bluuebunny/crossref_metadata_2025 huggingface dataset:
Quaternion-Kähler four-manifolds and Przanowski's function
Authors: Högner Moritz
Published: October 2012

Quaternion-Kähler four-manifolds, or equivalently anti-self-dual Einstein manifolds, are locally determined by one scalar function subject to Przanowski's equation. Using twistorial methods, we construct a Lax Pair for Przanowski's equation, confirming its integrability. The Lee form of a compatible local complex structure, which one can always find, gives rise to a conformally invariant differential operator acting on sections of a line bundle. Special cases of the associated generalised Laplace operator are the conformal Laplacian and the linearised Przanowski operator. We provide recursion relations that allow us to construct cohomology classes on twistor space from solutions of the generalised Laplace equation. Conversely, we can extract such solutions from twistor cohomology, leading to a contour integral formula for perturbations of Przanowski's function. Finally, we illuminate the relationship between Przanowski's function and the twistor description, in particular, we construct an algorithm to retrieve Przanowski's function from twistor data in the double-fibration picture. Using a number of examples, we demonstrate this procedure explicitly.
Optical properties of an organic dye from time-dependent density functional theory with explicit solvent: The case of alizarin
Authors: Douma Dick Hartmann , M’Passi-Mabiala Bernard , Gebauer Ralph
Published: October 2012

The influence of a water solvent on the optical absorption properties of alizarin is investigated using time-dependent density functional theory (TDDFT). The solvent is modeled at two different levels of theory: a structureless dielectric medium, using a polarizable continuum model, and the explicit inclusion of water molecules which are treated at the same level of theory as the solute. Thermal effects on the photoabsorption spectra are included by combining TDDFT with first principle molecular dynamics. The effect of molecular distortions on the excitation energies and oscillator strengths is analyzed, and a strong correlation between particular structural and optical properties is found.
Critical scaling dimension of D-module representations of ${\cal N}=4,7,8$N=4,7,8 superconformal algebras and constraints on superconformal mechanics
Authors: Khodaee Sadi , Toppan Francesco
Published: October 2012

At critical values of the scaling dimension λ, supermultiplets of the global \documentclass[12pt]{minimal}\begin{document}${\cal N}$\end{document}N-extended one-dimensional supersymmetry algebra induce D-module representations of finite superconformal algebras (the latters being identified in terms of the global supermultiplet and its critical scaling dimension). For \documentclass[12pt]{minimal}\begin{document}${\cal N}=4,8$\end{document}N=4,8 and global supermultiplets \documentclass[12pt]{minimal}\begin{document}$(k, {\cal N}, {\cal N}-k)$\end{document}(k,N,N−k), the exceptional superalgebras D(2, 1; α) are recovered for \documentclass[12pt]{minimal}\begin{document}${\cal N}=4$\end{document}N=4, with a relation between α and the scaling dimension given by α = (2 − k)λ. For \documentclass[12pt]{minimal}\begin{document}${\cal N}=8$\end{document}N=8 and k ≠ 4 all four \documentclass[12pt]{minimal}\begin{document}${\cal N}=8$\end{document}N=8 finite superconformal algebras are recovered, at the critical values \documentclass[12pt]{minimal}\begin{document}$\lambda _k = \frac{1}{k-4}$\end{document}λk=1k−4, with the following identifications: D(4, 1) for k = 0, 8, F(4) for k = 1, 7, A(3, 1) for k = 2, 6 and D(2, 2) for k = 3, 5. The \documentclass[12pt]{minimal}\begin{document}${\cal N}=7$\end{document}N=7 global supermultiplet (1, 7, 7, 1) induces, at \documentclass[12pt]{minimal}\begin{document}$\lambda = -\frac{1}{4}$\end{document}λ=−14, a D-module representation of the exceptional superalgebra G(3). D-module representations are applicable to the construction of superconformal mechanics in a Lagrangian setting. The isomorphism of the D(2, 1; α) algebras under an S3 group action on α, coupled with the relation between α and the scaling dimension λ, induces non-trivial constraints on the admissible models of \documentclass[12pt]{minimal}\begin{document}${\cal N}=4$\end{document}N=4 superconformal mechanics. The existence of new superconformal models is pointed out. For example, coupled (1, 4, 3) and (3, 4, 1) supermultiplets generate an \documentclass[12pt]{minimal}\begin{document}${\cal N}=4$\end{document}N=4 superconformal mechanics if λ is related to the golden ratio. The relation between classical versus quantum D-module representations is presented.
Future non-linear stability for solutions of the Einstein-Vlasov system of Bianchi types II and VI
Authors: Nungesser Ernesto
Published: October 2012

In a recent paper [E. Nungesser, “Future non-linear stability for reflection symmetric solutions of the Einstein-Vlasov system of Bianchi types II and VI,” Annales Henri Poincare (2012)10.1007/s00023-012-0201-0], we have treated the future nonlinear stability for reflection symmetric solutions of the Einstein-Vlasov system of Bianchi types II and VI0. We have been able now to remove the reflection symmetry assumption, thus treating the non-diagonal case. Apart from the increasing complexity, the methods have been essentially the same as in the diagonal case, showing that they are thus quite powerful. Here, the challenge was to put the equations in a form that permits the use of the previous results. We are able to conclude that after a possible basis change, the future of the non-diagonal spacetimes in consideration is asymptotically diagonal.
On the spin separation of algebraic two-component relativistic Hamiltonians
Authors: Li Zhendong , Xiao Yunlong , Liu Wenjian
Published: October 2012

