bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly resistive GaN layers formed by ion implantation of Zn along the c axis
Authors: Oishi Toshiyuki , Miura Naruhisa , Suita Muneyoshi , Nanjo Takuma , Abe Yuji , Ozeki Tatsuo , Ishikawa Hiroyasu , Egawa Takashi , Jimbo Takashi
Published: July 2003

Highly resistive layers are formed by the implantation of Zn ion along the c axis of GaN and AlGaN/GaN epitaxial layers. Heavy ions such as Zn have been desirable for the formation of highly resistive layers, because ions effectively transferred their energy to the crystal atoms rather than the electrons in GaN. A sheet resistance Rs as high as 3.8×1011 Ω/sq was obtained on GaN layers after the ion implantation. Rs increased up to 2.2×1013 Ω/sq after the annealing at 500 °C for 300 s in an N2 atmosphere. The thermal activation energy Er for this sample was 0.67 eV. It was found that the experimental data in current–voltage characteristics were fitted to the equation included the Poole–Frenkel current and resistive (ohmic) current. The difference of Rs between the as-implanted and 500 °C annealed samples was due to the Poole–Frenkel current. The Poole–Frenkel current overcame the resistive one, and dominated the current mechanism in the case of the samples annealed at 200 °C or less. On the other hand, for the samples annealed at 500 °C, the current was only resistive. Both Rs and Er decreased as the annealing temperature increased above 500 °C. Furthermore this implantation method was applied to the device isolation of AlGaN/GaN high electron mobility transistors (HEMTs). The high Rs of 5.9×1011 Ω/sq was observed for AlGaN/GaN structures as well as GaN layers which were not annealed. The HEMTs with a gate length of 1 μm had a high drain current of over 1 A/mm at the gate voltage of 1 V and a pinch off voltage of −7 V without a harmful leakage current.
Thermal stresses in the reflective x-ray optics for the Linac Coherent Light Source
Authors: Ryutov D. D.
Published: July 2003

Reflective optics for an intense x-ray beam generated by the planned Linac Coherent Light Source will have to accommodate very high fluence per pulse, at the repetition rate of 120 Hz. We analyze thermal stresses caused by the heating of a thin surface layer of the optics after every pulse. A conclusion is drawn that keeping this stress below the yield strength imposes stringent limitations on the fluence. Possible experiments for evaluating the number of pulses leading to a substantial degradation of the optics due to the thermal fatigue are briefly discussed.
Hall current effects in dynamic magnetic reconnection solutions
Authors: Craig I. J. D. , Heerikhuisen J. , Watson P. G.
Published: July 2003

The impact of Hall current contributions on flow driven planar magnetic merging solutions is discussed. The Hall current is important if the dimensionless Hall parameter (or normalized ion skin depth) satisfies cH>η, where η is the inverse Lundquist number for the plasma. A dynamic analysis of the problem shows, however, that the Hall current initially manifests itself, not by modifying the planar reconnection field, but by inducing a non-reconnecting perpendicular “separator” component in the magnetic field. Only if the stronger condition cH2>η is satisfied can Hall currents be expected to affect the planar merging. These analytic predictions are then tested by performing a series of numerical experiments in periodic geometry, using the full system of planar magnetohydrodynamic (MHD) equations. The numerical results confirm that the nature of the merging changes dramatically when the Hall coupling satisfies cH2>η. In line with the analytic treatment of sheared reconnection, the coupling provided by the Hall term leads to the emergence of multiple current layers that can enhance the global Ohmic dissipation at the expense of the reconnection rate. However, the details of the dissipation depend critically on the symmetries of the simulation, and when the merging is “head-on” (i.e., comprises fourfold symmetry) the reconnection rate can be enhanced.
Interplay between carrier dynamics and structure of poly(alkylthiophene) and poly(dialkylfluorene) films
Authors: Panozzo S. , Stéphan O. , Vial J.-C.
Published: July 2003

Carrier dynamics properties of poly(alkylthiophene) are investigated via their radiative and nonradiative recombination rates, depending on the length of the alkyl side chain. The recombination rates are determined by luminescence quantum efficiency and photoluminescence decay time measurements in the picosecond range. A large decrease in radiative rate, going along with an increase in nonradiative rate, was observed in the solid state when compared to dilute solution, and was associated with the well known π stacking of the thiophene rings. As already reported from field effect mobility measurements, the study of poly(hexylthiophene) and poly(octylthiophene) in the solid state showed an increase of the carrier transport for polythiophene with the shortest alkyl chain length. We then discuss the differences between poly(dinonylfluorene) and poly(alkylthiophene), both prone to aggregation. In the solid state, the origin of the emission band in the yellow part of the emission spectrum, which appears upon oxidative aging or annealing, is still controversial. Nevertheless, we explain here that this redshift results from fluorenone excimer/aggregate emission. However, the amount of aggregated species is too small to allow good carrier transport.
Multigrid particle-in-cell simulations of plasma microturbulence
Authors: Lewandowski J. L. V.
Published: July 2003

A new scheme to accurately retain kinetic electron effects in particle-in-cell (PIC) simulations for the case of electrostatic drift waves is presented. The splitting scheme, which is based on exact separation between adiabatic and nonadiabatic electron responses, is shown to yield more accurate linear growth rates than the standard δf scheme. The linear and nonlinear elliptic problems that arise in the splitting scheme are solved using a multigrid solver. The multigrid PIC approach offers an attractive path, both from the physics and numerical points of view, to simulate kinetic electron dynamics in global toroidal plasmas.
Nitrogen-vacancy-related defects and Fermi level pinning in n-GaN Schottky diodes
Authors: Lin Yow-Jon , Ker Quantum , Ho Ching-Yao , Chang Hsing-Cheng , Chien Feng-Tso
Published: July 2003

