bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlled catalytic growth and characterization of zinc oxide nanopillars on a-plane sapphire
Authors: Reiser A. , Ladenburger A. , Prinz G. M. , Schirra M. , Feneberg M. , Langlois A. , Enchelmaier R. , Li Y. , Sauer R. , Thonke K.
Published: March 2007

Using the vapor-liquid-solid (VLS) technique, we have grown well-aligned nanopillars on [112¯0]-sapphire (a-plane) substrates at atmospheric pressure in a horizontal tube furnace employing gold catalyst seeds of different sizes and densities. It was the aim of the present work to find experimental conditions (source and template temperatures, temperature gradients, carrier gas flow, gold cluster size and density) under which controlled catalytic growth of nanopillars takes place. The VLS process is expected to result in a correlation of the zinc oxide (ZnO) pillar diameters with the gold catalyst cluster size. This is indeed found to hold true except for very small gold clusters. A minimum value of the pillar diameter of about 20 nm on a-plane sapphire is obtained in our experiments, which apparently represents a general limit. Structure characterization relies on high-resolution x-ray diffraction, atomic force microscopy, and high-resolution scanning electron microscopy. Electronic characterization is done by Raman and standard luminescence measurements with large area (≈1 mm2) excitation. In particular, we have also studied individual nanopillars by spatially highly resolved cathodoluminescence spectroscopy. We find that luminescence averaged over large areas can be dominated by features which are not typical for well-shaped pillars but come from regions of irregular ZnO growth.
Local viscosity measurements using oscillating magnetic holes
Authors: Svåsand Eldrid , Skjeltorp Arne T. , Akselvoll Jørgen , Helgesen Geir
Published: March 2007

Many complex fluids are only available in tiny quantities or used in confined regions. The task of measuring their rheological properties is then a challenge. Here we present a method showing how the viscosity of very small volumes of ferrofluid may be measured using immersed nonmagnetic spherical microparticles. In the suspension these act as magnetic holes in the ferrofluid which may be manipulated by external magnetic fields. When the effects of nearby walls as well as other spheres are taken into account, the results are consistent with viscosity values reported from standard bulk measurement techniques.
Spatially and temporally resolving the degradation of n-channel poly-Si thin-film transistors under hot-carrier stressing
Authors: Lee Ming-Hsien , Chang Kai-Hsiang , Lin Horng-Chih
Published: March 2007

A test structure was proposed to investigate the spatial and temporal evolution of hot-carrier degradation in n-channel poly-Si thin-film transistors. Our experimental results clearly show that the initial damage during the early stage of hot-carrier stressing, which is still undetectable by conventional test structures, can be easily observed by the structure. In addition, the proposed test structure is also capable of resolving the evolution of the degradation along the channel, thus providing a powerful tool to study the location-dependent damage mechanisms.
Electrical and structural characterization of Mg-doped p-type Al0.69Ga0.31N films on SiC substrate
Authors: Chakraborty Arpan , Moe Craig G. , Wu Yuan , Mates Tom , Keller Stacia , Speck James S. , DenBaars Steven P. , Mishra Umesh K.
Published: March 2007

We report on the electrical and structural characterization of Mg-doped Al-rich p-type Al0.69Ga0.31N alloys on SiC substrate grown by metal organic chemical vapor deposition. The impact of growth conditions and dopant activation annealing conditions on the electrical conductivity was investigated. The most efficient activation was achieved by annealing in N2 gas at 1000°C for 3min in the presence of a SiO2 cap. The impact of p-GaN contact layer thickness was also studied. Higher growth temperature resulted in lower Mg incorporation, and for constant Mg concentration the resistivity increased with the increase in the growth temperature. Mg incorporation increased linearly with Mg effective flow. Transmission electron microscopy revealed the generation of vertical spike-like defects with increasing Mg doping. The resistivity also increased with the increase in Mg doping. A minimum resistivity of 10Ωcm was achieved at 670K.
Three-dimensional particle-in-cell simulations of 300GHz reflex klystrons
Authors: Jeon S. G. , Jin Y. S. , Kim J. I. , Kim G. J. , Shon C. H.
Published: March 2007

Three-dimensional (3D) particle-in-cell simulations of 300GHz reflex klystrons are presented. 300GHz electromagnetic wave generation in a resonant cavity is analyzed by using a 3D simulation model in which all the geometric parameters (such as the grid thickness, repeller shape, beam radius, etc.) are described. When an electron beam of an energy of 1.0keV and a net current of 8.9mA is used, the maximum electronic efficiency of energy transfer is observed when the gap transit angle is 0.7πrad, and the efficiency saturates when the beam current is over 10mA. Space charge forces produce a shift in the optimum repeller voltage. It is also shown that the effect of the beam temperature is not critical, even though the bunching wavelength of the electron beam is several times smaller than that in conventional vacuum electron devices. Our simulation results show that a microfabricated 300GHz reflex klystron can directly generate electromagnetic waves with output power levels of several tens of milliwatts.
Tunable thin film polarizer for the vacuum ultraviolet and soft x-ray spectral regions
Authors: Yang Minghong , Cobet Christoph , Esser Norbert
Published: March 2007

