bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unimolecular neutral and ion kinetics by variable‐time neutralization—reionization mass spectrometry
Authors: Kuhns David W. , Turecek Frantisek 
Published: May 2005

AbstractA new method is described for the determination of rate parameters of unimolecular dissociations of neutral intermediates and ions produced by collisional neutralization and reionization at kiloelectronvolt kinetic energies. The method utilizes variable time‐scales for neutral and ion dissociations to obtain time‐dependent survivor and product ion yields. Kinetic analysis then provides phenomenological rate constants for both neutral and ion dissociations. Neutralization with CH3I, NO, (C2H5)2O, C6H6 and Xe of methyl iodide cation radicals is shown to produce the intermediate neutral molecules with different internal energies, resulting in different rates of neutral and ion dissociations. Vibrational excitation in neutralized CH3I results in neutral dissociations with rate parameters in the (1–3) × 105 s–1 range. The origin of neutral excitation by fast collision is explained by the intermediate formation of highly excited Rydberg states that decay by photon emission to the vibrationally excited ground state of the molecule.
Electrospray vs. matrix‐assisted laser desorption/ionization. 1. Some examples in the protein field
Authors: Favretto Donata , Seraglia Roberta , Traldi Pietro , Curcuruto Ornella , Hamdan Mahmoud 
Published: May 2005

AbstractSeveral proteins in the relative molecular mass (RMM) range 1150–29000 are examined by means of both positive electrospray and matrix‐assisted laser desorption/ionization mass spectrometry. Accuracy of the measured RMMs, resolution and overall sensitivity are discussed. The presence of more than one component in a number of the investigated compounds permitted the assessment of both desorption methods for the analysis of mixtures. Solvent‐induced conformational changes are linked to charge‐state distribution shifts observed in some positive electrospray mass spectra.
Negative‐ion fast atom bombardment mass spectrometry in the characterization of deoxyfluorinated sugars
Authors: Coppola M. , Favretto D. , Traldi P. , Resnati G. 
Published: May 2005

AbstractNegative‐ion fast atom bombardment mass spectrometry and metastable ion studies were applied to the characterization of three isomeric fluorine‐containing sugars. Peculiar fragmentation processes were evidenced for each isomer, enabling their differentiation. Comparison with the behaviour of a non‐fluorinated analogue allowed investigation of the role of fluorine in the decomposition processes of these compounds.
Translational energy losses of LiF cluster ions
Authors: Vékey Károly , Ludányi Krisztina 
Published: May 2005

AbstractTranslation energy loss (TEL) values have been measured in the collision‐induced fragmentation of Li6F5+ cluster ions. TEL values varied between 1 and 8 eV in single collisions and showed a strong dependence on the centre‐of‐mass (com) collision energy. At large com collision energies (>800 eV) the TEL was small (˜1.5 eV) and is explained by internal excitation. At lower com collision energies, TEL values were larger (up to 8 eV), and these are explained in terms of kinetic energy uptake by the target gas. TEL values observed using LiF and CsI clusters are compared.
Mass spectral fragmentation pathways in some glycoluril‐type explosives. A study by collision‐induced dissociation and isotope labeling
Authors: Yinon J. , Bulusu S. , Axenrod T. , Yazdekhasti H. 
Published: May 2005

AbstractElectron impact (EI), chemical ionization and negative‐ion chemical ionization (NCI) mass spectra of 1,4‐dinitroglycoluril (DINGU), its 15N‐ and 2H‐labeled analogues and the dimethyl‐substituted derivatives were recorded. Tandem mass spectrometry with collision induced dissociation was used to study the fragmentation pathways of these compounds. It was found that the main EI fragmentation processes of DINGU are due to the cleavage of CN bonds and some rearrangement reactions.
Investigation of cationic organic dyes used as molecular probes by liquid secondary ion mass spectrometry
Authors: Carlson Richard E. , Busch Kenneth L. 
Published: May 2005

