bluuebunny/crossref_metadata_2025 huggingface dataset:
External triggering of plasmoid development at Saturn
Authors: Kidder A. , Paty C. S. , Winglee R. M. , Harnett E. M.
Published: May 2012

The Cassini spacecraft has encountered multiple plasmoids in Saturn's magnetotail thought to be produced by tail reconnection. However, single spacecraft measurements make it difficult to determine plasmoid size, where they form, the composition, and the geometry of the plasma sheet when plasmoids are produced. This paper examines these issues using 3D multifluid simulations of the Kronian magnetosphere. Plasmoids may develop in multiple sectors, form at different distances from the planet, and grow to sizes large relative to the system (∼25 RS), with varying widths and lengths. These plasmoids are composed primarily of water group ions and move downtail with speeds of ∼250 km/s (the local Alfvén speed). The plasma sheet is hinged upward both prior to and following plasmoid formation. Plasmoids can be externally triggered by both flips in the orientation of the interplanetary magnetic field (IMF) as well as a pulse in the solar wind dynamic pressure.
Sublattice magnetization in a two-sublattice ferrimagnetic with single-ion anisotropy in one of the sublattices
Authors: Butrim V. I. , Ivanov B. A. , Fridman Yu. A.
Published: May 2012

Temperature dependence of sublattice magnetization of an anisotropic ferrimagnetic is investigated. It is shown that the presence of even weak single-ion anisotropy results in a quantum reduction of the spin, and, consequently, changes the behavior of sublattice magnetization.
Evidence of the Griffiths phase in multiferroic BiMnO3 and BiFe0.5Mn0.5O3 films
Authors: Prokhorov V. G. , Kaminsky G. G. , Kim J. M. , Yoo Y. J. , Lee Y. P. , Svetchnikov V. L. , Levchenko G. G. , Nikolaenko Yu. M. , Khokhlov V. A.
Published: May 2012

Microstructure and magnetic properties of BiMnO3 and BiFe0.5Mn0.5O3 films, prepared by rf magnetron sputtering on LaAlO3 (001) single-crystalline substrate, are investigated. The selected-area electron diffraction analysis allows us to identify the crystal structure of the BiMnO3 film as orthorhombic, while the BiFe0.5Mn0.5O3 film has a hexagonal lattice symmetry. High-resolution electron microscopy study reveals the presence of strip-domain phase with a periodic spacing of about 3c in both films. Magnetic measurements show that in addition to the basic paramagnetic phase the films exhibit Griffiths phase behavior in a wide temperature range. We argue that the observed weak ferromagnetism is due to the strip-domain layered inclusions, rather than intrinsic physical origin of the films.
Magneto-optics of heterostructures with an InGaAs/GaAs quantum well and a ferromagnetic delta-layer of Mn
Authors: Zaitsev S. V.
Published: May 2012

Magneto-optics of heterostructures with an InGaAs/GaAs quantum well (QW) and a 3–5 nm spaced ultra-thin ferromagnetic δ-layer of Mn in the GaAs barrier is investigated in detail. While nonmagnetic structures demonstrate very low degree of circular polarization PC of QW photoluminescence, the existence of the close Mn δ-layer gives rise to high values of PC even above its Curie temperature TC ∼ 35 K. Fast growth of PC and Zeeman splitting of the QW emission band, observed at low B < 0.2 T, is followed by a slow linear increase at B > 0.5 T in heterostructures with strictly oriented GaAs (001) substrates. The characteristic fast increase slows down with temperature and disappears above TC. The effect depends non-monotonically on QW depth and is explained by the model of strong QW fluctuation potential caused by the highly charged Mn δ-layer. The spin polarization of carriers is believed to be related to the effective (p–d)-exchange interaction of holes in the QW with the ferromagnetic δ-layer and to appear due to a normal-to-plane magnetization emerging from the plane of the δ-layer with saturation of the normal component of magnetization at high magnetic fields.
Complex (dusty) plasmas—kinetic studies of strong coupling phenomena
Authors: Morfill Gregor E. , Ivlev Alexei V. , Thomas Hubertus M.
Published: May 2012

“Dusty plasmas” can be found almost everywhere—in the interstellar medium, in star and planet formation, in the solar system in the Earth’s atmosphere, and in the laboratory. In astrophysical plasmas, the dust component accounts for only about 1% of the mass, nevertheless this component has a profound influence on the thermodynamics, the chemistry, and the dynamics. Important physical processes are charging, sputtering, cooling, light absorption, and radiation pressure, connecting electromagnetic forces to gravity. Surface chemistry is another important aspect. In the laboratory, there is great interest in industrial processes (e.g., etching, vapor deposition) and—at the fundamental level—in the physics of strong coupling phenomena. Here, the dust (or microparticles) are the dominant component of the multi-species plasma. The particles can be observed in real time and space, individually resolved at all relevant length and time scales. This provides an unprecedented means for studying self-organisation processes in many-particle systems, including the onset of cooperative phenomena. Due to the comparatively large mass of the microparticles (10-12to10-9g), precision experiments are performed on the ISS. The following topics will be discussed: Phase transitions, phase separation, electrorheology, flow phenomena including the onset of turbulence at the kinetic level.
Changes in particle transport as a result of resonant magnetic perturbations in DIII-D
Authors: Mordijck S. , Doyle E. J. , McKee G. R. , Moyer R. A. , Rhodes T. L. , Zeng L. , Commaux N. , Fenstermacher M. E. , Gentle K. W. , Reimerdes H. , Schmitz O. , Solomon W. M. , Staebler G. M. , Wang G.
Published: May 2012