A low pass polarizer that suppresses higher-order diffraction light from vacuum ultraviolet and soft x-ray monochromators is presented in this paper. This vacuum ultraviolet and soft x-ray polarizer is based on a concept of sandwiched metal-dielectric-metal triple reflection configuration. By appropriate optimization of material and angle of incidence, the proposed Au–SiC–Au polarizer demonstrates the capability of matching to desired cutoff edge of photon energy. Furthermore, the optimized soft x-ray polarizer shows the possibility to tune cutoff photon energy in a broadband spectral region ranging from 80 down to down to 20eV.
Heat treatment of metal-capped SiO2 films containing Si nanocrystals
Authors: Jensen J. Skov , Buttenschön D. A. , Pedersen T. P. Leervad , Chevallier J. , Nielsen B. Bech , Larsen A. Nylandsted
Published: March 2007

SiO 2 films containing Si nanocrystals and capped with different metal layers (Al, Pd, and Pt) were annealed in a gas containing hydrogen and subsequently studied by photoluminescence (PL). All metal layers were found to greatly increase the photoluminescence from the Si nanocrystals. However, the Pt layer was found to be the most efficient giving rise to a PL increase of 32 times as compared to that of an untreated film.
Transport phenomena during direct metal deposition
Authors: He X. , Mazumder J.
Published: March 2007

The evolution of temperature and velocity fields during direct metal deposition with coaxial powder injection was simulated using a self-consistent three-dimensional model based on the solution of the equations of mass, momentum, energy conservation, and solute transport in the liquid pool. The basic physical phenomena, including heat transfer, phase changes, mass addition, fluid flow, and interactions between the laser beam and the coaxial powder flow, were considered in the model. The level-set method was implemented to track the evolution of the liquid/gas interface. The temperature and velocity fields, liquid/gas interface, and energy distribution at liquid/gas interface at different times were simulated. For verification purposes, the cladding depth and height were compared with experimental results.
Determining vibrational heat capacity and thermal expansivity and their change at glass-liquid transition
Authors: Johari G. P.
Published: March 2007

The vibrational parts of a liquid’s heat capacity Cp and thermal expansion coefficient α may be determined from dynamic measurements. The Cp data for Pd40Ni40P20 and 0.4Ca(NO3)2∙0.6 KNO3 have been analyzed accordingly, and it is found that change in the vibrational part at liquid-glass transformation is negligible. Analysis for α of poly(styrene) leads to the same conclusion. There is no discontinuity in the vibrational parts of Cp and α on structural unfreezing in the Tg range, and hence the change in Cp and α at Tg is almost entirely due to change in the configurational part. Crystallization decreases the vibrational part not because the molecular mobility is lost but because the density increases.
Main characteristics of the fast disruption mitigation valve
Authors: Bozhenkov S. A. , Finken K.-H. , Lehnen M. , Wolf R. C.
Published: March 2007

The article presents a detailed investigation of the fast disruption mitigation valve developed at FZJ Juelich. The essence of this study is the novel direct observation of the piston motion by means of a fast framing camera. The piston stroke and the injection duration are shown to strongly depend on the operational pressure and the used gas. The same is true for the valve throughput. The analysis revealing the leading contribution of the injection duration in this modification is given. The knowledge of the injection duration is also used to reconstruct the characteristic pressure decay rates and the gas outflow rates. The means to increase the gas outflow are discussed. The main found valve characteristics are: (1) valve reaction time, i.e., the delay between the application of the trigger signal and the achievement of reliably observable opening 0.5 mm, is about 0.3 ms; (2) the maximum achieved throughput is 7.5 bar l for argon and 9.5 bar l for helium; (3) the maximum delivery rates are 500 bar l s−1 for Ar and 1500 bar l s−1 for He.
A precise method to determine the angular distribution of backscattered light to high angles
Authors: Gross P. , Störzer M. , Fiebig S. , Clausen M. , Maret G. , Aegerter C. M.
Published: March 2007

We present an approach to measure the angular dependence of the diffusely scattered intensity of a multiple scattering sample in backscattering geometry. Increasing scattering strength give rise to an increased width of the coherent backscattering and sets higher demands on the angular detection range. This is of particular interest in the search for the transition to Anderson localization of light. To cover a range of −60° to +85° from direct back-reflection, we introduced a new parallel intensity recording technique. This allows one-shot measurements, with fast alignment and short measuring time, which prevents the influence of illumination variations. Configurational average is achieved by rotating the sample and singly scattered light is suppressed with the use of circularly polarized light up to 97%. This implies that backscattering enhancements of almost two can be achieved. In combination with a standard setup for measuring small angles up to ±3°, a full characterization of the coherent backscattering cone can be achieved. With this setup we are able to accurately determine transport mean free paths as low as 235 nm.
Red and near infrared polarized light emissions from polyfluorene copolymer based light emitting diodes
Authors: Gadisa Abay , Perzon Erik , Andersson Mats R. , Inganäs Olle
Published: March 2007

The authors report polarized red, electroluminescence peak at 705nm and near infrared, electroluminescence peak at 950nm, light emission from light emitting diodes based on two polyfluorene copolymers. The copolymers are synthesized from a fluorene monomer combined with donor-acceptor-donor comonomers and designed to have a low band gap and form birefringent liquid crystalline phases. Emission occurs from aligned thin films of polymer layers. The emissive layers are aligned by spin coating on a layer of rubbed conducting polymer poly(3,4-ethylene dioxythiophene)-poly(styrene sulphonate) and thermally converted into glassy nematic liquid crystalline state.
Radio-frequency dielectric-barrier glow discharges in atmospheric argon
Authors: Shi J. J. , Kong M. G.
Published: March 2007

