46 research outputs found
Biomechanical Properties of the Ocular Globe Based on Ex Vivo Testing and Multiscale Numerical Modelling
No full textThe present study is the culmination of quantifying and qualitative experimental and
numerical research representing biomechanical behaviour of the human eye.
A new experimental technique for testing intact eye globes in a form that is representative
of in vivo conditions is developed which is suitable for determining the material
properties of the complete outer ocular tunic.
A test rig has been developed to provide closed-loop control of either applied intraocular
pressure or resulting apical displacement, measurement of displacements across
the external surface of eye globe using high-resolution digital cameras and digital image
correlation software, prevention of rigid-body motion and protection of ocular surface
from environmental drying. The method has been demonstrated on one human and
i
one porcine eye globe, which were cyclically loaded. Finite element models based on
specimen specific tomography, free from rotational symmetry, were used along with
experimental pressure-displacement data in an inverse analysis process to derive the
mechanical properties of tissue in different regions of the eye’s outer tunic.
The test method enabled monitoring of mechanical response to intraocular pressure
variation across the surface of the eye globe. For the two eyes tested, the method
showed a gradual change in the sclera’s stiffness from a maximum at the limbus to
a minimum at the posterior pole, while in the cornea the stiffness was highest at the
centre and lowest in the peripheral zone. Further, for both the sclera and cornea, the
load-displacement behaviour did not vary significantly between loading cycles.
The first methodology capable of mechanically testing intact eye globes, with applied
loads and boundary conditions that closely represent in vivo conditions has been introduced.
The method enables determination of the regional variation in mechanical
behaviour across the ocular surface.
Two numerical models based in continuum mechanics theory have been developed
which represent the 3D anisotropic behaviour of the corneal stroma. Experimental
data has been gathered from a number of previous studies to provide the basis and
calibration parameters for the numerical modelling. The resulting models introduce
numerical representation of collagen fibril density and its related regional variation, interlamellar
cohesion and age-related stiffening in anisotropic and viscoelastic models of
the human cornea. Further, the models incorporate previous modelling developments
including representation of lamellae anisotropy and stiffness of the underlying matrix.
Wide angle X-ray scattering has provided measured data which quantifies relative fibril
anisotropy in the 2D domain. Accurate numerical description of material response to
deformation is essential to providing representative simulations of corneal behaviour.
Representing experimentally obtained 2D anisotropy and regional density variation in
the 3D domain is an essential component of this accuracy. The constitutive model was
incorporated into finite element analyses. Combining with inverse analysis, the model
was calibrated to an extensive experimental database of ex vivo corneal inflation tests
and ex vivo corneal shear tests. This model represented stiffness of the underlying matrix
which is 2−3 orders of magnitude lower than the mechanical response representing
the collagen fibrils in the lamellae. The presented model, along with its age dependent
material coefficients, allows finite element modelling for an individual patient with material
stiffness approximated based on their age. This has great potential to be used in
both daily clinical practice for the planning and optimisation of corrective procedures
and in pre-clinical optimisation of diagnostic procedures.
The second constitutive numerical model based on the continuum mechanics theory
was developed which extended the representation of the model above to include both
age-related viscoelastic stiffening behaviour of the human cornea. Experimental data
gathered from a number of previous studies on 48 ex vivo human cornea (inflation and
shear tests) enabled numerical model calibration. The present study suggests that stiffness
parallel to the lamellae of the cornea approximately doubles from an increase in
strain-rate of 0.5 − 5%/min. While the underlying stromal matrix provides a stiffness
2−3 orders of magnitude lower than the lamellae. The model has been simultaneously
calibrated to within 5% error across three age groups ranging from 50 − 95, multiple
strain-rates and multiple loading scenarios. Age and strain-rate dependent material
coefficients allow finite element modelling for an individual patient with material stiffness
approximated by their age under varying loading scenarios. This present study
addresses a significant gap in numerical representation of the cornea and has great
potential in both daily clinical practice particularly in highly viscoelastic dependent
simulations such as non-contact tomometry.
