bluuebunny/crossref_metadata_2025 huggingface dataset:
Corner Turning Research Test
Authors: Held Manfred
Published: May 2005

The so‐called corner turning research test according to Cox and Campbell gives beside of the corner turning distance — short CTD — also the area of the not fully detonating zone — the so‐called dark or dead zone — around the initiation axis. This is achieved by cutting the charge parallel and near to the booster axis and by observing this surface with multiple streak lines. With the help of a computer program the digitized data can be quickly analyzed.
The Kinetic Parameters and Parameter Effect Factors Calculation of multicomponent energetic materials decomposition reaction from a single differential thermal analysis curve
Authors: Luo Kuo‐Ming
Published: May 2005

The kinetic parameter of energetic materials with four components, i.e. lead thiocyanate, antimony sulfide, potassium chlorate, and trinitrotoluene, (PSKT), was analyzed with differential thermal analysis (DTA) technique. Kinetic parameter equations were derived for estimating a general nth‐order decomposition reaction from a single DTA curve. Three categories, for n < 1, n = 1, and n ≠ 1 were derived. Three kinetic parameters, namely, activation energy E, reaction order n, and pre‐exponential factor A can be calculated directly without any iteration from the characteristic temperatures To, Til, Tm, and Te that are the decomposition starting point, first inflection point, peak maximum point and end point on the DTA curve, respectively. The stability and compatibility of PSKT energetic material can be judged from experimental characteristic temperatures and calculated kinetic parameters. The effect factors of characteristic temperature and kinetic parameters were evaluated by means of Yates' algorithm.
Electrostatic calculations and model‐building suggest that DNA bound to CAP is sharply bent
Authors: Warwicker J. , Engelman B.P. , Steitz T.A.
Published: May 2005

Two observations suggest that DNA, upon binding to E. coli catabolite gene activator protein (CAP), is sharply bent by a total angle of at least 100–150 degrees: (1) The electrostatic protential field of CAP shows regions of positive potential that from a ramp on 3 sides of the protein. (2) The DNA binding site size as determined by DNA ethylation interference with binding, (Majors: “Control of the E. coli Lac Operon at the Molecular Level.” Ph.D. Thesis, Harvard University, Cambridge, 1977) and by relative affinities of DNA fragments of various lengths (Liu‐Johnson et al.: Cell 47:995–1005, 1986) requires severe bending of the DNA to maintain its favorable electrostatic contact with the protein.
Accommodation of single amino acid insertions by the native state of staphylococcal nuclease
Authors: Sondek John , Shortle David
Published: May 2005

Single alanine and glycine insertions were introduced at 20 randomly selected positions in staphylococcal nuclease. The resulting changes in catalytic activity and in stability to guanidine hydrochloride denaturation indicate that the native state structure is frequently able to accommodate the extra residue without great difficulty, even insertions within secondary structural elements such as alpha helices and beta sheets. On average, an inserted residue reduces the free energy of denaturation (ΔG) by an amount roughly comparable to an alanine or glycine substitution for one of the residues flanking the site of insertion. Several positions outside of the enzyme active site were found where insertions, but not substitutions, lead to structural changes that modify catalytic activity and the circular dichroism spectrum. Amino acid insertions represent a virtually unexplored class of genetic mutation that may prove complementary to amino acid substitutions for engineering proteins with altered functional and structural properties.
Comparative modeling methods: Application to the family of the mammalian serine proteases
Authors: Greer Jonathan
Published: May 2005

Comparative modeling methods are described that can be used to construct a three‐dimensional model structure of a new protein from knowledge of its sequence and of the experimental structure and sequences of other members of its homology family. The methods are illustrated with the mammalian serine protease family, for which seven experimental structures have been reported in the literature, and the sequence for over 35 different protein members of the family are available. The strategy for modeling these proteins is presented, and criteria are developed for determining and assigning the reliability of the modeled structure. Criteria are described that are specially designed to help detect cases in which it is likely that the local structure diverges significantly from the usual conformation of the family.
Functional interaction among catalytic residues in subtilisin BPN′
Authors: Carter Paul , Wells James A.
Published: May 2005

Variant of the serine protease, subtilisin BPN′, in which the catalytic triad residues (Ser‐221, His‐64, and Asp‐32) are replaced singly or in combination by alanine retain activities with the substrate N‐succinyl‐L‐Ala‐L‐Ala‐L‐Pro‐L‐Phe‐p‐nitroanilide (sAAPF‐pna) that are at at least 103 to 104 above the non‐enzymatic rate [Carter, P., Wells, J.A. Nature (London) 322:564–568, 1988]. A possible source of the residual activity was the hydrogen bond with the Nδ2 of Asn‐155 that helps to stabilize the oxyanion generated in the tetrahedral transition state during amide bond hydrolysis by the wild‐type enzyme. Replacing Asn‐155 by Gly (N155G) lowers the turnover number (kcat) for sAAPF‐pna by 150‐fold with virtually no change in the Michaelis constant (KM). However, upon combining the N155G and S221A mutations to give N155G:S221A, kcat is actually 5‐fold greater than for the S221A enzyme. Thus, the catalytic role of Asn‐155 is dependent upon the presence of Ser‐221. The residual activity of the N155G:S221A enzyme (∼104‐fold above the uncatalyzed rate) is not an artifact because it can be completely inhibited by the third domain of the turkey ovomucoid inhibitor (OMTKY3), which forms a strong 1:1 complex with the active site. the mutations N155G and S221A individually weaken the interaction between subtilisin and OMTKY3 by 1.8 and 2.0 kcal/mol, respectively, and in combination by 2.1 kcal/mol. This is consistent with disruption of stabilizing interactions around the reactive site carbonyl of the OMTKY3 inhibitor. These data suggest that Ser‐221 functions together with Asn‐155 to accelerate amide bond hydrolysis and that other transition state stabilizing interactions account for the residual rate enhancement of 103− to 104−fold. More generally, these studies illustrate the limitations of using site‐directed mutagenesis to probe the energetic importance of a single catalytic group whose function is dependent upon the interaction with others.
Quantitative organization of the known protein x‐ray structures. I. Methods and short‐length‐scale results
Authors: Rackovsky S.
Published: May 2005