In this letter, an experimental investigation is presented to characterize the properties and benefits of radio-frequency (rf) dielectric-barrier discharges (DBDs) in atmospheric argon. Compared to rf atmospheric glow discharges generated with bare electrodes, atmospheric argon rf DBDs are shown to remain stable and uniform over a large current range from the α and the γ modes. Optical emission spectroscopy is used to show an active underpinning plasma chemistry and a gas temperature range of 461–562K. These highlight the advantages of argon rf DBD as a surface processing technique over more expensive helium-based rf atmospheric glow discharges.
Electron capture acceleration channel in a slit laser beam
Authors: Wang P. X. , Scheid W. , Ho Y. K.
Published: March 2007

Using numerical simulations, the authors find that the electrons can be captured and accelerated to high energies (GeV) in a slit laser beam with an intensity of Iλ2∼1020W∕cm2μm2, where λ is the laser wavelength in units of μm. The range of the optimum incident energy is very wide, even up to GeV. These results are of interest for experiments because the relatively low intensity can be achieved with present chirped pulse amplification technique and a wide range of incident energies means that a multistage acceleration is possible.
Exchange bias effect and enhanced magnetoresistance in La0.67Sr0.33MnO3∕SrTiO3 superlattices
Authors: Zhu S. J. , Yuan J. , Zhu B. Y. , Zhang F. C. , Xu B. , Cao L. X. , Qiu X. G. , Zhao B. R. , Zhang P. X.
Published: March 2007

The magnetization and electrical transport in the superlattices consisting of ferromagnetic La0.67Sr0.33MnO3 and nonmagnetic insulating SrTiO3 layers have been investigated. A significant displacement of the hysteresis loop along the field axis is observed when the sample is field-cooled through the blocking temperature TB. The strength of displacement, termed as exchange field HE, is found to exponentially decay with temperature. The magnetoresistance in field-cooling process is obviously enhanced compared to that in zero-field-cooling process. The existence of the disordered spin state at the interface is suggested to be the origin of such phenomena.
Prototype dispenser photocathode: Demonstration and comparison to theory
Authors: Moody N. A. , Jensen K. L. , Feldman D. W. , O’Shea P. G. , Montgomery E. J.
Published: March 2007

A method to significantly extend the operational lifetime of alkali-based photocathodes by diffusing cesium to the surface at moderate temperature is presented and shown to restore the quantum efficiency (QE) of cesiated tungsten. Experimental measurements of QE as a function of surface cesium coverage compare exceptionally well with a recent theoretical photoemission model, notably without the use of adjustable parameters. A prototype cesium dispenser cell is demonstrated and validates the concept upon which long-life dispenser photocathodes can be based.
Electrochemical grafting of octyltrichlorosilane monolayer on Si
Authors: Koiry S. P. , Aswal D. K. , Saxena Vibha , Padma N. , Chauhan A. K. , Joshi N. , Gupta S. K. , Yakhmi J. V. , Guerin D. , Vuillaume D.
Published: March 2007

The octyltrichlorosilane (OTS) monolayer on hydrated Si (111) surfaces has been grafted by cyclic voltammetry (CV) using tetrabutylammonium perchlorate in dry methanol as supporting electrolyte. The percentage of OTS coverage, calculated from the current value at −1V, after 30 CV scans was found to be >97%, which is independently confirmed by atomic force microscopy. A mechanism of electrochemical grafting of OTS on Si via formation of Si–Si bonds is proposed. Current-voltage characteristics and impedance spectroscopic measurements on Al/OTS/Si structures reveal realization of a true OTS/Si interface.
Electron density dependence of in-plane spin relaxation anisotropy in GaAs∕AlGaAs two-dimensional electron gas
Authors: Liu Baoli , Zhao Hongming , Wang Jia , Liu Linsheng , Wang Wenxin , Chen Dongmin , Zhu Haijun
Published: March 2007

The authors investigated the spin dynamics of two-dimensional electrons in (001) GaAs∕AlGaAs heterostructure using the time-resolved Kerr rotation technique under a transverse magnetic field. The in-plane spin lifetime is found to be anisotropic below 150K due to the interference of Rashba [J. Phys. C 17, 6039 (1984)] and Dresselhaus [Phys. Rev. 100, 580 (1955)] spin-orbit coupling and D’yakonov-Perel [Sov. Phys. Solid State 13, 3023 (1972)] spin relaxation. The ratio of in-plane spin lifetimes is measured directly as a function of temperature and pump power, showing that the electron density in two-dimensional electron gas channel strongly affects the Rashba spin-orbit coupling.
Shape and composition of buried PbSe quantum dots determined by scanning tunneling microscopy
Authors: Springholz G. , Abtin L. , Holy V.
Published: March 2007

Capping of self-assembled semiconductor quantum dots usually alters their shape and composition due to alloying with the matrix material. To determine the structure of capped dots, a method is developed based on the analysis of surface displacements induced by buried dots measured by scanning tunneling microscopy. For self-assembled PbSe dots overgrown with PbTe layers, the buried dots are found to be highly truncated and extended in the lateral direction, and due to intermixing their composition is changed to PbSexTe1−x, with xSe of only 55%.
Nanoholes fabricated by self-assembled gallium nanodrill on GaAs(100)
Authors: Wang Zh. M. , Liang B. L. , Sablon K. A. , Salamo G. J.
Published: March 2007

