488 research outputs found
High frequency of the D allele of the angiotensin-converting enzyme gene in Arabic populations
<p>Abstract</p> <p>Background</p> <p>The angiotensin-converting enzyme (ACE) gene in humans has an insertion-deletion (I/D) polymorphic state in intron 16 on chromosome 17q23. This polymorphism has been widely investigated in different populations due to its association with the renin-angiotensin system. However, similar studies for Arab populations are limited. This study addresses the distribution of the ACE gene polymorphism in three Arab populations (Egyptians, Jordanians and Syrians).</p> <p>Findings</p> <p>The polymorphisms of ACE gene were investigated using polymerase chain reaction for detection of an I/D mutation. The results showed a high frequency of the ACE <it>D </it>allele among the three Arab populations, Egyptians (0.67), Jordanians (0.66) and Syrians (0.60), which is similar to those obtained from previous studies for Arab populations.</p> <p>Conclusion</p> <p>The relationship between ACE alleles and disease in these three Arab populations is still not known, but the present results clearly suggest that geographic origin should be carefully considered in the increasing number of studies on the association between ACE alleles and disease etiology. This study adds to the data showing the wide variation in the distribution of the ACE alleles in different populations and highlights that great care needs to be taken when interpreting clinical data on the association of the ACE alleles with different diseases.</p
Distribution of the HIV resistance CCR5-Δ32 allele among Egyptians and Syrians
A mutant allele of the β-chemokine receptor gene CCR5 bearing a 32-basepair (bp) deletion that prevents cell invasion by the primary transmitting strain of HIV-1 has recently been characterized. Individuals homozygous for the mutation are resistant to infection, even after repeated high-risk exposure, but this resistance appears not absolute, as isolated cases of HIV-positive deletion homozygotes are emerging. The consequence of the heterozygous state is not clear, but it may delay the progression to AIDS in infected individuals. In order to evaluate the frequency distribution of CCR5-Δ32 polymorphism among Egyptians, a total of 200 individuals (154 from Ismailia and 46 from Sinai) were tested. Only two heterozygous individuals from Ismailia carried the CCR5-Δ32 allele (0.6%), and no homozygous (Δ32/Δ32) individuals were detected among the tested samples. The presence of the CCR5-Δ32 allele among Egyptians may be attributed to the admixture with people of European descent. Thus we conclude that the protective deletion CCR5-Δ32 is largely absent in the Egyptian population. © 2006 Elsevier B.V. All rights reserved
Transient behaviour of a group of induction motors
The non-linear differential equations describing the
transient behaviour of a group of induction motors are developed
from the equations for a single machine. These equations enable
the behaviour of each machine in the group to be investigated,
either when the complete group is connected to a stiff supply
or when the supply is weak and the machine behaviour is interactive. A numerical solution of the equations using a digital
computer is used to predict the transient currents and torques
of a 0.75 kW/1.5 kW motor group and of a 0.75 kW/1.5 kW/2.25 kW
motor group, and the results obtained are compared with experimentally
obtained results. [Continues.
New approach to steady-state and dynamic nonlinear modelling of laminated salient-pole alternator systems
A complete mathematical model for a generator system consisting of an
isolated laminated salient-pole alternator, exciter and prime mover is
presented, with emphasis on the inherent electromagnetic nonlinearities
in the alternator and its exciter.
An equivalent circuit, representing the rotor circuits accurately, has
been adopted to model the al ternator in the dqo reference frame. A
computer program has been developed to calculate the unsaturated
parameters of the model using the machine design data.
A new approach has been developed to account for the electromagnetic
saturation effects on the model reactances. Consequently new
saturation factors, based on the machine design particulars have been
deri ved. The advantages of these saturation factors, compared with
conventional factors, are that both mutual saturation effects between
the main and leakage fluxes, and between the direct- and quadratureaxis
fluxes are considered.
A mathematical nonlinear model, utilising the new saturation factors,
is presented for a system containing an isolated laminated salientpole
alternator and a direct thyristor static exciter. A digital
computer program has been developed to simulate the system. The
predicted results, for some steady state and dynamic candi tions, showgood
agreement with test results and clear improvement over those
obtained if saturation is either neglected or considered using the
conventional saturation factors.
At high saturation levels, the conventional method of calculating the
machine transformer voltages, using static saturated reactances, gives
unacceptable errors. A method for calculating these voltages
correctly, in models utilising the currents as state space variables,
is presented using new derived dynamic saturated reactances. This
dynamic reactance concept is presented in a generalised form so that it can be applied to any machine with different saturation factors.
The previous mathematical model of the alternator system has been
modified according to the dynamic reactance concept, and the computer
program has been developed accordingly. The predicted results confirm
the need to apply this concept especially to dynamic conditions
characterised by high saturation levels.
To extend the analysis to a wider range of loading conditions, the
alternator has been modelled in the abc reference frame. The
unsaturated, static and dynamic saturated reactances of the machine in
this reference frame have been obtained using conventional dqo-abc
transformation techniques. Starting from the fundamental machine
relations, a new set of equations, in the phase reference frame, has
been derived employing the new dynamic reactance concept.
A comprehensive system consisting of an isolated laminated salientpole
alternator, brushless exciter, thyristor divert automatic voltage
regulator and a diesel prime mover has been studied. Both the
alternator and the exciter have been modelled in the abc frame to
comply with the nature of rectifier loading associated with the
exci ter. A complete steady state and dynamic mathematical model is
presented where the t~r technique has been applied to the dynamic
variable topology of the system electrical circuits. The model
presented covers all the possible modes of operation associated with
the exciter rotating bridge rectifier circuit. A digital computer
program has been developed to simUlate the system. The predicted
results obtained using the new set of saturation factors in
conjunction with the dynamic reactance concept show good agreement
with the test results.