In this paper, we introduce the first direct perturbed particle transport measurements in resonant magnetic perturbation (RMP) H-mode plasmas. The perturbed particle transport increases as a result of application of RMP deep into the core. In the core, a large reduction in E × B shear to a value below the linear growth rate, in conjunction with increasing density fluctuations, is consistent with an increase in turbulent particle transport. In the edge, the changes in turbulent particle transport are less obvious. There is a clear correlation between the linear growth rates and the density fluctuations measured at different scales, but it is uncertain which is the cause and which is the consequence.
L1-FePt based exchange coupled composite films with soft [Co/Ni]N multilayers
Authors: Guo H. H. , Liao J. L. , Ma B. , Zhang Z. Z. , Jin Q. Y. , Rui W. B. , Du J. , Wang H. , Wang J. P.
Published: May 2012

Perpendicular exchange coupled composite structures were prepared, utilizing L10-FePt as the magnetic hard layer and [Co/Ni]N multilayers as the soft layer. Sharp reduction of the switching field was observed with increasing periodic number N of [Co/Ni]N multilayers. By inserting a thin Pt interlayer between L10-FePt and [Co/Ni]N layers, it is found that in order to get the best of exchange coupled composites, different interlayer coupling stiffness was required in the composites with different soft layer thickness. Furthermore, the angular variation of the coercivity and remanent coercivity shows high angular tolerance to applied field angle, and reveals the evolution of magnetization reversal from incoherent rotational mode to dominant wall motion with increasing thickness of soft layer.
Effect of poloidal asymmetries on impurity peaking in tokamaks
Authors: Mollén A. , Pusztai I. , Fülöp T. , Kazakov Ye. O. , Moradi S.
Published: May 2012

Poloidal impurity asymmetries are frequently observed in tokamaks. In this paper, the effect of poloidal asymmetry on electrostatic turbulent transport is studied, including the effect of the E×B drift. Collisions are modeled by a Lorentz operator, and the gyrokinetic equation is solved with a variational approach. The impurity transport is shown to be sensitive to the magnetic shear and changes sign for s≳0.5 in the presence of inboard accumulation. The zero-flux impurity density gradient (peaking factor) is shown to be rather insensitive to collisions in both ion temperature gradient and trapped electron mode driven cases. Our results suggest that the asymmetry (both the location of its maximum and its strength) and the magnetic shear are the two most important parameters that affect the impurity peaking.
Numerical study on comparison of Navier-Stokes and Burgers equations
Authors: Ohkitani Koji , Dowker Mark
Published: May 2012

We compare freely decaying evolution of the Navier-Stokes equations with that of the 3D Burgers equations with the same kinematic viscosity and the same incompressible initial data by using direct numerical simulations. The Burgers equations are well-known to be regular by a maximum principle [A. A. Kiselev and O. A. Ladyzenskaya, “On existence and uniqueness of the solutions of the nonstationary problem for a viscous incompressible fluid,” Izv. Akad. Nauk SSSR Ser. Mat. 21, 655 (1957); A. A. Kiselev and O. A. Ladyzenskaya, Am. Math. Soc. Transl. 24, 79 (1957)] unlike the Navier-Stokes equations. It is found in the Burgers equations that the potential part of velocity becomes large in comparison with the solenoidal part which decays more quickly. The probability distribution of the nonlocal term \documentclass[12pt]{minimal}\begin{document}$-{\bm u}\cdot \nabla p$\end{document}−u·∇p, which spoils the maximum principle, in the local energy budget is studied in detail. It is basically symmetric, i.e., it can be either positive or negative with fluctuations. Its joint probability density functions with \documentclass[12pt]{minimal}\begin{document}$\frac{1}{2}|{\bm u}|^2$\end{document}12|u|2 and with \documentclass[12pt]{minimal}\begin{document}$\frac{1}{2}|{\bm \omega }|^2$\end{document}12|ω|2 are also found to be symmetric, fluctuating at the same times as the probability density function of \documentclass[12pt]{minimal}\begin{document}$-{\bm u}\cdot \nabla p$\end{document}−u·∇p. A power-law relationship is found in the mathematical bound for the enstrophy growth \documentclass[12pt]{minimal}\begin{document}$\dfrac{dQ}{dt} + 2 \nu P \propto \left(Q^a P^b\right)^\alpha ,$\end{document}dQdt+2νP∝QaPbα, where Q and P denote the enstrophy and the palinstrophy, respectively, and the exponents a and b are determined by calculus inequalities. We propose to quantify nonlinearity depletion by the exponent α on this basis.
Symmetric and asymmetric triple excitation corrections for the orbital-optimized coupled-cluster doubles method: Improving upon CCSD(T) and CCSD(T)Λ: Preliminary application
Authors: Bozkaya Uğur , Schaefer Henry F.
Published: May 2012

