Osmotic pressure estimation using the Pitzer equation for forward osmosis modelling.

Forward osmosis (FO) has received widespread recognition in the past decade due to its potential low energy production of water. This study presents a new model analysis for predicting the water flux in FO systems when inorganic-based draw solutions are used under variable experimental conditions for using a laboratory scale cross-flow single cell unit. The new model accounts for the adverse impact of concentration polarization (both ICP and ECP) incorporating the water activity by Pitzer to calculate the bulk osmotic pressures. Using the water activity provides a better correlation of experimental data than the classical van't Hoff equation. The nonlinear model also gave a better estimate for the structural parameter factor (S) of the membrane in its solution. Furthermore, the temperature and concentration of both the draw and feed solutions played a significant role in increasing the water flux, which could be interpreted in terms of the mass transfer coefficient representing ECP; a factor sensitive to the hydraulics of the system. The model provides greatly improved correlations for the experimental water fluxes.

Optimized Long-Range Corrected Density Functionals for Electronic and Optical Properties of Bare and Ligated CdSe Quantum Dots.

The reliable prediction of optical and fundamental gaps of finite size systems using density functional theory requires to account for the potential self-interaction error, which is notorious for degrading the description of charge transfer transitions. One solution is provided by parametrized long-range corrected functionals such as LC-BLYP, which can be tuned such as to describe certain properties of the particular system at hand. Here, bare and 3-mercaptoprotionic acid covered Cd33Se33 quantum dots are investigated using the optimally tuned LC-BLYP functional. The range separation parameter, which determines the switching on of the exact exchange contribution, is found to be 0.12 bohr-1 and 0.09 bohr-1 for the bare and covered quantum dot, respectively. It is shown that density functional optimization indeed yields optical and fundamental gaps and thus exciton binding energies, considerably different compared with standard functionals such as the popular PBE and B3LYP ones. This holds true, despite the well established fact that the leading transitions are localized on the quantum dot and do not show pronounced long-range charge transfer character.

CO2 sorption kinetics of scaled-up polyethylenimine-functionalized mesoporous silica sorbent.

Two CO2 solid sorbents based on polyethylenimine, PEI (M(n) ∼ 423 and 10K), impregnated into mesoporous silica (MPS) foam prepared in kilogram quantities via a scale-up process were synthesized and systematically characterized by a range of analytical and surface techniques. The mesoporous silica sorbent impregnated with lower molecular weight PEI, PEI-423/MPS, showed higher capacity toward CO2 sorption than the sorbent functionalized with the higher molecular weight PEI (PEI-10K/MPS). On the other hand, PEI-10K/MPS exhibited higher thermal stability than PEI-423/MPS. The kinetics of CO2 adsorption on both PEI/MPS fitted well with a double-exponential model. According to this model CO2 adsorption can be divided into two steps: the first is fast and is attributed to CO2 adsorption on the sorbent surface; the second is slower and can be related to the diffusion of CO2 within and between the mesoporous particles. In contrast, the desorption process obeyed first-order kinetics with activation energies of 64.3 and 140.7 kJ mol(-1) for PEI-423/MPS and PEI-10K/MPS, respectively. These studies suggest that the selection of amine is critical as it affects not only sorbent capacity and stability but also the energy penalty associated with sorbent regeneration.

Rhabdomyolysis associated with varicella infection.

Varicella infection is a common childhood disease that usually resolves without complications. However, children under 2 months of age, adolescents, some adults and immunocompromised individuals are at high risk of certain rare life-threatening complications. We report a case of primary varicella infection in an immunocompetent adult complicated by rhabdomyolysis. Recognition of this complication and aggressive fluid therapy with an antiviral agent helped to improve the outcome.

Childhood tuberculosis in the State of Qatar: the effect of a limited expatriate screening programme on the incidence of tuberculosis.

OBJECTIVE: To determine incidence rates and the effectiveness of the expatriate screening programme on paediatric tuberculosis (TB) in the State of Qatar. METHOD: A state-wide, population-based, retrospective analysis of all cases of tuberculosis among children 0-14 years of age reported to the TB Unit of the Division of Public Health during 1983-1996. RESULTS: One hundred and forty-four children with tuberculous disease were identified, with a steadily declining incidence rate (rate of notification) from 11/100000 children (0-14 years) population in 1983 to 7/100000 in 1996. This decrease in the childhood TB case notification rate correlated with foreign-born children, older children and the implementation of expatriate screening in 1986. Diagnosis in 56% of children was made abroad or within 3 months of arrival from vacation and 30% within one year of arrival. Comparison of the three age groups (<5, 5-9 and 10-14 years) showed no significant difference with regard to nationality, sex, type of TB, radiological findings and screening. However older children were more likely to be symptomatic (P < 0.0001) and to have positive tuberculin skin test (TST) reactivity (P = 0.012), culture (P < 0.0001), and gastric aspirates (P = 0.018). CONCLUSION: Although there was a 36% decrease in paediatric TB incidence after the implementation of expatriate screening in 1986, Qatar has a high rate of paediatric tuberculosis. The policy of BCG vaccination at birth should be continued, and screening children at school entry and on return from vacation would be useful for further case identification.