The separation of the spin-free and spin-dependent terms of a given relativistic Hamiltonian is usually facilitated by the Dirac identity. However, this is no longer possible for the recently developed exact two-component relativistic Hamiltonians derived from the matrix representation of the Dirac equation in a kinetically balanced basis. This stems from the fact that the decoupling matrix does not have an explicit form. To resolve this formal difficulty, we first define the spin-dependent term as the difference between a two-component Hamiltonian corresponding to the full Dirac equation and its one-component counterpart corresponding to the spin-free Dirac equation. The series expansion of the spin-dependent term is then developed in two different ways. One is in the spirit of the Douglas-Kroll-Hess (DKH) transformation and the other is based on the perturbative expansion of a two-component Hamiltonian of fixed structure, either the two-step Barysz-Sadlej-Snijders (BSS) or the one-step exact two-component (X2C) form. The algorithms for constructing arbitrary order terms are proposed for both schemes and their convergence patterns are assessed numerically. Truncating the expansions to finite orders leads naturally to a sequence of novel spin-dependent Hamiltonians. In particular, the order-by-order distinctions among the DKH, BSS, and X2C approaches can nicely be revealed. The well-known Pauli, zeroth-order regular approximation, and DKH1 spin-dependent Hamiltonians can also be recovered naturally by appropriately approximating the decoupling and renormalization matrices. On the practical side, the sf-X2C+so-DKH3 Hamiltonian, together with appropriately constructed generally contracted basis sets, is most promising for accounting for relativistic effects in two steps, first spin-free and then spin-dependent, with the latter applied either perturbatively or variationally.
A continuum glassy polymer model applicable to dynamic loading
Authors: Clements B. E.
Published: October 2012

A thermo-mechanical continuum model is proposed that is applicable to dynamically loaded glassy polymers. The underlying theory is based on an ansatz for the Helmholtz free energy where both the deviatoric and the volumetric terms in the free energy have non-equilibrium rate-dependent contributions. The requirement that the free energy is fully rate dependent arises from the desire to model the full range of dynamic conditions ranging from low-rate applications to those common in high-rate shock loading scenarios. A purely equilibrium equation of state (EOS) is found to be insufficient for this purpose. The resulting model suitably captures the thermo-mechanical behavior in both regimes. Polymethylmethacrylate (PMMA) is used as a representative polymer. Analysis is devoted to issues associated with a non-equilibrium equation of state. Because data are insufficient for the full determination of the model's non-equilibrium equation of state, several plausible conditions called the quasi-equilibrium hypothesis are put forth to complete the model. Comparisons of experimental and theoretical results over a wide-range of loading rates and conditions are reported.
Compact microwave cavity for high performance rubidium frequency standards
Authors: Stefanucci Camillo , Bandi Thejesh , Merli Francesco , Pellaton Matthieu , Affolderbach Christoph , Mileti Gaetano , Skrivervik Anja K.
Published: October 2012

The design, realization, and characterization of a compact magnetron-type microwave cavity operating with a TE011-like mode are presented. The resonator works at the rubidium hyperfine ground-state frequency (i.e., 6.835 GHz) by accommodating a glass cell of 25 mm diameter containing rubidium vapor. Its design analysis demonstrates the limitation of the loop-gap resonator lumped model when targeting such a large cell, thus numerical optimization was done to obtain the required performances. Microwave characterization of the realized prototype confirmed the expected working behavior. Double-resonance and Zeeman spectroscopy performed with this cavity indicated an excellent microwave magnetic field homogeneity: the performance validation of the cavity was done by achieving an excellent short-term clock stability as low as 2.4 × 10−13 τ−1/2. The achieved experimental results and the compact design make this resonator suitable for applications in portable atomic high-performance frequency standards for both terrestrial and space applications.
Fast convergence to equilibrium for long-chain polymer melts using a MD/continuum hybrid method
Authors: Senda Yasuhiro , Fujio Miyuki , Shimamura Shuji , Blomqvist Janne , Nieminen Risto M
Published: October 2012

Effective and fast convergence toward an equilibrium state for long-chain polymer melts is realized by a hybrid method coupling molecular dynamics and the elastic continuum. The required simulation time to achieve the equilibrium state is reduced compared with conventional equilibration methods. The polymers move on a wide range phase space due to large-scale fluctuation generated by the elastic continuum. A variety of chain structures is generated in the polymer melt which results in the fast convergence to the equilibrium state.
Near-field radiative heat transfer between chiral metamaterials
Authors: Cui Longji , Huang Yong , Wang Ju
Published: October 2012

