiliary symptoms and these patients are the subjects of this study. Among these two-hundred patients, one-hundred-eleven (55.5%) underwent ERCP after MRCP. The retrospective study design consisted in the systematic revision of all images from MRCP and EUS/ERCP performed by two radiologist with a long experience in biliary imaging, an experienced endoscopist and a senior consultant in Hepatobiliopancreatic surgery. A false positive was defined an MRCP showing calculi with no findings at EUS/ERCP; a true positive was defined as a concordance between MRCP and EUS/ERCP findings; a false negative was defined as the absence of images suggesting calculi at MRCP with calculi localization/extraction at EUS/ERCP and a true negative was defined as a patient with no calculi at MRCP ad at least 6 mo of asymptomatic follow-up. Biliary tree dilatation was defined as a common bile duct diameter larger than 6 mm in a patient who had an in situ gallbladder. A third blinded radiologist who examined the MRCP and ERCP data reviewed misdiagnosed cases. Once obtained overall data on sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) we divided patients in two groups composed of those having concordant MRCP and EUS/ERCP (Group A, 72 patients) and those having discordant MRCP and EUS/ERCP (Group B, 20 patients). Dataset comparisons had been made by the Student's t-test and χ (2) when appropriate. RESULTS: Two-hundred patients (91 men, 109 women, mean age 67.6 years, and range 25-98 years) underwent MRCP. All patients attended regular follow-up for at least 6 mo. Morbidity and mortality related to MRCP were null. MRCP was the only exam performed in 89 patients because it did show only calculi into the gallbladder with no signs of the presence of calculi into the bile duct and symptoms resolved within a few days or after colecistectomy. The patients remained asymptomatic for at least 6 mo, and we assumed they were true negatives. One hundred eleven (53 men, 58 women, mean age 69 years, range 25-98 years) underwent ERCP following MRCP. We did not find any difference between the two groups in terms of race, age, and sex. The overall median interval between MRCP and ERCP was 9 d. In detecting biliary stones MRCP Sensitivity was 77.4%, Specificity 100% and Accuracy 80.5% with a PPV of 100% and NPV of 85%; EUS showed 95% sensitivity, 100% specificity, 95.5% accuracy with 100% PPV and 57.1% NPV. The association of EUS with ERCP performed at 100% in all the evaluated parameters. When comparing the two groups, we did not find any statistically significant difference regarding age, sex, and race. Similarly, we did not find any differences regarding the number of extracted stones: 116 stones in Group A (median 2, range 1 to 9) and 27 in Group B (median 2, range 1 to 4). When we compared the size of the extracted stones we found that the patients in Group B had significantly smaller stones: 14.16 ± 8.11 mm in Group A and 5.15 ± 2.09 mm in Group B; 95% confidence interval = 5.89-12.13, standard error = 1.577; P < 0.05. We also found that in Group B there was a significantly higher incidence of stones smaller than 5 mm: 36 in Group A and 18 in Group B, P < 0.05. CONCLUSION: Major finding of the present study is that choledocholithiasis is still under-diagnosed in MRCP. Smaller stones (< 5 mm diameter) are hardly visualized on MRCP.nonePolistina, Fa; Frego, M; Bisello, M; Manzi, E; Vardanega, A; Perin, B.Polistina, Fa; Frego, M; Bisello, M; Manzi, E; Vardanega, A; Perin, B

Magnetic Resonance Enterography for Crohn's Disease: What the Surgeon Can Take Home

Background Crohn's disease (CD) is a life long, chronic, relapsing condition that involves the entire digestive tract requiring often morphological assessment. MR enterography (MRE) offers advantages of not using ionizing radiation and yielding intra luminal and intra abdom- inal informations. The aim of our study was to identify how MRE can be useful in planning surgical procedures. Patients and methods In this retrospective study 35 patients who underwent MRE and then surgery for CD were enrolled from 2006 to 2010. MRE findings were compared to intraoperative findings. Histology of operative specimens, systemic inflam- matory parameters (white blood cells count, platelets count, CRP, ESR, albumin, iron) and faecal lactoferrin were also evaluated. Cohen's kappa agreement test, sensitivity and sensibil- ity, uni/multivariate logistic regression and non parametric statistics were performed. Results MRE identified bowel stenosis with a sensitivity of 0.95 (95% CI 0.76-0.99), a specificity of 0.72 (95% CI 0.39-0.92). The concordance of MRE findings with intraoperative findings was high (Cohen's k= 0.72 (0.16). Abscesses were detected at MRE with a sensitivity of 0.92 (95% CI 0.62-0.99), a specificity of 0.90 (95% CI 0.69-0.98) with a Cohen's k= 0.82 (0.16). MRE identified bowel fistulas with a sensitivity of 0.71 (95% CI 0.42-0.90), a specificity of 0.76 (95% CI 0.52-0.90) and with Cohen's k= 0.47 (0.17). The grade of proximal bowel dilatation resulted to be a significant predictor of the possibility of using stricturoplasty instead of/associated to bowel resection either at univariate or at multivariate analysis. Conclusion Our study confirmed that MRE findings correlate significantly with disease activity. Once decided that the patient should undergo surgical treatment MRE can provide the surgeon useful and adequate information about abscess, stenosis and fistulae. Detailed information about abscess could suggest percutaneous drainage that could ease the following surgery or avoid emergency laparotomy. Proximal bowel dilatation can suggest the possibility to perform bowel sparing surgery such as stricturoplasty

Dataset related to article "Xpert Bladder Cancer Monitor May Avoid Cystoscopies in Patients Under "Active Surveillance" for Recurrent Bladder Cancer (BIAS Project): Longitudinal Cohort Study "

This record contains raw data related to article “Xpert Bladder Cancer Monitor May Avoid Cystoscopies in Patients Under "Active Surveillance" for Recurrent Bladder Cancer (BIAS Project): Longitudinal Cohort Study" Abstract Objectives: To test the hypothesis that patients under active surveillance (AS) for Non-muscle Invasive Bladder Cancer (NMIBC) who were negative on longitudinal re-testing by the Xpert® Bladder Cancer Monitor (Xpert BC Monitor) assay may avoid unnecessary cystoscopies and urine cytology (UC). Subjects/patients or materials and methods: This is a prospective cohort study of patients enrolled in the AS protocol for recurrent NMIBC (Bladder Cancer Italian Active Surveillance, BIAS project), whose urine samples were analyzed by Xpert BC Monitor upon entry in the study (T0). Patients who had a negative Xpert test and did not fail AS, underwent additional Xpert tests after 4 (T1), 8 (T2), and 12 (T3) months. The clinical utility of Xpert was assessed by determining the number of cystoscopies and UC that could be avoided within 1 year. Results: Overall, 139 patients were tested with Xpert at T0. Median follow-up was 23 (IQR 17-27) months. Sixty-eight (48.9%) patients failed AS, 65 (46.7%) are currently on AS, and 6 (4.3%) were lost at follow-up. At T0 57 (41.0%) patients had a negative test and 36 (63.2%) are still in AS. In patients with 2 consecutives negative Xpert tests, we could have avoided 73.9% of unnecessary cystoscopies, missing 26.4% failure, up to avoid all cystoscopies with 4 negative tests missing only 12% of failure. All the patients with negative Xpert had negative UC. Failure-free-survival at median follow-up (23 month) stratified for having 0, 1, or ≥2 negative tests was 67.0, 55.1. and 84.1, respectively. Conclusion: Our findings suggest that Xpert BC Monitor assay, when it is longitudinally repeated, could significantly reduce the number of unnecessary cystoscopies and UC during their follow-up