bluuebunny/crossref_metadata_2025 huggingface dataset:
Methodology of evaluating the influence of the resistance of contact regions in the measurements of sheet resistance on stripes of ultrathin high-resistance materials
Authors: Náhlík Josef , Kašpárková Irena , Fitl Přemysl
Published: July 2012

The paper reviews the problems of measurement of sheet resistance of ultrathin high-resistance layers of organic semiconductors and the essential underlying problems. Particular attention is paid to potential influence of the resistance of contact regions on the results of direct measurement of sheet resistance of stripe-shaped layers. In this connection, we present a methodology of double length stripe resistance measurement (DLSRM), used above all to minimise the influence of contact regions on the measurement results. We deduce theoretical as well as practical possibilities of DLSRM in the diagnostics and quantitative characterisation of unsuitable or even faulty contacts on high-resistance layers. The application efficiency of the DLSRM method is documented by the results of sheet resistance measurement on zinc phthalocyanine with cathode sputtered planar contacts of noble metals (gold, platinum, or palladium). As expected, gold is the best contact material, but even in its application one cannot neglect the influence of contact regions. The presented method is universal and generally applicable to all materials where sheet resistance is the relevant parameter, and its assessment is based on measurements of the layer resistance in stripe arrangement.
Tracer diffusion in colloidal suspensions under dilute and crowded conditions with hydrodynamic interactions
Authors: Tomilov A. , Videcoq A. , Chartier T. , Ala-Nissilä T. , Vattulainen I.
Published: July 2012

We consider tracer diffusion in colloidal suspensions under solid loading conditions, where hydrodynamic interactions play an important role. To this end, we carry out computer simulations based on the hybrid stochastic rotation dynamics-molecular dynamics (SRD-MD) technique. Many details of the simulation method are discussed in detail. In particular, our choices for the SRD-MD parameters and for the different scales are adapted to simulating colloidal suspensions under realistic conditions. Our simulation data are compared with published theoretical, experimental and numerical results and compared to Brownian dynamics simulation data. We demonstrate that our SRD-MD simulations reproduce many features of the hydrodynamics in colloidal fluids under finite loading. In particular, finite-size effects and the diffusive behavior of colloids for a range of volume fractions of the suspension show that hydrodynamic interactions are correctly included within the SRD-MD technique.
Simulation of tethered oligomers in nanochannels using multi-particle collision dynamics
Authors: Raghu Riyad Chetram , Schofield Jeremy
Published: July 2012

The effect of a high Reynold's number, pressure-driven flow of a compressible gas on the conformation of an oligomer tethered to the wall of a square channel is studied under both ideal solvent and poor solvent conditions using a hybrid multiparticle collision dynamics and molecular dynamics algorithm. Unlike previous studies, the flow field contains an elongational component in addition to a shear component as well as fluid slip near the walls and results in a Schmidt number for the polymer beads that is less than unity. In both solvent regimes the oligomer is found to extend in the direction of flow. Under the ideal solvent conditions, torsional twisting of the chain and aperiodic cyclical dynamics are observed for the end of the oligomer. Under poor solvent conditions, a metastable helix forms in the end of the chain despite the lack of any attractive potential between beads in the oligomeric chain. The formation of the helix is postulated to be the result of a solvent induced chain collapse that has been confined to a single dimension by a strong flow field.
Kr II and Xe II axial velocity distribution functions in a cross-field ion source
Authors: Lejeune A. , Bourgeois G. , Mazouffre S.
Published: July 2012

Laser induced fluorescence measurements were carried out in a cross-field ion source to examine the behaviour of the axial ion velocity distribution functions (VDFs) in the expanding plasma. In the present paper, we focus on the axial VDFs of Kr II and Xe II ions. We examine the contourplots in a 1D-phase space (x,vx) representation in front of the exhaust channel and along the centerline of the ion source. The main ion beam, whose momentum corresponds to the ions that are accelerated through the whole potential drop, is observed. A secondary structure reveals the ions coming from the opposite side of the channel. We show that the formation of the neutralized ion flow is governed by the annular geometry. The assumption of a collisionless shock or a double layer due to supersonic beam interaction is not necessary. A non-negligible fraction of slow ions originates in local ionization or charge-exchange collision events between ions of the expanding plasma and atoms of the background residual gas. Slow ions that are produced near the centerline in the vicinity of the exit plane are accelerated toward the source body with a negative velocity leading to a high sputtering of front face. On the contrary, the ions that are produced in the vicinity of the channel exit plane are partially accelerated by the extended electric field.
A different approach to obtain Mayer’s extension to stationary single particle Wigner distribution
Authors: Bose Anirban , Janaki M. S.
Published: July 2012

It is shown that the stationary collisionless single-particle Wigner equation in one dimension containing quantum corrections at the lowest order is satisfied by a distribution function that is similar in form to the Maxwellian distribution with an effective mass and a generalized potential. The distribution is used to study quantum corrections to electron hole solutions.
Suppression of drift waves in a linear magnetized plasma column
Authors: DuBois A. M. , Eadon A. C. , Thomas E.
Published: July 2012

