2,321 research outputs found
Cytokine Expression In Heart Tissue of Caspase 1 Knock Out, Community-Acquired MRSA Sepsis Infected Mice
No full textThis research was supported by the Undergraduate Research Opportunities Program (UROP).Elsheikh, Mohamed. (2014). Cytokine Expression In Heart Tissue of Caspase 1 Knock Out, Community-Acquired MRSA Sepsis Infected Mice. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/164624
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
Trimetallic Pd-based electrocatalysts for alkaline ethanol electrooxidation
No full textResearch data (physiochemical and electrochemical) of trimetallic samples based on Pd for ethanol oxidation
GIS Topographic Analysis Applied to Unit Hydrograph Models: Sensitivity to DEM Resolution and Threshold Area
No full textFormal specification terminology for demographic agent-based models of fixed-step single-clocked simulations
No full textThis document presents adequate formal terminology for the mathematical
specification of a subset of Agent Based Models (ABMs) in the field of
Demography. The simulation of the targeted ABMs follows a fixedstep
single-clocked pattern. The proposed terminology further improves the model
understanding and can act as a stand-alone protocol for the specification and
optionally the documentation of a significant set of (demographic) ABMs.
Nevertheless, it is imaginable the this terminology can serve as an inspiring
basis for further improvement to the largely-informal widely-used model
documentation and communication O.D.D. protocol [Grimm and et al., 2020,
Amouroux et al., 2010] to reduce many sources of ambiguity which hinder model
replications by other modelers. A published demographic model documentation,
largely simplified version of the Lone Parent Model [Gostoli and Silverman,
2020] is separately published in [Elsheikh, 2023c] as illustration for the
formal terminology presented here. The model was implemented in the Julia
language [Elsheikh, 2023b] based on the Agents.jl julia package [Datseris et
al., 2022].Comment: Major improvements. arXiv admin note: substantial text overlap with
arXiv:2307.1654
Verso una restaurazione silenziosa? Metamorfosi valoriali nei percorsi biografici degli adulti giovani in Italia.
No full textIl saggio analizza - attraverso i risultati qualitativi di una indagine PRIN - gli orientamenti valoriali degli adulti-giovani italiani
Biostratigraphy of the subsurface Oligocene sediments in the North Western Desert, Egypt
No full textHassan M.Y, Salloum G., Boukhary M.A., Elsheikh H. Biostratigraphy of the subsurface Oligocene sediments in the North Western Desert, Egypt. In: Géologie Méditerranéenne. Tome 11, numéro 1-2, 1984. C.A.M. IXe colloque africain de micropaléontologie. Paris, Museum d'Histoire Naturelle, du 3 au 6 octobre 1983. p. 241
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