bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conditional Lifetime Data Analysis Using the Limited Expected Value Function
Authors: Quigley John , Walls Lesley 
Published: March 2004

AbstractMuch failure, and other event, data are commonly highly censored. Consequently this limits the efficacy of many statistical analysis techniques. The limited expected value (LEV) function presents an alternative way of characterizing lifetime distributions. In essence the LEV provides a means of calculating a truncated mean time to failure (MTTF) (or mean time before failure (MTBF) if appropriate) that is adjusted at each of the censoring times and so appears potentially suitable for dealing with censored data structures. In theory, the LEV has been defined for many standard distributions, however its practical use is not well developed. This paper aims to extend the theory of LEV for typical censoring structures to develop procedures that will assist in model identification as well as parameter estimation. Applications to typical event data will be presented and the use of LEV in comparison with a selection of existing lifetime distributional analysis will be made based on some preliminary research. Copyright © 2004 John Wiley & Sons, Ltd.
On the Use of Imprecise Probabilities in Reliability
Authors: Coolen F. P. A. 
Published: March 2004

AbstractTheory of imprecise probability generalizes classical probability theory, by assigning to each event an interval instead of a single number. In this paper, we briefly discuss this generalization and some recently suggested applications of imprecise probabilities in reliability. We also comment on challenges for research and applications. Copyright © 2004 John Wiley & Sons, Ltd.
Non‐parametric Predictive Inference for Age Replacement with a Renewal Argument
Authors: Coolen‐Schrijner P. , Coolen F. P. A. 
Published: March 2004

AbstractWe consider an age replacement problem with cost function based on the renewal reward theorem. However, instead of assuming a known probability distribution for the lifetimes, we apply Hill's assumption $A_{(n)}$ for predicting probabilities for the lifetime of a future item. Lower and upper bounds for the survival function of a future item are used, resulting in upper and lower cost functions. Minimizing these upper and lower cost functions to obtain the optimal age replacement times is simplified due to the special form of these functions.To discuss some features of our approach, we first study the consequences of using $n$ equally spaced percentiles from a known distribution instead of $n$ observed data. Secondly, we report on a simulation study where the lifetimes are simulated from known distributions, so that the optimal replacement times corresponding to our approach can be compared with the theoretical optimal replacement times. Copyright © 2004 John Wiley & Sons, Ltd.
Assessing the Impact of Preventive Maintenance Based on Censored Data
Authors: Bedford Tim 
Published: March 2004

AbstractRecent work in the field of competing risks enables us to start an assessment of the impact of preventive maintenance on the failure characteristics of a piece of equipment. Competing risk is the term given when more than one factor conspires to take a piece of equipment out of service. A simple example of this is given by preventive maintenance and failure. Each could occur to a piece of equipment but only one actually can. The preventive maintenance time may censor the unobserved latent failure time, thus ensuring that the statistical analysis of the failure times is made more difficult. Maintenance optimization models require knowledge of the underlying failure distribution. The Kaplan–Meier estimator (and other similar techniques) is commonly used to remove the effect of the censoring variable on the estimate of the distribution of the variable of interest. When the censoring variable is preventative maintenance, however, it is most unlikely that the assumptions of the Kaplan–Meier estimator (independence between the latent failure and preventive maintenance times) are valid. In this paper we give an overview of some of the different methods which have recently emerged in this area. These make different assumptions about the relation between PM and failure to allow the PM censoring to be ‘removed’. Potentially, these methods would allow us to look at changing maintenance strategies. Although they are in the early stages of development they do already allow us to quantify the effect of some changes. Copyright © 2004 John Wiley & Sons, Ltd.
Spectroscopic constants and molecular properties of CN−, SiH−, PO−, SO−, SF−, and SiS−: Density functional study
Authors: Midda S. , Das A. K. 
Published: March 2004

AbstractSpectroscopic constants and molecular properties of selected diatomic anions namely CN−, SiH−, PO−, SO−, SF−, and SiS− in their ground states have been studied in detail using the hybrid HF/DF B3LYP method. The consistency of the calculated values has been verified with four different basis sets, with improved quality. The spectroscopic constants and molecular properties calculated with the aug‐cc‐pVTZ basis set agree very well with the experimental and theoretical values wherever available. Most of the spectroscopic constants and molecular properties of the selected diatomic anions, particularly the spectroscopic constants and molecular properties of SO− and SiS− are reported for the first time. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Three‐electron two‐center bonding in cycloimmonium ylides
Authors: Karafiloglou P. , Surpateanu G. 
Published: March 2004