We address herein the problem of delineating the relationships between the known protein structures. In order to study this problem, methods have been developed to represent arbitrarily sized fragments of biopolymer backbone, and to compare distributions of such fragments. These methods are applied to a classification of 123 structures representing the entire set of known x‐ray structures. The resulting data are analyzed (on the four‐Cα length scale) to determine both the large‐scale organization of the set of known structures (i.e., the relationships between large groups of structures, each comprised of proteins that are structurally related) and its local structure (i.e., the quantitative degree of similarity between any two specific structures). It is shown that the set of structures from a continuum of structural types, ranging from allhelical to all‐sheet/barrel proteins. It is further demonstrated that the density of protein structures is not uniform across this continuum, but rather that structures cluster in certain regions, separated by regions of lower population. The properties of the various regions of the structural space are determined. The existence is demonstrated of strong quantitative correlations between the contents of different types of four‐Cα fragments within protein structures, which imply significant constraints on the types of architecture that can occur in proteins. Analysis of the distribution of structures demonstrates some hitherto unsuspected similarities and suggests that, in some circumstances, neither structural similarity no sequence homology may be necessary conditions for evolutionary relationship between proteins. It is also suggested that these unsuspected similarities may imply similar folding mechanisms for structures of apparently different global architecture. Cases are also noted in which apparently similar structures may fold by different mechanisms. The connection between structure and dynamic properties is discussed, and a possible role of dynamics in the evolution of protein structures is suggested. The sensitivity of the methods presented herein to anomalies of structure refinement is demonstrated. It is suggested that present results provide a frame‐work for analyzing experimental results on structural similarity obtained using vibrational circular dichroism spectra, which are sensitive to local backbone structure.
A consensus prediction of the secondary structure for the 6‐phospho‐β‐D‐galactosidase superfamily
Authors: Gerloff Dietlind L. , Benner Steven A.
Published: May 2005

Two separate unrefined models for the secondary structure of two subfamilies of the 6‐phospho‐β‐D‐galactosidase superfamily were independently constructed by examining patterns of variation and conservation within homologous protein sequences, assigning surface, interior, parsing, and active site residues to positions in the alignment, and identifying periodicities in these. A consensus model for the secondary structure of the entire superfamily was then built. The prediction tests the limits of an unrefined prediction made using this approach in a large protein with substantial functional and sequence divergence within the family. The protein belongs to the (α–β class), with the core β strands aligned parallel. The supersecondary structural elements that are readily identified in this model is a parallel β sheet built by strands C, D, and E, with helices 2 and 3 connecting strands (C + D) and (D + E), respectively, and an analogous α–β unit (strand G and helix 7) toward the end of the sequence. The resemblance of the supersecondary model to the tertiary structure formed by 8‐fold α–β barrel proteins is almost certainly not coincidental. © 1995 Wiley‐Liss, Inc.
Knowledge‐based modeling of the D‐lactate dehydrogenase three‐dimensional structure
Authors: Vinals Carla , De Bolle Xavier , Depiereux Eric , Feytmans Ernest
Published: May 2005

A three‐dimensional structure of the NAD‐dependent D‐lactate dehydrogenase of Lactobacillus bulgaricus is modeled using the structure of the formate dehydrogenase of Pseudomonas sp. as template. Both sequences share only 22% of identical residues. Regions for knowledge‐based modeling are defined from the structurally conserved regions predicted by multiple alignment of a set of related protein sequences with low homology. The model of the D‐LDH subunit shows, as for the formate dehydrogenase, an α/β structure, with a catalytic domain and a coenzyme binding domain. It points out the catalytic histidine (His‐296) and supports the hypothetical catalytic mechanism. It also suggests that the other residues involved in the active site are Arg‐235, possibly involved in the binding of the carboxyl group of the pyruvate, and Phe‐299, a candidate for stabilizing the methyl group of the substrate. © 1995 Wiley‐Liss, Inc.
Mass spectrometry in environmental analysis
Authors: Medved Miran
Published: May 2005

The coupling of gas chromatography/mass spectrometry provides the most useful technique for structure elucidation and quantitative analysis of organic compounds in environmental samples. The technique finds its application in all environmental media: air, water, wastes, soil, particularly in connection with reliable sampling and sample preparation. Alternative separation and ionization techniques are used in practice on special occassions, such as the assessment of the health hazard caused by an unknown compound, when structure elucidation cannot be performed by the standard gas chromatography/mass spectrometry equipment.
Phase‐system switching in liquid chromatography/continuous‐flow fast‐atom bombardment mass spectrometry
Authors: Kokkonen P. S. , Niessen W. M. A. , Tjaden U. R. , van der Greef J.
Published: May 2005

