bluuebunny/crossref_metadata_2025 huggingface dataset:
A High Current Gain Si Metal Insulator Semiconductor Tunnel Emitter Transistor
Authors: Tomomi Yoshimoto Tomomi Yoshimoto , Kazuo Suzuki Kazuo Suzuki
Published: February 2005

A Si metal insulator semiconductor tunnel emitter transistor (Si MIS TET) was fabricated and investigated. The current gain of the Si MIS TET with a 32 Å SiO2emitter barrier was 76 at 300 K and 74 at 100 K. It was confirmed that the inversion base layer indeed functioned as a base of the Si MIS TET.
Observation of Atomic Steps on Vicinal Si(111) Annealed in Hydrogen Gas Flow by Scanning Tunneling Microscopy
Authors: Kuninori Kitahara Kuninori Kitahara , Osamu Ueda Osamu Ueda
Published: February 2005

The surface of vicinal Si(111) annealed in H2 flow was observed by equipping the chemical vapor deposition chamber with the scanning tunneling microscope. Samples were annealed at 1000°C for 10 min by passing an electric current under the H2 pressure of 7 Torr. Their surface morphology was compared with those annealed in ultrahigh vacuum (UHV) and in N2 flow at the same temperature. We found that the step motion during annealing in H2 was obviously smaller than that for annealing in UHV and N2. The multisteps formed during the annealing in UHV and N2 were not observed for H2 annealing except in the case of heating by direct current in the direction of lower to higher terraces. The mechanism of the interruption of the step motion is discussed from the viewpoint of the interaction between the surface and hydrogen.
Nucleation, Relaxation and Redistribution of Si Layers in GaAs
Authors: Brandt Oliver , Crook Gentry , Ploog Klaus , Bierwolf Rainer , Hohenstein Matthias , Maier Max , Wagner Joachim
Published: February 2005

We study the structural properties of Si layers of different thickness (0.1-1.3 nm) inserted in GaAs by solid-source molecular beam epitaxy. Using high-resolution electron microscopy, we demonstrate that the Si nucleation on GaAs takes place via the formation of Si nanoclusters in a highly regular arrangement. Thicker films (several monolayers) are found to be partially intermixed with GaAs. This intermixing is caused by the segregation of a considerable fraction of the deposited Si during overgrowth, as observed by secondary ion mass spectrometry. Finally, we show that the strain relief of Si films on GaAs occurs at a thickness of about 1.2 nm via the generation of stacking faults, whereas complete dislocations are not detected.
Preliminary Reliability Evaluations of GaAs/AlGaAs Electro-Optic Directional Coupler Switches
Authors: Hamamoto Kiichi , Anan Takayoshi , Keiro Komatsu Keiro Komatsu , Ikuo Mito Ikuo Mito
Published: February 2005

Reported here are the first preliminary reliability evaluation of GaAs/AlGaAs electro-optic directional coupler (EODC) switches. During a 1570-hour test period, significant DC drift phenomena was not observed. During a separate 2800-hour test period, the EODCs maintained normal I-V characteristics.
Chemical-Mechanical Polishing of Metalorganic Chemical-Vapor-Deposited Gold for LSI Interconnection
Authors: Hoshino Masataka , Suehiro Haruyoshi , Kazumi Kasai Kazumi Kasai , Junji Komeno Junji Komeno
Published: February 2005

We used a KI+I2+H2O solution and silica powder for chemical-mechanical polishing of metalorganic chemical-vapor-deposited gold. We used our technique to produce interconnection lines and plugs for LSI device multilayer interconnection. We obtained a flat surface for lines and vias filled with gold.
Crystal Growth of Bi-Sr-Ca-Cu-O (c0=39 Å) Single Crystals
Authors: Kishida Satoru , Tokutaka Heizo , Katayama Makoto , Nishimori Katsumi , Naganori Ishihara Naganori Ishihara , Takashi Yumoto Takashi Yumoto
Published: February 2005

Bi-Sr-Ca-Cu-O (Bi-based) single crystals were prepared by the self-flux method with a temperature-holding process. The prepared Bi-based single crystals were platelike with a size of about 2×2 mm2. From the X-ray diffraction patterns, we found that the Bi-based single crystal had a c-axis unit cell length of about 39 Å.
Interferometric Phase-Locking of Two Electronic Oscillators Based on a Cascade Electro-Optic Modulator
Authors: Pie-Yau Chien Pie-Yau Chien , Chen-Hsing Chao Chen-Hsing Chao
Published: February 2005

An optical phase-locked loop system based on a triangular phase-modulated cascade Mach-Zehnder modulator is demonstrated. A reference oscillator of 10 MHz is multiplied such that it can be used to lock a target oscillator of 120 MHz. The phase error of Δθe≤2.0×10-4 rad/Hz1/2 has been implemented in this system.
Time-Resolved Reflection High-Energy Electron Diffraction Monitoring of the Surface Structural Changes of Si{111} during Q-Switched Laser (532 nm) Annealing
Authors: Dimitrios Kitriotis Dimitrios Kitriotis , Yoshinobou Aoyagi Yoshinobou Aoyagi
Published: February 2005

Nanosecond surface structural changes during Q-switched laser annealing of a Si{111} crystal are studied with two-dimensional, time-resolved reflection of high-energy electron diffraction (RHEED) patterns obtained in real time synchronously with time-resolved optical reflectivity measurements. The detected Debye-Waller effect indicates the existence of a thermal process that results in melting of the surface. A transient crystalline surface phase is observed prior to recrystallization of the initial superstructure.
Outdiffusion and Subsequent Desorption of Volatile SiO Molecules during Annealing of Thick SiO2 Films in Vacuum
Authors: Takakuwa Yuji , Mizuhisa Nihei Mizuhisa Nihei , Nobuo Miyamoto Nobuo Miyamoto
Published: February 2005