Pattern of mycobacterial resistance to four anti-tuberculosis drugs in pulmonary tuberculosis patients in the state of Qatar after the implementation of DOTS and a limited expatriate screening programme.

OBJECTIVE: To determine the resistance pattern of Mycobacterium tuberculosis to four anti-tuberculosis drugs in pulmonary tuberculosis patients in the State of Qatar after the implementation of DOTS and an expatriate screening programme on arrival. METHOD: A state-wide, population-based, retrospective analysis of all cases of pulmonary tuberculosis with positive M. tuberculosis culture reported to the Division of Public Health TB Unit from January 1996 to December 1998. M. tuberculosis sensitivity testing was done by the Bactec method for isoniazid (INH), rifampicin (RMP), streptomycin (SM) and ethambutol (EMB). The results were interpreted as a daily change of the growth index of test vials (with drug) compared with controls. RESULTS: There were 406 isolates with positive M. tuberculosis culture. Sixty-one (15%) were resistant to one or more of the four anti-tuberculosis drugs, of which 58 (95%) were from newly diagnosed cases (primary) and three (5%) were from previously treated cases (acquired). Primary resistance was as follows: any resistance 15%, INH 12.4%, RMP 2%, SM 5.2%, EMB 0.8% and multidrug resistance (MDR, resistance to INH and RMP at least) was found in 0.8%. Acquired resistance was as follows: any resistance 15%, INH 15%, RMP 5%, SM 5% and MDR 5%. CONCLUSION: The prevalence of resistance to four anti-tuberculosis drugs is strikingly low due to the limited expatriate screening programme (chest radiography) and implementation of DOTS. The four-drug regimen is recommended for the initial phase of therapy until the results of sensitivity testing are known.

Primary tuberculosis of the breast in Qatar: ten year experience and review of the literature.

OBJECTIVE: To present our experience of isolated tuberculosis of the breast, 1988-98. DESIGN: Retrospective study of case notes and radiographs. SETTING: Hamad General Hospital, Qatar. SUBJECTS: 13 multiparous women with tuberculosis of the breast. MAIN OUTCOME MEASURES: Objective confirmation of diagnosis and adequacy of treatment. RESULTS: We found an overall incidence of histologically confirmed tuberculosis to be 0.4%/year. All patients presented with a lump, 2 had nipple discharge and one had a palpable axillary node on the same side. 7 were treated by excision biopsy, 3 by incision and drainage, and 3 had fine needle aspiration (FNA) as their only procedure. All diagnoses were confirmed histologically. 2 patients developed recurrences during treatment but these were successfully treated. CONCLUSION: Although the incidence of the disease is low, the diagnosis should be suspected in young multiparous women with a breast lump in whom malignancy has been excluded. The minimum of surgical intervention (incision or excision biopsy) together with antituberculous drugs seems to be the most successful treatment.

Erythrocyte sedimentation rate in childhood tuberculosis: is it still worthwhile?

OBJECTIVE: To evaluate the utility of the erythrocyte sedimentation rate (ESR) in the diagnosis of childhood tuberculosis. DESIGN: Data were collected retrospectively from the Qatar National Tuberculosis (TB) Registry for children (birth to 14 years of age) from 1983 to 1996. The diagnosis of active tuberculosis was based on positive sputum cultures (or histology) or an abnormal chest radiograph that responded to anti-tuberculosis chemotherapy. RESULTS: Of 144 childhood TB patients, 68 (47%) had an ESR documented at the time of diagnosis. Twenty-two children (33%) had a normal ESR (<10 mm/hour) and 46 children (67%) had an elevated ESR (> or =10 mm/hour) at the time of diagnosis. Culture positive and symptomatic children had significantly higher ESR values than culture negative and asymptomatic children, respectively, at the time of diagnosis. There was no significant difference in ESR values for children with extrapulmonary versus pulmonary disease, and likewise no significant correlation between either age or size of tuberculin skin test reactivity and ESR values. CONCLUSION: Although an elevated ESR may be expected in children with tuberculosis, this study found that one-third of children with TB had a normal ESR at the time of diagnosis, and consequently there would seem to be little value in using ESR as a diagnostic test for childhood tuberculosis.