A new, attractive application of the phase‐system switching (PSS) technique is demonstrated. The PSS system is used in combination with liquid chromatography coupled to continuous‐flow fast‐atom bombardment mass spectrometry (LC/CF‐FABMS) to achieve flow‐rate reduction from 1.0 mL/min in the high‐performace liquid chromatography (HPLC) system to 15μL/min going into the mass spectrometer. In PSS, a compound of interest, in this case erythromycin 2′‐ethylsuccinate, is enriched after the analytical separation, on a short trapping column, from which it is desorbed subsequently to the LC/MS interface. Optimal mobile phases and flow‐rates can be used for the HPLC separation as well as for the mass spectrometric detection. Desorption of the analyte is achieved either by using a flow‐rate of 15 μL/min without a splitter or a flow‐rate of 230 μL/min with a splitter. Compared to the LC/CF‐FAB MS methods using a conventional bore HPLC column and a splitter, improved detection limits for the model compound were achieved using the PSS method.
Transannular interaction in the gas phase
Authors: Vairamani M. , Rajeev M. S. , Kumar K. V. Siva
Published: May 2005

Acetone chemical ionization mass spectra of cycloalkenes clearly show the operation of transannular interaction in medium sized rings in the form of water loss from [M + 43]+ adduct ions. Based on labelling studies a mechanism has been proposed.
Heats of formation of BF ions and the fluorine anion affinity of BF3 molecules
Authors: Veljković M. , Nešković O. , Zmbov K. F. , Borshchevsky A. Ya. , Vaisberg V. E. , Sidorov L. N.
Published: May 2005

The effusion method, together with mass spectral analysis, has been used to study ion/molecule equilibria involving the negative ion BF. The experimental data obtained have made it possible to calculate enthalples for the reactions:
equation image
and the enthalpy of formation ΔHf(BF, 298) as ( −1716±8) kj/mol. The fluorine anion affinity of BF3 has been determined as FA((BF3)g, 298)=(331±8)kj/mol−1 and compared with Literature data.
Time‐of‐flight mass spectrometry with a compact two‐stage electrostatic mirror: Metastable‐ion studies with high mass resolution and ion emission from thick insulators
Authors: Brunelle A. , Della‐Negra S. , Depauw J. , Joret H. , Le Beyec Y.
Published: May 2005

A compact two‐grids mirror is described. Although analytical calculations and computer simulations are useful it is found that experimental adjustments of the mirror voltage and of the bias divider resistors are needed to achieve the optimum performance. The experimental procedure is given. It is shown that a second‐order time‐focusing mirror is appropriate for metastable‐ion studies with high mass resolution. Large variations of sample voltage can be compensated by the mirror. Thick insulators can be analysed.
High energy collision‐induced dissociation of alkali‐metal ion adducts of crown ehters and acyclic analogs
Authors: Maleknia Simin , Brodbelt Jenifer
Published: May 2005

High energy collision‐induced dissociation (CID) techniques were applied for structural elucidiation of alkli‐metal ion adducts of crown ethers. The CID of alkali‐metal adducts of tetraglyme and hexaethylene glycol were also evaluated to contrast the fragmentation pathways of the cyclic ethers with those of acylic analogs. A common fragmentation channel for alkali‐metal ion adducts of all the ethers, which results in distonic radical cations, is the homolytic cleavage of carbon—carbon bonds. Additionally, dissociation by carbob—oxygen bond cleavage occurs, and these processes are analogous to the fragmentation pathways observed for simple protonated ethers. The proposed fragmentation pathways for alkali‐metal ion adducts of crown ethers result mostly in odd‐electron, acyclic product ions. Dissociation of the alkali‐metal ion adducts of the acyclic ethers is dominated by losses of various neutral species after an initial hydride or proton transfer. The CID processes for all ethers are independent of alkali‐metal ion sizes; however, the extent of dissociation of the complexes to bare alkali‐metal ion increases with the size of the metal.
Proton affinity of arginine measured by the kinetic approach
Authors: Wu Zhuchun , Fenselau Catherine
Published: May 2005

The proton affinity of arginine is obtained from the kinetic method of dissociation of proton‐bound dimers, as 245.2kcal/mol with an uncertainty of ±0.5 kcal/mol higher than that of histidine, the next most basic of the commonly occuring mammalian amino acids, in contrast to the average difference of 1 kcal/mol between the other 19 amino acids. The order of proton affinity of these 20 amino acids is also determined and discussed.
Artefact interpretation in the tandem mass spectrum of the fragment ion at m/z 299 of N,N‐bissalicylidene 1,2‐phenylenediamine
Authors: Mouget Yves , Bertrand Michel J.
Published: May 2005