Self-assembled nanodrill technology based on droplet epitaxy growth was developed to obtain nanoholes on a GaAs(100) surface. In this technology, the gallium droplets act like “electrochemical drills” etching away the GaAs substrate beneath to give rise to nanoholes more than 10nm deep. The driving force of the nanodrill is attributed to the arsenic desorption underneath the gallium droplet at high growth temperatures and Ga-rich condition. This nanodrill technology provides an easy and flexible method to fabricate nanohole templates on GaAs(100) surface and has great potential for developing quantum dots and quantum dot molecules for quantum computation applications.
High pressure bulk synthesis and characterization of the predicted multiferroic Bi(Fe1∕2Cr1∕2)O3
Authors: Suchomel Matthew R. , Thomas Chris I. , Allix Mathieu , Rosseinsky Matthew J. , Fogg Andrew M. , Thomas Michael F.
Published: March 2007

Bi ( Fe 1 ∕ 2 Cr 1 ∕ 2 ) O 3 , a recently proposed candidate multiferroic perovskite, is prepared in a bulk form by high pressure solid-state synthesis. The material is isostructural with polar BiFeO3 but is paramagnetic at room temperature due to disorder of the Fe3+ and Cr3+ cations on the B site. Mössbauer and magnetization measurements show a transition to a cooperative magnetic state below 130K.
Dependence of breakdown field on dielectric (interelectrode) thickness in base-metal electroded multilayer capacitors
Authors: Milliken Alexander D. , Bell Andrew J. , Scott James F.
Published: March 2007

The authors have empirically determined the dependence of breakdown field EB versus dielectric thickness d (electrode separation) for a large number (4100) of BaTiO3-based multilayer capacitors with Ni base-metal electrodes. The data averaged over lateral area show for 6<d<22μm that EB=const×d−n, where n=0.50±0.06, a result compatible with macroscopic “thermal” dc breakdown mechanisms. More precisely, however, the results nearly perfectly fit a situation of breakdown occurring in connected defects from collision ionization resulting from field emission from the cathode.
Refractive femtosecond laser beam shaping for two-photon polymerization
Authors: Winfield R. J. , Bhuian B. , O’Brien S. , Crean G. M.
Published: March 2007

Three dimensional microstructure fabrication by two-photon polymerization is an established technique that normally uses single beam serial writing. Recently the use of a micro-optical element, to give multipoint beam delivery, was reported to give a degree of parallel processing. The authors describe an alternative approach to parallel processing using an axicon lens. This is a refractive element that, in combination with a high power microscope objective, efficiently transforms the laser beam from a Gaussian spot to an annulus. The authors demonstrate that the beam can polymerize a three dimensional shape, with nanoscale resolution. The use of more sophisticated refractive beam shaping is also discussed.
Analytical description of the motion of an acoustic-driven atomic force microscope cantilever in liquid
Authors: Jai Cédric , Cohen-Bouhacina Touria , Maali Abdelhamid
Published: March 2007

In this letter the authors present an analytical description that enables determining the motion of an acoustic-driven atomic force microscope cantilever in liquid. The authors show that for low quality factors the effective driving force that acts on the deflection motion depends on the damping. The authors derived equations that accurately give the amplitude and phase of the cantilever deflection and the authors also give the expressions of the damping and stiffness of the interaction.
Cerebellar GABAergic progenitors adopt an external granule cell-like phenotype in the absence of Ptf1a transcription factor expression
Authors: Pascual Marta , Abasolo Ibane , Mingorance-Le Meur Ana , Martínez Albert , Del Rio José A. , Wright Christopher V. E. , Real Francisco X. , Soriano Eduardo
Published: March 2007

We report in this study that, in the cerebellum, the pancreatic transcription factor Ptf1a is required for the specific generation of Purkinje cells (PCs) and interneurons. Moreover, granule cell progenitors in the external GCL (EGL) appear to be unaffected by deletion ofPtf1a. Cell lineage analysis inPtf1aCre/Cremice was used to establish that, in the absence ofPtf1aexpression, ventricular zone progenitors, normally fated to produce PCs and interneurons, aberrantly migrate to the EGL and express typical markers of these cells, such as Math1, Reelin, and Zic1/2. Furthermore, these cells have a fine structure typical of EGL progenitors, indicating that they adopt an EGL-like cell phenotype. These findings indicate thatPtf1ais necessary for the specification and normal production of PCs and cerebellar interneurons. Moreover, our results suggest thatPtf1ais also required for the suppression of the granule cell specification program in cerebellar ventricular zone precursors.
Lymphotoxin β receptor signaling is required for inflammatory lymphangiogenesis in the thyroid
Authors: Furtado Glaucia C. , Marinkovic Tatjana , Martin Andrea P. , Garin Alexandre , Hoch Benjamin , Hubner Wolfgang , Chen Benjamin K. , Genden Eric , Skobe Mihaela , Lira Sergio A.
Published: March 2007

