A. Di Benedetto

Venting of gas explosion through relief ducts: Interaction between internal and external explosions

Relief ducts fitted to venting openings is a widespread configuration in the industrial practice. The presence of a duct has been reported to severely increase the violence of the vented explosion posing a problem for the proper design of the venting device. Several studies have reported the leading importance--in the whole complex explosion phenomenology--of a secondary explosion in the duct. Modern approaches in the study of simply vented explosions (without ducts) have focused on the study of the interaction between internal and external explosion as a key issue in the mechanisms of pressure generation. The issue is even more relevant when a duct is fitted to the vent due the confined nature of the external explosion. In this work the interaction between internal and external events is experimentally investigated for gas explosions vented through a relief duct. The work has aimed at studying mechanisms underlying the pressure rise of this venting configuration. The study has put the emphasis on the mutual nature of the interaction. A larger scale than laboratory has been investigated allowing drawing results with a greater degree of generality with respect to data so far presented in literature.

Anemia and Chronic Renal Failure: The Possible Role of the Oxidative State of Glutathione

The authors have investigated the oxidative state of glutathione in red blood cells (RBC) and plasma from patients affected by chronic renal failure (CRF) and from age-matched healthy subjects. RBC-reduced glutathione (GSH) levels were significantly lower in CRF patients than in healthy subjects. Oxidized glutathione (GSSG) levels in plasma from CRF patients were higher than in plasma from controls. GSSG levels in RBC were similar in both groups. No differences were noted in GSH plasma levels between patients and controls. The GSSG/GSH ratios in RBC were similar in the two groups; on the contrary, the GSSG/GSH ratio in plasma was significantly higher in CRF patients. High levels of GSSG in plasma could exert two important effects on RBC: (1) inhibition of glucose-6-phosphate dehydrogenase activity, with a consequent alteration of the glutathione system; (2) GSSG easily reacts with hemoglobin to produce hemoglobin-glutathione mixed disulfides, with a consequent protein aggregation and precipitation. In vitro experiments have shown that RBC from CRF patients easily lyse when incubated with their same plasma, but not when incubated in saline buffer. Our results seem to demonstrate that plasma from CRF patients contains various oxidants which could affect the integrity of the glutathione system in RBC. This alteration could play a role in the pathogenesis of anemia in uremic patients.

Anemia and chronic renal failure: a therapeutical approach by reduced glutathione parenteral administration.

Authors report on the effect of reduced glutathione parenterally administered on the anemic status in patients suffering from chronic renal failure and undergoing hemodialysis. Twenty patients were studied for 180 days and were divided into two age- and sex-matched groups. The first group (10 patients) received placebo, the second group (10 patients) received the treatment (1,200 mg of reduced glutathione). Reduced glutathione and placebo were given for 120 days in a randomized double-blind fashion and the following measurements were performed: red blood cells reduced and oxidized glutathione, plasma reduced and oxidized glutathione, hematocrit, hemoglobin, reticulocytes, serum iron, transferrin, indirect bilirubin, urea, creatinine, calcium, phosphate, parathyroid hormone and alkaline phosphatase. In the treated group, during the supplementation period, there was an increase in the levels of red blood cells and plasma reduced glutathione, hematocrit and hemoglobin and a concomitant decrease in plasma oxidized glutathione and reticulocytes with a maximum effect on the 120th day of therapy. In the placebo-treated group there were no significant variations of the parameters considered during the study period. When the therapy, on patients undergoing treatment, was terminated there was a drop in the analyzed parameters, which fell to pretreatment values at the subsequent controls. These findings seem to indicate that reduced glutathione could represent a useful drug in the treatment and management of anemia in patients affected by chronic renal failure.

Mechanical properties of glass-bead filled polystyrene composites

Abstract The mechanical behaviour of polystyrene composites containing various percentages of glass microspheres has been investigated over a wide range of temperature. The effect of filler concentration on the elastic and ultimate tensile strength of the composites is reported. The viscoelastic properties of these materials have also been studied, in the temperature range of 60°C to 80°C. In the region of linear viscoelastic response, the presence of the filler has no effect on the shift factors used for constructing the master curve, according to the time/temperature superposition principle.

On the determination of the minimum ignition temperature for dust/air mixtures

temperature for dust/air mixtures A. Di Benedetto, V. Di Sarli and P. Russo 1 Istituto di Ricerche sulla Combustione, Consiglio Nazionale delle Ricerche (CNR), Via Diocleziano 328, 80124, Napoli, Italy. E-mail: dibenede@irc. cnr.it; disarli@irc.cnr.it 2 Dipartimento di Ingegneria Chimica e Alimentare, Universita di Salerno, via Ponte don Melillo, 84084 Fisciano (SA), Italy. E-mail: parusso@unisa.it

