A NEW TECHNOLOGY FOR THE CRYSTALLIZATION OF DEAD SEA POTASSIUM CHLORIDE

The aim of this article is to introduce a new technology for the production of Dead Sea potassium chloride. The new technology depends on using the power of ultrasound waves during a crystallization process to enhance potassium chloride precipitation and to improve the end-use properties of the produced crystals. This environmentally clean technology, which is called sonocrystallization, has received very intensive research in the past few years. It was used in this study to modify the crystallization process of potassium chloride from the decomposition of Dead Sea carnallite. Two crystallization runs were done; the first was performed without the application of ultrasound waves and the second was performed with this application. The effect of sonication on the crystallization process time and on crystal size distribution as well as on the purity of the crystals was studied. It was found that the required time for the un-sonicated process was about 150 min. This time was reduced to about 50 min when sonication was applied. The produced crystals were sieved, and the crystal size distribution (CSD) was determined for the two runs. For the sonicated process, finer but more uniform crystals were obtained with a mean average size of 0.2643 mm in comparison with 0.5727 mm for the un-sonicated process. The produced crystals were found to be of 96.07% KCl for the un-sonicated process and this purity was improved to 97.31% KCl by the application of ultrasound waves. Based on the results of this study, it seems to be feasible and economical to scale up the proposed technology for industrial applications.     

Human perception of robot safe speed and idle time

Operators and users of robotic systems perform tasks which require close proximity to dangerous moving parts. Two experiments were performed to assess human perception of safe robot arm speed and idling times. Experiment 1 was designed to determine the maximum safe speed of robots. Subjects were asked to adjust the robot speeds. Perceived safe speeds were indicated for two different types of robots. Experiment 2 was designed to determine safe programmed idle time of robots. Subjects were asked to enter the robot work envelope when a programmed idle was perceived to be caused by a malfunction. Safe idle times were reported for two different robot speeds during operational cycles.     

Orientation by weighted randomness

This paper deals with the problem of how motion control can be achieved in very simple systems under a minimal number of preconditions. The system's design is therefore as minimal as possible, reflecting the basal reflex arc as observed in biological systems. The model for the movement of the agent is a multiplicatively modified random walk, and thus does not represent a diffusion process of the Langevin type. The mobile agent shows a fast, reliable homing behavior toward a defined area, and finally stays in some defined neighborhood of this area. Moreover, obstacle avoidance is shown to be an immediate result of the system's properties.     

Outcome of moderate carotid artery stenosis in patients who are asymptomatic

PURPOSE: The incidence rate of disease progression and stroke after the diagnosis of a moderate (50% to 79%) carotid stenosis was determined by means of color-flow duplex scanning. METHODS: During a 4-year period, 344 male veterans with moderate internal carotid artery stenoses, on one or both sides, were examined at regular intervals for a mean period of 25 months. Carotid color-flow scans were obtained semiannually. Clinical follow-up was performed to determine the incidence rate of amaurosis fugax, transient ischemic attacks, nonhemispheric symptoms, and strokes. RESULTS: New neurologic symptoms developed in 75 patients (21.8%). Fifty-one (14.8%) had ipsilateral symptoms during follow-up: 18 amaurosis fugax (5.2%), 14 transient ischemic attacks (4%), 5 nonhemispheric symptoms (1.4%), and 14 strokes (4%). Twenty-four patients (6.9%) had contralateral symptoms: 20 strokes (5.8%) and 4 transient ischemic attacks (1.2%). Life-table analysis showed that the annual rate of ipsilateral neurologic events was 8.1%, and the annual rate of stroke was 2.1%. Seventy-five patients (22%) died in the follow-up period. Disease progression to 80% to 99% stenosis or occlusion occurred in 71 of 458 vessels (15.5%). The internal carotid arteries that showed evidence of disease progression had a significantly higher initial peak systolic velocity (251 vs 190 cm/s; P <.0001) and end diastolic velocity (74 vs 52 cm/s; P < 0.0001). Black patients and patients with ischemic heart disease were at a higher risk for disease progression. We could not identify any atherosclerotic risk factors that reliably predicted patients in whom future ipsilateral neurologic symptoms were more likely to develop. However, there was an increased risk of stroke associated with progression of disease. CONCLUSION: Patients who are asymptomatic and who have moderate carotid stenoses are at significant risk for neurologic symptoms and death, but have a relatively low incidence rate of ipsilateral events. The initial flow characteristics in the stenotic vessel are predictive of future disease progression, but they are not helpful in identifying patients in whom symptoms will develop.     

