THE RELATION BETWEEN WETTING EFFICIENCY AND LIQUID HOLDUP IN PACKED COLUMNS

Liquid holdup and wetting efficiency in packed columns were determined using a tracer method. A new model was developed considering axial dispersion, and analysis was made using the moment technique. The saturated solution of KG was used as an inert tracer and total liquid holdups were determined in the first part of experiments. As an adsorbable tracer, dioxane was utilized in the second part of the work and wetting efficiencies were obtained. Adsorption equilibrium constant was determined by the experiments conducted in a liquid full bed. A model proposed between liquid holdup and wetting efficiency gave good agreement with the experimental results. Axial dispersion effects were also taken into account during the work. It was also shown that axial dispersion of liquid phase should be considered especially in the small scale trickle bed reactors. @KEYWORDS:Packed beds,Wetting efficiency,Liquid holdup,Tracer method,Moment technique,Trickle bed reactors.     

Synthesis and characterization of uv-curable acrylated urethane prepolymers,I. Effects of reactive diluents and relative humidity on physical properties

A UV-curable acrylated urethane prepolymer was synthesized from tolylene-2,4-diisocyanate (TDI), a polyether polyol (Arcol 1131) and endcapped with 2-hydroxyethyl methacrylate (HEMA) by addition reaction in the presence of dibutyltin dilaurate as catalyst. UV curing was performed with either diethylene glycol diacrylate or thiodiethylene glycol diacrylate as reactive diluent. The effects of reactive diluent types, their concentrations and the humidity of environment on mechanical properties of cured films were investigated. Changes in the tensile strength, elongation and Young's modulus values of the cured films upon addition of reactive diluents with different concentrations were related to the effect of the diluent on the crosslinking density of cured films. The increase of relative humidity from 50 to 95% caused a decrease of tensile strength and Young's modulus values of cured films. It is proposed that the decrease of these physical properties in high relative humidity is due to the formation of hydrogen bonding in polymer chains caused by water molecules.     

Resource Leveling in Line‐of‐Balance Scheduling

Resource leveling involves minimizing resource fluctuations without changing the completion time of a project. A smooth distribution of resources minimizes logistical problems and results in cost savings. Line‐of‐balance (LOB) is a resource‐based scheduling system that is used in projects that exhibit repetitive characteristics, performs resource allocation as a matter of course, but does not deal with resource leveling. In the past, researchers experienced declines in productivity whenever they leveled resources in different linear scheduling models by adjusting activities’ production rates. The objective of this research is to develop a genetic algorithm‐based resource leveling model for LOB schedules that does not impact productivity negatively. This model is based on the “natural rhythm” principle, according to which a crew of optimum size will be able to complete an activity in the most productive way. The “natural rhythm” principle allows shifting the start time of an activity at different units by adjusting the number of crews without changing the duration of the activity in any one unit and without violating the precedence relationships between activities. An LOB schedule is established for a pipeline project and is used to illustrate the proposed resource leveling model. It was observed that the model provides a smoother resource utilization histogram. Performing resource leveling in LOB scheduling without sacrificing productivity is the major contribution of the proposed model.     

Evaluation of plate loading tests on some rock formations for assessing the ground bearing capacity

A significant proportion of the cost of winning minerals or aggregates in an open cast mine is related to the mass haul. The quality of the haul roads is an important factor in the efficiency and length of turn-round time. The paper reports a study into the use of plate loadings tests as a quick and easy means of establishing a preliminary bearing capacity. Various relationships have been obtained between bearing capacity and the results of field and laboratory tests. Good performance indices (r, RMSE, VAF) indicate they can be used for an initial assessment of the bearing capacity of rock units ranging from weak to strong. In addition, classes for bearing capacity of rock units have been suggested based on field observations and measurements.     