AbstractThe positive‐ion mass spectra of twelve organic dyes used as molecular probes were measured using liquid secondary ion mass spectrometry (LSIMS). Nine of the twelve dyes were singly charged cations and the other three were doubly charged cations. The mass spectra of each of the dyes in m‐nitrobenzyl alcohol contain abundant signals for the intact cation, C+ (singly charged cation dyes), or for singly‐charged forms of the doubly charged cation formed by proton loss, [C2+ H+]+, or halogen counter ion attachment, [C2+ + X−]+. Fragmentation is usually minimal under the conditions used. However, the cations of five of the singly charged compounds appear to undergo charge‐remote fragmentation. Collision‐induced dissociation experiments on a hybrid mass spectrometer of EBqQ geometry at collision energies up to 300 eV failed to access this fragmentation pathway. In contrast to the LSIMS of many other doubly charged organic compounds, two of the dicationic dyes produced a doubly charged ion of reasonable abundance (2–20%) in the mass spectrum. When glycerol was used as a matrix solvent, the addition of the matrix modifier trifluoroacetic acid increased the abundance of C2+.
Fragment ion formation from n‐alkanes and cycloalkanes by plasma desorption
Authors: Betts R. L. , Park M. A. , Shirey E. Lynn , Schweikert E. A. 
Published: May 2005

AbstractThe plasma desorption of hydrogen loss fragment ions from frozen films of several classes of aliphatic volatile hydrocarbons was investigated with 252Cf plasma desorption mass spectrometry. A time‐of‐flight instrument suitable for the reproducible sampling and analysis of volatile hydrocarbons in the solid state was designed for this study. Representative compounds from the n‐alkanes and cycloalkanes were analyzed. For all the compounds studied, radical molecular ions. M+., and hydrogen loss fragment ions, [M  mH]+ with m varying from 1 to 10, were produced. The length of the alkane chain, the size of the alkane rings and the stability of the resulting H‐loss ions affected the number and abundance of these ions. Smaller molecules underwent proportionally more hydrogen loss than larger molecules of the same class.
Fast atom bombardment mass and tandem mass spectra of protonated and alkali cationized aldobiouronic and pseudoaldobiouronic acid per‐O‐methyl derivatives
Authors: Kováčik Vladimír , Hirsch Ján , Heerma W. , de Koster C. G. , Haverkamp J. 
Published: May 2005

AbstractThe positive‐ion fast atom bombardment mass spectra of permethylated aldo‐ and pseudoaldobiouronic acids can be used to distinguish these classes of compounds. The collisional‐induced dissociation spectra of the [M + H]+ ions show fragment ions resulting from glycosidic bond cleavage and successive losses of methanol molecules. These spectra together with those of the [M + H  MeOH]+ oxonium ions allow the identification of the type of interglycosidic linkage. Collisional activation of the relatively stable [M + Na]+ ions show many fragmentations which are common to alkali cationized permethylated saccharides. Moreover, fragment ions resulting from two‐bond ring cleavage processes yield additional information with respect to the linkage between the hexose and uronic acid units.
Reactions of ionized dibutyl ether
Authors: Bowen Richard D. , Suh Dennis , Terlouw Johan K. 
Published: May 2005

AbstractThe reactions of ionized di‐n‐butyl ether are reported and compared with those of ionized n‐butyl sec‐butyl and di‐sec‐butyl ether. The main fragmentation of metastable (CH3CH2CH2CH2)2O+. is C2H5⋅ loss (˜85%), but minor amounts (2–4%) of CH3⋅, C4H7⋅, C4H9⋅, C4H10 and C4H10O are also eliminated. In contrast, C2H5⋅ elimination is of much lower abundance (20 and 4%, respectively) from metastable CH3CH2CH2CH2OCH(CH3)CH2CH3+. and [CH3CH2(CH3)CH]2O+., which expel mainly C2H6 and CH3⋅ (35–55%). Studies on collisional activation spectra of the C6H13O+ oxonium ions reveal that C2H5⋅ loss from (CH3CH2CH2CH2)2O+. gives the same product, (CH3CH2CH2CH2 +OCHCH3) as that formed by direct cleavage of CH3CH2CH2CH2OCH(CH3)CH2CH3+.. Elimination of C2H5⋅ from (CH3CH2CH2CH2)2O+. is interpreted by means of a mechanism in which a 1,4‐H shift to the oxygen atom initiates a unidirectional skeletal rearrangement to CH3CH2CH2CH2OCH(CH3)CH2CH3+., which then undergoes cleavage to CH3CH2CH2CH2+OCHCH3 and C2H5⋅. Further support for this mechanism is obtained from considering the collisional activation and neutralization‐reionization mass spectra of the (C4H9)2O+. species and the behaviour of labelled analogues of (CH3CH2CH2CH2)2O+.. The rate of ethyl radical loss is suppressed relative to those of alternative dissociations by deuteriation at the γ‐position of either or both butyl substituents. Moreover, C2H5⋅ loss via skeletal rearrangement and fragmentation of the unlabelled butyl group in CH3CH2CH2CH2OCH2CH2CD2CH3+. occurs approximately five times more rapidly than C2H4D⋅ expulsion via isomerization and fission of the labelled butyl substituent. These findings indicate that the initial 1,4‐hydrogen shift is influenced by a significant isotope effect, as would be expected if this step is rate limiting in ethyl radical loss.
Resin/fiber thermo‐oxidative interactions in pmr polyimide/graphite composites
Authors: Alston William B. 
Published: May 2005