The depth profile of so-called suboxides in the surface region for 1000-Å-thick SiO2 films annealed in vacuum at 800°C was measured by angle-resolved X-ray photoelectron spectroscopy. It was found that the amount of suboxide distributed under the surface increases rapidly and almost saturates with annealing time, while the change in the amount of suboxide present on the surface is very small and increases gradually with annealing time. This indicates that very fast outdiffusion of SiO molecules through thick SiO2 films takes place at as low as 800°C, leading to desorption from the SiO2 surface.
Blue Electroluminescence in Thin Films of Azomethin-Zinc Complexes
Authors: Hamada Yuji , Sano Takeshi , Fujita Masayuki , Fujii Takanori , Yoshitaka Nishio Yoshitaka Nishio , Kenichi Shibata Kenichi Shibata
Published: February 2005

Organic electroluminescent (EL) cells with azomethin-zinc complexes as an emitting layer showed bright blue emission. A cell structure of [indium-tin-oxide (ITO)/hole transport layer/emitting layer/MgIn] was employed. The color was blue, and emission peaks were 458∼470 nm. High luminance exceeding 1000 cd/m2 was obtained for the first time with an EL cell using a complex emitting material. The azomethin-zinc complexes exhibited good electron transport, as indicated by the high luminance obtained in two-layer EL cells.
High-Temperature Scanning Tunneling Microscopy Study of the Phase Transition of 16-Structure Appearing on a Si(110) Surface
Authors: Yamamoto Youiti , Sueyoshi Takashi , Tomoshige Sato Tomoshige Sato , Masashi Iwatsuki Masashi Iwatsuki
Published: February 2005

High-temperature scanning tunneling microscopy (HTSTM) has been developed which enables distortionless observation of the dynamic behavior of surface atoms at high temperatures up to 900°C on an atomic scale, and it was applied to analyze the mechanism of reversible phase transition between the 16-structure and the 1x1 structure appearing on a clean Si(110) surface. It has been found that, at first, the reconstruction and destruction of the 16-structure begin on the unit-cell level along the <112> direction and then progress along the <111> direction as a whole in order to complete the phase transition. The direct observation of the reconstruction at high temperatures is very important to investigate the mechanism of crystal growth.
Metalorganic Vapor Phase Epitaxy of CuAlxGa1-x(SySe1-y)2
Authors: Honda Tohru , Akita Hiroshi , Kitoh Shin-ichiro , Hara Kazuhiko , Junji Yoshino Junji Yoshino , Hiroshi Kukimoto Hiroshi Kukimoto
Published: February 2005

Epitaxial layers of the CuAl
x
Ga1-x
(S
y
Se1-y
)2 quaternary (x=0) and pentanary (x≠0) alloys lattice-matched to GaP substrates have been successfully grown by metalorganic vapor phase epitaxy using cyclopentadienyl-triethylphosphine-copper, triethylaluminum, triethylgallium, ditertiarybutylsulfide and diethylselenide as source materials. This pentanary alloy is the first ever grown to the best of our knowledge. Single and double heterostructures consisting of the quaternary and pentanary alloys have also been fabricated for the first time. A sample of the single heterostructure has shown stimulated emission at 77 K under pulsed light excitation.
Optical Absorption in CdTe Detected through Channel Conduction in CdTe/InSb/CdTe Single Quantum Well Grown by Molecular Beam Epitaxy
Authors: Kaneko Kazuhiko , Suzuki Takayuki , Libatique Nathaniel , Kimata Morihiko
Published: February 2005

The measurement of the photocurrent in an undoped thin layer of CdTe is difficult because of its high resistivity. However, if carriers generated by optical absorption in the CdTe layer fall into a single quantum well, it is easy to determine the number of these carriers through the measurement of the channel current in the quantum well. By means of this method, well-width-independent absorption spectra of CdTe are obtained. The molecular beam epitaxy grown samples used have the following structure: CdTe/InSb/CdTe/GaAs. However, we could not specify the origin of the absorption peak occurring in the lower energy side of the band edge.
Textured Bi-Sr-Ca-Cu-O Bulk Sample
Authors: Michishita Kazuo , Shimizu Noriyuki , Sugawara Yoshihiro , Ito Wataru , Sasaki Yukichi , Kubo Yukio , Nagaya Shigeo , Inoue Toshio
Published: February 2005

A textured structure with the c-axes of the 2212 crystal nearly parallel to each other was obtained in a bulk superconducting sample of Bi2.2Sr1.8CaCu2O
x
doped with 10 wt%Ag. When Ag-doping was not performed or a Bi2Sr2CaCu2O
y
composition was used, the textured structure was not obtained. The textured sample has an I
c value and magnetic field dependence superior to those of the untextured sample.
Quenching experiments were carried out to investigate the formation mechanism of the textured structure and it was revealed that the morphology of the interface between solid and melt in the textured sample was different from that in the untextured sample.
Optically Addressed Spatial Light Modulator Using an Antiferroelectric Liquid Crystal Doped with Azobenzene
Authors: Moriyama Takashi , Kajita Junji , Takanishi Yoichi , Ishikawa Ken , Hideo Takezoe Hideo Takezoe , Atsuo Fukuda Atsuo Fukuda
Published: February 2005