Effects of minor additions of ruthenium on the passivation of duplex stainless-steel corrosion in concentrated hydrochloric acid solutions

The effects of minor additions of ruthenium (0.14%, 0.22%, and 0.28%) on the passivation of duplex stainless-steel (DSS, Fe–22%Cr–9%Ni–3%Mo) corrosion in 2 M HCl solutions have been studied using open-circuit potential (OCP), potentiodynamic cyclic polarization, potentiostatic current–time, electrochemical impedance spectroscopy (EIS), and weight loss measurements. OCP measurements showed an increased shift in the corrosion potential to more positive values with increasing Ru content. Polarization and EIS experiments indicated that the presence of Ru and the increase of its content decrease the corrosion rate, critical and passive current density, and polarization resistance. Moreover, it shifts the corrosion and pitting potentials to more positive values. Current–time measurements at −100, −50, and 50 mV versus Ag/AgCl also confirmed that the severity of pitting corrosion decreases with an increasing Ru content. Weight-loss time data showed good agreement with the electrochemical measurements.     

Multiobjective shape optimization of speed humps

This paper presents a new approach to the shape optimization of road speed humps. The proposed approach is based on multiobjective genetic optimization of the hump profile while taking into account the separation phenomenon, which occurs when the front tires of the vehicle momentarily lose contact with the road surface. The optimization is carried out for speeds up to twice the authorized speed (throughout this article, the term authorized speed refers to speed limits enforced in speed reduction [bump] areas of the roads) rather than for illegally high speeds as adopted by many of the previous works. A 6-degree of freedom non-linear dynamic model is used to identify the speeds at which separation occurs, and hump profiles associated with these speeds are discarded as infeasible solutions. Three independent objective functions are selected for optimization. They include the maximum vertical acceleration experienced by the driver when crossing the hump below the authorized speed limit (to be minimized), the same vertical acceleration at speeds above the authorized speed (to be maximized), and the ascending ratio of the “speed—vertical acceleration” curve (to be maximized). These objective functions are evaluated for more than 10,000 humps of two popular profile types (sinusoidal and flat top with straight ramps) and optimum profiles for three speed limits of 20, 25, and 30km/h are determined using the multiobjective nondominated sorting genetic algorithm II. As a result, a Pareto front of at least ten optimal points is achieved for each of the two hump profile types. Furthermore, to incorporate the economical aspects of the real-world problem, Pareto optimal points for the two profile types were compared based on their lateral section areas (an indication of the manufacturing cost). The comparison shows that sinusoidal humps more often than not outdo their flat top rivals economically.     

Frequency- and time-varying scattering parameters of a photo-excited superconducting microbridge

The extended scattering parameters for linear time varying devices are used to model a high-temperature superconducting (HTS) bridge under time-harmonic optical irradiation. It is shown that this structure acts as a time-varying low-pass filter, which its transfer function characteristic changes periodically with time. This behavior makes this configuration ideal for applications where a time-varying filter is on demand.     

Engineering behavior of the Lisan Marl as a dyke foundation material: Dead Sea,Jordan

Problems have occurred with dykes constructed on the Lisan Marl to retain brine pumped from the Dead Sea, which is chemically processed to produce potash. In this study the engineering behavior, collapse potential and compressibility of the Lisan Marl were assessed by undertaking laboratory tests with both natural, distilled water and brine as the media. The results showed that the liquid limit and fine particles increased when the soil was mixed with fresh/distilled water compared with brine water. The soil can be classified as highly compressible with a low undrained shear strength. In terms of collapsibility, the soil could be classified as slightly collapsible upon inundation with distilled water and moderately collapsible when soaked in Dead Sea brine. The results are important when determining the height and nature of the dykes.      

Thermoeconomic optimization for a finned‐tube evaporator configuration of a roof‐top bus air‐conditioning system

This paper presents a methodology of a design optimization technique that can be useful in assessing the best configuration of a finned‐tube evaporator, using a thermoeconomic approach. The assessment has been carried out on a direct expansion finned‐tube evaporator of a vapor compression cycle for a roof‐top bus air‐conditioning (AC) system at a specified cooling capacity. The methodology has been conducted by studying the effect of some operational and geometrical design parameters for the evaporator on the entire cycle exergy destruction or irreversibility, AC system coefficient of performance (COP), and total annual cost. The heat exchangers for the bus AC system are featured by a very compact frontal area due to the stringent space limitations and structure standard for the system installation. Therefore, the current study also takes in its account the effect of the variation of the design parameters on the evaporator frontal area. The irreversibility due to heat transfer across the stream‐to‐stream temperature difference and due to frictional pressure drops is calculated as a function of the design parameters. A cost function is introduced, defined as the sum of two contributions, the investment expense of the evaporator material and the system compressor, and the operational expense of AC system that is usually driven by an auxiliary engine or coupled with the main bus engine. The optimal trade‐off between investment and operating cost is, therefore, investigated. A numerical example is discussed, in which a comparison between the commercial evaporator design and optimal design configuration has been presented in terms of the system COP and evaporator material cost. The results show that a significant improvement can be obtained for the optimal evaporator design compared with that of the commercial finned‐tube evaporator that is designed based on the conventional values of the design parameters. Copyright © 2007 John Wiley & Sons, Ltd.