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- Bakhiet, Salaheldin Farah Attallah, et al.
(författare)
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Understanding the Simber Effect : why is the age-dependent increase in children's cognitive ability smaller in Arab countries than in Britain?
- 2018
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Ingår i: Personality and Individual Differences. - : Elsevier. - 0191-8869 .- 1873-3549. ; 122, s. 38-42
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Tidskriftsartikel (refereegranskat)abstract
- Previous research indicates that the typical increase in IQ during childhood is greater in European countries than in Arab countries. A systematic literature review of age-dependent IQ in Arab countries is conducted, yielding relevant studies for 12 countries that fulfil the inclusion criteria. In almost all of these studies, Arab children exhibit an age-dependent IQ decline relative to Caucasian children, from 5 to about 12 years of age in particular. We term this phenomenon the Simber Effect. We propose two non-exclusive explanations. (1) The Flynn Effect is less intense in Arab countries because of localised differences, including poorer education quality and greater religiosity. (2) Those from Arab countries follow a faster Life History Strategy than Europeans, for environmental and possibly genetic reasons. Either way, the Simber Effect may amount to a Wilson Effect, meaning that the impact of genetic IQ increases with age.
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- Hakami, H., et al.
(författare)
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Gauged sleeve for controlled testing of rock
- 1987
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Ingår i: International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts. - : Elsevier BV. - 0148-9062 .- 1879-2073. ; 24:6, s. 375-378
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Tidskriftsartikel (refereegranskat)abstract
- Electrical resistance strain gages, each 5 cm in length, were embedded at a depth of 1 mm, inside a Cil Monothane sleeve of thickness 2 mm. Cil Monothane A80 is a single component and non-toxic, heat-cure-pour polyurethane elastomer. It has sound elasto-plastic properties when cured. It was supplied by Compounding Ingredients Ltd, England. The strain gages cover about 95% of the circumference of the sleeve. The position of the strain gages corresponds to the mid-height of the rock sample
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- Hakami, Hossein M.
(författare)
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Post-failure behaviour of brittle rock
- 1988
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The study of the post-failure behaviour of brittle rocks in the laboratory needs stiff and servo-controlled testing machines. Yet, the problem is not completely solved unless a suitable feedback signal is created for the servo-loop of the testing machine. A technique has been developed, with the aid of which a suitable feedback signal may be provided for the testing machine. A pair of resistance strain gauges, each 5 an in length were embedded in a 2 mm thick Cil Monothane sleeve. Positioned circumferentially and at the mid-height of the specimen, the long strain gauges provide a reliable feedback signal that makes the controlled loading possible. The technique is particularly suitable for controlled triaxial testing. With the aid of gauged sleeves, we have performed series of controlled uniaxial and triaxial experiments on different brittle rocks. Based on the shape of the experimental curves obtained, post-failure response of the tested rocks has been described, placing much emphasize on the role of the testing machine. Trying to simulate the prevailing state of stress in the Earth's crust, where a shear fracture may propagate, we have carried out nonfixed, controlled confining pressure triaxial experiments. In such an experiment the confining pressure does not remain constant, but rises in opposition to the dilational behaviour of rock sample in both pre and post-peak phases of deformation. Under such circumstance, the pressure medium bears a level of stiffness. Using the experimental results of non-fixed confining pressure experiments, stress drop and energy release rate, pertaining to the shear fracture propagation have been determined. Along with the evaluation of these two fracture parameters, relevant theoretical bases have been outlined. It has been tried to place the estimates of the fracture parameters in their right perspective, by resorting to the previously existing estimates obtained in different ways, by examining the influential aspects of triaxial testing details and through explanations relating the conditions of the propagated shear fracture surfaces to the different levels of the normal stress, acting across the fracture surfaces.
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- Hakami, H., et al.
(författare)
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Shear fracture energy of Stripa granite : Results of controlled triaxial testing
- 1990
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Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 35:4-5, s. 855-865
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Tidskriftsartikel (refereegranskat)abstract
- We have performed controlled triaxial experiments on Stripa granite in a 'nearly stiff' environment. This means that, before the commencement of loading, an initial confining pressure was 'locked' in the pressurizing chamber of the triaxial vessel. During the axial loading of the sample, the confining pressure was unavoidably increased, opposing largely the 'free' expansion of the sample due to overall microcracking. Further increase in confining pressure beyond the peak load resulted from the dilation of the formed shear fracture, during shear displacement. Under triaxial testing condition a reasonable assumption is that the shear fracture in the specimen is a consequence of pure shear (mode II) state of stress prevailing in the sample, in the vicinity of a 'bandlike' zone, from which the shear fracture propagated. Under this assumption and by the relevant fracture mechanics approach incorporating the 'slip weakening' model, shear fracture energy of Stripa granite was estimated. The results were compared with those estimated through controlled triaxial experiments at constant confining pressure, recently reported by other workers. Also, the influence of the testing method described here on the process of laboratory failure of rock in shear is discussed.
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