bluuebunny/crossref_metadata_2025 huggingface dataset:
Interatomic correlation in partially oriented polymer fibers
Authors: Hristov H. A. , Barton R. , Schultz J. M.
Published: May 2005

The atomic ordering in materials possessing cylindrical symmetry can be investigated by an approximation of the cylindrical distribution function in a given direction. The approximation gives correctly the extent of the interatomic correlation for a wide class of polymer fibers and reduces considerably the amount of the experimental and computational times.
Dispersion of Samples and Sample‐feeding for Counting Methods
Authors: Heidenreich Eberhard , Stintz G. Michael
Published: May 2005

The currently used methods of sample preparation are examined and found to be unsatisfactory in case of counting methods for particle size analysis. It is the purpose of this paper to review the results of investigations of two different measuring principles (light extinction and electrical resistance change) by use of the same signal handling equipment. The commonly used techniques and units are compared with regard to the resulting density distributions of particle size below 0.25 mm. The final conclusions including recommendations to the use of ultrasonic treatment and to improvements of the sampling and the sample‐feeding units are valid for all counting methods.
Online Measurement of the Grain Size Distribution of Sand 0–4 mm used for the production of concrete
Authors: Eder Theodor , Rötzer Harald , Donhoffer Dieter , Leo Riedlmayer , Volkmann Werner , Wallisch Karl , Zöhrer Johann
Published: May 2005

An apparatus is described for the fast and automatic measurement of the grain size distribution of sand ranging from 0 to 4 mm. A sample of sand continuously introduced at a rate of 30 g/min is separated by the apparatus into seven fractions of 0–0.063, 0.063–0.125, 0.125–0.25, 0.25–0.5, 0.5–1, 1–2, and 2–4 mm. The amount of sand in each of these fractions is determined and the results are given in time intervals of 1 minute. The sand is separated in a separation chamber through which water streams in a horizontal laminar flow. The samples are separated according to their settling velocities. The four coarse fractions descend to the bottom of the chamber. They are collected and weighed under water. The three fine fractions remain suspended in three effluent water streams. The quantity of sand is measured in flow cells by absorption of laser light. Control of the system as well as the collection and processing of the measured data are done by means of an electronic control unit and a microcomputer.
Application of an Electrical Conductivity Microprobe for the Characterization of bubble behavior in gas‐liquid bubble flow
Authors: Steinemann Jürgen , Buchholz Rainer
Published: May 2005

In this paper a new electrical conductivity technique for the measurement of bubble size and velocity is presented. This measuring system is able not only to estimate size and velocity of particles (bubbles and droplets in liquids) but also to give complete information on the space related motion of particles. Thus a significant improvement is achieved in the accuracy of measurement.

By using the simultanous measurement of both: bubble sizes and volumetric hold up of the dispersed phase, one is able to calculate the local interfacial area. In the first part of this paper the measuring system, its properties and limits are illustrated. In the second part results obtained in a bubble column will be presented.
Drop‐Size Distributions Produced by Pressure Nozzles
Authors: Schegk Claus‐Detlef , Löffler Friedrich
Published: May 2005

Measured drop‐size distributions are presented which were obtained by the atomization of water with hollow‐cone nozzles. The drop‐size distributions were determined using a scatteredlight particle size counting analyser at various locations in the droplet cone. These local distributions change systematically from the cone's axis to its border. To acquire the drop‐size distribution of all the drops the local distributions have to be superimposed. The spatial mass flow distribution in the cone can be calculated from these measurements.
The Influence of Particle Shape and Particle Size Distribution on fluidisation behaviour of granular activated carbon in the aqueous phase
Authors: van Lier Willem C.
Published: May 2005

This paper deals with the influence of particle shape and particle size distribution on the fluidisation behaviour of granular activated carbon in the aqueous phase. Methods for relating the degree of expansion, as a function of liquid velocity, to particle shape and particle size distribution are discussed and tested. Two different types of activated carbon, both containing irregularly shaped particles but with differences in shape, are used to test the models discussed. A tentative method which takes into account the influence of water temperature on fluidisation behaviour is proposed.
Data Reduction in Fluid Classification Methods
Authors: Svarovsky Ladislav , Mehrgan Hamid Reza
Published: May 2005

Fluid classification methods for particle size analysis are based on the concept of cut size. The particles suspended in a fluid are passed through several separation stages, of progressively finer cut‐size, so that each stage collects a fraction of the feed solids in the same way as each screen in a stack of sieves.

There is an inherent error involved in the data reduction, which often leads to a poor comparison between the results of fluid classification and sedimentation, although both in principle measure the equivalent Stokes' diameter.

