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This paper investigates an infinite buffer fluid queueing model driven by a state-dependent birth-death process prone to catastrophes. We use the Laplace-Stieltjes transform and continued fraction approaches to establish precise expression for the joint probability of the content of the buffer and the number of customers in an M/M/1 queueing model. The importance of the proposed system is that, in numerous practical situation, the service facility has defence mechanisms in place to deal with long waits. Under the strain of a significant backlog of work, the servers may improve their service rate. Therefore, considering the state-dependent character of queueing systems is of relevance. For example, congestion control technologies prevent long queues forming in computer and communication systems by adjusting packet transmission speeds based on the length of the queue (of packets) at the source or destination. Theoretical results are supported by numerical illustrations. [ABSTRACT FROM AUTHOR]

To develop Orthodontic Patient Information Leaflets (PILs) in Arabic. This study included five phases starting with Arabic translation of existing British Orthodontic Society leaflets; initial face validation with three orthodontists; content validation with ten orthodontists; final face validation with ten orthodontists, five postgraduate students, and ten patients; and re-translation to English prior to comparing the new documents with the original PILs to verify that all the necessary information were included. The content validity index (CVI) assessed item level (I-CVI) and scale level (S-CVI). The three Arabic PILs were face validated with inclusion of mini-screws, rapid maxillary expansion, and interproximal reduction. Content validity was perfect with no item I-CVI < 0.80. The S-CVI/Ave for PIL Fixed Appliances = 0.98, PIL Removable Appliances = 0.98 and PIL Functional Appliances = 0.97. In the final face validation, the three leaflets received 100% agreement from all observers for consistency of leaflet format and style, clarity, readability and use of adequate phrases. Finally, the leaflets were re-translated and the information was checked by native English speakers to ensure the completeness of information. There were no discrepancies and face validity was excellent. Valid PILs for Arabic-speaking patients undergoing orthodontic treatment with fixed, removable, and functional appliances have been developed. [ABSTRACT FROM AUTHOR]

This study shows the results of the experimental investigation of refinery wastewater treatment by the electro-Fenton process. The experiments were designed using Taguchi design approach with an orthogonal array (OA) of L16 runs. Four process variables (current density (CD), temperature (T), Fe2+ concentration (Fe2+), and time (t)) at four different levels were considered for the present design. Regression analysis was performed to predict a correlation for the response function (chemical oxygen demand (COD) reduction efficiency) of the treatment process by the electro-Fenton technique. Analysis of variance (ANOVA) was carried out to verify the significant variables that control COD reduction. Moreover, a linear model analysis was implemented for the signal to noise (S/N) ratios with "larger the better" and for means. Based on S/N ratios and means responses, the operating conditions for optimum COD reduction were: CD = 8 mA/cm², T = 60°C, Fe2+ = 0.4 mM, and t = 6 h, at which 87.35% of COD was reduced. ANOVA shows that the operating temperature had the most significant impact on COD reduction efficiency. The R-square value for the predicted COD reduction correlation was 90.00%. Considering ranks based on delta statistics, the relative magnitude of effects of the process variables were: T, Fe2+, t, and CD. [ABSTRACT FROM AUTHOR]

This study aimed to assess selection criteria for patients treated with fixed orthodontic appliance at the College of Dentistry, University of Baghdad, and to set a protocol of treatment in accordance with the Index of Orthodontic Treatment Need (IOTN). Medical records of 120 patients aged 10-30 years old, were retrieved, examined and scored according to IOTN. Results showed that 69% of patients fall within the definite treatment group (i.e. scores 4 and 5), none was in the no need group, 21% in the moderate need group and only about 10% of the sample was in the little need group. Females had the greater prevalence for each score, and the difference was much greater at scores 2 and 3. The criteria for patient selection according to the IOTN-DHC were applicable to Iraqi sample in this study, therefore, it is recommended to use this index to identify patients in need for treatment with some suggested modifications. [ABSTRACT FROM AUTHOR]

Nanofibers and nanotubes of TiO2 were decorated with CdO@CdS type core@shell particles, via a facile route consisting of cadmium electrodeposition on previously formed TiO2 nanostructures, its thermal oxidation to obtain CdO and later surface sulfidation by ion-exchange in Na2S aqueous solution. The diffraction patterns (XRD) of the resulting hetero-nanostructures confirm the formation of the cubic CdO and CdS phases, whereas their Photoelectron spectra (XPS) indicate the sole presence of CdS on the surface. Interestingly, tested as photoanodes in a home-made photoelectrochemical (PEC) cell, they exhibit better performances, toward water oxidation and hydrogen generation than pristine TiO2 nanostructures. These improvements are attributed to a higher visible light absorbance and a convenient band alignment between TiO2-CdO and CdO-CdS. Moreover, although TiO2 nanofibers present a higher surface area to be coupled with CdO@CdS, TiO2 nanotubes coupled with CdO@CdS achieved the maximum photoresponse at -0.25 V vs SCE, under 1 sun illumination. It indicates that this nanostructure, because of its ability for directional electron transport, is the most suitable matrix to build efficient TiO2-CdO@CdS photoanodes for PEC use. [ABSTRACT FROM AUTHOR]

