bluuebunny/crossref_metadata_2025 huggingface dataset:
Tunnel field-effect transistor without gate-drain overlap
Authors: Verhulst Anne S. , Vandenberghe William G. , Maex Karen , Groeseneken Guido
Published: July 2007

Tunnel field-effect transistors are promising successors of metal-oxide-semiconductor field-effect transistors because of the absence of short-channel effects and of a subthreshold-slope limit. However, the tunnel devices are ambipolar and, depending on device material properties, they may have low on-currents resulting in low switching speed. The authors have generalized the tunnel field-effect transistor configuration by allowing a shorter gate structure. The proposed device is especially attractive for vertical nanowire-based transistors. As illustrated with device simulations, the authors’ more flexible configuration allows of the reduction of ambipolar behavior, the increase of switching speed, and the decrease of processing complexity.
GaN ultraviolet photosensors capped by low-temperature aluminium nitride layer
Authors: Chang P. C.
Published: July 2007

GaN UV sensors with an in situ grown 30nm thick low-temperature aluminium nitride (LT-AlN) cap layer were fabricated. Scanning probe microscopy showed that surface pits of threading dislocations were almost invisible when the GaN active layer was capped with a LT-AlN layer. The dark leakage current of these sensors was comparably much smaller than that of conventional sensors without the LT-AlN cap layer, owing to a thicker and higher potential barrier of the LT-AlN cap layer and effective surface passivation. With −1V applied bias, it was found that the UV-to-visible rejection ratio was 3.42×103 for the sensor with the LT-AlN cap layer. In brief, incorporating a LT-AlN cap layer into the sensors can beneficially suppress the dark leakage current and improve the UV-to-visible rejection ratio.
Rearrangement of the oxide-semiconductor interface in annealed Al2O3∕4H-SiC structures
Authors: Avice M. , Diplas S. , Thøgersen A. , Christensen J. S. , Grossner U. , Svensson B. G. , Nilsen O. , Fjellvåg H. , Watts J. F.
Published: July 2007

Al 2 O 3 films with different thicknesses have been deposited on n-type (nitrogen-doped) 4H-SiC(0001) epitaxial samples by atomic layer chemical vapor deposition at 300°C and subsequently annealed in Ar atmosphere at temperatures up to 1000°C. The Al2O3∕4H-SiC structures were analyzed by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and transmission electron microscopy (TEM). The XPS and SIMS results indicate that the average composition in the wider interface area does not significantly change due to the annealing. However, as revealed by the TEM investigations in combination with XPS, the as-grown samples exhibit a double interface created by an intermediate suboxide SiOx layer (x<2). After annealing, this intermediate suboxide layer breaks up and transforms into SiO2 islands, resulting in a rather rough interface region and a high concentration of pure Si in the Al2O3 film. Furthermore, a pronounced accumulation of H is found in the rough interface region and this may play a key role for the low density of shallow electron states reported for annealed Al2O3∕4H-SiC structures.
Cross linking of thiolated carbon nanotubes: An ab initio study
Authors: Vasiliev Igor , Curran Seamus A.
Published: July 2007

We have studied the mechanism of covalent cross linking between carbon nanotubes functionalized with thiocarboxylic and dithiocarboxylic esters. The interconnected nanotube structures were modeled using density functional theory combined with the pseudopotential approximation. Our calculations revealed the important role of surface defects when forming chemical bonds that connect nanotubes to each other. The strength and stability of intertube bonds increased in the vicinity of defect sites. The computed binding energies and potential energy profiles of linked nanotubes were found to be sensitive to the choice of exchange-correlation functional used within the density functional formalism. The observed sensitivity could be explained by a nonuniform distribution of the electronic charge density near defect sites. This result suggests that gradient-corrected functionals are essential for accurate theoretical modeling of functionalized carbon nanotubes and nanotube-based composites.
Design and simulation of laser wakefield acceleration with external electron bunch injection in front of the laser pulse
Authors: Irman A. , Luttikhof M. J. H. , Khachatryan A. G. , van Goor F. A. , Verschuur J. W. J. , Bastiaens H. M. J. , Boller K.-J.
Published: July 2007

In this article we present a theoretical investigation on an experimental design of a laser wakefield accelerator in which electron bunches from a photocathode radio frequency linac are injected into a capillary discharge plasma channel just in front of a few tens of terawatt drive laser pulse. The electron bunch, with a kinetic energy of 2.9 MeV and an energy chirp imposed by the linac, is magnetically compressed by a factor of 8 to a duration of 250 fs, and is magnetically focused into the plasma channel where it matches the spot size of the drive laser (≈30 μm). The dynamics of the bunch, starting from the photocathode, through the linac, along the beam transportation line, through the magnetic compressor, and its focusing into the plasma channel are comprehensively simulated with the general particle tracer code. Further, we use our three-dimensional numerical codes to calculate the laser wakefield and to determine and optimize the trapping and acceleration of the injected bunch in the wakefield. We show that, injecting a 5 pC electron bunch of 250 fs duration, the experiment should deliver an electron bunch of approximately 744 MeV energy, with 1.1% relative energy spread, and with an extremely short duration (6 fs), after acceleration in a 5.4 cm long plasma channel.
Measurement approach of Brownian motion force by an abrupt tapered fiber optic tweezers
Authors: Yuan Libo , Liu Zhihai , Yang Jun
Published: July 2007