Infiltration of lymphocytes into the thyroid gland and formation of lymph node-like structures is a hallmark of Hashimoto's thyroiditis. Here we demonstrate that lymphatic vessels are present within these infiltrates. Mice overexpressing the chemokine CCL21 in the thyroid (TGCCL21 mice) developed similar lymphoid infiltrates and lymphatic vessels. TGCCL21 mice lacking mature T and B cells (RAGTGCCL21 mice) did not have cellular infiltrates or increased number of lymphatic vessels compared with controls. Transfer of CD3+CD4+T cells into RAGTGCCL21 mice promoted the development of LYVE-1+podoplanin+Prox-1+vessels in the thyroid. Genetic deletion of lymphotoxin β receptor or lymphotoxin α abrogated development of lymphatic vessels in the inflamed areas in the thyroid but did not affect development of neighboring lymphatics. These results define a model for the study of inflammatory lymphangiogenesis in the thyroid and implicate lymphotoxin β receptor signaling in this process.
Phylogeny and ancient DNA of
Sus
provides insights into neolithic expansion in Island Southeast Asia and Oceania
Authors: Larson Greger , Cucchi Thomas , Fujita Masakatsu , Matisoo-Smith Elizabeth , Robins Judith , Anderson Atholl , Rolett Barry , Spriggs Matthew , Dolman Gaynor , Kim Tae-Hun , Thuy Nguyen Thi Dieu , Randi Ettore , Doherty Moira , Due Rokus Awe , Bollt Robert , Djubiantono Tony , Griffin Bion , Intoh Michiko , Keane Emile , Kirch Patrick , Li Kuang-Ti , Morwood Michael , Pedriña Lolita M. , Piper Philip J. , Rabett Ryan J. , Shooter Peter , Van den Bergh Gert , West Eric , Wickler Stephen , Yuan Jing , Cooper Alan , Dobney Keith
Published: March 2007

Human settlement of Oceania marked the culmination of a global colonization process that began when humans first left Africa at least 90,000 years ago. The precise origins and dispersal routes of the Austronesian peoples and the associated Lapita culture remain contentious, and numerous disparate models of dispersal (based primarily on linguistic, genetic, and archeological data) have been proposed. Here, through the use of mtDNA from 781 modern and ancient
Sus
specimens, we provide evidence for an early human-mediated translocation of the Sulawesi warty pig (
Sus celebensis
) to Flores and Timor and two later separate human-mediated dispersals of domestic pig (
Sus scrofa
) through Island Southeast Asia into Oceania. Of the later dispersal routes, one is unequivocally associated with the Neolithic (Lapita) and later Polynesian migrations and links modern and archeological Javan, Sumatran, Wallacean, and Oceanic pigs with mainland Southeast Asian
S. scrofa
. Archeological and genetic evidence shows these pigs were certainly introduced to islands east of the Wallace Line, including New Guinea, and that so-called “wild” pigs within this region are most likely feral descendants of domestic pigs introduced by early agriculturalists. The other later pig dispersal links mainland East Asian pigs to western Micronesia, Taiwan, and the Philippines. These results provide important data with which to test current models for human dispersal in the region.
Crystal structures reveal a thiol protease-like catalytic triad in the C-terminal region ofPasteurella multocidatoxin
Authors: Kitadokoro Kengo , Kamitani Shigeki , Miyazawa Masayuki , Hanajima-Ozawa Miyuki , Fukui Aya , Miyake Masami , Horiguchi Yasuhiko
Published: March 2007

Pasteurella multocidatoxin (PMT), one of the virulence factors produced by the bacteria, exerts its toxicity by up-regulating various signaling cascades downstream of the heterotrimeric GTPases Gq and G12/13 in an unknown fashion. Here, we present the crystal structure of the C-terminal region (residues 575–1,285) of PMT, which carries an intracellularly active moiety. The overall structure of C-terminal region of PMT displays a Trojan horse-like shape, composed of three domains with a “feet”-,“body”-, and “head”-type arrangement, which were designated C1, C2, and C3 from the N to the C terminus, respectively. The C1 domain, showing marked similarity in steric structure to the N-terminal domain ofClostridium difficiletoxin B, was found to lead the toxin molecule to the plasma membrane. The C3 domain possesses the Cys–His–Asp catalytic triad that is organized only when the Cys is released from a disulfide bond. The steric alignment of the triad corresponded well to that of papain or other enzymes carrying Cys–His–Asp. PMT toxicities on target cells were completely abrogated when one of the amino acids constituting the triad was mutated. Our results indicate that PMT is an enzyme toxin carrying the cysteine protease-like catalytic triad dependent on the redox state and functions on the cytoplasmic face of the plasma membrane of target cells.
Tradeoffs between income, biodiversity, and ecosystem functioning during tropical rainforest conversion and agroforestry intensification
Authors: Steffan-Dewenter Ingolf , Kessler Michael , Barkmann Jan , Bos Merijn M. , Buchori Damayanti , Erasmi Stefan , Faust Heiko , Gerold Gerhard , Glenk Klaus , Gradstein S. Robbert , Guhardja Edi , Harteveld Marieke , Hertel Dietrich , Höhn Patrick , Kappas Martin , Köhler Stefan , Leuschner Christoph , Maertens Miet , Marggraf Rainer , Migge-Kleian Sonja , Mogea Johanis , Pitopang Ramadhaniel , Schaefer Matthias , Schwarze Stefan , Sporn Simone G. , Steingrebe Andrea , Tjitrosoedirdjo Sri S. , Tjitrosoemito Soekisman , Twele André , Weber Robert , Woltmann Lars , Zeller Manfred , Tscharntke Teja
Published: March 2007

