This paper presents computational predictions of adiabatic film cooling effectiveness for effusion cooling systems with 90o and 30o holes. Predictions are performed for a range of coolant injection mass flow rates per unit surface area, G, of 0.1kg/sm2 - 1.6 kg/sm2 for 90o holes with constant pitch-todiameter ratio of X/D = 11 and 10 rows of holes and for 30o inclined holes with X/D = 11 and 15 rows of holes over a 152mm surface length. The computational works performed are steady-state and the turbulent governing equations are solved by a control-volume-based finite difference method with second-order upwind scheme and the k-epsilon turbulence model. The velocity and pressure terms of momentum equations are solved by the SIMPLE method. The CFD prediction were validated by comparing the predictions with literature data for single rows of inclined holes and then applied to effusion cooling. The predictions included the use of a tracer gas in the coolant, which was used to predict the mixing of the coolant with the hot mainstream gases. Also the surface distribution of the tracer gas was a direct prediction of the cooling effectiveness. The mixing of coolant with the mainstream was studied and boundary layer temperature and coolant mixing profiles were predicted. These were compared with temperature measurement in a hot effusion cooling test rig. 

1. This study investigated the impact of textual cohesive conjunctives on the reading comprehension of Libyan university students studying English as a foreign language. Conjunctions as defined by Halliday and Hasan (1976) in their theory of textual cohesion provide the theoretical background to this work. The literature reviewed revealed contradictory findings in relation to the effect of conjunctions on reading comprehension. Many linguists and psycholinguists found that all conjunctive types (i. e. additives, adversatives, causals, and temporals) can facilitate reading comprehension. However, other studies came to the conclusion that conjunctives affected reading comprehension in different ways, or that they had no effect or a negative effect on the reading comprehension of native and foreign language readers. In order to explore the effects of conjunctions on the reading comprehension of university students for whom English was a foreign language (i. e. 4 `h year English department students in two Libyan universities) an intervention programme was designed. This programme involved the application of pre-post tests and only post-test of reading comprehension. The first experiment was organised in the Gharian English Department and the second took place in the Sabrata English Department. The participants were divided into comparative/control and treatment/intervention groups. The treatment group was explicitly taught conjunctions for three months. The comparative groups were taught their current traditional syllabus. The rationale behind having two different types of experiments in two English departmentsis the recommendatioonf Bryman( 1989)a nd otherm ethodologisttso be cautious of the possible negative effect of pre-testing. There is a possibility that the participants who attend the pre-test could benefit from this experience when they answer the same questions in the post-test, especially if the interval between the tests is short. By organising two experiments enough data were available for the study even if a negative effect from the pre- and the post-test experiment was discovered. That was followed by interviewing the participants of the treatment groups and asking them about the strategies they had used in answering the reading comprehension test. By organising semi-structured interviews, the researcher was able to explore the extent to which the participants had used their understanding of conjunctions to facilitate reading comprehension. Descriptive and inferential statistics were used to analyse the collected data. T-tests were conducted to find out if there were any significant differences between the means of the treatment group, and the comparative groups' pre and post-tests results. The results revealed that all of the conjunctive types investigated facilitated the reading comprehension of the fourth year English students in the two Libyan university English departments. However, it was found that some conjunctive types were more facilitative of reading comprehension than others. The pedagogical implications of the findings for the teaching of reading in Libyan universities and beyond are discussed.

تمت إضافة ثلاثة أنواع نباتية للفلورا الليبية هي Ruta montana + Pimpinella cretica + plantago bellardii

تمت إضافة ثلاثة أنواع نباتية للفلورا الليبية هي Lactuca saligna + Sanguisorba minor

The use of computers for handling image data in the healthcare is growing The amount of data produced by modem image generating techniques, such as Computed Tomography (CT) and Magnetic Resonance (MR), is vast. The amount of data might be a problem from a storage point of view or when the data is sent over a network. To overcome these problems data compression techniques adapted to these applications are needed Many classes of images contain some spatial regions which are more important than other regions. Compression methods which are capable of achieving higher reconstruction quality of important parts of the image have been implemented For medical images, only a small portion of the image might be diagnostically useful but the cost of wrong interpretation is high. Algorithms which deliver lossless compression within the regions of interest (ROJ), and lossy compression elsewhere in the image, might be the key to providing efficient and accurate image coding to the medical community. In this thesis both of compression techniques (lossy and lossless) of medical images using the JPEG algorithm (DCT), will be discussed.

    SiC particle reinforced aluminum metal matrix composites (SiCp/Al MMCs) are finding increasing applications in aerospace, automotive and microelectronic industries because of their excellent combination of high specific strength, high specific toughness, low coefficient of expansion and excellent wear resistance. However the addition of totally dissimilar reinforcements into the aluminum matrix and the great different in electrochemical properties between the aluminum metal matrix and the SiC reinforcement deteriorate the corrosion resistance and make the SiCp/6061Al MMC prone to corrosion attacks especially when servicing under electrochemical corrosive environments.

