bluuebunny/crossref_metadata_2025 huggingface dataset:
Transferrin receptor recycling in the absence of perinuclear recycling endosomes
Authors: Sheff David , Pelletier Laurence , O'Connell Christopher B. , Warren Graham , Mellman Ira
Published: July 2002

In mammalian cells, internalized receptors such as transferrin (Tfn) receptor are presumed to pass sequentially through early endosomes (EEs) and perinuclear recycling endosomes (REs) before returning to the plasma membrane. Whether passage through RE is obligatory, however, remains unclear. Kinetic analysis of endocytosis in CHO cells suggested that the majority of internalized Tfn bypassed REs returning to the surface from EEs. To determine directly if REs are dispensable for recycling, we studied Tfn recycling in cytoplasts microsurgically created to contain peripheral EEs but to exclude perinuclear REs. The cytoplasts actively internalized and recycled Tfn. Surprisingly, they also exhibited spatially and temporally distinct endosome populations. The first appeared to correspond to EEs, labeling initially with Tfn, being positive for early endosomal antigen 1 (EEA-1) and containing only small amounts of Rab11, an RE marker. The second was EEA-1 negative and with time recruited Rab11, suggesting that cytoplasts assembled functional REs. These results suggest that although perinuclear REs are not essential components of the Tfn recycling pathway, they are dynamic structures which preexist in the peripheral cytoplasm or can be regenerated from EE- and cytosol-derived components such as Rab11.
Signal Transducer and Activator of Transcription-3 (STAT3) Is Constitutively Activated in Normal, Self-renewing B-1 Cells but Only Inducibly Expressed in Conventional B Lymphocytes
Authors: Karras James G. , Wang Zihua , Huo Li , Howard Robert G. , Frank David A. , Rothstein Thomas L.
Published: July 2002

Cytokine and growth factor receptor engagement leads to the rapid phosphorylation and activation of latent, cytosolic signal transducers and activators of transcription (STAT) proteins, which then translocate to the nucleus where they regulate transcriptional events from specific promoter sequences. STAT3 expression in particular has been associated with Abl, Src, and HTLV-1 transformation of normal cells. B-1 lymphocytes are self-renewing, CD5+ B cells that display a propensity for malignant transformation and are the normal counterpart to human chronic lymphocytic leukemias. Further, B-1 cells are characterized by aberrant intracellular signaling, including hyperresponsiveness to phorbol ester PKC agonists. Here we demonstrate that B-1 lymphocytes constitutively express nuclear activated STAT3, which is not expressed by unmanipulated conventional (B-2) lymphocytes. In contrast, STAT3 activation is induced in B-2 cells after antigen receptor engagement in a delayed fashion (after 3 h). Induction of STAT3 is inhibited by both the serine/threonine protein kinase inhibitor H-7 and the immunosuppressive drug rapamycin and requires de novo protein synthesis, demonstrating novel coupling between sIg and STAT proteins that differs from the classical paradigm for STAT induction by cytokine receptors. The inability of prolonged stimulation of conventional B-2 cells with anti-Ig, a treatment sufficient to induce CD5 expression, to result in sustained STAT3 activation suggests that STAT3 is a specific nuclear marker for B-1 cells. Thus, STAT3 may play a role in B cell antigen-specific signaling responses, and its constitutive activation is associated with a normal cell population exhibiting intrinsic proliferative behavior.
A Skin Homing Molecule Defines the Langerhans Cell Progenitor in Human Peripheral Blood
Authors: Strunk Dirk , Egger Claudia , Leitner Gerda , Hanau Daniel , Stingl Georg
Published: July 2002

We have recently described a system for the generation of dendritic cells (DC) and Langerhans cells (LC) from defined CD34+ precursors purified from peripheral blood of healthy adult volunteers (1). This study has now been extended by the characterization of two distinct subpopulations of CD34+ cells in normal human peripheral blood as defined by the expression of the skin homing receptor cutaneous lymphocyte-associated antigen (CLA). CD34+/CLA+ cells from normal peripheral blood were found to be CD71LOW/CD11a+/CD11b+/CD49d+/ CD45RA+ whereas CD34+/CLA− cells displayed the CD71+/CD11aLOW/CD11bLOW/CD49d(+)/ CD45RALOW phenotype. To determine the differentiation pathways of these two cell populations, CD34+ cells were sorted into CLA+ and CLA− fractions, stimulated with GM-CSF and TNF-α in vitro, and then were cultured for 10 to 18 d. Similar to unfractionated CD34+ cells, the progeny of both cell populations contained sizable numbers (12–22%) of dendritically shaped, CD1a+/HLA-DR+++ cells. In addition to differences in their motility, the two dendritic cell populations generated differed from each other by the expression of LC-specific structures. Only the precursors expressing the skin homing receptor were found to differentiate into LC as evidenced by the presence of Birbeck granules. In contrast, CLA− precursor cells generated a CD1a+ DC population devoid of Birbeck granule–containing LC. Provided that comparable mechanisms as found in this study are also operative in vivo, we postulate that the topographic organization of the DC system is already determined, at least in part, at the progenitor level.
A Critical Role for Syk in Signal Transduction and Phagocytosis Mediated by Fcγ Receptors on Macrophages
Authors: Crowley Mary T. , Costello Patrick S. , Fitzer-Attas Cheryl J. , Turner Martin , Meng Fanying , Lowell Clifford , Tybulewicz Victor L. J. , DeFranco Anthony L.
Published: July 2002

