Hydrolysis of chlorpyrifos in aqueous and colloidal systems

Hydrolysis of chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate] to TCP (3,5,6-trichloro-2-pyridinol) is an important degradation process influencing the fate of chlorpyrifos in aquatic environments. The effects of water chemistry and suspended colloids (smectites, humic acid, and river sediment) on the hydrolysis of chlorpyrifos were investigated in this study. Chlorpyrifos was incubated in various aqueous and colloidal systems at 23 ± 2 °C for up to 100 days, and aqueous phase concentrations of chlorpyrifos and TCP were determined using solid phase extraction-high performance liquid chromatography (SPE-HPLC). Chlorpyrifos degraded in the aqueous solutions with half-lives ranging from 27 to 158 days, depending on the initial concentration of chlorpyrifos and the chemistry of the aqueous solutions. The rate of degradation was slower in systems containing low concentrations of suspended colloids (1 g L⁻¹ in 0.01 M CaCl₂) than in the control (0.01 M CaCl₂, with no colloids), and negligible hydrolysis of chlorpyrifos was found for concentrated colloidal systems (20 g L⁻¹ in 0.01 M CaCl₂). Total recoveries of chlorpyrifos for the concentrated colloidal systems ranged from 78% to 97%, with a tendency to decrease with incubation time. The study indicates that the formation of chlorpyrifos-colloid complexes inhibits the hydrolysis of chlorpyrifos in aqueous systems and that chlorpyrifos-colloid complexes may act as a buffer by slowly releasing chlorpyrifos to the aqueous phase.     

Cancer epigenetics comes of age

The discovery of numerous hypermethylated promoters of tumour-suppressor genes, along with a better understanding of gene-silencing mechanisms, has moved DNA methylation from obscurity to recognition as an alternative mechanism of tumour-suppressor inactivation in cancer. Epigenetic events can also facilitate genetic damage, as illustrated by the increased mutagenicity of 5-methylcytosine and the silencing of the MLH1 mismatch repair gene by DNA methylation in colorectal tumours. We review here current mechanistic understanding of the role of DNA methylation in malignant transformation, and suggest Knudson's two-hit hypothesis should now be expanded to include epigenetic mechanisms of gene inactivation.     

The diverging paths of German and United States policies for renewable energy: Sources of difference

The United States and Germany started out with very similar policies for renewable energy after the energy crisis of the 1970s. By the year 2000 they were on very different policy paths and, as a result, the German renewable energy industry has moved well ahead of that in the United States, both in terms of installed capacity in the country and in terms of creating a highly successful export market. In this paper, we reject some of the conventional explanations for this difference. Instead, these differences arise from the intersection of contingent historical events with the distinctive institutional and social structures that affect policy making in each country. Our analysis of the historical path-dependent dynamics of each country suggests that those who wish to further renewable energy policy in the United States need to take into account these institutional and social factors so that they will better be able to exploit the next set of favorable historical circumstances.     

The distinction between beliefs legitimizing aggression and deviant processing of social cues: Testing measurement validity and the hypothesis that biased processing mediates the effects of beliefs on aggression.

In 2 studies the authors examined knowledge and social information-processing mechanisms as 2 distinct sources of influence on child aggression. Data were collected from 387 boys and girls of diverse ethnicity in 3 successive years. In Study 1, confirmatory factor analyses demonstrated the discriminant validity of the knowledge construct of aggression beliefs and the processing constructs of hostile intent attributions, accessing of aggressive responses, and positive evaluation of aggressive outcomes. In Study 2, structural equation modeling analyses were used to test the mediation hypothesis that aggression beliefs would influence child aggression through the effects of deviant processing. A stronger belief that aggressive retaliation is acceptable predicted more deviant processing 1 year later and more aggression 2 years later. However, this latter effect was substantially accounted for by the intervening effects of deviant processing on aggression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

电磁兼容设计实践 第三部分 印制电路板的电磁兼容设计

重视电路板布线是减少单层和多层印制电路板辐射的关键 如果你的电子系统电磁兼容性令你颇为头疼,不妨先检查一下印制电路板,因为许多引发电磁兼容性问题的器件都在印制电路板中。一个好的印制板设计方案可以在花费极少的情况下解决一些令人头疼的问题。……     