This paper investigates the problem and attributes the above mentioned error to the difference between the equiprobable size and the analytical cut size. The paper presents a simple correlation which relates the analytical cut size and the equiprobable size if both the measured size distribution and the grade efficiency curve of the separator follow, approximately, log‐normal functions. The usefulness of the correlation is exemplified in the case of the Bahco analyser. Measured grade efficiency curves for each separation stage provide the necessary data for the above mentioned correction and this is then applied to examples of practical particle size analysis.
Particle Size Distribution Measurement by Automated Dual Wavelength Turbidimetry
Authors: Haseler Simon C.
Published: May 2005

Numerous methods have been reported in the literature for the measurement of (submicron) particle size distribution by turbidimetry. Attempts to apply some of these to coupler dispersions (oil‐in‐water emulsions of importance in the photographic industry) have not in general proved satisfactory, however, because small experimental errors lead to relatively large errors in the calculated distribution. In order to reduce this problem a turbidimetric technique involving measurements at two widely separated wavelengths, 400 nm and 2.22 μm, has been developed. Its accuracy has been demonstrated using polydisperse polystyrene latexes of known size distribution. With the aid of simple, purpose‐built equipment, linked to a desktop computer, the technique has been largely automated so that it is suitable for use by an unskilled operator working in a factory environment.
The Fractal Nature of Dendrites Formed by the Collection of Particles on Fibers
Authors: Ensor David S. , Mullins Michael E.
Published: May 2005

Aerosols or particles suspended in air are often filtered by pads of fibers. The particles collect on the surface of the fibers in chain‐like structures called dendrites. An example scanning electron micrograph of 4.1 μm diameter particles captured on a 25‐m̈m fiber was analyzed by a Richardson plot. The Richardson plot is the measured perimeter of an image as a function of the length of measure or stride length. Three distinct regions were identified. For long and short stride lengths, the linear fiber and spherical particles were Euclidean. In the intermediate stride length region, the dendrite was fractal with a dimension of 1.36. The fractal nature of dendrites results from the random position of particles approaching the fiber and the shadowing effect of collected particles. Fractal geometry is potentially a useful approach for describing the morphology of the dendritic structures.
Photometric On‐line Measurement of Surface Area of Powders
Authors: Leschonski Kurt , Boeck Thomas
Published: May 2005

Amongst the well known methods to measure surface area of particulate matter, preferably dry powders, only photometric methods can be used on‐line.

The basic equation for the photometric measurement of surface area is Lambert‐Beer's law, which describes the attenuation of light (extinction) due to the presence of particles in a light beam. The attenuation being dependent not only on the size distribution of the particles in the light beam but also on their volume concentration. Since both effects alter the attenuation simultaneously the solids volume concentration has to be measured independently of the attenuation in a true on‐line system. The instrument developed combines the extinction of white light with the absorption of γ‐rays.

Since the absorption of γ‐rays demands more particles in the measuring zone than the attenuation of light, an aerosol stream of rectangular cross section has been used which allows the simultaneous measurement of extinction and γ‐ray absorption.

Apart from a brief description of the theoretical background of the instrument experimental evidence will be given of its suitability for on‐line application [1, 2].
Applications of Recent Advances in Fineparticle Characterization to mineral processing
Authors: Kaye Brian H.
Published: May 2005

Fineparticle Science is the study of the production and the behavior of finely divided material. In recent years the technology of fineparticle science has expanded rapidly. Many of the new innovations in that science have important applications in mineral processing. An important recent development in the mathematics of fineparticle science is the use of fractal descriptors to describe rugged boundries. In this communication the use of fractals to describe cracks in N dimensional space and potential applications of fractal descriptions in liberation kinetics are discussed. Fractals can also be used to describe the progress of a water front in a secondary oil recovery system. The use of divers to study concentration gradients in settling suspensions (tailing ponds) are described. New studies aimed at the optimization of on‐line quality control of grinding circuits are reviewed.
The Measurement of Spatial Aerosol Distributions in Enclosures by Means of computed tomography
Authors: Luck Heinz O. , Siemund Bernd , Lorbeer Gerhard
Published: May 2005

A measurement method that approximates the spatial distribution of inhomogeneously distributed aerosols in a limited measurement plane is described. It is based on the evaluation of a comparably small number of infrared extinction measurements taken from the measurement plane boundary. The measured data are processed by means of computed tomography. The results are displayed on a monitor in a colour‐coded picture of the aerosol‐“density”‐pattern. The basic design and the principal characteristics of the method are mathematically described and verified by simulation tests and practical results which are obtained from an experimental set up using smoldering wood as an aerosol source.
Fractal Description of Extra Terrestrial Fineparticles
Authors: Kaye Brian H. , Clark Garry G.
Published: May 2005

A technique for measuring the fractal structure of the rugged boundaries exhibited by lunar dust and a cosmic dust fineparticle captured at the outer limits of earth's atmosphere are measured using a equipaced polygon construction measurement procedure. The measurement procedure is described and data illustrating the precision and accuracy of the method are presented. The technique can be automated using inexpensive equipment and is suitable for use in teaching laboratories. Comparative data is presented establishing that the equipaced polygon procedure generates data comparable to that generated by the structured walk exploration technique. It is suggested that the fractal structure of extra terrestrial fineparticles may be of interest not only to the cosmologist but to the mining engineer since lunar dust represents fractured material not subjected to attrition polishing. Models used to simulate the generation of soot in combustion processes are discussed and it is demonstrated that diffusion limited aggregation Monte Carlo routines generate an agglomerate that appears to have similar fractal structure to the cosmic dust fineparticle collected by Brownlee. The data presented also indicates that one should use caution when relating the fractal dimension of a projected perimeter profile in two dimensions to the three dimensional structure of a rugged fineparticle.
Pore Structure Analysis of Porous Particles by Modelless and Micropore Method
Authors: Yan Ji‐min , Zhang Qi‐yuan
Published: May 2005