The relationship between the surface states related to nitrogen-vacancy defects and surface Fermi level pinning has been investigated using x-ray photoelectron spectroscopy and capacitance–voltage measurements. Barrier heights of 1.09, 0.50, 1.20, and 0.50 eV, respectively, were obtained for Ni/(NH4)2Sx-treated n-GaN, Ni/etched n-GaN, Au/(NH4)2Sx-treated n-GaN and Au/etched n-GaN Schottky diodes. For Schottky diodes treated with (NH4)2Sx, the observed Schottky barrier height is very close to the Schottky limit, due to the reduction of the surface state density. This also suggests that a large number of surface states related to nitrogen-vacancy defects in the etched n-GaN surface would lead to the pinning of the Fermi level at 0.50 eV below the conduction band edge.
Dense plasma formation on the surface of a ferroelectric induced by a driving pulse with a fast fall time
Authors: Chirko K. , Krasik Ya. E. , Sayapin A. , Felsteiner J. , Bernshtam V.
Published: July 2003

Experimental results are presented of dense plasma formation on the surface of a BaTi-based ferroelectric sample during the fall time of a driving pulse. A negative or positive driving pulse (⩽14 kV), with a slow rise time (∼450 ns) and a fast fall time (40–200 ns), was applied to the rear electrode of the ferroelectric. It was found by different electrical, optical, and spectroscopic diagnostics that this method allows one to form a plasma with a larger density (∼3×1013 cm−3) as compared with that formed by a driving pulse with a fast rise time (⩽4×1012 cm−3). It was shown that the shorter the fall time of the driving pulse the more intense plasma formation occurs. The most uniform and dense plasma formation occurs with a positive driving pulse. In addition, it was found that the shorter the fall time of the positive driving pulse the larger are the current amplitude, the energy, and the divergence of the emitted electrons. The obtained results are discussed in terms of the surface plasma formation and the compensation process of the polarization surface charge of the ferroelectric sample.
Defect characterization of ZnBeSe solid solutions by means of positron annihilation and photoluminescence techniques
Authors: Plazaola F. , Flyktman J. , Saarinen K. , Dobrzynski L. , Firszt F. , Legowski S. , Meczynska H. , Paszkowicz W. , Reniewicz H.
Published: July 2003

Defect characterization of as-grown Zn1−xBexSe compound semiconductors was studied by positron lifetime and photoluminescence measurements. We obtain both experimental and theoretical evidence that the bulk lifetime of free positrons decreases linearly with Be alloying. The average positron lifetime increases with the temperature, indicating that both vacancies and negative ions trap positrons. The decomposition of the lifetime spectra shows that the positron lifetime of the vacancy decreases with an increase in Be content, as predicted by theoretical calculations. The concentration of vacancies and negative ions obtained from positron measurements follows the same trend with Be alloying. A comparison of positron measurements with theoretical calculations and photoluminescence experiments in Zn vapor annealed samples indicates that the vacancy corresponds to a Be vacancy. Besides, the negative ions trapping positrons at low temperatures have been attributed to Be interstitial atoms. The intensity of the B photoluminescence band correlates with the concentration of Be vacancies and Be interstitial atoms. We thus conclude that the electron levels of those defects are involved in the optical transition that leads to the B photoluminescence band.
Measurement of Si, SiF, and SiF2 radicals and SiF4 molecule using very high frequency capacitively coupled plasma employing SiF4
Authors: Ohta Takayuki , Hara Ken-ichiro , Ishida Tetsuro , Hori Masaru , Goto Toshio , Ito Masafumi , Kawakami Satoshi , Ishii Nobuo
Published: July 2003

The behavior of the densities of Si, SiF, and SiF2 radicals and SiF4 molecule were investigated for variations in electron density at pressure of 40 mTorr in a very high frequency (VHF) 60 MHz capacitively coupled plasma employing SiF4 gas. The SiF4 molecule was measured by infrared diode laser absorption spectroscopy, the SiF2 and SiF radicals were measured by laser-induced fluorescence, the Si atom was measured by ultraviolet absorption spectroscopy, and the F atom was measured by actinometric optical emission spectroscopy. The SiF4 density decreased with an increase in electron density, and the dissociation ratio of SiF4 was saturated to about 63% at electron densities of above 8.7×1010 cm−3. The SiF2 density decreased due to electron impact dissociation, whereas the F, Si, and SiF densities increased with an increase in electron density above 1.2×1011 cm−3. The total Si density was estimated to be of the order of 1010–1011 cm−3. Furthermore, the spatial distributions of SiF, SiF2, and SiF4 densities were investigated. They were almost flat inside the plasma region, but the SiF and SiF2 radicals decreased gradually outside the plasma region, and the SiF4 molecule increased. The behavior of the Si, SiF, and SiF2 radicals was in good agreement with the emission intensity of rare gases injected as trace gases. The kinetics of the species in VHF 60 MHz SiF4 plasma was clarified on the basis of the densities of the species and electrons measured. These experimental results are useful in predicting the radical densities of VHF SiF4 plasma using simulation.
Plasmon linac: A laser wake-field accelerator based on a solid-state plasma
Authors: Saito Naoko , Ogata Atsushi
Published: July 2003

A linac is proposed in which a laser first excites plasmons along the inner surface of a metallic acceleration tube. The potential of the plasmon oscillation then accelerates electron beams. This technique features a beam size in the nm range and good conversion efficiency from laser intensity to acceleration gradient; a MW laser will attain a gradient exceeding the GeV/m level, although the current is very small. Acceleration of ions is also discussed.
650-nm AlGaInP multiple-quantum-well lasers grown by metalorganic chemical vapor deposition using tertiarybutylphosphine
Authors: Dong Jian-Rong , Teng Jing-Hua , Chua Soo-Jin , Foo Boon-Chin , Wang Yan-Jun , Yuan Hai-Rong , Yuan Shu
Published: July 2003

