bluuebunny/crossref_metadata_2025 huggingface dataset:
A GENERAL COVARIANT SYMPLECTIC STRUCTURE FOR GRAVITATIONAL, ELECTROMAGNETIC AND DIRAC FIELDS
Authors: BASINI GIUSEPPE , CAPOZZIELLO SALVATORE
Published: July 2006

We derive a general covariant symplectic structure which leads to holonomic and anholonomic formulations of Hamilton equations of motion related to the hydrodynamic picture of mechanics. Such a structure can be achieved starting from generic bilinear Hamiltonians, constructed by covariant vector, bivector or tensor fields. This feature is gage-free and it realizes a deep link toward canonical quantization for interactions like electromagnetism, gravity and Dirac fields.
THE PROPERTIES OF MAIN GALAXY PAIRS IN THE SLOAN GREAT WALL
Authors: DENG XIN-FA , ZHANG QUN , JIANG PENG , SONG JUN , LIAO QING-HUA , HE JI-ZHOU
Published: July 2006

By using cluster analysis, we select a galaxy pair sample in the Sloan Great Wall and study its various properties. We find that in the Sloan Great Wall pair sample, most galaxies are brighter and smaller, and that there is a tendency for pair galaxies to have similar luminosity and size.
Influences of Annealing Temperature on Characteristics of Ge p-Channel Metal Oxide Semiconductor Field Effect Transistors with ZrO2 Gate Dielectrics
Authors: Kamata Yoshiki , Kamimuta Yuuichi , Ino Tsunehiro , Iijima Ryosuke , Koyama Masato , Nishiyama Akira
Published: July 2006

The dependence of gate leakage current and p+/n-junction characteristics on annealing temperature is investigated comprehensively in order to obtain good electrical characteristics of Ge p-channel metal oxide semiconductor field effect transistors (p-MOSFETs) with ZrO2 gate dielectrics. The upper limit of annealing temperature is restricted to 500 °C to preserve low gate leakage. Gate leakage current remains low even after Ge incorporation into ZrO2, because ZrO2/Ge gate stacks retain their band alignment to as high as 500 °C. The degradation of gate leakage at the high temperature of 700 °C is due to the emergence of void regions near the interface in the Ge substrate. On the other hand, the lower limit of the annealing temperature is restricted to 400 °C in order to activate dopant boron sufficiently. Good rectifying diode characteristics lead to promising p-MOSFET performance, such as an S-factor of 80 mV/decade. The effective hole mobility of the ZrO2/Ge gate stack without an intentional interfacial layer after annealing at the optimized temperature is as high as 100 cm2/(V·s).
Evolution of Carrier Distribution and Defects in InGaAsN/GaAs Quantum Wells with Composition Fluctuation
Authors: Chen Jenn-Fang , Hsiao Ru-Shang , Hsieh Pei-Chen , Chen Yu-Chih , Wang Jyh-Shyang , Chi Jim-Y
Published: July 2006

Carrier distribution and defect induction in In0.34Ga0.66As0.98N0.02/GaAs single quantum wells grown by molecular beam epitaxy at low growth rates are investigated by frequency-dependent capacitance–voltage (C–V) and deep-level transient spectroscopy (DLTS). The C–V studies show that lowering the growth rate of the InGaAsN layer splits the carrier accumulation in the well into a central and two side peaks with different frequency dispersions. The DLTS studies show that a continuum of states (0–0.083 eV) and a deep trap at 0.21–0.25 eV are responsible for the central and the side peaks, respectively. A comparison with photoluminescence (PL) spectra shows that these defects are induced by composition fluctuation. Lowering the growth rate degrades composition fluctuation by segregating the material into an InGaAsN phase and an N-depleted phase. Post-growth annealing can remove the deep trap and improve the InGaAsN emission, confirming that the deep trap degrades the InGaAsN phase. The feature of the continuum of states suggests that it may be the structural defects associated with lattice expansion or localized states introduced by composition fluctuation.
Fabrication of T-Shaped Gate Diamond Metal–Insulator–Semiconductor Field-Effect Transistors
Authors: Hirama Kazuyuki , Miyamoto Shingo , Matsudaira Hiroki , Umezawa Hitoshi , Kawarada Hiroshi
Published: July 2006

Diamond metal–insulator–semiconductor field effect transistors (MISFETs) with gates of 0.2–0.9 µm length and T-shape were realized by trilayer resist electron-beam lithography. FETs show a cut-off frequency ( f
T) of 11 GHz and maximum oscillation frequency ( f
max) of 22 GHz. The f
max/ f
T ratio of this FET was more than double that of FETs with a conventional gate structure and the same gate length. The f
T of 11 GHz was half the maximum for diamond FETs due to parasitic capacitance at the gate–drain and gate–source electrodes. The T-shaped gate structure and the source-to-drain spacing must be optimized to reduce parasitic capacitance between each electrode.
Magnetic Field Dependence on Electroluminescence Properties of Metal–Insulator–Metal Devices Consisting of Au/GaAs Junctions
Authors: Manago Takashi , Sun Zhi-Gang , Akinaga Hiro
Published: July 2006

We observed electroluminescence (EL) associated with a magnetic-field-dependent avalanche breakdown in a metal–insulator–metal device consisting of semi-insulating (SI-)GaAs with Au contacts. Above a threshold bias voltage, EL emission was observed due to the avalanche breakdown. The peak energy of the EL is approximately 1.4 eV at room temperature. The energy spectra of the EL emission revealed that the dominant charge transport occurs in the bulk region of GaAs and is not a hopping transport in surface states or at the deep levels of impurities on the surface. A magnetic field quenched the EL emission due to the magnetoresistive switch (MRS) effect. The peak energy of the EL spectra depends on current intensity. It is considered that a peak shift is caused by the current crowding effect due to the configuration of the electrodes.
Tribology and Removal Rate Characteristics of Chemical Mechanical Planarization Pads Containing Water Soluble Particles
Authors: Charns L. , Philipossian A.
Published: July 2006