We investigate the near-field radiative heat transfer between two dispersive and lossy chiral metamaterials. Our theory takes into account the magnetoelectric coupling effect compared with the existing theories. It is shown that the contribution of surface modes to heat transfer is strongly modulated by the magnetoelectric coupling effect. We predict that in the presence of strong coupling effect, the resonant tunneling modes with small parallel wavenumbers activate a novel energy transfer channel. We also find that the dissipation effect in material, which is characterized by the scattering rate, significantly influences the effect of magnetoelectric coupling on near-field heat transfer. We finally discuss the applications of these results in thermophotovoltaic energy conversion and the experimental realization of near-field heat transfer.
Light-induced magnetization reversal of high-anisotropy TbCo alloy films
Authors: Alebrand Sabine , Gottwald Matthias , Hehn Michel , Steil Daniel , Cinchetti Mirko , Lacour Daniel , Fullerton Eric E. , Aeschlimann Martin , Mangin Stéphane
Published: October 2012

Magnetization reversal using circularly polarized light provides a way to control magnetization without any external magnetic field and has the potential to revolutionize magnetic data storage. However, in order to reach ultra-high density data storage, high anisotropy media providing thermal stability are needed. Here, we evidence all-optical magnetization switching for different TbxCo1−x ferrimagnetic alloy compositions using fs- and ps-laser pulses and demonstrate all-optical switching for films with anisotropy fields reaching 6 T corresponding to anisotropy constants of 3 × 106 ergs/cm3. Optical magnetization switching is observed only for alloy compositions where the compensation temperature can be reached through sample heating.
Non-degenerated photoluminescence excitation correlation spectroscopy using an optical sampling technique
Authors: Hasegawa Takayuki , Masumoto Naofumi , Harada Tomonori , Makino Takayuki , Takagi Yoshihiro
Published: October 2012

We have developed a highly time-resolved photoluminescence spectroscopy based on the excitation correlation method. Successive irradiation of a pair of ultrashort light pulses with different wavelength combinations taken from two sub-picosecond lasers has exposed both temporal and energetic correlation in photoluminescence intensity associated with a nonlinear response of a sample. An optical sampling technique has been introduced successfully in order to avoid consideration of the synchronization control of ultrashort light pulses. We have demonstrated the abilities of this technique by applying to the nonlinear photoluminescence dynamics of organic dye molecules in solution.
In-situ synchrotron energy-dispersive x-ray diffraction study of thin Pd foils with Pd:D and Pd:H concentrations up to 1:1
Authors: Knies D. L. , Violante V. , Grabowski K. S. , Hu J. Z. , Dominguez D. D. , He J. H. , Qadri S. B. , Hubler G. K.
Published: October 2012

Time resolved, in-situ, energy dispersive x-ray diffraction was performed in an electrolysis cell during electrochemical loading of palladium foil cathodes with hydrogen and deuterium. Concentrations of H:Pd (D:Pd) up to 1:1 in 0.1 M LiOH (LiOD) in H2O (D2O) electrolyte were obtained, as determined by both the Pd lattice parameter and cathode resistivity. In addition, some indications on the kinetics of loading and deloading of hydrogen from the Pd surface were obtained. The alpha-beta phase transformations were clearly delineated but no new phases at high concentration were determined.
Preferentially directed flux motion in a very thin superconducting strip with nanostructured profile
Authors: Sabatino P. , Carapella G. , Gombos M.
Published: October 2012

We report an experimental and numerical study of the vortex matter moving in a very thin type II superconducting strip with asymmetrically nanostructured profile. The asymmetric thickness profile generates a geometrical force landscape that sets a preferential direction for vortex motion, resulting in an uncommon voltage-current curve of the strip, with vanishingly small asymmetry in the positive and negative critical currents but appreciably large asymmetry in the voltages. Experimental results as well as the geometrical force affecting the moving vortex matter are discussed in the framework of time dependent Ginzburg-Landau model for superconductors with variable thickness.
The influence of resistance drift on measurements of the activation energy of conduction for phase-change material in random access memory line cells
Authors: Oosthoek J. L. M. , Krebs D. , Salinga M. , Gravesteijn D. J. , Hurkx G. A. M. , Kooi B. J.
Published: October 2012

Temporal drift of the amorphous resistance in phase-change random access memory (PRAM) is a temperature accelerated process. Increasing the temperature will speed up the drift process which is shown to affect measurements of the activation energy of conduction (Ea, slope of log(R) versus 1/kT). Doped SbTe phase change (PRAM) line cells were brought to the amorphous state and were subjected to annealing experiments. First, it is shown that when the temperature is increased by a fixed rate, the resistance does not follow a unique function of temperature but depends on the heating rate. This can be attributed to resistance drift taking place during the ramp. Upon cooling, the drift process freezes and only then physically relevant, i.e., time independent, values for Ea can be obtained, because of the absence of additional drift. The observed increase in resistance as a function of annealing history (for various frozen-in drift levels) is modeled and well-reproduced using a trap limited band transport model. The model explains these observations by an increase of the temperature dependent band gap by about 47 meV due to drift at 418 K.
Electronic structure of TlGeI3, TlSnI3, and TlPbI3: Potential use for spectroscopic radiation detection
Authors: Singh David J.
Published: October 2012