The advantages offered by the scanning facility of a multisector hybrid mass spectrometer of E1BE2qQ geometry, with software featuring an ‘experimental design’ function, are used to elucidate the origin of an artefact observed at m/z 290.8 in the linked scan spectrum at constant B/E of the m/z 299 ion of N,N‐bissalicylidene 1,2‐phenylenediamine, when performed using a forward geometry (EB) instrument. A previously proposed explanation, whereby the artefact peak was thought to originate from a fragmentation in the first field‐free region, could not be verified by repeating the scan using an instrument of E1BE2qQ geometry, where E1 and E2 were linked during the scan at constant B/E. Several different scans were performed using an ‘experimental design’ scanning function, which allows analyzers to be scanned and linked by means of user‐defined relationships. Thus, a mass‐analysed ion kinetic energy (MIKE) (E2) scan, with E1 set to a value of 0.9725E0, revealed a peak at a value of 0.9462E0 which was subsequently determined to be due to an ion with a mass‐to‐charge ratio of 299, by using the quadrupole mass filter. A recently proposed graphical method, that allows the field values at which the artefact ion is transmitted to be plotted three dimensionally on a cube, illustrates that while the peak will appear in the spectrum obtained using a linked scan at constant B/E using an EB instrument, this will not be the case with an EBE geometry instrument. The EBE arrangement shows that the interference peak at m/z 290.8 appears to be the result of the transition of a higher‐mass ion within the first electrostatic sector.
Diels–Alder reactions of mass‐selected ions in an ion trap mass spectrometer
Authors: Soni Manish , Amy Jon , Frankevich Vladimir , Cooks R. Graham , Taylor Dennis , McKewan Andrew , Schwartz Jae C.
Published: May 2005

This Communication describes the use of a bench‐top ion trap mass spectrometer for the study of structurally diagnostic ion/molecule reactions. The power of the experiment is increased by the broad‐band ion‐isolation and tandem mass spectrometry capabilities of the ion trap which are used to isolate the reactant ion and study its reactions under controlled conditions. The availability of multiple‐stage mass spectrometry (MSn where n = number of stages) provides additional information on the nature of the productions. The compound to be ionized is conveniently introduced into the ion trap from aqueous solution using membrane introduction techniques while the neutral reagent is leaked into the trap through the calibration gas inlet. Polar Diels–Alder reactions of the [4 + 2+] type are investigated and comparisons are made between the reactions occurring in the ion trap and those in a pentaquadrupole mass spectrometer. Three‐stage tandem mass spectra (MS3) are used to characterize the ion/molecule reaction products in the quadrupole ion trap.
Tautomerism of some amino diol and amino alcohol derivatives in the gas, phase1
Authors: Pykäläinen Mika , Vainiotalo Pirjo , Lázár László , Fülöp Ferenc , Bernáth Gábor
Published: May 2005

The mass spectrometric behaviour of condensation products of nine substituted benzaldehydes with 3‐amino‐1,2‐propanediol and 3‐amino‐1‐phenoxy‐2‐propanol was studied under electron impact and chemical ionization. The 70 eV electron impact mass spectra showed that, as in solution, the amino diol derivatives existed as three different structural isomers in the gas phase: viz. open‐chain Schiff base, oxazolidine and tetrahydro‐1,3‐oxazine. The fragmentations revealed a large amount of the decomposed molecular ions to have the open‐chain structure, but also that the amount of both ring forms was considerable. In the same way, with the amino alcohol derivatives both the open‐chain and the oxazolidine ring forms were present in the gas phase. In all cases, the ring formation was much more favourable in the gas phase than in solution. Substituents at the phenyl ring caused changes in the relative amounts of the different forms: electron‐withdrawing substituents shifted the equilibria in favour of the ring forms while electron‐donating substituents favoured the open‐chain form. Under chemical ionization, methane, isobutane and acetone were used as reagent gas. Methane was the only reagent gas that led to some fragmentation of the protonated molecules.
Quantitative surface analysis by XPS: A comparison among different quantitative approaches
Authors: Battistoni C. , Mattogno G. , Paparazzo E.
Published: May 2005

Atomic ratio determinations in a series of pure inorganic compounds have been derived from XPS peak intensity measurements taken by area via the so‐called ‘first principles model’ (FPM) and the ‘elemental sensitivity factors’ (ESF) methods. The two methods show similar degrees of accuracy, with a typical error of about ±10% when a set of experimental ESF is developed.

A lower accuracy, as expected, has been obtained when the literature ESF have been applied, Some discrepancy between the two approaches are evident when the kinetic energy separations of the XPS elemental peaks involved in the atomic ratio calculations is large. This aspect is discussed in the light of the instrumental responses which are of primary concern for the transferability of ESF results from one instrument to another.
Ion induced surface compositional changes of α brass; a comparative study by AES and sputtered thermal ion mass spectrometry. Application to quantitative AES
Authors: Darque‐Ceretti E. , Delamare F. , Blaise G.
Published: May 2005

Surface concentrations and sputtered‐off atom concentrations of α brass are measured during ion bombardment, respectively by Auger spectroscopy and by a new quantitative sputtered thermal ion mass spectrometry method. A new formulation of the problem of surface composition change is proposed which leads to a definition of matrix effect coefficients, sputter elemental yields and a sputter correction factor μ, connecting surface concentrations to sputtered‐off atom concentrations. Implications in quantitative analysis by Auger spectroscopy or any mass spectrometry technique are discussed.
Surface analytical study of the initial stages of growth and composition of protecting oxide‐ and oxycarbide layers on FeAlTi alloys
Authors: Viefhaus H. , Peters J. , Grabke H. J.
Published: May 2005