Losses of biodiversity and ecosystem functioning due to rainforest destruction and agricultural intensification are prime concerns for science and society alike. Potentially, ecosystems show nonlinear responses to land-use intensification that would open management options with limited ecological losses but satisfying economic gains. However, multidisciplinary studies to quantify ecological losses and socioeconomic tradeoffs under different management options are rare. Here, we evaluate opposing land use strategies in cacao agroforestry in Sulawesi, Indonesia, by using data on species richness of nine plant and animal taxa, six related ecosystem functions, and on socioeconomic drivers of agroforestry expansion. Expansion of cacao cultivation by 230% in the last two decades was triggered not only by economic market mechanisms, but also by rarely considered cultural factors. Transformation from near-primary forest to agroforestry had little effect on overall species richness, but reduced plant biomass and carbon storage by ≈75% and species richness of forest-using species by ≈60%. In contrast, increased land use intensity in cacao agroforestry, coupled with a reduction in shade tree cover from 80% to 40%, caused only minor quantitative changes in biodiversity and maintained high levels of ecosystem functioning while doubling farmers' net income. However, unshaded systems further increased income by ≈40%, implying that current economic incentives and cultural preferences for new intensification practices put shaded systems at risk. We conclude that low-shade agroforestry provides the best available compromise between economic forces and ecological needs. Certification schemes for shade-grown crops may provide a market-based mechanism to slow down current intensification trends.
Modification of nuclear PML protein by SUMO-1 regulates Fas-induced apoptosis in rheumatoid arthritis synovial fibroblasts
Authors: Meinecke Ingmar , Cinski Antje , Baier Anja , Peters Marvin A. , Dankbar Berno , Wille Aline , Drynda Andreas , Mendoza Heidi , Gay Renate E. , Hay Ronald T. , Ink Barbara , Gay Steffen , Pap Thomas
Published: March 2007

The small ubiquitin-like modifier (SUMO)-1 is an important posttranslational regulator of different signaling pathways and involved in the formation of promyelocytic leukemia (PML) protein nuclear bodies (NBs). Overexpression of SUMO-1 has been associated with alterations in apoptosis, but the underlying mechanisms and their relevance for human diseases are not clear. Here, we show that the increased expression of SUMO-1 in rheumatoid arthritis (RA) synovial fibroblasts (SFs) contributes to the resistance of these cells against Fas-induced apoptosis through increased SUMOylation of nuclear PML protein and increased recruitment of the transcriptional repressor DAXX to PML NBs. We also show that the nuclear SUMO-protease SENP1, which is found at lower levels in RA SFs, can revert the apoptosis-inhibiting effects of SUMO-1 by releasing DAXX from PML NBs. Our findings indicate that in RA SFs overexpression of SENP1 can alter the SUMO-1-mediated recruitment of DAXX to PML NBs, thus influencing the proapoptotic effects of DAXX. Accumulation of DAXX in PML NBs by SUMO-1 may, therefore, contribute to the pathogenesis of inflammatory disorders.
Neural correlates of perceptual filling-in of an artificial scotoma in humans
Authors: Weil R. S. , Kilner J. M. , Haynes J. D. , Rees G.
Published: March 2007

When a uniformly illuminated surface is placed eccentrically on a dynamic textured background, after a few seconds, it is perceived to disappear and be replaced by the background texture. Such texture filling-in is thought to occur in retinotopic visual cortex, but it has proven difficult to distinguish the contributions of invisible target and visible background to signals measured in these areas. Here, we used magnetoencephalography to measure time-dependent brain responses in human observers experiencing texture completion. We measured responses specifically associated with the filled-in target, by isolating neural population signals entrained at the frequency of flicker of the target. When perceptual completion occurred, and the target became invisible, there was significant reduction in the magnetoencephalography power at the target frequency over contralateral posterior sensors. However, even a subjectively invisible target nevertheless evoked frequency-specific signals compared with a no-target baseline. These data represent evidence for a persistent target-specific representation even for stimuli rendered invisible because of perceptual filling-in.
Sustainable fuel for the transportation sector
Authors: Agrawal Rakesh , Singh Navneet R. , Ribeiro Fabio H. , Delgass W. Nicholas
Published: March 2007

A hybrid hydrogen-carbon (H
2
CAR) process for the production of liquid hydrocarbon fuels is proposed wherein biomass is the carbon source and hydrogen is supplied from carbon-free energy. To implement this concept, a process has been designed to co-feed a biomass gasifier with H
2
and CO
2
recycled from the H
2
-CO to liquid conversion reactor. Modeling of this biomass to liquids process has identified several major advantages of the H
2
CAR process. (
i
) The land area needed to grow the biomass is <40% of that needed by other routes that solely use biomass to support the entire transportation sector. (
ii
) Whereas the literature estimates known processes to be able to produce ≈30% of the United States transportation fuel from the annual biomass of 1.366 billion tons, the H
2
CAR process shows the potential to supply the entire United States transportation sector from that quantity of biomass. (
iii
) The synthesized liquid provides H
2
storage in an open loop system. (
iv
) Reduction to practice of the H
2
CAR route has the potential to provide the transportation sector for the foreseeable future, using the existing infrastructure. The rationale of using H
2
in the H
2
CAR process is explained by the significantly higher annualized average solar energy conversion efficiency for hydrogen generation versus that for biomass growth. For coal to liquids, the advantage of H
2
CAR is that there is no additional CO
2
release to the atmosphere due to the replacement of petroleum with coal, thus eliminating the need to sequester CO
2
.
Noninfectious entry of HIV-1 into peripheral and brain macrophages mediated by the mannose receptor
Authors: Trujillo J. Roberto , Rogers Rick , Molina Ramon M. , Dangond Fernando , McLane Mary Fran , Essex Max , Brain Joseph D.
Published: March 2007