A Brownian motion force measurement fiber optic probe is fabricated and demonstrated. The specially designed abrupt tapered fiber tip can be used to trap small particles. By way of comparing the value of Brownian motion random force with the trapping force exerted on the same particle at the ambient temperature T, the Brownian motion force can be measured.
Solute transport in porous media: Dispersion tensor of periodic networks
Authors: Goldsztein Guillermo H.
Published: July 2007

The authors study solute transport in periodic networks of channels. They identify the parameter regime where a local physical mechanism that occurs at the intersections of channels is the dominant cause of dispersion and obtain the macroscopic transport equation that the concentration of solute satisfies.
Formation of TaN nanocrystals embedded in silicon nitride by phase separation methods for nonvolatile memory applications
Authors: Choi Hyejung , Jung Seung-Jae , Park Hokyung , Lee Joon-Myung , Kwon Moonjae , Chang Man , Hasan Musarrat , Choi Sangmoo , Hwang Hyunsang
Published: July 2007

TaN nanocrystals (NCs) embedded in silicon nitride were investigated as a new charge-trapping layer of a silicon-oxide-nitride-oxide-silicon-type nonvolatile memory device. After annealing at 900°C, TaN NCs with average size of 3.5nm were formed by the phase separation method. Compared with a control sample without NC, memory devices with TaN NCs exhibit superior memory characteristics, such as a larger window of capacitance-voltage hysteresis and a lower charge loss rate. The improvement can be explained by the formation of high density TaN NCs with a deeper trap energy level.
Transmission electron microscopy based direct mathematical quantifiers for dispersion in nanocomposites
Authors: Basu S. K. , Tewari A. , Fasulo P. D. , Rodgers W. R.
Published: July 2007

A rigorous mathematical foundation and a procedure for quantifying three-dimensional exfoliation and dispersion of clay particles in polymer-clay nanocomposites from their two-dimensional transmission electron microscopy micrographs have been developed. Two independent parameters, exfoliation number and interparticle distance, have been proposed. The exfoliation number gives the percentage of exfoliation achieved, whereas the interparticle distance is a measure of spatial separation between particles. The quantitative description of the nanocomposite microstructure would enable the establishment of synthesis/processing-structure-property linkages in nanocomposites and provide a benchmark for other indirect characterization techniques, such as x-ray diffraction, rheology, etc.
Generation of high-quality optical vortex beams in free-space propagation by microfabricated wedge with spatial filtering technique
Authors: Yuan X.-C. , Ahluwalia B. P. S. , Chen H. L. , Bu J. , Lin J. , Burge R. E. , Peng X. , Niu H. B.
Published: July 2007

The authors propose a low-pass 2f spatial filter for improving optical vortex beams in terms of circular geometry generated by a microfabricated wedge in free space. Compared with a conventional wedge, they are able to realize high-quality vortex beams with Q value close to 1 in free-space propagation. Physical mechanism behind the technique is found that it removes the diffraction artifacts as well as higher spatial frequency components of the quasivortex beams based on a wedge and hence the filtered beam is reconstructed with minimized distortions.
Synthetic relationship between titanium and alloying elements in designing Ni-free Ti-based bulk metallic glass alloys
Authors: Oak Jeong-Jung , Louzguine-Luzgin Dmitri V. , Inoue Akihisa
Published: July 2007

Ni-free Ti-based bulk metallic glass (BMG) alloys were reported to have a high enough glass forming ability (GFA). In this study, the glass forming ability of Ti-based BMG alloys without Ni and Be additions is analyzed using Inoue’s empirical rules, bonding order (Bo), and molecular d-orbital energy values (Md). The developed Ti-based BMG alloys revealed a separable location on the Bo¯-Md¯ diagram which presents the direction for design of Ti-based BMG alloys with high GFA.
Recombination dynamics in ZnO nanoparticles produced by chemical vapor synthesis
Authors: Schneider L. , Zaitsev S. V. , Bacher G. , Jin W. , Winterer M.
Published: July 2007

ZnO nanoparticles produced by chemical vapor synthesis have been studied by means of time-resolved photoluminescence spectroscopy. A postannealing treatment improves significantly the emission efficiency and results in spectrally narrow bands with a linewidth down to 3.7 meV at low temperature. That allows us to study the dynamics of free and bound exciton recombination and to identify recombination channels up to room temperature.
Interfacial electronic structure of N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine/copper phthalocyanine:C60 composite/Au studied by ultraviolet photoemission spectroscopy
Authors: Cho Sang Wan , Yoo Kyung-Hwa , Jeong Kwangho , Whang Chung-Nam , Yi Yeonjin , Noh Myungkeun
Published: July 2007

The interfacial electronic structures of N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/copper phthalocyanine (CuPc)∕Au, NPB∕C60∕Au, and NPB∕CuPc:C60 composite/Au were investigated by in situ ultraviolet photoelectron spectroscopy to understand the highly efficient hole injection in organic light-emitting diode. The hole-injection barrier of CuPc:C60∕Au was 0.52eV, while those of CuPc∕Au and C60∕Au were 0.96 and 1.62eV, respectively. The lowered injection barrier is attributed to the smaller interface dipole of CuPc:C60 compared to that of pristine CuPc. This small interface dipole pulled up the highest occupied molecular orbital of CuPc in composite, which results in the decreased hole-injection barrier.
Electronic conductance of ion implanted and plasma modified polymers
Authors: Han Z. J. , Tay B. K. , Ha P. C. T. , Shakerzadeh M. , Cimmino A. A. , Prawer S. , McKenzie D.
Published: July 2007