Protecting layers against carburizing atmospheres are of great importance for high temperature alloys. Very good results have been obtained with a model alloy FeAl0.5Ti. For a single crystal sample of this alloy, the composition and growth of the protecting layers were studied by AES and LEED. Excellent epitaxial fit was observed for a titanium oxycarbide layer growing on (100) and (110) oriented samples at high temperatures by surface segregation of C and Ti in oxygen containing atmosphers. At the same time Al segregated to the surface and diffused through this carbide layer. Reaction with oxygen led to the formation of an epitaxial Al2O3 layer on top of the carbide. Both layers were very dense and well adherent even for high quenching rates. Only very small amounts of carbon impurity were able to penetrate through the dense Al2O3 layer and were captured by the oxycarbide layer.
Charge compensation in SIMS analysis of polymer foils using negative secondary ions
Authors: Wittmaack K.
Published: May 2005

The experimental conditions required for charge compensation in depth profiling of polymer foils have been investigated with reference to the analysis of negative secondary ions. Low energy (≤500 eV) electron beams were employed in combination with 8 keV Xe+ ion beams. The minimum electron current required for the appearance of a stable SIMS signal was found to be equal to the ion current. Optimum SIMS signals were achieved by sufficiently overcompensating the primary ion current. Signals due to electron stimulated desorption could be suppressed by appropriate adjustment of the target bias. Reproducible depth profiles were obtained without major difficulties.
Molecular beam epitaxy of semiconductor interfaces and quantum wells for advanced optoelectronic devices
Authors: Ploog Klaus
Published: May 2005

We present selected examples for the control of interface formation with monolayer precision during molecular beam epitaxial growth and its application to modify the bulk properties of semiconductors arbitrarily through bandgap (or wavefunction) engineering. These examples concentrate on the materials system GaAs/AlAs which is important for high‐speed photonic and electron devices. In addition, as an example for strained‐layer superlattice, we briefly discuss Si/Six Ge1‐x superlattices, where the ordering of the electronic bands is strongly affected by the built‐in strain.
The interaction of group IB metals with van der waals faces of semiconducting metal dichalcogenides
Authors: Jaegermann W. , Ohuchi F. S. , Parkinson B. A.
Published: May 2005

The interaction of UHV cleaved van der Waals surfaces of the layered semiconductors SnS2, SnSe2, ZrS2, MoS2 and WS2 with deposited Cu, Ag and Au has been studied with XPS and LEED. It was observed for Cu on SnS2 and for Cu and Ag on SnSe2 that a bulk reaction ocurs leading to the formation of a new phase containing reduced Sn and oxidized Cu or Ag. Even at high coverages a metallic overlayer was not formed. An interfacial reaction at low coverages and subsequently a metallic layer was obtained for Cu on ZrS2 and Ag on SnS2 and Au on SnSe2. Cu, Ag and Au on MoS2 or WS2 form a metallic overlayer with an atomically abrupt semiconductor/metal interface. Epitaxial growth of a Au(111) layer was observed on WS2(0001). The differences in reactivity are related to differences in electrochemical standard potentials of the involved redox processes, structural features and to kinetic factors, e.g. ion transport.
XPS investigation of oxide films on InP(100)
Authors: Hofmann A. , Streubel P. , Meisel A.
Published: May 2005

The effect of chemical etching and the oxide growth on the etched surfaces on n‐ and p‐InP(100) have been studied using X‐ray photoelectron spectroscopy. The samples were etched in HCI (1 molar in methanol) and then annealed at 650 K in a vacuum for 1 hour. After this procedure both samples were oxidized in air at room temperature for a long time. The stoichiometry of the oxide layer was determined by angle‐resolved analysis of core level spectra.

The surface treatment leads to an indium‐rich surface. After annealing the In/P atomic ratios amount to 2.0 and 1.5 for n‐InP and p‐InP, respectively. Most of the oxygen on the surface after etching and annealing is presented as In2O3 and In(OH)3.

Within the oxide layers of the air‐oxidized samples the In/P atomic ratios vary from 2.5 to 3.7 for both n‐ and p‐InP showing a depletion of P during the oxidation. From angle‐dependent measurements it is concluded that the oxide layers consist of InPO4 and In(OH)3 whereas the outer layer is InPO4‐rich. The presence of In2O3 can be suggested in the oxide layer of n‐InP only. The oxidized p‐type sample contains more oxygen than the n‐type one.
Calculations of electron inelastic mean free paths. III. Data for 15 inorganic compounds over the 50–2000 eV range
Authors: Tanuma S. , Powell C. J. , Penn D. R.
Published: May 2005

We report calculations of electron inelastic mean free aths (IMEPs) of 50–2000 eV electrons in a group of 15 inorganic compounds (Al2O3, GaAs, GaP, InAs, InP, InSb, KCl, LiF, NaCl, PbTe, SiC, Si3N4, SiO2 and ZnS). As was found in similar calculations for a group of 27 elements, there are substantial differences in the shapes of the IMFP versus energy curves from compound to compound for energies below 200 eV; these differences are associated with the different inelastic electron scattering characteristics of each material. Comparisons are made of the calculated IMFPs and the values calculated from the predictive IMFP formula TPP‐2 developed from the IMFP calculations for the elements. Deviations in this comparison are found, which correlated with uncertainties of the optical data from which the IMFPs were calculated. The TPP‐2 IMFP formula is therefore believed to be a more reliable means for determining IMFPs for these compounds than the direct calculations.
Some aspects of analysis and physical interpretation of LEIS spectra
Authors: Koksa Vít , Dřímal Jiří
Published: May 2005

There are a lot of open questions connected mainly with the quantitative interpretation of low‐energy ion scattering (LEIS) spectra. Interpretation of LEIS spectra from the qualitative point of view in terms of elemental composition is rather straightforward. The article is focused on spectra obtained by the scattering of inert gas ions and measured by electrostatic analyser. The spectra arising during scattering of non‐inert gas ions as well as the time‐of‐flight techniques are not discussed here.