Using tertiarybutylphosphine (TBP) as phosphorus precursor, high-quality AlGaInP epilayers and AlGaInP/GaInP multiple-quantum-well (MQW) structures have been grown by metalorganic chemical vapor deposition. The photoluminescence results indicate that the AlGaInP materials are as good as those grown using PH3 in terms of optical quality. Finally, AlGaInP MQW red laser structures have been grown, and the electrically pumped AlGaInP red lasers grown by TBP have been demonstrated with the emission wavelength of 647 nm, indicating that TBP can be used to grow high-quality AlGaInP epilayers and AlGaInP-based red lasers, which presently is dominated by the highly toxic gas source PH3.
Laser diode current controller with a high level of protection against electromagnetic interference
Authors: Lazar Josef , Jedlička Petr , Čı́p Ondřej , Růžička Bohdan
Published: July 2003

We present a current controller which satisfies the highest protection criteria of semiconductor lasers notorious for their great sensitivity to damage caused by induced electromagnetic interference. The core current source is supplied by linear isolating converter providing ripple free voltage. It is galvanically isolated, double shielded and current sense as well as current modulation are coupled via linear optocouplers. The current controller in this configuration makes safe operation of semiconductor lasers in laboratory conditions possible.
Mechanical stress effect on imprint behavior of integrated ferroelectric capacitors
Authors: Gruverman A. , Rodriguez B. J. , Kingon A. I. , Nemanich R. J. , Tagantsev A. K. , Cross J. S. , Tsukada M.
Published: July 2003

Stress-induced changes in the imprint and switching behavior of (111)-oriented Pb(Zr,Ti)O3 (PZT)-based capacitors have been studied using piezoresponse force microscopy. Visualization of polarization distribution and d33-loop measurements in individual 1×1.5-μm2 capacitors before and after stress application, generated by substrate bending, provided direct experimental evidence of stress-induced switching. Mechanical stress caused elastic switching in capacitors with the direction of the resulting polarization determined by the sign of the applied stress. In addition, stress application turned capacitors into a heavily imprinted state characterized by strongly shifted hysteresis loops and almost complete backswitching after application of the poling voltage. It is suggested that substrate bending generated a strain gradient in the PZT layer, which produced asymmetric lattice distortion with preferential polarization direction and triggered polarization switching due to the flexoelectric effect.
Cylindrical dust acoustic waves with transverse perturbation
Authors: Xue Ju-Kui
Published: July 2003

The nonlinear dust acoustic waves in dusty plasmas with the combined effects of bounded cylindrical geometry and the transverse perturbation are studied. Using the perturbation method, a cylindrical Kadomtsev–Petviashvili (CKP) equation that describes the dust acoustic waves is deduced for the first time. A particular solution of this CKP equation is also obtained. It is shown that the dust acoustic solitary waves can exist in the CKP equation.
Filamentary magnetohydrodynamic simulation model, current-vortex method
Authors: Yatsuyanagi Yuichi , Ebisuzaki Toshikazu , Hatori Tadatsugu , Kato Tomokazu
Published: July 2003

A two-dimensional simulation model of the “magnetohydrodynamic (MHD)” vortex method, current-vortex method, is developed. The concept is based on the previously developed current-vortex filament model in three-dimensional space. It is assumed that electric current and vorticity have discontinuous filamentary (point) distributions on the two-dimensional plane, and both the point electric current and the point vortex are confined in a filament. In other words, they share the same point on the two-dimensional plane, which is called the “current-vortex filament.” The spatial profiles of the electric current and the vorticity are determined by the sum of such filaments. Time development equations for a filament are obtained by integrating the two-dimensional MHD equations around the filament. It is found that a special-purpose computer, MDGRAPE-2, is capable not only of molecular dynamics simulations but also of MHD simulations, because MDGRAPE-2 accelerates calculations of the Biot–Savart integral. The current-vortex method on MDGRAPE-2 reproduces the result obtained by the traditional MHD code on a general-purpose computer.
Formation of BiOi, BiCs, and BiBsHi defects in e-irradiated or ion-implanted silicon containing boron
Authors: Adey J. , Jones R. , Briddon P. R.
Published: July 2003

The local density functional theory is used to study the electrical levels and thermal stabilities of complexes of interstitial boron with O and C and a boron dimer with H. The energy levels of these defects are compared with those found from deep level transient capacitance spectroscopy experiments on irradiated p-Si containing B. The levels observed at Ec−0.23, Ev+0.29, and Ev+0.51 eV are assigned to BiOi, BiCs, and BiBsHi respectively. BiCs is passivated by one H atom. Evidence for the existence of BiCs has implications for mechanisms involved in the suppression of transient-enhanced diffusion of boron in ion-implanted Si by C.
Room-temperature ultraviolet-emitting In2O3 nanowires
Authors: Cao Huaqiang , Qiu Xianqing , Liang Yu , Zhu Qiming , Zhao Meijuan
Published: July 2003

Semiconductor In2O3 nanowires embedded in an alumina template were fabricated using template technology. Scanning electron microscopy and transmission electron microscopy observations show that the In2O3 nanowire single crystal has an average diameter around 80 nm and a length over 10 μm. A strong photoluminescence (PL) emission with a peak at 398 nm (3.12 eV in photon energy) was detected upon excitation of the In2O3 nanowires at 274 nm (4.53 eV in photon energy) and 305 nm (4.08 eV in photon energy) under room temperature. The observed UV PL emission is attributed to the near band edge emission.
Trap-dominated minority-carrier recombination in GaInNAs pn junctions
Authors: Friedman D. J. , Geisz J. F. , Metzger W. K. , Johnston S. W.
Published: July 2003

