Stem cell mechanobiology

Stem cells are undifferentiated cells that are capable of proliferation, self-maintenance and differentiation towards specific cell phenotypes. These processes are controlled by a variety of cues including physicochemical factors associated with the specific mechanical environment in which the cells reside. The control of stem cell biology through mechanical factors remains poorly understood and is the focus of the developing field of mechanobiology. This review provides an insight into the current knowledge of the role of mechanical forces in the induction of differentiation of stem cells. While the details associated with individual studies are complex and typically associated with the stem cell type studied and model system adopted, certain key themes emerge. First, the differentiation process affects the mechanical properties of the cells and of specific subcellular components. Secondly, that stem cells are able to detect and respond to alterations in the stiffness of their surrounding microenvironment via induction of lineage-specific differentiation. Finally, the application of external mechanical forces to stem cells, transduced through a variety of mechanisms, can initiate and drive differentiation processes. The coalescence of these three key concepts permit the introduction of a new theory for the maintenance of stem cells and alternatively their differentiation via the concept of a stem cell 'mechano-niche', defined as a specific combination of cell mechanical properties, extracellular matrix stiffness and external mechanical cues conducive to the maintenance of the stem cell population.<br/

Temperature measurements behind reflected shock waves in air

A radiometric method for the measurement of gas temperature in self-absorbing gases has been applied in the study of shock tube generated flows. This method involves making two absolute intensity measurements at identical wavelengths, but for two different pathlengths in the same gas sample. Experimental results are presented for reflected shock waves in air at conditions corresponding to incident shock velocities from 7 to 10 km/s and an initial driven tube pressure of 1 torr. These results indicate that, with this technique, temperature measurements with an accuracy of + or - 5 percent can be carried out. The results also suggest certain facility related problems

Electronic structure of copper intercalated transition metal dichalcogenides: First-principles calculations

We report first principles calculations, within density functional theory, of copper intercalated titanium diselenides, CuxTiSe2, for values of x ranging from 0 to 0.11. The effect of intercalation on the energy bands and densities of states of the host material is studied in order to better understand the cause of the superconductivity that was recently observed in these structures. We find that charge transfer from the copper atoms to the metal dichalcogenide host layers causes a gradual reduction in the number of holes in the otherwise semi-metallic pristine TiSe2, thus suppressing the charge density wave transition at low temperatures, and a corresponding increase in the density of states at the Fermi level. These effects are probably what drive the superconducting transition in the intercalated systems.Comment: 8 pages, 6 figure

Corporate governance and voluntary disclosure in Kuwait

“A thesis submitted to the University of Bedfordshire, in partial fulfilment of the requirements for the degree of Doctor of Philosophy”.Failure of high profile companies such as Enron, World.com had initiated a call for an investigation to analyse the reason for such radical consequence to prevent further similar financial crises. One of the common factors identified by the researchers is the poor disclosure, transparency and Corporate Governance (CG) mechanisms. Similar to the UK, the compliance towards CG codes are voluntary for the majority of the countries around the globe including Kuwait. CG codes aimed to improve the governance of a company including transparency. Thus, voluntary disclosure had been examined by numerous academics to emphasise the importance of accountability, transparency that in turn increase the confidence of investors and creditors in the financial markets of emerging economies. This thesis is based on Kuwait, as it is a resource rich country and attracts foreign investments. The Central Bank of Kuwait (CBK) issued instructions for CG mechanism especially to the financial sector in 2004. From the research in hand, there was no longitudinal study in Kuwait concerning the impact of GC mechanism to voluntary disclosure. The sample in this thesis consists of 155 Kuwaiti listed companies from 2007 to 2010, 620 firm-year observations. A self-constructed index was developed to evaluate the level of voluntary disclosure and how it developed over time. Both univariate analysis and multivariate analysis were used. Most of the thesis results were consistent with previous studies; there was a gradual increase in the level of voluntary disclosure and its categories over the observed period. All CG mechanisms findings revealed significant associations with voluntary disclosure, except board size and role duality, have a negative significant association. Ownership structure indicates insignificant association with voluntary disclosure. Firm characteristics have a significant positive association with voluntary disclosure, except profitability, has a significant negative association, while gearing is found an insignificant association. Furthermore, the level of voluntary disclosure in the financial sector is higher than the non-financial sector. The contributions to knowledge in this thesis are; 1) It is the first empirical longitudinal study in Kuwait concerning voluntary disclosure, and its relationship with GC mechanism, ownership structure and firm characteristics, as far as the researcher is aware. 2) It provided evidence of the importance of CG to enhancing the level of voluntary disclosure in Kuwait business environment, especially that the level of voluntary disclosure in the financial sector is higher than the non-financial sector. 3) Employed many quantitative methods, such as OSL regression, Normal score, GLS regression, Tobit regression and Quantile regression (divided into 25%, 50% and 75%). 4) A self-constructed index, which was developed in this thesis, could be suitable for other Arab Gulf countries that are similar in the business environment and experiencing the same economic changes. 5) Provides evidence of the possibility of employing the disclosure theories derived from developed countries in emerging countries. 6) It is possible to generalise the results of the disclosure index to other companies not investigated in this thesis. Moreover, this thesis implies that the legislative and regulatory authorities, in particular, the capital markets authority Kuwaiti, need to increase efforts to enhance the role of corporate governance practices in Kuwaiti listed companie