Symmetric and asymmetric triple excitation corrections for the orbital-optimized coupled-cluster doubles (OO-CCD or simply “OD” for short) method are investigated. The conventional symmetric and asymmetric perturbative triples corrections [(T) and (T)Λ] are implemented, the latter one for the first time. Additionally, two new triples corrections, denoted as OD(Λ) and OD(Λ)T, are introduced. We applied the new methods to potential energy surfaces of the BH, HF, C2, N2, and CH4 molecules, and compare the errors in total energies, with respect to full configuration interaction, with those from the standard coupled-cluster singles and doubles (CCSD), with perturbative triples [CCSD(T)], and asymmetric triples correction (CCSD(T)Λ) methods. The CCSD(T) method fails badly at stretched geometries, the corresponding nonparallelity error is 7–281 kcal mol−1, although it gives reliable results near equilibrium geometries. The new symmetric triples correction, CCSD(Λ), noticeably improves upon CCSD(T) (by 4–14 kcal mol−1) for BH, HF, and CH4; however, its performance is worse than CCSD(T) (by 1.6–4.2 kcal mol−1) for C2 and N2. The asymmetric triples corrections, CCSD(T)Λ and CCSD(Λ)T, perform remarkably better than CCSD(T) (by 5–18 kcal mol−1) for the BH, HF, and CH4 molecules, while for C2 and N2 their results are similar to those of CCSD(T). Although the performance of CCSD and OD is similar, the situation is significantly different in the case of triples corrections, especially at stretched geometries. The OD(T) method improves upon CCSD(T) by 1–279 kcal mol−1. The new symmetric triples correction, OD(Λ), enhances the OD(T) results (by 0.01–2.0 kcal mol−1) for BH, HF, and CH4; however, its performance is worse than OD(T) (by 1.9–2.3 kcal mol−1) for C2 and N2. The asymmetric triples corrections, OD(T)Λ and OD(Λ)T, perform better than OD(T) (by 2.0–6.2 kcal mol−1). The latter method is slightly better for the BH, HF, and CH4 molecules. However, for C2 and N2 the new results are similar to those of OD(T). For the BH, HF, and CH4 molecules, OD(Λ)T provides the best potential energy curves among the considered methods, while for C2 and N2 the OD(T) method prevails. Hence, for single-bond breaking the OD(Λ)T method appears to be superior, whereas for multiple-bond breaking the OD(T) method is better.
On conversion of luminescence into absorption and the van Roosbroeck-Shockley relation
Authors: Bhattacharya Rupak , Pal Bipul , Bansal Bhavtosh
Published: May 2012

The problem of conversion of experimentally measured luminescence spectrum into the absorption cross section is revisited. The common practice of using the van Roosbroeck-Shockley (or Kubo-Martin-Schwinger or Kennard-Stepanov) relation in this context is incorrect because luminescence from semiconductors is essentially all due to the spontaneous emission component of the recombination of carriers distributed far-from-equilibrium. A simple, physically consistent, and practical prescription for converting the luminescence spectra into absorption is presented and its relation to the so-called nonequilibrium generalization of the van Roosbroeck-Shockley relationship is discussed.
Nano scale phase separation in Au-Ge system on ultra clean Si(100) surfaces
Authors: Rath A. , Dash J. K. , Juluri R. R. , Schowalter Marco , Mueller Knut , Rosenauer A. , Satyam P. V.
Published: May 2012

We report on the phase separation in Au–Ge system leading to the formation of lobe-lobe (bi-lobed) Au-Ge nanostructures under ultra high vacuum (UHV) conditions (≈3 × 10−10 mbar) on clean Si(100) surfaces. For this study, ≈2.0 nm thick Au samples were grown on the substrate surface by molecular beam epitaxy. Thermal annealing was carried out inside the UHV chamber at temperature ≈500 °C and following this, nearly square shaped AuxSi1-x nano structures of average length ≈48 nm were formed. A ≈2 nm Ge film was further deposited on the above surface while the substrate was kept at a temperature of ≈500 °C. Well ordered Au-Ge nanostructures where Au and Ge residing side by side (lobe-lobe structures) were formed. In our systematic studies, we show that, gold-silicide nanoalloy formation at the substrate (Si) surface is necessary for forming phase separated Au-Ge bilobed nanostructures. These results show that the Au–Ge bonding is unstable in nature. Electron microscopy (TEM, STEM–EDS, SEM) studies were carried out to determine the structure of Au–Ge nano systems. Rutherford backscattering spectrometry measurements show gold inter-diffusion into substrate while it is absent for Ge.
Magnetic diagnostics using the third-harmonic magnetic response for a molecule-based magnet networked by a single chiral ligand
Authors: Mito M. , Iriguchi K. , Deguchi H. , Kishine J. , Yoshida Y. , Inoue K.
Published: May 2012

We investigated complex magnetic domain formation on a chiral molecule-based magnet, [Cr(CN)6][Mn(R)-pnH(H2O)](H2O) (termed as R-GN), whose two-dimensional molecular network was constructed with the help of a single-handed chiral ligand ((R)-pn). There, the first- and third-harmonic magnetic responses (M1ω and M3ω) against the ac magnetic field were observed, and magnetic hysteresis in ac field of a few Oe was discussed in terms of Rayleigh loop. The diagnostics of this magnetic hysteresis clarified the complex process of magnetic domain formation against a change in temperature. For R-GN, it was reported that a giant M3ω (termed #4 in this paper) appeared just above the so-called “magnetic ordering temperature (TC).” In the present study, three M3ω responses (#1-3) were newly observed on the lower-temperature side of #4, and the ac field dependencies for all of #1-#4 were investigated. #1 also accompanied the giant M3ω, which suggests that a significant degree of magnetic fluctuation surviving below TC. This glassy behavior below TC is an attractive new phenomenon in molecule-based magnets with a single-handed chiral ligand. #2 and #3 exhibited magnetic ordering and the formation of a small magnetic domain, respectively. The M3ω responses of #1-3 were suppressed with increasing the amplitude of ac field, and the corresponding magnetic hysteresis was a normal Rayleigh loop accompanying the out-of-phase of the M1ω response. The M3ω response of #4 without the out-of-phase of M1ω was, however, enhanced with increasing the amplitude of ac field, and #4 represented a large magnetic hysteresis in the paramagnetic region, intrinsically different from those of #1-#3.
Coexistence of ferroelectric vortex domains and charged domain walls in epitaxial BiFeO3 film on (110)O GdScO3 substrate
Authors: Qi Yajun , Chen Zuhuang , Huang Chuanwei , Wang Lihua , Han Xiaodong , Wang Junling , Yang Ping , Sritharan Thirumany , Chen Lang
Published: May 2012

