Hydrogen-assisted cracking studies of 4340 steel by using the optical method of caustics

The optical method of caustics is used to measure the effect of hydrogen on the localized deformation within the fracture process zone (PZ). In particular, the role of the PZ in hydrogen-assisted cracking (HAC) of 4340 steel in hydrogen gas at 1 atm is examined. No change in the caustic diameter was detected prior to crack initiation but an “anomalous” enlargement of the caustic diameter as a function of crack growth was observed as a result of crack tunneling. The “center” of the caustic follows the position of the internal crack front, thus providing a simple means to monitor the growth of internal cracks. It is demonstrated that the technique provides a sensitive means for detecting HAC initiation (the smallest crack depth change detected is 35 μm) and insight into the three-dimensional character of the PZ.     

Electricity rates for the zero marginal cost grid

The electricity industry is rapidly changing: costs are increasingly dominated by capital and technology is turning loads into resources. This is similar to the early days of the Internet. Building on rate-structures used in the communications industry, utilities of the future should offer customers a portfolio of service contract options that provide a signal to the utility regarding the type and amount of infrastructure that should be deployed.     

Variable temperature UHV dual-range cell for spectroscopic surface studies

A stainless steel cell for transmission spectroscopy of surface compounds is described. This cell allows subsequent spectra recording of the sample in two spectral regions requiring different window materials. The sample temperature can be varied from 100 to 700 K, the pressure from 10(-6) to 10(5) Pa. The mean temperatue is measured inside the wafer with a thin platinum wire as a resistance thermometer.     

MS2 removal from high NOM content surface water by coagulation ‐ ceramic microfiltration,for potable water production

MS2 bacteriophages removal from surface water, characterized by high natural organic matter (NOM) content, was investigated by inline coagulation/flocculation pretreatment followed by ceramic microfiltration (MF). MS2 and DOC removal increased with lower pH and higher coagulant dose. Lowering the coagulant pH from 6.5 to 5.5 for polyaluminum chloride (PACl), and to 5.0 for iron chloride (FeCl), respectively, along with doubling of the coagulant dose from 2 to 4 mg Al/L, and from 4 to 8 mg Fe/L, respectively, maximized the virus removal, resulting in more than six log unit reductions up to complete virus retention. However, high residual metal concentrations were found under such conditions. Comparison of conventional two‐stage coagulation pretreatment with simple inline coagulation did not show any significant performance differences. Both investigated coagulants showed virus inactivation about two log units after 60 min contact time, which is equivalent to a virus inactivation of 99%. This inactivation was only reversible to a small extend by chemical or physical floc destruction. The investigated process combination can comply with modern hygienic barrier standards. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Targeted disruption of the mouse lecithin:cholesterol acyltransferase (LCAT) gene. Generation of a new animal model for human LCAT deficiency

We have established a mouse model for human LCAT deficiency by performing targeted disruption of the LCAT gene in mouse embryonic stem cells. Homozygous LCAT-deficient mice were healthy at birth and fertile. Compared with age-matched wild-type littermates, the LCAT activity in heterozygous and homozygous knockout mice was reduced by 30 and 99%, respectively. LCAT deficiency resulted in significant reductions in the plasma concentrations of total cholesterol, HDL cholesterol, and apoA-I in both LCAT -/- mice (25, 7, and 12%; p < 0. 001 of normal) and LCAT +/- mice (65 and 59%; p < 0.001 and 81%; not significant, p = 0.17 of normal). In addition, plasma triglycerides were significantly higher (212% of normal; p < 0.01) in male homozygous knockout mice compared with wild-type animals but remained normal in female knockout LCAT mice. Analyses of plasma lipoproteins by fast protein liquid chromatography and two-dimensional gel electrophoresis demonstrated the presence of heterogenous prebeta-migrating HDL, as well as triglyceride-enriched very low density lipoprotein. After 3 weeks on a high-fat high-cholesterol diet, LCAT -/- mice had significantly lower plasma concentrations of total cholesterol, reflecting reduced levels of both proatherogenic apoB-containing lipoproteins as well as HDL, compared with controls. Thus, we demonstrate for the first time that the absence of LCAT attenuates the rise of apoB-containing lipoproteins in response to dietary cholesterol. No evidence of corneal opacities or renal insufficiency was detected in 4-month-old homozygous knockout mice. The availability of a homozygous animal model for human LCAT deficiency states will permit further evaluation of the role that LCAT plays in atherosclerosis as well as the feasibility of performing gene transfer in human LCAT deficiency states.     

A new approach to stochastic adaptive control

The principal techniques used up to now for the analysis of stochastic adaptive control systems have been 1) super-martingale (often called stochastic Lyapunov) methods and 2) methods relying upon the strong consistency of some parameter estimation scheme. Optimal stochastic control and filtering methods have also been employed. Although there have been some successes, the extension of these techniques to a broader class of adaptive control problems, including the case of time-varying parameters, has been difficult. In this paper a new approach is adopted: if an underlying Markovian state-space system for the controlled process is available, and if this process possesses stationary transition probabilities, then the powerful ergodic theory of Markov processes may be applied. Subject to technical conditions, such as stability, one may deduce 1) the existence of an invariant measure for the process and 2) the convergence almost surely of the sample averages of a function of the state process (and of its expectation) to its conditional expectation. The technique is illustrated by an application to a previously unsolved problem involving a linear system with unbounded random time-varying parameters.     

Stability of queueing networks and scheduling policies

We develop a programmatic procedure for establishing the stability of queueing networks and scheduling policies. The method uses linear or nonlinear programming to determine what is an appropriate quadratic functional to use as a Lyapunov function. If the underlying system is Markovian, our method establishes not only positive recurrence and the existence of a steady-state probability distribution, but also the geometric convergence of an exponential moment. We illustrate this method on several example problems     

Stability of acyclic multiclass queueing networks

In this paper we study multiclass queueing networks with fluid arrival streams and service processes. Assuming that the arrival rate does not exceed the network capacity, we deduce stability of the network using the tools of ergodic theory. We show that the distributions of the process converge to a unique steady state value and that convergence takes place at a geometric rate under appropriate moment conditions     

Stability, convergence, and performance of an adaptive controlalgorithm applied to a randomly varying system

The stability and performance of a stochastic adaptive control algorithm applied to a randomly varying linear system are investigated. The authors demonstrate that: loss functions on the input-output process converge to their expectation with respect to an invariant probability at a geometric rate, and hence, a form of stochastic exponential asymptotic stability is established; and when the parameter variation and measurement noise are small, it is shown that the performance is nearly optimal, and if an excitation signal is added in the control law, near consistency of the parameter estimates is obtained. Further results include central limit theorems and the law of large numbers of the input-output and parameter processes