AbstractWe explore the possibility that a 3‐electron‐2‐center bonding exists in cycloimmonium ylides. To detect this bonding in a polyatomic system, 3‐electron‐1‐hole density operators, characterizing a Pauling 3‐electron bond, are used in the framework of second quantization formalism. The weights of 3‐electron resonance structures are calculated and compared with the weights of 2‐electron structures for the ylide bond of pyridinium dicyanomethylide; the correlations of (↑↓) and (↑) electronic events, involved in the 3‐electron resonance structures, are also investigated. The calculations are performed in various approximation levels, and both orthogonal and nonorthogonal natural atomic orbitals are adopted. All calculations show that a 3‐electron bond exists between N and C atoms of ylide bond, but this bonding is not extended in C atoms of the pyridinium group. The interactions of α,β electrons (at the configuration interaction [CI] level) increase the localization of electrons, the weights of 3‐electron resonance structures, and thus the probability for 3‐electron bonding. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
New model of the electronic structure of the [Mo6X8(CN)6]6− clusters (XS, Se) based on the study of electron density distribution in the inner part of the Mo6 polyhedron
Authors: Baranovski V. I. , Korolkov D. V. 
Published: March 2004

AbstractThe geometric structure and bonding in [Mo6S8(CN)6]6− cluster were studied on the basis of quantum chemical ab initio and DFT (B3LYP) calculations with different basis sets. The geometry parameters of the Mo6S8 core are in good agreement with the available crystal structure data. The electron density in the inner part of the Mo6 octahedron is almost constant (∼0.04–0.06 e/au3). There is also noticeable electron density on the edges and faces of the Mo6S8 polyhedron. The model of the electronic structure of the cluster under consideration starts from the mobile electrons moving in the potential well of the spherical symmetry. The resulting states are classified according to orbital quantum number l (e.g., 1s, 1p, 1d, 1f). Subsequent crystal field splitting leads to observable consequence of the one electron states of the Oh point group symmetry. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Bonding in FHF−, (HF)2, and FHF
Authors: Davidson Ernest R. 
Published: March 2004

AbstractBonding in FHF−, (HF)2, and FHF is compared from the molecular orbital and electrostatic bonding viewpoint. The electrostatic force is dominant in the formation of FHF− and HF dimer. Exchange repulsion dominates in preventing the formation of FHF and leads to a D∞h transition state for H exchange. At the D∞h stationary points for FHF− and FHF the electronic structure can be understood using delocalized symmetry orbitals, but this delocalization is not the primary driving force along the potential energy surface leading to these structures. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Theoretical study of reaction mechanism for CH2CHX(XH, F, Cl) with ozone
Authors: Li Lai‐Cai , Deng Ping , Xu Ming‐Hou , Wong Ning‐Bew 
Published: March 2004

AbstractIn this work, we study the reaction mechanism of the CH2CHX(XH, F, Cl) with ozone reactions, using ab initio MP2 method at 6‐311++g** basis set level. The geometric configurations of reactants, intermediates, transition states, and products were optimized, and the energies were obtained at the QCISD(T)/6‐311++G** level. The transition states and intermediates of the reactions were verified by the vibrational analysis. The results show that the ozonolysis of ethylene and its derivatives is reasonable and believable along the Criegee mechanism. The results also show that the activation energies of the controlling steps along the fluoroethylene and chloroethylene with ozone reaction pathways were lower than that along the ethylene with ozone reaction pathway. That is to say, the derivatives of ethylene have the higher activity to react with ozone and deplete the ozone layer. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Weakest bound electron potential model theory
Authors: Zheng Neng‐Wu , Wang Tao , Ma Dong‐Xia , Zhou Tao , Fan Jing 
Published: March 2004