Receptors on macrophages for the Fc region of IgG (FcγR) mediate a number of responses important for host immunity. Signaling events necessary for these responses are likely initiated by the activation of Src-family and Syk-family tyrosine kinases after FcγR cross-linking. Macrophages derived from Syk-deficient (Syk−) mice were defective in phagocytosis of particles bound by FcγRs, as well as in many FcγR-induced signaling events, including tyrosine phosphorylation of a number of cellular substrates and activation of MAP kinases. In contrast, Syk− macrophages exhibited normal responses to another potent macrophage stimulus, lipopolysaccharide. Phagocytosis of latex beads and Escherichia coli bacteria was also not affected. Syk− macrophages exhibited formation of polymerized actin structures opposing particles bound to the cells by FcγRs (actin cups), but failed to proceed to internalization. Interestingly, inhibitors of phosphatidylinositol 3-kinase also blocked FcγR-mediated phagocytosis at this stage. Thus, PI 3-kinase may participate in a Syk-dependent signaling pathway critical for FcγR-mediated phagocytosis. Macrophages derived from mice deficient for the three members of the Src-family of kinases expressed in these cells, Hck, Fgr, and Lyn, exhibited poor Syk activation upon FcγR engagement, accompanied by a delay in FcγR-mediated phagocytosis. These observations demonstrate that Syk is critical for FcγR-mediated phagocytosis, as well as for signal transduction in macrophages. Additionally, our findings provide evidence to support a model of sequential tyrosine kinase activation by FcγR's analogous to models of signaling by the B and T cell antigen receptors.
Major Histocompatibility Complex Class II Molecules Can Protect from Diabetes by Positively Selecting T Cells with Additional Specificities
Authors: Lühder Fred , Katz Jonathan , Benoist Christophe , Mathis Diane
Published: July 2002

Insulin-dependent diabetes is heavily influenced by genes encoded within the major histocompatibility complex (MHC), positively by some class II alleles and negatively by others. We have explored the mechanism of MHC class II–mediated protection from diabetes using a mouse model carrying the rearranged T cell receptor (TCR) transgenes from a diabetogenic T cell clone derived from a nonobese diabetic mouse. BDC2.5 TCR transgenics with C57Bl/6 background genes and two doses of the H-2g7 allele exhibited strong insulitis at ∼3 wk of age and most developed diabetes a few weeks later. When one of the H-2g7 alleles was replaced by H-2b, insulitis was still severe and only slightly delayed, but diabetes was markedly inhibited in both its penetrance and time of onset. The protective effect was mediated by the Aβb gene, and did not merely reflect haplozygosity of the Aβg7 gene. The only differences we observed in the T cell compartments of g7/g7 and g7/b mice were a decrease in CD4+ cells displaying the transgene-encoded TCR and an increase in cells expressing endogenously encoded TCR α-chains. When the synthesis of endogenously encoded α-chains was prevented, the g7/b animals were no longer protected from diabetes. g7/b mice did not have a general defect in the production of Ag7-restricted T cells, and antigen-presenting cells from g7/b animals were as effective as those from g7/g7 mice in stimulating Ag7-restricted T cell hybridomas. These results argue against mechanisms of protection involving clonal deletion or anergization of diabetogenic T cells, or one depending on capture of potentially pathogenic Ag7-restricted epitopes by Ab molecules. Rather, they support a mechanism based on MHC class II–mediated positive selection of T cells expressing additional specificities.
Malignant Transformation and Antineoplastic Actions of Nonsteroidal Antiinflammatory Drugs (Nsaids) on Cyclooxygenase-Null Embryo Fibroblasts
Authors: Zhang Xinping , Morham Scott G. , Langenbach Robert , Young Donald A.
Published: July 2002

In this study, we use primary embryonic fibroblasts derived from cyclooxygenase-deficient transgenic embryos to further investigate the role of the two cyclooxygenases, cyclooxygenase 1 (COX-1) and cyclooxygenase 2 (COX-2), in the process of neoplastic transformation. Cells with either, neither, or both of the cyclooxygenases were transformed by Ha-ras and/or SV40. Our results show that when a cyclooxygenase enzyme is present, the transformed cells have marked increases in COX-2 and/or COX-1 expression. Nevertheless, each type of cell, deficient in either or both cyclooxygenases, can be readily transformed at almost equal efficiency. Different nonsteroidal antiinflammatory drugs (NSAIDs) were used to examine their possible antineoplastic effects on the transformed cells, which have various levels of expression of COX-1 or COX-2. Our results show that NSAIDs suppress the colony formation in soft agar in a dosage-dependent manner in the absence of the cyclooxygenase(s). Thymidine incorporation and apoptosis analyses further demonstrate that the NSAIDs are effective in the cyclooxygenase-null cells. Our findings with cyclooxygenase knockout cells confirm recent reports that some of the antiproliferative and antineoplastic effects of NSAIDs are independent of the inhibition of either COX-1 or COX-2. They also show that transformation is independent of the status of cyclooxygenase expression, suggesting that the involvement of the cyclooxygenases in tumorigenesis may occur at later steps.
T Cell Receptor–Induced Calcineurin Activation Regulates T Helper Type 2 Cell Development by Modifying the Interleukin 4 Receptor Signaling Complex
Authors: Yamashita Masakatsu , Katsumata Makoto , Iwashima Makio , Kimura Motoko , Shimizu Chiori , Kamata Tohru , Shin Tahiro , Seki Nobuo , Suzuki Seiichi , Taniguchi Masaru , Nakayama Toshinori
Published: July 2002