The occurrence of ferroelectric charged domain walls (CDWs) which was thought to be energetically unstable is observed, together with a ferroelectric vortex structure composed of 109° and 180° domains near an epitaxial BiFeO3/GdScO3 interface. The CDW and vortex affect the domain arrangement, domain configuration, and hence tune the domain size distribution.
Structure, piezoelectric, and ferroelectric properties of BaZrO3 substituted Bi(Mg1/2Ti1/2)O3-PbTiO3 perovskite
Authors: Fan Longlong , Chen Jun , Kang Huajun , Liu Laijun , Fang Liang , Deng Jinxia , Yu Ranbo , Xing Xianran
Published: May 2012

The structure and electric properties of (0.9-x)Bi(Mg1/2Ti1/2)O3-xPbTiO3-0.1BaZrO3 (0.45 ≤ x ≤ 0.53) ceramics were investigated. The morphotropic phase boundary between tetragonal ferroelectric and pseudo-cubic relaxor phases is ascertained at x = 0.50. The BaZrO3 substitution can much reduce the coercive field of Bi(Mg1/2Ti1/2)O3-PbTiO3. The studies on temperature dependence of both ferroelectric and dielectric constant indicate a direct evidence for the antiferroelectric relaxor phase, which was ever suggested in the binary system of Bi(Mg1/2Ti1/2)O3-PbTiO3. The phase transition of ferroelectric to antiferroelectric relaxor produces the thermal depoling below the Curie temperature. The ceramic of BMT-0.47PT-0.1BZ exhibits a high strain 0.37% and a large-signal d33 (530 pm/V) in the antiferroelectric-relaxor phase. BaZrO3 substituted Bi(Mg1/2Ti1/2)O3-PbTiO3 shows an analogous phase diagram to that of lead-free (Bi, Na)TiO3-BaTiO3.
Programmable synthesis of shape-, structure-, and composition-modulated one-dimensional heterostructures by galvanic displacement reaction
Authors: Jung Hyunsung , Suh Hoyoung , Hangarter Carlos M. , Lim Jae Hong , Lee Young-In , Choa Yong-Ho , Hong Kimin , Myung Nosang V.
Published: May 2012

One-dimensional heterostructures consisting of periodically modulated bismuth telluride tube/wire were synthesized by galvanic displacement reaction of Co/Ni multi-segmented sacrificial nanowires. Utilizing the difference in redox potential and corrosion behavior of Co and Ni, segments, dimension, composition, and structure of the individual segments were also precisely engineered. The programmable ability to synthesize heterostructures with simultaneously modulation of various dimensions in ambient conditions may lead to an effective route to synthesize high performance nanodevices including nanoelectronics, optoelectronics, sensors, and thermoelectrics.
Charge-carrier mediated ferromagnetism in Mo-doped In2O3 films
Authors: Park Chang-Yup , You Chun-Yeol , Jeon Kun-Rok , Shin Sung-Chul
Published: May 2012

We investigated the correlation between the ferromagnetism and electric resistivity of Mo-doped (3–10 at. %) In2O3 films. We find that the saturation magnetization increases with the Mo concentration until it reaches its maximum at 7 at. % Mo doping (7.1 emu/cm3), after which it rapidly decreases upon higher doping concentration. Interestingly, the resistivity reveals opposite behavior with the Mo concentration, showing a minimum value at 7 at. % Mo doping. According to the temperature-dependent resistivity and the Hall effect measurements, we find that the samples with higher magnetization show metallic behavior with higher electron concentration. Notably, the samples show a linear relationship between the carrier concentration and the degree of magnetization. We believe the ferromagnetism in Mo-doped In2O3 is ascribed to the indirect exchange interaction mediated by the charge carriers.
High-spin electronic states of lanthanide-arene complexes: Nd(benzene) and Nd(naphthalene)
Authors: Lei Yuxiu , Wu Lu , Sohnlein Bradford R. , Yang Dong-Sheng
Published: May 2012

Neodymium (Nd) complexes of benzene and naphthalene were synthesized in a laser-ablation supersonic molecular beam source. High-resolution electron spectra of these complexes were obtained using pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy. Second-order Møller-Plesset perturbation calculations were employed to aid spectral and electronic-state assignments. The adiabatic ionization energies were measured to be 38 081 (5) cm−1 for Nd(benzene) and 37 815 (5) cm−1 for Nd(naphthalene). For the Nd(benzene) complex, the observed frequencies of 831 and 286 cm−1 were assigned to C–H out-of-plane bending and Nd+–C6H6 stretching modes in the 6A1 ion state and 256 cm−1 to the Nd–C6H6 stretching mode in the 7A1 neutral state. To confirm these assignments, the ZEKE spectrum of the deuterated species was recorded, and the corresponding vibrational frequencies were measured to be 710 and 277 cm−1 in the ion state and 236 cm−1 in the neutral state. For the Nd(naphthalene) complex, the observed vibrational modes were C10H8 bending (394 cm−1), Nd+–C10H8 stretching (286 and 271 cm−1), Nd+–C10H8 bending (80 cm−1), and C10H8 twisting (105 cm−1) in the 6A′ ion state and metal-ligand bending (60 cm−1) and ligand twisting (55 cm−1) in the 7A′ neutral state. The formation of the ground state of the Nd(benzene) complex requires 4f → 5d and 6s → 5d electron excitation of the Nd atom, whereas the formation of the ground state of Nd(naphthalene) involves the 6s → 5d electron promotion.
Nature of optical transitions involving cation vacancies and complexes in AlN and AlGaN
Authors: Sedhain A. , Lin J. Y. , Jiang H. X.
Published: May 2012