The authors used the plasma immersion ion implantation and deposition technique to modify polyethylene terephthalate (PET) and by using conductive atomic force microscope, the spatial distribution of ∼10nm size titanium nanoclusters embedded in PET matrices were observed. The I-V plots showed typical metal-semiconductor junction conductivity between the conductive tip and the surface. In addition, the authors also measured the temperature dependent conductivity and fitted it well to the Mott law, which implied that the conductance arose from electron hopping process. Such technique to create the surface structure of metal/polymer nanocomposites may open an alternative way for plastic nanoelectronics.
Random telegraph signals in n-type ZnO nanowire field effect transistors at low temperature
Authors: Xiong Hao D. , Wang Wenyong , Li Qiliang , Richter Curt A. , Suehle John S. , Hong Woong-Ki , Lee Takhee , Fleetwood Daniel M.
Published: July 2007

Single-crystal zinc oxide (ZnO) nanowires have been fabricated as field effect transistors (FETs). The characteristics of low frequency noise in the drain current of n-type ZnO FETs have been investigated through random telegraph signals (RTSs) at 4.2K. At room temperature, the noise power spectra have a classic 1∕f dependence with a Hooge parameter that is ∼5×10−3. At 4.2K, the device’s noise spectra change from 1∕f to Lorentzian type, and the current traces as a function of time show RTSs. The channel current RTSs are attributed to correlated carrier number and mobility fluctuation due to the trapping and emission of carriers by discrete border traps. At certain bias conditions, the current in the channel shows three-level switching events with amplitudes as high as 40%, from which two individual defects with energies close to the Fermi level in the ZnO channel can be distinguished.
Z-shaped graphene nanoribbon quantum dot device
Authors: Wang Z. F. , Shi Q. W. , Li Qunxiang , Wang Xiaoping , Hou J. G. , Zheng Huaixiu , Yao Yao , Chen Jie
Published: July 2007

Stimulated by recent advances in isolating graphene, the authors discovered that a quantum dot can be trapped in a Z-shaped graphene nanoribbon junction. The topological structure of the junction can completely confine electronic states. By varying the junction length, the authors can alter the spatial confinement and the number of discrete levels within the junction. In addition, a quantum dot can be realized regardless of substrate induced static disorder or irregularities on the edges of the junction. The method can be used to easily design quantum dot devices. The authors also provide a platform to design zero-dimensional functional nanoscale electronic devices using graphene ribbons.
Mesoscopic approach to progressive breakdown in ultrathin SiO2 layers
Authors: Miranda E.
Published: July 2007

The opening of a breakdown path across the ultrathin oxide layer in a metal-oxide-semiconductor structure caused by the application of electrical stress can be analyzed within the framework of the physics of mesoscopic conductors. Using the Landauer formula for a quantum point contact, the author is able to show that the saturation of the gate leakage current is linked to the progressive evolution of the constriction’s conductance toward the ballistic transport regime. The possible physical mechanisms responsible for energy dissipation inside the breakdown path as well as the limitations of the proposed approach are discussed.
Dramatic morphological change of scallop-type Cu6Sn5 formed on (001) single crystal copper in reaction between molten SnPb solder and Cu
Authors: Suh J. O. , Tu K. N. , Tamura N.
Published: July 2007

Wetting reaction between molten Sn-based solders and Cu produces scallop-type Cu6Sn5. In the present wetting study, a (001) single crystal Cu is used as substrate and a dramatic change in the morphology of Cu6Sn5 is observed: instead of scallop type, the authors observed a rooftop-type Cu6Sn5 grains, elongated along two preferred orientation directions. This was confirmed by electron beam backscattered diffraction and white beam synchrotron x-ray microdiffraction. The results indicate that the nucleation, growth, and ripening behavior of Cu6Sn5 on single crystal substrate can be quite different from the conventional case of wetting on randomly oriented polycrystalline Cu substrates.
Tailoring the long-range order of block copolymer based nanomasks on flat substrates
Authors: Puglisi R. A. , La Fata P. , Lombardo S.
Published: July 2007

The authors investigate the self-assembling of polystyrene/polymethylmethacrylate block copolymer films for the formation of nanotemplates on flat substrates. The macrodomain evolution is studied in terms of density, size, and relative orientation during the annealing promoting the self-assembling. The statistics is acquired through an original method based on the elaboration of the electronic micrographs in the reciprocal space. The results indicate that while the annealing conditions do not play a role in the pore-to-pore distance distribution, thus confirming previous results, they influence the macrodomain density and size distributions, inducing an onset of secondary grain growth crystallization behavior in this system.
Simultaneous optical trapping of microparticles in multiple planes by a modified self-imaging effect on a chip
Authors: Sun Y. Y. , Bu J. , Ong L. S. , Yuan X.-C.
Published: July 2007

The authors propose a three-dimensional (3D) optical trapping of microparticles in multiple planes simultaneously based on a modified self-imaging effect. Similar to the Talbot self-imaging effect, the modified self-imaging effect is induced by a layer of trapped particles and it is subsequently used as a periodic grating structure to generate its own self-imaging pattern in 3D. Based on this secondary layer-by-layer self-imaging effect, optical trapping of silica and polystyrene colloidal particles at different planes in a microchamber are demonstrated experimentally.
Charge control analysis of transistor laser operation
Authors: Feng M. , Holonyak N. , Then H. W. , Walter G.
Published: July 2007