Novel non-porous pads incorporating different amounts of embedded water soluble particles (WSP) have been characterized and compared to a conventional porous pad for interlayer dielectric (ILD) chemical mechanical planarization (CMP) applications. Removal rate results indicated that polishing with WSP pads was Prestonian in nature (similar to conventional porous pads). A decrease in removal rate at high combinations of pressure and velocity was observed during in-situ conditioning with WSP pads. This anomalous behavior was most likely due to the alternatively feeding and starving the wafer of slurry during in-situ conditioning since doubling the flow rate resolved the problem. The anomalous behavior, however, was not observed when conditioning was performed ex-situ. Frictional analysis indicated that polishing with WSP pads proceeded via boundary lubrication like the other porous pads with concentrically grooved surface geometries.
Investigation of NiSi Fully-Silicided Gate on SiO2 and HfO2 for Applications in Metal–Oxide–Semiconductor Field-Effect Transistors
Authors: Huang Chih-Feng , Tsui Bing-Yue
Published: July 2006

Effective work function modulation (Φm,eff) and the thermal/electrical stability of NiSi fully-silicided (FUSI) gates on SiO2 and HfO2 are investigated. A new method, implant-to-silicide, differing from the pre-doped method, is used to realize Φm,eff adjustments. The Φm,eff of NiSi FUSI gates on SiO2 can be tuned by incorporating BF2
+ or P+ dopants after silicidation. Nevertheless, the Fermi-pinning effect was observed in the NiSi/HfO2 gate which limits the Φm,eff adjustment. A thin SiO2 interfacial layer can reduce the Fermi-pinning effect. A NiSi FUSI gate on SiO2 is thermally stable up to 600 °C. The thermal stress and impurity diffusion after a prolonged 600 °C annealing degraded the oxide integration. The temperature of the post-silicidation process should be as low as possible to lessen the thermal stress and impurity diffusion.
Improvement of Variable Ratio of On-Chip Variable Inductors Using Side Shield
Authors: Yammouch Tackya , Sugawara Hirotaka , Okada Kenichi , Masu Kazuya
Published: July 2006

In this study, we propose a novel structure for a variable inductor to improve the variable ratio. To expand the variable ratio of inductance, a side shield is arranged around a conventional variable inductor. The inductor is evaluated using simulation and measured results. The inductance of the proposed inductor varies from 1.01 to 2.40 nH at 5 GHz. The maximum variable ratio of 2.38 is achieved, which is 13% higher than that of the conventional variable inductor.
Characteristics of Single Crystal ZnO Annealed in a Ceramic ZnO Box and Its Application for Epitaxial Growth of GaN
Authors: Kobayashi Atsushi , Ohta Jitsuo , Fujioka Hiroshi
Published: July 2006

We have found that the surfaces of ZnO(0001) annealed in a box made of ceramic ZnO exhibit atomically flat stepped and terraced structures. Structural and optical properties of ZnO are also improved by this annealing technique. Full width at half maximum of X-ray rocking curves of the ZnO substrates were decreased and green photoluminescence caused by defects were eliminated by the annealing. We have also found that epitaxial growth of GaN on atomically flat ZnO(0001) substrates at room temperature proceeds in a layer-by-layer mode, while growth on the as-received substrates results in formation of amorphous materials. These results indicate that the use of the annealing technique improves, not only crystal quality of ZnO substrates, but also morphology of the GaN films grown on them.
Low-Temperature Growth of MgB2Thin films with Tcabove 38 K
Authors: Ueda Kenji , Makimoto Toshiki
Published: July 2006

MgB2thin films with theTcabove 38 K have been fabricated using molecular beam epitaxy (MBE) at the growth temperature below 300 °C. TheTcof 38.2 K was obtained in 1.3-µm-thick MgB2films formed on SiC substrates with AlN buffer layers. TheTcis comparable to those of MgB2single crystals and the highest among MgB2films fabricated below 500 °C. Increase of the film thickness of MgB2above 1 µm was the key point to obtain high-quality films at low growth temperature.
Time-Resolved Coherent Anti-Stokes Raman Scattering of Cyclohexane under Shock Compression
Authors: Oguchi Shiro , Matsuda Akitaka , Kondo Ken-ichi , Nakamura Kazutaka G.
Published: July 2006

Time-resolved coherent anti-Stokes Raman scattering has been performed on cyclohexane under laser-driven shock compression of up to 2 GPa. The ring-breathing and C–C stretching modes exhibit blue shifts, which agree well with that obtained by static-compression experiments. The intensity increase of the shifted peak due to the propagation of the shock wave is observed. Shock velocity is obtained using anti-Stokes Raman scattering (CARS) signal intensity ratio, and agrees well with that estimated from the measured particle velocity and Hugoniot.
Improved Optical Transmittance and Crystal Characteristics of ZnS:TbOF Thin Film on Bi4Ti3O12/Indium Tin Oxide/Glass Substrate by Using a SiO2 Buffer Layer
Authors: Chia Wei-Kuo , Yokoyama Meiso , Yang Cheng-Fu , Chiang Wang-Ta , Chen Ying-Chung
Published: July 2006