The activation of downstream signaling pathways of both T cell receptor (TCR) and interleukin 4 receptor (IL-4R) is essential for T helper type 2 (Th2) cell development, which is central to understanding immune responses against helminthic parasites and in allergic and autoimmune diseases. However, little is known about how these two distinct signaling pathways cooperate with each other to induce Th2 cells. Here, we show that successful Th2 cell development depends on the effectiveness of TCR-induced activation of calcineurin. An inhibitor of calcineurin activation, FK506, inhibited the in vitro anti-TCR–induced Th2 cell generation in a dose-dependent manner. Furthermore, the development of Th2 cells was significantly impaired in naive T cells from dominant-negative calcineurin Aα transgenic mice, whereas that of Th1 cells was less affected. Efficient calcineurin activation in naive T cells upregulated Janus kinase (Jak)3 transcription and the amount of protein. The generation of Th2 cells induced in vitro by anti-TCR stimulation was inhibited significantly by the presence of Jak3 antisense oligonucleotides, suggesting that the Jak3 upregulation is an important event for the Th2 cell development. Interestingly, signal transducer and activator of transcription (STAT)5 became physically and functionally associated with the IL-4R in the anti-TCR–activated developing Th2 cells that received efficient calcineurin activation, and also in established cloned Th2 cells. In either cell population, the inhibition of STAT5 activation resulted in a diminished IL-4–induced proliferation. Moreover, our results suggest that IL-4–induced STAT5 activation is required for the expansion process of developing Th2 cells. Thus, Th2 cell development is controlled by TCR-mediated activation of the Ca2+/calcineurin pathway, at least in part, by modifying the functional structure of the IL-4R signaling complex.
Analysis of Immunoglobulin (Ig) Isotype Diversity and Igm/D Memory in the Response to Phenyl-Oxazolone
Authors: White Harry , Gray David
Published: July 2002

The distribution of immunoglobulin (Ig) isotypes within specific B cell clones in vivo after immunization is not well defined. Using an IgVH/CDR3- and isotype-specific reverse transcription polymerase chain reaction method, we have carried out a survey of the diversification of the isotype in a splenic response to phenyl-oxazolone (phOx) on a chicken serum albumin carrier. The phOx-specific VH (VHOx-1 with specific CDR3 motif) is associated with all of the heavy chains (μ, δ, α, γ, and ε) after simple immunization with antigen in alum. The kinetics of expression of each isotype are distinct and reproducible. Focusing mainly on the expression of secretory Ig transcripts, IgM, IgG1, and IgE are found after priming, whereas IgD and IgA appear after boosting. Secretory IgD transcripts are found reproducibly at moderate levels and may, therefore, contribute significantly to the secreted Ig response in mice. Most crucially, we find enhanced levels of secretory IgM/VHOx-1 transcripts (with ‘phOx-specific’ CDR3) after boosting, strongly indicating the existence of IgM memory cells that give rise to an enhanced specific IgM secretion in the secondary response.
Regulation of Elastinolytic Cysteine Proteinase Activity in Normal and Cathepsin K–Deficient Human Macrophages
Authors: Punturieri Antonello , Filippov Sergey , Allen Edward , Caras Ingrid , Murray Richard , Reddy Vivek , Weiss Stephen J.
Published: July 2002

Human macrophages mediate the dissolution of elastic lamina by mobilizing tissue-destructive cysteine proteinases. While macrophage-mediated elastin degradation has been linked to the expression of cathepsins L and S, these cells also express cathepsin K, a new member of the cysteine proteinase family whose elastinolytic potential exceeds that of all known elastases. To determine the relative role of cathepsin K in elastinolysis, monocytes were differentiated under conditions in which they recapitulated a gene expression profile similar to that observed at sites of tissue damage in vivo. After a 12-d culture period, monocyte-derived macrophages (MDMs) expressed cathepsin K in tandem with cathepsins L and S. Though cysteine proteinases are acidophilic and normally confined to the lysosomal network, MDMs secreted cathepsin K extracellularly in concert with cathepsins L and S. Simultaneously, MDMs increased the expression of vacuolar-type H+-ATPase components, acidified the pericellular milieu, and maintained extracellular cathepsin K in an active form. MDMs from a cathepsin K–deficient individual, however, retained the ability to express, process, and secrete cathepsins L and S, and displayed normal elastin-degrading activity. Thus, matrix-destructive MDMs exteriorize a complex mix of proteolytic cysteine proteinases, but maintain full elastinolytic potential in the absence of cathepsin K by mobilizing cathepsins L and S.
A Regulatory Role for Src Homology 2 Domain–Containing Inositol 5′-Phosphatase (Ship) in Phagocytosis Mediated by Fcγ Receptors and Complement Receptor 3 (αMβ2; Cd11b/Cd18)
Authors: Cox Dianne , Dale Benjamin M. , Kashiwada Masaki , Helgason Cheryl D. , Greenberg Steven
Published: July 2002