AbstractThe amounts of resin weight loss and fiber weight loss in four PMR polyimide/graphite fiber composites were calculated from the composite weight losses and the fiber/resin ratios of the composites after long term thermo‐oxidative aging in 600° F air. The accelerating effect of graphite fiber on resin weight loss, compared to neat resin weight loss, indicated the presence of a deleterious resin/fiber thermo‐oxidative interaction, presumably due to fiber impurities. Similarly, the declerating effect of the protective matrix resin on fiber weight loss, compared to bare fiber weight loss, was also demonstrated. The amount of hydrazine indigestible resin and the amount of loose surface graphite fiber that formed during 600° F exposure of the composites were quantitatively determined. The indigestible residual resin was also qualitatively studied by scanning electron microscopy.
Stress dependence of water diffusion in epoxy resin
Authors: Fahmy A. A. , Hurt J. C. 
Published: May 2005

AbstractThe effect of stress on the diffusion of water in glassy polymers is analytically treated. Utilizing the free volume concept the effect of stress on the free volume fraction is established and in turn is related to the diffusion coefficient yielding the following formula: Dσ = Doe(6 to 10)σ/G where Dσ and Do are the diffusion coefficients in the presence and absence of stress respectively, G is the shear modulus, and σ is the stress. Experiments are described which demonstrate that in a bent epoxy bar, more water is picked up at the tension side than at the compression side. Theory and experiment are discussed and compared.
Quality assurance of epoxy resin prepregs using liquid chromatography
Authors: Hagnauer Gary L. 
Published: May 2005

AbstractLiquid size exclusion, adsorption, and bonded‐phase high performance liquid chromatographic (HPLC) methods have been developed to monitor the chemical compositions of epoxy resin prepregs. Examples are given to illustrate how multiple detectors and oligomer analysis techniques may be used to identify prepreg components and to discriminate between epoxy resins obtained from different manufacturers. The results of a case study in which HPLC methods were used to monitor compositional variations in batches of a commercial prepreg over a four year period are discussed. Finally, examples demonstrate how HPLC may be applied to monitor prepreg aging and to measure the extent of prepreg staging.
Mechanical properties of glass microsphere‐filled composite materials
Authors: Micliaresi C. , Nicolais L. , Nicododemo L. , Di Benedetto A. T. 
Published: May 2005

AbstractThe mechanical behavior of epoxy, hydroxyethymetherylate and polystyrene composites containing various percentages of glass microspheres was investigated over a wide range of temperature. The effect of filler concentration of the ductile‐brittle transition and on the glass‐transition temperature of the composites is reported. The utility of various predictive models for the effect of filler concentration on mechanical properties is assessed.
Heat transfer in polymeric composites containing “thermally active” fillers
Authors: Migliaresi C. , Astarita G. , Nicolais L. , Joshi S. 
Published: May 2005

AbstractThermal properties of polystyrene composites with a filler showing a solid‐solid phase transition have been studied. Differential calorimeter analysis and typical insulation tests have been performed. An analysis of the experimental results has been done, by using the Stefan moving boundary theory, showing that it is inadequate to predict the thermal behavior of composites of the type studied.
Compounding of glass fiber‐reinforced polypropylene and investigation of its mechanical properties under simple and complex loading
Authors: Pandit S. N. , Gupta V. B. , Subramanian K. 
Published: May 2005