Although protein receptors on the plasma membrane involved in the initial steps of productive HIV-1 infection have been well characterized, little is known about interactions between cellular carbohydrate receptors and HIV-1. Here, we report the involvement of a carbohydrate receptor, the macrophage mannose receptor (MR), and its role in supporting HIV-1 binding and entry. HIV-1 can enter the cytoplasm of human macrophages and microglia as well as murine macrophages by MR, although no subsequent viral replication was observed. Correspondingly, HIV-1 entry into Cos-7 cells after induction of expression of MR by transfection with MR-cDNA did not demonstrate viral replication. Our studies suggest that whereas MR may serve as a binding and an entry site, the MR-mediated pathway does not lead to productive HIV-1 infection. In addition, we report that recombinant HIV-1 gp120 blocks MR-mediated phagocytosis in human and murine alveolar macrophages and microglial cells. Therefore, characterization of the HIV-1 noninfectious MR-mediated phagocytic pathway may foster advances in HIV-1 vaccine design and an improved understanding of HIV-1/AIDS pathogenesis and host defenses.
Dopamine modulation of neuronal Na
+
channels requires binding of A kinase-anchoring protein 15and PKA by a modified leucine zipper motif
Authors: Few W. Preston , Scheuer Todd , Catterall William A.
Published: March 2007

In hippocampal pyramidal cells, dopamine acts at D1 receptors to reduce peak Na
+
currents by activation of phosphorylation by PKA anchored via an A kinase-anchoring protein (AKAP15). However, the mechanism by which AKAP15 anchors PKA to neuronal Na
+
channels is not known. By using a strategy of coimmunoprecipitation from transfected tsA-201 cells, we have found that AKAP15 directly interacts with Na
v
1.2a channels via the intracellular loop between domains I and II. This loop contains key functional phosphorylation sites. Mutagenesis indicated that this interaction occurs through a modified leucine zipper motif near the N terminus of the loop. Whole-cell patch clamp recordings of acutely dissociated hippocampal pyramidal cells revealed that the D1 dopamine receptor agonist SKF 81297 reduces peak Na
+
current amplitude by 20.5%, as reported previously. Disruption of the leucine zipper interaction between Na
v
1.2a and AKAP15 through the inclusion of a small competing peptide in the patch pipette inhibited the SKF 81297-induced reduction in peak Na
+
current, whereas a control peptide with mutations in amino acids important for the leucine zipper interaction did not. Our results define the molecular mechanism by which G protein-coupled signaling pathways can rapidly and efficiently modulate neuronal excitability through local protein phosphorylation of Na
+
channels by specifically anchored PKA.
A lamin A protein isoform overexpressed in Hutchinson–Gilford progeria syndrome interferes with mitosis in progeria and normal cells
Authors: Cao Kan , Capell Brian C. , Erdos Michael R. , Djabali Karima , Collins Francis S.
Published: March 2007

Hutchinson–Gilford progeria syndrome (HGPS) is a rare genetic disorder characterized by dramatic premature aging. Classic HGPS is caused by a
de novo
point mutation in exon 11 (residue 1824, C → T) of the
LMNA
gene, activating a cryptic splice donor and resulting in a mutant lamin A (LA) protein termed “progerin/LAΔ50” that lacks the normal cleavage site to remove a C-terminal farnesyl group. During interphase, irreversibly farnesylated progerin/LAΔ50 anchors to the nuclear membrane and causes characteristic nuclear blebbing. Progerin/LAΔ50's localization and behavior during mitosis, however, are completely unknown. Here, we report that progerin/LAΔ50 mislocalizes into insoluble cytoplasmic aggregates and membranes during mitosis and causes abnormal chromosome segregation and binucleation. These phenotypes are largely rescued with either farnesyltransferase inhibitors or a farnesylation-incompetent mutant progerin/LAΔ50. Furthermore, we demonstrate that small amounts of progerin/LAΔ50 exist in normal fibroblasts, and a significant percentage of these progerin/LAΔ50-expressing normal cells are binucleated, implicating progerin/LAΔ50 as causing similar mitotic defects in the normal aging process. Our findings present evidence of mitotic abnormality in HGPS and may shed light on the general phenomenon of aging.
A model of immune regulation as a consequence of randomized lymphocyte division and death times
Authors: Hawkins E. D. , Turner M. L. , Dowling M. R. , van Gend C. , Hodgkin P. D.
Published: March 2007

The magnitude of an adaptive immune response is controlled by the interplay of lymphocyte quiescence, proliferation, and apoptosis. How lymphocytes integrate receptor-mediated signals influencing these cell fates is a fundamental question for understanding this complex system. We examined how lymphocytes interleave times to divide and die to develop a mathematical model of lymphocyte growth regulation. This model provides a powerful method for fitting and analyzing fluorescent division tracking data and reveals how summing receptor-mediated kinetic changes can modify the immune response progressively from rapid tolerance induction to strong immunity. An important consequence of our results is that intrinsic variability in otherwise identical cells, usually dismissed as noise, may have evolved to be an essential feature of immune regulation.
Sensitive ChIP-DSL technology reveals an extensive estrogen receptor α-binding program on human gene promoters
Authors: Kwon Young-Soo , Garcia-Bassets Ivan , Hutt Kasey R. , Cheng Christine S. , Jin Mingjie , Liu Dongyan , Benner Chris , Wang Dong , Ye Zhen , Bibikova Marina , Fan Jian-Bing , Duan Lingxun , Glass Christopher K. , Rosenfeld Michael G. , Fu Xiang-Dong
Published: March 2007

