bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comprehensive theory of the Fourier transform ion cyclotron resonance signal for all ion trap geometries
Authors: Grosshans Peter B. , Shields Patrick J. , Marshall Alan G. 
Published: July 2002

An analytic solution for the charge induced on each of the detection electrodes of a Fourier transform ion cyclotron resonance (FT/ICR) ion trap has been derived from basic electrostatics for both tetragonal and cylindrical traps of arbitrary aspect ratio, by use of a Green’s function formalism. Dunbar has shown that the result of that calculation is in general equivalent to that obtained from prior ‘‘reciprocity’’-based methods (see text). A primary advantage of the present treatment is its variety of functional forms arising from the various forms of the Green’s function, some of which may converge much more rapidly in numerical evaluation. (Moreover, because the Green’s function is the potential field of a unit point charge, the Green’s function must be employed in any treatment of ion–ion repulsions.)
The present results (a) exactly confirm prior analyses of the cubic and tetragonal traps; (b) provide the first complete analysis of the cylindrical trap; and (c) may be extended to any trap geometry for which the Green’s function is known. In the absence of an available Green’s function, the reciprocity-based treatment, either analytic or numerical, is the method of choice to solve for the induced charge for any ion trap geometry (e.g, unbroken or segmented hyperbolic). For circular orbits centered on the longitudinal axis of the trap, the presence of spectral components at odd multiples of the fundamental ICR orbital frequency is explained and a closed form solution for the relative magnitudes of these components is presented for tetragonal and cylindrical traps. The ratio of the spectral peak height at the third harmonic to that at the first (i.e., the ratio of the third to first Fourier coefficients) is a strong monotonic function of orbital radius; thus, measurement of that ratio provides a simple and direct means for determining the cyclotron orbital radius and hence its orbital translational energy.
The presence and location of magnetron and trapping sidebands of the fundamental peak are also predicted. In addition, we show that a cylindrical trap whose ring electrode is divided into equal quadrants is only slightly more sensitive than a tetragonal trap of the same aspect ratio. Finally, we develop a general circuit model which relates the charge induced on one or more detection electrodes to the detected voltage (i.e., the unamplified signal). Since the effect of trapped-ion motion on each detection electrode is modeled as a charge (or current) source relative to ground, the net signal from any given electrode arrangement and interconnection scheme can be accommodated simply by adding, subtracting, or grounding the signal from each detection electrode, e.g., single-electrode detection, Comisarow’s differential detection between two electrodes, or any of various multiple-electrode configurations. From the measured ICR signal and ICR orbital radius, the number of coherently orbiting ions may be determined.
Empirical and semiempirical interaction potentials for rare gas–rare gas and rare gas–halide systems
Authors: Mansky E. J. , Flannery M. R. 
Published: July 2002

The Tang–Toennies (TT) semiempirical model potentials for ion–atom systems is applied to the rare gas–halide negative ion exciplexes. The coefficients defining the repulsive Born–Mayer term in the TT semiempirical potentials are determined from the equilibrium bond length Re and dissociation energy De taken from ab initio calculations and from transport studies of these molecular ions. The damped dispersion and induction energy terms in the TT potentials are obtained from coupled Hartree–Fock calculations for the neutral rare gas atoms and F− and Cl− ions. The multipole polarizabilities for the heavier halogen atomic negative ions are estimated from a knowledge of polarizability ratios across isoelectronic sequences. The resultant semiempirical ionic potentials are compared to available ab initio calculations and the results of inversion of transport theory. To facilitate the comparison of the (sparse) ab initio data with the semiempirical potentials, a simple fitting procedure is presented for determining empirical potentials for diatomic molecules from a set of three constraint equations. The fitting procedure is applied to a total of 22 rare gas excimers and rare gas–halide exciplexes (both neutral and ionic) of interest to a variety of applications in gaseous discharges and excimer lasers. A three-term representation of the empirical potentials generated is accomplished with the use of a minimal data set which include the ‘‘geometric’’ parameters {R0,Re,De} and the additional parameters {αd, I.P., E.A.} needed for the dispersion and induction energy terms.A novel feature of the empirical procedure is the formulation of the constraint equations at two nuclear displacements (one constraint at R0, wherein the potential passes through zero, and two constraints at Re the equilibrium separation) which yields an accurate fit to available ab initio data and greatly extends the range of internuclear separations R for which an accurate piecewise analytical empirical potential can be generated. To test the relative importance of the different terms in the fitted three-term empirical representations, the classical orbiting cross section Qorbit(E) is computed using the full empirical potential and compared against the standard Langevin orbiting cross section Qpol(E) for a pure polarization interaction.
Ab initiocomputation of semiempirical π-electron methods. I. Constrained, transferable valence spaces in ℋν calculations
Authors: Martin Charles H. , Freed Karl F. 
Published: July 2002

