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Dynamic Analysis of Flexible Mechanisms with Clearance
No full textA Master of Science thesis in Mechanical Engineering by Mona Abdullah Hassan Ahmed albashir entitled, "Dynamic Analysis of Flexible Mechanisms with Clearance," submitted in November 2016. Thesis advisor is Dr. Lotfi Romdhane. Soft and hard copy available.This research is focused on studying the dynamic behavior of a four-bar mechanism with clearance. The presence of clearance in a revolute joint induces impacts between the journal and the sleeve. Therefore, it causes vibration, noise and decreases the efficiency of the mechanism. Two different methods are proposed to eliminate the undesirable effects of clearance in the joint through simulations and experiments. The first method, that is used to eliminate these impacts, relies on attaching a spring to a rigid four-bar mechanism. The impacts are predicted by monitoring the moment of the reaction force in the joint with clearance using MATLAB software simulations. It is shown that the impacts could be easily eliminated using adequate and optimized spring parameters. The optimization of the spring parameters is performed to keep the positive effects of adding the spring (eliminating the impacts) and to minimize its negative effects (high maximum input torque and its high fluctuations). The second method aims at studying the dynamic behavior of the mechanism with a flexible coupler link. The dynamic analysis of the flexible mechanism is investigated using two different materials of the coupler link (aluminum and steel) with two different thickness values for each material (3 and 4 mm for aluminum and 1.5 and 2 mm for the steel). The rigid mechanism is considered in this case with a coupler link made of steel with 5 mm thickness to highlight the difference between flexible and rigid mechanisms. The deformation of the flexible coupler links (using ideal joints) is investigated by measuring the strain values at three different speeds (277, 415 and 554 rpm). The obtained results show that the strain values are significantly affected by the crank speed and the thickness of the links. Experimental tests are performed to measure the accelerations for the follower of the four-bar mechanism using rigid and flexible coupler links. These measurements are done for the case of ideal joint (no clearance) and realistic joint with a clearance of 0.5 mm and 1 mm sizes at the three mentioned speeds for each case. The experimental results are validated through simulation tests using ADAMS software. These results confirm that the flexibility of the coupler has thus a role of a suspension for the mechanism.College of EngineeringDepartment of Mechanical EngineeringMaster of Science in Mechanical Engineering (MSME
The Dehortative in the Spoken Arabics of the Eastern Mediterranean
No full textA few authors mention a hortative mood in Arabic, formed in a variety of manners, usually involving a pre-verbal element and an unmarked imperfective verb, sometimes thought of as the jussive or subjunctive. Not an imperative, the Arabic hortative may apply to all three persons. Its opposite, the dehortative, similarly not a prohibitive, also applies to all three persons, and it, too, is expressed in a variety of manners, all involving the unmarked imperfective verb and preverbal elements, often not negators but expressing an inherent negation. It may also be formed with reflexes of the negator miš preceding an unmarked imperfective verb. Such negation has been remarked in Egyptian Arabic in five types of constructions: in contrastive, metalinguistic, and rhetorical negation, in negations of progressive aspect, and in the dehortative. Not restricted to Egyptian Arabic, verbal negation with miš/muš/mhūš occurs in Levantine Arabics, Tunisian Arabic, and the closely related Maltese
Efficient and simple protocol employing borohydride systems to design a selective osthol-zirconium (OST-Zr) library from potential natural products
No full text“Drug likeness” of a molecule is the prime criterion for a molecule to exhibit the desired pharmaceutical activity. A pharmacophore, which describes molecular features that are necessary for molecular recognition of a ligand by a biological macromolecule, is well altered by the Structure Activity Relationship (SAR) guidelines through Hydrophobic Lipophilic Balance (HLB) demonstrated by the system. The tailoring is best accomplished by organic functional group interconversion on a potent natural product via a variety of synthetic methodologies available to date. Metal borohydrides (MBH₄) in particular are promising compounds as they can potentially serve varying HLB systems. The reagent acts on the substrate to cause reduction, hydroboration, or a combination of both outcomes for the purpose of rearrangement and fragmentation. Indeed, Zr(BH₄)₄ is expected to be more active and selective as a reducing agent compared to NaBH₄ . This study aims at evaluating zirconium borohydride (Zr(BH₄)₄ ) in tetrahydrofuran (THF) as a reducing system to realize a more selective, meaningful and combinatorial osthol (OST) library from potential natural products and attempt to alternate preparation of the same in THF from known metal borohydrides, limiting reduction of the metal center versus metathesis