Bi4Ti3O12 thin films are deposited on indium tin oxide (ITO)/glass substrates using RF magnetron sputtering technology and are annealed at 675 °C in a rapid thermal annealing furnace in an oxygen atmosphere. The resulting films have high optical transmittances and good crystalline characteristics. ZnS:TbOF films are then deposited on the Bi4Ti3O12 films, causing the originally highly transparent specimens to blacken and to resemble a glass surface coated with carbon powder. The optical transmittance of the specimen is less than 15% under the visible wavelength range, and neither a crystalline phase nor a distinct ZnS grain structure is evident in X-ray diffractometer (XRD) and scanning electronic microscope (SEM). Secondary ion mass spectrometer (SIMS) analysis reveals the occurrence of interdiffusion between the ZnS and Bi4Ti3O12 layers. This suggests that one or more unknown chemical reactions take place among the elements Bi, S, and O at the interface during the deposition of ZnS:TbOF film on a Bi4Ti3O12/ITO/glass substrate. These reactions cause the visible transmittance of the specimens to deteriorate dramatically. To prevent interdiffusion, a silicon dioxide (SiO2) buffer layer 100 nm thick was grown on the Bi4Ti3O12/ITO/glass substrate using plasma-enhanced chemical vapor deposition (PECVD), then the ZnS:TbOF film was grown on the SiO2 buffer layer. The transmittance of the resulting specimen is enhanced approximately 8-fold in the visible region. XRD patterns reveal the ZnS(111)-oriented phase is dominant. Furthermore, dense, crack-free ZnS:TbOF grains are observed by SEM. The results imply that the SiO2 buffer layer sandwiched between the ZnS:TbOF and Bi4Ti3O2 layers effectively separates the two layers. Therefore, interdiffusion and chemical reactions are prevented at the interface of the two layers, and the crystalline characteristics of the ZnS:TbOF layer and the optical transmittance of the specimen are improved as a result. Finally, the dielectric constant of the stacked structure is lower than that of the single layer structure without SiO2, but the dielectric breakdown strength is enhanced.
Ceramic Disc Nonlinear Capacitor Composed of ZrO2-Doped Barium Strontium Titanate for Application in Electronic Switching Circuits
Authors: Chen Yih-Chien
Published: July 2006

Ceramic disc nonlinear capacitors composed of (Ba0.6Sr0.4)TiO3 and ZrO2-doped (Ba0.6Sr0.4)TiO3 for application in electronic switching circuits have been characterized. The grain size is maximum for (Ba0.6Sr0.4)TiO3 doped with 0.5 wt % ZrO2 content. All samples, including (Ba0.6Sr0.4)TiO3 and ZrO2-doped (Ba0.6Sr0.4)TiO3, are in a paraelectric state at room temperature. The capacitance of the specimens decreases with increasing DC biasing voltage. The variation in the energy reduction ratio of the specimens with ZrO2 content has the same trend as that of grain size. The energy reduction ratio is approximately 42% for (Ba0.6Sr0.4)TiO3 doped with 0.5 wt % ZrO2 content.
Stabilization of Bend Alignment Using Optical Polymerization of UV Curable Liquid Crystalline Monomers
Authors: Asakawa Youichi , Yokota Kouji , Nanaumi Makoto , Takatuka Naoki , Takahashi Taiju , Saito Susumu
Published: July 2006

Director profiles and electrooptical properties in polymer-stabilized π cells used in optically compensated bend (OCB) liquid crystal displays (LCDs) are theoretically investigated by introducing an additional term which expresses the effect of polymer stabilization on the free energy density. The conditions required to stabilize the bend alignment definitively have been theoretically clarified and experimentally confirmed. As a result, the bend alignment is successfully stabilized even if the twist state is more stable than the bend state before the application of polymer-stabilization treatment.
Deposition and Properties of the Pseudobinary Alloy (Al2O3)x(TiO2)1-x and Its Application for Silicon Surface Passivation
Authors: Vitanov P. , Harizanova A. , Ivanova T. , Alexieva Z. , Agostinelli G.
Published: July 2006

The electrical properties of (Al2O3)
x
(TiO2)1-x
thin films, obtained from sol solution by spin coating on Si substrates (c-Si or mc-Si), have been studied. By varying the ratios between Al2O3 and TiO2 components, the optical and dielectric characteristics can be changed. This deposition method can be used for effective engineering of physical properties of the dielectric layer. Surface recombination velocities as low as 150 cm/s have been obtained using (Al2O3)
x
(TiO2)1-x
layers on 1 Ω·cm Czochralski (CZ) silicon wafers. Low surface recombination is achieved by field induced surface passivation due to a high density of negative fixed charges.
Nanoimprinting of Thin Polymer Films Using Elementwise Patterned Stamp and Subsequent Application of Pressurized Air
Authors: Sohn Hyonkee , Jeong Jun-Ho , Sim Young-Suk , Kim Ki-Don , Lee Eung-Sug
Published: July 2006

To improve the throughput of ultraviolet nanoimprint lithography (UV-NIL), a cost-effective method of fabricating sub-100-nm-wide line patterns, research studies have been focused on employing a large-area nanostamp. In this paper, we present a new single-step UV-NIL process in which an elementwise patterned stamp (EPS), a 5''×5'' quartz stamp, is first used to imprint resin droplets against a 4'' Si wafer. The EPS consists of 16 elements, each of which is 10×10 mm2, i.e., the effective pattern area is 1,600 mm3. Pressurized air is subsequently applied to the bottom of wafer to improve directly the contact between the wafer and the elements, and resultantly, the uniformity of residual layer thickness. To examine the effects of the pressurized air on the uniformity, we have carried out experiments. Resin droplets with a viscosity of 7 mPa s were dispensed on each element. Results show that the air pressure range of 0.05–0.2 MPa does not significantly affect the average thickness distribution but the uniformity. Line patterns of 70 nm width were successfully imprinted at an air pressure of 0.1 MPa.
X-ray Absorption Fine Structure Study of the Local Structures of Activator Atoms in Gadolinium(3+) Oxy-Orthosilicate Single Crystal
Authors: Yagi Yasuhiro , Usui Tatsuya , Shimizu Shigenori , Kurashige Kazuhisa , Ishibashi Hiroyuki , Susa Kenzo , Honma Tetsuo
Published: July 2006