Surface-enhanced optical third-harmonic generation in Ag island films

Surface-enhanced optical third-harmonic generation (THG) is observed in silver island films. The THG intensity from Ag nanoparticles is enhanced by more than two orders of magnitude with respect to the THG intensity from a smooth and homogeneous silver surface. This enhancement is attributed to local plasmon excitation and resonance of the local field at the third-harmonic wavelength. The diffuse and depolarized component of the enhanced THG is associated with the third-order hyper-Rayleigh scattering in a 2-D random array of silver nanoparticles.Comment: 4 pages, 2 figure

Treatment of hyper-granulated limb wounds in horses

This study was performed to investigate the different methods of treating hyper granulation tissue on experimentally induced wounds in equine limbs. Wounds were induced by removal of a skin patch and subcutaneous tissue for about 5-7 cm width and 6-8 cm in length from the dorsal and lateral aspect of the fore and hind limbs below the carpal and tarsal joints. The wounds were left open without treatment and the animals were trained 2-2.5 hours every day for about 3-5 weeks until hyper granulation tissue was developed. The schedule for the treatment of hyper granulation was divided into five groups each contained eight wounds of hyper granulation tissue; each main group was divided into two subgroups. The subgroups of first, second, third, fourth and fifth groups were treated by the following schedules: bandage alone; copper sulphate ointment 10%; silver nitrate ointment 2%; red mercury ointment 11%; and laser therapy (at a total dose of 9.72 Joule / cm2) respectively. While the second subgroups were treated by surgical resection of the hyper granulation tissue, followed by the same treatments applied on the first subgroup. The bandage for all experimental groups was changed every 48 hours until healing was occurred. The clinical and histological observation of the first group revealed that the healing take long period comparing with other groups. The mean of wound healing were 65 days in non surgical removal of hyper granulation tissue subgroup, while 57 days in surgical removed of hyper granulation tissue subgroup. The results of the second, third, fourth groups revealed that the caustic material especially red mercury has a role in healing processes through depressing the hyper granulation tissue. The mean of wound healing of the second group was 42.25 days in non surgical removal of hyper granulation tissue subgroup while 37.25 days in surgically removed hyper granulation tissue subgroup. In the third group the mean of wound healing was 45.75 days in non surgical removal of hyper granulation tissue subgroup while 44.75 days in surgically removed hyper granulation tissue subgroup. While in the fourth group the mean of wound healing was 39 days in non surgical removal of hyper granulation tissue subgroup while 36 days in surgically removed hyper granulation tissue subgroup. In the fifth group the clinical and histological observation revealed that the using of laser lead to reduce the period for wound healing significantly comparing with other groups. The mean of wound healing was 25 days in non surgical removal of hyper granulation tissue subgroup while 20 days in surgically removed hyper granulation tissue subgroup, so that the laser was the best in this study and the using of surgical removal is better than of non surgical removal

A UPC++ Actor Library and Its Evaluation on a Shallow Water Proxy Application

Programmability is one of the key challenges of Exascale Computing. Using the actor model for distributed computations may be one solution. The actor model separates computation from communication while still enabling their over-lap. Each actor possesses specified communication endpoints to publish and receive information. Computations are undertaken based on the data available on these channels. We present a library that implements this programming model using UPC++, a PGAS library, and evaluate three different parallelization strategies, one based on rank-sequential execution, one based on multiple threads in a rank, and one based on OpenMP tasks. In an evaluation of our library using shallow water proxy applications, our solution compares favorably against an earlier implementation based on X10, and a BSP-based approach