Effect of pH, ultrasound frequency and power density on the release of calcein from stealth liposomes
No full textThe use of liposomes as carriers for chemotherapeutic agents in combination with ultrasound as a stimulus to control the time and space of the drug release is a promising approach for cancer treatment, as it can reduce the side effects caused by conventional chemotherapy. This in vitro study investigated the triggered release of calcein from stealth (PEGylated) and non-stealth (non-PEGylated) liposomes, using ultrasound at low (20 kHz) and high (1 and 3 MHz) frequencies, and at different power densities. Release was monitored by the increase in fluorescence due to relieving of calcein’s self-quenching upon dilution when the model drug leaks out of the liposomes. The results showed that, independent of the power density, the release was highest at 20 kHz. For the same frequency, release usually increased with increasing power densities. Additionally, for release at 20 kHz, a comparison was done for PEGylated and non-PEGylated liposomes, at two pH values: 5.2 and 7.4. The results were then compared to previously published studies. In all cases, the mechanism of release seems to involve cavitation events that either pierce a hole in or shear open the liposomes, as all the determined power densities are above the transient cavitation threshold
Investigation of a fecal contamination of groundwater and surface water at Al Wasit Nature Reserve, Sharjah, United Arab Emirates
No full textDomestic waste contamination has adverse health effects and detrimental ecological impact. This paper presents the results of an investigation of domestic waste contamination; specifically fecal contamination of ground and surface water in Al Wasit Nature Reserve in Sharjah, United Arab Emirates (UAE). This reserve, which comprises a broad hyper-saline wetland expanse on the outskirts of the city, is polluted due to chemical and organic waste dumping, perennial inundation, and sewage disposal, among others. A total of five ground and ten surface water samples were collected from the reserve in September, October and November of 2009, respectively and analyzed for major water quality parameters such as pH, chloride, Biochemical Oxygen Demand (BOD), total coliforms and E. coli. To help understand the spatial distribution of these parameters in the reserve, GIS representations were created in ArcGIS 10.1. Analysis results suggest no significant fecal contamination in groundwater in the reserve. However, there was evidence of fecal contamination in surface water, which is not believed to be from domestic sources. The results of this study support the decision by the Sharjah Municipality, to declare Al Wasit Nature Reserve a protected area
Rapid Separation of Bacteria from Blood - Review and Outlook
No full textThe high morbidity and mortality rate of bloodstream infections involving antibiotic‐resistant bacteria necessitate a rapid identification of the infectious organism and its resistance profile. Traditional methods based on culturing the blood typically require at least 24 h, and genetic amplification by PCR in the presence of blood components has been problematic. The rapid separation of bacteria from blood would facilitate their genetic identification by PCR or other methods so that the proper antibiotic regimen can quickly be selected for the septic patient. Microfluidic systems that separate bacteria from whole blood have been developed, but these are designed to process only microliter quantities of whole blood or only highly diluted blood. However, symptoms of clinical blood infections can be manifest with bacterial burdens perhaps as low as 10 CFU/mL, and thus milliliter quantities of blood must be processed to collect enough bacteria for reliable genetic analysis. This review considers the advantages and shortcomings of various methods to separate bacteria from blood, with emphasis on techniques that can be done in less than 10 min on milliliter‐quantities of whole blood. These techniques include filtration, screening, centrifugation, sedimentation, hydrodynamic focusing, chemical capture on surfaces or beads, field‐flow fractionation, and dielectrophoresis. Techniques with the most promise include screening, sedimentation, and magnetic bead capture, as they allow large quantities of blood to be processed quickly. Some microfluidic techniques can be scaled up
GIS-based study on the Susceptibility of Dubai Creek (UAE) to Eutrophication