     In this dissertation, laser surface melting, laser surface alloying with Ni-Cr-B alloy powders and laser cladding with Cu-Sn-Pb-Zn bronze powders were utilized to improve the corrosion resistance of P/M SiC particles reinforced metal matrix composite (P/M SiCp/6061Al MMC) by producing corrosion resistant surface layers or metallurgical coatings with rapidly solidified and effectively refined microstructure. The microstructure of the laser surface melted, laser surface alloyed and laser clad corrosion-resistant modified surface layers or coatings were characterized by OM, SEM, XRD as functions of laser surface processing parameters and contents of alloying elements. The hardness distribution along the laser surface modified coatings’ depth direction was tested using microhardness tester. The electrochemical corrosion resistance of laser surface melted, laser surface alloyed and the laser clad SiCp/6061Al MMC were evaluated under direct current anodic polarization electrochemical corrosion test conditions in NaCl water solutions and H₂SO₄ water solutions as functions of laser processing parameters and corrosion test conditions.

Results show that:

(1) During laser surface melting of SiCp/6061Al MMC with high power CO₂ laser beam, the SiC particles are completely dissolved and the laser surface melted layer has a rapidly solidified, homogeneous and refined microstructure consisting of aluminum silicon carbide Al₄SiC₄ aluminum carbide Al₄C₃ as well as crystalline silicon particles evenly distributed in the aluminum matrix. The microstructure as well as size and volume fraction of the newly produced phases in the laser surface melted layer on substrate of SiCp/6061Al MMC depend strongly on the laser processing parameters especially the laser linear energy density. Both the hardness and corrosion resistance of SiCp/6061Al MMC under direct current anodic polarization electrochemical corrosion test conditions in 0.1M NaCl water solutions are slightly enhanced after the laser surface melting treatment.

(2) Laser surface alloying of SiCp/6061Al MMC with Ni-Cr-B alloying powders leads to the production of rapidly solidified corrosion resistant surface layers having homogeneous and refined microstructure. The laser surface alloyed SiCp/6061Al MC is composed of fine rapidly solidified nickel aluminides of Al₃Ni_2, Al₃Ni and AlNi, and chromium borides of d-CrB and Cr₂B evenly distributed in the nickel solid solution. Microstructure of the laser surface alloyed layers is strongly dependent on the laser processing parameters and the chemical composition especially boron content of the Ni-Cr-B alloying powders. The laser surface alloyed SiCp/6061Al MMC has high hardness and excellent corrosion resistance to electrochemical corrosion under direct current anodic polarization electrochemical corrosion test conditions in NaCl water solutions.

(3) By laser cladding of SiCp/6061Al MMC with Cu-6Sn-6Pb-3Zn bronze powders a rapidly solidified homogeneous dendritic bronze coating is produced on substrate of SiCp/6061Al MMC with refined microstructure consisting of fine copper-base solid solution and the interdendritic Cu₃₁Sn₈ intermetallic particles_. The laser clad corrosion resistant coating is bonded to the substrate of SiCp/6061Al MMC, metallurgically. The corrosion resistance of SiCp/6061Al MMC to the electrochemical corrosion under direct current anodic polarization electrochemical test conditions in NaCl water solutions is significantly improved after laser cladding treatment with the bronze powders.

(4) Laser surface melting, laser surface alloying and laser cladding are demonstrated to be among the promising surface modification methods for enhancing corrosion resistance of SiCp/6061Al MMC.

Keywords:  SiCp/Al Metal Matrix Composites, Laser Surface Melting, Laser

Surface Alloying, Laser Cladding, Corrosion Resistance, Microstructure

We have studied the effects of the fine structure of energy levels on the dynamics of the atom and light field. A significant influence is exhibited in the collapse-revival behavior of atomic inversion, the light squeezing, the phase of the field, and the antibunching of a light beam. When the energy difference between the doublet is large (Δ≥20g, where g is the coupling constant), the dynamics of the atomic inversion becomes identical to that of the usual Jaynes-Cummings model, as expected. However, the fine-structure effects on the phase and the antibunching of the light field exist in a much larger range. In particular, for a strong field, the normally ordered variance of the photon-number operator exhibits complicated collapse and revival patterns and the light displays strong antibunching in each revival envelope. Numerical calculations also show that this model does not produce significant squeezing due to the influence of the fine structure. 

In our study of the interaction between few energy level atom and a coherent field, we considered the effect of the excited state's fine structure on the system dynamics. Significant influence exhibited on the collapse-revival behavior of atomic inversion and light squeezing. The numerical calculations show that for weak field, the effects of fine structure may cause disappearance of the collapse and revival phenomena. Our results also show the fine structure has opposite on the light squeezing, this observed on decrease of the amount of squeezing as the average photon number increased.