bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic flux array for spontaneous magnetic reconnection experiments
Authors: Kesich A. , Bonde J. , Egedal J. , Fox W. , Goodwin R. , Katz N. , Le A.
Published: June 2008

Experimental investigation of reconnection in magnetized plasmas relies on accurate characterization of the evolving magnetic fields. In experimental configurations where the plasma dynamics are reproducible, magnetic data can be collected in multiple discharges and combined to provide spatially resolved profiles of the plasma dynamics. However, in experiments on spontaneous magnetic reconnection recently undertaken at the Versatile Toroidal Facility at MIT, the reconnection process is not reproducible and all information on the plasma must be collected in a single discharge. This paper describes a newly developed magnetic flux array which directly measures the toroidal component of the magnetic vector potential, Aϕ. From the measured Aϕ, the magnetic field geometry, current density, and reconnection rate are readily obtained, facilitating studies of the three-dimensional dynamics of spontaneous magnetic reconnection. The novel design of the probe array allows for accurate characterization of profiles of Aϕ at multiple toroidal angles using a relatively small number of signal channels and with minimal disturbance of the plasma.
Modeling the interplay of inter- and intramolecular hydrogen bonding in conformational polymorphs
Authors: Karamertzanis Panagiotis G. , Day Graeme M. , Welch Gareth W. A. , Kendrick John , Leusen Frank J. J. , Neumann Marcus A. , Price Sarah L.
Published: June 2008

The predicted stability differences of the conformational polymorphs of oxalyl dihydrazide and ortho-acetamidobenzamide are unrealistically large when the modeling of intermolecular energies is solely based on the isolated-molecule charge density, neglecting charge density polarization. Ab initio calculated crystal electron densities showed qualitative differences depending on the spatial arrangement of molecules in the lattice with the greatest variations observed for polymorphs that differ in the extent of inter- and intramolecular hydrogen bonding. We show that accounting for induction dramatically alters the calculated stability order of the polymorphs and reduces their predicted stability differences to be in better agreement with experiment. Given the challenges in modeling conformational polymorphs with marked differences in hydrogen bonding geometries, we performed an extensive periodic density functional study with a range of exchange-correlation functionals using both atomic and plane wave basis sets. Although such electronic structure methods model the electrostatic and polarization contributions well, the underestimation of dispersion interactions by current exchange-correlation functionals limits their applicability. The use of an empirical dispersion-corrected density functional method consistently reduces the structural deviations between the experimental and energy minimized crystal structures and achieves plausible stability differences. Thus, we have established which types of models may give worthwhile relative energies for crystal structures and other condensed phases of flexible molecules with intra- and intermolecular hydrogen bonding capabilities, advancing the possibility of simulation studies on polymorphic pharmaceuticals.
Efficacy of TiOx optical spacer in bulk-heterojunction solar cells processed with 1,8-octanedithiol
Authors: Lee Jae Kwan , Coates Nelson E. , Cho Shinuk , Cho Nam Sung , Moses Daniel , Bazan Guillermo C. , Lee Kwanghee , Heeger Alan J.
Published: June 2008

The efficacy of TiOx as an optical spacer in bulk-heterojunction (BHJ) solar cells made from regioregular poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester films processed with 1,8-octanedithiol is investigated. The results indicate that the enhanced efficiency resulting from the TiOx optical spacer is anticorrelated to the concentration of the processing additive. The use of the processing additive induces surface roughness on the BHJ film and thereby diminishes the efficacy of the optical spacer. Solar cells fabricated with both the optical spacer and 1,8-octanedithiol yield efficiencies that are superior to those with either process alone.
Quantum vortices within the complex quantum Hamilton–Jacobi formalism
Authors: Chou Chia-Chun , Wyatt Robert E.
Published: June 2008

Quantum vortices are investigated in the framework of the quantum Hamilton-Jacobi formalism. A quantum vortex forms around a node in the wave function in the complex space, and the quantized circulation integral originates from the discontinuity in the real part of the complex action. Although the quantum momentum field displays hyperbolic flow around a node, the corresponding Pólya vector field displays circular flow. It is shown that the Pólya vector field of the quantum momentum function is parallel to contours of the probability density. A nonstationary state constructed from eigenstates of the harmonic oscillator is used to illustrate the formation of a transient excited state quantum vortex, and the coupled harmonic oscillator is used to illustrate quantization of the circulation integral in the multidimensional complex space. This study not only analyzes the formation of quantum vortices but also demonstrates the local structures for the quantum momentum field and for the Pólya vector field near a node of the wave function.
Unsteady propagation of a liquid plug in a liquid-lined straight tube
Authors: Fujioka Hideki , Takayama Shuichi , Grotberg James B.
Published: June 2008

This paper considers the propagation of a liquid plug driven by a constant pressure within a rigid axisymmetric tube whose inner surface is coated by a thin liquid film. The Navier–Stokes equations are solved using the finite-volume method and the SIMPLEST algorithm. The effects of precursor film thickness, initial plug length, pressure drop across the plug, and constant surface tension on the plug behavior and tube wall mechanical stresses are investigated. As a plug propagates through a liquid-lined tube, the plug gains liquid from the leading front film, and it deposits liquid into the trailing film. If the trailing film is thicker (thinner) than the precursor film, the plug volume decreases (increases) as it propagates. For a decreasing volume, eventually the plug ruptures. Under a specific set of conditions, the trailing film thickness equals the precursor film thickness, which leads to steady state results. The plug speed decreases as the precursor film thins because the resistance to the moving front meniscus increases. As the pressure drop across the plug decreases, the plug speed decreases resulting in thinning of the trailing film. As the plug length becomes longer, the viscous resistance in the plug core region increases, which slows the plug and causes the trailing film to become even thinner. The magnitude of the pressure and shear stress at the tube inner wall is maximum in the front meniscus region, and it increases with a thinner precursor film. As the surface tension increases, the plug propagation speed decreases, the strength of the wall pressure in the front meniscus region increases, and the pressure gradient around the peak pressure becomes steeper.
New conditions for validity of the centroid molecular dynamics and ring polymer molecular dynamics
Authors: Yoshimori Akira
Published: June 2008

