On the effects of doping calamitic and discotic nematics with materials of the opposite aspect ratio

In this paper the inter-mixing of calamitic and discotic materials is discussed. The systems are found to be immiscible near the middle of the phase diagram, as was predicted theoretically. However, a degree of miscibility is seen at each end of the phase diagram, allowing some interesting effects to be explored. A negative permittivity anisotropy is induced in a discotic material by dissolution of a polar calamitic dopant. The relaxation behaviour of the dopant in the material is studied and found to be similar to that in the pure calamitic, as far as can be determined in this experiment. The elastic constants of a calamitic mixture are enhanced by addition of a discotic dopant. This is believed to be due to the packing of the discotic molecules in such a way as to hinder director distortions, and may be useful for changing the values of calamitic elastic constants.     

Four-arm oligonucleotide Ni(II)-cyclam-centered complexes as precursors for the generation of supramolecular periodic assemblies

The development of a multiarm metal-centered DNA building block as a precursor for the construction of supramolecular assemblies has relied upon the preparation of a Ni(II)-1,4,8,11-tetrazacyclotetradecane ligand (cyclam) functionalized with four linkers. This complex can be incorporated into a support-bound DNA sequence and the remaining three linkers can then be elongated by DNA synthesis. The result is a Ni(II)-cyclam complex tethering four 20-mer DNA strands. This building block, designed to be tetrahedral in nature, can in principle be used to form tetrahedral assemblies. These assemblies can be designed to be of known size and composition or permitted to grow into complexes of essentially infinite size, ideally the macroscopic version of a crystal.     

Bulk synthesis of polymer-inorganic colloidal clusters

We describe a procedure to synthesize colloidal clusters with polyhedral morphologies in high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. We show that the synthesis initially used for silica-polystyrene hybrid clusters can be generalized to create clusters from other inorganic and polymer particles. We also show that high yields of particular morphologies can be obtained by precise control of the inorganic seed particle size, a finding that can be explained using a hard-sphere packing model. These clusters can be further chemically modified for a variety of applications. Introducing a cross-linker leads to colloidal clusters that can be index matched in an appropriate solvent, allowing them to be used for particle tracking or optical studies of colloidal self-assembly. Also, depositing a thin silica layer on these colloids allows the surface properties to be controlled using silane chemistry.     

Effects of shear rate on propagation of blood clotting determined using microfluidics and numerical simulations

This paper describes microfluidic experiments with human blood plasma and numerical simulations to determine the role of fluid flow in the regulation of propagation of blood clotting. We demonstrate that propagation of clotting can be regulated by different mechanisms depending on the volume-to-surface ratio of a channel. In small channels, propagation of clotting can be prevented by surface-bound inhibitors of clotting present on vessel walls. In large channels, where surface-bound inhibitors are ineffective, propagation of clotting can be prevented by a shear rate above a threshold value, in agreement with predictions of a simple reaction-diffusion mechanism. We also demonstrate that propagation of clotting in a channel with a large volume-to-surface ratio and a shear rate below a threshold shear rate can be slowed by decreasing the production of thrombin, an activator of clotting. These in vitro results make two predictions, which should be experimentally tested in vivo. First, propagation of clotting from superficial veins to deep veins may be regulated by shear rate, which might explain the correlation between superficial thrombosis and the development of deep vein thrombosis (DVT). Second, nontoxic thrombin inhibitors with high binding affinities could be locally administered to prevent recurrent thrombosis after a clot has been removed. In addition, these results demonstrate the utility of simplified mechanisms and microfluidics for generating and testing predictions about the dynamics of complex biochemical networks.     

Biocompatibility of nanofilm-encapsulated silicone and silicone-hydrogel contact lenses

A material placed in or in contact with a biological system, that causes the minimum perturbation that can be tolerated by the host biological system, can be considered to be biocompatible. The major effects caused by a contact lens can be considered to be 1) the blocking of the natural supply of oxygen to the epithelium cells of the cornea, 2) interference with the normal evaporation of water from the tear fluid layer, and 3) hindrance of the normal functions of blinking for replenishing oxygen-saturated tear fluid and removing dead epithelium cells, which result from apoptosis. The encapsulation of a highly oxygen-permeable contact lens by a nanofilm with an imperturbable surface state minimizes all these terms. The encapsulated contact lens can be worn safely in extended wear.     

