Pyrolytic formation of a carbonaceous solid for heavy metal adsorption

The solid-state pyrolysis of acetylenedicarboxylic acid, monopotassium salt at 300 °C in air results in bulk quantities of a micron-sized yet macroporous oxidized carbon, which inherently possesses high content of metal-binding sites, such as carboxylate groups, free radicals, and ether/hydroxyl units. Besides its high oxygen content, the solid is stable in water and does not leach or disorient, while it also exhibits an appreciable thermal stability, at temperature exceeding 200 °C in air. Several techniques including TEM/SEM, TGA, Raman/FT-IR, XPS, EPR, and potentiometric titrations were employed for the characterization of the solid. Furthermore, liquid phase adsorption experiments revealed that the material is an efficient heavy metal adsorbent due to the presence of diverse surface-accessible binding sites, showing unusually high metal uptake capacities for Pb²⁺ and Cu²⁺ ions (ca. 4.5 mmol g⁻¹).     

Pressure inactivation of hepatitis A virus in strawberry puree and sliced green onions

Hepatitis A can be acquired by ingesting contaminated produce. To investigate the potential of high-pressure processing as an intervention strategy for virus in produce, strawberry puree and sliced green onions were inoculated with > 10(6) PFU of hepatitis A virus and treated with pressures ranging from 225 to 375 megapascals (MPa) in 25-MPa increments at ambient temperature. Subsequent virus extraction and plaque assay determined that hepatitis A virus was inactivated in strawberry puree and sliced green onions after 5-min exposures to pressures of 375 MPa with log PFU reductions of 4.32 and 4.75, respectively. Hepatitis A virus was equally sensitive in puree and onions at pressures > or = 350 MPa. For treatments of < 325 MPa, the virus was more sensitive to pressure in strawberry puree than in sliced onions with log reductions of 1.2, 2.06, and 3.13 observed for strawberries and 0.28, 0.72, and 1.42 observed for onions after 5-min treatments at 250, 275, and 300 MPa, respectively. Although high-pressure processing may cause some organoleptic alterations to strawberries and onions, results show high-pressure processing will inactivate hepatitis A virus in these foods.     

Estimation in a Pareto Distribution: Theory & Computation

This paper treats the theoretical and computational problems of maximum likelihood parameter estimation in a Pareto distribution. Logarithmic likelihood estimating equations and the associated conditional log-likelihood function are derived, and expressions for the asymptotic variances and covariances of the parameters are given. Discussions pertinent to tests of hypotheses and the construction of simultaneous s-confidence contours are provided. The computations required for estimation are illustrated by an example in which the parameters are estimated by numerically maximizing the conditional log-likelihood function and by using an algorithm for global optimization which exploits the mathematical structure of this function. The parameter estimates obtained in this way are guaranteed to be those at which the likelihood function is globally maximum over the space of permissible parameter values. A Fortran program exists for performing these calculations.     

STOKES FLOW THROUGH A SYSTEM OF PARALLEL INFINITE CYLINDERS WITH AXES ORIENTED AT AN ANGLE TO THE DIRECTION Of MEAN FLOW

Theoretical models based on Stokes flow of air through a fibrous filter predict a significantly higher pressure drop than experimentally measured values. This discrepancy persists even when the interaction of the flow between) neighboring fibers is accounted for. Various authors have attributed this discrepancy to the inhomogeneity of the fiber distribution within the filter and to the possibility that some fibers are partially orientation in the directon of mean flow. It has been shown that fiber density inhomogeneity does indeed contribute to this discrepancy

In this paper, the effect on the flow and subsequent pressure drop when the fibers are oriented at an angle to the directon of mean flow is studied. The solution of the three dimensional equation for creeping, incompressible flow in a doubly periodic, infinite lattice of infinite circular cylinders when there is a constant mean flow whose direction makes an acute angle with the axes of the cylinders is given. If the volume fraction of fibers is small, the periodic boundary conditions can be replaced by requiring zero vorticity at the outer boundary of an imagined cylindrical cell of fluid surrounding one of the cylinders. The resulting parallel and transverse problems have known solutions and give an approximate solution to the flow through the periodic lattice. The resulting drag is used to compute the dimensionless pressure drop across a filter for several values of the volume fraction of fiber and is compared to the experimentally determined formula of Davies. It is shown that the average drag over a uniform distribution of fiber orientations yields a pressure drop which is significantly closer to the experimental values of Davies than that resulting from strictly transverse flow.     

Pressure inactivation kinetics of Yersinia enterocolitica ATCC 35669

The survival curves of Yersinia enterocolitica ATCC 35669 inactivated by high hydrostatic pressure were obtained at four pressure levels (300, 350, 400, and 450 MPa) in sodium phosphate buffer (0.1 M, pH 7.0) and four pressure levels (350, 400, 450, 500 MPa) in UHT whole milk. Tailing was observed in all the survival curves. A linear model and three nonlinear models were fitted to these data and the performances of these models were compared. The linear regression model for survival curves at four pressure levels had regression coefficients (R2) values of 0.785-0.962 and mean square error (MSE) of 0.265-0.893. A residual plot strongly suggested that a linear regression function was not appropriate as there was strong curvature in the plotted data. The nonlinear regression model using the log-logistic had R2 values of 0.946-0.982 and MSE values of 0.110-0.320. The Weibull model had R2 values of 0.944-0.975 and MSE values of 0.153-0.349. These results indicated that both were better models to describe the pressure inactivation kinetics of Y. enterocolitica in milk and buffer. Among the three nonlinear models studied, the modified Gompertz model produced the poorest fit to data. The number of parameters of the log-logistic model was reduced from four to two so that the model was greatly simplified. The reduced log-logistic model still produced a fit comparable to the full model. Since pressure had no significant effect on the shape factors of the Weibull model at the pressure levels of 300-400 MPa for buffer and 400-500 MPa for milk, models were developed to predict survival curves of Y. enterocolitica at pressures different from the experimental pressures.     