Measurement of X-ray absorption fine structure (XAFS) was applied to cerium(3+)-activated gadolinium(3+) oxy-orthosilicate system in order to estimate the local structure of the dopant atom. The experimental Ce-LIII edge spectra of X-ray absorption near edge structures of Gd2SiO5:Ce and Gd2SiO5:Ce,Zr indicated that both samples had only the trivalent Ce. The oscillations of extended X-ray absorption fine structures and the patterns of radial structure functions of these examined samples were compared with those of the reference Gd2SiO5. We found that Ce substitutes for Gd at the Gd sites in the matrix of the Gd2SiO5 crystal structure, although we could not proceed further than to show a possibility of Zr substitution at the Gd site. From the analysis using the FEFF simulation of Ce-K edge XAFS, it was revealed that Ce substitutes for Gd uniformly at the two Gd sites in the Gd2SiO5 crystal structure. We performed these experiments at the SPring-8, and succeeded in detecting the signals from the low-concentrated elements such as Ce and Zr in this system.
Enhancement of Barrier Properties Using Ultrathin Hybrid Passivation Layer for Organic Light Emitting Diodes
Authors: Bae Sung Jin , Lee Joo Won , Park Jung Soo , Kim Dong Young , Hwang Sung Woo , Kim Jai-Kyeong , Ju Byeong-Kwon
Published: July 2006

The hybrid thin-film (HTF) passivation layer composed of the UV curable acrylate layer and MS-31 (MgO:SiO2=3:1 wt %) layer was adopted in organic light emitting diode (OLED) to protect organic light emitting materials from penetrations of oxygen and water vapors. The moisture resistance of the deposited HTF layer was measured by the water vapor transmission rate (WVTR). The results showed that the HTF layer possessed a very low WVTR value of lower than 0.007 g/(m2 ·day) at 37.8 °C and 100% RH. Therefore, the HTF on the OLED was found to be very effective in protect what from the penetrations of oxygen and moisture.
Measurements of Heterodyne Efficiency for Ground-Based Coherent Doppler Lidar Using the Portable Diffuse Target
Authors: Sakaizawa Daisuke , Nagasawa Chikao , Mizutani Kohei
Published: July 2006

The heterodyne efficiency of the coherent Doppler lidar (CDL) is a key parameter in the determination of its operational performance. The spatial coherence of the backscattering signal is affected by the fluctuations in the atmospheric refractive index (caused by atmospheric fluctuations) during the propagation of the laser in the atmosphere. We present the analytical equation that includes atmospheric fluctuations and measure the heterodyne efficiency for a 2.0-µm CDL. The experimental results are in the good agreement with the simulated predictions and certify the validity of the analytical equation including the atmospheric fluctuations.
Production of Stable Ion Beam of Os3(CO)12 with Compact Metal-Cluster-Complex Ion Source
Authors: Fujiwara Yukio , Kondou Kouji , Teranishi Yoshikazu , Nonaka Hidehiko , Fujimoto Toshiyuki , Kurokawa Akira , Ichimura Shingo
Published: July 2006

Metal-cluster-complex ion beams were produced stably using a cluster ion source, which is compact enough to be installed in commonly used secondary ion mass spectrometry (SIMS) systems. As a metal cluster complex, triosmium dodecacarbonyl, Os3(CO)12, was utilized, which has a molecular weight of 906.7. Since precise temperature control is necessary to sublimate the metal cluster complex stably without thermal decomposition, the ion source was equipped with compact heat-removal devices in addition to an external heater. Experimental results showed that the crucible temperature of the metal cluster complex can be maintained at about 130 °C in continuous operation, which is an appropriate temperature for sublimation without the problem of decomposition. The ion source produced steady-state beams of Os3(CO)
n

+ (n=7 or 8) ions with a beam current exceeding 10 nA at 10 keV. Beam current increased with gas pressure, depending on the temperature of the crucible holding the metal cluster complex. The rate of the change in beam current was within a few percent per hour; hence, in view of stability, the ion source was confirmed as usable in SIMS. Furthermore, beam profile was investigated using a Faraday cup with a knife-edge as well as a GaAs/AlAs multilayer substrate as a beam target.
Effect of Interactive Damping on Vibration Sensitivities of V-Shaped Atomic Force Microscope Cantilevers
Authors: Lee Haw-Long , Yang Yu-Ching , Chang Win-Jin , Chu Shao-Shu
Published: July 2006

This article analyzes the interactive damping effect on the sensitivity of flexural and torsional vibration modes of a V-shaped atomic force microscope (AFM) cantilever. The interaction of the cantilever with the sample surface is modeled by a combination of a spring parallel to a dashpot in the normal direction and a similar combination in the lateral direction. An approximate form for the sensitivities of both modes was derived based on the method of Rayleigh–Ritz. Using the approximate formula, predictions of modal sensitivity may be made to design cantilevers with optimum sensitivity for specified uses. The results show that the effect of interactive damping is significant and should not be disregarded in the design of V-shaped AFM cantilevers. Interactive damping decreases the sensitivities of both flexural and torsional vibration modes when the contact stiffness is low.
Scanning Tunneling Microscopy Observations of Proton and Metal Cation Catching Behavior of Embedded Bipyridine Thiols in Alkanethiol Self-Assembled Monolayers on Au(111)
Authors: Ishida Takao , Koyama Emiko , Tokuhisa Hideo , Nakamura Tohru , Kanesato Masatoshi , Mizutani Wataru
Published: July 2006

