Description of an axially-dispersed plug flow model for the flow pattern in elements of fluid systems

The Laplace transforms of the output signals from a three-sectional system (i.e., fore-section, investigated vessel and after-section), in which the sections have different diameters, are described for δ-function, rectangular and arbitrary input signals by using the axially-dispersed plug flow model. Equations for the means residence time and the variance of the response of the system are reported. The results could be used to evaluate the axial dispersion cofficient flow analysis or process systems, for system modelling and optimization.     

Influence of the main parameters of single-line flow-injection systems without chemical reaction on the output signal : Part 1. Dispersion Characteristics of the Main Sections of the Flow System

Single-line flow-injection systems with valve, hydrodynamic, syringe or delta-function injection of the analyte are considered. Appropriate equations for calculating the Peclet numbers of their main sections (i.e., the fore-section, the injection section, the reactor, the measurement cell, and the after-section) are described. Two types of reactor with different dispersion characteristics (i.e., straight tube and coiled tube reactors) are considered. The detector is assumed to measure one of three concentrations: (1) the mean concentration in the cross-section of the flow situated in the middle of the measurement cell; (2) the average integral concentration in the whole volume of the measurement cell; or (3) the average integral surface concentration at the inner walls of the measurement cell. Equations for calculating the Laplace transform of the surface and the integral surface concentration, and for the mean and the variance of the corresponding concentration curves are derived. The conclusions made can be used to investigate the influence of the main parameters of single-line flow-injection systems on sample throughput by simulation of the mathematical models.     

Time-resolved fluorescence spectroscopy for illuminating complex systems

Over the years, the emissive characteristics (spectral, temporal, and polarization) of fluorophores have been widely used to probe a wide variety of systems. Fluorescence lifetime and rotational reorientation time measurements, in particular, offer a means to elucidate key details about complex systems. Further, because fluorescence occurs on the nanosecond (10⁻⁹ s) timescale, competing or perturbing kinetic processes like collisional quenching, solvent relaxation, energy transfer, and rotational reorientation can affect the fluorescence and hence be quantified. Thus, a carefully chosen and “placed” fluorophore can serve as an reporter on a wide range of nanosecond or faster events. This contribution is divided into three sections. The Theory section discusses time-resolved anisotropy and intensity decay kinetics (time and frequency domains), pump–probe spectroscopy, and up-conversion. The second section describes time-correlated single photon counting (TCSPC) and multifrequency phase-modulation fluorescence instruments. The final section is divided into subsections on the use of time-resolved fluorescence: (1) to study solvation dynamics, biochemical systems, polymer photophysics, and organized media; (2) as a tool in the separation sciences, microscopy, and sensing; and (3) coupled with multiphoton excitation strategies.     

Poly(ethyleneimine) as reducing and stabilizing agent for the formation of gold nanoparticles in w/o microemulsions

This paper is focused on the use of branched poly(ethyleneimine) (PEI) as reducing as well as stabilizing agent for the formation of gold nanoparticles in different media. The process of nanoparticle formation was investigated, in the absence of any other reducing agents, in microemulsion template phase in comparison to the nucleation process in aqueous polymer solution.

On the one hand, it was shown that the polyelectrolyte can be used for the controlled single-step synthesis and stabilization of gold nanoparticles via a nucleation reaction and particles with an average diameter of 7.1 nm can be produced.

On the other hand, it was demonstrated that the polymer can also act as reducing and stabilizing agent in much more complex systems, i.e. in water-in-oil (w/o) microemulsion droplets. The reverse microemulsion droplets of the quaternary system sodium dodecylsulfate (SDS)/toluene–pentanol (1:1)/water were successfully used for the synthesis of gold nanoparticles. The polymer, incorporated in the droplets, exhibits reducing properties, adsorbs on the surface of the nanoparticles and prevents their aggregation. Consequently, nanoparticles of 8.6 nm can be redispersed after solvent evaporation without a change of their size.

Nevertheless, the polymer acts already as a “template” during the formation of the nanoparticles in water and in microemulsion, so that an additional template effect of the microemulsion is not observed.