The study presented confirms the validity of the mathematical models
developed for the alternator systems. Also, it supports the metlxxi by
which the electromagnetic nonlinearity has been accounted for
Synthesis and characterization of metallic materials for membrane technology
AbstractPowder of metallic materials composed of Fe, Ni was proposed for membrane applications such as microfiltration devices. The powder was synthesized using thermal route of simultaneously sintering–reduction techniques. The resulting powder has specific porous structure and can be deposited on steel substrate. The formed phases were identified by X-ray phase analysis. The produced powder was characterized by reflected light microscope and scanning electron microscope along with energy-dispersive X-ray spectroscopy (EDX). The reduction behavior of metal oxides was followed up by thermogravimetric techniques. The kinetics data obtained from reduction process were used to elucidate the reduction mechanism under isothermal condition. The microstructure changes accompanying sintering–reduction processes were investigated under different experimental parameters such as temperature, holding time and gas composition. The results show that pure Fe0.64Ni0.36 with relatively high porosity can be fabricated via reduction route. The presence of NiO plays a significant role in the reduction of iron oxide as well as in the structural changes accompanying the reduction processes. The particle size distribution of the produced metallic materials is being controlled under the different operation conditions to get a homogenous porous metallic structure with well defined porosity. The main advantage of using porous ferroalloy materials is their narrow size distribution leading to a well defined pore size distribution after sintering and reduction
A new Solar Desalination System Design and Heat Recovery
The work evaluates experimentally technique toimprove fresh water production by careful energy recovery inthe vapour condensation processes; the recovered heat in turnon drives additional evaporation and preheats the feedwater. Apilot plant is designed and constructed in an arid area with 2 m2solar evaporation collector area to evaluate the process. Thisunit is tested on cold and hot days. The effect of mainparameters on fresh water production of the unit is studied. Theexperimental results show that, the production rate andefficiency of the system are strongly affected by solar radiationand level water in solar evaporation collector. Within the studiedranges, the maximum productivity reached to 16.1 kg/ m2day atTvap,av = 87.6 oC , solar radiation 842 W/m2 and level water 1.912kg. According to these results, fresher water production of thepresent system is higher than that solar still desalination systemin the previous studies
Allele frequencies of the human platelet antigen-1 in the Egyptian population
<p>Abstract</p> <p>Background</p> <p>The human platelet alloantigen system HPA-1 in the Egyptian population was examined by polymerase chain reaction using sequence-specific primers (PCR-SSP). The objectives of this study were to evaluate the allele frequency of HPA-1a and -1b in healthy Egyptian individuals and compare these with the international literature. Human platelet antigen (HPA) systems are associated with alloimmunization and organ transplantation rejection as well as the development of cardiovascular disease. Of the various HPA systems, HPA-1 specifically has been considered to be the most important antigenic system implicated in the Caucasian population. No study has yet examined this system in the Egyptian populations, however. We therefore investigated the allele frequency of the HPA-1 system in the Egyptian population.</p> <p>Findings</p> <p>To determine the allele frequency of the HPA-1a and -1b, we tested genomic DNAs from 206 healthy, unrelated Egyptian individuals using PCR-SSP. Our results showed that the 1a/1a genotype was the most predominant (59.22%) followed by 1a/1b (34.95%) and 1b/1b (5.83%) with allele frequencies for 1a and 1b of 0.77 and 0.23, respectively, in the population.</p> <p>Conclusion</p> <p>As compared with other geographic groups, a relatively high allele frequency of the HPA-1b in the Egyptian population may indicate a higher risk of alloimmunization. This study is the first to investigate the allele frequency of the HPA-1 system in the Egyptian population and serves as an outline for future clinical research associated with platelet disorders in this group.</p
SINEs of a nearly perfect character
Mobile elements have been recognized as powerful tools for phylogenetic and population-level analyses. However, issues regarding potential sources of homoplasy and other misleading events have been raised. We have collected available data for all phylogenetic and population level studies of primates utilizing Alu insertion data and examined them for potentially homoplasious and other misleading events. Very low levels of each potential confounding factor in a phylogenetic or population analysis (i.e., lineage sorting, parallel insertions, and precise excision) were found. Although taxa known to be subject to high levels of these types of events may indeed be subject to problems when using SINE analysis, we propose that most taxa will respond as the order Primates has-by the resolution of several long-standing problems observed using sequence-based methods. © 2006 Society of Systematic Biologists
Deep learning can improve early skin cancer detection
Skin cancer is the most common form of cancer affecting humans. Melanoma is the most dangerous type of skin cancer; and early diagnosis is extremely vital in curing the disease. So far, the human knowledge in this field is very limited, thus, developing a mechanism capable of identifying the disease early on can save lives, reduce intervention and cut unnecessary costs. In this paper, the researchers developed a new learning technique to classify skin lesions, with the purpose of observing and identifying the presence of melanoma. This new technique is based on a convolutional neural network solution with multiple configurations; where the researchers employed an International Skin Imaging Collaboration (ISIC) dataset. Optimal results are achieved through a convolutional neural network composed of 14 layers. This proposed system can successfully and reliably predict the correct classification of dermoscopic lesions with 97.78% accuracy
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