I use electronic structure calculations based on a newly developed functional that is designed to reliably predict band structure and band gaps of semiconductors to investigate the electronic structures and optical properties of TlPbI3, TlGeI3, and TlSnI3. The results indicate that TlPbI3 if activated may be a potentially useful low band gap scintillator. The possibility of using Sn as an activator is investigated.
Electrically tunable electron spin lifetimes in GaAs(111)B quantum wells
Authors: Biermann K. , Hernández-Mínguez A. , Hey R. , Santos P. V.
Published: October 2012

We investigate the electric tunability of the electron spin lifetime in GaAs(111) quantum wells (QWs) inserted in biased p-i-n and n-i-p diode-like structures. Due to the specific symmetry of these QWs, the Rashba contribution to the spin-orbit magnetic field induced by the applied bias is parallel to the intrinsic Dresselhaus contribution for all directions of the electron wavevector. In particular, the voltage applied to the diode, which controls the amplitude of the Rashba contribution, can be adjusted to attenuate the resulting spin-orbit field, thus strongly suppressing spin dephasing due to the Dyakonov-Perel relaxation mechanism for all spin orientations. Spin lifetimes from below 100 ps at an electric field of −20 kV/cm to values exceeding 4 ns at +8 kV/cm have been measured in 25 nm thick multiple QWs at a temperature of 20 K.
Conductance properties of topological insulator based ferromagnetic insulator/d-wave superconductor and normal metal/ferromagnetic insulator/d-wave superconductor junctions
Authors: Vali R. , Vali Mehran
Published: October 2012

We study theoretically the conductance properties of a ferromagnetic insulator/d-wave superconductor (FI/d-wave SC) junction and a normal metal/ferromagnetic insulator/d-wave superconductor (NM/FI/d-wave SC) junction formed on the surface of a three dimensional topological insulator, where the direction of the magnetization m in ferromagnetic region is perpendicular to the surface. We find that with increasing the magnetization of the ferromagnetic region, a conductance peak to conductance dip conversion occurs, at a bias voltage depending on the d-wave superconducting orientation angular. We find also that the gate voltage applied across the ferromagnetic region strongly affects the influence of the magnetization on the zero bias conductance of the NM/FI/d-wave SC junction.
Transient photoresponse and incident power dependence of high-efficiency germanium quantum dot photodetectors
Authors: Liu Pei , Cosentino S. , Le Son T. , Lee S. , Paine D. , Zaslavsky A. , Pacifici D. , Mirabella S. , Miritello M. , Crupi I. , Terrasi A.
Published: October 2012

We report a systematic study of time-resolved and power-dependent photoresponse in high-efficiency germanium quantum dot photodetectors (Ge-QD PDs), with internal quantum efficiencies greater than 100% over a broad wavelength, reverse bias, and incident power range. Turn-on and turn-off response times (τon and τoff) are shown to depend on series resistance, bias, optical power, and thickness (WQD) of the Ge-QD layer, with measured τoff values down to ∼40 ns. Two different photoconduction regimes are observed at low and high reverse bias, with a transition around −3 V. A transient current overshoot phenomenon is also observed, which depends on bias and illumination power.
Ion imaging study of reaction dynamics in the N+ + CH4 system
Authors: Pei Linsen , Farrar James M.
Published: October 2012

The velocity map ion imaging method is applied to the ion-molecule reactions of N+ with CH4. The velocity space images are collected at collision energies of 0.5 and 1.8 eV, providing both product kinetic energy and angular distributions for the reaction products CH4+, CH3+, and HCNH+. The charge transfer process is energy resonant and occurs by long-range electron transfer that results in minimal deflection of the products. The formation of the most abundant product, CH3+, proceeds by dissociative charge transfer rather than hydride transfer, as reported in earlier publications. The formation of HCNH+ by C–N bond formation appears to proceed by two different routes. The triplet state intermediates CH3NH+ and CH2NH2+ that are formed as N+(3P) approaches CH4 may undergo sequential loss of two hydrogen atoms to form ground state HCNH+ products on a spin-allowed pathway. However, the kinetic energy distributions for formation of HCNH+ extend past the thermochemical limit to form HCNH+ + 2H, implying that HCNH+ may also be formed in concert with molecular hydrogen, and requiring that intersystem crossing to the singlet manifold must occur in a significant (∼25%) fraction of reactive collisions. We also report GAUSSIAN G2 calculations of the energies and structures of important singlet and triplet [CNH4+] complexes that serve as precursors to product formation.
Perpendicular magnetic anisotropy in Nd-Co alloy films nanostructured by di-block copolymer templates
Authors: Valdés-Bango F. , García Alonso F. J. , Rodríguez-Rodríguez G. , Morán Fernandez L. , Anillo A. , Ruiz-Valdepeñas L. , Navarro E. , Vicent J. L. , Vélez M. , Martín J. I. , Alameda J. M.
Published: October 2012

Nd-Co amorphous magnetic films with perpendicular magnetic anisotropy have been grown on nanostructured templates prepared with self-organized di-block poly(styrene)-block-poly(4-vinylpyridine) copolymer layers with a periodic structure of 60 nm spaced pores. These templates modify both the magnetic film topography and mechanical strain on a local scale. The effect of these structural changes is particularly noticeable in the low thickness range of the magnetic films where the transition from in-plane to out-of plane magnetization takes place. The Nd-Co films grown on the copolymer template present lower perpendicular magnetic anisotropy and, also, stronger stripe domain pinning effects in comparison with reference films grown on flat Si substrates.
Numerical study of the characteristics of the ion and fast atom beams in an end-Hall ion source
Authors: Oudini N. , Garrigues L. , Hagelaar G. J. M. , Boeuf J. P.
Published: October 2012