Related to this thesis, the author has either primarily or secondarily authored the
following related journal articles which are included in this thesis in modified forms:
Whitford C. & Elsheikh A., Corneal Biomechanics Testing Methods, May 2014,
Chinese Journal of Optometry and Ophthalmology Visual Science;
Whitford C., Joda A., Jones S., Bao F., Rama P. & Elsheikh A., Ex-vivo Test-
ing of Intact Eye Globes Under Inflation Conditions to Determine Regional
Variation of Mechanical Stiffness, July 2016, Eye and Vision.
Elsheikh, A., Whitford, C., Hamarashid, R., Kassem, W., Joda, A., B¨uchler, P.,
Stress free configuration of the human eye. Febuary 2013, Medical Engineering
& Physics.
Yu J., Bao F., Feng Y., Whitford C., Ye T., Huang Y., Wang Q., Elsheikh A.,
Assessment of Corneal Biomechanical Behavior Under Posterior and Ante-
rior Pressure. January 2013, Journal of Refractive Surgery.
Whitford C., Studer H., Boote K., Meek K.M. & Elsheikh A., Biomechanical
Model of the Human Cornea: Considering Shear Stiffness and Regional
Variation of Collagen Anisotropy and Density, Feb 2015, Journal of the Mechanical
Behavior of Biomedical Materials.
Elsheikh A., McMonnies C.W., Whitford C. & Boneham G.C., In-vivo study of
Corneal Responses to Increased Intraocular Pressure, 2015, Eye and Vision.
An additional journal publication has been prepared from the content in this present
study:
Whitford C., Movchan N. & Elsheikh A., A Viscoelastic Hyperelastic Anisotropic
Model of the Human Cornea.
Further, two book chapters have been published which related to this thesis:
Whitford C., Studer H., Boote C., Meek K. & Elsheikh A., Modelo Biomecnico de
la Crnea Humana Considerando la Variacin Regional de la Anisotropa, la
Densidad y la Cohesin Interlaminar de las Fibrillas de Colgeno, in Biomec-
nica y Arquitectura Corneal, May 2014.
Geraghty B., Whitford C., Boote C., Akhtar R,. & Elsheikh A., Age-Related
Variation in the Biomechanical and Structural Properties of the Corneo-
Scleral Tunic, in Mechanical Properties of Ageing Soft Tissues, January 2015.
In addition, a number of conference proceedings have been published
Discovery and characterization of a novel KATP channel pharmacochaperone
No full textMy work resulted in the discovery of a novel KATP channel pharmacochaperone, Aekatperone, through AI-driven virtual screening of the drug binding site using the Cryo-EM structure of the KATP channel. Additionally, I functionally characterized the effects of Aekatperone on novel trafficking mutations associated with congenital hyperinsulinism
Projection-based Embedded Discrete Fracture Model (pEDFM) on Corner-point Grid Geometry for Subsurface Flow and Geothermal Modeling
No full textWe develop projection-based embedded discrete fracture model (pEDFM) on corner-point grids (CPG) for fluid flow and heat transfer in subsurface geological formations. The coupling between the flow and heat transfer is fully-implicit, to allow for stable simulations, specially in presence of highly contrasting fractures. We define independent CPG-based mesh for matrix rock and all 3D fractures, which allows for capturing geologically complex geometries. The connectivities between the non-neighbouring cells are described such that a consistent discrete representation of the embedded fractures are developed within the CPG geometry. Numerical rests are developed first to verify the CPG grid implementation compared with the Cartesian structured ones, and then to illustrate the applicability of the pEDFM for field-scale geologically complex reservoirs.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Numerical AnalysisReservoir Engineerin
Technical And Managerial Development For Raising Efficiency In
No full textThe present thesis is a research in the power generation field, specially in Dr.
Sharif Power Station. The author in the present research has got use of his long
experience in this field in the Sudan as well as abroad, where ultimately he dared to
cope with modern sophisticated technologies in power generation.
The author targeted from this thesis to reduce the generated power cost, and in
the same time, to raise the efficiency of the generating units to higher levels – through
practicing modern sophisticated technology that he aimed to introduce and transfer to
the Sudan.
As a product of a large number of processes, the electrical power generation
represents about 30% of the initial energy of the primary fuel used. This is a very low
figure, and partly explains the high cost of electricity compared with other sources of
energy
The electrical power generation is a result of processes of energy conversion.