Validity of the centroid molecular dynamics (CMD) and ring polymer molecular dynamics (RPMD) in quantum liquids is studied on an assumption that momenta of liquid particles relax fast. The projection operator method allows one to derive the generalized Langevin equation including a memory effect for the full-quantum canonical (Kubo-transformed) correlation function. Similar equations for the CMD and RPMD correlation functions can be derived too. The comparison of these equations leads to conditions under which the RPMD and CMD correlation functions agree approximately with the full-quantum canonical correlation function. The condition for the RPMD is that the memory effects of the full-quantum and RPMD equations vanish quickly with the same time constants. The CMD correlation function requires additional conditions concerning static correlation.
First-principles theoretical study of Alq3∕Al interfaces: Origin of the interfacial dipole
Authors: Yanagisawa Susumu , Lee Kyuho , Morikawa Yoshitada
Published: June 2008

We have studied the atomic geometries and the electronic properties of the tris-(8-hydroxyquinoline) aluminum (Alq3)∕Al interfaces by using density functional theoretical calculations, and clarified the origin of the interfacial dipole moment. We have examined various possible adsorption geometries of Alq3 on Al surfaces and calculated the work function change induced by adsorption of Alq3 on Al surfaces. We found that the stability depends crucially on the number of O-Al bonds formed at the interface, and Alq3 tends to expose its O atoms to the Al substrate side and its N atoms to the vacuum side. Although the binding energies are influenced by the poor description of the van der Waals interaction by the density functionals used, the resulting bonding configurations are found to give correct binding energies when the van der Waals interaction is taken into account based on the recently proposed van der Waals density functional [Dion et al., Phys. Rev. Lett. 92, 246401 (2004)]. This bonding configuration arranges molecular permanent dipoles of Alq3 directed towards the vacuum, leading to the decrease of the surface work function. The calculated interface dipoles agree reasonably well with the experimental results and the origin of the interface dipole formation mainly comes from the alignment of the permanent dipoles of Alq3. The HOMO levels of the Alq3 molecules significantly depend on the orientation of the molecular permanent dipoles and the interfacial gap state observed by experiments is ascribed to the coexistence of the two orientations of the molecular dipole moments.
Monolayer structure of tetracene on Cu (100) surface: Parallel geometry
Authors: Dou Weidong , Zhu Jiabao , Liao Qing , Zhang Hanjie , He Pimo , Bao Shining
Published: June 2008

The geometrical arrangement of tetracene on Cu (100) surface at monolayer coverage is studied by using scanning tunneling microscopy measurement and density functional theory (DFT) calculations. Tetracene molecule is found to be oriented with its molecular plane parallel to the substrate surface, and no perpendicular geometry is observed at this coverage. The molecule is aligned either in the [011] or [011¯] direction due to the fourfold symmetry of the Cu (100) surface. DFT calculations show that the molecule with the “flat-lying” mode has larger adsorption energy than that with the “upright standing” mode, indicating that the former is the more stable structure. With the flat-lying geometry, the carbon atoms prefer to be placed between surface Cu atoms. The molecular center prefers to be located at the bridge site between two nearest surface Cu atoms.
First-principles study of substitutional magnesium and zinc in hydroxyapatite and octacalcium phosphate
Authors: Matsunaga Katsuyuki
Published: June 2008

First-principles calculations are performed for Mg2+ and Zn2+ substitution in hydroxyapatite (HAp) and octacalcium phosphate (OCP), because the foreign ions are known to play an important role for bone formation. In order to study their possible location in the system of HAp in contact with the aqueous solution, OCP is considered as a structural model of the transition region between HAp and the solution. It is found that, when the foreign ions substitute for Ca sites, the surrounding oxygen ions undergo considerable inward relaxation, due to their smaller ionic sizes than Ca2+, which results in the smaller coordination numbers with oxygen as compared with those of Ca in bulk HAp and OCP. From the calculated defect formation energies, it is likely that the substitutional foreign ions are quite difficult to dissolve into HAp whereas can be more easily incorporated in OCP. In particular, Zn2+ can more favorably substitute for the specific Ca site of OCP, as compared to Mg2+, which is attributed with covalent bond formation between Zn and the surrounding oxygen ions. It is thus considered that zinc may play its role to promote bone formation by being incorporated into the transition region between HAp and the surrounding solution.
Character expansion method for supergroups and extended superversions of the Leutwyler–Smilga and Berezin–Karpelevich integrals
Authors: Lehner C. , Wettig T. , Guhr T. , Wei Y.
Published: June 2008

We introduce an extension of the character expansion method to the case of supergroups. This method allows us to calculate a superversion of the Leutwyler–Smilga integral which, to the best of our knowledge, has not been calculated before. We also use the method to generalize a previously calculated superversion of the Berezin–Karpelevich integral. Our character expansion method should also allow for the calculation of other supergroup integrals.
Pulsed recording of anisotropy and holographic polarization gratings in azo-polymethacrylates with different molecular architectures
Authors: Forcén Patricia , Oriol Luis , Sánchez Carlos , Alcalá Rafael , Jankova Katja , Hvilsted Søren
Published: June 2008