An end-Hall ion source is a cylindrical magnetized device of few centimeters in length able to generate an ion beam with a current of typically 1 A and ion energies in the range of 100 eV. This ion source does not use acceleration grids, has a relatively large ion beam divergence, and is well suited for ion assisted deposition processes. In this paper, a self-consistent two-dimensional quasi-neutral model of an end-Hall ion source is used to understand the parameters controlling the characteristics of the extracted. The model results underline the role of charge exchange collisions on beam properties. The calculated energy distribution functions reveal the existence of groups of slow ions and fast neutrals. Ion mean energy corresponds to roughly 60% of the discharge voltage, while the root mean square deviation from the mean energy corresponds to about 33% of the discharge voltage, as in experiments. The influence of the position of the electron emitting source on the ion angular distribution is also shown.
Long-lived electron spins in a modulation doped (100) GaAs quantum well
Authors: Colton J. S. , Meyer D. , Clark K. , Craft D. , Cutler J. , Park T. , White P.
Published: October 2012

We have measured T1 spin lifetimes of a 14 nm modulation-doped (100) GaAs quantum well using a time-resolved pump-probe Kerr rotation technique. The quantum well was selected by tuning the wavelength of the probe laser. T1 lifetimes in excess of 1 μs were measured at 1.5 K and 5.5 T, exceeding the typical T2* lifetimes that have been measured in GaAs and II-VI quantum wells by orders of magnitude. We observed effects from nuclear polarization, which were largely removable by simultaneous nuclear magnetic resonance, along with two distinct lifetimes under some conditions that likely result from probing two differently localized subsets of electrons.
A portable molecular beam epitaxy system for in situ x-ray investigations at synchrotron beamlines
Authors: Slobodskyy T. , Schroth P. , Grigoriev D. , Minkevich A. A. , Hu D. Z. , Schaadt D. M. , Baumbach T.
Published: October 2012

A portable synchrotron molecular beam epitaxy (MBE) system is designed and applied for in situ investigations. The growth chamber is equipped with all the standard MBE components such as effusion cells with shutters, main shutter, cooling shroud, manipulator, reflection high energy electron diffraction setup, and pressure gauges. The characteristic feature of the system is the beryllium windows which are used for in situ x-ray measurements. An UHV sample transfer case allows in vacuo transfer of samples prepared elsewhere. We describe the system design and demonstrate its performance by investigating the annealing process of buried InGaAs self-organized quantum dots.
Superconducting epitaxial thin films of CeNixBi2 with a bismuth square net structure
Authors: Buckow Alexander , Kupka Katharina , Retzlaff Reiner , Kurian Jose , Alff Lambert
Published: October 2012

We have grown highly epitaxial and phase pure thin films of the arsenic-free pnictide compound CeNixBi2 on (100) MgO substrates by reactive molecular beam epitaxy (RMBE). X-ray diffraction and reflection high-energy electron diffraction of the films confirm the ZrCuSiAs structure with a Bi square net layer. Superconductivity was observed in magnetization and resistivity measurements for x = 0.75 to 0.93 in these CeNixBi2 thin films with the highest critical temperature of 4.05 K and a resistive transition width of 0.1 K for x = 0.86. Our results indicate that thin film deposition by RMBE provides a tool to synthesize high-quality pnictide superconductors of the novel 112 type.
Liquid-like instabilities in gold nanowires fabricated by focused ion beam lithography
Authors: Naik J. P. , Das K. , Prewett P. D. , Raychaudhuri A. K. , Chen Yifang
Published: October 2012

Observation of liquid-like instabilities is reported in Au nanowires formed by nanopatterning of Au films using focused ion beam (FIB) on different types of Si substrates including those passivated with SiO2 or Si3N4 surfaces. The onset of the instability, which can ultimately lead to break up of the FIB patterned nanowires into gold islands, occurs when the diameter of the nanowire is below a critical range, which depends on the conductivity of the substrate and the extent of native oxide present on it. We also observe the formation of Taylor cones on very narrow nanowires grown on insulating substrates at the onset of instabilities. This effect is further strong evidence of liquid behaviour and is the result of charging of the wires during FIB nanofabrication.
Bistability patterns and nonlinear switching with very high contrast ratio in a 1550 nm quantum dash semiconductor laser
Authors: Hurtado A. , Nami M. , Henning I. D. , Adams M. J. , Lester L. F.
Published: October 2012

We report on the experimental observation of optical bistability (OB) and nonlinear switching (NS) in a nanostructure laser; specifically a 1550 nm quantum dash Fabry-Perot laser subject to external optical injection and operated in reflection. Different shapes of optical bistability and nonlinear switching, anticlockwise and clockwise, with very high on-off contrast ratio (up to 180:1) between output states were experimentally measured. These results added to the potential of nanostructure lasers for enhanced performance offer promise for use in fast all-optical signal processing applications in optical networks.
Graphene layer growth on silicon substrates with nickel film by pulse arc plasma deposition
Authors: Fujita K. , Banno K. , Aryal H. R. , Egawa T.
Published: October 2012