This article contains an overview of some phenomena influencing positions and shapes of peaks. A new effect—the shift of a peak position due to a neutralization phenomenon—is suggested here. A most simple model of collisions is used to provide some support for the choice of Gaussian functions in semi‐empirical models of the spectra. The simplicity of the model enables analytical treatment of the probability density function of the scattered particles. On the other hand, it excludes handling of realistic interaction potentials and of multiple collisions.
The cellular hydration state: role in apoptosis and proliferation
Authors: Schliess Freimut , Häussinger Dieter
Published: May 2005

Small cell volume changes occur within minutes in response to fluctuations of ambient osmolarity but also under the influence of hormones, substrates, second messengers, and oxidative stress. Isoosmotic cell swelling due to retention of inorganic ions and amino acids is obligatory during the cell cycle whereas cell shrinkage as a result of osmolyte release is an early hallmark of apoptosis known as apoptotic volume decrease. Cell volume changes are registered by osmosensing structures which trigger signals involved in the control of metabolism and gene expression. This review considers the hypothesis that cell volume‐dependent signals integrate into the overall signal transduction mediating apoptosis and cell cycle progression, respectively. Understanding the role of cell hydration changes in apoptosis and proliferation is of clinical relevance and provides novel therapeutic aspects.
Agitation scale‐up effects during VCM suspension polymerization
Authors: Lewis Max H. , Johnson Gary R.
Published: May 2005

Experimental data are presented showing the effect of reactor agitation intensity and reactor size on final resin properties during VCM suspension polymerization. Experiments were carried out in three stirred batch polymerization reactors covering a broad range of vessel sizes (bench scale, pilot plant, and commercial production units). Reactors' shapes were geometrically similar. The same charge recipe and operating procedure was also used for all three reactors. The effects of major agitation parameters such as impeller diameter, width, and speed are correlated against resin properties using the Weber number. The same characteristic U‐shaped curve is found for all three reactors when mean particle diameter is plotted versus Weber number. However, the curves do not lie on top of one another but are spread apart, the larger reactors having a higher Weber number. Another interesting feature is that the coefficient of variation (particle size standard deviation divided by mean diameter) decreases dramatically as reactor size is increased. Other resin properties also show improvement upon scale‐up. In summary, resin properties continue to improve as reactor size is increased over the range studied (bench‐to‐commercial large reactor scale), but a correct application of the complex scale‐up technology must be employed to take advantage of this observation.
The nature of poly (vinyl chloride) crystallinity—the microdomain structure
Authors: Summers James W.
Published: May 2005

The microstructure of polyvinyl chloride (PVC) controls much of its processing and property behavior. A model put together from X‐ray diffraction and small‐angle scattering data, swelling data, and processing data shows that PVC crystallites, of a wide melting range and spaced at 0.01 micron, act as crosslinks in a three‐dimensional network. Tie molecules limit swelling by plasticizer. The network prevents strong primary particle interaction at low melt temperatures. At higher temperatures, partial melting and then recrystallization leads to strong ties between particles and a tough product.
Effect of temperature, shear and blending conditions on the relaxation properties of milled and compression molded plasticized PVC compounds
Authors: Földes Enikö , Hedvig Péter
Published: May 2005

Blended, milled, and compression molded plasticized PVC compounds containing 30 wt percent of DIOP plasticizer were studied by combination of low effective frequency relaxation methods. The compounds were found to be heterogeneous and the ratio of plasticized and unplasticized phases dependent on the processing parameters. There is a correlation between the mechanical strength and the phase structure of the system.
Melt extensiometer investigation of PVC pipe compounds
Authors: Pazur A. S. , Uitenham L. C.
Published: May 2005

The Rheotens melt extensiometer can be a valuable tool for developing and studying rigid polyvinyl chloride compounds. The Rheotens can relate effects of variables such as processing aids, lubricants, and extrusion conditions on compound extrusion characteristics and changes in the melt on a morphological and molecular level, adding to the understanding of the processing and physical properties development of PVC materials.
Effect of extrusion temperature on elongational flow behavior of PVC melt
Authors: Park Im K.
Published: May 2005

The effect of the sample extrusion temperature between 160° and 180°C on the elongational flow properties of a low molecular weight suspension PVC (unplasticized) has been studied with the Rheometrics Extensional Rheometer. The results of both the tensile creep measurements at a constant stress of 24 KPa and the stretching experiment at a constant strain rate of 0.01 sec−1 indicated the existence of a rheological transition at 185°C marked by the dual valued flow activation energy and also by the temperature dependence of the tensile stress‐strain curves. Increasing extrusion temperature increased both the flow activation energy and the extensional viscosity below the transition temperature.
Gelatinization efficiency of PVC plasticizers
Authors: Šimoník Josef , Jurosz Jindřich , Chytílek Jaroslav , Drexler Jiǰí
Published: May 2005