In magnetically confined fusion plasmas, drift wave driven turbulence can lead to enhanced particle transport from the plasma. Because of this, a significant research emphasis has been placed on the suppression of drift waves in the plasma edge. However, the combination of the toroidal geometry and short plasma lifetimes can make it difficult to fully characterize the properties of these instabilities. Because linear magnetized plasma devices offer a combination of simpler geometry and steady state plasma generation, it is possible to perform detailed studies of many types of plasma instabilities—including drift waves. This paper reports on a recent experiment in which low frequency instabilities (ω ≤ ωci) in the Auburn Linear EXperiment for Instability Studies plasma device were characterized as drift waves and through changes in the parallel current, it is shown that it is possible to suppress these instabilities.
Efficient and reliable green organic light-emitting diodes with Cl2 plasma-etched indium tin oxide anode
Authors: Zhang Y. Q. , Acharya R. , Cao X. A.
Published: July 2012

The effects of brief etching with Cl2-based inductively coupled plasma (ICP) on the surface chemistry and properties of indium-tin-oxide (ITO) were investigated. Due to the low volatility of InClx, Cl2, and Cl2/BCl3 ICP etching created stable In-Cl polar bonds at the ITO surfaces, raising its work function by up to 1.0 eV. Green phosphorescent organic light-emitting diodes (OLEDs) built on ICP-etched ITO/glass substrates exhibited a brightness of 1.4 × 104 cd/m2 and a current efficiency of 70 cd/A at 20 mA/cm2, which were 40% higher than those of similar OLEDs with an O2 plasma-treated ITO anode. The OLEDs with plasma chlorinated ITO also showed better stability and reliability. These results suggest that brief chlorine plasma etching can result in stable chlorinated ITO surfaces with a high work function, leading to more balanced charge injection and performance enhancement of OLEDs.
Size and alloying induced changes in lattice constant, core, and valance band binding energy in Pd-Ag, Pd, and Ag nanoparticles: Effect of in-flight sintering temperature
Authors: Sengar Saurabh K. , Mehta B. R. , Govind
Published: July 2012

In the present study, we report the growth of size selected Pd, Ag, and Pd-Ag alloy nanoparticles by an integrated method comprising of the gas phase synthesis, electrical mobility size selection, and in-flight sintering steps. Effect of temperature during in-flight sintering on nanoparticle size, crystal structure, and electronic properties has been studied. XRD studies show lattice expansion in Pd and Ag nanoparticles and lattice contraction in Pd-Ag alloy nanoparticles on increasing the sintering temperatures. In case of Pd and Ag nanoparticles, size induced changes in lattice constants are consistent with the changes in the binding energy positions with respect to bulk values. In case of Pd-Ag alloy nanoparticles, change in nanoparticle size and composition on sintering affect the lattice constant and binding energy positions. Large changes in Pd4d valance band centroid in Pd-Ag nanoparticles are due to size and alloying effects. The results of this study are important for understanding the correlation between electronic properties and Pd-H interaction in Pd alloy nanoparticles.
Parameterization of the dielectric function of InP from 1.19 to 6.57 eV for temperatures from 25 to 700 K
Authors: Jung Kim Tae , Yong Hwang Soon , Seok Byun Jun , Diware Mangesh S. , Choi Junho , Gyeol Park Han , Dong Kim Young
Published: July 2012

We present an analytic expression that accurately represents the dielectric function ɛ = ɛ1 + iɛ2 of InP from 1.19 to 6.57 eV for temperatures from 25 to 700 K. The original data were obtained on a InP substrate by spectroscopic ellipsometry. The analytic representation is based on the parametric model, which is known to accurately portray ɛ without unphysical assumptions. The ɛ data are successfully reconstructed by eight Gaussian-broadened polynomials and a pole and can be used to determine ɛ as a continuous function of energy and temperature within the limits given above. Our results should be useful in a number of contexts, including device design and in situ monitoring of deposition. A representative deposition example is discussed.
Tailoring coercivity of unbiased exchange-coupled ferromagnet/antiferromagnet bilayers
Authors: Sossmeier K. D. , Schafer D. , Bastos A. P. O. , Schmidt J. E. , Geshev J.
Published: July 2012

This paper reports experimental results obtained on unconventional exchange-coupled ferromagnet/antiferromagnet (FM/AF) system showing zero net bias. The Curie temperature of the FM (NiCu) is lower than the blocking temperature of the AF (IrMn). Samples were either annealed or irradiated with He, Ar, or Ge ions at 40 keV. Due to the exchange coupling at the FM/AF interface, the coercivity (HC) of the as-deposited FM/AF bilayer is rather higher than that of the corresponding FM single layer. We found that by choosing a proper ion fluence or annealing temperature, it is possible to controllably vary HC. Ion irradiation of the FM single layer has lead to only a decrease of HC and annealing or He ion irradiation has not caused important changes at the FM/AF interface; nevertheless, a twofold increase of HC was obtained after these treatments. Even more significant enhancement of HC was attained after Ge ion irradiation and attributed to ion-implantation-induced modification of only the FM layer; damages of the FM/AF interface, on the other hand, decrease the coercivity.
Analysis of pinning effect at the Alq3/metal interface in organic light emitting diodes
Authors: Petrosino Mario , Rubino Alfredo
Published: July 2012

In order to study the improvement of electrons injection in organic light emitting diodes (OLEDs), we have realized ITO/PEDOT/PF6/Alq3/cathode OLEDs with four different metallic electrodes: Ca, Mg, Al, and Ag. The cathode barrier increment/decrement has been estimated between the four kinds of devices by using the thermionic injection theory. These results have allowed to see a very low dependence of the cathode barrier on the metal work function, explained in terms of pinning at the cathode interface. The authors propose that this pinning effect is due to the presence of a distribution of states at the Alq3/metal interface; the application of the Cowley-Sze model has returned a density of states of about 6 × 1014 eV−1 cm−2, high value satisfying the observed independence of the cathode barrier on the employed metallic electrodes.
Linear and nonlinear studies of velocity shear driven three dimensional electron-magnetohydrodynamics instability
Authors: Gaur Gurudatt , Das Amita
Published: July 2012