We use dark current–voltage measurements on GaInNAs pn junctions as a direct probe of the dominant recombination mechanism in this material. The dark current is dominated by recombination through traps. Using the classic theory of Sah, Noyce, and Shockley, we deduce trap energies and carrier capture lifetimes as a function of band gap Eg. The trap energy is found to be roughly constant at ∼0.4 eV below the conduction band or above the valence band as Eg decreases from ∼1.1 to 0.9 eV with increasing [N]. Concomitantly, the capture lifetimes decrease from 5 to 0.08 ns. This rapid decrease has important implications for performance of high-[N] minority-carrier devices.
Ohmic hole injection in poly(9,9-dioctylfluorene) polymer light-emitting diodes
Authors: Poplavskyy D. , Nelson J. , Bradley D. D. C.
Published: July 2003

Here we report the observation of ohmic hole injection from a conducting polymer anode into poly(9,9-dioctylfluorene) in a polymer light-emitting diode structure. Although initially nonohmic, the contact can be made locally ohmic by electrically conditioning the device at voltages higher than the electroluminescence onset voltage. The ohmic nature of the contact in selected regions is confirmed by the appearance of dark injection space-charge-limited transient currents, which yield hole mobilities in good agreement with those measured by the time-of-flight method. The appearance of ohmic injection is discussed within a model that assumes the existence of electron traps near the anode interface. When the sample is conditioned electrons are injected from the cathode and are trapped near the anode inducing an interfacial dipole that reduces the barrier for hole injection.
Second-harmonic generation through optimized modal phase matching in semiconductor waveguides
Authors: Moutzouris K. , Venugopal Rao S. , Ebrahimzadeh M. , De Rossi A. , Calligaro M. , Ortiz V. , Berger V.
Published: July 2003

We report optical second-harmonic generation (SHG) through modal phase matching in GaAs/AlGaAs semiconductor waveguides. Using femtosecond pulses, both type-I and type-II SHG is demonstrated for fundamental wavelengths near 1.55 μm.
IR induced cis↔trans isomerization of 2-naphthol: Catalytic role of hydrogen-bond in the photoinduced isomerization
Authors: Ebata Takayuki , Kouyama Kyouko , Mikami Naohiko
Published: July 2003

An infrared laser induced cis↔trans isomerization has been investigated for 2-naphthol and its hydrogen(H)-bonded cluster with NH3 in the S1 electronic state by UV–IR double resonance excitation in a supersonic jet. A specific isomer was pumped to a X–H (X=O, C or N) stretching vibration in S1 by a sequential UV–IR two-photon excitation, and the resultant product species were analyzed by dispersing their fluorescence. It was found that the IR excitation induces the isomerization for the H-bonded cluster with the excitation less than 3000 cm−1, while no isomerization was found to occur for bare 2NpOH even with an input energy of 3610 cm−1. The substantial reduction of the isomerization barrier height represents evidence of the catalytic nature of H-bonding in the conformational isomerization. It was also found that the isomerization efficiency is very high at low IR frequency and exhibits a marked IR frequency dependence.
XIAP-mediated Caspase Inhibition in Hodgkin's Lymphoma–derived B Cells
Authors: Kashkar Hamid , Haefs Christiane , Shin Hwain , Hamilton-Dutoit Stephen J. , Salvesen Guy S. , Krönke Martin , Jürgensmeier Juliane M.
Published: July 2003

The malignant Hodgkin and Reed-Sternberg cells of Hodgkin's lymphoma (HL) and HL-derived B cell lines were previously shown to be resistant to different apoptotic stimuli. We show here that cytochrome c fails to stimulate caspases-9 and -3 activation in cytosolic extracts of HL-derived B cells, which is due to high level expression of X-linked inhibitor of apoptosis (XIAP). Coimmunoprecipitation studies revealed that XIAP, apoptosis protease-activating factor–1, and caspase-3 are complexed in HL-derived B cell lysates. Even after stimulation with exogenous cytochrome c and dATP, XIAP impairs the proteolytic processing and activation of caspase-3. In cytosolic extracts, inhibition of XIAP by the second mitochondria-derived activator of caspases (Smac)/DIABLO, or immunodepletion of XIAP restores cytochrome c–triggered processing and activation of caspase-3. Smac or a Smac-derived agonistic peptide also sensitized intact HL-derived B cells for the apoptotic action of staurosporine. Finally, Hodgkin and Reed-Sternberg cells of primary tumor HL tissues also constitutively and abundantly express XIAP. The results of this paper suggest that high level XIAP expression is a hallmark of HL, which may play a crucial role in resistance to apoptosis.
Paired Activating and Inhibitory Immunoglobulin-like Receptors, MAIR-I and MAIR-II, Regulate Mast Cell and Macrophage Activation
Authors: Yotsumoto Katsumi , Okoshi Yasushi , Shibuya Kazuko , Yamazaki Satoshi , Tahara-Hanaoka Satoko , Honda Shin-ichiro , Osawa Mitsujiro , Kuroiwa Asato , Matsuda Yoichi , Tenen Daniel G. , Iwama Atsushi , Nakauchi Hiromitsu , Shibuya Akira
Published: July 2003

Immune responses are regulated by opposing positive and negative signals triggered by the interaction of activating and inhibitory cell surface receptors with their ligands. Here, we describe novel paired activating and inhibitory immunoglobulin-like receptors, designated myeloid-associated immunoglobulin-like receptor (MAIR) I and MAIR-II, whose extracellular domains are highly conserved by each other. MAIR-I, expressed on the majority of myeloid cells, including macrophages, granulocytes, mast cells, and dendritic cells, contains the tyrosine-based sorting motif and the immunoreceptor tyrosine-based inhibitory motif-like sequences in the cytoplasmic domain and mediates endocytosis of the receptor and inhibition of IgE-mediated degranulation from mast cells. On the other hand, MAIR-II, expressed on subsets of peritoneal macrophages and B cells, associates with the immunoreceptor tyrosine-based activation motif-bearing adaptor DAP12 and stimulates proinflammatory cytokines and chemokine secretions from macrophages. Thus, MAIR-I and MAIR-II play important regulatory roles in cell signaling and immune responses.
Potent Immune Response against HIV-1 and Protection from Virus Challenge in hu-PBL-SCID Mice Immunized with Inactivated Virus-pulsed Dendritic Cells Generated in the Presence of IFN-α
Authors: Lapenta Caterina , Santini Stefano M. , Logozzi Mariantonia , Spada Massimo , Andreotti Mauro , Di Pucchio Tiziana , Parlato Stefania , Belardelli Filippo
Published: July 2003

