Parameter identification in dynamic systems using the homotopy optimization approach

Identifying the parameters in a mathematical model governed by a system of ordinary differential equations is considered in this work. It is assumed that only partial state measurement is available from experiments, and that the parameters appear nonlinearly in the system equations. The problem of parameter identification is often posed as an optimization problem, and when deterministic methods are used for optimization, one often converges to a local minimum rather than the global minimum. To mitigate the problem of converging to local minima, a new approach is proposed for applying the homotopy technique to the problem of parameter identification. Several examples are used to demonstrate the effectiveness of the homotopy method for obtaining global minima, thereby successfully identifying the system parameters.     

pH‐sensitive crosslinked guar gum‐based superabsorbent hydrogels: Swelling response in simulated environments and water retention behavior in plant growth media

Crosslinked guar gum‐g‐polyacrylate (cl‐GG‐g‐PA) superabsorbent hydrogels were prepared to explore their potential as soil conditioners and carriers. The hydrogels were prepared by in situ grafting polymerization and crosslinking of acrylamide onto a natural GG followed by hydrolysis. Microwave‐initiated synthesis under the chosen experimental conditions did not exhibit any significant improvement over the conventional technique. The optimization studies of various synthesis parameters, namely, monomer concentration, crosslinker concentration, initiator concentration, quantity of water per unit reaction mass, particle size of backbone, and concentration of alkali were performed. The hydrogels were characterized by wide‐angle X‐ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and solid‐state ¹³C‐NMR spectroscopy. Swelling behavior of a candidate hydrogel [GG‐superabsorbent polymer (SAP)] in response to external stimuli, namely, salt solutions, fertilizer solutions, temperature, and pH, was studied. The GG‐SAP exhibited significant swelling in various environments. The effect of GG‐SAP on water absorption and the retention characteristics of sandy loam soil and soil‐less medium were also studied as a function of temperature and moisture tensions. The addition of GG‐SAP significantly improved the moisture characteristics of plant growth media (both soil and soil‐less), showing that it has tremendous potential for diverse applications in moisture stress agriculture. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41060.     

Density of additively-manufactured, 316L SS parts using laser powder-bed fusion at powers up to 400 W

Selective laser melting is a powder-based, additive-manufacturing process where a three-dimensional part is produced, layer by layer, by using a high-energy laser beam to fuse the metallic powder particles. A particular challenge in this process is the selection of appropriate process parameters that result in parts with desired properties. In this study, we describe an approach to selecting parameters for high-density (>99 %) parts using 316L stainless steel. Though there has been significant success in achieving near-full density for 316L parts, this work has been limited to laser powers <225 W. We discuss how we can exploit prior knowledge, design of computational experiments using a simple model of laser melting, and single-track experiments to determine the process parameters for use at laser powers up to 400 W. Our results show that, at higher power values, there is a large range of scan speeds over which the relative density remains >99 %, with the density reducing rapidly at high speeds due to insufficient melting, and less rapidly at low speeds due to the effect of voids created as the process enters keyhole mode.     

Antioxidant properties of commercial soft and hard winter wheats (Triticum aestivum L.) and their milling fractions

The total phenolic content (TPC), total antioxidant activity (TAA), 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) scavenging capacity, inhibition of coupled oxidation in a β‐carotene–linoleate model system, iron(II) chelation activity and inhibition of copper‐induced oxidation of human low‐density lipoprotein (hLDL) cholesterol of 80% ethanolic extracts of soft and hard winter wheat samples and their milling fractions, namely flour, germ, bran and shorts, were investigated. Soft wheat extracts examined demonstrated higher TPC and TAA compared to those of hard wheat extracts. The germ fraction possessed the highest TPC, followed by bran, shorts, whole grain and flour for both wheat types examined. The TAA of both wheat types showed similar results except that shorts performed better than bran in this assay. Free radical scavenging properties of whole grain and milling fractions of both soft and hard wheat samples were examined against DPPH radical. The germ and flour fractions demonstrated the highest and lowest DPPH radical scavenging activity, respectively, among wheat fractions. Wheat extracts were also efficient in preventing bleaching of β‐carotene, which is also known to be free radical mediated. In the iron(II) chelation assay the flour extracts demonstrated excellent activity, while the germ extracts showed a weak activity. The trends were similar in both soft and hard wheat for the iron(II) chelation assay. Wheat extracts also inhibited copper‐induced oxidation of hLDL. In LDL oxidation assay, wheat extracts performed better than the reference antioxidant, ferulic acid. Thus wheat phenolics may serve as effective antioxidative components as measured by in vitro techniques. Copyright © 2005 Society of Chemical Industry     

Potato starch-assisted green synthesis of nanoferrite and ferrite–semiconductor nanocomposites for effective visible light photocatalytic degradation of methylene blue

Journal of Materials Science - Biodegradable potato starch-assisted nanoferrite and ferrite–semiconductor nanocomposites have been synthesized by the co-precipitation method for the...     