A detailed experimental study was devoted to the anodic oxidation of oxalic acid using manganese dioxide rotating cylinder anode with the objective to evaluate in a systematic way the effect on the oxalic acid oxidation process of several relevant parameters, including the presence of sodium chloride, the current density (J), the rotation speed, the temperature, and the initial concentration of oxalic acid. Thin manganese dioxide film on graphite substrate has been prepared by electrochemical oxidation from MnSO4-H2SO4 electrolyte. The morphology of this electrode was investigated by XRD, SEM, EDS and AFM techniques. The results show that a firm γ-structure of MnO2 film on graphite rod can be obtained successfully. The results indicate that the presence of NaCl has a vital role on the performance of the oxalic acid incineration process. Also current density has the major effect on the removal and current efficiencies. Positive effect of temperature on the removal and current efficiencies and negative effect of rotation speed were observed. The best adopted operative conditions were T = 50°C, J = 40 mA/cm² and 200 rpm in the presence of 1g/l NaCl where a conversion of about 97% and a current efficiency close to 55% with energy consumption less than 28 kWh(kg of COD)-1 were obtained after four hours of electrolysis time. The findings of the present research validate that incineration of oxalic acid can be carried out successfully on MnO2 anode. [ABSTRACT FROM AUTHOR]

Background: Postoperative atrial fibrillation (AF) frequently complicates coronary artery bypass grafting (CABG) operations. As the frequency of obesity has increased in the United States, the number of obese patients undergoing CABG has kept pace. This study sought to define the association between body mass index (BMI) and postoperative AF. Methods: We studied 12,367 consecutive patients with no history of AF who underwent isolated CABG operations. BMI was stratified according to Centers for Disease Control and Prevention criteria, and differences in baseline clinical and operative characteristics were adjusted through multivariate logistic regression models. Results: The unadjusted incidence of new-onset postoperative AF demonstrated a U-shape with regard to BMI. The highest incidence (34%) was found in the “lean” stratum (BMI < 18.5 kg/m2), followed by 32% in the “severely obese” (BMI ≥ 40 kg/m2) stratum. Lower incidences were found in the “normal” stratum (30%), in the “obese” stratum (28%), and the lowest incidence (26%) was in the overweight stratum. Observed incidence was 50% greater than the expected incidence in the “severely obese” stratum (32% vs 21%). In multivariate regression analysis adjusted for age and other covariates, BMI remains a strong risk factor for new-onset postoperative AF. Compared with normal BMI, obesity (odds ratio, 1.24; 95% confidence interval, 1.08 to 1.42) and severe obesity (odds ratio, 2.00; 95% confidence interval, 1.54 to 2.57) both emerged as strong risk factors for postoperative AF. No association was found between a lean BMI and postoperative AF (odds ratio, 1.14; 95% confidence interval, 0.66 to 1.98). Conclusions: After adjusting for potential confounders, obesity, as reflected by the body mass index, remains an independent predictor of postoperative AF. [Copyright &y& Elsevier]

Background: We investigated the impact of extreme obesity (body mass index [kg/m 2 ] 50 or greater) on short-term clinical outcomes and report 1-year mortality. Methods: Fifty-seven patients were found to have a body mass index of 50 or greater among 14,449 patients who underwent cardiac surgery between July 2000 and June 2007. Multivariable logistic regression analyses were used to assess the independent influence of extreme obesity on the major outcomes. Results: Of the 57 patients, the mean age was 58 ± 11 years, mean body mass index was 55.1, and 63% of the patients were women. Forty patients underwent elective surgery. Forty-one patients had isolated coronary artery bypass graft surgery. The overall operative mortality was 9%; the mortality was 5% in isolated coronary artery bypass graft surgery and 5% in elective surgery. Fifteen patients had nonelective isolated coronary artery bypass graft surgery, and 2 patients had emergent active endocarditis surgery. Off-pump coronary artery bypass graft surgery was performed on 23 patients (23 of 41, 54%). After adjusting for known preoperative and operative risk factors through a multivariate logistic model, extreme obesity did not emerge as a significant risk factor for operative mortality (odds ratio, 1.75; p = 0.47) and other adverse outcomes ( p > 0.05) after elective surgery; however, extreme obesity was marginally associated with increased mortality (odds ratio, 2.69; p = 0.05) and was a risk predictor for longer intensive care unit stays (odds ratio, 2.43; p = 0.01) in overall surgery. The 1-year survival rate was 82.5%. Conclusions: Extreme obesity is not a contraindication to elective cardiac surgery. Studies stratifying the risk factors of mortality for nonelective surgery in extremely obese patients may be warranted. [Copyright &y& Elsevier]