No full textRapid urbanization in the UAE has led to some environmental implications, one of which concerns Dubai Creek – a major attraction in the city of Dubai. The creek’s water quality monitoring program showed increased concentrations of phosphorus- and nitrogen-based nutrients starting in 2008 and 2009. The creek has since been through redundant eutrophication, which has been attributed to the high levels of nutrients in addition to the creek’s poor flushing and irregular circulation processes. The aim of this study was to (a) assess the susceptibility of the creek to eutrophication considering its principal factors, and (b) to identify the pattern of this process (i.e., seasonal, cyclic, etc.). Principal component analysis was used to identify the principal factors from nitrates, phosphates, total nitrogen, chlorophyll-a, dissolved oxygen, and turbidity, which were collected as quarterly averages in 2012 and 2013. Logistic regression was utilized to assess the susceptibility of the creek to eutrophication considering the principal factors obtained by PCA. The analysis showed that three different factors, which included at least nitrates or phosphates, have contributed to eutrophication in every quarter of the year in the period of study. Further analysis showed weak correlation between principal factors of eutrophication in consecutive quarters. However, strong correlations were observed between these factors when the same quarters over the period of the study were considered, suggesting a possible seasonal pattern
Labor localization and human resource management practices in the Gulf countries
No full textThe chapter is organized as follows: first, we examine the literature on core issues pertinent to this theme, such as demographic and labor-market characteristics in the GCC, the objectives of these localisation programs, and the major components of localisation policies. Second, we review the literature on HRM practices that facilitate the implementation of localisation programs. Third, we review multiple challenges related to the implementation of these programs. Finally, we present some recommendations intended to enhance the impact of localisation efforts
Points of Identity
No full textA sculpture depicting a blue head by Kevin Badni entitled "Points of Identity" (materials: wood and acrylic ; size: w28 x h28 xd25). The sculpture was exhibited at the juried event OXYGEN – FRAGMENTED CITIES+IDENTITIES held at Jorge Jurado Gallery, Bogotá, Colombia, November 19 - December 19, 2016. The event was curated by Luca Curci, director of It's LIQUID Group
Evaluation of a Cold Thermal Energy Storage System Using Alternative Refrigerants
No full textA Master of Science thesis in Mechanical Engineering by Salah Ali Alshaibani entitled, "Evaluation of a Cold Thermal Energy Storage System Using Alternative Refrigerants," submitted in May 2016. Thesis advisor is Dr. Saad A. Ahmed and thesis co-advisor is Dr. Mohamed A. Gadalla. Soft and hard copy available.This study provides a detailed comparison study between clathrate hydrate of R134a and R404a refrigerants in a direct contact thermal energy storage system. Numerous closed loop cycles using hydrate of each refrigerant have been evaluated to compare the clathrate characteristics formation and the overall performance of the direct contact thermal storage closed loop system. The input parameters for conducting the comparison include the compressor speed and the mass flow rate of the refrigerant used to form refrigerant clathrate. Results of this investigation show that using R134a is better than R404a in forming the cold storage refrigerant clathrate. For R134a, the overall system coefficient of performance based on the first law of thermodynamics is evaluated under different operating conditions and found to be varying between 4.10 and 5.77. The exergy analysis shows that the exergy recovered varies between 50% and 66%. For R134a clathrate, a high system coefficient of performance of 5.77 (COP) and a high exergy recovered of 66% are obtained at the lowest tested compressor speed of 2300 rpm and a high refrigerant mass flow rate of 0.96 kg/min. At the compressor speed of 2300 rpm with refrigerant R134a, the system exergy recovered are 62%, 64% and 66% of the exergy input for mass flow rates of 0.48, 0.72, and 0.96 kg/min, respectively. On the other hand, the overall system coefficient of performance for R404a clathrate shows lower values when compared to R134a formation. For R404a, the system coefficient of performance varies between 2.9 and 3.48 while the exergetic efficiency varies between 38% and 58%. At the operating compressor speed of 2300 rpm and refrigerant R404a, the system exergy recovery are about 52%, 55% and 58% for mass flow rates of 0.48, 0.72 and 0.96 kg/min, respectively. Current results show that the thermal system operates more efficiently with R134a refrigerant than with R404a refrigerant. It also shows that the best system performance is achieved at the lowest compressor speed while the effect of refrigerant mass flow rate is insignificant. These results are in agreement with an earlier study by Kiatsiriroat et al. using refrigerant R12 and R22 [1] and [2]. Finally, the current research results conclude to use of R134a refrigerant to form the clathrate hydrate in thermal storage systems.College of EngineeringDepartment of Mechanical EngineeringMaster of Science in Mechanical Engineering (MSME