The study of electron velocity shear driven instability in electron magnetohydrodynamics (EMHD) regime in three dimensions has been carried out. It is well known that the instability is non-local in the plane defined by the flow direction and that of the shear, which is the usual Kelvin-Helmholtz mode, often termed as the sausage mode in the context of EMHD. On the other hand, a local instability with perturbations in the plane defined by the shear and the magnetic field direction exists which is termed as kink mode. The interplay of these two modes for simple sheared flow case as well as that when an external magnetic field exists has been studied extensively in the present manuscript in both linear and nonlinear regimes. Finally, these instability processes have been investigated for the exact 2D dipole solutions of EMHD equations [M. B. Isichenko and A. N. Marnachev, Sov. Phys. JETP 66, 702 (1987)] for which the electron flow velocity is sheared. It has been shown that dipoles are very robust and stable against the sausage mode as the unstable wavelengths are typically longer than the dipole size. However, we observe that they do get destabilized by the local kink mode.
Isorotation and differential rotation in a magnetic mirror with imposed E×B rotation
Authors: Romero-Talamás C. A. , Elton R. C. , Young W. C. , Reid R. , Ellis R. F.
Published: July 2012

Doppler spectroscopy of helium impurities in the Maryland Centrifugal Experiment reveals the simultaneous existence of isorotating and differentially rotating magnetic surfaces. Differential rotation occurs at the innermost surfaces and is conjectured to cause plasma voltage oscillations of hundreds of kilohertz by periodically changing the current path inductance. High-speed images show the periodic expulsion of plasma near the mirror ends at the same frequencies. In spite of this, the critical ionization velocity limit is exceeded, with respect to the vacuum field definition, for at least 0.5 ms.
Design of a correlation electron cyclotron emission diagnostic for Alcator C-Mod
Authors: Sung C. , White A. E. , Irby J. H. , Leccacorvi R. , Vieira R. , Oi C. Y. , Peebles W. A. , Nguyen X.
Published: July 2012

A correlation electron cyclotron emission (CECE) diagnostic has been installed in Alcator C-Mod. In order to measure electron temperature fluctuations, this diagnostic uses a spectral decorrelation technique. Constraints obtained with nonlinear gyrokinetic simulations guided the design of the optical system and receiver. The CECE diagnostic is designed to measure temperature fluctuations which have kθ ≤ 4.8 cm−1 (kθρs < 0.5) using a well-focused beam pattern. Because the CECE diagnostic is a dedicated turbulence diagnostic, the optical system is also flexible, which allows for various collimating lenses and antenna to be used. The system overview and the demonstration of its operability as designed are presented in this paper.
Imaging x-ray Thomson scattering spectrometer design and demonstration (invited)
Authors: Gamboa E. J. , Huntington C. M. , Trantham M. R. , Keiter P. A. , Drake R. P. , Montgomery D. S. , Benage J. F. , Letzring S. A.
Published: July 2012

In many laboratory astrophysics experiments, intense laser irradiation creates novel material conditions with large, one-dimensional gradients in the temperature, density, and ionization state. X-ray Thomson scattering is a powerful technique for measuring these plasma parameters. However, the scattered signal has previously been measured with little or no spatial resolution, which limits the ability to diagnose inhomogeneous plasmas. We report on the development of a new imaging x-ray Thomson spectrometer (IXTS) for the Omega laser facility. The diffraction of x-rays from a toroidally curved crystal creates high-resolution images that are spatially resolved along a one-dimensional profile while spectrally dispersing the radiation. This focusing geometry allows for high brightness while localizing noise sources and improving the linearity of the dispersion. Preliminary results are presented from a scattering experiment that used the IXTS to measure the temperature profile of a shocked carbon foam.
Frequency-dependent dielectric response model for polyimide-poly(vinilydenefluoride) multilayered dielectrics
Authors: Di Lillo Luigi , Bergamini Andrea , Albino Carnelli Dario , Ermanni Paolo
Published: July 2012

A physical model for the frequency-dependent dielectric response of multilayered structures is reported. Two frequency regimes defined by the relative permittivities and volume resistivities of the layers have been analytically identified and experimentally investigated on a structure consisting of polyimide and poly(vinilydenefluoride) layers. The relative permittivity follows an effective medium model at high frequency while showing a dependence on the volume resistivity at low frequency. In this regime, relative permittivities exceeding those expected from effective medium model are recorded. These findings provide insights into inhomogeneous dielectrics behavior for the development of high energy density dielectric films.
Controlled facile synthesis, growth mechanism, and exothermic properties of large-area Co3O4 nanowalls and nanowires on silicon substrates
Authors: Qiao Zhiqiang , Xu Daguo , Nie Fude , Yang Guangcheng , Zhang Kaili
Published: July 2012