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Background: The premise of coronary revascularization without cardiopulmonary bypass (off-pump coronary artery bypass graft [CABG]) proposes that patient morbidity and, potentially, mortality can be reduced without compromising the excellent results of conventional revascularization techniques (on-pump CABG). High-risk patients may benefit the most from off-pump CABG. The aim of this study was to compare early and mid-term clinical outcomes after off-pump CABG with on-pump CABG in a subset of high-risk patients. Methods: Between January 1, 2000 and December 31, 2000, 513 high-risk patients with a Parsonnet''s risk scores of 20 or higher underwent CABG; 38.6% (n = 198) underwent on-pump CABG, and 61.4% (n = 315) had off-pump CABG. Logistic regression was used to calculate the probability of being selected for on-pump CABG given a set of preoperative risk factors. Propensity scores or the probability of being selected for on-pump CABG were computed. Relative risks, heterogeneity among strata, and interactions between surgery type and the propensity score were assessed by a multivariate Cox proportional-hazards regression for the outcomes mortality and major adverse cardiac events (death, acute myocardial infarction, stroke, reoperative CABG, percutaneous coronary intervention). Results: Operative mortality was lower after off-pump versus on-pump CABG between the two groups after controlling for preoperative risk factors using the propensity score (odds ratio = 2.10; 95% confidence intervals = 1.02 to 4.36, p = 0.04). In the Cox-regression analysis, off-pump CABG was associated with an improved survival rate compared with on-pump CABG (p = 0.03). Off-pump CABG was associated with a comparable event-free survival (p = 0.14) compared with on-pump CABG. Conclusions: Off-pump CABG can be performed with a reasonably low morbidity and lower early and late mortality in high-risk patients. Off-pump CABG may be a better operative strategy in this subset of patients. [Copyright &y& Elsevier]

Background: Cerebral embolization of atherosclerotic plaque debris caused by aortic manipulation during conventional coronary artery bypass grafting (CABG) is a major mechanism of postoperative cerebrovascular accidents (CVA). Off-pump CABG (OPCABG) reduces stroke rates by minimizing aortic manipulation. Consequently, the effect of different levels of aortic manipulation on neurologic outcomes after CABG surgery was examined.Methods: From January 1998 to June 2002, 7,272 patients underwent isolated CABG surgery through three levels of aortic manipulation: full plus tangential (side-biting) aortic clamp application (on-pump surgery; n = 4,269), only tangential aortic clamp application (OPCABG surgery; n = 2,527) or an “aortic no-touch” technique (OPCABG surgery; n = 476). A risk-adjusted logistic regression analysis was performed to establish the likelihood of postoperative stroke with each technique. Preoperative risk factors for stroke from the literature, and those found significant in a univariable model were used.Results: A significant association for postoperative stroke correspondingly increasing with the extent of aortic manipulation was demonstrated by the univariable analysis (CVA incidence respectively increasing from 0.8% to 1.6% to a maximum of 2.2%, p < 0.01). In the logistic regression model, patients who had a full and a tangential aortic clamp applied were 1.8 times more likely to have a stroke versus those without any aortic manipulation (95% confidence interval: 1.15 to 2.74, p < 0.01) and 1.7 times more likely to develop a postoperative stroke than those with only a tangential aortic clamp applied (95% confidence interval: 1.11 to 2.48, p < 0.01).Conclusions: Aortic manipulation during CABG is a contributing mechanism for postoperative stroke. The incidence of postoperative stroke increases with increased levels of aortic manipulation. [Copyright &y& Elsevier]

Background. Postoperative stroke is a serious complication after coronary artery bypass grafting with cardiopulmonary bypass (on-pump), and portends higher morbidity and mortality. It is unknown whether an off-pump cardiopulmonary bypass (OPCAB) approach may yield a lower stroke rate over conventional on-pump coronary artery bypass grafting.Methods. From June 1994 to December 2000, OPCAB was performed in 2,320 patients and compared with 8,069 patients who had on-pump coronary artery bypass grafting, during the same period of time. The patients undergoing OPCAB were randomly matched to on-pump patients by propensity score. A logistic regression model was used to test the difference in the postoperative stroke rate between OPCAB and on-pump procedures controlling for the correlation between matched sets. A multiple logistic regression model predicting the risk of stroke adjusted by stroke risk factors and operation type was also computed.Results. Matches by propensity score were found for 72% of the patients undergoing OPCAB. Patients undergoing on-pump coronary artery bypass grafting were 1.8 (95% confidence interval 1.0 to 3.1, p = 0.03) times more likely to suffer a stroke postoperatively than OPCAB patients after controlling for preoperative risk factors through matching. Independent predictors of stroke identified from the multiple logistic model included on-pump operation (versus OPCAB operation), female gender, 4 to 6 vessels grafted (versus <4 grafts), hypertension, history of previous cerebrovascular accident, carotid artery disease, chronic obstructive pulmonary disease, and depressed ejection fraction.Conclusions. Off-pump cardiopulmonary bypass avoids the risks of cardiopulmonary bypass and atrial trauma. A substantially lower stroke rate suggests that OPCAB is a neurologically safe treatment option for revascularization. [Copyright &y& Elsevier]