The use of uncertainty estimates of test results in comparisons with acceptance limits

When a test is performed in order to qualify a material or a product for a certain use, the result is generally compared with an acceptance limit. The test result has an uncertainty which should be estimated and stated (e.g. in accordance with GUM). Very often this is not the case. Further, discussions often arise on the issue of how the uncertainty shall be considered in relationship to the acceptance limit. The intention of this note is to describe, in simple terms, the statistical background and to give some recommendations. In short, there are two clean-cut, extreme situations. The first case is when the uncertainty of the testing procedure is the dominating factor. Here it is found that the estimates of single laboratories cannot, generally, be used for comparisons with acceptance limits. One should have standardised, well-verified estimates based on comprehensive investigations of the method. It can also be concluded that comparisons between test results and acceptance limits have to be made with regard to the actual circumstances, as, e.g. how the acceptance limit is related to the risk. In the second case, the variation in the property of the material or product dominates and the uncertainty of the testing procedure is negligible. When the results are non-quantitative (go – no go), statistical methods can be used to estimate the risk taken with a certain sampling and acceptance strategy that a certain proportion of the batch to be delivered does not qualify. This should be considered more often in standardisation of product test methods. When the results are quantitative, a statistical analysis should be performed and the uncertainty should be compared with the acceptance limit as before, from the actual circumstances. When effects of testing uncertainty and product variation are comparable a sound treatment requires extensive experimental work. No short cuts can be made without loss of confidence! Received: 17 August 2001 Accepted: 21 March 2002     

An error model for evaluation and interpretation of proficiency testing

Data from proficiency testing can be used to increase our knowledge of the performance of populations of laboratories, individual laboratories and different measurement methods. To support the evaluation and interpretation of results from proficiency testing an error model containing different random and systematic components is presented. From a single round of a proficiency testing scheme the total variation in a population of laboratories can be estimated. With results from several rounds the random variation can be separated into a laboratory and time component and for individual laboratories it is then also possible to evaluate stability and bias in relation to the population mean. By comparing results from laboratories using different methods systematic differences between methods may be indicated. By using results from several rounds a systematic difference can be partitioned into two components: a common systematic difference, possibly depending on the level, and a sample-specific component. It is essential to distinguish between these two components as the former may be eliminated by a correction while the latter must be treated as a random component in the evaluation of uncertainty. Received: 20 November 2000 Accepted: 3 January 2001     

Measurement of near zero concentration: recording and reporting results that fall close to or below the detection limit

Issues relating to the recording and reporting of analytical data obtained where the concentration of analyte is around or below the detection limit are discussed. The following recommendations are proposed. Analytical results should be recorded by the analyst exactly as they occur, including any negative results, and such records retained for an appropriate length of time. For the purposes of quality assurance in the laboratory (including method validation, internal quality control, and proficiency testing), negative results should be used as they stand. Analytical results reported to a customer should be accompanied by a statement of uncertainty including, in the present context, uncertainty at low concentrations of analyte. The method of editing of reported results must be a contractual matter between the analyst and the customer, but a statement of the procedure used should accompany the results and should be explicit. Normally such editing should be restricted to setting negative results to zero. The customer should be encouraged to pass on the statement to all end users. Data intended for the public domain should be accompanied by a statement detailing the uncertainty, the method of editing, and the location of the unedited data. Most types of statistical processing of datasets containing low concentrations of analyte should be undertaken on the unedited data.     

Microcapillary electrophoresis chips utilizing controllable micro-lens structures and buried optical fibers for on-line optical detection

In this study, a new design of a controllable micro-lens structure capable of the enhancement of LIF detection system has been demonstrated, which can be further integrated with buried optical fibers on a micro-CE chip for sample separation and detection. Two pneumatic side-chambers were placed between a micro-CE channel and an optical fiber channel. The intervals between the side-chamber and the microchannel were used to form two surfaces of the controllable micro-lens structure. Deformations of the two surfaces can be generated after pressurized index-matching fluid was injected into the pneumatic side-chambers. The side-chambers can be deflected as a double convex lens to focus both the excitation light source and the fluorescent emission signal. The profile and the focal length of the micro-lens structure can be actively adjusted by applying different liquid pressures so that biosamples with a low concentration can be detected. Using low-cost polymeric materials such as polydimethylsiloxane, rapid and reliable fabrication techniques involving standard lithography and replication process was employed for the formation of the proposed chip device. Experimental results revealed the controllable micro-lens structure can be successfully deformed as a convex lens to focus the laser light source and the collected fluorescence signal can be enhanced accordingly. The power amplitude of excitation laser light can be enhanced by 5.4-fold. FITC dye and DNA markers were then utilized for micro-CE testing. The results indicated that the signal amplitude could be enhanced 2.5-fold when compared to the case without the activation of the micro-lens. According to the experimental results, the developed device has a great potential to be integrated with other microfluidic devices for further biomedical applications.     

Comparison of Neural Networks and Theoretical Correction Models

In x-ray fluorescence spectrometry, matrix effects have to be corrected. The empiric equations, the theoretical coefficients and the fundamental parameters can be applied in the purpose. The classical matrix correction models include mainly Lachance-Trail,Rousseau, De Jongh, Claisse-Quentin, COLA algorithms,etc. The good results can be obtained by using a number of standards or the theoretical Alpha coefficients if the range of component concentrations in samples is not very wide. When unknown samples with a wide range of concentrations are predicted, a recalculation process of the theoretical Alpha coefficients has to be made. In addition, a spline function may be chosen to split wide range in several segments.     