Recording of anisotropy and holographic polarization gratings using 532nm, 4ns light pulses has been carried out in thin films of polymers with the same azobenzene content (20wt%) and different molecular architectures. Random and block copolymers comprising azobenzene and methylmethacrylate (MMA) moieties as well as statistical terpolymers with azobenzene, biphenyl, and MMA units have been compared in terms of recording sensitivity and stability upon pulsed excitation. Photoinduced anisotropy just after the pulse was significantly higher in the case of the block copolymers than in the two statistical copolymers. The stability of the recorded anisotropy has also been studied. While a stationary value of the photoinduced anisotropy (approximately 50% of the initial photoinduced value) is reached for the block copolymer, photoinduced anisotropy almost vanished after a few hours in the statistical copolymers. Polarization holographic gratings have been registered using two orthogonally circularly polarized light beams. The results are qualitatively similar to those of photoinduced anisotropy, that is, stability of the registered grating and larger values of diffraction efficiency for the block copolymer as compared with the random copolymers. The recording of holographic gratings with submicron period in films several microns thick, showing both polarization and angular selectivity, has also been demonstrated. Block copolymers showed a lamellar block nanosegregated morphology. The interaction among azo chromophores within the nanosegregated azo blocks seems to be the reason for the stability and the photoresponse enhancement in the block copolymer as compared with the statistical ones.
A whole-field polariscope using a liquid crystal polarization rotator
Authors: Wang Pin , Asundi Anand
Published: June 2008

A novel polariscope using a liquid crystal (LC) polarization rotator is proposed for full-field subfringe photoelastic stress analysis. The system uses a light-emitting diode-based modified Senarmont polariscope with an added liquid crystal polarization rotator to generate phase shifts by applying suitable voltages to the LC element. Four phase shift polariscope images are captured and analyzed to get the stress distribution. A comparative study with the gray-field polariscope method which uses a rotating analyzer shows good agreement.
Evidence for a modified-stannite crystal structure in wide band gap Cu-poor CuIn1−xGaxSe2: Impact on the optical properties
Authors: Souilah M. , Lafond A. , Barreau N. , Guillot-Deudon C. , Kessler J.
Published: June 2008

The crystal structure of high Ga-content CuIn1−xGaxSe2 (CIGSe) compounds has been further investigated with the help of single crystal x-ray diffraction technique. It is known that CIGSe compounds adopt the chalcopyrite crystal structure. In the case of Cu-poor, Ga-rich CIGSe, the present study shows that an alternative structure should be considered. This structure is derived from that of stannite in which there is a Ga∕In segregation on two different atomic planes. The diffuse reflectance measurements of the Cu-poor compound reveal a slightly different band gap and a smoother transition compared with those of the stoichiometric compound.
Liquid microlens with tunable focal length and light transmission
Authors: Xiong Gui-Rong , Han Yong-Hao , Sun Cheng , Sun Li-Guo , Han Guo-Zhi , Gu Zhong-Ze
Published: June 2008

A microfluidic design was created to allow liquid microlens to control focal length and light transmission. The focal length of the microlens was controlled by varying the volume of liquid infused into the liquid cell. The cell extruded a polydimethylsiloxane film and produced a changeable curvature. The imaging ability of the microlens was tuned by taking advantage of the phase transition of poly-N-isopropylacrylamide in the liquid. The phase transition temperature was controlled in the range of 25.6–34.5°C by changing the ion concentration.
Signature of varicose wave packets in the viscous sublayer
Authors: Brücker Ch.
Published: June 2008

Waviness of the wall-shear stress (WSS) field of a turbulent boundary layer is investigated experimentally. Arrays of flexible micropillars are used as sensors for WSS in the turbulent boundary layer of a flat plate in a zero pressure gradient flow channel. The pillars and flow conditions are chosen such that accurate dynamic measurements of the two-dimensional (2D) WSS vectors at the sensor locations are obtained for the mean and the fluctuating part simultaneously. Time-resolved measurements reveal for the first time the orientation of the 2D WSS vectors and their spatiotemporal correlation. The results show trains or packets of varicose wavelike disturbances of the near wall flow with strong anticorrelation of the spanwise WSS component, which appear periodically and can be related to the signature of coherent packets of vortex loops. In addition these structures may represent the near-wall state of secondary varicose instability of sublayer streaks.
High Kα x-ray conversion efficiency from extended source gas jet targets irradiated by ultra short laser pulses
Authors: Kugland N. L. , Constantin C. G. , Neumayer P. , Chung H.-K. , Collette A. , Dewald E. L. , Froula D. H. , Glenzer S. H. , Kemp A. , Kritcher A. L. , Ross J. S. , Niemann C.
Published: June 2008

The absolute laser conversion efficiency to Kα-like inner shell x-rays (integrated from Kα to Kβ) is observed to be an order of magnitude higher in argon gas jets than in solid targets due to enhanced emission from higher ionization stages following ultrashort pulse laser irradiation. Particle-in-cell and spectral simulations indicate that these observations are consistent with Kα emission from a warm Ar plasma subject to hot electron inner-shell ionization. These results demonstrate that gas jet targets are bright, high conversion efficiency, high repetition rate, debris-free multi-keV x-ray sources for spectrally resolved scattering and backlighting of rapidly evolving dense matter.
Dramatic enhancement of photo-oxidation stability of a conjugated polymer in blends with organic acceptor
Authors: Golovnin Ilya V. , Bakulin Artem A. , Zapunidy Sergey A. , Nechvolodova Elena M. , Paraschuk Dmitry Yu.
Published: June 2008