We have fabricated an optically addressed bistable light modulator operable under a bias voltage using an antiferroelectric liquid crystal doped with photochromic dye molecules. The photoreaction is based on the change in the threshold voltage in the field-induced antiferroelectric-ferroelectric phase transition, which is driven by the cis-trans photoisomerization. A response time of 30 ms was achieved by irradiation of a 10 mW Ar+ laser without focusing. We demonstrated the recording ability of continuous gray levels by changing either light intensity or pulse duration.
First Observation of the Si(111)-7×7↔1×1 Phase Transition by the Optical Second Harmonic Generation
Authors: Hirabayashi Takanori Suzuki
Published: February 2005

Temperature dependence of the second harmonic generation of the Si(111)-7×7 surface was measured in the temperature range from 550°C to 1100°C. For the first time Si(111)-7×7↔1×1 phase transition around 860°C was observed as an abrupt intensity change of the SH signal within 15 degrees using an optical technique. A hysteretic behavior with temperature difference of 2°C was observed in heating and cooling processes over the transition region. A gradual decrease of the SH intensity with temperature was also observed.
X-Ray Evaluation of Microroughness of Mechanochemically Polished Silicon Surfaces
Authors: Sakata Osami , Andrei Y. Nikulin Andrei Y. Nikulin , Hiroo Hashizume Hiroo Hashizume
Published: February 2005

Microroughness of mechanochemically polished (100) silicon surfaces has been determined from X-ray reflectivity data. An optical interferometer showed equally smooth surfaces (3∼4 Å rms) for all samples examined. X-ray Fresnel reflectivity data revealed distinct decay features of the scattering profiles from samples polished using different relative strengths of mechanical and chemical factors. Profile fits were used to evaluate the Gaussian rms roughness at 11∼12 Å under oxide layers of a density close to 2.0 g/cm3. A stoichiometry not far from that of SiO2 was found for the overlayer oxide.
ESR Study of Natural Oxidation Processes of HF-Treated Silicon (111) Surfaces
Authors: Ken'etsu Yokogawa Ken'etsu Yokogawa , Tatsumi Mizutani Tatsumi Mizutani
Published: February 2005

Natural oxidation processes on hydrogen fluoride (HF) treated silicon (111) surface were measured by ESR and X-ray photoelectron spectroscopy (XPS). After etched samples were exposed to air, Pb centers were observed by ESR, and XPS showed step-like increases in oxide thickness. Despite the first step in oxide thickness occurring at 200-300 h and remaining roughly constant from 300 to 800 h, the Pb center density increased monotonically and saturated after about 700 h. This increase in Pb center density has been interpreted in terms of continuous reconstruction at the interface during oxidation.
Se Adsorption on (001) GaAs under Various As4 Pressures
Authors: Eriko T. Sano Eriko T. Sano , Yoshiji Horikoshi Yoshiji Horikoshi
Published: February 2005

We used reflection high-energy electron diffraction (RHEED) to investigate the adsorption fo Se on (001) GaAs surfaces under different residual As4 pressures at a substrate temperature of 510 °C. Under a fixed Se pressure of 5 ×10-9 Torr, the diffraction pattern showed a (2 ×4) reconstruction when the As4 pressure was 5 ×10-8 Torr. When the As4 pressure was reduced to the level of Se pressure, the surface showed (4 ×3) reconstruction. When the As4 pressure was further reduced to 5 ×10-9 Torr, the diffraction spots in the RHED pattern disappeared, and a halo pattern became dominant. These results show that even at a fixed substrate temperature, the surface structure of Se-adsorbed (001) GaAs can be sensitively changed by varying the As4 pressure.
Preparation of Substituted Y3Fe5O12 Waveguide Directional Coupler Using Ion-Beam Etching
Authors: Sugimoto Naoto , Katoh Yujiro , Akiyuki Tate Akiyuki Tate , Atsushi Shibukawa Atsushi Shibukawa
Published: February 2005

The rib waveguide directional coupler of an epitaxially grown 4-µm-thick substituted Y3Fe5O12 (YIG) monolayer film on a [111]-oriented Gd3Ga5O12 (GGG) substrate is prepared by argon ion-beam etching. A Ta/organic layer double-layer mask is utilized during ion-beam etching. The basic operation of the directional coupler at λ=1.55 µm is demonstrated.
Fabrication of YBaCuO-Josephson-Junctions on MgO-Substrates Damaged by a Focused Ion Beam Prior to Film Deposition
Authors: Neumann Christian , Suzuki Katsumi , Youichi Enomoto Youichi Enomoto , Shoji Tanaka Shoji Tanaka
Published: February 2005

By using a focused Ga-ion-beam we have damaged micro-areas of MgO-substrates through a protective gold-layer. Two different types of damage are produced: the flat type is to damage the surface by the implantation of Ga-ions whereas the groove type is simply geometrical damage to the substrates by sputtering the MgO. A YBa2Cu3O7-x
(YBaCuO)-film was deposited on the as prepared substrates and the final junction was then defined by photolithography and Ar-milling over the damaged region. Under microwave irradiation Shapiro-steps were observed on these junctions, and a R
n×I
c of up to 3 mV at 4.2 K was achieved for the flat type junctions.
Observation of Flux Movement in Quench-and-Melt-Grown YBCO Generated by a Pulsed Magnetic Field
Authors: Takizawa Takeo , Kanbara Kohji , Morita Mitsuru , Hashimoto Misao
Published: February 2005

The dynamics of the quantized flux in a ring-shaped YBa2Cu3O7 sample has been studied through the observation of the magnetic flux motion generated by a pulsed magnetic field. The flux speed is obtained as a function of the rise rate of the external field and as a function of temperature. It is shown that the flux speed is not intrinsic as determined by the creep theory but is determined by the external field and the J
c value. To interpret the slow rise of the observed signal, a distribution of different kinds of pinning centers in a sample is suggested.
P-GaN/N-InGaN/N-GaN Double-Heterostructure Blue-Light-Emitting Diodes
Authors: Nakamura Shuji , Masayuki Senoh Masayuki Senoh , Takashi Mukai Takashi Mukai
Published: February 2005