ChIP coupled with microarray provides a powerful tool to determine
in vivo
binding profiling of transcription factors to deduce regulatory circuitries in mammalian cells. Aiming at improving the specificity and sensitivity of such analysis, we developed a new technology called ChIP-DSL using the DNA selection and ligation (DSL) strategy, permitting robust analysis with much reduced materials compared with standard procedures. We profiled general and sequence-specific DNA binding transcription factors using a full human genome promoter array based on the ChIP-DSL technology, revealing an unprecedented number of the estrogen receptor (ERα) target genes in MCF-7 cells. Coupled with gene expression profiling, we found that only a fraction of these direct ERα target genes were highly responsive to estrogen and that the expression of those ERα-bound, estrogen-inducible genes was associated with breast cancer progression in humans. This study demonstrates the power of the ChIP-DSL technology in revealing regulatory gene expression programs that have been previously invisible in the human genome.
Ca
2+
sparks operated by membrane depolarization require isoform 3 ryanodine receptor channels in skeletal muscle
Authors: Pouvreau Sandrine , Royer Leandro , Yi Jianxun , Brum Gustavo , Meissner Gerhard , Ríos Eduardo , Zhou Jingsong
Published: March 2007

Stimuli are translated to intracellular calcium signals via opening of inositol trisphosphate receptor and ryanodine receptor (RyR) channels of the sarcoplasmic reticulum or endoplasmic reticulum. In cardiac and skeletal muscle of amphibians the stimulus is depolarization of the transverse tubular membrane, transduced by voltage sensors at tubular–sarcoplasmic reticulum junctions, and the unit signal is the Ca
2+
spark, caused by concerted opening of multiple RyR channels. Mammalian muscles instead lose postnatally the ability to produce sparks, and they also lose RyR3, an isoform abundant in spark-producing skeletal muscles. What does it take for cells to respond to membrane depolarization with Ca
2+
sparks? To answer this question we made skeletal muscles of adult mice expressing exogenous RyR3, demonstrated as immunoreactivity at triad junctions. These muscles showed abundant sparks upon depolarization. Sparks produced thusly were found to amplify the response to depolarization in a manner characteristic of Ca
2+
-induced Ca
2+
release processes. The amplification was particularly effective in responses to brief depolarizations, as in action potentials. We also induced expression of exogenous RyR1 or yellow fluorescent protein-tagged RyR1 in muscles of adult mice. In these, tag fluorescence was present at triad junctions. RyR1-transfected muscle lacked voltage-operated sparks. Therefore, the voltage-operated sparks phenotype is specific to the RyR3 isoform. Because RyR3 does not contact voltage sensors, their opening was probably activated by Ca
2+
, secondarily to Ca
2+
release through junctional RyR1. Physiologically voltage-controlled Ca
2+
sparks thus require a voltage sensor, a master junctional RyR1 channel that provides trigger Ca
2+
, and a slave parajunctional RyR3 cohort.
Alterations in mitosis and cell cycle progression caused by a mutant lamin A known to accelerate human aging
Authors: Dechat Thomas , Shimi Takeshi , Adam Stephen A. , Rusinol Antonio E. , Andres Douglas A. , Spielmann H. Peter , Sinensky Michael S. , Goldman Robert D.
Published: March 2007

Mutations in the gene encoding nuclear lamin A (LA) cause the premature aging disease Hutchinson–Gilford Progeria Syndrome. The most common of these mutations results in the expression of a mutant LA, with a 50-aa deletion within its C terminus. In this study, we demonstrate that this deletion leads to a stable farnesylation and carboxymethylation of the mutant LA (LAΔ50/progerin). These modifications cause an abnormal association of LAΔ50/progerin with membranes during mitosis, which delays the onset and progression of cytokinesis. Furthermore, we demonstrate that the targeting of nuclear envelope/lamina components into daughter cell nuclei in early G
1
is impaired in cells expressing LAΔ50/progerin. The mutant LA also appears to be responsible for defects in the retinoblastoma protein-mediated transition into S-phase, most likely by inhibiting the hyperphosphorylation of retinoblastoma protein by cyclin D1/cdk4. These results provide insights into the mechanisms responsible for premature aging and also shed light on the role of lamins in the normal process of human aging.
Human herpesvirus 6A accelerates AIDS progression in macaques
Authors: Lusso Paolo , Crowley Richard W. , Malnati Mauro S. , Di Serio Clelia , Ponzoni Maurilio , Biancotto Angelique , Markham Phillip D. , Gallo Robert C.
Published: March 2007

Although HIV is the necessary and sufficient causative agent of AIDS, genetic and environmental factors markedly influence the pace of disease progression. Clinical and experimental evidence suggests that human herpesvirus 6A (HHV-6A), a cytopathic T-lymphotropic DNA virus, fosters the progression to AIDS in synergy with HIV-1. In this study, we investigated the effect of coinfection with HHV-6A on the progression of simian immunodeficiency virus (SIV) disease in pig-tailed macaques (Macaca nemestrina). Inoculation of HHV-6A resulted in a rapid appearance of plasma viremia associated with transient clinical manifestations and followed by antibody seroconversion, indicating that this primate species is susceptible to HHV-6A infection. Whereas animals infected with HHV-6A alone did not show any long-term clinical and immunological sequelae, a progressive loss of CD4+T cells was observed in all of the macaques inoculated with SIV. However, progression to full-blown AIDS was dramatically accelerated by coinfection with HHV-6A. Rapid disease development in dually infected animals was heralded by an early depletion of both CD4+and CD8+T cells. These results providein vivoevidence that HHV-6A may act as a promoting factor in AIDS progression.