Incremental Hole Drilling Residual Stress Measurement in Thin Aluminum Alloy Plates Subjected to Laser Shock Peening

Experimental Mechanics - The American standard ASTM E837 presents a standard procedure to determine residual stresses in isotropic materials using the incremental hole drilling technique (IHD). The...     

Xylose reductase and xylitol dehydrogenase activities of Candida guilliermondii as a function of different treatments of sugarcane bagasse hemicellulosic hydrolysate employing experimental design

The sugarcane bagasse hydrolysate, which is rich in xylose, can be used as culture medium for Candida guilliermondii in xylitol production. However, the hydrolysate obtained from bagasse by acid hydrolysis at 120°C for 20 min has by-products (acetic acid and furfural, among others), which are toxic to the yeast over certain concentrations. So, the hydrolysate must be pretreated before using in fermentation. The pretreatment variables considered were: adsorption time (15,37.5, and 60 min), type of acid used (H2So4 and H3Po4), hydrolysate concentration (original, twofold, and fourfold. concentrated), and active charcoal (0.5, 1.75 and 3.0%). The suitability of the pretreatment was followed by measuring the xylose reductase (XR) and xylitol dehydrogenase (XD) activity of yeast grown in each treated hydrolysate. The response surface methodology (2⁴ full factorial design with a centered face) indicated that the hydrolysate might be concentrated fourfold and the pH adjusted to 7.0 with CaO, followed by reduction to 5.5 with H₃PO₄. After that it was treated with active charcoal (3.0%) by 60 min. This pretreated hydrolysate attained the high XR/XD ratio of 4.5.     

On the mathematics of emergence

We describe a setting where convergence to consensus in a population of autonomous agents can be formally addressed and prove some general results establishing conditions under which such convergence occurs. Both continuous and discrete time are considered and a number of particular examples, notably the way in which a population of animals move together, are considered as particular instances of our setting. This article is based on the 1st Takagi Lectures that the second author delivered at Research Institute for Mathematical Sciences, Kyoto University on November 25 and 26, 2006. Steve Smale Partially supported by an NSF grant.     

Study of the Ternary Complex Formation between Vanadium(III)-Cysteine and Small Blood Serum Bioligands

The complex species formed between vanadium(III) cysteine and small blood serum bioligands: lactic, oxalic, citric and phosphoric acids were studied in aqueous solution by means of electromotive force measurements, Emf(H), at 25 °C and 3.0 mol⋅dm⁻³ KCl as the ionic medium. The ternary complexes were studied by potentiometric measurements and the data analyzed using the least-squares computational program LETAGROP to obtain the respective stability constants and stoichiometric coefficients. The UV-Vis spectrophotometric measurements were done in order to make a qualitative characterization of the complexes formed in aqueous solution.     

Noise-controlled self-replicating patterns

We present novel numerical evidence of spot self-replication controlled by noise in a simple autocatalytic reaction-diffusion system. The system dynamics exhibits a noise controlled transition from stripe growth to spot replication. The growth kinetics is also controlled by noise, and there is an optimal noise intensity for which the multiplication rate of spots is maximal. For larger noise intensities, the spots become unstable and the system is attracted by the trivial steady state. Some of the effects are reminiscent of both polymer chain and cell colony formation in random environments.     

Operational readiness and survivability of network systems

A method is developed for obtaining the operational readiness and the survivability of a network in terms of its branches. The procedure is based on graph theory concepts.     

Solving linear programs with finite precision: I. Condition numbers and random programs

We define a condition number (A,b,c) for a linear program min x s.t. Ax=b,x0 and give two characterizations via distances to degeneracy and singularity. We also give bounds for the expected value, as well as for higher moments, of log (A,b,c) when the entries of A,b and c are i.i.d. random variables with normal distribution. This work has been substantially funded by a grant from the Research Grants Council of the Hong Kong SAR (project number CityU 1085/02P)     

Algebraic Decay in Hierarchical Graphs

We study the algebraic decay of the survival probability in open hierarchical graphs. We present a model of a persistent random walk on a hierarchical graph and study the spectral properties of the Frobenius–Perron operator. Using a perturbative scheme, we derive the exponent of the classical algebraic decay in terms of two parameters of the model. One parameter defines the geometrical relation between the length scales on the graph, and the other relates to the probabilities for the random walker to go from one level of the hierarchy to another. The scattering resonances of the corresponding hierarchical quantum graphs are also studied. The width distribution shows the scaling behavior P()1/.     

Preliminary kinetic characterization of xylose reductase and xylitol dehydrogenase extracted from Candida guilliermondii FTI 20037 cultivated in sugarcane bagasse hydrolysate for xylitol production

Candida guilliermondii FTI 20037 was cultured in sugarcane bagasse hydrolysate supplemented with 2.0 g/L of (NH₄)₂SO₄, 0.1 g/L of CaCl₂·2H₂O, and 20.0 g/L of rice bran at 35°C; pH 4.0; agitation of 300 rpm; and aeration of 0.4, 0.6, or 0.8 vvm. The high xylitol production (20.0 g/L) and xylose reductase (XR) activity (658.8 U/mg of protein) occurred at an aeration of 0.4 vvm. Under this condition, the xylitol dehydrogenase (XD) activity was low. The apparent K _M for XR and XD against substrates and cofactors were as follows: for XR, 6.4×10⁻² M (xylose) and 9.5×10⁻³ mM (NADPH); for XD, 1.6×10⁻¹ M (xylitol) and 9.9×10⁻² mM (NAD+). Because XR requires about 10-fold less xylose and cofactor than XD for the condition in which the reaction rate is half of the V _max, some interference on the overall xylitol production by the yeast could be expected.     

Numerical methods for inferring phylogenies

Molecular phylogenies describe the study of evolution relationships between living beings, protein and genetic sequences and other molecular taxons. In recent years there has been increased interest in producing large and accurate phylogenies trees using some numerical computational methods approach. One class of molecular phylogenies is the distance matrices method, with the matrix whose entries represent the distinctions between the taxons under study. To construct large and accurate trees for a large number of taxons, the computational processing increases and parallel computing can be helpful. So far we have tested some methods to solve the linear systems, being driven to important conclusions, like which is the best tested method, and having also reached some questions about communication. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)