The authors report the calculation of the minority carrier distribution in the base region of the transistor laser (TL) employing the relevant continuity equations and experimental carrier lifetimes, spontaneous and stimulated, extracted from the transistor I-V characteristics. A charge control model of the TL is developed, consistent with the short recombination lifetime of the quantum-well base (which competes with the short emitter-to-collector transit time). The absence of carrier-photon resonance of a TL is demonstrated with the 3dB bandwidth (IB∕IB,th=1.5) estimated to be 30GHz for a 400μm long laser cavity length and 70GHz for a 150μm cavity.
Equivalent point-mass models of continuous atomic force microscope probes
Authors: Melcher John , Hu Shuiqing , Raman Arvind
Published: July 2007

The theoretical foundations of dynamic atomic force microscopy (AFM) are based on point-mass models of continuous, micromechanical oscillators with nanoscale tips that probe local tip-sample interaction forces. In this letter, the authors present the conditions necessary for a continuous AFM probe to be faithfully represented as a point-mass model, and derive the equivalent point-mass model for a general eigenmode of arbitrarily shaped AFM probes based on the equivalence of kinetic, strain, and tip-sample interaction energies. They also demonstrate that common formulas in dynamic AFM change significantly when these models are used in place of the traditional ad hoc point-mass models.
GaInNAs double-barrier quantum well infrared photodetector with the photodetection at 1.24μm
Authors: Ma B. S. , Fan W. J. , Dang Y. X. , Cheah W. K. , Loke W. K. , Liu W. , Li D. S. , Yoon S. F. , Zhang D. H. , Wang H. , Tung C. H.
Published: July 2007

A GaInNAs∕AlAs∕AlGaAs double-barrier quantum well infrared photodetector was grown by molecular beam epitaxy and fabricated by standard device processes. The growth structure of the as-grown sample was verified by x-ray diffraction measurement. The photoluminescence emission peak, which is related to the interband transition in the GaInNAs well, was observed at ∼1.2eV. After annealing at 650°C, a large blueshift of 40meV was observed. The photocurrent peak at 1.24μm is associated with the intersubband transitions in the conduction band of the GaInNAs quantum well. The ten-band k∙p calculations agree with the above observations.
Dielectric abnormities in BaTi0.9(Ni1∕2W1∕2)0.1O3 giant dielectric constant ceramics
Authors: Zhao Fei , Yue Zhenxing , Pei Jing , Yang Donghai , Gui Zhilun , Li Longtu
Published: July 2007

Ba Ti 0.9 ( Ni 1 ∕ 2 W 1 ∕ 2 ) 0.1 O 3 ceramics were fabricated and their dielectric properties were investigated. With the sintering temperature increasing from 1250to1280°C, the grain size abruptly increases from 1–2to20–40μm, accompanying significant changes in dielectric response. The samples with larger grains exhibit giant dielectric constant characteristics, which are considered to be mainly attributed to the domain boundary effect. The activation energies of the dielectric relaxation Erelax=0.325eV reveal the existence of microdomains in larger grains. The ac conductivity results also give the evidence of the domain boundary effect in the present ceramics.
35% magnetocurrent with spin transport through Si
Authors: Huang Biqin , Zhao Lai , Monsma Douwe J. , Appelbaum Ian
Published: July 2007

Efficient injection of spin-polarized electrons into the conduction band of silicon is limited by the formation of a silicide at the ferromagnetic metal (FM)/silicon interface. In the present work, this “magnetically dead” silicide (where strong spin scattering significantly reduces injected spin polarization) is eliminated by moving the FM in the spin injector from the tunnel junction base anode to the emitter cathode and away from the silicon surface. This results in over an order-of-magnitude increase in spin injection efficiency, from a previously reported magnetocurrent ratio of ≈2% to ≈35% and an estimated spin polarization in Si from ≈1% to at least ≈15%. The injector tunnel junction bias dependence of this spin transport signal is also measured, demonstrating the importance of low bias voltage to preserve high injected spin polarization.
Structural and magnetic properties of spin- and charge-doped Sr0.8La0.2Ti0.9Co0.1O3
Authors: Yang J. , Lee Y. P. , Lee B. W.
Published: July 2007

The structural and the magnetic properties of spin- and charge-doped Sr0.8La0.2Ti0.9Co0.1O3 have been investigated. The sample shows a cubic structure at room temperature. The temperature dependence of magnetization (M) of Sr0.8La0.2Ti0.9Co0.1O3, in both zero-field-cooled (ZFC) and field-cooled (FC) modes between 100 and 70000Oe, was measured. It is found that the sample undergoes the paramagnetic-ferrimagnetic phase transition at around 50K, and the MZFC curve lies above the MFC one below 32K when the applied field is less than 2000Oe. This unusual behavior can be understood as a superposition of ferrimagnetic and paramagnetic contributions to the magnetization.
Balanced charge injection in multilayer polymer light-emitting diode with water soluble nonconjugated polymer dispersed by ionic compounds
Authors: Park Dong-Kyu , Chun A-Rum , Kim Soo-Hong , Kim Min-Sook , Kim Choong-Gi , Kwon Tae-Woo , Cho Seong-Jin , Woo Hyung-Suk , Lee Jae-Gyoung , Lee Suck-Hyun , Guo Zhi-Xin
Published: July 2007

The authors have fabricated highly efficient polymeric light-emitting diode (PLED) from ionic compound dispersed water soluble nonconjugated polymer, polyurethane (PU), which was used as an ultrathin hole blocking and electron injection layer (HB-EIL) on the top of commercially available blue-emitting polymer, polyfluorene. The device with HB-EIL showed a maximum quantum efficiency of 1.7%, while the one without HB-EIL showed an efficiency of 0.6%. They propose that the better performance in PLED with PU layer was due to a well balanced charge injection in emitting layer after the enhanced electron injection due to ionic compound in the insulating PU layer.
Cavity-enhanced blue single-photon emission from a single InGaN∕GaN quantum dot
Authors: Jarjour Anas F. , Taylor Robert A. , Oliver Rachel A. , Kappers Menno J. , Humphreys Colin J. , Tahraoui Abbes
Published: July 2007