A major challenge of AIDS research is the development of therapeutic vaccine strategies capable of inducing the humoral and cellular arms of the immune responses against HIV-1. In this work, we evaluated the capability of DCs pulsed with aldrithiol-2–inactivated HIV-1 in inducing a protective antiviral human immune response in SCID mice reconstituted with human PBL (hu-PBL-SCID mice). Immunization of hu-PBL-SCID mice with DCs generated after exposure of monocytes to GM-CSF/IFN-α (IFN-DCs) and pulsed with inactivated HIV-1 resulted in a marked induction of human anti–HIV-1 antibodies, which was associated with the detection of anti-HIV neutralizing activity in the serum. This vaccination schedule also promoted the generation of a human CD8+ T cell response against HIV-1, as measured by IFN-γ Elispot analysis. Notably, when the hu-PBL-SCID mice immunized with antigen-pulsed IFN-DCs were infected with HIV-1, inhibition of virus infection was observed as compared with control animals. These results suggest that IFN-DCs pulsed with inactivated HIV-1 can represent a valuable approach of immune intervention in HIV-1–infected patients.
The Early Progenitors of Mouse Dendritic Cells and Plasmacytoid Predendritic Cells Are within the Bone Marrow Hemopoietic Precursors Expressing Flt3
Authors: D'Amico Angela , Wu Li
Published: July 2003

Flt3 ligand (Flt3L) is a growth factor for hemopoietic progenitors and can promote the expansion of both conventional dendritic cells (DCs) and plasmacytoid predendritic cells (p-preDCs). The cells responding to Flt3L treatment and the precursors for the DCs and p-preDCs had not been fully characterized. We examined different mouse bone marrow (BM) hemopoietic precursor populations for the surface expression of Flt3 and tested them for early DC and p-preDC precursor activity. Most DC precursor activity, other than that given by multipotent hemopoietic stem cells, was within the downstream precursors expressing Flt3. The majority of mouse BM common lymphoid precursors expressed high levels of Flt3 and these were the most efficient precursors of both DCs and p-preDCs. In contrast, only a small proportion of the common myeloid precursors (CMPs) expressed Flt3, but the precursor activity for both DCs and p-preDCs was within this minor Flt3+ CMP fraction. The granulocyte and macrophage precursors and pro-B cells did not express Flt3 and had no DC or p-preDC precursor activity. These findings demonstrate that the early precursors for all DC subtypes are within the BM Flt3+ precursor populations, regardless of their lymphoid or myeloid lineage orientation.
Antigen-dependent Proliferation of CD4+ CD25+ Regulatory T Cells In Vivo
Authors: Walker Lucy S.K. , Chodos Anna , Eggena Mark , Dooms Hans , Abbas Abul K.
Published: July 2003

The failure of CD25+ regulatory T cells (Tregs) to proliferate after T cell receptor (TCR) stimulation in vitro has lead to their classification as naturally anergic. Here we use Tregs expressing a transgenic TCR to show that despite anergy in vitro, Tregs proliferate in response to immunization in vivo. Tregs also proliferate and accumulate locally in response to transgenically expressed tissue antigen whereas their CD25− counterparts are depleted at such sites. Collectively, these data suggest that the anergic state that characterizes CD25+ Tregs in vitro may not accurately reflect their responsiveness in vivo. These observations support a model in which Treg population dynamics are shaped by the local antigenic environment.
Flt3 Ligand Regulates Dendritic Cell Development from Flt3+ Lymphoid and Myeloid-committed Progenitors to Flt3+ Dendritic Cells In Vivo
Authors: Karsunky Holger , Merad Miriam , Cozzio Antonio , Weissman Irving L. , Manz Markus G.
Published: July 2003

Stimulation of Flt3 receptor tyrosine kinase through its cognate ligand expands early hematopoietic progenitor and dendritic cells (DCs) in humans and mice. The exact developmental stages at which hematopoietic progenitors express Flt3, are responsive to its ligand, and subsequently develop to DCs, are not known. Here we show that common lymphoid and common myeloid progenitors, as well as steady state DCs in thymus, spleen, and epidermis, express Flt3. The receptor is down-regulated once definitive B cell, T cell, and megakaryocyte/erythrocyte commitment occurs, and Flt3 is not detectable on other steady state hematopoietic cell populations. Upon in vivo Flt3 ligand (Flt3L) administration, Flt3+ progenitor cells and their progeny DCs are expanded, whereas Flt3− downstream progenitors are not, or are only slightly increased. Transplantation of common lymphoid and common myeloid progenitors and subsequent Flt3L injection increases progeny DCs of both precursor populations. These findings provide a definitive map of Flt3 expression in the hematopoietic hierarchy and directly demonstrate that Flt3L can drive DC development along both the lymphoid and myeloid developmental pathways from Flt3+ progenitors to Flt3+ DCs.
Activation of Natural Killer T Cells by α-Galactosylceramide Rapidly Induces the Full Maturation of Dendritic Cells In Vivo and Thereby Acts as an Adjuvant for Combined CD4 and CD8 T Cell Immunity to a Coadministered Protein
Authors: Fujii Shin-ichiro , Shimizu Kanako , Smith Caroline , Bonifaz Laura , Steinman Ralph M.
Published: July 2003