Carbon layer has been grown on a Ni/SiO2/Si(111) substrate under high vacuum pressure by pulse arc plasma deposition. From the results of Raman spectroscopy for the sample, it is found that graphene was formed by ex-situ annealing of sample grown at room temperature. Furthermore, for the sample grown at high temperature, graphene formation was shown and optimum temperature was around 1000 °C. Transmission electron microscopy observation of the sample suggests that the graphene was grown from step site caused by grain of Ni film. The results show that the pulse arc plasma technique has the possibility for acquiring homogenous graphene layer with controlled layer thickness.
Measurement of electric-field induced second harmonic generation in hydrogenated amorphous silicon
Authors: He Long , Walker James D. , Branz Howard M. , Rogers Charles T. , Teplin Charles W.
Published: October 2012

We quantitatively separate interface optical second harmonic generation (SHG) and electric-field induced second harmonic generation (EFISH) from hydrogenated amorphous silicon (a-Si:H) interfaces and bulk. Using a 1.51 eV probe laser, we measure SHG signals from indium tin oxide (ITO) ITO/a-Si:H/ITO sandwich structures and vary the electric fields in the a-Si:H layer using an applied voltage bias. The a-Si:H/ITO interfaces form back-to-back diodes. Because of finite optical penetration depth, SHG probes only the front diode. When the front diode is reverse biased, the EFISH contribution dominates the SHG signal and probes the electric field in the ∼30 nm adjacent to the interface. Through fitting of the SHG data, we find that in this near-interface region, the electric field is proportional to the square root of the applied bias. The fitting measures the interfacial ITO/a-Si:H built-in voltage to be ∼0.2 V.
Surface-plasmon enhanced absorption in organic solar cells by employing a periodically corrugated metallic electrode
Authors: Jin Yu , Feng Jing , Zhang Xu-Lin , Xu Ming , Bi Yan-Gang , Chen Qi-Dai , Wang Hai-Yu , Sun Hong-Bo
Published: October 2012

We demonstrate improved efficiency of organic solar cells (OSCs) by employing a periodically corrugated metallic electrode in the OSCs. The improved efficiency can be attributed to the absorption enhancement resulted from the excitation of propagating surface-plasmon polariton (SPP) modes at the corrugated metal/organic interface. Through tuning the SPP resonance to the intrinsic absorption region, the short circuit current of the corrugated device with appropriate period has been increased from 4.1 mA/cm2 for planar device to 5.5 mA/cm2. The power conversion efficiency exhibits an enhancement of 35%.
Note: 15-fs, 15-μJ green pulses from two-stage temporal compressor of ytterbium laser pulses
Authors: Konyashchenko A. V. , Kostryukov P. V. , Losev L. L. , Tenyakov S. Yu.
Published: October 2012

15-fs, 15-μJ light pulses at the central wavelength of 515 nm were generated by two-stage nonlinear compression of 300-fs, 150-μJ ytterbium laser pulses. The compression was based on the pulse spectrum broadening by self-phase modulation in gas filled capillary and second harmonic generation in crystal.
Robustness to noise in synchronization of network motifs: Experimental results
Authors: Buscarino Arturo , Fortuna Luigi , Frasca Mattia , Iachello Marco , Pham Viet-Thanh
Published: October 2012

In this work, we experimentally investigate the robustness to noise of synchronization in all the four-nodes network motifs. The experimental setup consists of four Chua's circuits diffusively coupled in order to implement the six different undirected network motifs that can be obtained with four nodes. In this experimental setup, synchronization in the presence of noise injected in one of the network nodes is investigated and network motifs are compared in terms of the synchronization error obtained. The analysis has been then extended to some selected case studies of networks with five and six nodes. Numerical simulations have been also performed and results in agreement with experiments have been obtained. A correlation between node degree and robustness to noise has been found also in these networks.
Potential contour shaping and sheath behavior with wall electrodes and near-wall magnetic fields in Hall thrusters
Authors: Xu K. G. , Dao H. , Walker M. L. R.
Published: October 2012

Graphite electrodes are embedded within the discharge channel of a Hall effect thruster to focus ions for improved performance. Cusp-shaped magnetic fields are added around the electrodes to shield the electrodes from high electron current. Internal plasma potential measurements inside the discharge channel show that the presence of floating graphite does not significantly affect the potential contours at 150 V anode potential. Creation of closed contour pockets are observed with the electrodes biased 10 and 30 V above the anode potential. The electrodes also cause a compression of the acceleration region in the thruster. The cause of the changes in the potential contours is attributed to a shifting of discharge electrode from the anode to the electrodes and an expansion of the near-wall plasma sheath. The presence of the cusp magnetic fields is shown to affect the current collected by the electrodes, a behavior associated with modification of the plasma sheath properties due to magnetization of electrons.
Observation of partial Meissner effect and flux pinning in superconducting lead containing non-superconducting parts
Authors: Treimer W. , Ebrahimi O. , Karakas N.
Published: October 2012