Co3O4 nanowalls and nanowires have been synthesized onto silicon substrates by low-temperature thermal oxidation of sputtered Co thin films in static air. The synthesis method is very simple and suitable for large-scale fabrication. The effects of the thermal oxidation temperature and duration on the size, amount, and length of the nanowires and nanowalls are systematically investigated both by scanning electron microscopy characterization and differential scanning calorimetry thermal analysis. It is found that the Co/CoO oxidation and Co3O4 decomposition are important factors contributing to the growth of the Co3O4 nanowalls and nanowires. The mechanical adhesion between the Co3O4 nanowalls/nanowires/film and the silicon substrate is observed to be very strong, which is beneficial for many practical applications. Based on the experimental observations, the detailed growth mechanisms of the nanowalls and nanowires are presented. Finally, the promising novel exothermic reaction properties of the Co3O4 nanowalls and nanowires with Al are investigated by thermal analysis.
Calibration techniques for fast-ion Dα diagnostics
Authors: Heidbrink W. W. , Bortolon A. , Muscatello C. M. , Ruskov E. , Grierson B. A. , Podestá M.
Published: July 2012

Fast-ion Dα measurements are an application of visible charge-exchange recombination (CER) spectroscopy that provide information about the energetic ion population. Like other CER diagnostics, the standard intensity calibration is obtained with an integrating sphere during a vacuum vessel opening. An alternative approach is to create plasmas where the fast-ion population is known, then calculate the expected signals with a synthetic diagnostic code. The two methods sometimes agree well but are discrepant in other cases. Different background subtraction techniques and simultaneous measurements of visible bremsstrahlung and of beam emission provide useful checks on the calibrations and calculations.
Near midplane scintillator-based fast ion loss detector on DIII-D
Authors: Chen X. , Fisher R. K. , Pace D. C. , García-Muñoz M. , Chavez J. A. , Heidbrink W. W. , Van Zeeland M. A.
Published: July 2012

A new scintillator-based fast-ion loss detector (FILD) installed near the outer midplane of the plasma has been commissioned on DIII-D. This detector successfully measures coherent fast ion losses produced by fast-ion driven instabilities (≤500 kHz). Combined with the first FILD at ∼45° below the outer midplane [R. K. Fisher, et al., Rev. Sci. Instrum. 81, 10D307 (2010)10.1063/1.3490020], the two-detector system measures poloidal variation of losses. The phase space sensitivity of the new detector (gyroradius rL ∼ [1.5–8] cm and pitch angle α ∼ [35°–85°]) is calibrated using neutral beam first orbit loss measurements. Since fast ion losses are localized poloidally, having two FILDs at different poloidal locations allows for the study of losses over a wider range of plasma shapes and types of loss orbits.
Abnormal pseudospin-degenerate states in a graphene quantum dot with double vacancy defects
Authors: Zhou Aiping , Sheng Weidong
Published: July 2012

We study valley-polarized states in an armchair graphene quantum dot with double vacancy defects. Half-filled doubly degenerate states are found in the middle of the gap only when two vacancies occupy certain specific sites in each of the sublattices of the quantum dot. The doubly degenerate states forming around the vacancies are shown to be entirely localized in their respective sublattice, which results in that the two parallel-spin electrons in the degenerate Fermi level carry purely opposite valley pseudospins. Surprisingly, the pseudospin-degenerate states are found to be symmetric even when the reflection symmetry of the structure has been broken by the vacancies. It is further shown that the pseudospin degeneracy, similar to the Kramer’s degeneracy lifted by a magnetic field, can be removed by an applied electric field. Like the Zeeman effect, the split states would retain their original valley pseudospins and exhibit linear splitting energy with respect to the applied field.
Resistive switching behavior of a thin amorphous rare-earth scandate: Effects of oxygen content
Authors: Chang W. Z. , Chu J. P. , Wang S. F.
Published: July 2012

In addition to beneficial ∼3 orders of magnitude in the resistance ratio, the amorphous HoScOx film exhibits excellent resistive switching (RS) properties of low electrical stress, thin thickness (36 nm), and simple process without forming or annealing, making it potentially useful for nonvolatile memory applications. Obvious oxygen effects are seen: no apparent RS property is detected in the near-stoichiometric film with 57.6 at. % oxygen, whereas distinct RS characteristics are observed in the oxygen-deficient (50.7 at. %) film. The RS property obtained is thought to be dominated by the high oxygen vacancy concentration, which serves as the filamentary conduction in the sample.
Strong blue light emission from a-SiNx:O films via localized surface plasmon enhancement
Authors: Ma Zhongyuan , Yan Minyi , Jiang Xiaofan , Yang Huafeng , Xia Guoyin , Ni Xiaodong , Ling Tao , Li Wei , Xu Ling , Chen Kunji , Huang Xinfan , Feng Duan
Published: July 2012

Strong and stable blue photoluminescence (PL) at room temperature has been observed from amorphous oxidized silicon nitride (a-SiNx:O) films with Ag nanoparticles inserted between a-SiNx:O films and Si substrates. The resonant excitation of localized surface plasmons (LSPs) with the emission of a-SiNx:O films has resulted in an increase in the internal quantum efficiency, from 3.9% to 8.4%. We have found that the PL efficiency ratio induced by resonant coupling is close to the enhancement of the spontaneous emission rate of a-SiNx:O, which demonstrates that a-SiNx:O films with LSP-enhanced blue emission is promising for silicon-based light-emitting applications.
Tailoring effective thermoelectric tensors and high-density power generation in a tubular Bi0.5Sb1.5Te3/Ni composite with cylindrical anisotropy
Authors: Kanno Tsutomu , Sakai Akihiro , Takahashi Kouhei , Omote Atsushi , Adachi Hideaki , Yamada Yuka
Published: July 2012