In vitro accessibility of β‐carotene from cooked Sri Lankan green leafy vegetables and their estimated contribution to vitamin A requirement

Vitamin A deficiency is an important issue for public health in Sri Lanka, where pro‐vitamin A carotenoids from green leafy vegetables provide most of the dietary vitamin A. The objective of this study was to analyse the β‐carotene content of seven types of green leafy vegetables and calculate the contribution of one traditionally cooked portion to the recommended daily allowance (RDA) of retinol. The total amount and in vitro accessibility of β‐carotene were determined using HPLC. The in vitro method simulates the conditions in the human intestinal tract. The all‐trans‐β‐carotene content in the fresh blanched vegetables ranged from 149 µg g^?1 dry weight (DW) in leaves of Alternanthera sessilis (mukunuwanna) to 565 µg g^?1 DW in Amaranthus caudatus (thampala). One portion (100 g) of green leaves cooked without fat (coconut) only contributed from 140 to 180 µg mg^?1 of the recommended daily allowance. A. sessilis, Centella asiatica (gotukola), Spinacea oleracea (nivithi) and A. caudatus, cooked with coconut fat contributed 140–680 µg mg^?1. However, stir‐fried or ‘malluma’ preparations (with coconut products) of Sesbania grandiflora (kathurumurunga) and Manihot esculenta (manioc) may provide more than 1.59–4.37 times the RDA of retinol. These results show that not only the choice of green leaves used but also the addition of fat while cooking is of great importance. Copyright © 2005 Society of Chemical Industry     

Antioxidant activity of white and black sesame seeds and their hull fractions

The total phenolic content (TPC), total antioxidant status (TAS), free radical scavenging capacity, inhibition of low density lipoprotein (LDL) cholesterol and metal chelating capacity of extracts of whole black and whole white sesame seeds and their hull fractions in 80% aqueous ethanol were investigated. The TPC of whole black sesame seeds and hull extracts were 29.9 ± 0.6 and 146.6 ± 0.6 mg catechin equivalents/g crude ethanolic extract, respectively. The corresponding values for white sesame were 10.6 ± 1.6 and 29.7 ± 0.9 mg catechin equivalents/g crude ethanolic extract. The TAS as determined by Trolox equivalent antioxidant capacity assay and expressed as Trolox equivalents was highest for black sesame hulls (65.9 ± 1.7) while white seeds showed the lowest (4.4 ± 0.6). Free radical scavenging capacity of sesame extracts (5–40 μg/mL) was measured using 2,2-diphenyl-1-picrylhydrazyl radical. The highest scavenging capacity was obtained at 40 μg/mL and was 94.9 ± 0.8, 25.1 ± 0.4, 14.4 ± 0.9 and 2.5 ± 0.4 for black sesame hulls, black sesame seeds, white sesame hulls and white sesame seeds, respectively. Inhibition of LDL oxidation at 100 ppm level was highest for black sesame hulls (96.7%) followed by those for white sesame hulls (84.6%), black sesame (78.4%) and white sesame seeds (57.3%). Sesame products displayed good ferrous ion chelating capacities, which ranged from 12% to 46% and 17% to 62% at 50 and 100 ppm levels, respectively. Results demonstrated considerable antioxidant activity of sesame products tested especially black sesame hulls.     

Development of Single-Stranded DNA Bisintercalating Inhibitors of Primase DnaG as Antibiotics

Many essential enzymes in bacteria remain promising potential targets of antibacterial agents. In this study, we discovered that dequalinium, a topical antibacterial agent, is an inhibitor of Staphylococcus aureus primase DnaG (SaDnaG) with low-micromolar minimum inhibitory concentrations against several S. aureus strains, including methicillin-resistant bacteria. Mechanistic studies of dequalinium and a series of nine of its synthesized analogues revealed that these compounds are single-stranded DNA bisintercalators that penetrate a bacterium by compromising its membrane. The best compound of this series likely interacts with DnaG directly, inhibits both staphylococcal cell growth and biofilm formation, and displays no significant hemolytic activity or toxicity to mammalian cells. This compound is an excellent lead for further development of a novel anti-staphylococcal therapeutic.     

A projection method for solving nonsymmetric linear systems on multiprocessors

We consider the iterative solution of large sparse linear systems of equations arising from elliptic and parabolic partial differential equations in two or three space dimensions. Specifically, we focus our attention on nonsymmetric systems of equations whose eigenvalues lie on both sides of the imaginary axis, or whose symmetric part is not positive definite. This system of equation is solved using a block Kaczmarz projection method with conjugate gradient acceleration. The algorithm has been designed with special emphasis on its suitability for multiprocessors. In the first part of the paper, we study the numerical properties of the algorithm and compare its performance with other algorithms such as the conjugate gradient method on the normal equations, and conjugate gradient-like schemes such as ORTHOMIN(k), GCR(k) and GMRES(k). We also study the effect of using various preconditioners with these methods. In the second part of the paper, we describe the implementation of our algorithm on the CRAY X-MP/48 multiprocessor, and study its behavior as the number of processors is increased.     

Antioxidant and free radical scavenging activities of whole wheat and milling fractions

The effects of milling on the phenolic content and antioxidant capacity of two wheat cultivars, namely CWAD (Canadian Western Amber Durum; Triticum turgidum L. var. durum) and CWRS (Canadian Western hard red spring; Triticum aestivum L.) were studied. The milling of wheat afforded several fractions, namely bran, flour, shorts and feed flour. In addition, semolina was the end-product of durum wheat milling. Among different milling fractions the bran had the highest phenolic content while the endosperm possessed the lowest amount and this was also reflected in free radical and reactive oxygen species (ROS) scavenging capacity, reducing power and iron (II) chelation capacity of different milling fractions in the two cultivars. This study demonstrated the importance of bran in the antioxidant activity of wheat, hence consumption of whole wheat grain may render beneficial health effects.