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Projected Surface Finite Elements for Elliptic Equations
Get PDFIn this article, we define a new finite element method for numerically approximating solutions of elliptic partial differential equations defined on “arbitrary” smooth surfaces S in RN+1. By “arbitrary” smooth surfaces, we mean surfaces that can be implicitly represented as level sets of smooth functions. The key idea is to first approximate the surface S by a polyhedral surface Sh, which is a union of planar triangles whose vertices lie on S; then to project Sh onto S. With this method, we can also approximate the eigenvalues and eigenfunctions of th Laplace-Beltrami operator on these “arbitrary” surfaces
Global Dynamics of a Water-Borne Disease Model with Multiple Transmission Pathways
Get PDFWe propose and analyze a water born disease model introducing water-to-person and person-toperson transmission and saturated incidence. The disease-free equilibrium and the existence criterion of endemic equilibrium are investigated. Trans critical bifurcation at the disease-free equilibrium is obtained when the basic reproductive number is one. The local stability of both the equilibria is shown and a Lyapunov functional approach is also applied to explore the global stability of the system around the equilibria. We display the effects of pathogen contaminated water and infection through contact on the system dynamics in the absence of person-to-person contact as well as in the presence of water-to-person contact. It is shown that in the presence of water-to-person transmission, the model system globally stable around both the disease-free and endemic equilibria. Lastly, some numerical simulations are provided to verify our analytical results
Graphic Illustration of the Transmission Resonances for the DKP Particles
Get PDFWe consider the Duffin-Kemmer-Petiau (DKP) equation in the presence of a spatially one-dimensional Woods-Saxon (WS) potential and we show by graphics how the zero-reflection condition on the Klein interval depends on the shape of the potential
Degradation of Untreated Switchgrass Biomass into Reducing Sugars in 1-(Alkylsulfonic)-3-Methylimidazolium Brönsted Acidic Ionic Liquid Medium Under Mild Conditions
No full textSwitchgrass biomass samples collected at three different stages of maturity were seen degrading into reducing sugars and glucose when exposed to 1-(alkylsulfonic)-3-methylimidazolium Brönsted acidic ionic liquids under thermal and microwave conditions. The highest reducing sugar (58. 1 ± 2. 1 %) and glucose (15. 3 ± 0. 5 %) yields were obtained for switchgrass samples dissolved in 1-(butylsulfonic)-3-methylimidazolium chloride ionic liquid by heating at 70 °C for 1 h followed by treatment with 0. 22 g water/g switchgrass and then heating at 70 °C for 1 h for the hydrolysis of polysaccharides. The samples treated under microwave conditions produced relatively lower yields of reducing sugar (22. 0 ± 1. 5-37. 2 ± 1. 8 %) and glucose (8. 0 ± 0. 2-12. 8 ± 0. 4 %) yields, compared to heat-treated samples. © 2012 Springer Science+Business Media New York
Forest management for timber and carbon sequestration in the presence of climate change: The case of Pinus Sylvestris
No full textClimatic changes will affect the dynamics of a forest ecosystem. Consequently, carbon sequestration costs can only be estimated correctly if changes in climatic conditions are considered. This article determines the changes in mitigation costs of an optimal forest management regime in the presence of climatic changes and varying prices, and takes account of substitution processes between timber production and carbon sequestration at the stand level. The study demonstrates that in the presence of climate change the sequestration costs per ton of carbon increase with higher amounts of carbon sequestered per hectare. This finding can be used to identify a threshold for the amount of sequestered carbon per hectare below which the costs of carbon sequestration are hardly influenced by climate change. © 2012 Elsevier B.V
New results on continuous-time switched linear systems with actuator saturation
No full textThis paper further studies the analysis and control problems of continuous-time switched linear systems subject to actuator saturation. Using the norm-bounded differential inclusion (NDI) description of the saturated systems and the minimal switching rule, a set of switched output feedback controllers is designed to minimize the disturbance attenuation level defined by the re- gional L2 gain over a class of energy-bounded disturbances. The synthesis conditions are expressed as bilinear matrix inequalities (BMIs) and can be solved by numerical search coupled with lin- ear matrix inequality (LMI) optimization. Compared to the pre- vious method based on polytopic differential inclusion (PDI), the proposed approach has good scalability and potentially renders better performance. Numerical examples are provided to verify effectiveness of the proposed approach. Copyright © 2013 by ASME
Grasses provide new insights into regulation of shoot branching