The modelless (ML) and micropore (MP) methods for the pore structure analysis of porous particles have been studied. Concerning the ML method, it has been shown that the Kiselev equation can only be used to describe condensation and evaporation in capillaries, but cannot be used to describe the increase and decrease of the thickness of the adsorption layer. Strictly speaking, therefore, the ML method is not modelless even for the pore core size distribution. A comparison between the ML method and methods using an equivalent pore model is given. The results of using the ML method in conjunction with a certain pore model are little less accurate than those obtained by adopting the equivalent pore model straightaway. The parameters required for the calculation of both the pore core size and the pore size distribution as well as the conversion between these two calculations are given.

Concerning the MP method, it has been shown that the three types of v‐t curves, the theoretical foundation of the MP method, are not in one to one correspondance to the three kinds of adsorption mechanism. From the viewpoint of accuracy, the MP method has no advantage over the methods which are based on the condensation mechanism, both have their own merits.
Applications of Nuclear Magnetic Resonance Imaging in Particle Technology
Authors: Gladden Lynn F.
Published: May 2005

During the past decade, the application of Nuclear Magnetic Resonance (NMR) imaging techniques to problems of relevance to the process industries has been identified. In the context of particle technology, NMR imaging, in addition to the more routinely used techniques of Pulsed Gradient Spin Echo (PGSE) NMR and NMR spectroscopy, offer new methods of characterising pore structure, adsorption and diffusion processes within particles and packed beds of particles, as well as enabling time‐resolved in‐situ study of processes such as twophase flow, aggregation, polymerisation, crystallisation and phase separation phenomena. This paper reviews recent work in these areas, and also highlights the new insights NMR imaging can give us regarding the characterisation of porous materials, and the influence of the structure of the pore space on the transport processes occuring within a given porous solid.
Particle Manipulation by Ultrasonic Standing Wave Fields to complement dynamic light scattering experiments
Authors: Holwill Ian L. , Davies Gareth B. , Titchener‐Hooker Nigel J. , Hoare Michael
Published: May 2005

Dynamic light scattering is a widely used technique for the sizing of colloidal suspensions. It is capable of measuring particles across the size range from approximately 1 nm to several microns. However the larger particle sizes tend to pose problems for the interpretation of the scattered light signal either by virtue of their light scattering efficiency relative to the smaller species present or the departure of the scattered light signal from Gaussian statistics. Rapid removal of such particles in‐situ could extend the use of dynamic light scattering particularly in on‐line analysis or laboratory automated measurement. In this paper a method is demonstrated for the in‐situ removal of larger particles in suspension by means of ultrasonic standing waves and concurrent dynamic light scattering measurement. The theory behind ultrasonic particle manipulation and its effect on the motion of the particles is discussed. Data from a scattering cell designed to incorporate the ultrasonic technology is presented showing that dynamic light scattering measurements may be carried out under such conditions. Varying the energy density of the ultrasonic field allows particles greater than a defined cut‐off diameter to be removed from the measurement region. Theory shows that the minimum cut‐off size may be as small as 100 nm. Results presented here demonstrate complete removal at a lower diameter threshold of approximately 2000 nm.
Comparative Test of Methods to Determine Particle Size and Particle Size Distribution in the Submicron Range
Authors: Lange Heinz
Published: May 2005

Among the most important characteristic properties of disperse systems such as latices, pigments, ceramic materials or drug formulations are the particle size and the particle size distribution. To measure these quantities, several methods and measuring instruments based on different physical principles are available. These include turbidimetry, dynamic and static light scattering, electron microscopy with image analysis, ultra‐ and disc centrifugation, light diffraction and the electrical sensing zone method. All these measuring techniques are doubtless necessary because of the large product variety and the broad particle size range. However, some problems arise if different techniques are used and the results are compared uncritically without considering to the application range and the resolution of the methods. An extensive comparative test was therefore carried out using seven latices in the submicron range with defined monomodal, bimodal and hexamodal particle size distributions. The most important methods of determining average particle size values and particle size distributions were tested and compared. Of the methods to determine only average particle sizes, turbidimetry is the most efficient, followed by dynamic light scattering with cumulants evaluation. Static light scattering only yields accurate results for small particles with narrow particle size distributions. Of the methods to determine particle size distributions, ultracentrifugation and, somewhat less, disc centrifugation and electron microscopy with image analysis are the most efficient. Dynamic light scattering only yields reliable results in the case of small particles with narrow distribution curves. Light diffraction and the electrical sensing zone method are less suitable for the submicron range.
Characterising the Dynamic Shape and Transport Behaviour of Coarse Particles
Authors: Brown Gareth J. , Miles Nick J.
Published: May 2005

The dynamic shape of coarse particles was determined by catastrophic tumbling studies performed in a rotating cylinder. Here, the dynamic shape was defined as the deviation from ideally regular and predictable tumbling behaviour.