Transverse thermoelectric responses in heterogeneous composites made of periodically laminated Bi0.5Sb1.5Te3/Ni in a tubular shape were investigated. Numerical calculations quantitatively clarify the relationship between geometrical parameters and effective thermoelectric tensors. In the present tubular heterogeneous composites, the temperature gradient across the radial direction yields a transverse voltage along the axial direction due to the unnatural cylindrical anisotropy. The tubular configuration allows for direct and efficient heat transfer from fluid heat sources. A high-density power generation of 417 W m−2 was achieved under the small temperature difference of 83 K.
Transistors with chemically synthesized layered semiconductor WS2 exhibiting 105 room temperature modulation and ambipolar behavior
Authors: Sik Hwang Wan , Remskar Maja , Yan Rusen , Protasenko Vladimir , Tahy Kristof , Doo Chae Soo , Zhao Pei , Konar Aniruddha , (Grace) Xing Huili , Seabaugh Alan , Jena Debdeep
Published: July 2012

We report the realization of field-effect transistors (FETs) made with chemically synthesized multilayer crystal semiconductor WS2. The Schottky-barrier FETs demonstrate ambipolar behavior and a high (∼105×) on/off current ratio at room temperature with current saturation. The behavior is attributed to the presence of an energy bandgap in the ultrathin layered semiconductor crystal material. The FETs also show clear photo response to visible light. The promising electronic and optical characteristics of the devices combined with the chemical synthesis, and flexibility of layered semiconductor crystals such as WS2 make them attractive for future electronic and optical devices.
Electrical properties of GaAs photonic crystal cavity lateral p-i-n diodes
Authors: Petykiewicz Jan , Shambat Gary , Ellis Bryan , Vučković Jelena
Published: July 2012

We investigate conduction and free-carrier injection in laterally doped GaAs p-i-n diodes formed in one and two-dimensional photonic crystal (PC) nanocavities. Finite element simulations show that the lateral geometry exhibits high conductivity for a wide range of PC parameters and allows for precise control over current flow, enabling efficient carrier injection despite fast surface recombination. Thermal simulations indicate that the temperature increase during steady-state operation is only 3.3 K in nanobeams and 0.29 K in L3 defect nanocavities. The results affirm the suitability of lateral doping in PC devices and indicate criteria for further design optimization.
Tunable room-temperature zero temperature coefficient of resistivity in antiperovskite compounds Ga1−xCFe3 and Ga1−yAlyCFe3
Authors: Lin S. , Wang B. S. , Lin J. C. , Huang Y. N. , Lu W. J. , Zhao B. C. , Tong P. , Song W. H. , Sun Y. P.
Published: July 2012

The effects of the Ga content and the substitution of Al for Ga on the temperature coefficient of resistivity (TCR) of antiperovskite GaCFe3 have been investigated systematically. Our results indicate the value of TCR and its temperature range can be tuned by altering chemical compositions. With decreasing the Ga content in Ga1−xCFe3 or increasing Al dopant in Ga1−yAlyCFe3, the sign of TCR changes from positive to negative and room-temperature zero TCR material can be achieved. Typically, the optimized TCR values are about −5.72 ppm/K(265–315 K) and −14.68 ppm/K(280–320 K) for Ga0.95CFe3 and Ga0.85Al0.15CFe3, respectively. The possible mechanisms for the observed low TCR are discussed.
Impedance spectroscopy of the superprotonic conduction in LiH2PO4
Authors: Jung Kweon Jin , Won Lee Kyu , Eui Lee Cheol , Lee Kwang-Sei , Jo Y. J.
Published: July 2012

Superprotonic conduction in the LiH2PO4 (LDP) system has been studied by means of impedance spectroscopy. A dielectric dispersion associated with room-temperature superionic conduction is manifested, as the temperature-dependent dielectric constant displays a broad peak shifting toward the high temperatures with increasing measuring frequency. In particular, our impedance spectroscopic analysis in distinct temperature ranges has revealed the evolution of the microscopic proton dynamics and inhomogeneous electric environments associated with the dynamics of the two distinct hydrogen-bond types in LDP.
Spin-polarized scanning tunneling microscopy study of Mn/Co/Cu(001) using a bulk Fe ring probe
Authors: Wu Chii-Bin , Song Jiaming , Kuch Wolfgang
Published: July 2012

A bulk ring probe made of pure iron wire with diameter of 0.125 mm was prepared for spin-polarized scanning tunneling microscopy at room temperature in ultrahigh vacuum. The layerwise antiferromagnetic spin contrast of 2.8 atomic monolayers (ML) Mn/4.5 ML Co/Cu(001) observed with such a probe revealed a spin asymmetry of 14% and a signal-to-noise ratio of 1.8. Areas of reversed spin contrast on the same atomic layer of Mn were observed and attributed to the influence from underlying Co steps and islands. This demonstrates the simplicity of preparation and capability of such bulk Fe ring probes.
On the radiation hardness of (Mg,Zn)O thin films grown by pulsed-laser deposition
Authors: Schmidt Florian , Wenckstern Holger von , Spemann Daniel , Grundmann Marius
Published: July 2012

We report on electrical properties and the generation of the E4 defect in pulsed-laser deposited MgxZn1−xO thin films irradiated with 2.25 MeV protons. Whereas the electrical properties of the Schottky diodes as well as the net doping density of the samples did not change due to irradiation, the concentration of the E4 defect increased proportional to the applied dose as revealed by deep level transient spectroscopy. The generation rate η, is for binary ZnO thin films about 40  cm−1, a factor of 3 higher than in melt-grown single crystals, and increases to about 100  cm−1 for the Mg-alloyed thin films.
Investigation of deep-level defects in conductive polymer on n-type 4H- and 6H-silicon carbide substrates using I-V and deep level transient spectroscopy techniques
Authors: Felix J. F. , Aziz M. , da Cunha D. L. , Seidel K. F. , Hümmelgen I. A. , de Azevedo W. M. , da Silva E. F. , Taylor D. , Henini M.
Published: July 2012