A targeted reweighting method for accelerating the exploration of high-dimensional configuration space

Time scales available to biomolecular simulations are limited by barriers among states in a high-dimensional configuration space. If equilibrium averages are to be computed, methods that accelerate barrier passage can be carried out by non-Boltzmann sampling. Barriers can be reduced by modifying the potential-energy function and running dynamics on the modified surface. The Boltzmann average can be restored by reweighting each point along the trajectory. We introduce a targeted reweighting scheme where some barriers are reduced, while others are not modified. If only equilibrium properties are desired, trajectories in configuration space can be generated by Langevin dynamics. Once past a transient time, these trajectories guarantee equilibrium sampling when reweighted. A relatively high-order stochastic integration method can be used to generate trajectories. The targeted reweighting scheme is illustrated by a series of double-well models with varying degrees of freedom and shown to be a very efficient method to provide the correct equilibrium distributions, in comparison with analytic results. The scheme is applied to a protein model consisting of a chain of connected beads characterized by dihedral angles and the van der Waals interactions among the beads. We investigate the sampling of configuration space for a model of a helix-turn-helix motif. The targeted reweighting is found to be essential to permit the original all-helical conformation to bend and generate turn structures while still maintaining the alpha-helical segments.     

A discrete look at localization

This article introduces a set of localized orthonormal functions to serve as basis functions for quantum calculations. They are defined to be eigenfunctions of the position operator in a function space. Their properties, including their variances, for a one-dimensional system are developed. The application to simple harmonic motion is considered as an example and, in particular, the time evolution of an initially localized function is calculated and shown to be periodic. The theory can be interpreted as producing a discrete quantization of space with Hamiltonian interactions that are predominantly between nearest neighbors. These functions can also be used in approximate calculations. To illustrate their accuracy, the example of a Morse oscillator treated as a perturbation of a harmonic oscillator is reconsidered. It is shown that the localized functions in a variational calculation lead to a result that is a good approximation for the lowest states. Furthermore, the use of a wave function that is defined only at discrete points can be justified as the first approximation to this, so that its accuracy can also be discussed. © 1995 John Wiley & Sons, Inc.     

Spectroelectrochemistry study on the electrochemical reduction of ethidium bromide.

The electrochemical reduction mechanism of ethidium bromide was first studied by spectroelectrochemistry. This reduction was proved to be a two-step process by cyclic voltammetry, differential pulse voltammetry and spectroelectrochemistry, in which each step was proved to be a one-electron transfer process by a spectropotentiostatic fluorescence technique. Hydroethidine was confirmed to be the final product by comparing the spectrum of the product of the electrochemical reduction to that of the product of the chemical reduction of ethidium bromide, and a carbon-centered radical was concluded to be a reasonable intermediate product during the electrochemical reduction of ethidium bromide.     

Photofission for the detection of actinides

Nuclear waste management cost at CEA is a heavy budget share. Therefore, it is important, in order to minimize that cost, to select the most suitable repository for the waste. Significant cost savings are obtained, for example, whenever a medium activity waste drum initially filed to end up in a geological repository can be measured accurately enough to be accepted by the Centre de Stockage de l’Aube (CSA). Photofission can be used as a non-destructive technique to measure the actinide content embedded in a nuclear waste drum. It can even be applied when the waste is packaged in its heavy concrete shielding. It is equally sensitive to non-fissile nuclear material. However, the present state of art suffers from a lack of sensitivity to be able to help redirecting the waste to the proper repository. A new program called INPHO is proposed at CEA Saclay aiming at enhancing the sensitivity sufficiently to be applicable for waste characterization.     

High-contrast flicker luminescence on dynamic covalent structure based nanoaggregates

In nanoscience, molecular switches have played a significant role to deliver different control abilities to practical functions,whereas high-contrast luminescence switchable manipulation at nanoscale is still limited. Since the tuning for emission behavior with high contrast ratio strongly connects to numerous visualized sensing and optoelectronic applications, we here report that autonomous p H control can be enrolled to address a high-contrast molecular emission change at the nanoaggregated level, for gaining a flicker luminescence performance in aqueous media. Employing a BODIPY contained dynamic covalent dye, we find its luminescent signal and nanoaggregate size can be spontaneously adjusted in water. On this basis, high-contrast luminescence switching of the material can be achieved upon the alternate introduction of base and acid into the aggregation state. Such a behavior can be attributed to a p H triggered photo-induced electron transfer regulation process. The dye aggregates can be well endocytosed for bioimaging and its luminescent variation can be autonomously displayed as a flicker effect. These results provide new visions for the design and development of smart materials with a dynamic luminescence behavior.     