A new closed vessel for determining the ballistic performance of high energy solid and liquid gun propellants

Abstract

A new closed vessel, designed and build by Cranfield University under contract to the UK Defence Evaluation and Research Agency (DERA), is described. The jacketed vessel, which can be operated at high pressure (500 MPa) and has the capability of firing liquid monopropellants, is fitted with a single instrumented head and a detachable liner. The internal surface profile of the combustion chamber is shaped so as to prevent the build up of shock waves which can occur between parallel surfaces and this feature leads to improved output signal quality. Vessel venting following a firing is carried out by remote control via a proprietary air-actuated high pressure valve. The vessel can be fitted with optical windows or converted to a vented device for gas erosion studies.     

Ferrofluidic adaptive mirrors

A magnetic liquid mirror based on ferrofluids was demonstrated. Magnetic liquid mirrors represent a major departure from solid mirror technology. They present both advantages and disadvantages with respect to established technologies. Stroke (from a fraction of a wave to several hundreds of micrometers), cost (a few dollars per actuator), and scalability (hundreds of thousands of actuators) are the main advantages. Very large mirrors having diameters of the order of a meter should be feasible. There are a few disadvantages. The most important disadvantage is the time response, which is of the order of a few milliseconds. Although this time response could be further decreased with additional technical developments, it is unlikely to match the speed of solid mirrors. The technology is still in its infancy, and considerable work must still be done. However, the advantages are such that the technology is worth pursuing.     

A nonlinear programming approach for estimation of transmission parameters in childhood infectious disease using a continuous time model

Mathematical models can enhance our understanding of childhood infectious disease dynamics, but these models depend on appropriate parameter values that are often unknown and must be estimated from disease case data. In this paper, we develop a framework for efficient estimation of childhood infectious disease models with seasonal transmission parameters using continuous differential equations containing model and measurement noise. The problem is formulated using the simultaneous approach where all state variables are discretized, and the discretized differential equations are included as constraints, giving a large-scale algebraic nonlinear programming problem that is solved using a nonlinear primal–dual interior-point solver. The technique is demonstrated using measles case data from three different locations having different school holiday schedules, and our estimates of the seasonality of the transmission parameter show strong correlation to school term holidays. Our approach gives dramatic efficiency gains, showing a 40–400-fold reduction in solution time over other published methods. While our approach has an increased susceptibility to bias over techniques that integrate over the entire unknown state-space, a detailed simulation study shows no evidence of bias. Furthermore, the computational efficiency of our approach allows for investigation of a large model space compared with more computationally intensive approaches.     

On the nature of eutectic carbides in Cr-Ni white cast irons

The mechanical and tribological properties of white cast irons are strongly dependent on whether they contain M₇C₃ or M₃C carbides (M = Fe, Cr,etc.). In an effort to improve the wear resistance of such materials, the United States Bureau of Mines has studied the effects of adding 0.3 to 2.3 wt pct (throughout) Si to hypoeutectic irons containing approximately 8.5 pct Cr and 6.0 pct Ni. The eutectic carbides formed were identified by electron microprobe analysis, X-ray diffraction, and scanning electron (SEM) and optical microscopies. In addition, differential thermal analysis (DTA) was used to study the process of solidification. At Si contents of 0.3 and 1.2 pct, the eutectic carbides exhibited a duplex structure, consisting of cores of M₇C₃ surrounded by shells of M₃C. Additionally, the microstructure contained ledeburite (M₃C + γFe (austenite)). At the higher Si content of 1.6 pct, the eutectic carbides consisted entirely of M₇C₃, and some ledeburite remained. Last, when the Si content was raised to 2.3 pct, the eutectic carbides again consisted entirely of M₇C₃, but ledeburite was no longer formed. These observations can be explained in terms of the effects of Si and, to a lesser extent, of Ni on the shape of the liquidus surface of the metastable Fe-Cr-C phase diagram. The addition of Si reduces the roles played by the four-phase class IIp reactionL + M₇C₃ → M₃C + γFe and the ledeburitic eutectic reactionL → M₃C + γFe in the overall process of solidification. N.H. Macmillan, for-merly with the Albany Research Center.