bluuebunny/crossref_metadata_2025_split huggingface dataset:
Testing a new photocentrifuge for submicron particles with silica spheres
Authors: Niemann Jochen , Weichert Reiner 
Published: May 2005

AbstractA 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

AbstractA 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

AbstractThis 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

AbstractThe 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

AbstractThis 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

AbstractUsing 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

AbstractAn 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

AbstractThe 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

AbstractCoherent 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

AbstractIn 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

AbstractThe 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

AbstractRecent 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

AbstractOligonucleotide‐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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractA 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.
Structural features of ribonucleotide reductase
Authors: Nikas Ioannis , McLauchlan John , Davison Andrew J. , Taylor William R. , Clements J. Barklie 
Published: May 2005

AbstractHerpes simplex virus type 1 (HSV‐1) encodes a ribonucleotide reductase which comprises two polypeptides with sizes of 136,000 (RR1) and 38,000 mol. wt. (RR2). We have determined the entire DNA sequence specifying HSV‐1 RR1 and have identified two adjacent open reading frames in varicella‐zoster virus (VZV) which have homology to HSV RR1 and RR2; the predicted sizes for the VZV RR1 and RR2 polypeptides are 87,000 and 35,000 mol. wt. respectively. Amino acid comparisons with RR1 and RR2 polypeptides from other organisms indicate that HSV‐1 RR1 contains a unique N‐terminal domain which is absent from other RR1 polypeptides apart from HSV‐2 RR1. These N‐terminal amino acid sequences are poorly conserved between HSV‐1 and HSV‐2 in contrast to the remainder of the protein which shows greater than 90% homology. Polypeptide structural predictions suggest that the HSV‐1 N‐terminal domain may be separated into two regions, namely, a β‐sheet structure followed by a nonstructured area. Across the remainder of RR1 and RR2, comparisons also reveal blocks of amino acids conserved between the different ribonucleotide reductases, and these may be important for enzyme activity. From predictions on the structure of these conserved blocks, we have proposed that the location of a substrate binding site within RR1 is centered on three conserved glycine residues in a region which is predicted to adopt a β‐sheet/turn/α‐helical structure;this approximates to the structure for ADP nucleotide binding folds. Finally, we propose that the promoters for the HSV and Eptein‐Barr virus (EBV) RR2 transcripts have evolved by separate evolutionary routes.
Detection of human somatic cell structural gene mutations by two‐dimensional electrophoresis
Authors: Hanash S.M. , Chu E.H.Y. , Kuick R. , Skolnick M. , Neel J. , Strahler J. , Pivirotto S. , Niezgoda W. 
Published: May 2005

AbstractThe feasibility of detecting human somatic structural gene mutations by two dimensional electrophoresis has been investigated. A lymphoblastoid cell line was grown as a mass culture in the presence of ethylnitrosourea, after which cells were regrown as single cell clones. A total of 257 polypeptide spots were analyzed in gels derived from 186 clones. Four structural mutations were detected by visual analysis of the gels. Computer analysis of gels corresponding to the mutant clones was also undertaken. At a spot size threshold of 200 spots to be matched using a computer algorithm, all four mutant polypeptides were detected. These results indicate the usefulness of the two‐dimensional approach for mutagenesis studies at the protein level.