P-GaN/n-InGaN/n-GaN double-heterostructure (DH) blue-light-emitting diodes (LEDs) were fabricated successfully for the first time. The output power was 125 µW and the external quantum efficiency was as high as 0.22% at a forward current of 20 mA at room temperature. The peak wavelength and the full width at half-maximum (FWHM) of the electroluminescence (EL) were 440 nm and 180 meV, respectively. This value FWHM of was the smallest ever reported for blue GaN LEDs.
Integratable Tunable Twin-Guide Laser on Semi-Insulating Substrate
Authors: Thulke Wolfgang , Achatz Vera , Borchert Bernd , Stefan Illek Stefan Illek , Thomas Wolf Thomas Wolf
Published: February 2005

The continuously tunable twin-guide (TTG) distributed feedback (DFB) laser has been fabricated on semi-insulating substrate for the first time. A new contacting scheme is applied with all three contacts on top of the laser chip. The fabrication requires only four metalorganic vapour phase epitaxy (MOVPE) stages, i.e. only as many as that of simple TTG-DFB lasers on p-type substrate. An electronic tuning range of 1.2 nm has been achieved despite a high series resistance, which will be considerably reduced by optimising the structure. The fabrication on semi-insulating substrates makes the TTG-DFB laser suitable for integration in a heterodyne receiver chip.
Ferroelectric Properties of (Bi1/2Pb1/2)(Ni1/4Ti3/4)O3for New Piezoelectric Ceramics
Authors: Tadashi Takenaka Tadashi Takenaka , Masatoshi Yamada Masatoshi Yamada
Published: February 2005

Bismuth lead nickel titanate, (Bi1/2Pb1/2)(Ni1/4Ti3/4)O3(BPNT), is studied on the basis of its ferroelectric, piezoelectric and mechanical properties as a new group of piezoelectric ceramics. The crystal phase of BPNT is a tetragonal perovskite type with a large crystalline anisotropy. The Curie temperature,Tc, is 430°C and the dielectric constant, εs, is 690 at room temperature. The D-E hysteresis loop is observed with a large remanent polarization,Pr=31.4 µC/cm2, and a large coercive field,Ec=45.4 kV/cm. The electromechanical coupling factors,ktandkp, in the thickness and the planar modes are 49% and 31%, respectively. The mechanical strength was slightly higher than that of the conventional PZT system.
Photoisomerization Observed by Means of Scanning Tunneling Microscopy
Authors: Umemoto Takeshi , Ishikawa Ken , Takezoe Hideo , Fukuda Atsuo , Sasaki Takeo , Ikeda Tomiki
Published: February 2005

We have studied the interfacial structure of a photochromic molecule, 4,4'-dioctyloxyazobenzene (8AB8), on molybdenum disulphide by means of scanning tunneling microscopy (STM) with molecular resolution. We found at least two interfacial structures. The STM image of one of the structures was easily distorted upon irradiation with UV light, while that of the other structure was quite stable under UV light irradiation. In a wide area of several hundred nanometers, we observed that some steps with equal height changes of 1.1 nm moved during the irradiation. We interpreted that trans-cis photoisomerization causes molecular layers to be torn off one by one.
Reflection High-Energy Electron Diffraction Observation of Anti-Phase Domain Ordering of the 2×1 Reconstructed (111) Surface of Chemical-Vapor-Deposited Diamond
Authors: Kondoh Eiichi , Kenji Tanaka Kenji Tanaka , Tomohiro Ohta Tomohiro Ohta
Published: February 2005

The chemical vapor-deposited homoepitaxial (111) diamond surface is studied by reflection high-energy electron diffraction (RHEED). The obtained diffraction patterns showed the presence of anti-phase domain ordering of 2×1 surface unit cells. The anti-phase boundary was determined to be <110>.
Study on Molecular Dimerization Inducing the Antiferroelectric Liquid Crystalline Phase by Measuring the Smectic Layer Thickness in Various Compounds
Authors: Ikeda Asako , Takanishi Yoichi , Hideo Takezoe Hideo Takezoe , Atsuo Fukuda Atsuo Fukuda
Published: February 2005

We have closely measured the layer thicknesses of three different series of liquid crystals by X-ray diffraction. The layer thickness in the three series of compounds was found to be correlated with the degree of stabilizing ability for the antiferroelectric structure, though the molecular structures are almost the same. The compounds with the antiferroelectric SmCA
* phase were of somewhat lesser layer thickness than that which the stable SmC* phase would be expected to have. This fact supports a previously proposed idea that the molecular dimerization in adjacent layers is important as the origin for the appearance of the SmCA
* phase.
Observation of Microdefects in As-Grown Czochralski Silicon Crystals by Synchrotron Radiation Topography
Authors: Sugita Yoshimitsu , Iida Satoshi , Aoki Yoshirou , Okitsu Kouhei , Tsuneda Masayuki , Takeno Hiroshi , Abe Takao , Kawata Hiroshi
Published: February 2005

Microdefects in as-grown Czochralski silicon crystals have been investigated by means of X-ray topography using 60 keV radiation from a synchrotron radiation source. In crystals grown at the pulling rate of 0.4 mm/min, very fine defects were observed and their density was about 1×103/cm3, which was in agreement with the result obtained by the flow pattern technique using Secco preferential etching. The strain field of the defects was analyzed from the topographic image height of defects using the kinematical diffraction theory. The values of the defect strength that gave a measure of the size of the defects were from 2 to 40×10-20m3.
Deep Level Transient Spectroscopy Characterization of Electron Irradiation Induced Hole Traps in p-GaAs Grown by Molecular Beam Epitaxy
Authors: Auret F. D. , Goodman S. A. , Meyer W. E. , R. M. Erasmus R. M. Erasmus , G. Myburg G. Myburg
Published: February 2005