AbstractDiffering from the self‐consistent field (SCF) method, in which an N‐electron atom problem is treated as a one‐electron problem with the use of a basic assumption of average potential, we develop a unified weakest bound electron potential model (WBEPM) theory. The relativistic form of the theory is given for the first time and is combined with the nonrelativistic form introduced in previous work to arrive at the unified WBEPM theory. The theory has two main ideas. First, from consideration of viewpoints of the dynamic successive ionization and the choice of zero of energy in quantum mechanics, an N‐electron atom system can be subdivided into N subsystems only containing a weakest bound electron (WBE) in each of subsystems. For each subsystem by separation of WBE and non‐weakest bound electrons (NWBE), WBE is believed to move in an approximate potential field provided by a “core” consisting of NWBEs and the nucleus. Thus, a complicated N‐electron problem is reduced to a simple analytical one‐electron problem of WBE. Second, the properties of an atom, such as total wave function, total energy, atomic energy levels, and transition between energy levels, can be investigated through the behaviors of a WBE or several WBEs, or up to all WBEs. Several excellent illustrative results show that the theory is capable of attaining very good computational accuracy. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Spin‐coupled study of addition reactions of singlet dihalocarbenes with ethene
Authors: Blavins Joshua J. , Cooper David L. , Karadakov Peter B. 
Published: March 2004

AbstractModern valence bond theory, in its spin‐coupled form, is used to examine the electronic rearrangements that take place during the gas‐phase additions of singlet CF2 and of singlet CCl2 to ethene. Both reactions are found to follow homolytic pathways, during which the ethene π‐bond breaks and the orbitals that were originally involved in this bond interact with the singlet orbital pair on the carbene. The formation of the two new σ bonds that close the cyclopropane ring proceeds in a markedly asynchronous manner, so that the systems attain considerable diradical character, as quantified by the composition of the active‐space spin‐coupling pattern. The rearrangement of the electron spins from a reactant‐like form to one better suited to the product takes place much later in the case of the reaction between CCl2 and ethene than in the corresponding reaction of CF2. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Symbolic calculation in chemistry: Selected examples
Authors: Barnett Michael P. , Capitani Joseph F. , von zur Gathen Joachim , Gerhard Jürgen 
Published: March 2004

AbstractA selective classified bibliography of symbolic computation in some areas of chemistry is provided together with some examples of computer algebra algorithms and techniques to facilitate future joint work of chemists and computer scientists. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Dynamic headspace: a single‐step extraction for isotopic analysis of μg/L concentrations of dissolved chlorinated ethenes
Authors: Morrill Penny L. , Lacrampe‐Couloume Georges , Lollar Barbara Sherwood 
Published: March 2004

AbstractIn this study a dynamic headspace method was developed to measure the carbon isotope values of dissolved chlorinated ethenes at μg/L concentrations. A gas chromatograph/combustion/isotope ratio mass spectrometer (GC/C/IRMS) was modified to include a headspace extraction system followed by a cryogenic trap. Extracting headspace from a 160 mL vial with 80 mL of aqueous solution and 40 g of NaCl for 8–12 min resulted in accurate and reproducible δ13C values for trichloroethene (TCE) and cis‐1,2‐dichloroethene (cDCE) at concentrations of 50–75 μg/L. Based on these results a conservative lower limit of quantitation of 38 μg/L can be calculated for these compounds. For more volatile compounds such as tetrachloroethene (PCE) and vinyl chloride (VC), field data analyzed using this method indicate a lower limit of quantitation in the tens of μg /L range. Copyright © 2004 John Wiley & Sons, Ltd.
Characterization of a model Phillips catalyst by mass spectrometry
Authors: Di Croce Pascal Gabriel , Aubriet Frédéric , Chéty‐Gimondo Rachel , Muller Jean‐François , Grange Paul 
Published: March 2004

AbstractA model Phillips catalyst for ethylene polymerization, prepared by spin coating a Cr(III)(Cr(acac)3) precursor on a silicon wafer, was submitted to an oxidative activation. Laser ablation Fourier transform mass spectrometry provided direct information on molecular species at the silicon wafer surface during activation. At 350°C the chromium precursor was degraded, while chromium oxide species were formed. The chromium concentration decreased with temperature. The activated model catalyst was active for ethylene polymerization. Using complementary techniques (Fourier transform infrared spectroscopy, laser desorption/ionization mass spectrometry), the polymer was identified as crystalline polyethylene. After 1 h of polymerization at 160°C, dome‐like structures were observed by atomic force microscopy. Their morphologies were constituted of regions of parallel aligned lamellae of polymer. Copyright © 2004 John Wiley & Sons, Ltd.
Linking protein fractionation with multidimensional monolithic reversed‐phase peptide chromatography/mass spectrometry enhances protein identification from complex mixtures even in the presence of abundant proteins
Authors: Wienkoop Stefanie , Glinski Mirko , Tanaka Nobuo , Tolstikov Vladimir , Fiehn Oliver , Weckwerth Wolfram 
Published: March 2004

