Flaw-tolerance of nonlocal discrete systems and interpretation according to network theory

Discrete systems are modeled as a network of nodes (particles, molecules, or atoms) linked by nonlinear springs to simulate the action of van der Waals forces. Such systems are nonlocal if links connecting non-adjacent nodes are introduced. For their topological characterization, a nonlocality index (NLI) inspired by network theory is proposed. The mechanical response of 1D and 2D nonlocal discrete systems is predicted according to finite element (FE) simulations based on a nonlinear spring element for large displacements implemented in the FE programme FEAP. Uniaxial force-displacement responses of intact and defective systems (with links or nodes removed) are numerically simulated. Strain localization phenomena, size-scale effects and the ability to tolerate defects are investigated by varying the degree of nonlocality

A power and energy procedure in operating photovoltaic systems to quantify the losses according to the causes

Recently, after high feed-in tariffs in Italy, retroactive cuts in the energy payments have generated economic concern about several grid-connected photovoltaic (PV) systems with poor performance. In this paper the proposed procedure suggests some rules for determining the sources of losses and thus minimizing poor performance in the energy production. The on-site field inspection, the identification of the irradiance sensors, as close as possible the PV system, and the assessment of energy production are three preliminary steps which do not require experimental tests. The fourth step is to test the arrays of PV modules on-site. The fifth step is to test only the PV strings or single modules belonging to arrays with poor performance (e.g., I-V mismatch). The sixth step is to use the thermo-graphic camera and the electroluminescence at the PV-module level. The seventh step is to monitor the DC racks of each inverter or the individual inverter, if equipped with only one Maximum Power Point Tracker (MPPT). Experimental results on real PV systems show the effectiveness of this procedure

Effectiveness of infection control measures in controlling a nosocomial outbreak of multidrug-resistant tuberculosis among HIV patients in Italy

SETTING: Between October 1992 and February 1994, 33 cases of multidrug-resistant tuberculosis (MDR-TB) were diagnosed among patients infected by the human immunodeficiency virus (HIV) and hospitalised in an HIV ward in Milan, Italy. This outbreak was part of a much larger outbreak, begun in another hospital and probably transferred through a patient. OBJECTIVE: TO evaluate risk factors for transmission and the effectiveness of infection control measures. DESIGN: 1) Active follow-up of exposed patients, 2) cohort study among HIV-infected patients exposed to MDR-TB cases before and after the implementation of control measures, 3) screening of close contacts of MDR-TB cases, and 1) molecular typing by restriction fragment length polymorphism (RFLP) analysis. RESULTS: The risk of MDR-TB was higher in patients with lower CD4+ lymphocyte percentages and longer duration of exposure. No difference in the daily risk was observed for in-patients vs day-hospital patients or by room distance from an infectious case. Of the 90 patients exposed before the implementation of infection control measures (i,e,, October 1992-June 1993) 26 (28.9%) developed MDR-TB, whereas none of the 44 patients exclusively exposed after implementation developed MDR-TB, despite the continuing presence of infectious MDR-TB cases in the ward. CONCLUSION: Simple control measures were effective in significantly reducing nosocomial transmission among patients

Diagnosis and follow-up of treatment of latent tuberculosis; the utility of the QuantiFERON-TB Gold In-tube assay in outpatients from a tuberculosis low-endemic country

<p>Abstract</p> <p>Background</p> <p>Interferon-gamma (IFN-γ) Release Assays (IGRA) are more specific than the tuberculosis skin test (TST) in the diagnosis of latent tuberculosis (TB) infection (LTBI). We present the performance of the QuantiFERON^®-TB Gold In-tube (QFT-TB) assay as diagnostic test and during follow-up of preventive TB therapy in outpatients from a TB low-endemic country.</p> <p>Methods</p> <p>481 persons with suspected TB infection were tested with QFT-TB. Thoracic X-ray and sputum samples were performed and a questionnaire concerning risk factors for TB was filled. Three months of isoniazid and rifampicin were given to patients with LTBI and QFT-TB tests were performed after three and 15 months.</p> <p>Results</p> <p>The QFT-TB test was positive in 30.8% (148/481) of the total, in 66.9% (111/166) of persons with origin from a TB endemic country, in 71.4% (20/28) previously treated for TB and in 100% (15/15) of those diagnosed with active TB with no inconclusive results. The QFT-TB test was more frequently positive in those with TST ≥ 15 mm (47.5%) compared to TST 11-14 mm (21.3%) and TST 6-10 mm (10.5%), (p < 0.001). Origin from a TB endemic country (OR 6.82, 95% CI 1.73-26.82), recent stay in a TB endemic country (OR 1.32, 95% CI 1.09-1.59), duration of TB exposure (OR 1.59, 95% CI 1.14-2.22) and previous TB disease (OR 11.60, 95% CI 2.02-66.73) were all independently associated with a positive QFT-TB test. After preventive therapy, 35/40 (87.5%) and 22/26 (84.6%) were still QFT-TB positive after three and 15 months, respectively. IFN-γ responses were comparable at start (mean 6.13 IU/ml ± SD 3.99) and after three months (mean 5.65 IU/ml ± SD 3.66) and 15 months (mean 5.65 IU/ml ± SD 4.14), (p > 0.05).</p> <p>Conclusion</p> <p>Only one third of those with suspected TB infection had a positive QFT-TB test. Recent immigration from TB endemic countries and long duration of exposure are risk factors for a positive QFT-TB test and these groups should be targeted through screening. Since most patients remained QFT-TB positive after therapy, the test should not be used to monitor the effect of preventive therapy. Prospective studies are needed in order to determine the usefulness of IGRA tests during therapy.</p

Analysis of the stress field in photovoltaic modules due to impact loadings

In the present work the stress field due to hail impacts on semi-flexible photovoltaic (PV) modules is analysed. Experimental tests and finite element simulations have been performed by considering different arrangements for the stack of layers of the panels and different kind of substrates in order to identify the type of support that minimizes the extension of the solar cell region where high tensile stresses take place under impacts. Practical hints for production and installation of the modules are derived from the obtained results