Schottky barrier diodes on Be-doped p-type GaAs grown by molecular beam epitaxy (MBE) were irradiated with electrons (beta particles) from a Sr-90 radio-nuclide. Using deep level transient spectroscopy (DLTS), the radiation induced hole traps, labelled Hβ1-Hβ7, were characterized. The three most prominent defects, Hβ1, Hβ4 and Hβ5, have energy levels at 0.08, 0.20 and 0.30 eV, respectively, above the valence band. The introduction rate of Hβ1 is close to those of the electron irradiation induced electron traps E1 and E2 in n-GaAs, which have been identified as two charge states of the isolated As vacancy, V
As. Defect Hβ4, whose concentration decreases with depth below the metal-GaAs interface, has not yet been reported for electron irradiated GaAs.
Thin-Base InGaAs Heterojunction Bipolar Transistor with Parabolically Graded InGaAlAs Emitter
Authors: Koch Steffen , Waho Takao , Takashi Kobayashi Takashi Kobayashi , Tadao Ishibashi Tadao Ishibashi
Published: February 2005

We describe an InGaAs heterojunction bipolar transistor lattice-matched to InP with a parabolically graded quaternary In(Ga1-x
Al
x
)As emitter and a thin base. We obtain a room-temperature common-emitter DC current gain of more than 100, indicating the successful operation of the parabolic grading. High-frequency properties are equally promising, with current gain cutoff frequencies up to 125 GHz. These studies provide evidence for a significant reduction of base and collector transit times at high current densities, due to the velocity overshoot effect.
Joint synchrony of reciprocal hormonal signaling in human paradigms of both ACTH excess and cortisol depletion
Authors: Liu Peter Y. , Pincus Steven M. , Keenan Daniel M. , Roelfsema Ferdinand , Veldhuis Johannes D.
Published: February 2005

The hypothalamo-pituitary-adrenal axis is a stress-adaptive neuroendocrine ensemble, in which adrenocorticotropin (ACTH) drives cortisol secretion (feedforward) and cortisol restrains ACTH outflow (feedback). Quantifying direction- and pathway-specific adjustments within this and other interlinked systems by noninvasive means remains difficult. The present study tests the hypothesis that forward and reverse cross-approximate entropy (X-ApEn), a lag-, scale-, and model-independent measure of two-signal synchrony, would allow quantifiable discrimination of feedforward (ACTH → cortisol) and feedback (cortisol → ACTH) control. To this end, forward X-ApEn was defined by employing serial ACTH concentrations as a template to appraise pair-wise synchrony with cortisol secretion rates and vice versa for reverse X-ApEn. Coupled hormone profiles included normal ACTH-normal cortisol, high ACTH-high cortisol, and high ACTH-low cortisol concentrations in 35 healthy subjects, 21 patients with tumoral ACTH secretion, and 9 volunteers given placebo and a steroidogenic inhibitor, respectively. We used forward and reverse X-ApEn analyses to identify marked and equivalent losses of feedforward and feedback linkages (both P < 0.001) in patients with tumoral ACTH secretion. An identical analytical strategy revealed that ACTH → cortisol feedforward synchrony decreases ( P < 0.001), whereas cortisol → ACTH feedback synchrony increases ( P < 0.001), in response to hypocortisolemia. The collective outcomes establish precedence for pathway-specific adaptations in a major neurohormonal system. Thus quantification of directionally defined joint synchrony of biologically coupled signals offers a noninvasive strategy to dissect feedforward- and feedback-selective adaptations in an interactive axis.
Presence of the nucleic acid channel in renal brush-border membranes: allosteric modulation by extracellular calcium
Authors: Leal-Pinto Edgar , Teixeira Avelino , Tran Baohuong , Hanss Basil , Klotman Paul E.
Published: February 2005

We have previously described a cell surface channel complex that is highly selective for nucleic acid ( 6 , 7 ). The channel complex was purified to homogeneity by solubilizing renal brush-border membranes (BBM) with CHAPS and separation by liquid chromatography. It was characterized by reconstitution in planar lipid bilayers. The channel consists of a pore-forming subunit that is blocked by heparan sulfate and a regulatory subunit that is blocked by l-malate ( 7 ). The current studies were performed to compare the characteristics of the nucleic acid-conducting channel in native BBM with the characteristics that have been determined for the complex reconstituted from purified proteins. BBM were purified by differential centrifugation and reconstituted in lipid bilayers. Current was not observed until oligodeoxynucleotide (ODN) was added. Conductance was 9.1 ± 0.9 pS; rectification and voltage dependence were not observed. Reversal potential ( Erev) shifted to +14 ± 0.1 mV by a 10-fold gradient for ODN but was not altered when gradients were created for any other ion. Open probability increased significantly with an increase in Ca2+on the trans chamber of the bilayer apparatus. Changes in cis Ca2+were without effect. Addition of l-malate to the cis chamber or heparan sulfate to the trans chamber significantly reduced the open probability of the channel. These data demonstrate that the nucleic acid channel in BBM is electrophysiologically and pharmacologically identical to that previously reported for purified protein and demonstrate that a nucleic acid-conducting channel is a component of renal BBM.
Resistance to oxidative stress by chronic infusion of angiotensin II in mouse kidney is not mediated by the AT2receptor
Authors: Wesseling Sebastiaan , Ishola David A. , Joles Jaap A. , Bluyssen Hans A. , Koomans Hein A. , Braam Branko
Published: February 2005