Photo-oxidation of a prototype conjugated polymer poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) in blended films with 2,4,7-trinitrofluorenone (TNF) is drastically suppressed upon exposure to green laser radiation under ambient conditions that was observed by using Fourier transform infrared spectroscopy. By increasing the TNF concentration in MEH-PPV, we have found that the photo-oxidation rate and the photoluminescence intensity drop together in a correlated way by three orders of magnitude. We suggest that triplet exciton formation in the MEH-PPV/TNF blends is deeply suppressed blocking the photo-oxidation. These findings may open a way to intrinsically photostable conjugated polymer materials for photonic and photoelectric applications.
Ion irradiation-induced local structural changes in amorphous Ge2Sb2Te5 thin film
Authors: De Bastiani R. , Piro A. M. , Grimaldi M. G. , Rimini E. , Baratta G. A. , Strazzulla G.
Published: June 2008

The crystallization kinetics of as-deposited and ion implanted amorphous Ge2Sb2Te5 thin films has been measured by time resolved reflectivity. An enhancement of the crystallization process occurred in the implanted samples. Raman scattering analysis was used to correlate the stability of the amorphous phase to its structure. The variation of the Raman signal after ion irradiation is consistent with a reduction in Ge–Te tetrahedral bonds, characteristic of the Ge coordination in amorphous Ge2Sb2Te5.
Multilayer atom chips for versatile atom micromanipulation
Authors: Trinker M. , Groth S. , Haslinger S. , Manz S. , Betz T. , Schneider S. , Bar-Joseph I. , Schumm T. , Schmiedmayer J.
Published: June 2008

We employ a combination of optical and electron-beam lithography to create an atom chip combining submicron wire structures with larger conventional wires on a single substrate. The multilayer fabrication enables crossed wire configurations, greatly enhancing the flexibility in designing potentials for ultracold quantum gases and Bose–Einstein condensates. Large current densities of >6×107A∕cm2 and high voltages of up to 65V across 0.3μm gaps are supported by even the smallest wire structures. We experimentally demonstrate the flexibility of the next generation atom chip by producing Bose–Einstein condensates in magnetic traps created by a combination of wires involving all different fabrication methods and structure sizes.
Relating linear vibrational spectroscopy to condensed-phase hydrogen-bonded structures: Liquid-to-supercritical water
Authors: Kandratsenka Alexander , Schwarzer Dirk , Vöhringer Peter
Published: June 2008

The pressure and temperature-dependent linear absorption spectrum of partially deuterated water HOD dissolved in heavy water D2O was measured in the OH-stretching spectral region. The temperature was varied in the interval of 298K⩽T⩽700K while the density was changed within the range of 12mol∕l⩽ρ⩽58mol∕l corresponding to the liquid and the supercritical phases of the fluid solution. The spectra were analyzed in terms of the temperature and density dependent frequency of maximal absorbance ν̃max(T,ρ) and their full widths at half maximum Δν̃(T,ρ). In parallel, molecular dynamics simulations of the fluid solution were carried out to obtain the average nearest neighbor O–O distance ⟨rOO(1)⟩(T,ρ) and its dispersion ⟨ΔrOO(1)⟩(T,ρ) at any state point (T,ρ) for which an absorption spectrum was recorded. A correlation is presented between the experimental spectroscopic quantities ν̃max(T,ρ) and Δν̃(T,ρ) on the one hand and the local structural quantities ⟨rOO(1)⟩(T,ρ) and ⟨ΔrOO(1)⟩(T,ρ) on the other. This intuitive correlation can be used as a critical test for future perturbational simulations of the OH-stretching frequency shifts with hydrogen-bond geometry. Finally, a connection is made to the average hydrogen-bond connectivity in the fluid via the temperature and density dependent dielectric constant of water.
Temperature dependent vibrational spectra and bond dynamics in hydrogenated amorphous silicon
Authors: Kupchak I. M. , Gaspari F. , Shkrebtii A. I. , Perz J. M.
Published: June 2008

We present the results of extensive modeling of hydrogenated amorphous silicon (a-Si:H) by combined ab initio molecular dynamics, an improved signal processing technique, and computer visualization, focusing on vibrational properties of a-Si:H. By comparing the theoretical and experimental vibrational spectra we correlate the hydrogen and silicon dynamics with the structural stability, bonding geometry, and diffusion in the a-Si:H material. Microscopic characteristics that cannot be obtained by other techniques, namely, hydrogen migration, bond switching, and silicon dangling bond passivation, are extracted from the atomic dynamics. We also demonstrate that this method offers the possibility of accessing other important macroscopic characteristics of a-Si:H and its stability in general. The approach we have developed can be used as well to model all aspects of a-Si:H dynamics, including the detrimental Staebler–Wronski effect.
Size-dependent ordering and Curie temperatures of FePt nanoparticles
Authors: Lu H. M. , Cao Z. H. , Zhao C. L. , Li P. Y. , Meng X. K.
Published: June 2008