N-H carbazole synthesis from 2-chloroanilines via consecutive amination and C-H activation

N-H carbazoles can be produced from 2-chloroanilines and aryl bromides via consecutive catalytic amination and C-H activation. In many instances, this can be done in a tandem manner in one pot. The methodologies developed can be used in the synthesis of a range of carbazoles, including the natural products Clausine P and glycozolidine and a precursor in the synthesis of Clausines H, K, O, and 7-methoxy-O-methylmukonal, and can be extended to the synthesis of indoles.     

Chelate formation of ammonium aurintricarboxylate with bivalent copper : Micro-determination of copper by the colorimetric method

The formation of a coloured copper II chelate by ammonium aurintricarboxylate with λmax at 540 mμ may be utilised in the colorimetric determination of cupric ions on a micro-scale. It has been found that, for satisfactory results, at least a twentyfold molar excess of the reagent should be added. The colour intensity can be measured by using a spectrophotometer or a photoelectric colorimeter with a suitable filter.The colour is stable at room temperature for sufficiently long periods, but the intensity decreases above 30°C. For the formation of a colour suitable for measurement, the pH should be within 5.3–6.7. The smallest amount of copper that can be detected by the reagent is 1.7 p.p m. Details have been worked out for the use of this reagent, and the interference by various foreign ions has been noted and tolerance limits determined spectrophotometrically.     

Inorganic Crystal Structure Data to be Presented in a Form More Useful for Further Studies

To make inorganic structure data more useful for further studies a five-point list of simple procedures to be followed by authors of crystal structure papers is proposed. 1. A crystal structure should be described with the space group corresponding to its true symmetry. 2. A new structure proposal should be tested, if it is realistic in principle. 3. A structure should be described with a space group in a setting given in the International Tables. 4. For a comparison with other structures the structure data should be standardized with the program STRUCTURE TIDY. 5.“New” structure data should be checked in the databases, Chemical Abstracts or on-line intemet resources, if they are really new. The list is supplemented with many explanations, commentaries, examoles and references.     

A versatile twisted optical fiber sensor

An optical sensor sensitive to changes in light absorption and other optical interactions, and consisting of two fibers twisted around each other, is described. The sensor can be used as a refractometer, is very sensitive to the presence of water in oil, can be used to determine the amount of a solvent in oil, and might be useful in monitoring degradation of internal combustion engine oil. In addition, by surrounding the fibers with a film of solution, and observing the changes in ouput over time, additional information can be obtained. Used in this manner, the sensor can be used to identify specific solutions.     

Modulation-induced error in comprehensive two-dimensional gas chromatographic separations

There is a fundamental difference between data collected in comprehensive two-dimensional gas chromatographic (GCxGC) separations and data collected by one-dimensional GC techniques (or heart-cut GC techniques). This difference can be ascribed to the fact that GCxGC generates multiple sub-peaks for each analyte, as opposed to other GC techniques that generate only a single chromatographic peak for each analyte. In order to calculate the total signal for the analyte, the most commonly used approach is to consider the cumulative area that results from the integration of each sub-peak. Alternately, the data may be considered using higher order techniques such as the generalized rank annihilation method (GRAM). Regardless of the approach, the potential errors are expected to be greater for trace analytes where the sub-peaks are close to the limit of detection (LOD). This error is also expected to be compounded with phase-induced error, a phenomenon foreign to the measurement of single peaks. Here these sources of error are investigated for the first time using both the traditional integration-based approach and GRAM analysis. The use of simulated data permits the sources of error to be controlled and independently evaluated in a manner not possible with real data. The results of this study show that the error introduced by the modulation process is at worst 1% for analyte signals with a base peak height of 10xLOD and either approach to quantitation is used. Errors due to phase shifting are shown to be of greater concern, especially for trace analytes with only one or two visible sub-peaks. In this case, the error could be as great as 6.4% for symmetrical peaks when a conventional integration approach is used. This is contrasted by GRAM which provides a much more precise result, at worst 1.8% and 0.6% when the modulation ratio (MR) is 1.5 or 3.0, respectively for symmetrical peaks. The data show that for analyses demanding high precision, a MR of 3 should be targeted as a minimum, especially if multivariate techniques are to be used so as to maintain data density in the primary dimension. For rapid screening techniques where precision is not as critical lower MR values can be tolerated. When integration is used, if there are 4-5 visible sub-peaks included for a symmetrical peak at MR=3.0, the data will be reasonably free from phase-shift-induced errors or a negative bias. At MR=1.5, at least 3 sub-peaks must be included for a symmetrical peak. The proposed guidelines should be equally relevant to LCxLC and other similar techniques.