Wild-type mice are resistant to ANG II-induced renal injury and hence form an attractive model to study renal defense against ANG II. The present study tested whether ANG II induces expression of antioxidative genes via the AT2receptor in renal cortex and thereby counteracts prooxidative forces. ANG II was infused in female C57BL/6J mice for 28 days and a subgroup received AT2receptor antagonist (PD-123,319) for the last 3 days. ANG II induced hypertension and aortic hypertrophy; proteinuria and renal injury were absent. Urinary nitric oxide metabolites (NOx) were decreased, and lipid peroxide (TBARS) excretion remained unchanged. Expression of NADPH oxidase components was decreased in renal cortex but induced in aorta. Heme oxygenase-1 (HO-1) was induced in both renal cortex and aorta. In contrast, ANG II suggestively increased AT2receptor expression in kidney but not in aorta. AT2receptor blockade enhanced hypertension in ANG II-infused mice, reversed ANG II effects on NOxexcretion, but did not affect TBARS. Despite its prohypertensive effect, expression of prooxidative genes in the renal cortex decreased rather than increased after short-term AT2receptor blockade and renal HO-1 induction after ANG II was normalized. Thus chronic ANG II infusion in mice induces hypertension but not oxidative stress. In contrast to the response in aorta, gene expression of components of NADPH-oxidase was not enhanced in renal cortex. Although ANG II administration induced renal cortical AT2receptor expression, blockade of that receptor did not unveil the AT2receptor as intrarenal dampening factor of prooxidative forces.
Direct Evidence for a Position Input to the Smooth Pursuit System
Authors: Blohm Gunnar , Missal Marcus , Lefèvre Philippe
Published: February 2005

When objects move in our environment, the orientation of the visual axis in space requires the coordination of two types of eye movements: saccades and smooth pursuit. The principal input to the saccadic system is position error, whereas it is velocity error for the smooth pursuit system. Recently, it has been shown that catch-up saccades to moving targets are triggered and programmed by using velocity error in addition to position error. Here, we show that, when a visual target is flashed during ongoing smooth pursuit, it evokes a smooth eye movement toward the flash. The velocity of this evoked smooth movement is proportional to the position error of the flash; it is neither influenced by the velocity of the ongoing smooth pursuit eye movement nor by the occurrence of a saccade, but the effect is absent if the flash is ignored by the subject. Furthermore, the response started around 85 ms after the flash presentation and decayed with an average time constant of 276 ms. Thus this is the first direct evidence of a position input to the smooth pursuit system. This study shows further evidence for a coupling between saccadic and smooth pursuit systems. It also suggests that there is an interaction between position and velocity error signals in the control of more complex movements.
Identification of genes that are differentially expressed in hemocytes of the Pacific blue shrimp (Litopenaeus stylirostris) surviving an infection withVibrio penaeicida
Authors: de Lorgeril Julien , Saulnier Denis , Janech Michael G. , Gueguen Yannick , Bachère Evelyne
Published: February 2005

Considerable progress has been made in the field of invertebrate immunity through the characterization of genes involved in the response to infection and/or stress. However, the mechanisms by which commercially important marine invertebrates can successfully survive an infection remain largely unknown. For the first time in an invertebrate model, we have searched to discover genes involved in the survival capacity of shrimp using the highly pathogenic bacteria, Vibrio penaeicida. In the present study, we applied the technique of suppression subtractive hybridization (SSH) to hemocyte cDNAs from infected and uninfected shrimp, only using samples from individuals that had survived 96 h postinfection. The resulting library contains 260 expressed sequence tagged (EST) cDNA clones potentially representing highly expressed genes in surviving shrimp. Sequence similarity comparisons were made, and putative identities were assigned to clones that were at least 51% identical to known genes. This analysis showed two functional categories that were highly represented: those of genes involved in immune reactions (10.7% of the ESTs) and those involved in proliferation-hematopoiesis (10.3%). Expression pattern profile analyses of selected ESTs at different times postinfection confirmed the differential expression of the genes and efficiency of the SSH method. Differences in gene transcript abundance, for select ESTs encoding antimicrobial effectors, were evidenced by real-time PCR between shrimp that survived acute Vibrio infection and those individuals that did not survive acute Vibrio infection. These results suggest there are basic differences at the level of transcript abundance for genes directly involved in immune and hematopoietic processes from shrimp that survive and do not survive infection.
Tobacco smoke dysregulates endothelial vasoregulatory transcripts in vivo
Authors: Maresh J. Gregory , Xu Huaxia , Jiang Nan , Gairola C. Gary , Shohet Ralph V.
Published: February 2005

We hypothesized that human smoking and its deleterious effects on endothelial function can be modeled by exposure of mice to tobacco smoke, and further that these changes would be reflected in gene regulation in vascular endothelium. We used for these studies a mouse strain that expresses green fluorescent protein under the control of an endothelial-specific promoter, Tie-2. Mice were exposed to sidestream smoke from reference cigarettes at 34 mg total suspended particulates/m3. After exposure for 5 days/wk for 1 and 6 wk, aortas were pooled from treatment and control groups. Endothelial cells were rapidly isolated by collagenase treatment followed by fluorescent activated cell sorting to yield populations of >95% purity. RNA isolated from >500 endothelial cells was amplified and analyzed on deeply representative long oligo microarrays. Transcripts dysregulated by >2.5-fold were confirmed by real-time PCR and selected proteins by immunofluorescent localization. In the endothelial cells, the observed more than threefold upregulation of complement factor H (Cfh), calcitonin receptor-like (Calcr1), and soluble epoxide hydrolase (Epxh2) may play a role in hypertensive responses of the vasculature to smoking. We have identified gene regulation in vivo in vascular endothelium that potentially underlies hypertensive responses to tobacco smoke.
Prospects for the UK Economy
Authors: Kirby Simon , Metz Robert , Riley Rebecca
Published: February 2005