Photoluminescence spectroscopy was employed to probe the nature of optical transitions involving Al vacancy (VAl) and vacancy-oxygen complex (VAl-ON) in AlN. An emission line near 2 eV due to the recombination between the 2− charge state of (VAl-ON)2−/1−, and the valence band was directly observed under a below bandgap excitation scheme. This photoluminescence (PL) band was further resolved into two emission lines at 1.9 and 2.1 eV, due to the anisotropic binding energies of VAl-ON complex caused by two different bonding configurations–the substitutional ON sits along c-axis or sits on one of the three equivalent tetrahedral positions. Moreover, under an above bandgap excitation scheme, a donor-acceptor pair like transition involving shallow donors and (VAl-ON)2−/1− deep acceptors, which is the “yellow-luminescence” band counterpart in AlN, was also seen to split into two emission lines at 3.884 and 4.026 eV for the same physical reason. Together with previous results, a more complete picture for the optical transitions involving cation vacancy related deep centers in AlGaN alloy system has been constructed.
Optimal design of quarter-wave plate with wideband and wide viewing angle for three-dimensional liquid crystal display
Authors: Seok Kang Wan , Mun Byung-June , Lee Gi-Dong , Ho Lee Joun , Koo Kim Byeong , Chul Choi Hyun , Jin Lim Young , Hee Lee Seung
Published: May 2012

In this paper, we propose an optical structure for a circular polarizer-containing film patterned retarder (FPR), which has wideband and wide-view properties in a stereoscopic three-dimensional (3D) display. The FPR consists of a patterned λ/4 A-plate, a biaxial λ/2 plate, and a positive C-plate. We calculate the phase retardation of each film in the entire visible wavelength with the Stokes vector and the Muller matrix method. We demonstrate the excellent 3D characteristics of the proposed polarizer in the oblique direction by comparing the calculated light leakage of the proposed optical configuration with that of the conventional configuration. We calculate that the crosstalk of the proposed configuration is reduced to 0.39% for the left image and 0.29% for the right image in the horizontal oblique direction and to 0.37% for the left image and 0.29% for the right image in the vertical oblique direction (polar angle = 70°). These results indicate that the proposed configuration improves crosstalk by approximately 90% compared to the conventional mode.
GaAsSb bandgap, surface fermi level, and surface state density studied by photoreflectance modulation spectroscopy
Authors: Hwang J. S. , Tsai J. T. , Su I. C. , Lin H. C. , Lu Y. T. , Chiu P. C. , Chyi J. I.
Published: May 2012

The bandgap, surface Fermi level, and surface state density of a series of GaAs1−xSbx surface intrinsic-n+ structures with GaAs as substrate are determined for various Sb mole fractions x by the photoreflectance modulation spectroscopy. The dependence of the bandgap on the mole composition x is in good agreement with previous measurements as well as predictions calculated using the dielectric model of Van Vechten and Bergstresser in Phys. Rev. B 1, 3551 (1970). For a particular composition x, the surface Fermi level is always strongly pinned within the bandgap of GaAs1−xSbx and we find its variation with composition x is well described by a function EF = 0.70 − 0.192 x for 0 ≦ x ≦ 0.35, a result which is notably different from that reported by Chouaib et al. [Appl. Phys. Lett. 93, 041913 (2008)]. Our results suggest that the surface Fermi level is pinned at the midgap of GaAs and near the valence band of the GaSb.
Transport and magnetic properties of the Co2MnSi/Al/Co2MnSi trilayer
Authors: Yu H. L. , Zhang H. B. , Jiang X. F. , Zheng Y. , Yang G. W.
Published: May 2012

Using density functional theory and non-equilibrium Green’s function analysis, we studied the interface structure, interface stability, and magnetic and transport properties of the Co2MnSi/Al/Co2MnSi trilayer. It was found that only the CoCo/Al architecture is thermodynamically stable among four interfacial architectures, CoCo/Al, MnSi/Al, MnMn/Al, and SiSi/Al, and the other interface architectures are not accessible within the limits set under thermodynamic equilibrium with other phases. Calculations of the transmission spectrum, conductance, and resistance-area product showed that the Co2MnSi/Al/Co2MnSi trilayer is a promising candidate for the next-generation of recording sensors in ultrahigh-density hard disks.
Carbon inputs by wheat and vetch roots to an irrigated Vertosol
Authors: Hulugalle N. R. , Weaver T. B. , Finlay L. A.
Published: May 2012