The authors report on the generation of single photons in the blue spectral region from a single InGaN∕GaN quantum dot. The collection efficiency was enhanced by embedding the quantum dot layer in the middle of a low-Q microcavity. The microphotoluminescence is observed to be approximately ten times stronger than typical InGaN quantum dot emission without a cavity. The measurements were performed using nonlinear excitation spectroscopy in order to suppress the background emission from the underlying wetting layer.
Fringe-shifting interferometric laser lithography with optical nonlinearity for micro- and nanofabrications
Authors: Amako Jun , Sawaki Daisuke , Kato Makoto
Published: July 2007

The authors demonstrate an interferometric laser lithography process armed with a fringe-shifting technique, which utilizes nonlinear light-matter interaction. With this method, multiphoton-sensitive materials are ablated using ultrashort pulse interference fringes, enabling the ablated regions to be spaced by a fraction of the fringe pitch. For concept-proving experiments, confocal optics equipped with a diffractive beam splitter and a phase shifter are built to perform a fringe shift. This creates a phase difference between split beams that interfere with each other, producing high-contrast fringes. Precise control of beam intensity and beam phase is essential.
Enhanced thermal stability of nickel germanide on thin epitaxial germanium by adding an ultrathin titanium layer
Authors: Zhu Shiyang , Yu M. B. , Lo G. Q. , Kwong D. L.
Published: July 2007

The thermal stability of NiGe films formed on epitaxial Ge on Si substrates was improved from 450to550°C by simply adding an ultrathin (∼1nm) Ti layer during Ni deposition, either as an intermediate layer between Ni and Ge or as a capping layer on Ni. The improvement was attributed to the formation of ternary Ni1−xTixGe phase near the NiGe surface, which acts as a capping layer to suppress agglomeration of the underlying NiGe film at an elevated temperature, as well as modification of the NiGe grain boundaries. The resistivity of NiGe is also slightly reduced by the Ti incorporation, making this method very promising for the germanium technology.
Orbital Period Modulation in SW Cygni
Authors: Manzoori Davood
Published: July 2007

The O–C curve of the Algol-type eclipsing binary SW Cyg was analyzed using the Kalimeris method. The observed period variations with time, the P(E) function and its rate of change dP/dE, were calculated. The plots of O–C values as well as of P(E) and dP/dE against ephemeris (E) all show rather regular period variations in this system. To reveal any cyclic period variations, the P(E) function was subjected to Fourier analysis. A cyclic period change of average ≈27.8-yr duration was obtained. Also a relative mass transfer rate of Δm/m = −1.1 × 10−9 yr−1 was estimated. Finally the existence of a third companion is suggested, and possible causes of period variations in the system are discussed.
Hα Emission from the Magellanic Bridge
Authors: Muller E. , Parker Q. A.
Published: July 2007

We present here a preliminary report and commentary of recently processed observations of Hα emission towards the Magellanic Bridge. These data have been analysed in an attempt to quantify the extent to which the stellar population is capable of reshaping the local ISM. We find that the Hα emission regions are small, weak and sparsely distributed, consistent with a relatively quiescent and inactive ISM where radiative and collisional ionisation is inefficient and sporadic. This suggests that energetic processes at the small scale (i.e. ∼tens of pc) do not dominate the energy balance within the ISM of the Bridge, which therefore hosts a pristine turbulent structure, otherwise inaccessible within our own Galaxy. We find Hα emission that is well correlated with detected 12CO(1–0) line emission (a proxy for molecular hydrogen), as well as other easily identified ring-like Hı features.
Observation Scheduling for a Network of Small-Aperture Telescopes
Authors: Duncan A. R.
Published: July 2007

Over the past several years, a system for accepting, servicing and returning the results from a large number of imaging requests has been developed for use with automated optical telescopes. One of the primary goals of this project is to increase the accessibility of astronomy to school, college and university students. A key component of this system is a request scheduling engine, which produces schedules for each telescope for its current night. This engine is dynamic, adjusting schedules to accommodate new requests and rescheduling failed requests on a time scale of the order of ten minutes. If a telescope is unavailable for an extended period, imaging requests will be reallocated to other telescopes in the network. Various models of dynamic scheduling are considered, and the current implementation is explored with a number of numerical experiments.
Howard Hang: Posttranslational pathogenesis
Authors: LeBrasseur Nicole
Published: July 2007

Howard Hang is cutting through the forest of posttranslational modifications in an attempt to better understand how human pathogens alter this terrain.
An ACAP1-containing clathrin coat complex for endocytic recycling
Authors: Li Jian , Peters Peter J. , Bai Ming , Dai Jun , Bos Erik , Kirchhausen Tomas , Kandror Konstantin V. , Hsu Victor W.
Published: July 2007

Whether coat proteins play a widespread role in endocytic recycling remains unclear. We find that ACAP1, a GTPase-activating protein (GAP) for ADP-ribosylation factor (ARF) 6, is part of a novel clathrin coat complex that is regulated by ARF6 for endocytic recycling in two key physiological settings, stimulation-dependent recycling of integrin that is critical for cell migration and insulin-stimulated recycling of glucose transporter type 4 (Glut4), which is required for glucose homeostasis. These findings not only advance a basic understanding of an early mechanistic step in endocytic recycling but also shed key mechanistic insights into major physiological events for which this transport plays a critical role.
The neurite outgrowth multiadaptor RhoGAP, NOMA-GAP, regulates neurite extension through SHP2 and Cdc42
Authors: Rosário Marta , Franke Renate , Bednarski Christien , Birchmeier Walter
Published: July 2007