The particle formation for both methods is checked by means of UV–vis spectroscopy and the particle size and size distribution are investigated via dynamic light scattering and transmission electron microscopy (TEM).     

Performance of a sound card as data acquisition system and a lock-in emulated by software in capillary electrophoresis

The performance of fluorescence detectors in capillary electrophoresis is maximized when the excitation light intensity is modulated in time with optimal frequencies. This is especially true when photomultiplier tubes are used to detect the fluorescent light. The photomultiplier tube amplified raw output signal can in principle be captured directly by a personal computer sound card (PCSC) and processed by a lock-in emulated by software. This possibility is demonstrated in the present work and the performance of this new setup is compared with a traditional data acquisition system. The results obtained with this “PCSC and lock-in emulated by software” were of the same quality or even better compared to that obtained by conventional time integrators (Boxcars) and data acquisition boards. With PCSC the limits of detection (LOD) found for both naphthalene-2,3-dicarboxaldehyde-derivatized tyrosine and alanine were 3.3 and 3.5 fmol (injection of 5 nL of samples at 0.66 and 0.70 μmol/L), respectively. This is at least three times better compared to conventional systems when light emitting diodes (LEDs) are used as the excitation source in fluorescence detectors. The PCSC linear response range was also larger compared to conventional data acquisition boards. This scheme showed to be a practical and convenient alternative of data acquisition and signal processing for detection systems used in capillary electrophoresis.     

How gamma radiation processing systems are benefiting from the latest advances in information technology

This paper discusses how gamma irradiation plants are putting the latest advances in computer and information technology to use for better process control, cost savings, and strategic advantages.

Some irradiator operations are gaining significant benefits by integrating computer technology and robotics with real-time information processing, multi-user databases, and communication networks. The paper reports on several irradiation facilities that are making good use of client/server LANs, user-friendly graphics interfaces, supervisory control and data acquisition (SCADA) systems, distributed I/O with real-time sensor devices, trending analysis, real-time product tracking, dynamic product scheduling, and automated dosimetry reading. These plants are lowering costs by fast and reliable reconciliation of dosimetry data, easier validation to GMP requirements, optimizing production flow, and faster release of sterilized products to market.

There is a trend in the manufacturing sector towards total automation using “predictive process control”. Real-time verification of process parameters “on-the-run” allows control parameters to be adjusted appropriately, before the process strays out of limits. Applying this technology to the gamma radiation process, control will be based on monitoring the key parameters such as time, and making adjustments during the process to optimize quality and throughput. Dosimetry results will be used as a quality control measurement rather than as a final monitor for the release of the product. Results are correlated with the irradiation process data to quickly and confidently reconcile variations. Ultimately, a parametric process control system utilizing responsive control, feedback and verification will not only increase productivity and process efficiency, but can also result in operating within tighter dose control set points.     

Evolution of Porosity by Freeze Casting and Sintering of Sol-Gel Derived Ceramics

Freeze cast of aqueous ceramic powder slurries is described as a versatile process to fabricate complex-shaped ceramic parts. Since freezing of aqueous sols or powder suspensions include the nucleation and growth of ice crystals the evolving microstructure in particular the pore characteristics which are left behind after elimination of the solvent can be controlled by the freezing process. The freezing kinetics have then to be used to manifest the conditions for the formation of the intended porosity. The temperature profile in the freezing slurry was measured and calculated, in particular the movement of the freezing front through the slurry was determined. The results show that a homogeneous microstructure is reached in the surface region of the consolidated part. Individual ice crystals are detected within a distance of some hundred micrometers from the surface. The final pores are dendritic in shape with an elliptical cross section. The pores can grow up to several millimeters in length under the process conditions used in this study. The limits of freeze-sensitive slurry compositions should be investigated in further studies and the approach should be followed to increase the porosity by additional foaming steps.     