The data suggested that even with a comprehensive description of a static particle its transport properties cannot be accurately predicted.

The fractal dimension in data space of the time series of events presents a method that can identify limits of predictability, and thus show regions that should be avoided to‐ minimise the emergence of chaotic behaviour.
Inlet Efficiency Study for the TSI Aerodynamic Particle Sizer
Authors: Kinney Patrick D. , Pui David Y. H.
Published: May 2005

The paper reports on the particle. sampling efficiency of the inlet system for the Aerodynamic Particle Sizer (TSI, Inc., St. Paul MN). Large particles are depleted from the sampled aerosol by two mechanisms: super‐isokinetic sampling at the entrance of the inlet, and inertial impaction on the inner nozzle. A fluorometric technique was used to separately characterize these mechanisms. Numerical studies were also performed. The experimental results show that the inlet's overall efficiency drops from around 90% for 3 μm particles to less than 45% for particles larger than 10 gm. Several high efficiency inlets were developed and tested. These inlets provide higher sampling efficiencies, but reduce the instrument's sizing resolution. Measurements of 7.3 μm oleic acid particles with a high efficiency inlet showed a 5% spread in measured diameter at 50% count, while less than a 1076 spread was observed using the standard inlet. It was also found that the super‐isokinetic condition reduces particle losses on the inner nozzle. The standard inlet is recommended for verifying test aerosol monodispersity. An alternative to the standard inlet is suggested for measurement of size distributions.
Particle Size Analysis: A comparative study of various methods
Authors: Etzler Frank M. , Sanderson Marie S.
Published: May 2005

The particle size distribution of component materials can be important parameter governing the proper function of many industrial products. At present, accurate determination of particle size by currently available methods is difficult for both theoretical and practical reasons. In this paper, some elementary notions regarding particle sizing are reviewed as is the relative performance of commercially available particle sizing instrumentation which could be used for particle size analysis of dry powders. Our results indicate that various particle size instruments yield significantly (even vastly) different particle size distributions for the same material. Without great care on the part of the investigator, the results obtained from any given instrument may not accurately describe the powder in question and thus may cause incorrect technical recommendations. The use of Fraunhofer diffraction instruments on samples containing irregularly shaped small ( < 10 μm) particles of low refractive index requires considerable caution.
Internal‐Field Characteristics of Spherical Particles
Authors: Kai Li , D'Alessio Antonio
Published: May 2005

The finely stratified sphere model was used to calculate electromagnetic fields inside homogeneous and radially inhomogeneous spheres which are illuminated by electromagnetic plane waves. A complete picture of the internal fields is given for spheres whose diameters are comparable to the wavelength (α = 1.5 and 5, where α = 2 πa/γs is the size parameter of the sphere) and spheres whose diameters are much larger than the, wavelength (α as high as 150), for coated spheres (spheres composed of a homogeneous core and a homogeneous shell) and gradient‐index spheres (spheres with a continuous of refractive index), for spheres at states of morphology‐dependent resonances (MDRs) and those at non‐resonant states.
Ultrasonic Measurement of Sub‐Micron Particles
Authors: Scott David M. , Boxman Arthur , Edwin Jochen C.
Published: May 2005

Based on technology described in a Du Pont patent for an offline system, we have developed a prototype in‐line ultrasonic cell for measuring particle size distribution. We have used this cell to verify the Allegra‐Hawley model of ultrasonic attenuation in dilute (< 5 % vol) slurries of sub‐micron ceramic particles, and we are developing a model that can cope with the multiple scattering effects occuring at higher concentrations.

In this paper we present the results of attenuation measurements for ultrasound (2–50 MHz) in slurries with concentrations ranging from 0.5 010 to 38 010 (vol). The attenuation is proportional to slurry concentration up to 5 010 (vol) and is predicted by single scattering models. Above approximately 100% concentration, the attenuation is actually lower than expected. For the dilute slurries we find excellent agreement between our measurements and the Allegra‐Hawley calculations, and the effects of the particle size distribution are evident in the ultrasonic attenuation spectrum. These ultrasonic data can be inverted to determine the particle size and concentration in aqueous slurries of sub‐micron particles.
The Use of Small Angle Light Scattering to Study Structure of Flocs
Authors: Jung Suk‐Jo , Amal Rose , Raper Judy A.
Published: May 2005