The analytic models for size-dependent ordering and Curie temperatures of FePt nanoparticles have been proposed in terms of the size-dependent melting temperature. It is found that the order-disorder transition temperature TO and Curie temperature TC decrease with decreasing the particle size D, and the drop becomes dramatic once the size decreases to about 3 and 6 nm below for TO and TC, respectively. Moreover, the suppression in TC(D) is nearly twice as large as that in TO(D) when D is in the range of 5–20 nm. The accuracy of the developed model is verified by the recent experimental and computer simulation results.
Multilayer white polymer light-emitting diodes with deoxyribonucleic acid-cetyltrimetylammonium complex as a hole-transporting/electron-blocking layer
Authors: Sun Qingjiang , Chang Dong Wook , Dai Liming , Grote James , Naik Rajesh
Published: June 2008

Using a thin film of deoxyribonucleic acid-cetyltrimetylammonium (DNA-CTMA) complex as a hole-transporting/electron-blocking layer, we have developed a sequential solution-processing approach for constructing multilayer (up to five layers) white polymer light-emitting diodes, incorporating the poly(9,9-dioctylfluorene-2,7-diyl)/poly[2-methoxy-5(2′-ethyl-hexyloxy)-1, 4-phenylene vinylene] emissive layer. These devices were demonstrated to show a low turn-on voltage (∼5V), high efficiency (10.0cd∕A), and high brightness (10500cd∕m2) with an improved white-color stability.
Paramagnetic adsorbates on graphene: A charge transfer analysis
Authors: Leenaerts O. , Partoens B. , Peeters F. M.
Published: June 2008

We introduce a modified version of the Hirshfeld charge analysis method and demonstrate its accurateness by calculating the charge transfer between the paramagnetic molecule NO2 and graphene. The charge transfer between paramagnetic molecules and a graphene layer as calculated with ab initio methods can crucially depend on the size of the supercell used in the calculation. This has important consequences for adsorption studies involving paramagnetic molecules such as NO2 physisorbed on graphene or on carbon nanotubes.
Nanoepitaxy to improve the efficiency of InGaN light-emitting diodes
Authors: Zang K. Y. , Chua S. J. , Teng J. H. , Ang N. S. S. , Yong A. M. , Chow S. Y.
Published: June 2008

In Ga N ∕ Ga N blue light-emitting diode (LED) structures are grown on nanoepitaxial lateral overgrown (NELO) GaN template on sapphire substrates by metal organic chemical vapor deposition. Nanopore arrays in SiO2 film are fabricated on the underlying GaN using anodic alumina as etch masks, resulting in a nanoporous SiO2 mask layer with an average nanopore diameter and interpore distance of 60 and 110nm, respectively. The LED on NELO GaN demonstrates low defect density, which is revealed by cross-sectional transmission electron microscopy. More importantly, the LED on NELO GaN demonstrates a higher output power, one order of magnitude higher at 80mA, and an enhancement of the emission efficiency compared to that of the LED on planar GaN. This is mainly attributed to the improvement of light extraction efficiency by random scattering at the interface of the nanoporous SiO2 mask. The nanoporous SiO2 mask acts as both a threading dislocation reduction layer and a light scattering layer to enhance both internal quantum efficiency and external light extraction efficiency. The use of NELO method improves both internal quantum efficiency and external quantum efficiency for III-nitrides based optoelectronic devices.
Preparation and characterization of (001)- and (110)-oriented 0.6FeTiO3⋅0.4Fe2O3 films for room temperature magnetic semiconductors
Authors: Takada Yusuke , Nakanishi Makoto , Fujii Tatsuo , Takada Jun
Published: June 2008

Thin films of ilmenite-hematite solid solution 0.6FeTiO3⋅0.4Fe2O3 were prepared on α-Al2O3 (001) and (110) single-crystalline substrates. The oxide phases formed in the thin films strongly depended on the oxygen partial pressure (PO2) during deposition. At PO2=1.3×10−3Pa, regardless of thesubstrate orientation, well-ordered 0.6FeTiO3⋅0.4Fe2O3 films with R3¯ symmetry were epitaxially formed. Large saturation magnetization at room temperature was observed in both (001)- and (110)-oriented films. The differences in the magnetization and electrical resistivity curves between the (001)- and (110)-oriented films indicated the anisotropic nature of 0.6FeTiO3⋅0.4Fe2O3.
Shaped graded materials with an apparent negative thermal conductivity
Authors: Fan C. Z. , Gao Y. , Huang J. P.
Published: June 2008

Based on a first-principles approach, we exploit a class of shaped graded materials in which thermal energy is apparently controlled to transfer from a region of lower temperature to a region of higher temperature. This phenomenon, which is in contrast to our common intuition, is indicative of an apparent negative thermal conductivity (ANTC). Further analysis shows that the ANTC is related to a symmetric oscillation of paired thermal conductivities with specific gradation profiles, which are shown to satisfy a sum rule. Such shaped graded materials can serve as good candidates for thermal rectification.
Silicon resonant cavity enhanced photodetector based on the internal photoemission effect at 1.55μm: Fabrication and characterization
Authors: Casalino M. , Sirleto L. , Moretti L. , Gioffrè M. , Coppola G. , Rendina Ivo
Published: June 2008

In this paper, the realization and the characterization of a resonant cavity enhanced (RCE) photodetector, completely silicon compatible and working at 1.55μm, are reported. The detector is a RCE structure incorporating a Schottky diode and its working principle is based on the internal photoemission effect. Taking advantage of a Cu∕Si Schottky diode fed on a high reflectivity Bragg mirror, an improvement in responsivity at 1.55μm is experimentally demonstrated.
Intensity-dependent enhancement of saturable absorption in PbS–Au4 nanohybrid composites: Evidence for resonant energy transfer by Auger recombination
Authors: Elim Hendry I. , Ji Wei , Yang Jian , Lee Jim Yang
Published: June 2008