The Src homology 2 domain–containing inositol 5′-phosphatase (SHIP) is recruited to immunoreceptor tyrosine-based inhibition motif (ITIM)–containing proteins, thereby suppressing phosphatidylinositol 3-kinase (PI 3-kinase)–dependent pathways. The role of SHIP in phagocytosis, a PI 3-kinase–dependent pathway, is unknown. Overexpression of SHIP in macrophages led to an inhibition of phagocytosis mediated by receptors for the Fc portion of IgG (FcγRs). In contrast, macrophages expressing catalytically inactive SHIP or lacking SHIP expression demonstrated enhanced phagocytosis. To determine whether SHIP regulates phagocytosis mediated by receptors that are not known to recruit ITIMs, we determined the effect of SHIP expression on complement receptor 3 (CR3; CD11b/CD18; αMβ2)–dependent phagocytosis. Macrophages overexpressing SHIP demonstrated impaired CR3-mediated phagocytosis, whereas macrophages expressing catalytically inactive SHIP demonstrated enhanced phagocytosis. CR3-mediated phagocytosis in macrophages derived from SHIP−/− mice was up to 2.5 times as efficient as that observed in macrophages derived from littermate controls. SHIP was localized to FcγR- and CR3-containing phagocytic cups and was recruited to the cytoskeleton upon clustering of CR3. In a transfected COS cell model of activation-independent CR3-mediated phagocytosis, catalytically active but not inactive SHIP also inhibited phagocytosis. We conclude that PI 3-kinase(s) and SHIP regulate multiple forms of phagocytosis and that endogenous SHIP plays a role in modulating β2 integrin outside-in signaling.
Treatment of Allergic Airway Inflammation and Hyperresponsiveness by Antisense-Induced Local Blockade of Gata-3 Expression
Authors: Finotto Susetta , De Sanctis George T. , Lehr Hans A. , Herz Udo , Buerke Michael , Schipp Mechthild , Bartsch Brigitte , Atreya Raja , Schmitt Edgar , Galle Peter R. , Renz Harald , Neurath Markus F.
Published: July 2002

Recent studies in transgenic mice have revealed that expression of a dominant negative form of the transcription factor GATA-3 in T cells can prevent T helper cell type 2 (Th2)-mediated allergic airway inflammation in mice. However, it remains unclear whether GATA-3 plays a role in the effector phase of allergic airway inflammation and whether antagonizing the expression and/or function of GATA-3 can be used for the therapy of allergic airway inflammation and hyperresponsiveness. Here, we analyzed the effects of locally antagonizing GATA-3 function in a murine model of asthma. We could suppress GATA-3 expression in interleukin (IL)-4–producing T cells in vitro and in vivo by an antisense phosphorothioate oligonucleotide overlapping the translation start site of GATA-3, whereas nonsense control oligonucleotides were virtually inactive. In a murine model of asthma associated with allergic pulmonary inflammation and hyperresponsiveness in ovalbumin (OVA)-sensitized mice, local intranasal administration of fluorescein isothiocyanate–labeled GATA-3 antisense oligonucleotides led to DNA uptake in lung cells associated with a reduction of intracellular GATA-3 expression. Such intrapulmonary blockade of GATA-3 expression caused an abrogation of signs of lung inflammation including infiltration of eosinophils and Th2 cytokine production. Furthermore, treatment with antisense but not nonsense oligonucleotides induced a significant reduction of airway hyperresponsiveness in OVA-sensitized mice to levels comparable to saline-treated control mice, as assessed by both enhanced pause (PenH) responses and pulmonary resistance determined by body plethysmography. These data indicate a critical role for GATA-3 in the effector phase of a murine asthma model and suggest that local delivery of GATA-3 antisense oligonucleotides may be a novel approach for the treatment of airway hyperresponsiveness such as in asthma. This approach has the potential advantage of suppressing the expression of various proinflammatory Th2 cytokines simultaneously rather than suppressing the activity of a single cytokine.
Cytokine-driven Proliferation and Differentiation of Human Naive, Central Memory, and Effector Memory CD4+ T Cells
Authors: Geginat Jens , Sallusto Federica , Lanzavecchia Antonio
Published: July 2002

Memory T lymphocytes proliferate in vivo in the absence of antigen maintaining a pool of central memory T cells (TCM) and effector memory T cells (TEM) with distinct effector function and homing capacity. We compared human CD4+ naive T, TCM, and TEM cells for their capacity to proliferate in response to cytokines, that have been implicated in T cell homeostasis. Interleukin (IL)-7 and IL-15 expanded with very high efficiency TEM, while TCM were less responsive and naive T cells failed to respond. Dendritic cells (DCs) and DC-derived cytokines allowed naive T cells to proliferate selectively in response to IL-4, and potently boosted the response of TCM to IL-7 and IL-15 by increasing the expression of the IL-2/IL-15Rβ and the common γ chain (γc). The extracellular signal regulated kinase and the p38 mitogen-activated protein (MAP) kinases were selectively required for TCR and cytokine-driven proliferation, respectively. Importantly, in cytokine-driven cultures, some of the proliferating TCM differentiated to TEM-like cells acquiring effector function and switching chemokine receptor expression from CCR7 to CCR5. The sustained antigen-independent generation of TEM from a pool of TCM cells provides a plausible mechanism for the maintenance of a polyclonal and functionally diverse repertoire of human CD4+ memory T cells.
Critical Role for Tumor Necrosis Factor–related Apoptosis-inducing Ligand in Immune Surveillance Against Tumor Development
Authors: Takeda Kazuyoshi , Smyth Mark J. , Cretney Erika , Hayakawa Yoshihiro , Kayagaki Nobuhiko , Yagita Hideo , Okumura Ko
Published: July 2002

Natural killer (NK) cells and interferon (IFN)-γ have been implicated in immune surveillance against tumor development. Here we show that tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) plays a critical role in the NK cell–mediated and IFN-γ–dependent tumor surveillance. Administration of neutralizing monoclonal antibody against TRAIL promoted tumor development in mice subcutaneously inoculated with a chemical carcinogen methylcholanthrene (MCA). This protective effect of TRAIL was at least partly mediated by NK cells and totally dependent on IFN-γ. In the absence of TRAIL, NK cells, or IFN-γ, TRAIL-sensitive sarcomas preferentially emerged in MCA-inoculated mice. Moreover, development of spontaneous tumors in p53+/− mice was also promoted by neutralization of TRAIL. These results indicated a substantial role of TRAIL as an effector molecule that eliminates developing tumors.
Responses of Xenopus laevis Water Nose to Water-Soluble and Volatile Odorants
Authors: Iida Akio , Kashiwayanagi Makoto
Published: July 2002