GDP growth slowed below trend in the second half of last year. At the time of writing, before the initial estimates of GDP growth for the fourth quarter of 2004 are released, we estimate that GDP expanded by 0.4 per cent in the final quarter of last year. The weakness in GDP growth reflects in large part the poor performance of industrial production in the second half of last year.
Effects of Case Management on Parolee Misconduct
Authors: Longshore Douglas , Turner Susan , Fain Terry
Published: February 2005

The Bay Area Services Network (BASN) provides case management, drug abuse treatment, and links to other health/social services for drug-involved parolees in the San Francisco Bay Area. In a quasi-experimental evaluation, the authors found no difference between BASN and comparison parolees in treatment duration, access to health/social services, drug use days, or criminal recidivism. However, mean scores for dose of case management (number of contacts with case manager) and treatment duration were low among BASN parolees overall. In analyses using BASN parolees only, the authors found those with a stronger case management dose reported fewer drug use days and property offenses. These findings persisted when self-reported abstinence motivation was controlled for as a proxy for self-selection. The effect of case management dose on drug use days was mediated by treatment duration. BASN case management may have had favorable effects on recidivism and drug use when delivered in a sufficient dose.
Sustained signaling through the B-cell receptor induces Mcl-1 and promotes survival of chronic lymphocytic leukemia B cells
Authors: Petlickovski Aleksandar , Laurenti Luca , Li Xiaoping , Marietti Sara , Chiusolo Patrizia , Sica Simona , Leone Giuseppe , Efremov Dimitar G.
Published: February 2005

The clinical course of chronic lymphocytic leukemia (CLL) differs significantly between patients with mutated (M-CLL) and unmutated (U-CLL) immunoglobulin (Ig) variable heavy-chain (VH) genes, implying a role for B-cell receptor (BCR) signaling in the pathogenesis of this disease. We have now investigated activation of downstream BCR signaling pathways in U-CLL and M-CLL B cells using soluble anti-IgM (sol-IgM) and immobilized anti-IgM (imm-IgM) antibodies as models for antigenic stimulation. Ligation of the BCR with sol-IgM induced incomplete responses in both CLL subsets, resembling the pattern described for tolerant B cells. This response was characterized by transient phosphorylation of extracellular signal-related kinase (ERK) and Akt (protein kinase B [PKB]), lack of activation of c-JUN NH2-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK), and variable activation of phospholipase Cγ2 (PLCγ2) and nuclear factor-κB (NF-κB). Stimulation with imm-IgM elicited a more complete BCR signal and significantly prolonged phosphorylation of ERK and Akt, indicating persistent or repetitive BCR signaling. Moreover, this type of stimulation increased the levels of the antiapoptotic protein myeloid cell leukemia-1 (Mcl-1) and protected from chemotherapy-induced apoptosis, whereas induction of apoptosis and down-regulation of Mcl-1 was observed following stimulation with sol-IgM. These data demonstrate that only sustained BCR signaling can promote survival of CLL B cells and indicate that the main difference between CLL with mutated and unmutated VH genes may reside in the availability of such stimulation. (Blood. 2005;105:4820-4827)
A subset of natural killer cells achieves self-tolerance without expressing inhibitory receptors specific for self-MHC molecules
Authors: Fernandez Nadine C. , Treiner Emmanuel , Vance Russell E. , Jamieson Amanda M. , Lemieux Suzanne , Raulet David H.
Published: February 2005

It is widely believed that self-tolerance of natural killer (NK) cells occurs because each NK cell expresses at least one inhibitory receptor specific for a host major histocompatibility complex (MHC) class I molecule. Here we report that some NK cells lack all known self-MHC–specific inhibitory receptors, yet are nevertheless self-tolerant. These NK cells exhibit a normal cell surface phenotype and some functional activity. However, they respond poorly to class I–deficient normal cells, tumor cells, or cross-linking of stimulatory receptors, suggesting that self-tolerance is established by dampening stimulatory signaling. Thus, self-tolerance of NK cells in normal animals can occur independently of MHC-mediated inhibition, and hyporesponsiveness plays a role in self-tolerance of NK cells, as also proposed for B and T cells.
The homeobox gene HEX regulates proliferation and differentiation of hemangioblasts and endothelial cells during ES cell differentiation
Authors: Kubo Atsushi , Chen Vincent , Kennedy Marion , Zahradka Elizabeth , Daley George Q. , Keller Gordon
Published: February 2005

In this report we have investigated the role of the homeobox gene Hex in the development and differentiation of the blast colony-forming cell (BL-CFC), a progenitor with hemangioblast characteristics generated in embryonic stem (ES) cell-derived embryoid bodies (EBs). Molecular analysis showed that Hex is expressed in mesoderm, in populations that contain BL-CFCs, and in blast cell colonies, the progeny of the BL-CFCs. Hex-/- EBs displayed a defect in macrophage development but generated higher numbers of BL-CFCs than did wild-type EBs. In addition to differences in these progenitor populations, we also found that endothelial cells from the Hex-/- EBs showed enhanced proliferative potential compared with those from wild-type EBs. Forced expression of Hex at the onset of ES cell differentiation resulted in reduced EB cellularity, fetal liver kinase-1 (Flk-1) expression, and BL-CFC development. Taken together, these findings demonstrate that Hex functions at multiple stages of development within the differentiating EBs and uncover a novel role for this transcription factor as a negative regulator of the hemangioblast and the endothelial lineage. (Blood. 2005;105: 4590-4597)
HIV-1 incorporates ABO histo-blood group antigens that sensitize virions to complement-mediated inactivation
Authors: Neil Stuart J. D. , McKnight Áine , Gustafsson Kenth , Weiss Robin A.
Published: February 2005