Research on the amounts of carbon that can be added to Vertosols of New South Wales and Queensland by crop roots in irrigated cotton farming systems is sparse. The objective of this study was to determine the amounts of carbon added to soil by roots of wheat (Triticum aestivum L.) and purple vetch (Vicia benghalensis L.) sown in rotation with irrigated cotton (Gossypium hirsutum L.). Measurements were made from 2008 to 2010 in an ongoing experiment near Narrabri, northern NSW, using a combination of soil cores and minirhizotron observations. The experimental treatments were: cotton monoculture; cotton–vetch (CV); cotton–wheat, in which wheat stubble was incorporated into the beds with a disc-hiller (CW); and cotton–wheat–vetch, in which wheat stubble was retained as in-situ mulch (CWV). Vetch was killed by a combination of mowing and contact herbicides, and the residues were retained as in situ mulch. Root length per unit area of vetch in CWV and wheat in both CW and CWV was comparable, although wheat had a higher concentration of roots in surface 0.10 m. Root growth of the CV treatment was sparse. Root carbon available for addition to soil was greater with vetch than with wheat and was in the order: vetch in CWV (5.1 t C/ha.year) > vetch in CV (1.9 t C/ha.year) > wheat in CW (1.6 t C/ha.year) = wheat in CWV (1.7 t C/ha.year). Intra-seasonal root mortality accounted for 12% of total root carbon in vetch and 36% in wheat. The remaining fraction consisted of carbon in the root mass at the end of the growing season. Carbon sequestered by root inputs of the rotation crops was estimated to be ~0.34 t C/ha.year for the vetch and wheat crops in the CWV rotation, 0.10 t C/ha.year for vetch in CV, and 0.08 t C/ha.year for wheat in CW. Rotation CWV was, therefore, the most effective in sequestering carbon from roots.
Enrichment, inter-relationship, and fractionation of heavy metals in road-deposited sediments of Sydney, Australia
Authors: Mohammed Thamer , Loganathan Paripurnanda , Kinsela Andrew , Vigneswaran Saravanamuthu , Kandasamy Jayakumar
Published: May 2012

Urban road-deposited sediments (RDS) are potential sources of heavy metal pollution of both terrestrial and aquatic environments. We determined the heavy metals enrichments, their possible sources, and potential bioavailability and mobility in RDS from nine sites along major motorways of Sydney, the largest city with highest road traffic density in Australia. Mean total concentrations of metals in the RDS decreased in the order: Fe > Mn > Zn > Cu > Cr > Pb > Ni > Cd. The corresponding order in the background soils (minimally contaminated from roads) was: Fe > Mn > Zn ~ Ni > Cu ~ Pb > Cr > Cd. Both the pollution index (PI) and metal enrichment factor (EF), which are comparative measures between contaminated and uncontaminated sites, were highest for Cu and Zn. Inputs of Cu and Zn to RDS were likely to be mainly the result of brake and tyre wear, respectively. Cluster and correlation analyses showed that while the concentrations of these two metals were related in the soil, they were not correlated in RDS. Low PI and EF values as well as the close inter-relationships of Fe, Mn, Cr, and Ni in both RDS and soils suggest that these metals were derived mainly from natural sources. Metal fractionation data showed 50–95% of Cr and Fe in RDS to be present in the immobile and bio-unavailable residual fraction, whereas 15–65% of Zn was contained in the exchangeable fraction, which is considered to be mobile and bioavailable.
Evaluation of humic and fulvic acid extracts of compost, oilcake, and soils on complex formation with arsenic
Authors: Ghosh K. , Das I. , Das D. K. , Sanyal S. K.
Published: May 2012

Fulvic acid (FA) and humic acid (HA) were extracted from compost, oilcake, and surface soils collected from arsenic-contaminated and uncontaminated sites of West Bengal. These HA/FA samples were characterised by pH–potentiometric titrations, viscometric measurements, visible spectrophotometry, and surface tension determinations. The results were correlated with coiling–decoiling behaviour, as well as aliphatic/aromatic balance of HA/FAs. The stability constant (logK) of the complexes formed by the natural HA/FA fractions of the given soils were quite stable, and the HA/FA fractions of the organic manures with arsenate in aqueous phases suggested the dependence of such complexation on the nature and properties of the humic polymers, which, in turn, would affect the retention/release of arsenate in soil.
The release potential of arsenic from the arsenate–HA/FA complexes by soluble sulfate and nitrate salts was also examined in terms of the appropriate exchange isotherms. In general, sulfate demonstrated a moderately greater degree of exchangeability with arsenate than did nitrate, at higher concentrations.
Fluvial landscapes of the Harappan civilization
Authors: Giosan Liviu , Clift Peter D. , Macklin Mark G. , Fuller Dorian Q. , Constantinescu Stefan , Durcan Julie A. , Stevens Thomas , Duller Geoff A. T. , Tabrez Ali R. , Gangal Kavita , Adhikari Ronojoy , Alizai Anwar , Filip Florin , VanLaningham Sam , Syvitski James P. M.
Published: May 2012