Using the whole-cell mode of the patch-clamp technique, we recorded action potentials, voltage-activated cationic currents, and inward currents in response to water-soluble and volatile odorants from receptor neurons in the lateral diverticulum (water nose) of the olfactory sensory epithelium of Xenopus laevis. The resting membrane potential was −46.5 ± 1.2 mV \documentclass[10pt]{article}\usepackage{amsmath}\usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy}\usepackage{mathrsfs}\usepackage[Euler]{upgreek}\pagestyle{empty}\oddsidemargin -1.0in\begin{document}\begin{equation*}({\mathrm{mean}}\;{\pm}\;{\mathrm{SEM}},\;n\;=\;68)\end{equation*}\end{document}, and a current injection of 1–3 pA induced overshooting action potentials. Under voltage-clamp conditions, a voltage-dependent Na+ inward current, a sustained outward K+ current, and a Ca2+-activated K+ current were identified. Application of an amino acid cocktail induced inward currents in 32 of 238 olfactory neurons in the lateral diverticulum under voltage-clamp conditions. Application of volatile odorant cocktails also induced current responses in 23 of 238 olfactory neurons. These results suggest that the olfactory neurons respond to both water-soluble and volatile odorants. The application of alanine or arginine induced inward currents in a dose-dependent manner. More than 50% of the single olfactory neurons responded to multiple types of amino acids, including acidic, neutral, and basic amino acids applied at 100 μM or 1 mM. These results suggest that olfactory neurons in the lateral diverticulum have receptors for amino acids and volatile odorants.
Energy transfer in organic systems VI. Fluorescence response functions and scintillation pulse shapes
Authors: J B Birks
Published: July 2002

Expressions are derived for the fluorescence response functions of organic solution systems in which non-radiative energy transfer occurs and obeys either Stern-Volmer or Förster kinetics. Scintillation pulse shapes are evaluated for typical crystals, binary and ternary liquid solutions, and binary plastic solutions. The scintillation decay time is inadequate to describe the time characteristics of a solution system, and alternative parameters are introduced. Criteria for a fast solution scintillator are established, and binary liquid and plastic scintillators with improved time characteristics are proposed.
Energy transfer in organic systems VII. Effect of diffusion on fluorescence decay
Authors: J B Birks  , S Georghiou
Published: July 2002

The effect of non-radiative energy transfer and diffusion on the fluorescence decay of phenanthrene in the presence of acridine was observed in six solvents of viscosity η = 0.4 cp to 64.6 cp. The system obeys Stern-Volmer kinetics at low η, Förster kinetics at high η and intermediate kinetics at medium η. At η = 64.6 cp the decay obeys the Förster relation. At lower η it agrees satisfactorily with the relation of Yokota and Tanimoto, but it is less rapid than that predicted by Voltz et al.
A study of resonance structure in helium using metastable excitation by electron impact with high energy resolution
Authors: J N H Brunt  , G C King  , F H Read
Published: July 2002

The cross section for excitation of metastable states of helium by electron impact has been studied as a function of incident energy up to the ionization potential. The energy scale is established by determining accurately the position on the metastable spectra of the 23S and 21S levels, whose energies are precisely known from spectroscopic data. The positions of the numerous resonance structures observed in the cross section are determined and the values obtained compared with the results of previous electron transmission and metastable excitation experiments. The energy of the 22S resonance, observed in an elastic scattering experiment performed simultaneously, is found to be 19.367+or-0.007 eV. A modified Rydberg formula is used to predict energies of the n=3 and 4 resonance states, and the correspondences between the predicted and observed energies are used to suggest classifications for the observed resonances.
Spectroscopic studies of the Stark-broadened wings of Lyman-α
Authors: R C Preston
Published: July 2002

An argon wall-stabilized arc operating at an axial temperature of 13800K and electron density of 2.1*1023m-3has been used to study the Stark-broadened wings of Lyman- alpha at wavelength separations from the line centre hitherto unexamined. Absolute calibration techniques using black-body-limited lines and hydrogen concentration measurements using HB have been applied. Comparison has been made of the experimental profiles with the theories of Kepple and Griem (1968) and Vidal et al. (1973). Satisfactory agreement is obtained with the latter theory, apart from considerable asymmetry which is observed to extend over the whole of the measured profile. Two satellite features have been observed in the red wing at 3.7 and 19 nm from the line centre and these are attributed to an argon-ion quasi-molecular perturbation.
Energy transfer in organic systems. XII. Mixed crystals
Authors: S J Al-Obaidi  , J B Birks  , D J S Birch  , A Hallam  , R E Imhof
Published: July 2002

The fluorescence response functions and quantum yields of four mixed crystal systems (naphthalene and p-terphenyl hosts; anthracene and tetracene guests) have been measured and analysed. The results are consistent with time-dependent exciton transfer, and the Powell-Kepler effect is not observed. It is concluded that the latter requires higher defect concentrations.
Ramsauer-Townsend minima in the electron-scattering cross sections of polyatomic gases: methane, ethane, propane, butane, and neopentane
Authors: D L McCorkle  , L G Christophorou  , D V Maxey  , J G Carter
Published: July 2002