Intensity-dependent enhancement of saturable absorption in a film of PbS–Au4 nanohybrid composites has been observed by femtosecond time-resolved transient absorption measurement at 780nm. The nonlinear absorption coefficient (α2) of saturable absorption in PbS–Au4 nanohybrid composites is found to be dependent on excitation irradiance and it is determined to be −2.9cm∕GW at 78GW∕cm2, an enhancement of nearly fourfold in comparison with that of pure PbS quantum dots (QDs). The enhancement is attributed to the excitation of surface plasmon by resonant energy transfer between PbS QDs and Au nanoparticles through Auger recombination.
Fast photorefractive response and high sensitivity of Zr and Fe codoped LiNbO3 crystals
Authors: Kong Yongfa , Wu Shengqing , Liu Shiguo , Chen Shaolin , Xu Jingjun
Published: June 2008

A series of Zr and Fe codoped LiNbO3 crystals was grown and their photorefractive properties have been investigated. Compared with LiNbO3:Fe,Hf, the concentration of Fe2+ ions is strongly increased in LiNbO3:Fe,Zr. As a result, the photorefractive response speed of these as-grown LiNbO3:Fe,Zr crystals is only 2s and the sensitivity is larger than 12cm∕J while the saturation diffraction efficiency still remains at a high level. These findings prove that LiNbO3:Fe,Zr is an excellent choice for volume holographic storage.
General anesthetics activate a nociceptive ion channel to enhance pain and inflammation
Authors: Matta José A. , Cornett Paul M. , Miyares Rosa L. , Abe Ken , Sahibzada Niaz , Ahern Gerard P.
Published: June 2008

General anesthetics (GAs) have transformed surgery through their actions to depress the central nervous system and blunt the perception of surgical insults. Counterintuitively, many of these agents activate peripheral nociceptive neurons. However, the underlying mechanisms and significance of these effects have not been explored. Here, we show that clinical concentrations of noxious i.v. and inhalation GAs excite sensory neurons by selectively activating TRPA1, a key ion channel in the pain pathway. Further, these GAs induce pain-related responses in mice that are abolished in TRPA1-null animals. Significantly, TRPA1-dependent neurogenic inflammation is greater in mice anesthetized with pungent compared with nonpungent anesthetics. Thus, our results show that TRPA1 is essential for sensing noxious GAs. The pronociceptive effects of GAs combined with surgical tissue damage could lead to a paradoxical increase in postoperative pain and inflammation.
Contextual priming: Where people vote affects how they vote
Authors: Berger Jonah , Meredith Marc , Wheeler S. Christian
Published: June 2008

American voters are assigned to vote at a particular polling location (e.g., a church, school, etc.). We show these assigned polling locations can influence how people vote. Analysis of a recent general election demonstrates that people who were assigned to vote in schools were more likely to support a school funding initiative. This effect persisted even when controlling for voters' political views, demographics, and unobservable characteristics of individuals living near schools. A follow-up experiment using random assignment suggests that priming underlies these effects, and that they can occur outside of conscious awareness. These findings underscore the subtle power of situational context to shape important real-world decisions.
MLST of housekeeping genes captures geographic population structure and suggests a European origin ofBorrelia burgdorferi
Authors: Margos Gabriele , Gatewood Anne G. , Aanensen David M. , Hanincová Klára , Terekhova Darya , Vollmer Stephanie A. , Cornet Muriel , Piesman Joseph , Donaghy Michael , Bormane Antra , Hurn Merrilee A. , Feil Edward J. , Fish Durland , Casjens Sherwood , Wormser Gary P. , Schwartz Ira , Kurtenbach Klaus
Published: June 2008

Lyme borreliosis, caused by the tick-borne bacteriumBorrelia burgdorferi, has become the most common vector-borne disease in North America over the last three decades. To understand the dynamics of the epizootic spread and to predict the evolutionary trajectories ofB. burgdorferi, accurate information on the population structure and the evolutionary relationships of the pathogen is crucial. We, therefore, developed a multilocus sequence typing (MLST) scheme forB. burgdorferibased on eight chromosomal housekeeping genes. We validated the MLST scheme onB. burgdorferispecimens from North America and Europe, comprising both cultured isolates and infected ticks. These data were compared with sequences for the commonly used genetic markersrrs-rrlAintergenic spacer (IGS) and the gene encoding the outer surface protein C (ospC). The study demonstrates that the concatenated sequences of the housekeeping genes ofB. burgdorferiprovide highly resolved phylogenetic signals and that the housekeeping genes evolve differently compared with the IGS locus andospC. Using sequence data, the study reveals that North American and European populations ofB. burgdorfericorrespond to genetically distinct populations. Importantly, the MLST data suggest thatB. burgdorferioriginated in Europe rather than in North America as proposed previously.
Affinity maturation of antibodies assisted byin silicomodeling
Authors: Barderas Rodrigo , Desmet Johan , Timmerman Peter , Meloen Rob , Casal J. Ignacio
Published: June 2008