We studied the ion catching behavior of nanoscale molecular domains of bipyridine thiol embedded in alkanethiol self-assembled monolayers (SAMs) on Au(111) by scanning tunneling microscopy (STM) to construct and demonstrate the possibility of a molecular sensor. We used a bromine-terminated bipyridine thiol molecule, in which a bipyridine unit is connected to a conjugated phenylene–ethynylene system, and then successfully observed the protonation response of the bipyridine molecule. When the Au substrate was immersed into dilute CF3SO3H solution, the apparent height of bipyridine spots became lower after this treatment. On the other hand, when the substrate was immersed into 0.1 mM Pd complex solution, the apparent height of bipyridine spots became higher than that in the initial state. These findings demonstrate the possibility of constructing cation sensor using several molecular domains, and the different ion catching behaviors of bipyridine molecules may lead to the development of highly selective molecular sensors.
Effects of Strong Static Magnetic Fields on Amphibian Development and Gene Expression
Authors: Kawakami Satomi , Kashiwagi Keiko , Furuno Nobuaki , Yamashita Masamichi , Kashiwagi Akihiko , Tanimoto Yoshifumi
Published: July 2006

This investigation attempts to clarify the effects of strong vertical and static magnetic fields (SMFs) of 11–15 T on Xenopus laevis development and on Xotx2 (an important regulator of fore- and midbrain morphogenesis) and Xag1 (essential for cement gland formation) gene expression. Results showed that (1) a strong SMF significantly retarded normal development and induced microcephaly, two heads, abnormal cement glands and multiple malformations, indicating that SMF inhibits normal embryonic development, (2) a strong SMF suppressed Xotx2 and Xag1 expression.
Regulation of Commissural Axon Pathfinding by Slit and its Robo Receptors
Authors: Dickson Barry J. , Gilestro Giorgio F.
Published: July 2006

Commissural axons grow along complex pathways toward, across, and beyond the midline of the central nervous system. Taking commissural axons in the vertebrate spinal cord and the Drosophila ventral nerve cord as examples, we examine how commissural axon pathfinding is regulated by the Slit family of guidance cues and their Robo family receptors. We extract several principles that seem likely to apply to other axons and other contexts, such as the reiterative use of the same guidance molecules in distinct pathfinding decisions, the transcriptional specification of a pathway, the posttranscriptional regulation of growth along the pathway, and the possible role of feedback mechanisms to ensure the fidelity of pathfinding choices. Such mechanisms may help explain how a relatively small number of guidance molecules can generate complex and stereotyped wiring patterns. We also highlight the many gaps in our understanding of commissural axon pathfinding and question some widely accepted views. We hope that this review encourages further efforts to tackle these questions, in the expectation that this system will continue to reveal the general principles of axon pathfinding.
Epidermal Stem Cells of the Skin
Authors: Blanpain Cédric , Fuchs Elaine
Published: July 2006

The skin constantly renews itself throughout adult life, and the hair follicle undergoes a perpetual cycle of growth and degeneration. Stem cells (SCs) residing in the epidermis and hair follicle ensure the maintenance of adult skin homeostasis and hair regeneration, but they also participate in the repair of the epidermis after injuries. We summarize here the current knowledge of epidermal SCs of the adult skin. We discuss their fundamental characteristics, the methods recently designed to isolate these cells, the genes preferentially expressed in the multipotent SC niche, and the signaling pathways involved in SC niche formation, SC maintenance, and activation. Finally, we speculate on how the deregulation of these pathways may lead to cancer formation.
Assessing the Vulnerability of Social-Environmental Systems
Authors: Eakin Hallie , Luers Amy Lynd
Published: July 2006

▪ Abstract  In this review, we highlight new insights into the conceptualization of the vulnerability of social-environmental systems and identify critical points of convergence of what otherwise might be characterized as disparate fields of research. We argue that a diversity of approaches to studying vulnerability is necessary in order to address the full complexity of the concept and that the approaches are in large part complementary. An emerging consensus on the issues of critical importance to vulnerability reduction—including concerns of equity and social justice—and growing synergy among conceptual frameworks promise even greater relevancy and utility for decision makers in the near future. We synthesize the current literature with an outline of core assessment components and key questions to guide the trajectory of future research.
Global Marine Biodiversity Trends
Authors: Sala Enric , Knowlton Nancy
Published: July 2006

▪ Abstract  Marine biodiversity encompasses all levels of complexity of life in the sea, from within species to across ecosystems. At all levels, marine biodiversity has naturally exhibited a general, slow trajectory of increase, punctuated by mass extinctions at the evolutionary scale and by disturbances at the ecological scale. In historical times, a synergy of human threats, including overfishing, global warming, biological introductions, and pollution, has caused a rapid decline in global marine biodiversity, as measured by species extinctions, population depletions, and community homogenization. The consequences of this biodiversity loss include changes in ecosystem function and a reduction in the provision of ecosystem services. Global biodiversity loss will continue and likely accelerate in the future, with potentially more frequent ecological collapses and community-wide shifts. However, the timing and magnitude of these catastrophic events are probably unpredictable.
Soils: A Contemporary Perspective
Authors: Palm Cheryl , Sanchez Pedro , Ahamed Sonya , Awiti Alex
Published: July 2006