In this paper, a new approach using small angle light scattering to study the structure of large micron sized flocs is described. The flocs were made up from uniformly sized, approximately spherical hematite particles, induced to aggregate using 250 mM KCl to ensure that growth was governed by diffusion limited aggregation alone. The fractal dimensions of the hematite aggregates changed from 1.73 to 2.23 ± 0.05 as the aggregation proceeded, indicating that restructuring occurred during aggregation. The fractal dimensions obtained from the small angle light scattering technique are compared with those obtained from the combination of volume fraction and floc size measurement. The steady state fractal dimensions (2.23 ± 0.05) obtained by small angle light scattering are comparable to the fractal dimensions obtained from determining the slope of the relationship between floc volume fraction and floc size (2.09 and 2.14 ± 0.05). The discrepancy between the fractal dimensions obtained by these techniques during the initial stages of aggregation is due to the fact that the latter method measures the average fractal dimensions, whilst the former method measures the fractal dimensions at any particular instant.
On‐Line Simulation as a Methodology to Recover Size Distributions from dynamic light scattering experiments
Authors: van Criekinge Wim , van der Meeren Paul , Vanderdeelen Jan , Baert Leon
Published: May 2005

It is generally recognized that fundamental limitations make data analysis for dynamic light scattering (DLS) not straightforward. In addition to experimental problems such as multiple scattering, number fluctuation and noise, there are intrinsic problems. Data analysis is a so‐called reverse problem which, owing to the mathematical equations, becomes “allergic” to noise (an ill‐posed inverted problem). In an attempt to overcome at least some of these limitations, a software solution was developed. This mainly aimed to implement a tool that makes it easy to evaluate physically plausible solutions, rather than to determine many (less accurate) parameters related to the size distribution. One of the major goals was to create a “white‐box” program. The software is in essence an easy‐to‐use graphical interface between user and computer. The most important motivation to apply the concept of on‐line simulation is the limited information content of DLS autocorrelation functions. In the present approach, the user, rather than the software, has to evaluate the physically plausible solutions and select the most appropriate one. The computer becomes a mirror that calculates but leaves the decision making to the user. Using this software environment, the resolving power of the technique in ideal and noisy conditions was investigated. Results were obtained for monomodal samples where the mean diameter seems to be far more reliable than the polydispersity. For bimodal samples, the convergence of the solution to a monomodal distribution was observed when the noise level increased. The goal is to put into perspective the results as obtained in most “black‐box” software without having to use heavy mathematical approaches. One of the major applications is the use of the program as an interactive introductory tool to become acquainted with the power and, above all, with the limitations of DLS.
Testing a new photocentrifuge for submicron particles with silica spheres
Authors: Niemann Jochen , Weichert Reiner
Published: May 2005

A theory has been developed for spectral photosedimentation in a centrifuge. The use of several wavelengths allows particle size analyses in the submicron range without a knowledge of the optical material properties and is not restricted to spherical particles. As a result of this theory the extinction efficiency and the particle size distribution of the analysed particles can be calculated even for non‐spherical particles from an experiment.

A photocentrifuge has been built according to the developed theory. The theory has been verified by the measurement of spherical particles for which Mie theory is applicable. The experimentally obtained extinction efficiency agrees well with computations according to Mie theory. The accuracy of measured particle size distributions is comparable to those measured with other sedimentometers.
High‐Resolution Phase Doppler Particle Sizing based on Hilbert transform signal processing
Authors: Lehmann Peter , Schombacher E. Hanno , Wriedt Thomas
Published: May 2005

A new phase Doppler anemometry (PDA) signal processing method based on a Hilbert transform algorithm is introduced and analysed. By generating a 90° phase‐shifted burst signal in the time domain, the envelope of the Doppler burst can be determined. In addition, this envelope is approximated by a Gaussian exponential function. The difference of the maxima of these Gaussian approximations for two related PDA bursts gives an estimate of the time difference between these time shifted signals. With the introduction of this estimation method, the restriction to the [0,360°] interval resulting from conventional signal analysis may be avoided in many cases. To investigate the dependence on SNR, burst position, burst frequency and sampling rate, results of computer simulations are presented. The feasibility of the method is demonstrated briefly by experimental results. Phase differences of more than 2000° arising from the measurement of monodisperse droplets by a conventional PDA setup could be determined.
Behavior of Ultrafine Particles generated from organic vapors by corona ionizers
Authors: Ichitsubo Hirokazu , Alonso Manuel , Ishii Mayumi , Endo Yoshiyuki , Kousaka Yasuo , Sato Katsumi
Published: May 2005

This paper reports an experimental study on the stability, coagulation and diffusion of molecular clusters and ultrafine particles generated from organic vapors by corona ionizers. Upon leaving the ionizer, particles are made to flow within several types of vessels: depending on the specific geometry of the flow system, clusters either coagulate into large particles or are deposited on the walls. Particles larger than 4nm and molecular clusters penetrate through a wire‐screen type diffusion battery, but particles in the size range between 2 and 4nm are collected. Among the organic compounds tested (aromatics, alcohols, ketones and others), only aromatic compounds appear to yield unstable clusters which grow into detectable particles (>2nm) through Brownian coagulation. The other compounds either do not undergo the gas‐to‐particle conversion process or are too small to be detected. Furthermore, the presence of moisture seems to be of fundamental importance in the particle generation phenomenon. The addition of alcohols to the vapor mixture inhibits particle formation.
History of Development of the Phase‐Doppler Particle‐Sizing Velocimeter
Authors: Dan Hirleman E.
Published: May 2005