The current-voltage (I–V) characteristics of Au/sulfonated polyaniline (SPAN)/n-SiC heterojunctions have been investigated in detail over a wide range of temperatures between 20 and 440 K. The measured I–V characteristics of all devices show a good rectification behavior at all temperatures. The room temperature rectification ratios (forward to reverse currents ratio, IF/IR) at 0.6 V for SPAN/n-type 4H-SiC and SPAN/n-type 6H-SiC heterojunctions are 2 × 104 and 7 × 106, respectively. The value of rectification of SPAN/6H-SiC heterojunction is four orders of magnitutude higher than the state-of-the art sulfonated polyaniline thin films deposited on n-type silicon substrates. A self-assembly technique and copolymerization were used to fabricate a self-doped polyaniline films on SiC substrates. The experimental I–V data were analysed using the Werner model, which includes the series resistance of the heterojunctions. The diode parameters such as the ideality factor and the barrier height are determined from the experimental data using I–V analysis method. The effect of the temperature on these parameters is presented. Deep level transient spectroscopy (DLTS) and Laplace DLTS techniques were used to investigate the electrically active defects present in these heterostructure devices.
Fast detection of single-charge tunneling to a graphene quantum dot in a multi-level regime
Authors: Müller T. , Güttinger J. , Bischoff D. , Hellmüller S. , Ensslin K. , Ihn T.
Published: July 2012

In situ-tunable radio-frequency reflectometry is used for fast charge-detection measurements on a graphene single quantum dot. The variable capacitance of our special matching network both grants tunability and compensates for the large stray capacitance between the charge sensor’s contacts and the doped silicon oxide backgate. To demonstrate the high detection bandwidth thus achieved, the rates for tunneling into and out of the dot through the same barrier are determined. Finally, an analytical model for calculating these rates in the multi-level tunneling regime is presented and found to correspond very well to our experimental observations.
Ultrafast all-optical gated amplifier based on ZnO nanowire lasing
Authors: Versteegh Marijn A. M. , van Capel Peter J. S. , Dijkhuis Jaap I.
Published: July 2012

We present an ultrafast all-optical gated amplifier, or transistor, consisting of a forest of ZnO nanowire lasers. A gate light pulse creates a dense electron-hole plasma and excites laser action inside the nanowires. Source light traversing the nanolaser forest is amplified, partly as it is guided through the nanowires, and partly as it propagates diffusively through the forest. We have measured transmission increases at the drain up to a factor 34 for 385-nm light. Time-resolved amplification measurements show that the lasing is rapidly self-quenching, yielding pulse responses as short as 1.2 ps.
Racial Segregation by Legislative Zoning and Company Law: An Empirical Hong Kong Study
Authors: Lai Lawrence W C , Kwong Valerius W C
Published: July 2012

In this paper we employ readily available categories of public data, rarely used in the literature on racial segregation, to scrutinise three research questions about the proposition of Lai and Yu (2001 Environment and Planning B: Planning and Design 28 295–314) that statutory zoning, which discriminates against a certain class of citizens, can be a form of price control. The key findings are that there was a large Chinese population on the Peak in Hong Kong even when the law did not allow Chinese people to own property there, that the process of acquiring European properties for residential purposes after the removal of the law was slow, and the Peak remained predominantly European until the 1980s. In other words, the factual evidence supports the argument that racially discriminatory zoning in the Peak District had not been predicated on racial animosity or aversion. The residential history of the Peak and another exclusively European housing enclave in Shek O established prewar under company law points towards the reality that the attempt to prevent the Chinese from buying properties in certain areas of Hong Kong was driven by idiosyncratic demands for a particular housing style. These two case studies demonstrated that contractual planning is much more capable of preserving the character of a neighbourhood than obligatory planning by edict. Some economic reasons behind the resilience of planning by mutual agreement and their implications for sustainable development are discussed.
Assessing the Efficacy of Dynamic Adaptive Planning of Infrastructure: Results from Computational Experiments
Authors: Kwakkel Jan H , Walker Warren E , Marchau Vincent A W J
Published: July 2012

In this paper we assess the efficacy of a dynamic adaptive planning (DAP) approach for guiding the long-term development of infrastructure. The efficacy of the approach is tested on the specific case of airport strategic planning. Utilizing a fast and simple model of an airport, and a composition of small models that can generate a wide spectrum of alternative futures, the performance of a dynamic adaptive plan is compared with the performance of a static, rigid implementation plan across a wide spectrum of conceivable futures. These computational experiments reveal that the static rigid plan outperforms the dynamic adaptive plan in only a small part of the spectrum. Moreover, given the wide array of possible futures, the dynamic adaptive plan has a narrower spread of outcomes than the static rigid plan, implying that the dynamic adaptive plan exposes planners to less uncertainty about its future performance despite the wide variety of uncertainties that are present. These computational results confirm theoretical hypotheses in the literature that DAP approaches are more efficacious for planning under uncertainty.
Similarities of artificial photosystems by ruthenium oxo complexes and native water splitting systems
Authors: Tanaka Koji , Isobe Hiroshi , Yamanaka Shusuke , Yamaguchi Kizashi
Published: July 2012