Soils are viewed in the context of ecosystem services, soil processes and properties, and key attributes and constraints. The framework used is based on the premise that the natural capital of soils that underlies ecosystem services is primarily determined by three core soil properties: texture, mineralogy, and soil organic matter. Up-to-date descriptions and geographical distribution of soil orders as well as soil attributes and constraints are given, along with the relationships between soil orders, properties, and biomes. We then relate ecosystem services to specific soil processes, soil properties, and soil constraints and attributes. Soil degradation at present is not adequately assessed and quantified. The use of an approach combining digital soil maps, pedotransfer functions, remote sensing, spectral analysis, and soil inference systems is suggested for simultaneous characterization of various chemical, physical, and biological properties to overcome the great limitations and costs of conventional methods of soil assessments.
Genome-Wide Analysis of Protein-DNA Interactions
Authors: Kim Tae Hoon , Ren Bing
Published: July 2006

The human genome is predominantly composed of nonprotein-coding sequences whose function remains largely undefined. A significant portion of the noncoding DNA is believed to serve as transcriptional regulatory elements that control gene expression in specific cell types at appropriate developmental stages. Identifying these regulatory sequences and determining the mechanisms by which they act present a great challenge in the postgenomic era. Previous investigations using genetic, molecular, and biochemical approaches have uncovered a large number of proteins involved in regulating transcription. Knowledge of the genomic locations of DNA binding for these proteins in the nucleus should define the identity and nature of the transcriptional regulatory sequences and reveal the gene regulatory networks in cells. Chromatin immunoprecipitation (ChIP) is a common method for detecting interactions between a protein and a DNA sequence in vivo. In recent years, this method has been combined with DNA microarrays and other high-throughput technologies to enable genome-wide identification of DNA-binding sites for various nuclear proteins. Here, we review recent advances in ChIP-based methods for genome-wide detection of protein-DNA interactions, and discuss their significance in enhancing our knowledge of the gene regulatory networks and epigenetic mechanisms in cells.
The Biology of theCryptococcus neoformansSpecies Complex
Authors: Lin Xiaorong , Heitman Joseph
Published: July 2006

Cryptococcus neoformans is a major cause of fungal meningoencephalitis in immunocompromised patients. Despite recent advances in the genetics and molecular biology of C. neoformans, and improved techniques for molecular epidemiology, aspects of the ecology, population structure, and mode of reproduction of this environmental pathogen remain to be established. Application of recent insights into the life cycle of C. neoformans and its different ways of engaging in sexual reproduction under laboratory conditions has just begun to affect research on the ecology and epidemiology of this human pathogenic fungus. The melding of these disparate disciplines should yield rich dividends in our understanding of the evolution of microbial pathogens, providing insights relevant to diagnosis, treatment, and prevention.
Environmental Biology of the Marine Roseobacter Lineage
Authors: Wagner-Döbler Irene , Biebl Hanno
Published: July 2006

The Roseobacter lineage is a phylogenetically coherent, physiologically heterogeneous group of α-Proteobacteria comprising up to 25% of marine microbial communities, especially in coastal and polar oceans, and it is the only lineage in which cultivated bacteria are closely related to environmental clones. Currently 41 subclusters are described, covering all major marine ecological niches (seawater, algal blooms, microbial mats, sediments, sea ice, marine invertebrates). Members of the Roseobacter lineage play an important role for the global carbon and sulfur cycle and the climate, since they have the trait of aerobic anoxygenic photosynthesis, oxidize the greenhouse gas carbon monoxide, and produce the climate-relevant gas dimethylsulfide through the degradation of algal osmolytes. Production of bioactive metabolites and quorum-sensing-regulated control of gene expression mediate their success in complex communities. Studies of representative isolates in culture, whole-genome sequencing, e.g., of Silicibacter pomeroyi, and the analysis of marine metagenome libraries have started to reveal the environmental biology of this important marine group.
Radical Enzymes in Anaerobes
Authors: Buckel Wolfgang , Golding Bernard T.
Published: July 2006

This review describes enzymes that contain radicals and/or catalyze reactions with radical intermediates. Because radicals irreversibly react with dioxygen, most of these enzymes occur in anaerobic bacteria and archaea. Exceptions are the families of coenzyme B12- and S-adenosylmethionine (SAM)-dependent radical enzymes, of which some members also occur in aerobes. Especially oxygen-sensitive radical enzymes are the glycyl radical enzymes and 2-hydroxyacyl-CoA dehydratases. The latter are activated by an ATP-dependent one-electron transfer and act via a ketyl radical anion mechanism. Related enzymes are the ATP-dependent benzoyl-CoA reductase and the ATP-independent 4-hydroxybenzoyl-CoA reductase. Ketyl radical anions may also be generated by one-electron oxidation as shown by the flavin-adenine-dinucleotide (FAD)- and [4Fe-4S]-containing 4-hydroxybutyryl-CoA dehydratase. Finally, two radical enzymes are discussed, pyruvate:ferredoxin oxidoreductase and methane-forming methyl-CoM reductase, which catalyze their main reaction in two-electron steps, but subsequent electron transfers proceed via radicals.
Streamlining and Simplification of Microbial Genome Architecture
Authors: Lynch Michael
Published: July 2006