Partially suppressed Meissner effect and magnetic flux trapping in the bulk of poly-crystalline Pb samples with virtually zero demagnetization and large (cm3) volume containing non-superconducting parts could be visualized by polarized neutrons and quantified with respect to the shape and amount of the trapped flux in the intermediate state of lead. These measurements provided a unique look at the macroscopic Quantum mechanics effects and the coexistence of superconducting state, intermediate state, and normal conducting parts in the same sample, respectively.
A Critical Review of Aqueous Solubilities, Vapor Pressures, Henry’s Law Constants, and Octanol–Water Partition Coefficients of the Polychlorinated Biphenyls
Authors: Shiu Wan Ying , Mackay Donald
Published: October 2012

Relationships between the environmentally relevant physical chemical properties of the polychlorinated biphenyls, namely, aqueous solubility, vapor pressure, Henry’s law constant, and octanol–water partition coefficient are discussed. Reported experimental data are tabulated and critically reviewed. Recommended values are given for 42 of the 209 congeners; however, procedures are suggested for estimating the properties of the other congeners. Properties of mixtures are not treated.
The Diffusion of Violence in the North Caucasus of Russia, 1999–2010
Authors: O'Loughlin John , Witmer Frank D W
Published: October 2012

Despite an increase in attention to ‘geography’ in civil war research, local dynamics in violence remain poorly understood. To address this gap, we analyze disaggregated violent event data for the North Caucasus of Russia from the start of the second Chechen war, in August 1999, to July 2010. We employ a diffusion perspective to examine the spread of the conflict from its Chechen nucleus and we identify the tit-for-tat nature of the conflict between the rebels and the military/police forces as especially significant in understanding the conflict's dynamics and spread to neighboring republics. A space—time analysis shows that violence is concentrated at short temporal intervals and geographic distances. As the insurgents in the violence have changed from dominantly nationalist to Islamist, the geography of the war has become more diffuse across the Muslim republics of the region, rendering the Russian counterinsurgency efforts more challenging.
The Local Environmental Regulatory Regime in China: Changes in Pro-Environment Orientation, Institutional Capacity, and External Political Support in Guangzhou
Authors: Francesch-Huidobro Maria , Lo Carlos Wing-Hung , Tang Shui-Yan
Published: October 2012

In the first decade of this millennium China has demonstrated a stronger commitment to environmental protection. Yet, there remains a significant gap between environmental laws and regulations and the quality of the environment. In this paper, we propose an integrated framework for analysis that we apply to investigate the factors that account for this gap in implementation. We analyse the results of surveys conducted in 2000 and 2006 and interviews carried out in 2006 and 2007 in eleven jurisdictions of Guangzhou municipality on three factors: pro-environment orientation, institutional capacity, and external political support for environmental units. The results show that, after several decades of environmental protection regulations, the pro-environment orientation of environmental officials in Guangzhou has been strengthened, whereas the institutional capacity of environmental agencies, although often beefed up in real terms, remains inadequate due to the heightened expectations of state and society actors. It is the external political support received by environmental agencies that drives the success or failure of environmental protection enforcement. More often than not, the strength or weakness of political support is embedded in the policy design and implementation structure and is associated with the policy orientation of political leaders.
Residential Mobility of Urban Middle Classes in the Field of Parenthood
Authors: Boterman Willem R
Published: October 2012

There is common understanding that gentrifiers and new middle classes more generally share an urban orientation and may share a ‘metropolitan habitus’. The urban geography of Western metropolises and the formation and reproduction of specific middle-class groups are intrinsically connected. The specific urban habitus of these new middle classes, however, is challenged by events in the life course. When urban middle classes settle down and have children, many suburbanise. Using two waves of longitudinal data from a representative sample of middle-class couples expecting their first child, this study investigates the residential practices of middle classes that live in the central areas of Amsterdam when they become first-time parents. Building on prior work on urban middle classes, inspired by the theoretical concepts of Bourdieu, through a multilevel analysis, this study seeks to understand how various orientations of capital influence the decision whether to stay in the city or move to suburban areas. Controlling for a range of individual and neighbourhood variables, this study demonstrates that couples with high economic capital and relatively low cultural capital have a higher propensity to move out of the central city, whereas couples with high cultural capital and low economic capital have a smaller chance of suburbanising. Furthermore, this study confirms that the degree of social and economic connectedness through social networks and work in the city also play an important part in determining the propensity to move out of the city.
Greening Cosmopolitan Urbanism? On the Transnational Mobility of Low-Carbon Formats in Northern European and East Asian Cities
Authors: Blok Anders
Published: October 2012