Large basis set ℋν calculations are performed for ethylene, cyclobutadiene, and trans-butadiene in order to examine the accuracy of approximate ℋν calculations specifically designed to reproduce a Pariser–Parr–Pople-like (PPP) semiempirical model from first principles. This is the first ℋν study in which systematic, semiempirical-like approximations to ℋν are examined for their accuracy and basis set dependence in computations of vertical excitation energies and ionization and potentials for large, polyatomic molecules. We focus explicitly on two fundamental semiempirical-like approximations to ab initio ℋν calculations. First, it is shown that ab initio ℋν calculations can produce reasonably accurate vertical excitation energies and ionization potentials for the low-lying valencelike states when using valence orbitals ‘‘constrained’’ to be linear combinations of transferable, carbon atom pπ orbitals. The differences between full ab initio ℋν and constrained ℋν calculations for all states (with one exception each in trans- and cyclobutadiene) range between roughly 0.00 and 0.25 eV for all states and, furthermore, these constrained errors show no basis set dependence. Second, it is shown that the excitation energies and ionization potentials are not influenced significantly by the nonclassical ℋν three- and four-body operators. When neglecting these interactions, errors of only a few tenths of an electron volt are again encountered, and these errors also display no basis set dependence.These conclusions are shown to be consistent with previous ab initio ℋν calculations. Because the three- and four-body ℋν terms are neglected as a leading approximation, the computed oneand two-body empirical parameters which appear in the PPP-like model. The present calculations explain the errors expected to occur in further, approximate ℋν calculations, the states which can be reasonably described with both approximate ℋν calculations and PPP-like models, and the ab initio basis set requirements for future ab initio ℋν studies of these models.
Random walk models for particle displacements in inhomogeneous unsteady turbulent flows
Authors: van Dop H. , Nieuwstadt F. T. M. , Hunt J. C. R. 
Published: July 2002

First a small time analysis is developed for the first and second moments of the velocity (W) and displacement (Z) in one direction of particles marked at a given point in an inhomogeneous unsteady turbulent flow, in terms of the local energy dissipation rate, and the local derivatives of the second and third moments of the vertical component of the velocity field, ∂∼(u23)/∂z and ∼(∂u33)/∂z. Then the appropriate form of a Langevin equation in inhomogeneous turbulence is suggested, namely, dW=(−W/TL+a1)dt+a1/22 dωt where a1, a2, and TL are functions of the particle position and time, and dωt is a random Gaussian velocity increment with ∼(dωt)=0 and ∼((dωt))2=dt. For simplicity, only one component of the particle motion, W(t), is considered. The functions a1 and a2 are determined by relating the random walk model to the Eulerian conservation equations for the mass of the contaminant and volume of the flow (i.e., the continuity equation), using the Fokker–Planck equation and the Eulerian equations for the moments of a vertical velocity. The coefficients a1 and a2 reduce to the same form as that obtained by the statistical analysis, namely a1=∂∼(u23)/∂z, (≊dW̄/dt, when t → 0) and a2=2∼(u23)/TL +d∼(u23)/dt (≊2∼(W′2)/TL+d∼(W′2)/dt, when t → 0).
It is shown that the random walk model has the correct behavior as t/TL → 0. The theory is shown to agree reasonably well with the measurements of mean height and mean vertical displacement of particles released in a convective boundary layer [Q. J. R. Meteorol. Soc. 102, 427 (1976)]. Yaglom’s [Isv. Atmos. Oceanic Phys. 8, 333 (1972)] surface similarity result is recovered as a special case. For t ≫ TL, and in a zero-skewness steady turbulence, the random walk model reduces to the familiar K-diffusion equation. Some examples are presented to show that mean and mean square particle displacements from the random walk model are virtually identical to those obtained from the analytical solution of the corresponding Eulerian moment equations. Careful analysis is still required when concentration distributions in turbulent flows near a boundary are evaluated using random walk models.
Heroin‐related deaths in South Western Sydney, Australia, 1992–96
Authors: DARKE SHANE , ROSS JOANNE 
Published: July 2002