Spontaneous Oscillations in Lean Premixed Combustors : CFD Simulation

Abstract Lean premixed (LPM) combustors allow reduction of NOx emissions, but they often experience instabilities that are detrimental for engines structural integrity and performances. Most of the works dealing with LPM combustors oscillations address the occurrence of dynamic regimes to system instabilities, i.e., to the coupling between variations of heat release from the flame and acoustic modes of the combustion chamber. However, premixed flames may be prone to intrinsic instabilities: the flame itself oscillates, independently from the coupling with combustor acoustics. In the present article, RANS-based CFD simulations were performed to study the dynamic behavior of an LPM combustor by varying the length of the inlect duct, the inlet gas velocity and fuel equivalence ratio, and the combustor wall temperature. The model results show that the LPM combustor oscillations may be different in nature: they may originate from system instabilities or from the propagation to the whole combustor of the flame intrinsic oscillations due to heat losses (thermo-kinetic oscillations). Furthermore, it is found that whatever the driving mechanism (system or flame instability) a whole acoustic mode is excited and, accordingly, Rayleighs criterion is always verified. Conversely, the widely used re-statement of Rayleighs criterion based on the time-delay approach is verified only for the oscillations originated by system instability, while it fails with the thermo-kinetic oscillations. A way to discern between the different mechanisms exciting the oscillations in an LPM combustor is then suggested.

High prevalence of myocardial ischemia and vasoconstrictive hormonal release in hypertension during chronic renal failure.

OBJECTIVE Indexes of myocardial ischemia and vasoconstrictive hormonal release were evaluated in order to investigate the difference between essential hypertension and hypertension during chronic renal failure. BACKGROUND Arterial hypertension induces several cardiovascular alterations that reflect themselves either on the heart and/or on the coronary blood flow enhancing the cardiovascular risk. Since chronic renal failure can influence the neuroendocrine response, various mechanisms involved in hypertension during chronic renal failure are still unclear. High endothelin 1 (ET-1) levels have been found both in arterial hypertension and during chronic renal failure. Interestingly, either ET-1 or catecholamines seem also to be implied in the pathogenesis of myocardial ischemia. METHODS 20 hypertensive uremic and 20 essentially hypertensive patients underwent echocardiographic wall motion and wall thickening analysis performed at baseline and immediately after the end of exercise. Simultaneously, myocardial perfusion was evaluated by 99mTc-MIBI-SPECT. In addition, plasma norepinephrine and ET-1 concentrations were measured at baseline and at peak exercise. RESULTS The segmental radionuclide analysis showed a greater ischemic degree in hypertensive uremic patients. Yet, we were able to identify one or more regions of the left ventricle in which both systolic thickening measurements and wall motion after exercise were impaired. After exercise, wall thickening impairment was correlated with both wall motion abnormalities (r = 0.72, p < 0.01) and MIBI ischemic grade (r = 0.82, p < 0.001). Basal and after-exercise plasmatic norepinephrine and endothelin levels were higher in hypertensive uremic than in essentially hypertensive patients. Moreover, there was a significant correlation between increments in norepinephrine concentration and MIBI perfusion defects, and between the increment in ET-1 concentration and both MIBI perfusion defects, or kinetic alterations assessed by wall motion as well as by wall thickening. CONCLUSIONS This is the first cross-sectional study in which a higher degree of myocardial ischemia has been observed in hypertensive uremic patients combined with an enhanced plasma release of both norepinephrine and ET-1. This phenomenon may contribute to enhance the cardiovascular risk of these patients.

Relations between vasoactive hormones and diastolic function in hypertensive uraemic patients

Background. Arterial hypertension is a significant risk factor for the high rate of cardiovascular disease in chronic uraemic (CU) patients. Any role that hypertension may play in CU patient outcomes assumes added significance. The elevation of some hormonal factors in early clinical stage could represent a valuable marker of cardiac disease in CU.

Influence of system parameters on the dynamic behaviour of an LPM combustor: Bifurcation analysis through CFD simulations

Lean premixed (LPM) combustion allows lowering flame temperatures, thus reducing thermal NOx production. Unfortunately, at low equivalence ratios a loss of combustor stability may arise, leading to spontaneous oscillations of pressure and temperature. These oscillations must be controlled and limited, as they reduce engine performance and endanger structural integrity. In this paper, unsteady-RANS simulations are performed of a lab-scale LPM combustor in order to address the effects of geometric (length of the inlet duct) and operating (inlet gas velocity, temperature and fuel equivalence ratio) parameters on the occurrence of oscillating behaviours and on their properties (amplitude and frequency). The results obtained are analysed in the framework of the bifurcation theory. Self-excited oscillations are found originating from two different instability mechanisms identified by applying a time lag re-formulation of Rayleighs criterion: feed mixture instability and thermo-kinetic instability owing to heat losses. It is observed that these mechanisms exhibit opposite trends of amplitude and frequency as functions of the parameters investigated. In addition, it is found that, at different initial conditions (and constant parameters), different regimes (steady and dynamic) establish, thus suggesting the presence of state multiplicity.

Anti-HCV Antibody Presence in Hemodialyzed Patients: Assessment after One Year Regarding Some Preventive Measures Chosen

The authors report on the presence of anti-HCV antibodies in a uremic chronic (UC) patient population after 6 months and 1 year with regard to certain selective preventive measures. The nonincreased number of HCV-positive subjects among the UC population could lead to the conclusion that the risk of environmental spreading of HCV is less than the risk of HBV diffusion.