AbstractRecently, multidimensional shotgun proteomics has proven to be an alternative technology able to identify hundreds of proteins from single samples. Two major limitations of the technology are the presence of high abundance proteins (e.g. RUBISCO in plant leaf tissue) and the enormous number of co‐eluting peptides that overstrain the loading and resolving capacity of conventional particle‐packed columns as well as the capacity of electrospray ionisation due to ion suppression. Here, the coupling of fast performance liquid chromatography (FPLC) pre‐fractionation of an Arabidopsis leaf protein extract and subsequent two‐dimensional liquid chromatography/mass spectrometry with improved resolution using a monolithic silica C18 capillary column allowed the identification of 1032 unique proteins in a single 4 mg total protein plant leaf tissue sample. The reassignment of peptide IDs to distinct FPLC protein fractions enhances the identification procedure, especially in the case of present protein isoforms. The proposed strategy is useful to detect proteins otherwise not seen in conventional multidimensional chromatography/mass spectrometry approaches. Copyright © 2004 John Wiley & Sons, Ltd.
Specific recognition of DNA bulge structure by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry
Authors: Chen Yu‐Ju , Chen Po‐Jui , Wang Hsueh‐Ting , Cheng Chien‐Chung 
Published: March 2004

AbstractThis study reports a novel approach utilizing an octahedral CoII(HAPP)(TFA)2 reagent in the presence of H2O2 with analysis by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) to serve as an efficient probe for bulged DNA structures. Elucidation of DNA bulge‐specific recognition pathways and cleavage mechanisms is demonstrated by characterization of bulge‐specific cleavage products and other backbone lesion fragments. The cleavage specificity of CoII(HAPP)(TFA)2/H2O2 arises from sugar oxidative strand scission, for which the position of the abstracted hydrogen is unambiguously determined as the 4′‐H of the deoxyribose moiety. Furthermore, differentiation between bulge‐specific recognition and diffusion‐controlled non‐selective cleavage can be clarified through time‐dependent MALDI‐TOFMS studies. The present results demonstrate that MALDI‐TOFMS can be a sensitive and efficient technique for complex mechanistic studies of this kind, providing information for future rational drug design targeting bulged DNA structures. Copyright © 2004 John Wiley & Sons, Ltd.
Structural characterization of novel chemotactic and mastoparan peptides from the venom of the social wasp Agelaiapallipes pallipes by high‐performance liquid chromatography/electrospray ionization tandem mass spectrometry
Authors: Mendes Maria Anita , Monson de Souza Bibiana , Delazari dos Santos Lucilene , Palma Mario Sergio 
Published: March 2004

AbstractHigh‐performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESI‐MS) and high‐performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC‐ESI‐MS/MS) techniques were applied for the detection, purification, monitoring, and sequencing of two novel and biologically active peptides occurring at very low levels in the venom of the wasp Agelaia pallipes pallipes. These peptides were sequenced under LC/ESI‐MS/MS conditions and designated as Agelaia‐CP (I/L‐L‐G‐T‐I‐L‐G‐L‐L‐K‐G‐I/L‐NH2, MW 1207.8 Da) and Agelaia‐MP (I/L‐N‐W‐L‐K‐L‐G‐K‐A‐I‐I‐D‐A‐I/L‐NH2, MW 1565.0 Da). The peptide Agelaia‐CP showed no hemolytic activity, but it behaved as a mast cell degranulator and induced a potent chemotaxis in polymorphonucleated leukocyte (PMNL) cells, typical of a wasp chemotactic peptide. The peptide Agelaia‐MP showed both powerful mast cell degranulation and hemolysis of washed rat red blood cells, and is thus assigned as a new member of the mastoparan family of peptides. Both peptides seem to be directly involved in the strong inflammatory reactions associated with wasp stings. Copyright © 2004 John Wiley & Sons, Ltd.
Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry and nuclear magnetic resonance analyses of end‐functionalized saccharidic polymers: an example of a useful analytical technique combination
Authors: D'Agosto F. , Charreyre M. T. , Pichot C. , Dessalces G. , Delolme F. 
Published: March 2004