Predictive aging results in radiation environments

We have previously derived a time-temperature-dose rate superposition methodology, which, when applicable, can be used to predict polymer degradation versus dose rate, temperature and exposure time. This methodology results in predictive capabilities at the low dose rates and long time periods appropriate, for instance, to ambient nuclear power plant environments. The methodology was successfully applied to several polymeric cable materials and then verified for two of the materials by comparisons of the model predictions with 12 year, low-dose-rate aging data on these materials from a nuclear environment. In this paper, we provide a more detailed discussion of the methodology and apply it to data obtained on a number of additional nuclear power plant cable insulation (a hypalon, a silicone rubber and two ethylene-tetrafluoroethylenes) and jacket (a hypalon) materials. We then show that the predicted, low-dose-rate results for our materials are in excellent agreement with long-term (7–9 year) low-dose-rate results recently obtained for the same material types actually aged under bnuclear power plant conditions. Based on a combination of the modelling and long-term results, we find indications of reasonably similar degradation responses among several different commercial formulations for each of the following “generic” materials: hypalon, ethylene-tetrafluoroethylene, silicone rubber and PVC. If such “generic” behavior can be further substantiated through modelling and long-term results on additional formulations, predictions of cable life for other commercial materials of the same generic types would be greatly facilitated.     

A spectrophotometric flow procedure for the determination of cationic surfactants in natural waters using a solenoid micro-pump for fluid propulsion

An automatic flow-analysis procedure for spectrophotometric determination of cationic surfactants in surface water using a solenoid micro-pump for propelling solutions of reagents and sample is described. The proposed method is based on a ternary formation complex between chromazurol S, the Fe(III) ion, and the cationic surfactant. The flow network comprised four solenoid micro-pumps controlled by a microcomputer, which performed the sampling step by loading a reaction coil with sample and reagent solutions and displacing the sample zone through the analytical path. The system is simple, easy to operate, and very flexible, with sufficient sensitivity to determine cationic surfactants in water without any pre-concentration or separation step. After determining the best operational conditions, favourable features such as a linear response between 0.34 and 10.2?mg?L^?1 of surfactant (R?=?0.999), a relative standard deviation of 0.6% (n?=?11) for a sample containing 3.4?mg?L^?1 of surfactant, a detection limit of 0.035?mg?L^?1 of surfactant, and a sampling throughput of 72 determinations per hour were achieved. The system was used to determine cationic surfactant in river-water samples, and recovery values between 91 and 106% were achieved.     

The adiabatic approximation in time-dependent density matrix functional theory: response properties from dynamics of phase-including natural orbitals

The adiabatic approximation is problematic in time-dependent density matrix functional theory. With pure density matrix functionals (invariant under phase change of the natural orbitals) it leads to lack of response in the occupation numbers, hence wrong frequency dependent responses, in particular α(ω→0)≠α(0) (the static polarizability). We propose to relinquish the requirement that the functional must be a pure one-body reduced density matrix (1RDM) functional, and to introduce additional variables which can be interpreted as phases of the one-particle states of the independent particle reference system formed with the natural orbitals, thus obtaining so-called phase-including natural orbital (PINO) functionals. We also stress the importance of the correct choice of the complex conjugation in the two-electron integrals in the commonly used functionals (they should not be of exchange type). We demonstrate with the Lo?wdin-Shull energy expression for two-electron systems, which is an example of a PINO functional, that for two-electron systems exact responses (polarizabilities, excitation energies) are obtained, while writing this energy expression in the usual way as a 1RDM functional yields erroneous responses.     

Noise response in monomolecular closed systems

One of the primary interests in understanding biological systems is the interaction between noise and cellular regulation. Noise levels can be altered by rate constant perturbations, which may result in an imbalance of important biological functions. Although the theory of noise localization can estimate noise perturbation response, it is currently limited to open systems, where the majority of biological networks belong. However, during their lifetime, some components of biological systems participate in reactions that can be categorized under a closed system. Therefore, a counterpart theory for closed systems is desirable. In this work, steady-state perturbations of monomolecular closed systems and ways to estimate the response of noise as (co)variances are explored. We extend the structural sensitivity analysis for analyzing noise response patterns by using additional clues derived from multinomial assumptions. We identified scenarios in which this combination might fail in noise prediction, which we call noise flip, arising from the nonlinear dependence of variance upon composition. Nevertheless, theoretical intuition and simulation show that noise flip diminishes with increasing system size. This work provides an efficient and scalable means to estimate noise responses with potential applications in model discrimination, network-wide response scanning, and reconstruction.     