The chemical energy of fuels is converted to heat energy in the furnace or combustion
chamber, which in its turn is converted to mechanical energy in the prime mover (e.g.
gas turbine, steam turbine or diesel engine) which rotates the rotor of the generator,
where it is converted to electrical power. During this process a large number of
energy is dissipated as heat in the cooling water and in the exhaust gases, as we will
see later.
In the early 1970s an oil crisis took place due to the Middle East war of 1973.
The prices of oil shot up from US 30 per barrel. Due to
high cost of fuel, which represents at present 70% of the total electrical power
generation cost, the energy conversion in power generation process has become more
essential for efficient operations. The modern technology in power generation has led
to efficiency improvement, and hence has led to running cost saving, e.g. using
energy recovery methods leads to financial gain by reducing the cost of electricity
production, and mainly by reducing fuel consumption. Through history the thermal
efficiency has increased from 5% for the old steam engine to 30% for the gas turbine
and to 33% for the steam turbine and finally to 52.5% for the combined cycle. The gas
turbine and steam turbine efficiencies can be more raised by utilizing sophisticated
technologies, e.g. air inlet chillers for gas turbines, and steam reheating for steam
turbines, as we see later.
The electrical energy consumed by a nation is directly proportional to its
standard of living or its Gross National Product. For example, the under-developed
countries use about 0.5 kW per person, compared with a rate in the developed world
of between 5 and 10 kW per person (ref. 5).
The subject matter of the authors M.Sc also dealt with Dr. Sharif Power Station,
but from different aspects other than what will appear in the present Ph.D thesis. It is
beneficial to show briefly herewith, the aspects of the M.Sc thesis in order to create a
general concept to the reader about Dr. Sharif power station progress
Wireless decode-and-forward relay channels: time allocation strategies for cooperation and optimum operation
No full textRelay channels have been in use for decades as an effective means to tackle some of the challenges facing wireless transmission. Recent studies considered re-employing the relay channel to serve modern wireless systems. Material offered in this book was originally presented by the author as a thesis for the degree of Ph.D. to University College London. In this book two-hop and multi-hop D&F relay channels with half-duplex constraint on relays are studied. Channel's mutual information and outage probability are investigated for AWGN and Rayleigh fading channels. Optimum routing and optimum time allocation policies are also considered. In addition, a scheme is presented for user cooperation. Material offered in this book is useful to further investigate the visibility of relaying in wireless transmission and to develop user cooperative schemes. This book can be of use to communication and information theoretic researchers investigating relay channels, routing in wireless networks, cross-layer design, ad hoc networks, user cooperative communications and cognitive systems
Diya of the Miseria Tribe after the Abolition of Native Administration
No full textThis paper had been presented for promotion at the University of Khartoum. To get the full text please contact the other at [email protected]• Diya (blood money) is normally paid in murder cases to the family of the victim and Miseria calls it ‘mihaya al-dam’ which means in Arabic (the blood eraser). It is paid in all cases irrespective whether the accused is convicted or acquitted. If accepted no revenge shall take place and it hence acts as a deterrence mechanism for further violence. Before diya is agreed upon and paid tribal conciliation ‘sulh’ is required between the family of the accused and the family of the victims. The author argues that conciliation is normally accomplished through Agaweed (credible conciliators) normally agreed upon by both parties to the conflict.
• Miseria have two types of diya: (a) diya of ‘Saf’ and; (b)diya of ‘Badna’. However, the mount of diya varies and depends on the gravity of the crime. For example, murder in the context of tribal fight or intentional murder requires payment of 60 cows if the victim is a male and 30 cows if the victim is a female. In cases of manslaughter or unintentional murder diya is 30 cows for a male victim and 15 cows for a female victim. Other types of compensation fall short of diya are applied in cases of grievous bodily harm (GBH), deliberate limb amputation or loss of body parts (i.e. eye, nose, ear, teeth etc..) 30 cows is payable if the aggrieved person is a male and 15 cows if a female.
• When diya is paid to members of the family of the victim, they are prohibited to take any sort of revenge otherwise social sanctions will be imposed on them and the family will regarded as socially outcast and no longer belongs to the tribe. The author argues that the system of diya as practiced by the Meseria tribe has assumed a vital role in resolving social and communal disputes particularly in the absence of the Police in the tribal areas to maintain law and order.