The genomes of unicellular species, particularly prokaryotes, are greatly reduced in size and simplified in terms of gene structure relative to those of multicellular eukaryotes. Arguments proposed to explain this disparity include selection for metabolic efficiency and elevated rates of deletion in microbes, but the evidence in support of these hypotheses is at best equivocal. An alternative explanation based on fundamental population-genetic principles is proposed here. By increasing the mutational target sizes of associated genes, most forms of nonfunctional DNA are opposed by weak selection. Free-living microbial species have elevated effective population sizes, and the consequent reduction in the power of random genetic drift appears to be sufficient to enable natural selection to inhibit the accumulation of excess DNA. This hypothesis provides a potentially unifying explanation for the continuity in genomic scaling from prokaryotes to multicellular eukaryotes, the divergent patterns of mitochondrial evolution in animals and land plants, and various aspects of genomic modification in microbial endosymbionts.
Curvature and tortuosity of the superficial femoral artery: a possible risk factor for peripheral arterial disease
Authors: Wood N. B. , Zhao S. Z. , Zambanini A. , Jackson M. , Gedroyc W. , Thom S. A. , Hughes A. D. , Xu X. Y.
Published: July 2006

Atherosclerosis in the superficial femoral artery (SFA) resulting in peripheral arterial disease is more common in men than women and shows a predilection for the region of the adductor canal. Blood flow patterns are related to development of atherosclerosis, and we investigated if curvature and tortuosity of the femoral artery differed between young men and women and if differences resulted in adverse flow patterns. Magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) were combined in 18 young adult volunteers (9 men) to assess the relationship of flow features to likely sites of future atherosclerosis formation. Subjects underwent MRI of the right SFA, three-dimensional vascular geometry was reconstructed, and measures of tortuosity and curvature were calculated. Tortuosity and curvature were significantly greater for men than women, and this was related to increased body surface area, body mass index, or weight in men. In both sexes, “tortuosity” increased from the midthigh to the popliteal fossa. The greatest curvature was found within the distal quarter of the SFA. CFD modeling was undertaken on MRI-based reconstructions of the SFA. Wall shear stresses (WSS) were extracted from the computations. WSS showed greater spatial variation in the men than in the women, and the men exhibited lower mean WSS. These data indicate that sex differences related to body size and anatomical course of the femoral artery may contribute to the enhanced risk of focal atherosclerosis in the adductor canal.
Dynamic modulation of upper airway function during sleep: a novel single-breath method
Authors: Kirkness Jason P. , Schwartz Alan R. , Patil Susheel P. , Pichard Luis E. , Marx Jason J. , Smith Philip L. , Schneider Harmut
Published: July 2006

To examine the dynamic modulation of upper airway (UA) function during sleep, we devised a novel approach to measuring the critical pressure (Pcrit) within a single breath in tracheostomized sleep apnea patients. We hypothesized that the UA continuously modulates airflow dynamics during transtracheal insufflation. In this study, we examine tidal pressure-flow relationships throughout the respiratory cycle to compare phasic differences in UA collapsibility between closure and reopening. Five apneic subjects (with tracheostomy) were recruited (2 men, 3 women; 18–50 yr; 20–35 kg/m2; apnea-hypopnea index >20) for this polysomnographic study. Outgoing airflow through the UA (face mask pneumotachograph) and tracheal pressure were recorded during brief transtracheal administration of insufflated airflow via a catheter. Pressure-flow relationships were generated from deflation (approaching Pcrit) and inflation (after Pcrit) of the UA during non-rapid eye movement sleep. During each breath, UA function was described by a pressure-flow relationship that defined the collapsibility (Pcrit) and upstream resistance (Rus). UA characteristics were examined in the presence and absence of complete UA occlusion. We demonstrated that Pcrit and Rus changed dynamically throughout the respiratory cycle. The UA closing pressure (4.4 ± 2.0 cmH2O) was significantly lower than the opening pressure (10.8 ± 2.4 cmH2O). Rus was higher for deflation (18.1 ± 2.4 cmH2O·l−1·s) than during inflation (7.5 ± 1.9 cmH2O·l−1·s) of the UA. Preventing occlusion decreases UA pressure-flow loop hysteresis by ∼4 cmH2O. These findings indicate that UA collapsibility varies dynamically throughout the respiratory cycle and that both local mechanical and neuromuscular factors may be responsible for this dynamic modulation of UA function during sleep.
Convergent validity of six methods to assess physical activity in daily life
Authors: Macfarlane Duncan J. , Lee Cherry C. Y. , Ho Edmond Y. K. , Chan K. L. , Chan Dionise
Published: July 2006

The purpose was to examine the agreement (convergent validity) between six common measures of habitual physical activity to estimate durations of light, moderate, vigorous, and total activity in a range of free-living individuals. Over 7 consecutive days, 49 ethnic Chinese (30 men, 19 women), aged 15–55 yr, wore a Polar heart rate monitor, a uniaxial MTI, and triaxial Tritrac accelerometer, plus a Yamax pedometer for ≥600 min/day. They also completed a daily physical activity log and on day 8 a Chinese version of the 7-day International Physical Activity Questionnaire. At each level of activity, there was good agreement between the two questionnaire-derived instruments and the two accelerometry-derived instruments, but wide variation across different instruments, with two- to fourfold differences in mean durations often seen. The heart rate monitor overestimated light activity and underestimated moderate activity compared with all other measures. Spearman correlation coefficients were low to moderate (0.2–0.5) across most measures of activity, with the pedometer showing correlations with total activity that were often superior to the other movement sensors. We conclude that, with the use of commonly accepted cut points for defining light, moderate, vigorous, and total activity, little convergent validity across the instruments was evident, suggesting these measures are sampling different levels of habitual physical activity and care is needed when comparing their results. To provide a more stable comparison of activity among different people, across studies, or against accepted physical activity promotion guidelines, further work is needed to fine tune the different cut points across a range of common activity monitors to provide more consistent results during free-living conditions.
Molecular Dissection of 17q12 Amplicon in Upper Gastrointestinal Adenocarcinomas
Authors: Maqani Nazif , Belkhiri Abbes , Moskaluk Christopher , Knuutila Sakari , Dar Altaf A. , El-Rifai Wael
Published: July 2006