The collapse of the Bronze Age Harappan, one of the earliest urban civilizations, remains an enigma. Urbanism flourished in the western region of the Indo-Gangetic Plain for approximately 600 y, but since approximately 3,900 y ago, the total settled area and settlement sizes declined, many sites were abandoned, and a significant shift in site numbers and density towards the east is recorded. We report morphologic and chronologic evidence indicating that fluvial landscapes in Harappan territory became remarkably stable during the late Holocene as aridification intensified in the region after approximately 5,000 BP. Upstream on the alluvial plain, the large Himalayan rivers in Punjab stopped incising, while downstream, sedimentation slowed on the distinctive mega-fluvial ridge, which the Indus built in Sindh. This fluvial quiescence suggests a gradual decrease in flood intensity that probably stimulated intensive agriculture initially and encouraged urbanization around 4,500 BP. However, further decline in monsoon precipitation led to conditions adverse to both inundation- and rain-based farming. Contrary to earlier assumptions that a large glacier-fed Himalayan river, identified by some with the mythical Sarasvati, watered the Harappan heartland on the interfluve between the Indus and Ganges basins, we show that only monsoonal-fed rivers were active there during the Holocene. As the monsoon weakened, monsoonal rivers gradually dried or became seasonal, affecting habitability along their courses. Hydroclimatic stress increased the vulnerability of agricultural production supporting Harappan urbanism, leading to settlement downsizing, diversification of crops, and a drastic increase in settlements in the moister monsoon regions of the upper Punjab, Haryana, and Uttar Pradesh.
Community differentiation and kinship among Europe’s first farmers
Authors: Bentley R. Alexander , Bickle Penny , Fibiger Linda , Nowell Geoff M. , Dale Christopher W. , Hedges Robert E. M. , Hamilton Julie , Wahl Joachim , Francken Michael , Grupe Gisela , Lenneis Eva , Teschler-Nicola Maria , Arbogast Rose-Marie , Hofmann Daniela , Whittle Alasdair
Published: May 2012

Community differentiation is a fundamental topic of the social sciences, and its prehistoric origins in Europe are typically assumed to lie among the complex, densely populated societies that developed millennia after their Neolithic predecessors. Here we present the earliest, statistically significant evidence for such differentiation among the first farmers of Neolithic Europe. By using strontium isotopic data from more than 300 early Neolithic human skeletons, we find significantly less variance in geographic signatures among males than we find among females, and less variance among burials with ground stone adzes than burials without such adzes. From this, in context with other available evidence, we infer differential land use in early Neolithic central Europe within a patrilocal kinship system.
Flexibility of the metal-binding region in apo-cupredoxins
Authors: Zaballa María-Eugenia , Abriata Luciano A. , Donaire Antonio , Vila Alejandro J.
Published: May 2012

Protein-mediated electron transfer is an essential event in many biochemical processes. Efficient electron transfer requires the reorganization energy of the redox event to be minimized, which is ensured by the presence of rigid donor and acceptor sites. Electron transfer copper sites are present in the ubiquitous cupredoxin fold, able to bind one or two copper ions. The low reorganization energy in these metal centers has been accounted for by assuming that the protein scaffold creates an entatic/rack-induced state, which gives rise to a rigid environment by means of a preformed metal chelating site. However, this notion is incompatible with the need for an exposed metal-binding site and protein–protein interactions enabling metallochaperone-mediated assembly of the copper site. Here we report an NMR study that reveals a high degree of structural heterogeneity in the metal-binding region of the nonmetallated CuA-binding cupredoxin domain, arising from microsecond to second dynamics that are quenched upon metal binding. We also report similar dynamic features in apo-azurin, a paradigmatic blue copper protein, suggesting a general behavior. These findings reveal that the entatic/rack-induced state, governing the features of the metal center in the copper-loaded protein, does not require a preformed metal-binding site. Instead, metal binding is a major contributor to the rigidity of electron transfer copper centers. These results reconcile the seemingly contradictory requirements of a rigid, occluded center for electron transfer, and an accessible, dynamic site required for in vivo copper uptake.
Structure of the receptor-binding carboxy-terminal domain of bacteriophage T7 tail fibers
Authors: Garcia-Doval Carmela , van Raaij Mark J.
Published: May 2012

The six bacteriophage T7 tail fibers, homo-trimers of gene product 17, are thought to be responsible for the first specific, albeit reversible, attachment to
Escherichia coli
lipopolysaccharide. The protein trimer forms kinked fibers comprised of an amino-terminal tail-attachment domain, a slender shaft, and a carboxyl-terminal domain composed of several nodules. Previously, we expressed, purified, and crystallized a carboxyl-terminal fragment comprising residues 371–553. Here, we report the structure of this protein trimer, solved using anomalous diffraction and refined at 2 Å resolution. Amino acids 371–447 form a tapered pyramid with a triangular cross-section composed of interlocked β-sheets from each of the three chains. The triangular pyramid domain has three α-helices at its narrow end, which are connected to a carboxyl-terminal three-blade β-propeller tip domain by flexible loops. The monomers of this tip domain each contain an eight-stranded β-sandwich. The exact topology of the β-sandwich fold is novel, but similar to that of knob domains of other viral fibers and the phage Sf6 needle. Several host-range change mutants have been mapped to loops located on the top of this tip domain, suggesting that this surface of the tip domain interacts with receptors on the cell surface.
Sex-lethal
enables germline stem cell differentiation by down-regulating Nanos protein levels during
Drosophila
oogenesis
Authors: Chau Johnnie , Kulnane Laura Shapiro , Salz Helen K.
Published: May 2012

Drosophila
ovarian germ cells require
Sex-lethal (Sxl)
to exit from the stem cell state and to enter the differentiation pathway.
Sxl
encodes a female-specific RNA binding protein and in somatic cells serves as the developmental switch gene for somatic sex determination and X-chromosome dosage compensation. None of the known
Sxl
target genes are required for germline differentiation, leaving open the question of how
Sxl
promotes the transition from stem cell to committed daughter cell. We address the mechanism by which
Sxl
regulates this transition through the identification of
nanos
as one of its target genes. Previous studies have shown that Nanos protein is necessary for GSC self-renewal and is rapidly down-regulated in the daughter cells fated to differentiate in the adult ovary. We find that this dynamic expression pattern is limited to female germ cells and is under
Sxl
control. In the absence of
Sxl,
or in male germ cells, Nanos protein is continuously expressed. Furthermore, this female-specific expression pattern is dependent on the presence of canonical Sxl binding sites located in the
nanos
3′ untranslated region. These results, combined with the observation that
nanos
RNA associates with the Sxl protein in ovarian extracts and loss and gain of function studies, suggest that
Sxl
enables the switch from germline stem cell to committed daughter cell by posttranscriptional down-regulation of
nanos
expression. These findings connect sexual identity to the stem cell self-renewal/differentiation decision and highlight the importance of posttranscriptional gene regulatory networks in controlling stem cell behavior.
Ice-binding site of snow mold fungus antifreeze protein deviates from structural regularity and high conservation
Authors: Kondo Hidemasa , Hanada Yuichi , Sugimoto Hiroshi , Hoshino Tamotsu , Garnham Christopher P. , Davies Peter L. , Tsuda Sakae
Published: May 2012