Rheological properties of nanopowder alumina coated with adsorbed fatty acids

The rheological properties of a nanosized alumina powder coated with fatty acid steric stabilizers of varying chain length were investigated. The storage and loss moduli of the complex modulus were measured to characterize the behavior of the flocculated systems. As chain length increased, there was a transition from an elastic response to fluid behavior. However, the fluid system developed elastic characteristics at relatively low volume fractions of 22%. The length of the steric barrier required to produce the fluid dispersion was estimated to be approximately 2 nm and correlates with attractive interactions on the order of the system thermal energy. Moreover, in the flocculated systems, the storage modulus was found to be higher than reported previously in the literature. These higher values were related to the additional attractive forces due to van der Waals attractions between the hydrocarbon tails of the adsorbed fatty acid layers.     

Washing frozen red blood cell concentrates using hollow fibres

Today the cryopreservation of human blood products is routine. However, before reinfusion the cryoprotectant, often glycerol, has to be removed. We have designed a combined microfiltration diafiltration process using microporous hollow fibres for removing glycerol from frozen red blood cell concentrates. As the system can be closed to the atmosphere there is no possibility of infection of the “washed” blood. Thus the post-thaw shelf life of the blood may be greatly increased. The process has been optimized by minimizing both the processing time and diluent volume required. Finally a hollow fibre module capable of completing the entire washing process in 30 min has been developed. We show that such a module requires hollow fibres with an inside diameter of 200 μm. The design equations we present are generally applicable to the design of hollow fibre microfiltration systems.     

Correlation of resonances of strongly coupled spin systems via responses due to strong coupling in homonuclear two-dimensional j-resolved spectra: Total assignment of the 1H-NMR spectrum of 2-(2′-pyridyl)-1,8-naphthyridine

Homonuclear two-dimensional J-resolved (2DJ) spectra of molecules containing strongly coupled spin systems contain additional responses and thus additional information, the responses arising from the mixing effects of the 180° pulse employed to create the spin echo upon which the experiment is based. Although additional responses due to strong coupling are generally considered to be an undesirable complication inherent to the experiment, it is shown that they can serve a useful correlation function. Total assignment of the ¹H-nmr spectrum of 2-(2′-pyridyl)-1,8-naphthyridine at 100 MHz is reported, and members of the three strongly coupled spin systems of the molecule are identified via the additional responses due to strong coupling.     

Geometrical aspects of self diffusion in liquid water

In the late 1950s Cohen and Turnbull proposed a model for the self diffusion process in high density fluids, which considers the diffusion process as driven by the free volume fluctuations. An explicit expression was derived for the diffusion coefficient on hard sphere systems, and the results were consistent with molecular dynamic simulations. However the model is not able to reproduce experimental or simulation results for associated fluids, particularly in liquid water, where there is a huge variation of the diffusion coefficient without a significant change in the density. This implies that other properties, besides the free volume, have to be considered in modelling the diffusion process. The model we propose here takes into account both the volume and the shape of the “cage” surrounding the molecules. The “cage” is defined through the Voronoi polyhedra which are calculated from molecular dynamics simulations. The resulting diffusion coefficients, which have been calculated making use only of structural properties, are in good agreement with those evaluated directly from the long time behaviour of the molecular mean square displacements during the molecular dynamics runs.     