A method of evaluating the gelatination ability of selected plasticizers can determine flow curves, critical temperatures, and times of gelation, and activation energies of flow for polyvinyl chloride/plasticizer mixtures. The flow analysis is based on transition of the heterogeneous mixture into the gelatination state based on changes in aggregation.
Fusion of PVC‐vinyl acetate copolymer plastisols
Authors: Garcia L. G.
Published: May 2005

Microscopic viscoelastic, and bulk property analyses of the fusion process of plastisols found that the viscoelastic analysis is a facile and sensitive tool for determining gelation and fusion characteristics. The viscoelastic measurements can be used to gauge the effects of molecular weight, different plasticizers, and percent vinyl acetate content on the fusion characteristics.
Role of poly(vinylchloride) and Di‐2‐ethyl hexyl‐phthalate in the smoke formation from plasticized poly(vinylchloride)
Authors: Michel Alain , Sainrat Alain , Bert Michel
Published: May 2005

The increase of the smoke level from PVC plasticized with di‐2‐ethyl hexyl phthalate with respect to the rigid PVC is caused mainly by interaction of the plasticizer with HCl evolved from the polymer when the temperature is higher than 200°C. This interaction causes the increase of the yield of phthalic anhydride probably through HCl as catalyst for DOP decomposition but phthalic anhydride formation parallels the formation of products enabled to increase the smoke level such as phthalic acid. In the presence of metallic compounds (iron, zinc, aluminium) it is possible to favor the formation of phthalic anhydride with respect to these products which are responsible for the smoke production. Then phthalic anhydride can be used as a tracer to estimate the efficiency of an additive or a combination of additives as smoke suppressant for DOP because its smoke level varies inversely with the yield of phthalic anhydride. The best combination to reduce the smoke level from plasticized PVC is obtained with the binary systems based upon copper compound, mainly efficient as smoke suppressant for PVC and either zinc or aluminium compounds, mainly efficient as smoke suppressant for DOP.
Three‐dimensional torque rheometry mapping of rigid PVC compounds
Authors: Pedersen Thomas C.
Published: May 2005

This paper presents an improved method for presenting torque rheometer data as it applies to rigid PVC extrusion compounds. During extrusion of rigid PVC, the compound is subjected to various degrees of heating, shearing, and compression. Three‐dimensional torque rheometry mapping can provide the rigid PVC formulator with greater insights into how a rigid PVC compound will perform on production extrusion equipment.
Electrical conduction and ultrasound wave propagation in particulate and short fiber composites of PVC. II: PVC‐Al coated glass fiber composites
Authors: Dutta A. L. , Misra A. K. , Singh R. P.
Published: May 2005

Poly(vinylch1oride) composites containing 2 to 20 wt% of aluminum coated glass fiber (AlCGF) were prepared by the mechanical mixing and hot compression technique. Their electrical conduction and ultrasound wave propagation at frequencies of 2 to 9 MHz were studied. The electrical resistivity of these composites was lowered because of fiber‐fiber contact formation, which is evident from optical photomicrographs of the composites. Other morphological investigations, such as X‐ray diffraction and DTA, show matrix‐filler interaction. The limiting resistivity of PVC/AlCGF composite is 10 ohm‐cm at 14 wt% (8.11 vol%) of fiber concentration. Ultrasound wave propagation through these composites having fiber‐fiber contacts has shown that both absorption and velocity are high at 9 MHz. Other ultrasound parameters were studied, such as excess absorption, relative velocity, relative modulus variation with composition as well as with propagation constant. No definite correlation exists between electrical conduction due to fiber‐fiber contact formation and ultrasound wave propagation.
EMI shielding of intinsically conductive polymers
Authors: Shacklette L. W. , Colaneri N. F. , Kulkarni V. G. , Wessling B.
Published: May 2005

Results of this study, in which shielding efficiencies are measured for a number of blends containing various conductive fillers including intrinsically conductive polymers, are reported. It is shown that a very high level of shielding performance can be achieved by use of intrinsically conductive polymers in thermoplastic blends and that the most reliable measure of this performance is obtained from far‐field shielding measurements. However, near‐field measurements provide a useful method for comparing the relative shielding effectiveness of different samples. A PVC blend containing nearly uniformly dispersed intrinsically conductive polymer proved to be the best performing sample.
Analogien zwischen der Röntgenstreuanalyse und der Röntgenfluoreszenzanalyse
Authors: Ebel H. , Ebel M. F.
Published: May 2005

Es werden die Gleichungen fur die Primä, Sekundär‐ und Tertiäranregung bei der RFA verwendet, um aus Analogiebetrachtungen die Verhältnisse bei der Einfach‐, Zweifach‐ und Dreifachstreuung quantitativ behandeln zu können. Der charakteristische Quotient aus körent und inkohärent gestreuter Intensität wird sodann fur verschiedene Kohlenwasserstoffe berechnet und mit den experimentell gefundenen verglichen. Die Ursachen für den etwa 15 Prozent betragenden Unterschied werden diskutiert.
Some applications of a computer program for quantitative spectrochemical analysis
Authors: Gould R. W. , Bates S. R.
Published: May 2005