Electron drift velocities, w, as a function of temperature were measured and on the basis of these data, Ramsauer-Townsend (RT) minima were found in the cross section for momentum transfer, sigma m, for all these gases. The position of the RT minimum and the magnitude of the corresponding sigma m at the energy where the minimum occurs are 0.12, 0.14, 0.14, and 0.25 eV and 1.2, 3.0, 4.6, and 5.8*10-16 cm2 for ethane, propane, butane, and neopentane, respectively. The density dependence of the w for neopentane was also investigated. This latter investigation and similar ones in the literature on methane, ethane, and propane are discussed in connection with the observed RT minima and the mobility of thermal electrons in the low- and high-pressure vapours and the liquids of these compounds.
A classical trajectory study of T-V energy transfer of a highly vibrationally excited Morse oscillator in collinear collision with an atom. II. Excitation and dissociation processes
Authors: E O Sire  , G H Kohlmaier  , E Novak
Published: July 2002

For pt.I see ibid., vol.11, no.18, p.3145 (1978). A classical trajectory analysis for T to V excitation and CID processes of highly vibrationally excited Morse diatomics in Cinfinitycollisions with atoms, assuming a pure repulsive exponential interaction, is presented. Phase-averaged energy transfer and CID probabilities have been obtained for a wide range of mass distributions and initial energies. Effects of vibrational inhibition/enhancement and 'double' impacts on CID probabilities are investigated. Some analytical results for the hard-sphere limit are also presented.
The K-shell ionisation of atoms by relativistic protons
Authors: D M Davidovic  , B L Moiseiwitsch  , P H Norrington
Published: July 2002

The K-shell ionisation is investigated using an extension of the first-order time-dependent perturbation-theory treatment of Moller (1932) taking Dirac plane waves for the description of the incident and scattered protons and the Darwin approximation for the relativistic wavefunctions of the K-shell atomic electrons and the ejected electron. The differential cross sections delta2sigma / delta k delta q and d sigma /dk, where k is the wavenumber of the ejected electron and hq is the momentum change of the proton, are calculated. The double differential cross section for collisions in which a change of spin of the atomic electron occurs is less sharply peaked for small q, and has a broader overall distribution with respect to q, than the double differential cross section for collisions without spin change, although being much less in magnitude than the latter for small q. This leads to total K-shell ionisation cross sections sigma with significant contributions coming from collisions with spin change of the atomic electron for large atomic numbers at high energies of impact.
Collisions between metastable O(5S) atoms and rare gases in the velocity range 1-10 x 105 cm s-1
Authors: J Windrich  , H D Wolf  , J Fricke
Published: July 2002

Collisions between metastable O(5S) atoms and rare-gas atoms were studied in the energy range from 0.1 eV to about 10 eV. The use of a beam-attenuation technique yielded total cross sections for O(5S) in Ne, Ar, Kr, and Xe. Sensitised fluorescence was observed near the thresholds for production of excited O(3S), Kr(3P1), Xe(1P1) and Xe(3P1). No sensitised fluorescence was observed in the lighter rare gases, Ne and Ar. Total cross sections for O(5S) attenuation were obtained as functions of velocity by pulsing the metastable source and using appropriate time-of-flight techniques.
Charge transfer to the continuum for 15 to 1500 keV H+in He, Ne, Ar and H2gases under single-collision conditions
Authors: M Rodbro  , F D Andersen
Published: July 2002

Capture of an electron into the continuum of a fast proton is studied by measuring the energy spectra of the emitted electrons at zero emission angle relative to the direction of the incident proton beam. The data include doubly differential cross sections as well as peak yields for 15 to 1500 keV impact energies and targets of He, Ne, Ar and H2under single-collision conditions.
Intermediate energy electron scattering from potassium
Authors: S J Buckman  , C J Noble  , P J O Teubner
Published: July 2002

Differential cross sections for elastic and inelastic electron scattering from potassium are presented in the energy range 54.4 to 217.7 eV and over the angular range from 2 degrees to 145 degrees . The experimental cross sections for elastic scattering are compared with our optical-model calculation which is in excellent agreement with the experiments at 200 eV. At lower energies the agreement becomes progressively worse. Comparison is also made with other intermediate energy theories. The inelastic differential cross sections are compared with previous theoretical calculations where it is found that the theories are inadequate in their description of the differential cross section over the entire angular range. Total cross sections for the resonance transition have been deduced by integrating the differential cross sections. These cross sections are in good agreement with previous measurements.
Zero-point vibration in low-energy electron-molecule scattering theory
Authors: A Klonover  , U Kaldor
Published: July 2002

The effect of taking proper account of zero-point vibration in adiabatic-nuclei calculations of cross sections for low-energy (1-10 eV) e-H2scattering is investigated. Explicit integration over internuclear separation leads to significant changes in integral cross sections over fixed-R results, where the molecule is frozen at its equilibrium separation. Increases ranging up to 5% for elastic scattering and 40% for rotational excitation are observed, with the largest changes occurring at the lower end of the energy range. Angular distributions are also affected. Adiabatic-nuclei cross sections are in good agreement with experiment over the whole energy range.
Off-diagonal potentials in the distorted-wave expansion for electron-atom scattering
Authors: R Vanderpoorten  , K H Winters
Published: July 2002

A formal discussion of the distorted-wave expansion is presented for the case of arbitrary optical distorting potentials. The authors show that the use, without further modifications, of such potentials of order greater than n in a DW expansion limited to order n results in multiple counting. Several local approximations to the second-order off-diagonal potential are examined. These potentials, along with the partial-wave amplitudes to which they give rise, are compared with the results of an exactly equivalent potential treatment for the 1s to 2s excitation of atomic hydrogen at energies of 100 eV and above.
The effect of attachment cooling in oxygen and oxygen-nitrogen mixtures
Authors: R W Crompton  , R Hegerberg  , H R Skullerud
Published: July 2002