AbstractThe living cationic polymerization of a saccharidic monomer (1,2:3,4‐di‐O‐isopropylidene‐6‐O‐(2‐vinyloxyethyl)‐D‐galactopyranose, GVE) gives rise to aldehyde end‐capped polymers (PGVECHO) of low molar masses (<10 000 Da) and low molar mass distribution (<1.2). These polymers were derivatized by selective introduction of either hexamethylenediamine (PGVE‐NH2) or 9‐fluorenylmethyl carbazate (PGVE‐Fmoc) end groups. The resulting polymers were fully characterized by complementary use of nuclear magnetic resonance (1H NMR) and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS). The expected structure according to the polymerization mechanism, the occurrence of side reactions and the success of the post‐functionalization reactions were confirmed. Copyright © 2004 John Wiley & Sons, Ltd.
The formation of complexes by tetraethylresorcarene with planar guest ions studied by electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry
Authors: Mäkinen Marko , Vainiotalo Pirjo 
Published: March 2004

AbstractResorcarenes have become a popular subject of study in the field of supramolecular chemistry. In this work the formation of host–guest complexes between a synthetic macrocyclic host, tetraethylresorcarene, and various eligible planar guests, was studied by mass spectrometric methods. The size and nature of the guest ion strongly influenced the complex formation. Collision‐induced dissociation experiments revealed the fragmentation patterns of the resorcarene skeleton and the differences in fragmentation induced by the guest ions. Copyright © 2004 John Wiley & Sons, Ltd.
Collision‐activated cleavage of a peptide/antibiotic disulfide linkage: possible evidence for intramolecular disulfide bond rearrangement upon collisional activation
Authors: Fagerquist Clifton K. 
Published: March 2004

AbstractCeftiofur is an important veterinary β‐lactam antibiotic whose bioactive metabolite, desfuroylceftiofur, has a free thiol group. Desfuroylceftiofur (DFC) was reacted with two peptides, [Arg8]‐vasopressin and reduced glutathione, both of which have cysteine residues to form disulfide‐linked peptide/antibiotic complexes. The products of the reaction, [vasopressin + (DFC‐H) + (DFC‐H) + H]+, [(vasopressin+H) + (DFC‐H) + H]+ and [(glutathione‐H) + (DFC‐H) + H]+, were analyzed using collision‐activated dissociation (CAD) with a quadrupole ion trap tandem mass spectrometer. MS/MS of [vasopressin + (DFC‐H) + (DFC‐H) + H]+ resulted in facile dissociative loss of one and two covalently bound DFC moieties. Loss of one DFC resulted from either homolytic or heterolytic dissociation of the peptide/antibiotic disulfide bond with equal or unequal partitioning of the two sulfur atoms between the fragment ion and neutral loss. Hydrogen migration preceded heterolytic dissociation. Loss of two DFC moieties from [vasopressin + (DFC‐H) + (DFC‐H) + H]+ appears to result from collision‐activated intramolecular disulfide bond rearrangement (IDBR) to produce cyclic [vasopressin + H]+ (at m/z 1084) as well as other cyclic fragment ions at m/z 1084 ± 32 and +64. The cyclic structure of these ions could only be inferred as MS/MS may result in rearrangement to non‐cyclic structures prior to dissociative loss. IDBR was also detected from MS3 experiments of [vasopressin + (DFC‐H) + (DFC‐H) + H]+ fragment ions. MS/MS of [(glutathione‐H) + (DFC‐H) + H]+ resulted in cleavage of the peptide backbone with retention of the DFC moiety as well as heterolytic cleavage of the peptide/antibiotic disulfide bond to produce the fragment ion: [(DFC‐2H) + H]+. These results demonstrate the facile dissociative loss by CAD of DFC moieties covalently attached to peptides through disulfide bonds. Published in 2004 by John Wiley & Sons, Ltd.