The ability to routinely make simultaneous measurements of the size and velocity of individual spherical particles is identified as a crucial component of advances in the science and technology of multiphase systems and processes. Since it is the dual beam interferometer identified here as the phase‐Doppler particle‐sizing velocimeter (PD) that has provided this capability, and since 1995 marks twenty years from a seminal paper by Durst and Zaré, a historical review is warranted and is presented. The roots and context of the development of PD are traced from the days of laser Doppler velocimetry (LDV) in the early 1970's through work culminating at several laboratories in the mid 1980's. A number of important contributions and the engineers and scientists responsible for those contributions are recognized.
Exploring PDA Configurations
Authors: Buchhave Preben , von Benzon Hans‐Henrik
Published: May 2005

This paper reviews the principle of the phase‐Doppler particle sizer by means of examples of the effects of varying the various experimental parameters. The examples are computed by means of a comprehensive numerical model of a complete phase‐Doppler system including many practical aspects such as aperture size, polarization filters and detector properties. First the phase‐Doppler principle is explained as a logical development of an interferometric measurement of the phase of the light scattered from a particle. Then the standard phase‐Doppler analyzer (PDA) is decribed followed by some newer or less known variations of the principle intended to measure, e.g., in the backscatter direction, to size very small particles or to determine the refractive index of a particle. Finally, the trajectory problem in PDA measurements is briefly discussed.
Reflection Phenomena in Particle Sizing by static and dynamic light scattering
Authors: De Meulenaer Bruno , Van der Meeren Paul , Vanderdeelen Jan , Baert Leon
Published: May 2005

Using a monodisperse poly(methyl methacrylate) dispersion it was shown that light reflection at the sample cuvette walls may greatly influence the results of both static (SLS) and dynamic (DLS) light scattering experiments. Considering SLS, this reflection phenomenon mostly causes an overestimation of the scattered intensity at high scattering angles, which may give rise to the emergence of an additional, artificial peak in the lower region of the particle size distribution. On the other hand, the influence of reflection on DLS experiments was shown to be particularly important in the upper region of the particle size distribution. The experimentally observed phenomena were explained from basic principles of both particle sizing methods. Finally, it was shown that the disturbing effect of reflection could be avoided by modifying either the hardware or the software of the SLS and DLS techniques.
A Light Scattering Instrument for Sizing Mixtures of small and large particles
Authors: Card Jacqueline B. A. , Jones Alan R. , Zhao Hua
Published: May 2005

An instrument is proposed for the visualisation and measurement of mixtures of small and large particles. The original concept was to use spectral extinction for sub‐micron particles and scattering patterns for larger sizes. However, the former method is sensitive to the refractive index, which may be unknown or vary with wavelength in an unknown way. The experiments demonstrated this to be a problem. The forward scatter, on the other hand, is not so sensitive to this. It is shown here that the combination of scattered intensity as a function of both angle and Wavelength provides scatter diagrams for which there is good agreement between theory and experiment. The influence of quite small volume fractions of particles as small as 0.3μm mixed with 90μ particles is easily seen. The scatter diagrams suggest the use of image analysis for size measurement and quality control.
Aqueous Droplet Sizing by Inertial Classification
Authors: Roth Christa , Gebhart Josef
Published: May 2005

The particle size distribution of an aerosol generated from an aqueous system is difficult to analyse because of the shrinkage of the droplets due to solvent evaporation. These problems are very important for the characterization of medical nebulizers, since most of the drugs delivered via inhalation are water soluble. In situ methods for droplet size analysis, such as laser diffraction, phase Doppler anemometry and light scattering, do not determine either the initial or the equilibrium size distribution. With the residual technique, which means evaporating the droplets and measuring the size and concentration of the residuals, the instability of the aqueous droplets plays no role and the necessary radioactive labelling of the sprayed material allows a direct determination of the mass flow rate at the mouthpiece of the nebulizer. In this way it is possible to discriminate between the delivered drug solution and the water necessary to humidify the incoming air. The output of nebulizers of different designs is given for various operating conditions, filling volumes and solution concentrations. The measured droplet size distribution of a nebulizer is found to be fixed mainly by its internal impaction system.
Coherent Transmission and Reflection by a monolayer of discrete scatterers
Authors: Loiko Valery A. , Molochko Vladimir I.
Published: May 2005

Coherent transmission and reflection of a plane wave through a monolayer of discrete particles are considered on the basis of simple and physically transparent formulae for the single scattering approximation (SSA) corrected by introducing a multiple scattering permittivity factor. This factor allows for multiple scattering of Waves between monolayer particles, opposite to the SSA. The multiple scattering permittivity factor is considered on the basis of the quasi‐crystalline approximation (QCA) via Ť matrix formalism. The multiple scattering permittivity factor and parameters for obtaining coherent transmission and reflection coefficients (the effective extinction coefficient and the transmission and reflection coefficients due to rescattering) are calculated within the scope of QCA and plotted for comparison with SSA results. The expressions for these values are simplified for small Rayleigh particles to simple analytical formulae.
Particle size analysis: A comparison of various methods ii
Authors: Etzler Frank M. , Deanne Richard
Published: May 2005