Measurements of the attachment rate coefficient nua/N2for thermal electrons in O2and O2-N2mixtures using the Cavalleri electron sampling technique (1969) show an unexpected pressure dependence. This dependence is explained in terms of a perturbation to the expected Maxwellian energy distribution function caused by the selective loss of electrons by attachment at the resonance energy for the process. Theoretical analysis of the problem predicts the general features of the experimental observations but overestimates the effect when commonly accepted values of the cross sections are used.
Rotational analysis of the A1Π → X1Σ+system of germanium monosulphide: GeS
Authors: P Magat  , A C Le Floch  , J Lebreton
Published: July 2002

A rotational analysis of the A1Pi to X1Sigma+system of74Ge32S molecule is performed by a direct fit of 645 lines involving six vibronic levels (2-1, 2-0, 3-0, 4-0, 2-10, 3-11 bands). Constants of the A1Pi state are determined (in cm-1): Te=32888.88(9), Y10( approximately omegae)=373.87(4), Y01( approximately Be)=0.16093(2), -104Y11( approximately 104alphae)=9.84(6), -Y20( approximately xeomegae)=1.314(6), -107Y02( approximately 107De)=1.30(6). New vibrational constants of the X1Sigma+state are also recommended: Y10( approximately omegae)=574.19(2), -Y20( approximately xeomegae)=1.631(3), Y30( approximately yeomegae)=-1.6(2)*10-3.
The binding effect in deuteron- and alpha-induced K-shell ionisation
Authors: J S Lopes  , A P Jesus  , M F da Silva
Published: July 2002

Experimental deuteron- and alpha-induced ionisation cross sections and cross section ratios for elements Ca to Cu (Z=20-29) in the incident energy range 0.2-0.45 MeV u-1are presented. The experimental ratios R= sigmaalpha/4 sigmadare larger than the corresponding theoretical values and do not show the same dependence on incident projectile velocity. It is argued that this discrepancy is mainly due to the way in which the binding effect is accounted for because other effects important in the low incident velocity region approximately cancel out in the cross section ratios. The absolute values of the deuteron-and alpha-induced cross sections are also compared with theory using the procedures recommended by Brandt and Lapicki (1981) to correct for the relativistic, binding Coulomb and energy-loss effects. There is fair agreement for deuterons while the theoretical alpha-induced cross sections decrease too fast with decreasing incident velocity.
Positron lifetime parameters in H2, CO2and CH4
Authors: G L Wright  , M Charlton  , G Clark  , T C Griffith  , G R Heyland
Published: July 2002

Free positron and ortho-positronium lifetimes have been measured, along with the positronium formation fractions, for the three molecular gases H2, CO2and CH4in the intermediate density range. The measurements are compared with other existing data where possible and significant discrepancies between earlier results and those presented have been found. The complex behaviour observed for all three parameters has been discussed in terms of current models where applicable.
Photoelectron polarisation in resonant two-photon ionisation with superstrong continuous excitation
Authors: R Parzynski
Published: July 2002

Non-perturbative completely analytic calculations of the spin polarisation of photoelectrons produced in resonant two-photon ionisation of alkali atoms with exciting and ionising light beams are presented. A well justified alkali atom model composed of four discrete states and the continuum is applied. Contrary to simpler models it enabled one to obtain results valid when the effective resonance Rabi frequency exceeds the frequency separation between the two components forming a given fine-structure energy doublet at resonance. It is shown that in this limit the photoelectron polarisation depends critically on whether a light or heavy alkali atom is ionised. In the former case the photoelectron polarisation is proved to be a copy of the electronic polarisation of the atom, whereas in the case of heavier alkalis it departs appreciably from that of the ionised atom due entirely to spin-orbit perturbation of radial wavefunctions of P discrete states. It is also shown how the author's present results go over into those previously obtained for weaker exciting fields.
Measurements of complex scattering amplitudes for electron impact excitation of the 31D and 31P states of helium
Authors: H B van Linden van den Heuvell  , E M van Gasteren  , J van Eck  , H G M Heideman
Published: July 2002

In a scattered-electron cascaded-photon coincidence experiment the authors have studied the electron impact excitation of the in=3 singlet states of helium for incident electron energies between 28 and 46 eV and for a scattering angle of 35 degrees . This was done by measuring the angular distribution of the 31P to 11S photons (the later resulting from the 31D(31S) to 21P to 11S cascade) in coincidence with the n=3 scattered electrons, both in the scattering plane and in the plane perpendicular to the direction of the incoming electrons. At an incident electron energy of 45.6 eV they found a small 31D contribution to the coincidence peak. The 31P results at this energy are in perfect agreement with previously reported experimental data. At an energy of 34.6 eV this is not the case. At this and lower energies they observe, apart from the dominant 31P contribution, a significant 31D contribution to the coincidence signal. The authors present new experimental data for the orientation and alignment of both excitations at 34.6, 31.5 and 28.5 eV and for the ratios of the cross sections at these energies.
Total cross section measurements for positron and electron scattering on molecular hydrogen between 8 and 400 eV
Authors: A Deuring  , K Floeder  , D Fromme  , W Raith  , A Schwab  , G Sinapius  , P W Zitzewitz  , J Krug
Published: July 2002