The maturation of dendritic cells (DCs) allows these antigen-presenting cells to initiate immunity. We pursued this concept in situ by studying the adjuvant action of α-galactosylceramide (αGalCer) in mice. A single i.v. injection of glycolipid induced the full maturation of splenic DCs, beginning within 4 h. Maturation was manifest by marked increases in costimulator and major histocompatibility complex class II expression, interferon (IFN)-γ production, and stimulation of the mixed leukocyte reaction. These changes were not induced directly by αGalCer but required natural killer T (NKT) cells acting independently of the MyD88 adaptor protein. To establish that DC maturation was responsible for the adjuvant role of αGalCer, mice were given αGalCer together with soluble or cell-associated ovalbumin antigen. Th1 type CD4+ and CD8+ T cell responses developed, and the mice became resistant to challenge with ovalbumin-expressing tumor. DCs from mice given ovalbumin plus adjuvant, but not the non-DCs, stimulated ovalbumin-specific proliferative responses and importantly, induced antigen-specific, IFN-γ producing, CD4+ and CD8+ T cells upon transfer into naive animals. In the latter instance, immune priming did not require further exposure to ovalbumin, αGalCer, NKT, or NK cells. Therefore a single dose of αGalCer i.v. rapidly stimulates the full maturation of DCs in situ, and this accounts for the induction of combined Th1 CD4+ and CD8+ T cell immunity to a coadministered protein.
Direct Expansion of Functional CD25+ CD4+ Regulatory T Cells by Antigen-processing Dendritic Cells
Authors: Yamazaki Sayuri , Iyoda Tomonori , Tarbell Kristin , Olson Kara , Velinzon Klara , Inaba Kayo , Steinman Ralph M.
Published: July 2003

An important pathway for immune tolerance is provided by thymic-derived CD25+ CD4+ T cells that suppress other CD25− autoimmune disease–inducing T cells. The antigen-presenting cell (APC) requirements for the control of CD25+ CD4+ suppressor T cells remain to be identified, hampering their study in experimental and clinical situations. CD25+ CD4+ T cells are classically anergic, unable to proliferate in response to mitogenic antibodies to the T cell receptor complex. We now find that CD25+ CD4+ T cells can proliferate in the absence of added cytokines in culture and in vivo when stimulated by antigen-loaded dendritic cells (DCs), especially mature DCs. With high doses of DCs in culture, CD25+ CD4+ and CD25− CD4+ populations initially proliferate to a comparable extent. With current methods, one third of the antigen-reactive T cell receptor transgenic T cells enter into cycle for an average of three divisions in 3 d. The expansion of CD25+ CD4+ T cells stops by day 5, in the absence or presence of exogenous interleukin (IL)-2, whereas CD25− CD4+ T cells continue to grow. CD25+ CD4+ T cell growth requires DC–T cell contact and is partially dependent upon the production of small amounts of IL-2 by the T cells and B7 costimulation by the DCs. After antigen-specific expansion, the CD25+ CD4+ T cells retain their known surface features and actively suppress CD25− CD4+ T cell proliferation to splenic APCs. DCs also can expand CD25+ CD4+ T cells in the absence of specific antigen but in the presence of exogenous IL-2. In vivo, both steady state and mature antigen-processing DCs induce proliferation of adoptively transferred CD25+ CD4+ T cells. The capacity to expand CD25+ CD4+ T cells provides DCs with an additional mechanism to regulate autoimmunity and other immune responses.
Dendritic Cells Are Responsible for the Capacity of CpG Oligodeoxynucleotides to Act as an Adjuvant for Protective Vaccine Immunity Against Leishmania major in Mice
Authors: Shah Javeed A. , Darrah Patricia A. , Ambrozak David R. , Turon Tara N. , Mendez Susana , Kirman Joanna , Wu Chang-You , Glaichenhaus Nicolas , Seder Robert A.
Published: July 2003

Vaccination with leishmanial Ag and CpG oligodeoxynucleotides (ODN) confers sustained cellular immunity and protection to infectious challenge up to 6 mo after immunization. To define the cellular mechanism by which CpG ODN mediate their adjuvant effects in vivo, the functional capacity of distinct dendritic cell (DC) subsets was assessed in the lymph nodes (LNs) of BALB/c mice, 36 h after immunization with the leishmanial antigen (LACK) and CpG ODN. After this immunization, there was a striking decrease in the frequency of the CD11c+B220+ plasmacytoid DCs with a proportionate increase in CD11c+CD8−B220− cells. CD11c+CD8+B220− cells were the most potent producers of interleukin (IL)-12 p70 and interferon (IFN)-γ, while plasmacytoid DCs were the only subset capable of secreting IFN-α. In terms of antigen presenting capacity, plasmacytoid DCs were far less efficient compared with the other DC subsets. To certify that DCs were responsible for effective vaccination, we isolated CD11c+ and CD11c− cells 36 h after immunization and used such cells to elicit protective immunity after adoptive transfer in naive, Leishmania major susceptible BALB/c mice. CD11c+ cells but not 10-fold higher numbers of CD11c− cells from such immunized mice mediated protection. Therefore, the combination of LACK antigen and CpG ODN adjuvant leads to the presence of CD11c+ DCs in the draining LN that are capable of vaccinating naive mice in the absence of further antigen or adjuvant.
CD4+ CD25+ Regulatory T Cells Control T Helper Cell Type 1 Responses to Foreign Antigens Induced by Mature Dendritic Cells In Vivo
Authors: Oldenhove Guillaume , de Heusch Magali , Urbain-Vansanten Georgette , Urbain Jacques , Maliszewski Charlie , Leo Oberdan , Moser Muriel
Published: July 2003