In previous work, the relative performance of various methods used to characterize the particle size distribution of powders composed of fine irregularly shaped particles was assessed. It was found that methods employing Fraunhofer diffraction theory were inferior with respect to particle counting methods. Furthermore, calculated particle size distributions varied considerably between manufactures of Fraunhofer devices. It is well known that the Mie optical model can also be used to analyze the data collected by laser diffraction instruments. Here, we have compared particle size distributions collected using two Laser diffraction instruments to those determined by the Aerosizer. In our earlier work the Aerosizer was shown to produce results nearly identical to those determined by image analysis. The results of this study indicate that the use of the Mie optical model does not correct for deficiencies previously noted for laser diffraction methods. Considerable variation exists between the results obtained on laser diffraction instruments manufactured by different companies. Our earlier recommendation to use extreme caution when employing laser diffraction instruments to characterize fine powders continues to be supported in the present work.
Influence of surface roughness of conducting spheres on the response of a phase‐doppler anemometer
Authors: Göbel Gerhard , Doicu Adrian , Bauckhage Klaus , Wriedt Thomas
Published: May 2005

The influence of the surface roughness of solid conducting spheres on the response of a phase‐Doppler anemometer (PDA) is described by using a ray theory model. A rough particle surface is modeled as an ensemble of distorted spheres. First‐ and second‐order reflection and diffraction are considered for far‐field calculations of the PDA phase difference. The numerical simulations are accompanied and supported by experimental results. Single rough Sn spheres are captured inside an electro‐dynamic trap and investigated with a standard phase‐Doppler system.
The design and production of semisynthetic ribonucleases with increased thermostability by incorporation of S‐peptide analogues with enhanced helical stability
Authors: Mitchinson Colin , Baldwin Robert L.
Published: May 2005

Recent work has shown that, with synthetic analogues of C‐peptide (residues 1–13 of ribonuclease A), the stability of the peptide helix in H2O depends strongly on the charge on the N‐terminal residue. We have asked whether, in semisynthetic ribonuclease S reconstituted from S‐protein plus an analogue of S‐peptide (1–15), the stability of the peptide helix is correlated with the Tm of the reconstituted ribonuclease S. Six peptides have been made, which contain Glu9 → Leu, a blocked α‐COO− group (CONH2), and either Gln11 or Glu11. The N‐terminal residue has been varied; its charge varies from +2 (Lys) to −1 (succinyl‐Ala). We have measured the stability of the peptide helix, the affinity of the peptide for S‐protein (by C.D. titration), and the thermal stability of the reconstituted ribonuclease S.

All six peptide analogues show strongly enhanced helix formation compared to either S‐peptide (1–15) or (1–19), and the helix content increases as the charge on the N‐terminal residue changes from +2 to −1. All six peptides show increased affinity for S‐protein compared to S‐peptide (1–19), and all six reconstituted ribonucleases S show an increase in Tm compared to the protein with S‐peptide (1–19). The Tm increases as the charge on residue 1 changes from +2 to −1. The largest increment in Tm is 6°.

The results suggest that the stability of a protein can be increased by enhancing the stability of its secondary structure.
Stabilization of λ repressor against thermal denaturation by site‐directed Gly→Ala changes in α‐helix 3
Authors: Hecht Michael H. , Sturtevant Julian M. , Sauer Robert T.
Published: May 2005

Oligonucleotide‐directed mutagenesis has been used to replace α‐helical glycines in the N‐terminal domain of λ repressor with alanines. Since alanine is a significantly better helix‐forming residue than glycine, these changes were predicted to have a stabilizing effect. We show that the Gly46→Ala substitution, the Gly48→Ala substitution, and the double substitution increase the melting temperature of the N‐terminal domain by 3–6°.
The galactan‐binding immunoglobulin Fab J539: An x‐ray diffraction study at 2.6‐Å resolution
Authors: Suh Se Won , Bhat T. N. , Navia Manuel A. , Cohen Gerson H. , Rao D. N. , Rudikoff Stuart , Davies David R.
Published: May 2005

The crystal structure of the Fab of the galactan‐binding immunoglobulin J539 (a mouse IgA,κ) has been determined at a resolution of approximately 2.6 Å by X‐ray diffraction. The starting model was that obtained from the real space search described previously (Navia, M.A., Segal, D.M., Padlan, E.A., Davies, D.R., Rao, D.N., Rudikoff, S. and Potter, M. “Crystal structure of galactan‐binding mouse immunoglobulin J539 Fab at 4.5 Å resolution.” Proc. Nat. Acad. Sci. USA, 76:4071–4074, 1979). This Fab structure has now been refined by restrained least‐squares procedures to an R‐value of 19% for the 11,690 unique reflections between 8.0 Å and 2.6 Å. The rms deviation from ideal bond lengths is 0.025 Å. The overall structure differs from McPC603 Fab, another mouse IgA,κ antibody, in that the elbow bend, relating the variable and constant parts of the molecule, is 145° vs. 133° for McPC603. The region of the molecule expected to be the antigen binding site contains a large cavity with two clefts leading away from it. This has been fitted with a model of an oligo‐galactan.
A novel method for selective isolation of C‐terminal peptides from tryptic digests of proteins by immobilized anhydrotrypsin: Application to structural analyses of the tail sheath and tube proteins from bacteriophage T4
Authors: Kumazaki Takashi , Nakako Tatsushi , Arisaka Fumio , Ishii Shin‐Ichi
Published: May 2005