Neuronal differentiation involves the formation and extension of neuronal processes. We have identified a novel regulator of neurite formation and extension, the neurite outgrowth multiadaptor, NOMA-GAP, which belongs to a new family of multiadaptor proteins with RhoGAP activity. We show that NOMA-GAP is essential for NGF-stimulated neuronal differentiation and for the regulation of the ERK5 MAP kinase and the Cdc42 signaling pathways downstream of NGF. NOMA-GAP binds directly to the NGF receptor, TrkA, and becomes tyrosine phosphorylated upon receptor activation, thus enabling recruitment and activation of the tyrosine phosphatase SHP2. Recruitment of SHP2 is required for the stimulation of neuronal process extension and for sustained activation of ERK5 downstream of NOMA-GAP. In addition, we show that NOMA-GAP promotes neurite outgrowth by tempering activation of the Cdc42/PAK signaling pathway in response to NGF. NOMA-GAP, through its dual function as a multiadaptor and RhoGAP protein, thus plays an essential role downstream of NGF in promoting neurite outgrowth and extension.
Myosin VI and vinculin cooperate during the morphogenesis of cadherin cell–cell contacts in mammalian epithelial cells
Authors: Maddugoda Madhavi P. , Crampton Matthew S. , Shewan Annette M. , Yap Alpha S.
Published: July 2007

Cooperation between cadherins and the actin cytoskeleton controls many aspects of epithelial biogenesis. We report here that myosin VI critically regulates the morphogenesis of epithelial cell–cell contacts. As epithelial monolayers mature in culture, discontinuous cell–cell contacts are initially replaced by continuous (cohesive) contacts. Myosin VI is recruited to cell contacts as they become linear and cohesive, where it forms a biochemical complex with epithelial cadherin (E-cadherin). Myosin VI is necessary for strong cadherin adhesion, for cells to form cohesive linear contacts, and for the integrity of the apical junctional complex. We find that vinculin mediates this effect of myosin VI. Myosin VI is necessary for vinculin and E-cadherin to interact. A combination of gain and loss of function approaches identifies vinculin as a downstream effector of myosin VI that is necessary for the integrity of intercellular contacts. We propose that myosin VI and vinculin form a molecular apparatus that generates cohesive cell–cell contacts in cultured mammalian epithelia.
A vesicle surface tyrosine kinase regulates phagosome maturation
Authors: Fang Jun , Brzostowski Joseph A. , Ou Stephen , Isik Nilgun , Nair Vinod , Jin Tian
Published: July 2007

Phagocytosis is crucial for host defense against microbial pathogens and for obtaining nutrients in Dictyostelium discoideum. Phagocytosed particles are delivered via a complex route from phagosomes to lysosomes for degradation, but the molecular mechanisms involved in the phagosome maturation process are not well understood. Here, we identify a novel vesicle-associated receptor tyrosine kinase-like protein, VSK3, in D. discoideum. We demonstrate how VSK3 is involved in phagosome maturation. VSK3 resides on the membrane of late endosomes/lysosomes with its C-terminal kinase domain facing the cytoplasm. Inactivation of VSK3 by gene disruption reduces the rate of phagocytosis in cells, which is rescued by re-expression of VSK3. We found that the in vivo function of VSK3 depends on the presence of the kinase domain and vesicle localization. Furthermore, VSK3 is not essential for engulfment, but instead, is required for the fusion of phagosomes with late endosomes/lysosomes. Our findings suggest that localized tyrosine kinase signaling on the surface of endosome/lysosomes represents a control mechanism for phagosome maturation.
uPAR induces epithelial–mesenchymal transition in hypoxic breast cancer cells
Authors: Lester Robin D. , Jo Minji , Montel Valérie , Takimoto Shinako , Gonias Steven L.
Published: July 2007

Hypoxia activates genetic programs that facilitate cell survival; however, in cancer, it may promote invasion and metastasis. In this study, we show that breast cancer cells cultured in 1.0% O2 demonstrate changes consistent with epithelial–mesenchymal transition (EMT). Snail translocates to the nucleus, and E-cadherin is lost from plasma membranes. Vimentin expression, cell migration, Matrigel invasion, and collagen remodeling are increased. Hypoxia-induced EMT is accompanied by increased expression of the urokinase-type plasminogen activator receptor (uPAR) and activation of cell signaling factors downstream of uPAR, including Akt and Rac1. Glycogen synthase kinase-3β is phosphorylated, and Snail expression is increased. Hypoxia-induced EMT is blocked by uPAR gene silencing and mimicked by uPAR overexpression in normoxia. Antagonizing Rac1 or phosphatidylinositol 3-kinase also inhibits development of cellular properties associated with EMT in hypoxia. Breast cancer cells implanted on chick chorioallantoic membranes and treated with CoCl2, to model hypoxia, demonstrate increased dissemination. We conclude that in hypoxia, uPAR activates diverse cell signaling pathways that cooperatively induce EMT and may promote cancer metastasis.
Astrin is required for the maintenance of sister chromatid cohesion and centrosome integrity
Authors: Thein Kerstin H. , Kleylein-Sohn Julia , Nigg Erich A. , Gruneberg Ulrike
Published: July 2007

