A Petrov type-III perfect fluid solution of Einstein's equations

An exact solution of Einstein's perfect fluid field equations is presented. The Weyl tensor of this space-time is of Petrov type III.This work was carried out while the author was on an SRC grant at the Department of Mathematics, Queen Elizabeth College, University of London.     

Evaluation of different machines used to quantify genetic modification by real-time PCR

Quantification of genetic modification (GM) is often undertaken to test for compliance with the European Union GM labeling threshold in food. Different control laboratories will often use common validated methods, but with different models of real-time PCR machines. We performed two separate ring trials to evaluate the relative precision and accuracy of different types of real-time PCR machines used to quantify the concentration of GM maize. Both trials used dual-labeled fluorogenic probes for quantification. The first ring trial used separate GM and reference assays (a single fluorescence channel), and the second used a combined duplex assay (two simultaneous fluorescence channels). Five manufacturers and seven models--including a 96-well microtiter-plate, rotary, and portable machines--were examined. In one trial, the machine used had a significant effect on precision, but in the other it did not. Overall, the degree of variation due to the machine model was lower than other factors. No significant repeatable difference in accuracy was observed between machine models. It was not possible to use sufficient replication of machine type in each laboratory to examine all sources of variation in this study, but the results strongly indicate that factors other than machine type or manufacturer (e.g., method or laboratory) contribute more to variation in a GM quantification result.     

PBXL Fluorescent Dyes for Ultrasensitive Direct Detection

PBXL dyes are a group of phycobilisome-based fluors that provide high sensitivity in direct fluorescent detection formats. Phycobilisomes are proteinaceous, supramolecular complexes that are photosynthetic antennae complexes in red algae and cyanobacteria. For the PBXL dyes, the phycobilisome has been chemically cross-linked in such a way that it remains water soluble and stable. Stabilized phycobilisomes (PBXL dyes) have high complex weights (between 10 and 15 million daltons) and Stokes shifts (up to 121 nm). They contain many hundreds of chromophores coordinated to transfer green and yellow light efficiently down an energy gradient to emit red light at wavelengths around 666 nm. Each PBXL dye can deliver up to 1400 chromophores per binding event without additional signal generation steps, signal amplification, or enzyme substrates. PBXL dyes provide a physical amplification of signal, enabling ultrasensitive, direct fluorescent detection of specific binding events. A number of studies done in our laboratory and in collaborating laboratories are summarized in this article. These studies demonstrated the utility of PBXL dyes in select high-sensitivity applications, such as a thyroid stimulating hormone (TSH) microplate immunoassay, detection of the low-density cell surface marker CD56 using flow cytometry, BSA–biotin, and actin detection in a western blot format and paternity testing using a DNA array on glass slides. PBXL dyes have the potential for providing a highly sensitive, simple, and direct fluorescent detection method to a wide range of targets and assay formats that could reduce costs associated with reagents and labor as well as decreasing the time to the first result.     

有机硅活性中间体的研究 II. 一些含环丙基的有机硅化合物的合成及其结构

用锂有机物的方法合成了四种含有环丙基有机硅化合物,对上述每种化合物中可能存在着的立体异构进行了分离和和构型测定。     

Phosphorescent particle tracking, a novel optical technique with which to visualise the interaction of gas flowstreams within the cylinder of an IC engine

Flow tracing within the cylinder of an IC engine has been successfully carried out for well over a decade. This paper proposes a new concept in which it will be possible to visualise the interaction of two flowstreams simultaneously within the cylinder of an IC engine. This is achieved by the addition of small phosphorescent tracer particles of differing colours to each flowstream. This paper describes the concept and the evolution of the method. Some preliminary results are shown that confirm the ability of the method to provide information on mixing flow streams. Whilst the technique was developed for IC engine evaluation it has potential applications in other mixing flow studies.     

The microwave heating of two-dimensional slabs with small Arrhenius absorptivity

The microwave heating of two-dimensional slabs in a long rectangularwaveguide propagating the TE₁₀ mode is examined. The temperaturedependency of the electrical conductivity and the thermal absorptivityis assumed to be governed by the Arrhenius law, while both theelectrical permittivity and the magnetic permeability are assumedconstant. The governing equations are the forced heat equationand the steady-state version of Maxwell's equation while theboundary conditions take into account both convective and radiativeheat loss. Approximate analytical solutions, valid for smallthermal absorptivity, are found for the temperature and theelectric-field amplitude using the Galerkin method. As the Arrheniuslaw is not amenable analytically, it is approximated by a rational-cubicfunction. At the steady state the temperature versus power relationshipis found to be multivalued; at the critical power level thermalrunaway occurs when the temperature jumps from the lower (cool)temperature branch to the upper (hot) temperature branch ofthe solution. In the steady-state limit the approximate analyticalsolutions are compared with the numerical solutions of the governingequations for various special cases. These are the limits ofsmall and large heat loss and an intermediate case involvingradiative heat loss. Results are also presented for a case wheredifferential cooling occurs on the different sides on the slab.An alternative heating scenario, where one end of the waveguideis blocked by a short, is also considered. The approximate solutionsare found for this geometry and compared in the small Biot-numberlimit to Kriegsmann (1997). Also, a control process is presented,which allows thermal runaway to be avoided and the desired finalsteady state to be reached. Various special cases of the feedbackparameters associated with the control process are examined.     

Bi-directional modulation of AMPA receptor unitary conductance by synaptic activity

Background  

Knowledge of how synapses alter their efficiency of communication is central to the understanding of learning and memory. The most extensively studied forms of synaptic plasticity are long-term potentiation (LTP) and its counterpart long-term depression (LTD) of AMPA receptor-mediated synaptic transmission. In the CA1 region of the hippocampus, it has been shown that LTP often involves a rapid increase in the unitary conductance of AMPA receptor channels. However, LTP can also occur in the absence of any alteration in AMPA receptor unitary conductance. In the present study we have used whole-cell dendritic recording, failures analysis and non-stationary fluctuation analysis to investigate the mechanism of depotentiation of LTP.     

Twisting DNA: single molecule studies

Over the past 10 years a number of new techniques have emerged that allow the manipulation of single DNA molecules and other biopolymers (RNA, proteins, etc.). These experiments have permitted the measurement of the DNA stretching and twisting elasticity and have consequently revealed the essential role played by the DNA mechanical properties in its interactions with proteins. We shall first describe the different methods used to stretch and twist single DNA molecules. We will then focus on its behaviour under torsion, especially by discussing the different methods used to estimate its torsional modulus.     

PROMOT: A Modeling Tool for Chemical Processes

The novel process modeling tool PROMOT supports the object-oriented modeling of chemical processes for the simulation environment DIVA. In PROMOT, differential-algebraic process models can be built by aggregating structural and behavioral modeling entities that represent the topological structure or the dynamic and steady-state behavior, respectively, of the investigated chemical processes. Process models and their modeling entities may be defined either in an object-oriented modeling language or with a graphical user interface. This paper discusses the modeling concept, the modeling language, the knowledge representation aspects, and the implementation of PROMOT.