Rational engineering methods can be applied with reasonable success to optimize physicochemical characteristics of proteins, in particular, antibodies. Here, we describe a combined CDR3 walking randomization and rational design-based approach to enhance the affinity of the human anti-gastrin TA4 scFv. The application of this methodology to TA4 scFv, displaying only a weak overall affinity for gastrin17 (KD= 6 μM), resulted in a set of nine affinity-matured scFv variants with near-nanomolar affinity (KD= 13.2 nM for scFv TA4.112). First, CDR-H3 and CDR-L3 randomization resulted in three scFvs with an overall affinity improvement of 15- to 35-fold over the parental. Then, the modeling of two scFv constructs selected from the previous step (TA4.11 and TA4.13) was followed by a combination of manual and molecular dynamics-based docking of gastrin17 into the respective binding sites, analysis of apparent packing defects, and selection of residues for mutagenesis through phage display. Nine scFv mutants were obtained from the second maturation step. A final 454-fold improvement in affinity compared with TA4 was obtained. These scFvs showed an enhanced potency to inhibit gastrin-induced proliferation in Colo 320 WT and BxPc3 tumoral cells. In conclusion, we propose a structure-based rational method to accelerate the development of affinity-matured antibody constructs with enhanced potential for therapeutic use.
Recruitment of Stat1 to chromatin is required for interferon-induced serine phosphorylation of Stat1 transactivation domain
Authors: Sadzak Iwona , Schiff Melanie , Gattermeier Irene , Glinitzer Reingard , Sauer Ines , Saalmüller Armin , Yang Edward , Schaljo Barbara , Kovarik Pavel
Published: June 2008

The transcription factor Stat1 plays an essential role in responses to interferons (IFNs). Activation of Stat1 is achieved by phosphorylation on Y701 that is followed by nuclear accumulation. For full transcriptional activity and biological function Stat1 must also be phosphorylated on S727. The molecular mechanisms underlying the IFN-induced S727 phosphorylation are incompletely understood. Here, we show that both Stat1 Y701 phosphorylation and nuclear translocation are required for IFN-induced S727 phosphorylation. We further show that Stat1 mutants lacking the ability to stably associate with chromatin are poorly serine-phosphorylated in response to IFN-γ. The S727 phosphorylation of these mutants is restored on IFN-β treatment that induces the formation of the ISGF3 complex (Stat1/Stat2/Irf9) where Irf9 represents the main DNA binding subunit. These findings indicate that Stat1 needs to be assembled into chromatin-associated transcriptional complexes to become S727-phosphorylated and fully biologically active in response to IFNs. This control mechanism, which may be used by other Stat proteins as well, restricts the final activation step to the chromatin-tethered transcription factor.
Communication between subunits critical to DNA binding by hexameric helicase of bacteriophage T7
Authors: Lee Seung-Joo , Qimron Udi , Richardson Charles C.
Published: June 2008

The DNA helicase encoded by bacteriophage T7 consists of six identical subunits that form a ring through which the DNA passes. Binding of ssDNA is a prior step to translocation and unwinding of DNA by the helicase. Arg-493 is located at a conserved structural motif within the interior cavity of the helicase and plays an important role in DNA binding. Replacement of Arg-493 with lysine or histidine reduces the ability of the helicase to bind DNA, hydrolyze dTTP, and unwind dsDNA. In contrast, replacement of Arg-493 with glutamine abolishes these activities, suggesting that positive charge at the position is essential. Based on the crystallographic structure of the helicase, Asp-468 is in the range to form a hydrogen bonding with Arg-493 on the adjacent subunit.
In vivo
complementation results indicate that an interaction between Asp-468 and Arg-493 is critical for a functional helicase and those residues can be swapped without losing the helicase activity. This study suggests that hydrogen bonding between Arg-493 and Asp-468 from adjacent subunits is critical for DNA binding ability of the T7 hexameric helicase.
Topoisomerase levels determine chemotherapy response
in vitro
and
in vivo
Authors: Burgess Darren J. , Doles Jason , Zender Lars , Xue Wen , Ma Beicong , McCombie W. Richard , Hannon Gregory J. , Lowe Scott W. , Hemann Michael T.
Published: June 2008

Topoisomerase poisons are chemotherapeutic agents that are used extensively for treating human malignancies. These drugs can be highly effective, yet tumors are frequently refractory to treatment or become resistant upon tumor relapse. Using a pool-based RNAi screening approach and a well characterized mouse model of lymphoma, we explored the genetic basis for heterogeneous responses to topoisomerase poisons
in vitro
and
in vivo
. These experiments identified
Top2A
expression levels as major determinants of response to the topoisomerase 2 poison doxorubicin and showed that suppression of
Top2A
produces resistance to doxorubicin
in vitro
and
in vivo
. Analogously, using a targeted RNAi approach, we demonstrated that suppression of
Top1
produces resistance to the topoisomerase 1 poison camptothecin yet hypersensitizes cancer cells to doxorubicin. Importantly, lymphomas relapsing after treatment display spontaneous changes in topoisomerase levels as predicted by
in vitro
gene knockdown studies. These results highlight the utility of pooled shRNA screens for identifying genetic determinants of chemotherapy response and suggest strategies for improving the effectiveness of topoisomerase poisons in the clinic.
The direction of gut looping is established by changes in the extracellular matrix and in cell:cell adhesion
Authors: Kurpios Natasza A. , Ibañes Marta , Davis Nicole M. , Lui Wei , Katz Tamar , Martin James F. , Belmonte Juan Carlos Izpisúa , Tabin Clifford J.
Published: June 2008