On choosing a reference redox system for electrochemical measurements: a cautionary tale

The potential of a quasi-reference electrode can be determined by introducing an internal reference redox system (IRRS) which comprises either the oxidizable or reducible form of a reversible (and, ideally, outer-sphere) redox couple and then observing the cyclic voltammetric responses. The objective is to choose the IRRS so that the cyclic voltammetric response for the simultaneously present electroactive analyte system (ANS) can be observed independently of the IRRS response. We identify three fundamental paradigms describing the relative positioning of the IRRS and ANS on the potential scale, the operative redox components for the IRRS and ANS, and the starting potential (E _start), reversing potential (E _rev), and ending potential (E _end) for the cyclic voltammetric scan as follows: paradigm A, an optimal paradigm which can produce completely independent cyclic voltammetric responses for the IRRS or for ANS; paradigm B, a less-than-optimal paradigm which can produce an independent cyclic voltammetry (CV) response for the ANS or a mixed response for the IRRS with that response on top of the ANS response; paradigm C, a problematic paradigm that can produce an independent CV response for the IRRS or a mixed response for the ANS with that response on top of the IRRS response; and any mixed response produces a thermodynamically favored redox cross-reaction which couples the IRRS and ANS systems and which can complicate the analysis of the ANS and IRRS responses. The conclusion is that paradigm C is to be avoided.     

An electronic aid for line selection for scanning inductively coupled plasma atomic emission spectrometers

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). Accompanying this hard copy text is a disk containing the program, source flies, data files and a brief manual along with a few programming notes. The main article discusses the purpose of this work, and the Appendix provides brief instruction on the use of the program, manipulation of the data, and source code. An automatic file selection system for the control of a rapid scanning spectrometer performing atomic emission spectrometry has been developed using the PROLOG language. The system can be “taught” the elemental composition of a given sample type. It uses this information (when available) to generate a linear search strategy which minimizes the number of lines that need to be measured. The rules used by the system can be observed during system operation to allow a trace of the logic. Reading of the initial data base takes no more than 6 s and then decisions are made in less than 1 s per line.     

ISO radiation sterilization standards

This presentation provides an overview of the current status of the ISO radiation sterilization standards. The ISO standards are voluntary standards which detail both the validation and routine control of the sterilization process. ISO 11137 was approved in 1994 and published in 1995. When reviewing the standard you will note that less than 20% of the standard is devoted to requirements and the remainder is guidance on how to comply with the requirements.

Future standards developments in radiation sterilization are being focused on providing additional guidance. The guidance that is currently provided in informative annexes of ISO 11137 includes: device/packaging materials, dose setting methods, and dosimeters and dose measurement, currently, there are four Technical Reports being developed to provide additional guidance:

1. 1. AAMI Draft TIR, “Radiation Sterilization Material Qualification”

2. 2. ISO TR 13409-1996, “Sterilization of health care products — Radiation sterilization — Substantiation of 25 kGy as a sterilization dose for small or infrequent production batches”

3. 3. ISO Draft TR, “Sterilization of health care products — Radiation sterilization Selection of a sterilization dose for a single production batch” li]4. ISO Draft TR, “Sterilization of health care products — Radiation sterilization-Product Families, Plans for Sampling and Frequency of Dose Audits.”

     

UV tuning of the electro-optical and morphology properties in polymer-dispersed liquid crystals

Polymer-dispersed liquid crystal (PDLC) films operating in reverse mode are transparent electro-optical devices, which can be turned into an opaque state by application of a suitable electric field. The effect was investigated of different UV powers, used during the polymerization process, on the electro-optical and morphology properties of PDLCs, working in reverse mode operation. Films were obtained by UV polymerization of mixtures of a low molecular weight nematic liquid crystal and a photopolymerizable liquid crystal monomer, homeotropically aligned by rough conductive surfaces. The electro-optical and morphology properties of samples were related to the polymerization conditions. Samples polymerized by lower UV powers exhibited “polymer ball” morphology and an electro-optical response due to the liquid crystal director reorientation, whereas samples obtained at higher UV powers showed a “Swiss cheese” morphology and an electro-optical response due to dynamic scattering. In addition, we observed by conductivity and IR measurements that UV exposure induces a degradation of the nematic liquid crystal.