Current Issue : April - June Volume : 2015 Issue Number : 2 Articles : 7 Articles
This study proposes a new analytical\nmodel to predict shear stress in a fully encapsulated\nrock bolt in jointed rocks. The main characteristics of\nthe analytical model consider the bolt profile and jump\nplane under pull test conditions. The performance of\nthe proposed analytical model, for different bolt\nprofile configurations, is validated by ANSYS software\nand field. The results show there is a good\nagreement between analytical and numerical methods.\nStudies indicate that the rate of shear stress from the\nbolt to the rock exponentially decayed. This exponential\nreduction in shear stress is dependent on the bolt\ncharacteristics such as: rib height, rib spacing, rib\nwidth and resin thickness, material and joint\nproperties....
The ionic contamination on printed circuit boards (PCB) having different surface finishes was examined\nusing ionograph. The study was performed at the RT on three types of PCBs covered with: (i) hot air solder\nleveling (HASL LF), (ii) electroless nickel immersion gold (ENIG), and (iii) organic surface protectant\n(OSP), all on Cu substrates, as well as two types of fluxes, namely EF2202 and RF800. In the group of\nboards without soldered components, the lowest average value of contamination was for the ENIG 18 ?m\nsurface (0.01 ?g NaCl/cm2). Boards with soldered components were more contaminated (from 0.29 ?g\nNaCl/cm2 for the HASL LF 18 ?m surface). After spraying boards with fluxing agents, the values of\ncontaminants were the highest. The influence of phosphorus content in Ni-P layer of ENIG finish on ionic\ncontamination was examined. In the group of PCBs with Au coating, the smallest amount of surface\ncontaminants (0.32 lg NaCl/cm2) was for Ni-2-5%P layer. PCBs with Ni-11%P layer were higher contaminated\n(0.47 ?g NaCl/cm2), and another with Ni-8%P layer had 0.81 ?g NaCl/cm2. PCBs without Au\ncoating, had the lowest contamination (0.48 ?g NaCl/cm2) at phosphorous content equal 11%P. Higher\ncontamination (0.67 ?g NaCl/cm2) was at 2-5%P, up to 1.98 ?g NaCl/cm2 for 8% of P. Boards with Au\nfinish have lower value of contamination than identical boards without Au layer thus contributing to better\nreliability of electronic assemblies, since its failures due to current leakage and corrosion can be caused by\ncontaminants....
The fracture toughness of a rock often varies\ndepending on the specimen shape and the loading type used\nto measure it. To investigate the mode I fracture toughness\nusing semi-circular bend (SCB) specimens, we experimentally\nstudied the fracture toughness using SCB and\nchevron bend (CB) specimens, the latter being one of the\nspecimens used extensively as an International Society for\nRock Mechanics (ISRM) suggested method, for comparison.\nThe mode I fracture toughness measured using SCB\nspecimens is lower than both the level I and level II fracture\ntoughness values measured using CB specimens. A\nnumerical study based on discontinuum mechanics was\nconducted using a two-dimensional distinct element\nmethod (DEM) for evaluating crack propagation in the\nSCB specimen during loading. The numerical results\nindicate subcritical crack growth as well as sudden crack\npropagation when the load reaches the maximum. A Kresistance\ncurve is drawn using the crack extension and the\nload at the point of evaluation. The fracture toughness\nevaluated by the K-resistance curve is in agreement with\nthe level II fracture toughness measured using CB specimens.\nTherefore, the SCB specimen yields an improved\nvalue for fracture toughness when the increase of K-resistance\nwith stable crack propagation is considered....
Manufacturing enterprises can face obstacles that make productivity improvement efforts ineffective or even prevent improvement\noperations. This paper reports on an investigation of the internal obstacles restraining productivity improvement programs in the\nmanufacturing enterprises of developing countries, using Oman as a case study.Data required for this study were collected through a\nquestionnaire given to production and operations managers at 51 manufacturing enterprises in Oman.The results of applying factor\nanalysis to a data set of 15 obstacles showed that these obstacles can be reduced to three major factors. Ranked according to their\nimportance, these factors are poor management practices, employee job dissatisfaction, and poor human resource management.\nThe findings of this research are of value to production and operations managers of manufacturing enterprises who are interested\nin conducting productivity improvement programs not only in Oman but also in developing countries with environments similar\nto that of Oman, such as the Gulf Cooperation Council (GCC) countries....
The CdTe nano crystals were successfully synthesized\nusing a facile room temperature method with\nnon-toxic and environmentally friendly capping agent. The\nobtained CdTe nano crystals were characterized by UVââ?¬â??Vis\nabsorption spectroscopy, transmission electron microscopy,\nand z-scan technique. A photo luminescence peak with full\nwidth at half maximum of around 15 nm could be obtained,\nwhich indicates a homogeneous and narrow size distribution\nfor the CdTe nano crystals. The magnitude and sign\nof the third-order nonlinear refractive index (n2) and nonlinear\nabsorption coefficient (?) of the CdTe nano crystals\nwere determined by using of the closed- and open-aperture\nz-scan at different intensities, respectively. The negative\nsign of n2 indicated that there is a self-de focusing effect\nin the sample. The nonlinear refractive index, n2, and\nthe nonlinear absorption coefficient, ?, were in order of\n10?7 cm2W?1 and 10?2ââ?¬â??10?3 cmW?1, respectively....
Recent studies have shown that thermographic\nphosphor particles are suitable tracers for simultaneous\ntemperature and velocity imaging in gas flows. For the\ndevelopment of this thermographic particle image velocimetry\ntechnique, the choice of phosphor is a key consideration\nand new phosphor materials need to be identified and\ntheir luminescence properties thoroughly characterised.\nThis paper describes a method for investigating phosphor\nparticles for gas thermometry. The method consists of performing\nspectroscopic experiments on particles dispersed\nin the gas, while simultaneously measuring the number\ndensity of tracer particles using a particle counting system,\nwhich is based on high-resolution Mie-scattering images.\nThe measurement of the seeding density allows a direct\ncomparison of different phosphors on a ââ?¬Å?per particleââ?¬Â basis\nand estimation of the effect of the particles on the gas thermal\nproperties. The effect of parameters such as the excitation\nfluence, gas composition and temperature on the luminescence\nemission intensity can be studied independently\nof the seeding density. As a demonstration, this system is\nused to investigate micron-size BAM:Eu2+ particles. The\nnecessary seeding density for precise temperature measurements\nis determined, and a nonlinear dependence of the\nluminescence emission intensity on the excitation fluence\nis identified....
This paper discusses irrational transfer function\nrepresentation for a typical thick-walled double pipe heat\nexchanger. Closed-form analytical expressions for the\nindividual elements of 2 9 2 transfer function matrix are\nderived both for the parallel- and the counter-flow configurations\nusing the Laplace transform method. Based on the\ntransfer function representation, its frequency responses are\ndemonstrated both in the form of three-dimensional graphs\nas well as classical, two-dimensional Bode and Nyquist\nplots. Finally, steady-state temperature profiles are presented\nand compared for both flow arrangements\nconsidered....
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