ABO histo-blood group antigens have been postulated to modify pathogen spread through the action of natural antibodies and complement. The antigens are generated by a polymorphic glycosyl-transferase encoded by 2 dominant active and a recessive inactive allele. In this study we investigated whether ABO sugars are incorporated into the envelope of HIV-1 virions. HIV vectors derived from cells expressing ABO antigens displayed sensitivity to fresh human serum analogous to ABO incompatibility, and ABO histo-blood group sugars were detected on the viral envelope protein, glycoprotein 120 (gp120). Moreover, lymphocyte-derived virus also displayed serum sensitivity, reflecting the ABO phenotype of the host when cultured in autologous serum due to adsorption of antigens to cell surfaces. Serum sensitivity required both active complement and specific anti-ABO antibodies. Thus, incorporation of ABO antigens by HIV-1 may affect transmission of virus between individuals of discordant blood groups by interaction with host natural antibody and complement. (Blood. 2005;105:4693-4699)
CXCR3/CXCL10 interactions in the development of hypersensitivity pneumonitis
Authors: Agostini Carlo , Calabrese Fiorella , Poletti Venerino , Marcer Guido , Facco Monica , Miorin Marta , Cabrelle Anna , Baesso Ilenia , Zambello Renato , Trentin Livio , Semenzato Gianpietro
Published: February 2005

Background

Hypersensitivity pneumonitis (HP) is an interstitial lung disease caused by repeated inhalations of finely dispersed organic particles or low molecular weight chemicals. The disease is characterized by an alveolitis sustained by CD8(+) cytotoxic T lymphocytes, granuloma formation, and, whenever antigenic exposition continues, fibrosis. Although it is known that T-cell migration into the lungs is crucial in HP reaction, mechanisms implicated in this process remain undefined.

Methods

Using flow cytometry, immunohistochemistry, confocal microscopy analysis and chemotaxis assays we evaluated whether CXCL10 and its receptor CXCR3 regulate the trafficking of CD8(+) T cells in HP lung.

Results

Our data demonstrated that lymphocytes infiltrating lung biopsies are CD8 T cells which strongly stain for CXCR3. However, T cells accumulating in the BAL of HP were CXCR3(+)/IFNγ(+) Tc1 cells exhibiting a strong in vitro migratory capability in response to CXCL10. Alveolar macrophages expressed and secreted, in response to IFN-γ, definite levels of CXCL10 capable of inducing chemotaxis of the CXCR3(+) T-cell line. Interestingly, striking levels of CXCR3 ligands could be demonstrated in the fluid component of the BAL in individuals with HP.

Conclusion

These data indicate that IFN-γ mediates the recruitment of lymphocytes into the lung via production of the chemokine CXCL10, resulting in Tc1-cell alveolitis and granuloma formation.
Two-part permutation tests for DNA methylation and microarray data
Authors: Neuhäuser Markus , Boes Tanja , Jöckel Karl-Heinz
Published: February 2005

Background

One important application of microarray experiments is to identify differentially expressed genes. Often, small and negative expression levels were clipped-off to be equal to an arbitrarily chosen cutoff value before a statistical test is carried out. Then, there are two types of data: truncated values and original observations. The truncated values are not just another point on the continuum of possible values and, therefore, it is appropriate to combine two statistical tests in a two-part model rather than using standard statistical methods. A similar situation occurs when DNA methylation data are investigated. In that case, there are null values (undetectable methylation) and observed positive values. For these data, we propose a two-part permutation test.

Results

The proposed permutation test leads to smaller p-values in comparison to the original two-part test. We found this for both DNA methylation data and microarray data. With a simulation study we confirmed this result and could show that the two-part permutation test is, on average, more powerful. The new test also reduces, without any loss of power, to a standard test when there are no null or truncated values.

Conclusion

The two-part permutation test can be used in routine analyses since it reduces to a standard test when there are positive values only. Further advantages of the new test are that it opens the possibility to use other test statistics to construct the two-part test and that it avoids the use of any asymptotic distribution. The latter advantage is particularly important for the analysis of microarrays since sample sizes are usually small.
GANN: Genetic algorithm neural networks for the detection of conserved combinations of features in DNA
Authors: Beiko Robert G , Charlebois Robert L
Published: February 2005

Background

The multitude of motif detection algorithms developed to date have largely focused on the detection of patterns in primary sequence. Since sequence-dependent DNA structure and flexibility may also play a role in protein-DNA interactions, the simultaneous exploration of sequence- and structure-based hypotheses about the composition of binding sites and the ordering of features in a regulatory region should be considered as well. The consideration of structural features requires the development of new detection tools that can deal with data types other than primary sequence.

Results

GANN (available at http://bioinformatics.org.au/gann) is a machine learning tool for the detection of conserved features in DNA. The software suite contains programs to extract different regions of genomic DNA from flat files and convert these sequences to indices that reflect sequence and structural composition or the presence of specific protein binding sites. The machine learning component allows the classification of different types of sequences based on subsamples of these indices, and can identify the best combinations of indices and machine learning architecture for sequence discrimination. Another key feature of GANN is the replicated splitting of data into training and test sets, and the implementation of negative controls. In validation experiments, GANN successfully merged important sequence and structural features to yield good predictive models for synthetic and real regulatory regions.

Conclusion

GANN is a flexible tool that can search through large sets of sequence and structural feature combinations to identify those that best characterize a set of sequences.