The nature of chemical bonds of ruthenium(Ru)–quinine(Q) complexes, mononuclear [Ru(trpy)(3,5-
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2
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2
)](ClO
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2
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,2
′′
-terpyridine, 3,5-di-
tert
-butyl-1,2-benzoquinone) (
1
), and binuclear [Ru
2
(btpyan)(3,6-di-Bu
2
Q)
2
(OH
2
)]
2+
(btpyan = 1,8-bis(2,2
′
:6
′
,2
′′
-terpyrid-4
′
-yl)anthracene, 3,6-
t
-Bu
2
Q = 3,6-di-
tert
-butyl-1,2-benzoquinone) (
2
), has been investigated by broken-symmetry (BS) hybrid density functional (DFT) methods. BS DFT computations for the Ru complexes have elucidated that the closed-shell structure (
2b
) Ru(II)–Q complex is less stable than the open-shell structure (
2bb
) consisting of Ru(III) and semiquinone (SQ) radical fragments. These computations have also elucidated eight different electronic and spin structures of tetraradical intermediates that may be generated in the course of water splitting reaction. The Heisenberg spin Hamiltonian model for these species has been derived to elucidate six different effective exchange interactions (
J
) for four spin systems. Six
J
values have been determined using total energies of the eight (or seven) BS solutions for different spin configurations. The natural orbital analyses of these BS DFT solutions have also been performed in order to obtain natural orbitals and their occupation numbers, which are useful for the lucid understanding of the nature of chemical bonds of the Ru complexes. Implications of the computational results are discussed in relation to the proposed reaction mechanisms of water splitting reaction in artificial photosynthesis systems and the similarity between artificial and native water splitting systems.
Modeling human cortical development in vitro using induced pluripotent stem cells
Authors: Mariani Jessica , Simonini Maria Vittoria , Palejev Dean , Tomasini Livia , Coppola Gianfilippo , Szekely Anna M. , Horvath Tamas L. , Vaccarino Flora M.
Published: July 2012

Human induced pluripotent stem cells (hiPSCs) are emerging as a tool for understanding human brain development at cellular, molecular, and genomic levels. Here we show that hiPSCs grown in suspension in the presence of rostral neuralizing factors can generate 3D structures containing polarized radial glia, intermediate progenitors, and a spectrum of layer-specific cortical neurons reminiscent of their organization in vivo. The hiPSC-derived multilayered structures express a gene expression profile typical of the embryonic telencephalon but not that of other CNS regions. Their transcriptome is highly enriched in transcription factors controlling the specification, growth, and patterning of the dorsal telencephalon and displays highest correlation with that of the early human cerebral cortical wall at 8–10 wk after conception. Thus, hiPSC are capable of enacting a transcriptional program specifying human telencephalic (pallial) development. This model will allow the study of human brain development as well as disorders of the human cerebral cortex.
A soluble bone morphogenetic protein type IA receptor increases bone mass and bone strength
Authors: Baud’huin Marc , Solban Nicolas , Cornwall-Brady Milton , Sako Dianne , Kawamoto Yoshimi , Liharska Katia , Lath Darren , Bouxsein Mary L. , Underwood Kathryn W. , Ucran Jeffrey , Kumar Ravindra , Pobre Eileen , Grinberg Asya , Seehra Jasbir , Canalis Ernesto , Pearsall R. Scott , Croucher Peter I.
Published: July 2012

Diseases such as osteoporosis are associated with reduced bone mass. Therapies to prevent bone loss exist, but there are few that stimulate bone formation and restore bone mass. Bone morphogenetic proteins (BMPs) are members of the TGFβ superfamily, which act as pleiotropic regulators of skeletal organogenesis and bone homeostasis. Ablation of the BMPR1A receptor in osteoblasts increases bone mass, suggesting that inhibition of BMPR1A signaling may have therapeutic benefit. The aim of this study was to determine the skeletal effects of systemic administration of a soluble BMPR1A fusion protein (mBMPR1A–mFc) in vivo. mBMPR1A–mFc was shown to bind BMP2/4 specifically and with high affinity and prevent downstream signaling. mBMPR1A–mFc treatment of immature and mature mice increased bone mineral density, cortical thickness, trabecular bone volume, thickness and number, and decreased trabecular separation. The increase in bone mass was due to an early increase in osteoblast number and bone formation rate, mediated by a suppression of Dickkopf-1 expression. This was followed by a decrease in osteoclast number and eroded surface, which was associated with a decrease in receptor activator of NF-κB ligand (RANKL) production, an increase in osteoprotegerin expression, and a decrease in serum tartrate-resistant acid phosphatase (TRAP5b) concentration. mBMPR1A treatment also increased bone mass and strength in mice with bone loss due to estrogen deficiency. In conclusion, mBMPR1A–mFc stimulates osteoblastic bone formation and decreases bone resorption, which leads to an increase in bone mass, and offers a promising unique alternative for the treatment of bone-related disorders.
Structural insights into triple-helical collagen cleavage by matrix metalloproteinase 1
Authors: Manka Szymon W. , Carafoli Federico , Visse Robert , Bihan Dominique , Raynal Nicolas , Farndale Richard W. , Murphy Gillian , Enghild Jan J. , Hohenester Erhard , Nagase Hideaki
Published: July 2012