AbstractPolypropylene is one of the important thermoplastics that has been reinforced with glass fibers to give a reasonably good engineering plastic. Because of its inert nature, it does not easily adhere to the glass surface and hence some improvement in mechanical properties. In the present study a vinyltriethoxysilane coupling agent in polymeric form has been tried and seen to improve the properties. Tests have been carried out at (a) constant strain rate (in the Instron testing machine), and (b)constant stress rate (water loading on a biaxial testing machine). Under constant strain rate only tensile properties have been studied while under constant stress rate, the tensile, torsional and combined tensile‐torsional tests have been carried out. In each of the above cases, a considerable improvement in elastic modulus has been observed. The Tensile strength is improved to the extent of about 25 percent. There is only a slight improvement in torsional strength. Different fiber volume contents were used and their effect studied on modulus and strength. The mechanical data for reinforced‐polypropylene samples have been discussed in terms of the fiber‐length distribution in the composite. Detailed analysis of tensile data suggests that at low strains, when the critical length is relatively low, the fibers contribute to a high modulus. With increasing strain the critical length increases and the load carrying capacity of the fibers is reduced. Consequently the gain in strength is relatively less. The effect of fiber length distribution in torsion and combined tension‐torsion tests would be expected to be similar and the results seem to confirm this.
Molding and torsional testing of tubular specimens of glass fiber‐reinforced polypropylene
Authors: Pandit S. N. , Gupta V. B. 
Published: May 2005

AbstractThis paper describes a torsion pendulum based on the free vibration method and designed for studies on tubular samples. The design and fabrication of the injection mold used for molding the tubular specimens is also described. Tubular specimens were injection molded form polypropylene and glass fiber‐reinforced polypropylene having different glass fiber contents. The sample, which is enclosed in an insulated chamber, can be cooled with the help of liquid nitrogen and heated electrically. The damped oscillations were recorded on a moving chart paper using a lamp and a photodyne between −40 to 100°C. The results indicate that both storage modulus and the logarithmic decrement are affected by the glass fiber and its content. The reinforcing effect of glass fiber and the suppression of viscoelastic effects are briefly discussed.
Comparison of primary and secondary aminosilance coupling agents in anhuydride‐curde epoxy fiberglass composites
Authors: Chiang Chwan‐Hwa , Koenig Jack L. 
Published: May 2005

AbstractFourier transform infrared spectroscopy (FT‐IR) has been utilized to investigate the interfacial chemical bonding at the interfaces of the aminosilanes and the nedic methyl anhydiride cured epoxy matrix in fiber‐reinforced composites. It is found that the nedic methyl anhydride can react with γ‐aminopropyltriethoxysilane (APS) and N‐methylaminoproplytrimethoxysilane (MAPS). In comparing the relative reactivities of two coupling agents to the epoxy resin, the secondary aminosilance has a higher reactivity than the primary aminosilance. An elevated temperature is required for the copolymerization to take place between the silane and the epoxy resin. The results indicate that covalent bonds form at the coupling agents. The molecular structure of the interface in MAPS treated fiberglass reinforced composites is different from that of the APS treated fiber composites. In addition, an accelerated copolymerization initiated by the coupling agent treated surface is also found in the resin interphase which may be important in determining the mechanical properties of the composites.
Fracture of adhesive joints
Authors: Wang S. S. , McGarry F. J. , Mandell J. F. 
Published: May 2005

AbstractThis paper presents some of the important results obtained from a series of studies on cohesive fracture in adhesively bonded joints. Due to the complex nature of the adhesive joint fracture, an accurate and efficient numerical method particularly suitable for the present problem has been developed, based on a hybrid‐stress finite element formulation. Fracture characteristics in adhesively bonded joints are described in terms of local crack‐tip deformation and stress fields in the polymeric adhesive layer. Effects of material properties, joint geometry, and bond‐line thickness on the crack behavior are studied for classical lap‐shear and currently used double‐cantilever‐beam joints. Of particular interest are the crack‐tip stress intensities in the adhesive layer; their values are obtained for several cases of practical importance.
Environmental testing of high strength molding compounds
Authors: Edwards Dale B. , Sridharan N. S. 
Published: May 2005

AbstractTensile and short beam shear tests were performed on five high strength vinyl ester molding compounds after immersion in water at various temperatures. These tests were conducted in order to characterize the degradation of these properties with environmental exposure and to isolate problem areas which contribute to the degradation. Reductions of up to 70 percent were found for both tensile and short beam shear strength, when tested at high temperatures. This loss of properties is primarily a result of degradation of the glass/resin interface and is essentially irreversible.
Joining strength of sheet molding compounds
Authors: Hoa S. V. , Feldman D. 
Published: May 2005