An apparatus for the measurement of positron and electron total cross sections on gases is described. The low-energy positrons are produced by moderating high-energy positrons from beta -decay sources. The authors used a11C positron source, produced at a proton accelerator and, alternatively, a22Na source, combined with various moderators. For electron measurements the secondary electrons originating from the moderator are used. The beam transport system consists of electrostatic lenses and a weak magnetic lens located in the middle of the gas cell. The discrimination against forward scattering is characterised by a cut-off angle of about 6 degrees . The authors' e+-H2and e--H2data are compared with the results of recent measurements of similar accuracy performed at University College, London, and Wayne State University (Detroit), and with other e--H2data. The agreement is satisfactory.
Hydrogen atoms in arbitrary magnetic fields. I. Energy levels and wavefunctions
Authors: W Rosner  , G Wunner  , H Herold  , H Ruder
Published: July 2002

The energy values of many low-lying states of the one-electron problem in the presence of a homogeneous magnetic field of arbitrary strength (0<B<or=4.7*108T) are calculated with high numerical accuracy for a sufficiently dense mesh of B. The wavefunctions are expanded either in terms of spherical harmonics (weak and moderate fields) or in terms of Landau states (strong and very strong fields), with r- or z-dependent expansion functions that are determined with the use of an adopted version of the MCHF code of Froese Fischer (1978). At intermediate field strengths up to 24 expansion terms are included. The structural change of the wavefunctions with magnetic field is discussed quantitatively for a few representative states. As an application, the splittings of the components of the Lyman- alpha , beta , and the Balmer- alpha lines of the hydrogen atom are presented (including the effects of the finite proton mass) as continuous functions of the field strength over the whole range of B considered.
Pressure broadening and pressure shift of the 410 nm indium line perturbed by foreign gases
Authors: J Eberz  , G Huber  , T Kuhl  , G Ulm
Published: July 2002

The broadening and shift of the indium line (5p2P12/-6s2S12/, lambda =410.2 nm) caused by the noble gases He, Ne, Ar, Kr, and Xe, and the molecular gases H2and N2have been measured by laser fluorescence with a single-mode dye laser. The measurements were carried out at a temperature of 748K and the foreign-gas pressure was varied from 0 to 450 mbar. The collision broadening and shift parameters have been determined. Both the linewidth and the lineshift are found to increase linearly with perturbing gas density and are interpreted in terms of the impact theory of collision broadening, assuming a van der Waals and Lennard-Jones potential interaction between radiating and perturbing atoms.
A simple variational basis for the study of hydrogen atoms in strong magnetic fields
Authors: D Baye  , M Vincke
Published: July 2002

A variational basis with cylindrical symmetry is shown to provide highly accurate results for the lowest m=0 to -4 levels of a hydrogen atom in a strong magnetic field (B>2.35*105T). The simplicity of the calculation and formulae summarising the behaviour of the variational parameters make the results easy to reproduce.
A quantitative study of the role of molecular impurities in the emission spectroscopy of He I in pulsed discharges
Authors: A Kunde  , N J Wiegart  , H -J Kunze
Published: July 2002

The intensities of He2and H2lines relative to He I line intensities have been measured as functions of the discharge parameters in a pulsed experiment. Numerical calculations show that the plasma behaviour is well understood and all relevant processes are known. An extrapolation of the measured data allows one to define parameter ranges where molecular emission is so weak that spectroscopic techniques involving the evaluation of He I line profiles (e.g. high-frequency Stark effect measurements) may be used without special precautions.
Importance of the kinetic energy expression for the bound electron in the binary collision theory of ionization
Authors: D N Tripathi  , D K Rai
Published: July 2002

Electron impact ionization cross sections of alkali metal atoms have been calculated using Gryzinski (1965), Vriens (1964) and Burgess formulae. Kinetic energy of the bound electron has been estimated by Slater's rule. Comparison with experimental results has been made.
Uncertainty relationship and perturbation theory
Authors: B Tsapline
Published: July 2002

Integral functions and perturbation theory are used for estimating the magnitude of the Heisenberg uncertainty in simple atomic systems.
Measured lifetimes of the two vibrational levels of the b3Σ+state of CO
Authors: A J Smith  , R E Imhof  , F H Read
Published: July 2002

The authors have measured the lifetimes of the first two vibronic levels of the b3Sigma+state of carbon monoxide using the inelastic electron-photon coincidence technique. Their respective values are 53.6+or-0.3 and 69.1+or-2.1 ns. In addition it is found that the lifetime for the v=1 level decreases with increasing pressure, showing a large cross section for collisional transfer of excitation. It is considered that the lifetime of the v=1 level may be affected by the perturbations known to exist in its rotational levels.
Nonempirical calculations on the electronic spectrum of the molecular ion C2
-
Authors: J Barsuhn
Published: July 2002

Ab initio SCF and CI calculations are reported for the molecular ion C2
- using an atomic basis set of contracted Gaussian lobe functions from a work of Whitten and employing a moderate configuration interaction which includes only valence excited configurations. Reasonable agreement is obtained with the spectroscopic constants re and omega e of the upper and the lower state of the Herzberg-Lagerqvist band system (2 Sigma u
+;2 Sigma g
+), while the transition energy T0 is overestimated by approximately 30%. Two hitherto unobserved electronic states are predicted: a low-lying 2 Pi u state (re=1.32 AA, omega e=1700 cm-1, Te=4800 cm-1) and a 4 Sigma u
+ state about 0.6 eV higher than the 2 Sigma u
+ state. The accuracy of the SCF results is tested by comparative calculations of other 13-electron molecules (CN, CO+), which are better known from experiment. The CI results are compared with previous calculations on C2.