AbstractThe coronial files of all 176 heroin‐related fatalities that occurred in the South Western Sydney region over the period 1992–96 were inspected. Heroin‐related fatalities rose from 20 in 1992 to 54 in 1996. The mean age of cases was 29.9 years, 89% were male and 92% were classified as dependent on heroin at the time of death. There was a significant increase over the study period in the proportion of fatalities that occurred in public settings. No intervention occurred in 71% of cases. Morphine concentrations rose over the study period from 0.16mg/l in 1992 to 0.37mg/l in 1996. The majority of cases involved heroin in combination with other drugs: alcohol (40%), benzodiazepines (30%) and antidepressants (9%). In only a third of cases was morphine the sole drug detected.
Diamorphine treatment for opiate dependence: putative markers of concomitant heroin misuse
Authors: Mclachlan‐Troup Neil , Taylor Graham W. , Trathen Bruce C. 
Published: July 2002

AbstractThe supply of substitute opioid medication as a treatment for heroin dependence is now common practice. There is growing international interest in the prescription of injectable diamorphine for subgroups of patients who are unable to stop injecting opiate drugs; in the United Kingdom it is estimated that there are currently 300 patients prescribed diamorphine for this purpose. The detection of illicit heroin misuse (through urinary diamorphine metabolites) is confounded in subjects prescribed diamorphine. We investigated the potential to distinguish between the use of street heroin and pharmaceutical diamorphine through the detection in urine of various opiate alkaloids originating in the opium poppy, Papaver somniferum. Over a 7‐week period, 532 clients of an urban substance misuse service provided a total of 1122 urine samples for clinical purposes. Using a novel mixed‐mode solid‐phase extraction and gas chromatography/mass spectrometry technique, we screened samples for morphine, 6‐monoacetylmorphine, codeine, meconine, papaverine, noscapine, thebaine and their metabolites. All urine samples from diamorphine‐treated patients were positive for morphine. Of samples from patients receiving other treatments, 30% (95%CI: 27–33%) were positive for morphine, indicating probable street heroin misuse. Of morphine‐positive samples, 61% (95%CI: 55–67%), from the “other treatments” group were positive for at least one of codeine, meconine and putative noscapine or papaverine metabolites. This was reduced to 56% (95%CI: 50–62%) when excluding codeine. Only one sample (0.1%) was positive for any one of these putative markers in the absence of morphine, when excluding codeine. These findings show that the detection of urinary noscapine and papaverine metabolites is useful in distinguishing between use of pharmaceutical diamorphine and street heroin. This may be of benefit to promote safer and more effective prescribing of diamorphine in opiate dependency, and as an outcome measure in trials of diamorphine prescribing.
Association between catechol‐O‐methyltransferase (COMT) polymorphism and severe alcoholic withdrawal symptoms in male Japanese alcoholics
Authors: Nakamura Ataru , Inada Toshiya , Kitao Yoshie , Katayama Yoshirou 
Published: July 2002