In Situ Characterization of Induced Stiction in a MEMS

Stiction remains a limiting factor in the performance and lifetime of MEMS devices. We have developed experimental tools for inducing and quantifying changes in stiction on a large array of MEMS actuators. Thousands of elements were subjected to aggressive wear in order to produce shearing forces that contributed to the degradation of contacting surfaces. Custom electronics were developed to accomplish nonstandard actuation of the MEMS array. Optical techniques were used to characterize the induction of and progression of stiction. A model incorporating experimental and geometrical values was used to determine stiction force as a function of actuation duration and packaging. For a depackaged array, an increase in stiction force of ~230nN (per element) was induced through three days of high-speed actuation     

Fitting three-parameter lognormal models by numerical global optimization — an improved algorithm

The theoretical maximum likelihood point estimates of the parameters of the three-parameter lognormal distribution (LD) for complete, ungrouped samples are infeasible values for which the likelihood function is positively infinite. This has prompted the search for usable point estimates which are called local-maximum likelihood estimates (LMLE's) and which correspond to the largest finite local maximum of the log-likelihood function (LLF). Previously published work has shown that an effective way to obtain LMLE's is to numerically maximize the conditional LLF of the observations using sequential interior penalty and barrier function methods. These methods are robust but necessitate the numerical solution of a sequence of maximization problems.This paper describes an algorithm for computing LMLE's which involves only a single numerical maximization of a suitably transformed conditional LLF. The results of computational tests indicate that the algorithm, when implemented using computationally efficient and reliable univariate global optimization methods, is a computationally robust method for computing LMLE's of LD parameters.     

Pressure inactivation kinetics of phage lambda cI 857

Inactivation curves of phage lambda cI 857 inactivated by high hydrostatic pressure were obtained at three pressure levels (300, 350, and 400 MPa) in buffered media and ultrahigh-temperature 2% reduced fat milk. Pressurization of phage lambda in buffered media at 300 MPa for 300 min, 350 MPa for 36 min, and 400 MPa for 8 min reduced the titer of phage lambda by 7.5, 6.7, and 7.7 log, respectively. Pressurization of phage lambda in milk at 300 MPa for 400 min, 350 MPa for 80 min, and 400 MPa for 20 min reduced the titer of phage lambda by 5.4, 6.4, and 7.1 log, respectively. Tailing was observed in all inactivation curves, indicating that the linear model was not adequate for describing these curves. Among the three nonlinear models studied, the Weibull and log-logistic models consistently produced best fits to all inactivation curves, and the modified Gompertz model the poorest. Because there were no significant differences in the values of shape factor (n) for suspension medium buffer, we reduced the number of parameters in the Weibull model from two to one by setting n at the mean value. The simplified Weibull model produced a fit comparable to the full model. Additionally, the simplified Weibull model allowed predictions to be made at pressures different from the experimental pressures. Menstruum was found to significantly affect the pressure resistance of phage lambda. Comparison of pressure inactivation of hepatitis A virus and phage lambda indicated that phage lambda is more sensitive to pressure than hepatitis A virus in Dulbecco's modified Eagle medium with 10% fetal bovine sera.     

Characterization of the acid/base and redox chemistry of phytochelatin analogue peptides

The phytochelatins are a family of polydisperse, thiol-rich peptides that are synthesized by plants in response to exposure to heavy metals. The amino acid sequence of the phytochelatin peptides is (gamma-glutamyl-cysteinyl)n-glycine, where n typically ranges from 2 to 5. In the first phase of a program to characterize the coordination chemistry of the phytochelatins with heavy metals, the phytochelatin analogue peptides acetyl(gamma-glutamyl-cysteinyl)n-glycine amide (Ac-(gamma-Glu-Cys)n-NH2, n = 2-6) have been synthesized by solid-phase peptide synthesis methods and characterized by 1H NMR spectroscopy. The 1H NMR spectra of the analogue peptides were completely assigned by using band-selective homonuclear-decoupled (BASHD) two-dimensional NMR experiments to achieve spectral resolution. The acid dissociation constant of each cysteine residue in each peptide was determined from chemical shift-pH titration data for the CalphaH protons of the cysteine residues. The resonances for the CalphaH protons were resolved in BASHD-total correlation spectroscopy spectra that were measured as a function of pH. The pKA values for a given thiol group depend on the position of the cysteine residue in the sequence, with the thiol group of the cysteine residue attached to the C-terminal glycine being the most acidic. The pKA values also depend on the size of the peptide, increasing as the size, and thus the negative charge, of the peptide increases. The redox potential for oxidation of the two thiol groups of Ac(gamma-Glu-Cys)2-NH2 to form an intramolecular disulfide bond was also determined by measuring the equilibrium constant for its thiol/disulfide exchange reaction with glutathione.