Influence of the gas—liquid separator design on hydrodynamic and mass transfer performance of split-channel airlift reactors

Three geometric configurations of gas–liquid separators were used in split-channel airlift reactors (0·1 m³ liquid volume; riser-to-downcomer cross-sectional area ratio = 0·7; aspect ratio = 3.6) to test the effect of geometry on hydrodynamic performance and oxygen transfer behaviour. For otherwise fixed conditions, the design of gas–liquid separators affected the induced liquid circulation rate, the depth of penetration of the bubble layer in the downcomer, the gas holdup in the downcomer, the mixing time and the overall volumetric gas–liquid oxygen transfer coefficient. The gas holdup in the riser was only marginally affected by the design of the separator. The impact of the various separator designs on hydrodynamic behaviour could be explained as emanating from a combination of the gas–liquid separating ability of the design and its hydraulic resistance.     

Nasopharyngeal carcinoma: clinical trends

Nasopharyngeal carcinoma (NPC) is one of the most difficult diseases to diagnose at an early stage. The clinical presentation of 122 patients with confirmed NPC is described and the findings analysed. The common modes of presentation and cases where detailed nasopharyngeal examination need to be performed are highlighted. We emphasize the importance of health education and training for primary care physicians for early detection of these cases.     

Corneal transplant for keratoconus: results in early and late disease

PURPOSE: To evaluate the results and complications rates associated with corneal transplantation for keratoconus and assess the prospects of using penetrating keratoplasty at a much earlier stage. SETTING: Buzard Eye Institute, Las Vegas, Nevada, USA. METHODS: In this prospective clinical study, 104 eyes of 76 patients had corneal transplantation for keratoconus identified by corneal topography, keratometry, pachymetry, and/or retinoscopy. Sutures were removed at a mean of 15 months; mean follow-up was 42 months. All surgeries were performed by one surgeon using a torque-antitorque suture method. Eyes were grouped according to severity of the disease: early (n = 24); moderate (n = 47); high (n = 33). Preoperative keratometry was 40.00 to 49.00, 50.00 to 59.00, and 60.00 to 90.00 diopters (D), respectively. The criteria for corneal transplant were a best spectacle-corrected visual acuity of 20/40 or worse and keratoconus clearly identified by one of the above methods. Secondary procedures included repair of wound dehiscence (33 eyes, 31%), relaxing incisions (33 eyes, 31%), wedge resections (5 eyes, 5%), and automated lamellar keratoplasty (4 eyes, 4%). RESULTS: Mean postoperative uncorrected visual acuity at last follow-up was 0.43 +/- 0.3 (20/50), with 46 eyes (44%) achieving 20/40 or better. Mean best corrected visual acuity (BCVA) at last follow-up was 0.83 +/- 0.2 (20/25). Sixty eyes (58%) achieved 20/40 or better BCVA at 1 month and 92 eyes (88%), at 3 months. At last follow-up, mean average keratometric astigmatism was 3.10 +/- 1.70 D, mean keratometry was 43.30 +/- 2.20 D, and mean spherical equivalent was -1.70 +/- 3.00 D. Complications included 21 graft rejections (20%); 19 were successfully treated with topical and oral steroids. No expulsive hemorrhage or endophthalmitis occurred. CONCLUSIONS: The risk-benefit for corneal transplantation has been significantly altered by improved surgical and postoperative techniques. The improved results, low complication rate, and postoperative enhancement management indicate that corneal transplantation is a viable option early in the clinical course of keratoconus.     

Differences in myocardial velocity gradient measured throughout the cardiac cycle in patients with hypertrophic cardiomyopathy, athletes and patients with left ventricular hypertrophy due to hypertension