Faithful chromosome segregation in mitosis requires the formation of a bipolar mitotic spindle with stably attached chromosomes. Once all of the chromosomes are aligned, the connection between the sister chromatids is severed by the cysteine protease separase. Separase also promotes centriole disengagement at the end of mitosis. Temporal coordination of these two activities with the rest of the cell cycle is required for the successful completion of mitosis. In this study, we report that depletion of the microtubule and kinetochore protein astrin results in checkpoint-arrested cells with multipolar spindles and separated sister chromatids, which is consistent with untimely separase activation. Supporting this idea, astrin-depleted cells contain active separase, and separase depletion suppresses the premature sister chromatid separation and centriole disengagement in these cells. We suggest that astrin contributes to the regulatory network that controls separase activity.
Facilitation versus depression in cultured hippocampal neurons determined by targeting of Ca2+ channel Cavβ4 versus Cavβ2 subunits to synaptic terminals
Authors: Xie Mian , Li Xiang , Han Jing , Vogt Daniel L. , Wittemann Silke , Mark Melanie D. , Herlitze Stefan
Published: July 2007

Ca2+ channel β subunits determine the transport and physiological properties of high voltage–activated Ca2+ channel complexes. Our analysis of the distribution of the Cavβ subunit family members in hippocampal neurons correlates their synaptic distribution with their involvement in transmitter release. We find that exogenously expressed Cavβ4b and Cavβ2a subunits distribute in clusters and localize to synapses, whereas Cavβ1b and Cavβ3 are homogenously distributed. According to their localization, Cavβ2a and Cavβ4b subunits modulate the synaptic plasticity of autaptic hippocampal neurons (i.e., Cavβ2a induces depression, whereas Cavβ4b induces paired-pulse facilitation [PPF] followed by synaptic depression during longer stimuli trains). The induction of PPF by Cavβ4b correlates with a reduction in the release probability and cooperativity of the transmitter release. These results suggest that Cavβ subunits determine the gating properties of the presynaptic Ca2+ channels within the presynaptic terminal in a subunit-specific manner and may be involved in organization of the Ca2+ channel relative to the release machinery.
Cyclin E overexpression impairs progression through mitosis by inhibiting APCCdh1
Authors: Keck Jamie M. , Summers Matthew K. , Tedesco Donato , Ekholm-Reed Susanna , Chuang Li-Chiou , Jackson Peter K. , Reed Steven I.
Published: July 2007

Overexpression of cyclin E, an activator of cyclin-dependent kinase 2, has been linked to human cancer. In cell culture models, the forced expression of cyclin E leads to aneuploidy and polyploidy, which is consistent with a direct role of cyclin E overexpression in tumorigenesis. In this study, we show that the overexpression of cyclin E has a direct effect on progression through the latter stages of mitotic prometaphase before the complete alignment of chromosomes at the metaphase plate. In some cases, such cells fail to divide chromosomes, resulting in polyploidy. In others, cells proceed to anaphase without the complete alignment of chromosomes. These phenotypes can be explained by an ability of overexpressed cyclin E to inhibit residual anaphase-promoting complex (APCCdh1) activity that persists as cells progress up to and through the early stages of mitosis, resulting in the abnormal accumulation of APCCdh1 substrates as cells enter mitosis. We further show that the accumulation of securin and cyclin B1 can account for the cyclin E–mediated mitotic phenotype.
Modulation of Extracellular Proton Fluxes from Retinal Horizontal Cells of the Catfish by Depolarization and Glutamate
Authors: Kreitzer Matthew A. , Collis Leon P. , Molina Anthony J.A. , Smith Peter J.S. , Malchow Robert Paul
Published: July 2007

Self-referencing H+-selective microelectrodes were used to measure extracellular proton fluxes from cone-driven horizontal cells isolated from the retina of the catfish (Ictalurus punctatus). The neurotransmitter glutamate induced an alkalinization of the area adjacent to the external face of the cell membrane. The effect of glutamate occurred regardless of whether the external solution was buffered with 1 mM HEPES, 3 mM phosphate, or 24 mM bicarbonate. The AMPA/kainate receptor agonist kainate and the NMDA receptor agonist N-methyl-d-aspartate both mimicked the effect of glutamate. The effect of kainate on proton flux was inhibited by the AMPA/kainate receptor blocker CNQX, and the effect of NMDA was abolished by the NMDA receptor antagonist DAP-5. Metabotropic glutamate receptor agonists produced no alteration in proton fluxes from horizontal cells. Depolarization of cells either by increasing extracellular potassium or directly by voltage clamp also produced an alkalinization adjacent to the cell membrane. The effects of depolarization on proton flux were blocked by 10 μM nifedipine, an inhibitor of L-type calcium channels. The plasmalemma Ca2+/H+ ATPase (PMCA) blocker 5(6)-carboxyeosin also significantly reduced proton flux modulation by glutamate. Our results are consistent with the hypothesis that glutamate-induced extracellular alkalinizations arise from activation of the PMCA pump following increased intracellular calcium entry into cells. This process might help to relieve suppression of photoreceptor neurotransmitter release that results from exocytosed protons from photoreceptor synaptic terminals. Our findings argue strongly against the hypothesis that protons released by horizontal cells act as the inhibitory feedback neurotransmitter that creates the surround portion of the receptive fields of retinal neurons.
Responses of Rat P2X2 Receptors to Ultrashort Pulses of ATP Provide Insights into ATP Binding and Channel Gating
Authors: Moffatt Luciano , Hume Richard I.
Published: July 2007