The effects of subthreshold visual stimulation on P300 response

The effects of the subthreshold visual stimuli on the electrical activity of the brain were investigated by an oddball-like paradigm and a single-stimulus paradigm. In the oddball-like paradigm, suprathreshold and subthreshold stimuli were presented randomly where the suprathreshold stimulus probability was 0.24. The single-stimulus paradigm contained only the suprathreshold stimuli and was identical to the oddball-like paradigm apart from the absence of subthreshold stimuli. Suprathreshold P3b amplitude was larger for the oddball-like than for the single-stimulus condition particularly in the centro-parietal region. This result suggests that at least one component of the P300 wave could be assigned to an automatic comparison and memory updating process which runs unconsciously.     

Quantitative evaluation of renal parenchymal mass with 99mtechnetium dimercapto-succinic acid scintigraphy after nephrolithotomy

PURPOSE: We detected renal parenchymal damage after nephrolithotomy. MATERIALS AND METHODS: We studied 12 patients with renal stones treated with nephrolithotomy. Renal function was determined with serum blood urea nitrogen (BUN) and creatinine values, and 99mtechnetium dimercapto-succinic acid scintigraphy of renal parenchymal tissue was performed before, and 7 days and 3 months after nephrolithotomy. Qualitative and quantitative analyses were done with the Wilcoxon signed rank test. RESULTS: There was no visual difference in size and appearance of the nephrotomy site between preoperative and postoperative visual scintigraphic evaluations. Quantitative data did not reveal any significant difference between kidneys with and without a nephrotomy incision (p > 0.05), as well as between nephrotomy regions and intact parenchyma within the same kidney (p > 0.05) 3 months after nephrolithotomy. There was no significant difference in serum BUN and creatinine levels between values preoperatively and 3 months postoperatively (p > 0.05). CONCLUSIONS: There was no significant change in renal cortical function and functioning renal parenchymal mass after nephrolithotomy as shown by serum BUN and creatinine levels, and 99mtechnetium dimercapto-succinic acid scintigraphy.     

Effect of preparation pH on properties of silica gel

Silica gels were obtained by drying the silica hydrogels formed at pH values between 1 and 4 at 100°C. The bulk density of the 2–3 mm diameter fraction decreased from 0·62 g cm^?3 to 0·20 g cm^?3 as the preparation pH increased from pH 3 to pH 3·65. The apparent density of silica gels was between 1·43 and 1·95 g cm^?3. Isotherms for the adsorption of water vapour on samples prepared at different pH values showed hysteresis in all cases. Thermogravimetry analysis showed that the amount of bound water was in the range of 4·4 to 5·5% on a dry weight basis. Specific heats were determined by a differential scanning calorimetry method using a sapphire standard and were between 0·82 and 0·97 J g^?1 K¹.     

NATURAL ZEOLITES IN AIR DRYING

The local clinoptilolite from Bigadis region in Turkiye, was used for air drying in packed column. The effective diffusion coefficient of water in natural zeolite was found as 5×10^-10 m² s^-1 from isothermal uptake measurements. Effects of packing height and airvelocity on breakthrough curves were studied.     

Influence of the ER,CR:YSGG laser and different irrigation methods on push-out bond strength of fiber post

Er,Cr:YSGG lasers are currently being investigated for disinfecting the root canal treatment. The aim of this study was to compare the effects of various irrigation protocols on push-out bond strength of fiber posts. Fifty maxillary anterior teeth were divided into five groups (n = 10) according to the protocol that applied into the post space. Group-1: distilled water, Group-2: 5% NaOCl, Group-3: 2% CHX, Group-4: Er,Cr:YSGG laser (1.5 W, 20 Hz, 85 air, 75 water, 26.7 J/cm²), Group-5: Er,Cr:YSGG laser (1.25 W, 50 Hz, 34 air, 24 water, 12.7 J/cm²). Fiber posts were cemented with resin cement. The remaining part of the root, three slices were obtained from each specimen and push-out test was performed. One-way ANOVA and Duncan’s test at a 5% level of significance were used for the statistical analysis. Post space irradiation with Er,Cr:YSGG laser (1.5 W 20 Hz, 85 air, 75 water, 26.7 J/cm²) increases push-out bond strength of fiber post to root canal dentin. Further investigations are needed to establish and optimize ER,Cr:YSGG laser parameters to increase the push-out bond strength of fiber posts.