A novel method useful for selective isolation of the C‐terminal peptide from a tryptic digestion mixture of a protein has been developed by taking advantage of a unique property of anhydrotrypsin, which has a strong specific affinity for the peptides containing arginine or lysine at their C‐termini. Briefly, peptides produced by tryptic digestion of a protein are fractionated by affinity chromatography on a column of immobilized anhydrotrypsin. The C‐terminal peptide is recovered in a breakthrough fraction, which the remainders are adsorbed on the column (unless the protein ends in arginine or lysine). The breakthrough fraction is then subjected to reversed‐phase high‐perfomance liquid chromatography in order to purify the C‐terminal peptide. Using this method, we have successfully isolated the C‐terminal peptides from tryptic digests of the sheath protein (gp 18) and the tube protein (gp 19) of bacteriophage T4. The analytical results on these peptides, together with the information on the N‐terminal structures of the original proteins and on the nucleotide sequences of genes 18 and 19, allowed us to establish the complete primary structures of the two proteins.
Stabilization of the ribonuclease S‐peptide α‐helix by trifluoroethanol
Authors: Nelson Jeffrey W. , Kallenbach Neville R.
Published: May 2005

The effects of trifluoroethanol (TFE) on the stability of the α‐helix formed by ribonuclease S‐peptide, residues 1–19 of ribonuclease A, were studied by measuring circular dichroism as a function of TFE concentration, pH, and temperature. The S‐peptide forms an unusually stable α‐helix, which is known to be stabilized by TFE. The magnitude of the effect of charged groups on the peptide, manifested by the change in α‐helix stability as a function of pH, was not altered significantly by either TFE concentration or temperature, indicating that the lower dielectric constant of TFE is not important in the stabilization of this α‐helix. This suggests that the α‐helix might be stabilized by many interactions in addition to the effects of charges. The titration curve of circular dichroism vs. TFE concentration appears to be cooperative at 0°C, but becomes progressively less cooperative at temperatures between 25 and 75°C. The properties of the TFE stabilization indicate that TFE might be a useful probe with which to measure the stability of marginally stable peptides and small proteins.
Calculating three‐dimensional changes in protein structure due to amino‐acid substitutions: The variable region of immunoglobulins
Authors: Snow Mark E. , Amzel L. Mario
Published: May 2005

A procedure (coupled perturbation procedure, CPP) is introduced as a specific method for calculating the detailed three‐dimensional structure of a protein molecule which has a nummber of amino‐acid substitutions relative to some previously determined “parent” protein structure. The accuracy of the procedure is tested by calculating the conformation of a region of the human immunoglobulin fragment Fab Kol based on the analogous region of the human immunoglobulin fragment Fab New. Both structures have previously been determined crystallographically. The calculated model is accurate to the extent that both of the sequence differences in the region are modeled correctly and that conformational changes in a number of nearby residues are correctly identified. CPP is shown to give better results than other commonly used modeling procedures when applied to the same problem.
Proteases of enhanced stability: Characteization of a thermostable variant of subtilisin
Authors: Brayan Philip N. , Rollence Michele L. , Pantoliano Michael W. , Wood James , Finzel Barry C. , Gilliland Gary L. , Howard Andrew J. , Poulos Thomas L.
Published: May 2005

A Procedure has been developed for the isolation and identification of mutants in the bacterial serine protease subtilisin that exhibit enhanced thermal stability. The cloned subtilisin BPN'gene from Bacillus amyloliquefaciens was treated with bisulfite, a chemical mutagen that deaminates cytosine to uracil in single‐stranded DNA. Strains containing the cloned, mutagenized subtilisin gene which produced subtilisin with enhanced thermal stability were selected by a simple plate assay procedure which screens for esterase activity on nitrocellulose filters after preincubation at elevated temperatures. One thermostable subtilisin variant, designated 7150, has been fully characterized and found to differ from wild‐type subtilisin by a single substitution of Ser for Asn at position 218. The 7150 enzyme was found to undergo thermal inactivation at onefourth the rate of the wild‐type enzyme when incubated at elevated temperatures. Moreover, the midpoint in the thermally induced transition from the folded to unfolded state was found to be 2.4–3.9°C higher for 7150 as determined by differential scanning calorimetry under a variety of conditions. The refined, 1.8‐Å crystal structures of the wild‐type and 7150 subtilisin have been compared in detail, leading to the conclusion that slight improvements in hydrogen bond parameters in the vicinity of position 218 result in the enhanced thermal stability of 7150.