Collagenases of the matrix metalloproteinase (MMP) family play major roles in morphogenesis, tissue repair, and human diseases, but how they recognize and cleave the collagen triple helix is not fully understood. Here, we report temperature-dependent binding of a catalytically inactive MMP-1 mutant (E200A) to collagen through the cooperative action of its catalytic and hemopexin domains. Contact between the two molecules was mapped by screening the Collagen Toolkit peptide library and by hydrogen/deuterium exchange. The crystal structure of MMP-1(E200A) bound to a triple-helical collagen peptide revealed extensive interactions of the 115-Å–long triple helix with both MMP-1 domains. An exosite in the hemopexin domain, which binds the leucine 10 residues C-terminal to the scissile bond, is critical for collagenolysis and represents a unique target for inhibitor development. The scissile bond is not correctly positioned for hydrolysis in the crystallized complex. A productive binding mode is readily modeled, without altering the MMP-1 structure or the exosite interactions, by axial rotation of the collagen homotrimer. Interdomain flexing of the enzyme and a localized excursion of the collagen chain closest to the active site, facilitated by thermal loosening of the substrate, may lead to the first transition state of collagenolysis.
Intrinsic particle-induced lateral transport in microchannels
Authors: Amini Hamed , Sollier Elodie , Weaver Westbrook M. , Di Carlo Dino
Published: July 2012

In microfluidic systems at low Reynolds number, the flow field around a particle is assumed to maintain fore-aft symmetry, with fluid diverted by the presence of a particle, returning to its original streamline downstream. This current model considers particles as passive components of the system. However, we demonstrate that at finite Reynolds number, when inertia is taken into consideration, particles are not passive elements in the flow but significantly disturb and modify it. In response to the flow field, particles translate downstream while rotating. The combined effect of the flow of fluid around particles, particle rotation, channel confinement (i.e., particle dimensions approaching those of the channel), and finite fluid inertia creates a net recirculating flow perpendicular to the primary flow direction within straight channels that resembles the well-known Dean flow in curved channels. Significantly, the particle generating this flow remains laterally fixed as it translates downstream and only the fluid is laterally transferred. Therefore, as the particles remain inertially focused, operations can be performed around the particles in a way that is compatible with downstream assays such as flow cytometry. We apply this particle-induced transfer to perform fluid switching and mixing around rigid microparticles as well as deformable cells. This transport phenomenon, requiring only a simple channel geometry with no external forces to operate, offers a practical approach for fluid transfer at high flow rates with a wide range of applications, including sample preparation, flow reaction, and heat transfer.
A forward genetic screen reveals roles for
Nfkbid
,
Zeb1
, and
Ruvbl2
in humoral immunity
Authors: Arnold Carrie N. , Pirie Elaine , Dosenovic Pia , McInerney Gerald M. , Xia Yu , Wang Nathaniel , Li Xiaohong , Siggs Owen M. , Karlsson Hedestam Gunilla B. , Beutler Bruce
Published: July 2012

Using chemical germ-line mutagenesis, we screened mice for defects in the humoral immune response to a type II T-independent immunogen and an experimental alphavirus vector. A total of 26 mutations that impair humoral immunity were recovered, and 19 of these mutations have been positionally cloned. Among the phenovariants were
bumble
,
cellophane
, and
Worker
ascribed to mutations in
Nfkbid
,
Zeb1
, and
Ruvbl2
, respectively. We show that IκBNS, the nuclear IκB-like protein encoded by
Nfkbid
, is required for the development of marginal zone and peritoneal B-1 B cells and additionally required for extrafollicular antibody responses to T-independent and -dependent immunogens.
Zeb1
is also required for marginal zone and peritoneal B-1 B-cell development as well as T-cell development, germinal center formation, and memory B-cell responses. Finally,
Ruvbl2
is required for T-cell development and maximal T-dependent antibody responses. Collectively, the mutations that we identified give us insight into the points at which disruption of an antibody response can occur. All of the mutations identified to date directly affect lymphocyte development or function; none have an exclusive effect on cells of the innate immune system.
South African English as a late 19th-century extraterritorial variety
Authors: Bekker Ian
Published: July 2012

This article argues that the external history of South African English (SAfE) points towards the merits of conceptualizing SAfE as the product of a three-stage koinéization process, the last stage of which takes place contemporaneously with the establishment of Johannesburg. This is at odds with the standard position, which views SAfE as an early-to-mid 19th-century variety with its characteristic features having been fixed during the earlier colonization of the Cape and Natal. This reconceptualization is, in turn, usefully employed to solve Trudgill’s (2004) so-called “South African puzzle’’: in essence, the postulation of SAfE as a late 19th-century English explains why START-Backing has occurred in SAfE but not in the closely related Australasian varieties.
The hypothetical subjunctive in South Asian Englishes
Authors: Hundt Marianne , Hoffmann Sebastian , Mukherjee Joybrato
Published: July 2012

This paper studies the distribution and usage patterns in hypothetical if-clauses in a set of South Asian Englishes (SAEs), namely Indian, Pakistani, Bangladeshi and Sri Lankan English on the basis of web-derived newspaper data. Comparative evidence comes from newspaper texts in the British National Corpus (BNC). It looks at the use of subjunctive were, indicative was and modal would as variant verb forms in the if-clause. The qualitative analyses also consider tense sequencing in the main and subordinate clause. In terms of overall frequencies, the SAEs do not cluster together in their use of the subjunctive but form a gradient or cline with British English at one end. Similarities between the SAEs emerge from the qualitative analyses. An additional, serendipitous result of the study concerns the local use in SAEs of the subordinator on if meaning ‘whether’, a pattern that is likely to have its origin in Indian English.