This paper engages key social theories of transnational mobilities in order to forge the concept of urban ‘green’ cosmopolitization, posited as a social scientific contribution to epochal conversations on climate change. Bringing Ulrich Beck's notion of ‘cosmopolitization’ to bear on recent work around ‘urban policy mobilities’, I analyze professional planning practices in large-scale world cities as privileged sites for contemporary imaginings and material implementations of low-carbon sociotechnical change. Focusing on the regions of Europe and Asia, I show how specific policies and technologies of urban greening circulate in intercity sustainability networks. These networks, I suggest, serve to organize processes of professional engagement with climate change around notions of innovation, learning, and ‘best practice’ policy transfer among urban professionals—thereby also excluding more ‘radically’ alternative futures. The paper then turns to explore how such green cosmopolitization works as a social force within specific urban localities, employing two ethnographic case studies into ‘ambitious’ low-carbon planning projects in Copenhagen and Kyoto, respectively. In particular, my analysis explores how place-based notions of ‘culture’ are mobilized in the urban visions of architects and engineers as resources for addressing global environmental risks. These spaces of urban green cosmopolitization, I conclude, emerge at the intersection of professional and vernacular ethico-political attachments, thereby reworking—in often contentious ways—how particular urban materials and spaces can be understood in reference to an emerging moral geography of shared climatic risks.
Flood-Risk Management, Mapping, and Planning: The Institutional Politics of Decision Support in England
Authors: Porter James , Demeritt David
Published: October 2012

Flood maps play an increasingly prominent role in government strategies for flood-risk management. Maps are instruments not just for defining and communicating flood risks, but also for regulating them and for rationalizing the inevitable limits and failures of those controls. Drawing on policy document analysis, official statistics, and 66 key-informant interviews, this paper explores the institutional conflicts over the use of the Environment Agency (EA) Flood Map to support decision making by English local planning authorities (LPAs), whose local political mandate, statutory obligations, and professionalized planning culture put them at odds with the narrower bureaucratic imperative of the Agency to restrict developments at risk of flooding. The paper shows how the Flood Map was designed to standardize and script the planning process and ensure that LPA decisions were aligned with EA views about avoiding development in zones at risk of flooding without actually banning such development outright. But technologies are also shaped by their users, and so the paper documents how planners accommodated and resisted this technology of indirect rule. Their concerns about sterilizing areas depicted as being at risk of flooding and about the difficulties of actually using the Flood Map for speedy and defensible development-control decisions were crucial in its eventual replacement by a new decision-support technology, Strategic Flood Risk Assessments, which then led to the descripting of the Flood Map to influence a new set of users: the public. The paper closes with some wider reflections on the significance of the case for risk-based governance.
The European Waste Hierarchy: From the Sociomateriality of Waste to a Politics of Consumption
Authors: Hultman Johan , Corvellec Hervé
Published: October 2012

Municipal solid waste is a central concern for environmental policy, and the sociomateriality of waste—the ways in which waste is socially defined and dealt with—is an important issue for sustainability. We show how applying the European Union's waste policy through the European Waste Hierarchy (EWH) affects the sociomateriality of waste. The EWH ranks the desirability of different waste-management approaches according to their environmental impact. We investigate how the EWH has been acknowledged and interpreted in five different organizational contexts with relevance for Swedish waste management: EU environmental policy, the Swedish EPA, two municipal waste-management companies, and the trade organization Swedish Waste Management which represents the interests of municipal bodies involved with waste. In addition to preventing the production of waste, the EWH aims to disassemble, circulate, and reintroduce as much material as possible into production processes. We show how these aims shape paradoxical relationships between economy and society on the one hand, and environment and nature on the other, and open the way for a discussion of a politics of consumption through material management.
Reconsidering Private Sector Engagement in Subnational Economic Governance
Authors: Syrett Stephen , Bertotti Marcello
Published: October 2012

One consequence of the economic downturn and pressure for public sector reform is a renewed focus upon private sector engagement (PSE) within subnational economic governance. Yet past attempts to promote PSE within urban and regional development policy and governance have been routinely characterised by the partial and uneven involvement of business interests. Adopting a strategic—relational approach, and building upon insights from the developing literature on business—society relations, this paper critically examines how PSE unfolded in a specific spatial and temporal context, through empirical investigation of the evolution of the City Growth Strategy as realised within two areas in London. This analysis explores the difference between policy script and business performance and identifies key dimensions of material self-interest, nonmarket-based rationales, and divergent private/public discourses as critical to the selective nature of emergent PSE strategies and tactics. Critically, these issues remain largely unaddressed within current moves to put in place a private sector led subnational agenda, with clear consequences for understanding its likely impact across differentially constituted urban and regional contexts.
A Therapeutics of Exile: Isaiah Berlin, Liberal Pluralism and the Psyche of Assimilation
Authors: Dubow Jessica
Published: October 2012

This paper focuses on the (now ‘unfashionable’) figure of the liberal political philosopher Isaiah Berlin. It argues the ways in which Berlin's distinctive understanding of liberal pluralism carries a hidden spatial and therapeutic premise that bears upon the displaced life of the émigré/assimilated subject as upon the negotiations of internal dividedness and ‘nonviolent’ conflict effectuated by it. Set in the context of the meeting between Isaiah Berlin and the dissident Soviet poet, Anna Akhmatova, in St Petersburg in 1941, and reading Berlin via certain key concepts of another émigré subject, Sigmund Freud, I suggest that political pluralism and the therapeutic ‘cure’ share profound structural similarities. From this interpretative angle, I then draw a series of analogies which correlate the condition of exile to the state of melancholia and, conversely, the process of assimilation to the work of mourning. So understood, it becomes possible to translate Berlin's political liberalism into psychoanalytic terms, viewing liberal identity as enabled by the subject's release from the ‘monism’ of territorial attachment and thus by its enlivened embrace of psychic loss and dislocation.