AbstractBonding and bolting strengths of a sheet molding compound (SMC‐R30) are investigated. Epoxy adhesives are found to give good bonding strength. Surface pretreatment does not affect bond strength. Artificial weathering has practically no effect upon bond strength. Bolting strength depends on the width of the specimen for a certain bolt size. Bolting gives stronger joints than bonding.
Application of a gripping system to test a uniaxial graphite fiber‐reinforced composite (PMR 15/celion 6000) in tension at 316°C
Authors: Whittenberger J. Daniel , Hurwitz Frances I. 
Published: May 2005

AbstractA gripping system has been developed to test uniaxial, 0° orientation PMR 15/Celion 6000 composites at elevated temperatures. The method involves compression of grit‐blasted laminate between grit‐blasted metal to give a non‐slipping interface for load transfer. Tensile testing at both 316°C and room temperature indicated that deformation was elastic to fracture and that the variation in tensile properties for one laminate is the same as that for several panels. In addition, the tensile properties for uniaxial PMR 15/Celion 6000 are identical at 316°C and room temperature. For nominally 51 volume percent fiber, the elastic modulus is 119.6 GPa, the fracture stress is 1370 MPa, and the strain to fracture is about 1.15 percent. In addition, data are presented which indicate that the gripping system can be used for long term, elevated temperature testing of composite materials.
Influence of injection‐molding parameters on the morphology and mechanical properties of glass fiber‐reinforced polypropylene composites
Authors: Xavier S. F. , Tyagi D. , Misra A. 
Published: May 2005

AbstractPolypropylene reinforced with glass fiber (28 percent by weight) was injection molded under different processing conditions. The influence of injection‐molding parameters such as pressure, injection speed, and injection temperature on the morphology and mechanical properties was studied using standard techniques, viz. polarizing microscope, scanning electron microscope, and Instron Universal testing machine. The observed mechanical properties were explained in terms of skin‐core‐morphology, transcrystallinity, fiber orientation and void volume. This study attempts to correlate processing conditions with morphology and mechanical properties. Such a study would help in optimizing processing conditions to give composites with desired properties.
Melt processible fluoropolymer composites
Authors: Crosby J. M. , Carreno C. A. , Talley K. L. 
Published: May 2005

AbstractA series of melt‐processible fluoropolymer compounds including ethylene‐tetrafluoroethylene (ETFE), poly(vinylidene fluoride) (PVF2), ethylene‐chlorotrifluoroethylene copolymer (ECTFE), perfluoroalkoxy modified tetrafluoroethylene (PFA), and fluorinated ethylene‐propylene copolymer (FEP) containing reinforcing glass fiber, milled glass fiber, carbon fiber, minerals, poly(tetrafluoroethylene) (PTFE) lubricant powder, graphite powder and MoS2 were prepared and characterized. The mechanical, physical, thermal, and tribiological properties of these composites were compared and ranked for suitability in various applications. These composites represent the first comprehensive evaluation of reinforced and filled meltprocessible fluoropolymer composites.
Polymer impregnation of tuff
Authors: Aurisicchio S. , Masi P. , Nicolais L. , Evangelista A. , Pellegrino A. 
Published: May 2005

AbstractPolymer impregnation has been proven to increase environmental and mechanical resistance of tuff (a soft volcanic rock), suggesting its potential application for restoration of monuments or reinforcement of structures. The influence of monomer viscosity and applied pressure on the penetration rate of the liquid into pores, the monomer evaporation from the pores, and the effect of the curing temperature on the polymerization rate were studied. The data are analyzed in terms of the existing phenomenological or analytical models. The results can be used to develop a practical and economical large‐scale process.
Exact and approximate strain‐optic laws for photoelastic composites
Authors: Agarwal B. D. , Chaturvedi S. K. 
Published: May 2005

AbstractAn exact strain‐optic law for othotropic materials has been derived using Pockels' theory of crystalline photoelasticity. The law requires three experimentally determined photoelastic constants. Photoelastic response of materials such as glass‐fiber‐reinforced epoxy or polyester composites subjected to any state of strain can be predicted through this law. However, due to practical difficulties, this law is not sufficient to solve for principal strain differences or the direction of principal strain from conventional measurements in a polariscope. An approximate strain‐optic law, which has been derived by minimizing square of the error between predictions of exact and approximate laws, can be employed to estimate the difference between principal strains and their directions. The error in using the approximate law appears to be small. The approximate strain‐optic law has been found to be preferable over an approximate stress‐optic law.