• The author then highlights obstacles facing the implementation of the diya system after its abolition. He argues that in the past Nazir of the tribe, aided by Omda, is a key figure in the administration and distribution of the diya system and his role as a presiding Judge of Native Court as regulated by the Administration of Courts Act. This Act empowers or entrusts native courts to apply customary law when adjudicating cases. However, after the abolition of native administration, the role of the tribal justice was weakened and undermined. The author then has raised serious questions such as whether government local councils will be able to replace it, particularly the Local Popular Government Act entrusted the executive councils to engage in arbitration and tribal conciliation ( section 5 (10)
Promising and worth-to-try future directions for advancing state-of-the-art surrogates methods of agent-based models in social and health computational sciences
No full textThe execution and runtime performance of model-based analysis tools for
realistic large-scale ABMs (Agent-Based Models) can be excessively long. This
due to the computational demand exponentially proportional to the model size
(e.g. Population size) and the number of model parameters. Even the runtime of
a single simulation of a realistic ABM may demand huge computational resources
when attempting to employ realistic population size. The main aim of this
ad-hoc brief report is to highlight some of surrogate models that were adequate
and computationally less demanding for nonlinear dynamical models in various
modeling application areas.To the author knowledge, these methods have been
not, at least extensively, employed for ABMs within the field of (SHCS) Social
Health Computational Sciences, yet. Thus, they might be, but not necessarily,
useful in progressing state of the art for establishing surrogate models for
ABMs in the field of SHCS.Comment: 4 page
Dynamic duo: Kir6 and SUR in KATP channel structure and function
No full textKATP channels are ligand-gated potassium channels that couple cellular energetics with membrane potential to regulate cell activity. Each channel is an eight subunit complex comprising four central pore-forming Kir6 inward rectifier potassium channel subunits surrounded by four regulatory subunits known as the sulfonylurea receptor, SUR, which confer homeostatic metabolic control of KATP gating. SUR is an ATP binding cassette (ABC) protein family homolog that lacks membrane transport activity but is essential for KATP expression and function. For more than four decades, understanding the structure-function relationship of Kir6 and SUR has remained a central objective of clinical significance. Here, we review progress in correlating the wealth of functional data in the literature with recent KATP cryoEM structures
Recommended from our members
The international law on the right of the child to survival and development /
No full textThis comprehensive and in-depth study on the understanding and interpretation of the child's right to survival and development provides a compact assessment of article 6(2) of the Convention on the Rights of the Child (CRC) in light of its drafting history, the reports of the Committee on the Rights of the Child and other relevant sources appropriate to the discipline of international human rights law. The author analyses the travaux preparatoires of the CRC and the academic work of some of its drafters. The book includes an interview with one of the drafters and explores the literature of the Committee on the Rights of the Child with respect to article 6(2) and how its understanding and interpretations of this article have developed over time. It examines the weaknesses and strengths in relation to the observations it has made and explores the legal effects of the Committee's classifications and makes suggestions for others as well. Importantly, the book also discusses the relationship between the right of the child to survival and development and his/her dignity. It provides an understanding of the child's physical, mental, spiritual, moral and cognitive development in the context of his/her right to survival and development. In addition, the author discusses various State obligations aiming at the enjoyment of the right to survival and development and also touches on global warming and its relationship with the right of the child to survival and development. The reader will gain an understanding of different approaches to the interpretation of human rights treaties in general, and attitudes towards the assessment of the work of the Committee on the Rights of the Child. He will also learn about the connection between the right to development and the economic and social rights of the child on the one hand, and the right of the child to survival and development on the other hand. Moreover, the book introduces the concept of comprehensiveness and individuality of the right of the child to survival and development and fundamentally argues that there is still more to add to the understanding and interpretations of article 6(2) of the CRC
Development of duststorm attenuation model for microwave links
No full textDuststorms are significant meteorological phenomenon occur for a significant percentage of time in
arid and semi arid areas especially at African Sahara and Middle East. Measurements at existing
microwave links show that the duststorms can potentially result in serious attenuation in signal level
especially at Ku band and higher frequencies with direct impact on telecommunications system
performance. Very limited research has been done to predict the attenuation even the scarcity of measured
data forces the researcher to work for the duststorm prediction modeling
