Simulation-based solution of stochastic mathematical programs with complementarity constraints: Sample-path analysis

We consider a class of stochastic mathematical programs with complementarity constraints, in which both the objective and the constraints involve limit functions or expectations that need to be estimated or approximated. Such programs can be used for modeling \\average" or steady-state behavior of complex stochastic systems. Recently, simulation-based methods have been successfully used for solving challenging stochastic optimization problems and equilibrium models. Here we broaden the applicability of so-called the sample-path method to include the solution of certain stochastic mathematical programs with equilibrium constraints. The convergence analysis of sample-path methods rely heavily on stability conditions. We first review necessary sensitivity results, then describe the method, and provide sufficient conditions for its almost-sure convergence. Alongside we provide a complementary sensitivity result for the corresponding deterministic problems. In addition, we also provide a unifying discussion on alternative set of sufficient conditions, derive a complementary result regarding the analysis of stochastic variational inequalities, and prove the equivalence of two different regularity conditions.simulation;mathematical programs with equilibrium constraints;stability;regularity conditions;sample-path methods;stochastic mathematical programs with complementarity constraints

Hemorrhoidectomy in Patients with Grade III or IV Disease: Harmonic Scalpel Compared With Conventional Closed Technique.

AbstractBackground: Harmonic scalpel (Ultracision) is a device that simultaneously cuts and coagulates soft tissues through ultrasonic vibration. In this study we aimed to determine the operative and postoperative characteristics of hemorrhoidectomy using the harmonic scalpel compared with the conventional closed technique.Methods and Findings: Patients with grade III or IV hemorrhoids, operated between 2010 and 2013, using the harmonic scalpel (n=21) or the conventional closed technique (n=42) were included in the study. Exclusion criteria were thrombosed or strangulated hemorrhoids, concomitant perianal disease, history of recurrent perianal surgery and known tendency for bleeding. Patient characteristics, duration of operation, complications, postoperative pain measured on a visual analog scale (VAS), hospital stay, and return to regular activity were compared between the two groups retrospectively.Patient characteristics (female:male ratio, mean age, hemorrhoid grade, and symptom duration) were similar between the two groups. Harmonic scalpel and conventional hemorrhoidectomy patients did not differ significantly in terms of VAS score of pain, complications, hospital stay or return to regular activity. However, duration of operation was significantly shorter with harmonic scalpel (24.2 vs. 36.2 min, p<0.05).Conclusion: There is no clear evidence to support the routine use of harmonic scalpel system in hemorrhoid surgery

Formation and evolution of compact binaries in globular clusters: II. Binaries with neutron stars

In this paper, the second of a series, we study the stellar dynamical and evolutionary processes leading to the formation of compact binaries containing neutron stars (NSs) in dense globular clusters (GCs). For this study, 70 dense clusters were simulated independently, with a total stellar mass ~2x10^7Msun, exceeding the total mass of all dense GCs in our Galaxy. We find that, in order to reproduce the empirically derived formation rate of low-mass X-ray binaries (LMXBs), we must assume that NSs can be formed via electron-capture supernovae (ECS) with typical natal kicks smaller than in core-collapse supernovae. Our results explain the observed dependence of the number of LMXBs on ``collision number'' as well as the large scatter observed between different GCs. We predict that the number of quiescent LMXBs in different GCs should not have a strong metallicity dependence. In our cluster model the following mass-gaining events create populations of MSPs that do not match the observations: (i) accretion during a common envelope event with a NS formed through ECS, and (ii) mass transfer (MT) from a WD donor. Some processes lead only to a mild recycling. In addition, for MSPs, we distinguish low-magnetic-field (long-lived) and high-magnetic-field (short-lived) populations. With this distinction and by considering only those mass-gaining events that appear to lead to NS recycling, we obtain good agreement of our models with the numbers and characteristics of observed MSPs in 47 Tuc and Terzan 5, as well as with the cumulative statistics for MSPs detected in GCs of different dynamical properties. We find that significant production of merging double NSs potentially detectable as short gamma-ray bursts occurs only in very dense, most likely core-collapsed GCs. (abridged)Comment: 25 pages, 7 figures, 12 tables, MNRAS accepte