OBJECTIVES: We sought to compare the myocardial velocity gradient (MVG) measured across the left ventricular (LV) posterior wall during the cardiac cycle between patients with hypertrophic cardiomyopathy (HCM), athletes and patients with LV hypertrophy due to systemic hypertension and to determine whether it might be used to discriminate these groups. BACKGROUND: The MVG is a new ultrasound variable, based on the color Doppler technique, that quantifies the spatial distribution of transmyocardial velocities. METHODS: A cohort of 158 subjects was subdivided by age into two groups: Group I (mean [+/-SD] 30 +/- 7 years) and Group II (58 +/- 8 years). Within each group there were three categories of subjects: Group Ia consisted of patients with HCM (n = 25), Group Ib consisted of athletes (n = 21), and Group Ic consisted of normal subjects; Group IIa consisted of patients with HCM (n = 19), Group IIb consisted of hypertensive patients (n = 27), and Group IIc consisted of normal subjects (n = 33). RESULTS: The MVG (mean [+/-SD] s-1) measured in systole was lower (p < 0.01) in patients with HCM (Group Ia 3.2 +/- 1.1; Group IIa 2.9 +/- 1.2) compared with athletes (Group Ib 4.6 +/- 1.1), hypertensive patients (Group IIb 4.2 +/- 1.8) and normal subjects (Group Ic 4.4 +/- 0.8; Group IIc 4.8 +/- 0.8). In early diastole, the MVG was lower (p < 0.05) in patients with HCM (Group Ia 3.7 +/- 1.5; Group IIa 2.6 +/- 0.9) than in athletes (Group Ib 9.9 +/- 1.9) and normal subjects (Group Ic 9.2 +/- 2.0; Group IIc 3.6 +/- 1.5), but not hypertensive patients (Group IIb 3.3 +/- 1.3). In late diastole, the MVG in patients with HCM (Group Ia 1.3 +/- 0.8; Group IIa 1.4 +/- 0.8) was lower (p < 0.01) than that in hypertensive patients (Group IIb 4.3 +/- 1.7) and normal subjects (Group IIc 3.8 +/- 0.9). An MVG < or = 7 s-1, as a single diagnostic approach, differentiated accurately (0.96 positive and 0.94 negative predictive value) between patients with HCM and athletes when the measurements were taken during early diastole. CONCLUSIONS: In both age groups, the MVG was lower in both systole and diastole in patients with HCM than in athletes, hypertensive patients or normal subjects. The MVG measured in early diastole in a group of subjects 18 to 45 years old would appear to be an accurate variable used to discriminate between HCM and hypertrophy in athletes.     

On the phase diagram of the system hydroxypropylcellulose-water

The phase diagram of the system hydroxypropylcellulose (HPC)-H₂O has been investigated using differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy and¹H (NMR) nuclear magnetic resonance spectroscopy. A peritectic line at higher temperatures has been found similar to the lytropic systems described before. This phase transition, from a solution consisting of solvate aggregates and free solvent, into a crystal solvate-isotropic phase system is completely reversible. The formation of crystal solvate phases is independent of the water content of the system until the system transforms into a thermotropic system. The solvent molecules are strongly associated with the macromolecules.     

Idiosyncratic variation in chemical defenses among individual generalist grasshoppers

The defensive secretion of the lubber grasshopper,Romalea microptera, shows extreme chemical variation among individual adults of the same sex within a single wild population. Certain phenolic compounds were absent in some individuals and present in others. Concentrations of compounds, when present, varied over two to three orders of magnitude. Chemical variation attributable to individuals accounted for 60–88% of the total quantitative variation and was evenly contributed by all individuals in both sexes. Cluster and regression analyses showed no discernible predictable patterns in the defensive secretion variation. The specificity of chemical cues used by predators may explain why these defenses are so idiosyncratic.     

Enhancement of radiosensitivity of rat rhabdomyosarcoma R1H with normobaric carbogen and hyperbaric oxygen (HBO) using conventionally fractionated irradiation

Hypoxic clonogenic cells are an important contributory factor in tumour radioresistance. The objective of the present study was to evaluate whether hyperbaric oxygen enhances tumour radiosensitivity, using a conventionally fractionated irradiation schedule, and whether the radiosensitizing potential is different from carbogen. Experiments were performed using the rhabdomyosarcoma R1H model transplanted subcutaneously in the flank of WAG/Rij rats. A total of 30 X-ray fractions of 2 Gy were given either in air, normobaric carbogen or high pressure oxygen (HPO) (240 kPa, 2.37 atm) without anaesthesia. The time taken to achieve complete remission was 38.7 +/- 3.6 days, 36.7 +/- 2.7 days and 32.4 +/- 4.1 days for air, normobaric carbogen and HBO, respectively. The differences between air and HBO (p = 0.002) and carbogen and HBO (p = 0.015) were significant. Use of carbogen and HBO produced the same local control probability at 150 days and this was significantly higher than local control under ambient conditions (p < 0.0001). It was concluded that the time to achieve complete remission of the rat rhabdomyosarcoma R1H can be shortened by HBO. Furthermore, both HBO and carbogen give higher local control probabilities than treatment under ambient conditions when used with a conventionally fractionated radiation schedule.