AbstractCatechol‐O‐methyltransferase (COMT) plays a crucial role in central dopaminergic systems. The allelic association of a functional polymorphism of the COMT gene with the onset, course and clinical characteristics of alcoholism in 91 male Japanese alcoholics and 114 male Japanese controls was examined. There were no statistically significant differences in the frequency of the allele between the alcoholics and the controls. Visual disturbances and auditory disturbances among alcoholic withdrawal symptoms were, however, significantly different among the three groups (p < 0.05). The present results suggest that COMT activity could partially effect the phenotype of alcoholism, especially the appearance of delirium tremens, in these subjects.
Desmoplastic Small Round Cell Tumour of Childhood: A Report of Four Cases Demonstrating Wider Clinical Features and Variable Outcome
Authors: Ray Ruma , Traunecker Heidi C. L. , Raafat Faro , Stevens Michael C. G. 
Published: July 2002

Purpose. Four further cases of desmoplastic small round cell tumour with multi
phenotypic differentiation are described.Subjects. Two patients were typical (male, adolescent with peritoneal tumour and, in one case, liver metastases) and
did not respond well to treatment. Two other patients showed less usual features (young, female with retroperitoneal
disease, both with intraspinal extension and renal tract obstruction). Both responded favourably to multi‐modal treatment
regimens including extensive and invasive supportive care.Results. Histologically, all tumours showed clear features of this diagnosis, namely angulated nests of small cells in a
background of fibrovascular stroma. Immunohistochemistry typically showed divergent differentiation with neural, muscle
and epithelial marker positivity. All four tumours stained positive for the Wilms′ tumour 1 suppressor gene product.
Electron microscopy showed intercellular tight junctions, cytoplasmatic intermediate filaments and absence of microvilli.
Rare neurosecretory‐type granules were observed.Discussion. These cases illustrate a broader spectrum of clinical presentation than previously
associated with this diagnosis.
LIV‐1 Breast Cancer Protein Belongs to New Family of Histidine‐Rich Membrane Proteins with Potential to Control Intracellular Zn2+ Homeostasis
Authors: Taylor K. M. 
Published: July 2002

AbstractInvestigation of the protein product of the oestrogen‐regulated gene LIV‐1, implicated in metastatic breast cancer, has revealed 10 protein sequences of unknown function that belong to a new family with potential to control intracellular Zn2+ homeostasis. Sequence alignment highlights the similarity in transmembrane domains and extramembrane charged residues, indicating potential ion‐transport ability. This family has a novel highly conserved motif of 66 residues, including a transmembrane domain and a catalytic zinc‐binding sequence of zinc metalloproteases, containing conserved (indicated in bold type) proline and glutamine residues, HEXPHEXGD. These proteins contain more plentiful histidine‐rich repeats than zinc transporters, suggesting an ability to bind or transport zinc across membranes. I propose that these 11 proteins form a new family with the potential to control intracellular Zn2+ homeostasis.
Chromatin Remodeling and T Helper Subset Differentiation
Authors: Miyatake Shoichiro , Arai Naoko , Arai Ken‐Ichi 
Published: July 2002

AbstractThe T helper subsets Th1 and Th2 regulate specific types of immune responses by producing distinct sets of cytokines. Differentiation of the T helper subsets from their common precursors, naive CD4+ T cells, is induced by antigen stimulation and controlled by various other conditions. Of these conditions, the contributions of the cytokine environment have been the best characterized. The presence of interleukin‐4 (IL‐4) directs the differentiation towards Th2 cells, whereas IL‐12 induces Th1 differentiation. The Th2 signature cytokine genes encoding IL‐4, IL‐13, and IL‐5 are clustered, and noncoding regions such as the intergenic region of the IL‐4 and IL‐13 genes are highly conserved from mice to humans. Alteration of the chromatin structure of this Th2 cytokine cluster region is detected as nuclease‐accessible regions specific to Th2 cells. Activation of STAT6 promotes Th2 differentiation by inducing Th2‐specific transcription factors, including GATA3. Expression of GATA3 induces Th2 differentiation and enhances the Th2 cell?specific chromatin accessibility, indicating that GATA3 is a key protein that regulates differentiation through chromatin remodeling. T helper subset differentiation provides a good system to study gene expression regulation at the chromatin level.
A Natural Hepatocyte Growth Factor/Scatter Factor Autocrine Loop in Myoblast Cells and the Effect of the ConstitutiveMetKinase Activation on Myogenic Differentiation
Authors: Anastasi Sergio , Giordano Silvia , Sthandier Olga , Gambarotta Giovanna , Maione Rossella , Comoglio Paolo , Amati Paolo 
Published: July 2002