No full textTillering (branching) is a major determinant of crop yield that is controlled by complex interactions between hormonal, developmental, and environmental factors. Historically, research on shoot branching has focused on eudicots, mainly due to the ease of manipulating branching by shoot decapitation and grafting in these species. These studies demonstrated hormonal control of branching. Recent studies in monocots have contributed to our knowledge of tillering/branching by identifying novel branching genes and regulatory mechanisms. A comparison of branching controls in eudicots and monocots reveals that the regulatory signals and genes are broadly conserved, but that there are differences in the detail. © 2012
Polycaprolactone scaffolds and hydroxyapatite/polycaprolactone composite scaffolds for bone tissue engineering
No full textScaffolds fabricated from biodegradable polymers and bioactive materials together with living cells are often used in tissue engineering. This paper reports the thermally induced phase separation technique (TIPS) for the formation of three-dimensional porous scaffolds based on biodegradable polymers for bone tissue engineering applications. For the production of tissue engineering scaffolds, poly(Caprolactone) (PCL) which is a biodegradable and biocompatible polymer was used. The effect of different parameters involved in the fabrication process was studied. In the TIPS process, HA nanoparticles were successfully incorporated in PCL scaffolds to make composite scaffolds, rendering the scaffolds osteoconductive. In the PCL polymer scaffold matrix, HA nanoparticles were found to be well discreted. It was observed that the porosity and pore sizes decreased with the incorporation of HA nanoparticles. The compressive mechanical properties increased in the HA/PCL composite scaffold. Freezing at -18° yielded better pore size distribution which was controlled by the polymer and solvent phase crystallization. The PCL scaffolds were systematically evaluated using various techniques. Scaffolds with high porosity, low density, pore sizes ranging from several microns to 200 microns and good compressive mechanical properties were obtained by optimizing the processing and material parameters. The characteristics of PCL and HA/PCL scaffolds investigated in the current study show promises for bone tissue regeneration. Copyright © 2013 American Scientific Publishers. All rights reserved
Biodegradable PHBV polymer-based scaffolds for bone tissue engineering
No full textThis chapter reports the emulsion freezing/freeze-drying technique for the formation of three-dimensional porous scaffolds for bone tissue engineering applications. Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), which is a natural, biodegradable polymer, was used as the main polymer for fabricating various tissue engineering scaffolds. Nano-sized hydroxyapatite (HA), a widely used bioceramic, was incorporated in the scaffolds in order to obtain bioactive (i.e., osteoconductive) composite scaffolds. The chapter focused in two areas: (1) investigations into scaffold fabrication using the emulsion freezing/freeze-drying technique and the influence of processing parameters on the formation of PHBV polymer scaffolds, HA/PHBV composite scaffolds and HA-containing PHBV/PLLA blend-based composite scaffolds; (2) evaluation of different scaffolds in terms of their porous structure, porosity, pore size, polymer crystallinity, compressive mechanical properties, in vitro biodegradation behavior and in vitro biological performance
Endocrine control of bull fertility
No full textMale fertility-the ability to produce viable sperm that are able to support fertilization and oocyte activation and to sustain development during embryogenesis and beyond-is essential for success of mammalian reproduction and development. Production of quality semen depends on the existence of an effective male reproduction system that is consistently able to produce viable gametes. This requires a male with a fertility phenotype that has evolved under the influence of its genetics, environment, and epistasis to a high degree of efficacy. As the sperm from one bull can be used to inseminate tens of thousands of cows, bull fertility has an enormous influence on the efficiency and success of the cattle breeding and reproduction. Even among bulls that produce ample amounts of sperm having apparent normal morphology, some of these animals will still not exhibit high fertility. Despite large investments to study the causes of low fertility as well as research on methods to prevent, diagnose, and treat subpar male fertility, only limited success has been achieved, and the problem remains poorly defined. The objectives of this paper are to review the male reproductive system and the endocrine regulation of male fertility. It will explore the functions of specific hormones regulating male fertility, hormonal control of sperm viability, as well as environmental factors influencing male fertility. The bovine will be the species of focus, but key aspects of male fertility of other mammals (pigs, goats, horses, monkeys and humans) will be included. This review is intended to be a useful source of information for both basic and applied research, as well as for animal production and human andrologists. © 2013 by Nova Science Publishers, Inc. All rights reserved