The counterclockwise coiling of the intestines is initiated by a leftward tilt of the primitive gut tube, imparted by left–right asymmetries in the architecture of the dorsal mesentery.
In silico
analysis suggests that this is achieved by synergistic changes in its epithelium and mesenchyme. Within the mesenchymal compartment, cells are more densely packed on the left than on the right.
In silico
results indicate that this property can result from asymmetries in both extracellular matrix (ECM) and cell:cell adhesion. We find that the dorsal mesentery ECM is indeed left–right asymmetric and moreover that the adhesion molecule N-cadherin is expressed exclusively on the left side. These asymmetries are regulated by the asymmetrically expressed transcription factors
Pitx2
and
Isl1
. Functional studies demonstrate that N-cadherin acts upstream of the changes in the ECM and is both necessary and sufficient to explain the asymmetric packing of the mesenchymal cells.
Beta-caryophyllene is a dietary cannabinoid
Authors: Gertsch Jürg , Leonti Marco , Raduner Stefan , Racz Ildiko , Chen Jian-Zhong , Xie Xiang-Qun , Altmann Karl-Heinz , Karsak Meliha , Zimmer Andreas
Published: June 2008

The psychoactive cannabinoids fromCannabis sativaL. and the arachidonic acid-derived endocannabinoids are nonselective natural ligands for cannabinoid receptor type 1 (CB1) and CB2receptors. Although the CB1receptor is responsible for the psychomodulatory effects, activation of the CB2receptor is a potential therapeutic strategy for the treatment of inflammation, pain, atherosclerosis, and osteoporosis. Here, we report that the widespread plant volatile (E)-β-caryophyllene [(E)-BCP] selectively binds to the CB2receptor (Ki= 155 ± 4 nM) and that it is a functional CB2agonist. Intriguingly, (E)-BCP is a common constituent of the essential oils of numerous spice and food plants and a major component inCannabis. Molecular docking simulations have identified a putative binding site of (E)-BCP in the CB2receptor, showing ligand π–π stacking interactions with residues F117 and W258. Upon binding to the CB2receptor, (E)-BCP inhibits adenylate cylcase, leads to intracellular calcium transients and weakly activates the mitogen-activated kinases Erk1/2 and p38 in primary human monocytes. (E)-BCP (500 nM) inhibits lipopolysaccharide (LPS)-induced proinflammatory cytokine expression in peripheral blood and attenuates LPS-stimulated Erk1/2 and JNK1/2 phosphorylation in monocytes. Furthermore, peroral (E)-BCP at 5 mg/kg strongly reduces the carrageenan-induced inflammatory response in wild-type mice but not in mice lacking CB2receptors, providing evidence that this natural product exerts cannabimimetic effectsin vivo. These results identify (E)-BCP as a functional nonpsychoactive CB2receptor ligand in foodstuff and as a macrocyclic antiinflammatory cannabinoid inCannabis.
South Africa: Revisiting Capital's ‘Formative Action’
Authors: Bassett Carolyn
Published: June 2008

This article revisits Saul and Gelb's 1981 analysis of South African capital's ‘formative action’, employing their framework to assess how capital hasshaped the economic framework since 1990. I show that once prominentbusiness leaders became committed to non‐racial democracy, the privatesector became enormously influential in shaping the economic programme.The policy changes permitted South African firms to restructure theiroperations largely on their own terms, becoming major investors elsewherein Africa and around the world. Despite their ostensible success, the neoliberal framework they cultivated may lack durability, simply because the ‘historical bloc’ underpinning it is so narrow that the programme has notoffered many benefits to the majority. Despite measures taken by thegovernment since 2000 to broaden the political coalition supporting the neoliberal restructuring, the recent crisis over presidential succession reflects the failure to vest the economic changes in a hegemonic programme.
Tanzania: Decentralising Power or Spreading Poverty?
Authors: Pallotti Arrigo
Published: June 2008

This essay investigates the complex relationships between the decentralisation reform and implementation of the 1999 land laws in the rural areas of Tanzania. After critically reviewing the aims, content and early outcomes of the Local Government Reform Programme (LGRP), the essay considers the political implications of the neo‐liberal citizenship model the reform tries to promote at the local level, with a particular focus on its link with the implementation of the Village Land Act of 1999. Behind the rhetoric of poverty reduction and community development lies a government effort to promote a market model of citizenship in the rural areas. Indeed, the implementation of the LGRP and land tenure reform represent part of this broader effort. The paper concludes that these policies will have far‐reaching effects on resource access and democracy at the local level.
‘Uncomfortable Collaborations’: Contesting Constructions of the ‘Poor’ in South Africa
Authors: Walsh Shannon , Bond Patrick , Desai Ashwin , Walsh Shannon
Published: June 2008

This article deconstructs the problematic way the ‘Poor’ are represented by the intellectual ‘Left’ as a fixed, virtuous subject. Even while this fixed identity is actively mobilised by people themselves to gain symbolic and real power, I argue that the philosopher's fixation on the singular subjectivity of the oppressed confines the ‘Poor’ to their very subjugation. Instead, I propose a more nuanced understanding of how agency and oppression occur within the ‘uncomfortable collaborations' that are forged between various actors. My argument is grounded in experiences with the shack dwellers movement in Durban (Abahlali baseMjondolo, ABM), and young AIDS activists in Khayelitsha and Atlantis, South Africa.
Egypt: The Anatomy of Succession
Authors: Stacher Joshua
Published: June 2008

This article examines how the procedural aspects of Egypt's first presidential elections permitted the ruling regime to persist without a serious challenge. By taking stock of how the procedural rules of the game were manipulated to favour the incumbent, and the creation of an administrative body with extrajudicial powers guaranteeing the known result, this article will argue that the character of Constitutional Amendment 76 sET a precedent that will likely favour the succession in 2011 of Hosni Mubarak's son, Gamal.