Oscillatory natural convection of water-glycerin mixture in a tall rectangular cavity: Transition to the chaos

This paper presents results of a numerical investigation involving bifurcation sequence leading to chaos in natural convection inside a vertically tall rectangular cavity having an aspect ratio equal to 15 and a Prandtl number equal to 125, corresponding to water-glycerin mixture. The flow is characterized by a vertical stratification of the temperature field for Grashof numbers greater than or equal to 200 that is outside the conduction regime and it is stationary monocellular up to a critical value Gr_c = 2800 where a periodic oscillatory regime appears. As Grashof number is increased, a transition from a steady periodic bicellular flow to an oscillatory multicellular flow, with 2 main central cells and 2 secondary cells, occurs. The regime remains periodic until Gr = 3100 where there is a first appearance of the chaotic regime which extends over a narrow interval of the Grashof number delimited by Gr = 3200.     

Sedimentology, mineralogical evaluation and industrial applications of the Pleistocene Al-Yamaniyyah clay deposits, near 'Agaba, Southern Jordan

Three clay horizons of different physical properties and different thicknesses were recognized in the study area. These horizons are intercalating with silt, sand and segregated salt crystals. The sediments were deposited during the Pleistocene in a nearshore environment and separated from sea by old reef terraces. Two alluvial terraces were found. The Al-Yamaniyyah clayey deposits contain considerable amounts of clay minerals, namely for the greater part smectite, vermiculite and kaolinite. Illite/mica, chlorite and goethite were present as minor constituents. The studied clay materials have indicated to be suitable for potteries and heavy ceramic products.     

Engineering prediction of soot concentration in the primary zone of the gas turbine combustor

The trends towards using heavier fuel oil in the gas turbine engine will increase the soot formation rate in the primary zone, which increases flame radiation and impairs flame tube durability. Therefore, devising a method to determine quantitiatively the soot concentration is of paramount importance, as it helps in combustor design and pollution control. The method proposed adopts the Schmidt technique for radiation measurements together with soot formation and oxidation models. The soot concentration predictions from this method have been compared with those calculated from measurements of radiation in the primary zone and exhaust smoke at the combustor exit. Favourable comparison was achieved, especially under full load conditions.     

Integrated laser/phototransistor optoelectronic switching device by organometallic vapour phase epitaxy

Computer-controlled organometallic vapour phase epitaxy has been used to optimise AlGaAs/GaAs quantum well lasers and bipolar phototransistors separately. Here the two structures are combined In a single growth to realise a high-performance two-terminal optoelectronic switch. DC I/V characteristics are typical of an npnp structure; however, the feedback mechanism is optical rather than electronic. Threshold switching voltage is determined by the optical input in the range 1.3?23 V and sensitivity is 2.5 V/?W. Output is both optical (laser) and electrical current. Gain is provided by the phototransistor and optical feedback and exceeds 104. Switching speed is determined to be less than 1 ns.     

THERMAL CRACKING (VISBREAKING) STUDIES ON QUYARAH RESIDUES

Visbreaking experiments on Quyarah long residue have been conducted in a continuous laboratory-scale visbreaking unit at different temperatures from 435^°C to 490^°C at one pressure (7 bar) and constant residence time (90 sec.). Data on yield of different products have been reported. Further, thermal cracking experiments on visbroken vacuum gas oil under relatively high severity were also given in the same unit in order to reduce the residual yield of Quyarah crude.     

Modelling of stress-strain behaviour of plain concrete using a plasticity framework

A constitutive model based on the theory of plasticity is proposed to characterize the stress-strain behaviour of plain concrete under three-dimensional loading. The model incorporates the third stress invariant in the formulation that allows variation of shear strength with the orientation of stress paths on the octahedral plane. Also, it allows variation of the shape of the yield surface on the octahedral plane with confining pressure. An algorithm is developed and used to evaluate the associated material constants in the optimum manner. Stress-strain responses are back-predicted for a number of stress paths using the proposed model and the results are compared with experimental observations. Overall, good agreement between the experimental data and predicted response is obtained.     

Observation of high-frequency high-field instability inGaAs/InGaAs/AlGaAs DH-MODFETs at K band

The authors report the observation of high-field instability at room temperature with oscillation frequency as high as 24 GHz in GaAs/InGaAs/AlGaAs double-heterojunction-MODFETs (DH-MODFETs) of 1.2 μm gate length. Negative drain differential resistance was also observed in these devices under various forward gate biases. The nature of this instability is believed to be caused by the efficient removal of the real-space transferred hot two-dimensional electrons in the AlGaAs layer through the forward-biased Schottky gate. A tuned oscillator, with a fundamental oscillation frequency as high as 19.68 GHz, has also been demonstrated at a gate bias of 1.3 V     

PERFORMANCE OF AUTOMOTIVE RECIPROCATING ENGINES WITH DIFFERENT FUELS

A single cylinder reciprocating engine test rig was used to measure power output, specific fuel consumption, exhaust gas temperature and energy balance for different speeds, air-fuel ratios and compression ratios with gasoline and diesel oil as fuels. Comparison of the results for the same compression ratios and range of running speeds shows that gasoline produces higher power and exhaust temperatures than diesel oil. However, it produced less thermal efficiency up to 2000 rpm speed. The energy balance shows slightly higher percentage in power and exhaust energy but markedly less radiation energy to the atmosphere with diesel oil.