To gain insight into the way that P2X2 receptors localized at synapses might function, we explored the properties of outside-out patches containing many of these channels as ATP was very rapidly applied and removed. Using a new method to calibrate the speed of exchange of solution over intact patches, we were able to reliably produce applications of ATP lasting <200 μs. For all concentrations of ATP, there was a delay of at least 80 μs between the time when ATP arrived at the receptor and the first detectable flow of inward current. In response to 200-μs pulses of ATP, the time constant of the rising phase of the current was ∼600 μs. Thus, most channel openings occurred when no free ATP was present. The current deactivated with a time constant of ∼60 ms. The amplitude of the peak response to a brief pulse of a saturating concentration of ATP was ∼70% of that obtained during a long application of the same concentration of ATP. Thus, ATP leaves fully liganded channels without producing an opening at least 30% of the time. Extensive kinetic modeling revealed three different schemes that fit the data well, a sequential model and two allosteric models. To account for the delay in opening at saturating ATP, it was necessary to incorporate an intermediate closed state into all three schemes. These kinetic properties indicate that responses to ATP at synapses that use homomeric P2X2 receptors would be expected to greatly outlast the duration of the synaptic ATP transient produced by a single presynaptic spike. Like NMDA receptors, P2X2 receptors provide the potential for complex patterns of synaptic integration over a time scale of hundreds of milliseconds.
Enzymatic Suppression of the Membrane Conductance Associated with the Glutamine Transporter SNAT3 Expressed in Xenopus Oocytes by Carbonic Anhydrase II
Authors: Weise Alexandra , Becker Holger M. , Deitmer Joachim W.
Published: July 2007

The transport activity of the glutamine/neutral amino acid transporter SNAT3 (former SN1, SLC38A3), expressed in oocytes of the frog Xenopus laevis is associated with a non-stoichiometrical membrane conductance selective for Na+ and/or H+ (Schneider, H.P., S. Bröer, A. Bröer, and J.W. Deitmer. 2007. J. Biol. Chem. 282:3788–3798). When we expressed SNAT3 in frog oocytes, the glutamine-induced membrane conductance was suppressed, when carbonic anhydrase isoform II (CAII) had been injected into the oocytes. Transport of substrate, however, was not affected by CAII. The reduction of the membrane conductance by CAII was dependent on the presence of CO2/HCO3−, and could be reversed by blocking the catalytic activity of CAII by ethoxyzolamide (10 μM). Coexpression of wild-type CAII or a N-terminal CAII mutant with SNAT3 also reduced the SNAT3- associated membrane conductance. The catalytically inactive CAII mutant V143Y coexpressed in oocytes did not affect SNAT3-associated membrane conductance. Our results reveal a new type of interaction between CAII and a transporter-associated cation conductance, and support the hypothesis that the transport of substrate and the non-stoichiometrical ion conductance are independent of each other. This study also emphasizes the importance of carbonic anhydrase activity and the presence of CO2-bicarbonate buffers for membrane transport processes.
Cytoplasmic ATP Inhibition of CLC-1 Is Enhanced by Low pH
Authors: Tseng Pang-Yen , Bennetts Brett , Chen Tsung-Yu
Published: July 2007

The CLC-1 Cl− channel is abundantly expressed on the plasma membrane of muscle cells, and the membrane potential of muscle cells is largely controlled by the activity of this Cl− channel. Previous studies showed that low intracellular pH increases the overall open probability of recombinant CLC-1 channels in various expression systems. Low intracellular pH, however, is known to inhibit the Cl− conductance on the native muscle membrane, contradicting the findings from the recombinant CLC-1 channels in expressed systems. Here we show that in the presence of physiological concentrations of ATP, reduction of the intracellular pH indeed inhibits the expressed CLC-1, mostly by decreasing the open probability of the common gate of the channel.
High risk of pituitary dysfunction due to aneurysmal subarachnoid haemorrhage: a prospective investigation of anterior pituitary function in the acute phase and 12 months after the event
Authors: Tanriverdi Fatih , Dagli Ahmet Turan , Karaca Zuleyha , Unluhizarci Kursad , Selcuklu Ahmet , Casanueva Felipe F. , Kelestimur Fahrettin
Published: July 2007

Objective  Recent investigations have provided evidence for a high prevalence of pituitary dysfunction in patients with subarachnoid haemorrhage (SAH). However, apart from one study, all of the previous data were obtained from retrospective studies. To our knowledge there is no previously reported study in which pituitary function was investigated in the same patients immediately after SAH and 12 months later. The aim of this study was to understand the prevalence and progression of anterior pituitary hormone deficiencies both in the acute phase of SAH and 12 months after the event.

Patients and design  Twenty‐two SAH patients (11 men, 11 women) were included in the study. Pituitary function was evaluated in the early acute phase (within 24 h of admission) and after 12 months.

Results  Pituitary hormone deficiencies in the acute phase were as follows: 31·8% had gonadotrophin, 22·7% had ACTH and 22·7% had GH deficiencies. At 12 months after SAH: 0·0% had gonadotrophin, 13·6% had ACTH and 36·4% had GH deficiencies. Overall, after 12 months, pituitary hormone deficiencies recovered in 15 (68·2%) patients and new‐onset pituitary hormone deficiencies were present in nine (40·9%) patients.

Conclusions  GH deficiency (GHD) was the most common pituitary deficit at 12 months after SAH and the majority of the patients (87·5%) had isolated GHD. During the 12‐month follow‐up, pituitary function was found to either improve or worsen in a considerable number of patients.