Recent evidence suggests that in addition to their well known stimulatory properties, dendritic cells (DCs) may play a major role in peripheral tolerance. It is still unclear whether a distinct subtype or activation status of DC exists that promotes the differentiation of suppressor rather than effector T cells from naive precursors. In this work, we tested whether the naturally occurring CD4+ CD25+ regulatory T cells (Treg) may control immune responses induced by DCs in vivo. We characterized the immune response induced by adoptive transfer of antigen-pulsed mature DCs into mice depleted or not of CD25+ cells. We found that the development of major histocompatibility complex class I and II–restricted interferon γ–producing cells was consistently enhanced in the absence of Treg. By contrast, T helper cell (Th)2 priming was down-regulated in the same conditions. This regulation was independent of interleukin 10 production by DCs. Of note, splenic DCs incubated in vitro with Toll-like receptor ligands (lipopolysaccharide or CpG) activated immune responses that remained sensitive to Treg function. Our data further show that mature DCs induced higher cytotoxic activity in CD25-depleted recipients as compared with untreated hosts. We conclude that Treg naturally exert a negative feedback mechanism on Th1-type responses induced by mature DCs in vivo.
Macrophages Control the Retention and Trafficking of B Lymphocytes in the Splenic Marginal Zone
Authors: Karlsson Mikael C.I. , Guinamard Rodolphe , Bolland Silvia , Sankala Marko , Steinman Ralph M. , Ravetch Jeffrey V.
Published: July 2003

The marginal zone of the spleen is a precisely ordered region that contains specialized subsets of B lymphocytes and macrophages. Disruption of the negative signaling inositol phosphatase, SH2-containing inositol-5-phosphatase 1 (SHIP), results in the loss of marginal zone B cells (MZBs) with reorganization of marginal zone macrophages (MZMOs) to the red pulp of the spleen. This primary macrophage defect, as revealed by selectively depleting SHIP in myeloid cells shows that MZMOs are specifically required for the retention of MZBs. The MZMO phenotype was reverted in SHIP/Bruton's tyrosine kinase (Btk) double knockout mice, thus identifying the Btk activating pathway as an essential component being regulated by SHIP. Furthermore, we identified a direct interaction between the MARCO scavenger receptor on MZMOs and MZBs. Activation or disruption of this interaction results in MZB migration to the follicle. The migration of the MZMOs was further studied after the response to Staphylococcus aureus, which induced MZMOs to move into the red pulp while MZBs migrated into the follicular zone. The marginal zone is therefore a dynamic structure in which retention and trafficking of B cells requires specific macrophage–B cell interactions.
Acute Encephalopathy Associated with Influenza A Virus Infection
Authors: Steininger Christoph , Popow-Kraupp Theresia , Laferl Hermann , Seiser Andreas , Gödl Irene , Djamshidian Schiva , Stöckl Elisabeth Puchhammer
Published: July 2003

Twenty-one patients aged 4–78 years with influenza A virus–associated acute encephalopathy were studied. Influenza A virus could be detected only in a cerebrospinal fluid (CSF) specimen obtained from 1 of 18 patients, despite the use of a highly sensitive polymerase chain reaction assay. Six patients experienced influenzal encephalopathy during the course of respiratory illness. Five of these patients had hypoprothrombinemia and 4 had increased serum creatinine levels, indicating hepatic and/or renal dysfunction. Fourteen patients experienced postinfluenzal encephalopathy ⩽3 weeks after resolution of acute respiratory symptoms. In 6 patients, focal areas of high signal intensity were visible on T2-weighted magnetic resonance images of the brain. Adenovirus DNA was detected in CSF specimens obtained from 4 (36%) of 11 patients with postinfluenzal encephalopathy. Thus, influenzal encephalopathy is frequently associated with metabolic disorders, whereas postinfluenzal encephalopathy appears to have different possible etiologies.
A limit theorem for the Shannon capacities of odd cycles I
Authors: Bohman Tom
Published: July 2003

This paper contains a construction for independent sets in the powers of odd cycles. It follows from this construction that the limit asnngoes to infinity ofn+1/2−Θ(C2n+1)n + 1/2 - \Theta ( C_{2n+1} )is zero, whereΘ(G)\Theta (G)is the Shannon capacity of the graphGG.
Tychonoff expansions by independent families
Authors: Hu Wanjun
Published: July 2003

A method for Tychonoff expansions using independent families is introduced. Using this method we prove that every countable Tychonoff space which admits a partition into infinitely many open-hereditarily irresolvable dense subspaces has a Tychonoff expansion that is

ω
\omega

-resolvable but not strongly extraresolvable. We also show that, under Luzin’s Hypothesis (

2

ω
1

=

2
ω

2^{\omega _1} = 2^\omega

), there exists an

ω
\omega

-resolvable Tychonoff space of size

ω
1

\omega _1

which is not maximally resolvable.
A {̄∂}∂–Poincaré lemma for forms near an isolated complex singularity
Authors: Harris Adam , Tonegawa Yoshihiro
Published: July 2003

Let

X
X

be an analytic subvariety of complex Euclidean space with isolated singularity at the origin, and let

η
\eta

be a smooth form of type

(
1.1
)

(1.1)

defined on

X
∖
{
0
}

X \setminus \{0\}

. The main result of this note is a criterion for solubility of the equation

∂
¯

∂
u
=
η

\bar {\partial }\partial u = \eta

. This implies a criterion for triviality of a Hermitian– holomorphic line bundle

(
L
,
h
)
→
X
∖
{
0
}

(L,h)\to X\setminus \{0\}

in a neighbourhood of the origin.
𝜋₁ of Hamiltonian 𝑆¹ manifolds
Authors: Li Hui
Published: July 2003

Let

(
M
,
ω
)

(M, \omega )

be a connected, compact symplectic manifold equipped with a Hamiltonian

S
1

S^1

action. We prove that, as fundamental groups of topological spaces,
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="pi 1 left-parenthesis upper M right-parenthesis equals pi 1 left-parenthesis normal m normal i normal n normal i normal m normal u normal m right-parenthesis equals pi 1 left-parenthesis normal m normal a normal x normal i normal m normal u normal m right-parenthesis equals pi 1 left-parenthesis upper M Subscript r e d Baseline right-parenthesis">