DNA amplification at 17q is frequently detected in upper gastrointestinal adenocarcinomas (UGC; stomach and esophagus). In this study, we did fluorescence in situ hybridization on a tissue microarray that contained 304 UGCs and 89 normal stomach samples using a ∼168-kb BAC clone (CTD-2019C10) that maps to 17q12-q21.1. This 168-kb region contains the following genes: PPP1R1B/DARPP-32, STARD3, TCAP, PNMT, PERLD1, ERBB2, C17orf37, and GRB7 as well as the first two exons of ZNFN1A3. DNA amplification (≥5 signals) was detected in 85 of 282 (30%) of UGCs, and high-level amplification (≥10 signals) was seen in 28 of 282 (10%) of all tumors. Adenocarcinomas of gastroesophageal junction and lower esophagus had the highest frequency of amplification (45%) compared with stomach tumors (27%; P = 0.04). On the other hand, 38% of tumors with intestinal-type morphology had amplification compared with 26% of diffuse-type tumors (P = 0.02). We further did quantitative real-time reverse transcription-PCR on 74 frozen tissue samples from UGCs for 11 genes located within or adjacent to the boundaries of this ∼168-kb genomic region. These genes include all 9 genes that are fully or partially located inside the CTD-2019C10 clone as well as 2 additional adjacent genes (NEUROD and TOP2A). Overexpression of PPP1R1B/DARPP-32, TCAP, and TOP2A was seen in approximately half of the tumors, whereas STARD3 and ZNFN1A3 were rarely overexpressed (12%). Interestingly, there was a statistical correlation between expression of all 8 genes that map between PPP1R1B/DARPP-32 and GRB7, whereas expression of NEUROD, ZNFN1A3, and TOP2A that are partially inside or adjacent to the boundaries of the CTD-2019C10 clone did not correlate with the expression of any of these 8 genes. These data show a transcriptionally active oncogenomic region bounded by PPP1R1B/DARPP-32 and GRB7 in UGCs and provide further insight into expression levels of several critical genes. (Mol Cancer Res 2006;4(7):449–55)
Vocal Loading-Related Changes in Male Teachers’ Voices Investigated before and after a Working Day
Authors: Laukkanen Anne-Maria , Kankare Elina
Published: July 2006

Vocal loading-related changes have mainly been investigated in female voice users. The present study investigated male teachers’ voices before and after a working day. A questionnaire was used to select 22 male teachers as subjects from a larger group. Ten reported suffering often from symptoms of vocal fatigue (MC = multiple complaints group), 12 reported few vocal complaints (FC group). The subjects recorded a text reading sample at habitual loudness and loudly, and sustained vowel [a:] before and after an approximately 6-hour working day. Text samples were analyzed for total sound pressure level (SPL) and SPL at three frequency regions (50–1,000 Hz, 1–2 kHz, 2–5 kHz), fundamental frequency (F0) and alpha ratio [(SPL 1–5 kHz) – SPL (50 Hz–1 kHz)]. Jitter and shimmer were calculated from the vowel. The subjects filled in a questionnaire about vocal sensations. The MC group reported more symptoms of vocal fatigue, and the symptoms increased during the working day. F0 and SPL increased in both groups. Alpha ratio increased in the MC group but remained the same in the FC group. The MC group had higher values of jitter and shimmer. Jitter diminished in the FC group but did not change significantly in the MC group. The differences between the groups reflect either different strategies for coping with vocal loading or different loading-induced changes in the vocal organ.
Utility of the Type D Scale 16 and Voice Handicap Index to Assist Voice Care in Student Teachers and Teachers
Authors: Thomas G. , de Jong F.I.C.R.S. , Kooijman P.G.C. , Cremers C.W.R.J.
Published: July 2006

An epidemiological cross-sectional survey study was performed among female student teachers and teachers for primary education, using a general questionnaire, the Type D Scale 16 (DS16) and Voice Handicap Index (VHI). Type D personality is the combination of high ‘negative affectivity’ and high ‘social inhibition’, and the DS16 has been considered to be a reliable and valid measure of these two stable personality traits. The objectives of the study were to assess the VHI of type D subjects in comparison to non-type-D subjects, to explore the utility of the DS16 and the VHI to assess whether subjects with a type D personality were more handicapped due to their voice complaints, and whether they behaved differently in seeking voice care. It was investigated whether subjects of the type D group in comparison to the non-type-D group had a voice handicap even when they did not report voice complaints. The type D group did not report more voice complaints than the non-type-D group. However, the type D group had higher VHI scores compared to the non-type-D group. Furthermore, significantly more type D subjects had a VHI score greater than the 75th percentile than the non-type-D subjects, and they sought less voice care than the non-type-D subjects. Also among subjects who reported voice complaints, the type D group sought less care than the non-type-D group. Even among the subjects who did not report voice complaints, significantly more type D than non-type-D subjects had VHI scores higher than the 75th percentile. The findings indicated that type D subjects were apparently more bothered by their voice than the non-type-D subjects (high VHI scores); however, they did not report more voice complaints, and they also sought less voice care. The DS16 used along with the VHI was useful to identify subjects of the type D trait with a voice handicap. This enables specific voice care, encompassing not only physical, but also psychosocial aspects of vocal health.