As a rule, hepatocyte growth factor/scatter factor (HGF/SF) is produced by mesenchymal cells, while its receptor, the tyrosine kinase encoded by the met proto-oncogene, is expressed by the neighboring epithelial cells in a canonical paracrine fashion. In the present work we show that both HGF/SF and met are coexpressed by undifferentiated C2 mouse myoblasts. In growing cells, the autocrine loop is active as the receptor exhibits a constitutive phosphorylation on tyrosine that can be abrogated by exogenously added anti-HGF/SF neutralizing antibodies. The transcription of HGF/SF and met genes is downregulated when myoblasts stop proliferating and differentiate. The coexpression of HGF/SF and met genes is not exclusive to C2 cells since it has been assessed also in other myogenic cell lines and in mouse primary satellite cells, suggesting that HGF/SF could play a role in muscle development through an autocrine way.To analyze the biological effects of HGF/SF receptor activation, we stably expressed the constitutively activated receptor catalytic domain (p65tpr-met) in C2 cells. This active kinase determined profound changes in cell shape and inhibited myogenesis at both morphological and biochemical levels. Notably, a complete absence of muscle regulatory markers such as MyoD and myogenin was observed in p65tpr-met highly expressing C2 clones. We also studied the effects of the ectopic expression of human isoforms of met receptor (h-met) and of HGF/SF (h-HGF/SF) in stable transfected C2 cells. Single constitutive expression of h-met or h-HGF/SF does not alter substantially the growth and differentiation properties of the myoblast cells, probably because of a species-specific ligand–receptor interaction. A C2 clone expressing simultaneously both h-met and h-HGF/SF is able to grow in soft agar and shows a decrease in myogenic potential comparable to that promoted by p65tpr-met kinase. These data indicate that a met kinase signal released from differentiation-dependent control provides a negative stimulus for the onset of myogenic differentiation.
Association Between the Rat Homologue of CO-029, a Metastasis-associated Tetraspanin Molecule and Consumption Coagulopathy
Authors: Claas Christoph , Seiter Simone , Claas Andreas , Savelyeva Larissa , Schwab Manfred , Zöller Margot 
Published: July 2002

Recently, we have described a panel of metastasis-associated antigens in the rat, i.e., of molecules expressed on metastasizing, but not on nonmetastasizing tumor lines. One of these molecules, recognized by the monoclonal antibody D6.1 and named accordingly D6.1A, was found to be abundantly expressed predominantly on mesenchyme-derived cells. The DNA of the antigen has been isolated and cloned. Surprisingly, the gene product proved to interfere strongly with coagulation.
The 1.182-kb cDNA codes for a 235–amino acid long molecule with a 74.2% homology in the nucleotide and a 70% homology in the amino acid sequence to CO-029, a human tumor-associated molecule. According to the distribution of hydrophobic and hydrophilic amino acids, D6.1A belongs to the tetraspanin superfamily. Western blotting of D6.1A-positive metastasizing tumor lines revealed that the D6.1A, like many tetraspanin molecules, is linked to further membrane molecules, one of which could be identified as α6β1 integrin. Transfection of a low-metastasizing tumor cell line with D6.1A cDNA resulted in increased metastatic potential and provided a clue as to the functional role of D6.1A. We noted massive bleeding around the metastases and, possibly as a consequence, local infarctions predominantly in the mesenteric region and all signs of a consumption coagulopathy. By application of the D6.1 antibody the coagulopathy was counterregulated, though not prevented.
It has been known for many years that tumor growth and progression is frequently accompanied by thrombotic disorders. Our data suggest that the phenomenon could well be associated with the expression of tetraspanin molecules.