Cell-walls of growing plant cells

The plant primary cell wall is a three-dimensional interwoven network of cellulose microfibrils, cross-linked by xyloglucan and dispersed in a pectin matrix. It has been suggested that in the wall of growing plant cells, xyloglucan is bound to the rigid cellulose microfibrils by hydrogen bonds and holds the microfibrils together by forming molecular tethers, which is referred to as the ‘sticky network’ model. Plant growth occurs when these tethers are peeled from the microfibrils by expansins or broken by glycosidases or transglycosylases. A number of researchers have presented theoretical difficulties and observations inconsistent with this model and a new hypothesis has been proposed, claiming that the cellulose – xyloglucan cross-links may act as ‘scaffolds’ holding the microfibrils apart. Analogies with synthetic polymers suggests that the spacing between the cellulose microfibrils may be an important determinant of the mechanical properties of the cell wall and the results presented in this thesis support this hypothesis. Water contents of Acetobacter xylinus synthesized cellulose based cell wall analogues (as a mimic of primary cell wall) and sunflower hypocotyl cell walls were altered using high molecular weight polyethylene glycol (PEG) solution, and their extension under a constant load was measured using a creep extensiometer and showed that there were clear reduction (30-35%) in extensibility suggesting that water content of the wall and therefore the cell wall free volume directly influence wall extensibility. When hydration of A. xylinus cellulose composite pellicles was reduced using PEG 6000 solution and re-hydrated in buffer solution, followed by treatment with α-expansin or snail acetone powder extract, it was found that expansin and snail powder extracts caused a rapid rehydration of the composites and that the pellicles only returned to their original weights after these treatments, suggesting that expansin and snail powder can increase the free volume of the wall perhaps contributing to the increases in extensibility that they cause. Assays on cell wall fragments also indicated that expansin increased the cell wall free volume, demonstrated by changes of the turbidity of fragment suspensions. The role of pectic polysaccharide, RG-II, in cell wall biomechanics was also investigated using mechanical and biochemical testing of available Arabidopsis thaliana cell wall mutants and by incorporating RG-II (purified from red wine) with Acetobacter cellulose. It was demonstrated that RG-II significantly increased the hydration of cellulose composite; hydration rate was 15 -16% more than the composite without RG-II and thus increased the pellicle extensibility. From the results, it is evidenced that cell wall extension is not only the consequences of breaking hydrogen bonds between cellulose microfibrils and xyloglucan by expansins or glycosidases and transglycosylases, but also a wider range of factors are involved including cell wall water content, cell wall free volume and the pectic polymers, especially RG-II

On the existence of periodic solution of perturbed generalized Li\'enard equations

Under conditions of Levinson-Smith type, we prove the existence of a $\tau$-periodic solution for the perturbed generalized Li\'enard equation u''+\phi(u,u')u'+\psi(u)=\epsilon\omega(\frac{t}{\tau},u,u') with periodic forcing term. Also we deduce sufficient condition for existence of a periodic solution for the equation u''+\sum_{k=0}^{2s+1} p_k(u){u'}^k=\epsilon\omega(\frac{t}{\tau},u,u'). Our method can be applied also to the equation u''+[u^2+(u+u')^2-1]u'+u=\epsilon\omega(\frac{t}{\tau},u,u'). The results obtained are illustrated with numerical examples.Comment: 15 pages, 5 figure

Inequality and economic growth in Bangladesh- a diversified evidence on Kuznets pattern 'U' hypothesis

The study of inequality and economic growth to the developing countries are now a days a comprehensive issue since growth stimulate the standard of living to the poor people and accordingly reduce income inequality.The improvement of inequality and growth may reduce the social movement to the government and may keep the economic and social integrity amongst the different ethnic groups by efficient resource allocation and income redistribution in Bangladesh. The objective of this research is to assess the long term relationship between inequality and growth in Bangladesh with a methodology of Kuznets pattern inverted U hypothesis first introduced by Simon Kuznets since 1955. The popular concept of Kuznets hypothesis suggests that as economic growth occurs,income inequality first increase and then decline after a certain turning point. The study of Kuznets hypothesis is popular to the international economic environment rather than domestic, especially to the developing countries where the per capita GDP is below the level of world average. This study found the evidence that the presumption of Kuznets hypothesis has satisfy in the economy of Bangladesh in national level. In low income countries, structural adjustment is necessary to satisfy the Kuznets hypothesis.Kuznets Hypothesis, Inequality, Growth

3D Camouflaging Object using RGB-D Sensors

This paper proposes a new optical camouflage system that uses RGB-D cameras, for acquiring point cloud of background scene, and tracking observers eyes. This system enables a user to conceal an object located behind a display that surrounded by 3D objects. If we considered here the tracked point of observer s eyes is a light source, the system will work on estimating shadow shape of the display device that falls on the objects in background. The system uses the 3d observer s eyes and the locations of display corners to predict their shadow points which have nearest neighbors in the constructed point cloud of background scene.Comment: 6 pages, 12 figures, 2017 IEEE International Conference on SM