π
1

(
M
)
=

π
1

(

m
i
n
i
m
u
m

)
=

π
1

(

m
a
x
i
m
u
m

)
=

π
1

(

M

r
e
d

)

\pi _1(M)=\pi _1(\mathrm {minimum})=\pi _1(\mathrm {maximum})=\pi _1(M_{red})

, where

M

r
e
d

M_{red}

is the symplectic quotient at any value in the image of the moment map

ϕ
\phi

.
Condensations of projective sets onto compacta
Authors: Michalewski Henryk
Published: July 2003

For a coanalytic–complete or

\wideutilde {\Pi }^1_2–complete subspace

X
X

of a Polish space we prove that there exists a continuous bijection of

X
X

onto the Hilbert cube

[
0
,
1

]

N

[0,1]^{\mathbb {N}}

. This extends results of Pytkeev. As an application of our main theorem we give an answer to some questions of Arkhangelskii and Christensen. Under the assumption of Projective Determinacy we also give some generalizations of these results to higher projective classes.
Nehari and Carathéodory-Fejér type extension results for operator-valued functions on groups
Authors: Bakonyi Mihály
Published: July 2003

Let

G
G

be a compact abelian group having the property that its character group

Γ
\Gamma

is totally ordered by a semigroup

P
P

. We prove that every operator-valued function

k
k

on

G
G

of the form

k
(
x
)
=

∑

γ
∈
(
−
P
)

γ
(
x
)

k

γ

k(x)=\sum \limits _{\gamma \in (-P)}\gamma (x)k_{\gamma }

, such that the Hankel operator

H
k

H_k

is bounded, has an essentially bounded extension

K
K

with

|

|

K

|

|

∞

=

|

|

H
k

|

|

||K||_{\infty }=||H_k||

. The proof is based on Arveson’s Extension Theorem for completely positive functions on

C
∗

C^*

-algebras. Among the corollaries we have a Carathéodory-Fejér type result for analytic operator-valued functions defined on such groups.
Circle maps having an infinite 𝜔-limit set which contains a periodic orbit have positive topological entropy
Authors: Chinen Naotsugu
Published: July 2003

Let

f
f

be a continuous map from the circle to itself. The main result of this paper is that the topological entropy of

f
f

is positive if and only if

f
f

has an infinite

ω
\omega

-limit set which contains a periodic orbit.
A simple proof of the modular identity for theta functions
Authors: Couwenberg Wim
Published: July 2003

The modular identity arises in the theory of theta functions in one complex variable. It states a relation between theta functions for parameters

τ
\tau

and

−
1

/

τ

-1/\tau

situated in the complex upper half-plane. A standard proof uses Poisson summation and hence builds on results from Fourier theory. This paper presents a simple proof using only a uniqueness property and the heat equation.
Linear maps preserving ideals of C*-algebras
Authors: Cui Jianlian , Hou Jinchuan
Published: July 2003

We show that every unital linear bijection which preserves the maximal left ideals from a semi-simple Banach algebra onto a C

∗

^{*}

-algebra of real rank zero is a Jordan isomorphism. Furthermore, every unital self-adjoint linear bijection on a countably decomposable factor von Neumann algebra is maximal left ideal preserving if and only if it is a *-automorphism.
The Gromov-Lawson-Rosenberg conjecture for cocompact Fuchsian groups
Authors: Davis James , Pearson Kimberly
Published: July 2003

We prove the Gromov-Lawson-Rosenberg conjecture for cocompact Fuchsian groups, thereby giving necessary and sufficient conditions for a closed spin manifold of dimension greater than four with fundamental group cocompact Fuchsian to admit a metric of positive scalar curvature.
Local bifurcation from the second eigenvalue of the Laplacian in a square
Authors: del Pino Manuel , García-Melián Jorge , Musso Monica
Published: July 2003

In this work we study local bifurcation from the branch of trivial solutions for a class of semilinear elliptic equations, at the second eigenvalue

λ
2

\lambda _2

of a square. We find that the bifurcation set can be locally described as the union of exactly four bifurcation branches of nontrivial solutions which cross the bifurcation point

(

λ
2

,
0
)

(\lambda _2,0)

. We also compute the Morse index of the solutions in the four branches.
The rank of finitely generated modules over group algebras
Authors: Elek Gábor
Published: July 2003

We show the existence of a rank function on finitely generated modules over group algebras

K
Γ

K\Gamma

, where

K
K

is an arbitrary field and

Γ
\Gamma

is a finitely generated amenable group. This extends a result of W. Lück (1998).
The Hochschild cohomology ring of a selfinjective algebra of finite representation type
Authors: Green Edward , Snashall Nicole , Solberg Øyvind
Published: July 2003

This paper describes the Hochschild cohomology ring of a selfinjective algebra

Λ
\Lambda

of finite representation type over an algebraically closed field

K
K

, showing that the quotient

HH
∗

⁡
(
Λ
)

/

N

\operatorname {HH}^*(\Lambda )/\mathcal {N}

of the Hochschild cohomology ring by the ideal

N

{\mathcal N}

generated by all homogeneous nilpotent elements is isomorphic to either

K
K

or

K
[
x
]

K[x]

, and is thus finitely generated as an algebra. We also consider more generally the property of a finite dimensional algebra being selfinjective, and as a consequence show that if all simple

Λ
\Lambda

-modules are

Ω
\Omega

-periodic, then

Λ
\Lambda

is selfinjective.
Whitney’s example by way of Assouad’s embedding
Authors: Hajłasz Piotr
Published: July 2003

In this note we show how to use the Assouad embedding theorem (about almost bi-Lipschitz embeddings) to construct examples of

C
m

C^m

functions which are not constant on a critical set homeomorphic to the

n
n

-dimensional cube. This extends the famous example of Whitney. Our examples are shown to be sharp.