In the general application of the X‐ray spectrographic method, it is often difficult to obtain standards which closely approximate the unknown being analysed. One of the possible ways around this problem is to utilise a matrix correction procedure which does not, in principle, require large numbers of standard samples. One such method has been described by Birks and Criss and this paper describes the application of their program at the University of Florida where a wide variety of samples are encountered. Also discussed in the paper is the basis of the so‐called ‘Fundamental Parameter’ method which has provided the means of analysing with great accuracy certain binary and tertiary alloys. It seems that the method holds considerable promise for the analysis of ore deposits and the prediction of inter‐element effects.
A die for pelletizing samples for X‐ray fluorescence analysis
Authors: Fabbi B. P.
Published: May 2005

The preparation of pellets of powdered geological samples is a critical step in X‐ray fluorescence analysis. A special die has been designed to produce smooth surfaces on extremely durable pellets and to provide a protective, hard outer ring and backing. The outer ring minimises the deterioration of the edge that has in the past limited the usable life of the pellet. Repetitive preparations have shown reproducibility and homogeneity to be within normal counting statistics.
FeKβ1,3 X‐ray emission spectra from complexes which contain ferric iron in unconventional spin states
Authors: Urch D. S. , Webber S.
Published: May 2005

Iron Kβ′, Kβ1,3 X‐ray emission spectra are reported for complexes with spin‐states S = 5/2, 3/2 and 1/2. It is proposed that the highly asymmetric shape of the Kβ1,3 peak might be due to charge‐transfer processes occurring simultaneously with the 3p → 1s transition. Since these processes vary greatly with the nature of the ligands, only a qualitative relationship exists between the relative intensity of Kβ′ (to Kβ1,3) and the number of unpaired 3d electrons. However, if the ligand environment is held constant, then it seems reasonable to use Kβ′ : Kβ1,3 to determine the number of unpaired electrons.
X‐ray spectrometric analysis of trace elements in rocks. Correction for instrumental interferences
Authors: Bougault H. , Cambon P. , Toulhoat H.
Published: May 2005

Investigating trace element determination in rocks and taking into account possible instrumental interferences, it is shown that the general relationship between I (net peak intensity) and c (fluorescent element concentration) is (I – I0) M = Ac + B where M is the matrix effect correction factor and A is a constant proportional to the efficiency of excitation; B and I0 correspond to the intensities due to, respectively the scattering (especially, by the sample) of any instrumental interfering radiation, and a possible stray emission by the instrument itself. Using this equation under optimized conditions allows interferences as high as 200 ppm (if expressed in equivalent concentration) to be compensated without any significant decrease regarding the general accuracy of determinations.
Improved spatial resolution microanalysis in a scanning transmission electron microscope
Authors: Faulkner R. G. , Hopkins T. C. , Norrgård K.
Published: May 2005

The attachment of energy‐dispersive analysers to scanning transmission electron microscopes makes possible accurate high spatial resolution microanalysis. This paper quantifies the X‐ray spatial resolution obtainable for good sensitivity microanalysis as a function of microscope lens settings and primary electron beam accelerating voltage in a 200 k V scanning transmission electron microscope. It is shown that at 200 k V a resolution of approximately 500 Å is possible with a 1500 Å thick nickel–iron–chromium alloy specimen. At 100 k V the resolution drops to nearer 1000 Å These figures are supported by Monte Carlo calculations of electron trajectories in thin films. Comparisons of experimentally measured and theoretically predicted X‐ray intensities suggest a severe loss of signal intensity within the microscope; this loss becomes greater at higher accelerating voltages. The influence on microanalysis of angle of specimen inclination to beam and to the detector is considered and precautions necessary to limit beam drift during 1000 s analyses are discussed. The application of high sensitivity, high resolution microanalysis methods to a grain boundary segregation effect in an austenitic creep resistant steel is described. It is shown that titanium segregates in a zone 1000–1500 Å thick on either side of the grain boundary to a level of approximately three times the matrix concentration.
X‐ray spectrochemical matrix correction in the analysis of copper ores
Authors: Hall Stephen H. , Harbison L. E.
Published: May 2005

A graphical method of X‐ray fluorescence matrix correction is presented. Experimental evidence is based upon copper assays where sample matrix varies widely in the ore and smelter samples studied. Corrections are performed on concentrated, solvated samples, but the analyte peak alone is observed in practice.
Some comments on the deterioration of rubidium acid phthalate analysing crystals
Authors: Fregerslev Sidsel
Published: May 2005

Rubidium acid phthalate crystals are observed to decrease in reflectivity after being used for some time. During a period of three years the counts s−1 per % Na dropped by 80% compared with the new crystal. Very careful washing with water restored the counts s−1 per % Na to 70% compared with the new crystal.
Qualitative and quantitative analysis of technical aluminium phosphide
Authors: Mantler M. , Wernisch J.
Published: May 2005

The qualitative and quantitative composition of technical aluminium phosphide was studied employing X‐ray electron spectrometry, X‐ray fluorescence analysis and X‐ray diffractometry as well as gravimetric and gas volumetric methods. In addition to aluminium phosphide, AIN (8%), Al(1%) and Al(OH)3 (10%) were found. Al(OH)3 is produced by the reaction of AlP with H2O. Models describing this reaction in humid air and allowing for quantitative analysis are presented.