Optical emission from massive donors in ULX binary systems

We present evolutionary tracks of binary systems with high mass companion stars and stellar-through-intermediate mass BHs. Using Eggleton's stellar evolution code, we compute the luminosity produced by accretion from the donor during its entire evolution. We compute also the evolution of the optical spectrum of the binary system taking the disc contribution and irradiation effects into account. The calculations presented here can be used to constrain the properties of the donor stars in Ultraluminous X-ray Sources by comparing their position on the HR or color-magnitude diagrams with the evolutionary tracks of massive BH binaries. This approach may actually provide interesting clues also on the properties of the binary system itself, including the BH mass. We found that, on the basis of their position on the color-magnitude diagram, some of the candidate counterparts considered can be ruled out and more stringent constraints can be applied to the donor masses.Comment: 11 pages, 7 figures. Submitted to MNRA

Acute hypoxemic respiratory failure in immunocompromised patients: the Efraim multinational prospective cohort study

Background: In immunocompromised patients with acute hypoxemic respiratory failure (ARF), initial management aims primarily to avoid invasive mechanical ventilation (IMV). Methods: To assess the impact of initial management on IMV and mortality rates, we performed a multinational observational prospective cohort study in 16 countries (68 centers). Results: A total of 1611 patients were enrolled (hematological malignancies 51.9%, solid tumors 35.2%, systemic diseases 17.3%, and solid organ transplantation 8.8%). The main ARF etiologies were bacterial (29.5%), viral (15.4%), and fungal infections (14.7%), or undetermined (13.2%). On admission, 915 (56.8%) patients were not intubated. They received standard oxygen (N = 496, 53.9%), high-flow oxygen (HFNC, N = 187, 20.3%), noninvasive ventilation (NIV, N = 153, 17.2%), and NIV + HFNC (N = 79, 8.6%). Factors associated with IMV included age (hazard ratio = 0.92/year, 95% CI 0.86â\u80\u930.99), day-1 SOFA (1.09/point, 1.06â\u80\u931.13), day-1 PaO2/FiO2(1.47, 1.05â\u80\u932.07), ARF etiology (Pneumocystis jirovecii pneumonia (2.11, 1.42â\u80\u933.14), invasive pulmonary aspergillosis (1.85, 1.21â\u80\u932.85), and undetermined cause (1.46, 1.09â\u80\u931.98). After propensity score matching, HFNC, but not NIV, had an effect on IMV rate (HR = 0.77, 95% CI 0.59â\u80\u931.00, p = 0.05). ICU, hospital, and day-90 mortality rates were 32.4, 44.1, and 56.4%, respectively. Factors independently associated with hospital mortality included age (odds ratio = 1.18/year, 1.09â\u80\u931.27), direct admission to the ICU (0.69, 0.54â\u80\u930.87), day-1 SOFA excluding respiratory score (1.12/point, 1.08â\u80\u931.16), PaO2/FiO2 < 100 (1.60, 1.03â\u80\u932.48), and undetermined ARF etiology (1.43, 1.04â\u80\u931.97). Initial oxygenation strategy did not affect mortality; however, IMV was associated with mortality, the odds ratio depending on IMV conditions: NIV + HFNC failure (2.31, 1.09â\u80\u934.91), first-line IMV (2.55, 1.94â\u80\u933.29), NIV failure (3.65, 2.05â\u80\u936.53), standard oxygen failure (4.16, 2.91â\u80\u935.93), and HFNC failure (5.54, 3.27â\u80\u939.38). Conclusion: HFNC has an effect on intubation but not on mortality rates. Failure to identify ARF etiology is associated with higher rates of both intubation and mortality. This suggests that in addition to selecting the appropriate oxygenation device, clinicians should strive to identify the etiology of ARF