Antifreeze proteins (AFPs) are found in organisms ranging from fish to bacteria, where they serve different functions to facilitate survival of their host. AFPs that protect freeze-intolerant fish and insects from internal ice growth bind to ice using a regular array of well-conserved residues/motifs. Less is known about the role of AFPs in freeze-tolerant species, which might be to beneficially alter the structure of ice in or around the host. Here we report the 0.95-Å high-resolution crystal structure of a 223-residue secreted AFP from the snow mold fungus
Typhula ishikariensis
. Its main structural element is an irregular β-helix with six loops of 18 or more residues that lies alongside an α-helix. β-Helices have independently evolved as AFPs on several occasions and seem ideally structured to bind to several planes of ice, including the basal plane. A novelty of the β-helical fold is the nonsequential arrangement of loops that places the N- and C termini inside the solenoid of β-helical coils. The ice-binding site (IBS), which could not be predicted from sequence or structure, was located by site-directed mutagenesis to the flattest surface of the protein. It is remarkable for its lack of regularity and its poor conservation in homologs from psychrophilic diatoms and bacteria and other fungi.
Floral humidity as a reliable sensory cue for profitability assessment by nectar-foraging hawkmoths
Authors: von Arx Martin , Goyret Joaquín , Davidowitz Goggy , Raguso Robert A.
Published: May 2012

Most research on plant–pollinator communication has focused on sensory and behavioral responses to relatively static cues. Floral rewards such as nectar, however, are dynamic, and foraging animals will increase their energetic profit if they can make use of floral cues that more accurately indicate nectar availability. Here we document such a cue—transient humidity gradients—using the night blooming flowers of
Oenothera cespitosa
(Onagraceae). The headspace of newly opened flowers reaches levels of about 4% above ambient relative humidity due to additive evapotranspirational water loss through petals and water-saturated air from the nectar tube. Floral humidity plumes differ from ambient levels only during the first 30 min after anthesis (before nectar is depleted in wild populations), whereas other floral traits (scent, shape, and color) persist for 12–24 h. Manipulative experiments indicated that floral humidity gradients are mechanistically linked to nectar volume and therefore contain information about energy rewards to floral visitors. Behavioral assays with
Hyles lineata
(Sphingidae) and artificial flowers with appropriate humidity gradients suggest that these hawkmoth pollinators distinguish between subtle differences in relative humidity when other floral cues are held constant. Moths consistently approached and probed flowers with elevated humidity over those with ambient humidity levels. Because floral humidity gradients are largely produced by the evaporation of nectar itself, they represent condition-informative cues that facilitate remote sensing of floral profitability by discriminating foragers. In a xeric environment, this level of honest communication should be adaptive when plant reproductive success is pollinator limited, due to intense competition for the attention of a specialized pollinator.
Erythropoietin-induced changes in brain gene expression reveal induction of synaptic plasticity genes in experimental stroke
Authors: Mengozzi Manuela , Cervellini Ilaria , Villa Pia , Erbayraktar Zübeyde , Gökmen Necati , Yilmaz Osman , Erbayraktar Serhat , Manohasandra Mathini , Van Hummelen Paul , Vandenabeele Peter , Chernajovsky Yuti , Annenkov Alexander , Ghezzi Pietro
Published: May 2012

Erythropoietin (EPO) is a neuroprotective cytokine in models of ischemic and nervous system injury, where it reduces neuronal apoptosis and inflammatory cytokines and increases neurogenesis and angiogenesis. EPO also improves cognition in healthy volunteers and schizophrenic patients. We studied the effect of EPO administration on the gene-expression profile in the ischemic cortex of rats after cerebral ischemia at early time points (2 and 6 h). EPO treatment up-regulated genes already increased by ischemia. Hierarchical clustering and analysis of overrepresented functional categories identified genes implicated in synaptic plasticity—
Arc
, BDNF
,
Egr1
, and
Egr2
, of which
Egr2
was the most significantly regulated. Up-regulation of
Arc
,
BDNF
,
Dusp5
,
Egr1
,
Egr2
,
Egr4
, and
Nr4a3
was confirmed by quantitative PCR. We investigated the up-regulation of
Egr2
/
Krox20
further because of its role in neuronal plasticity. Its elevation by EPO was confirmed in an independent in vivo experiment of cerebral ischemia in rats. Using the rat neuroblastoma B104, we found that wild-type cells that do not express EPO receptor (EPOR) do not respond to EPO by inducing
Egr2
. However, EPOR-expressing B104 cells induce
Egr2
early upon incubation with EPO, indicating that
Egr2
induction is a direct effect of EPO and that EPOR mediates this effect. Because these changes occur in vivo before decreased inflammatory cytokines or neuronal apoptosis is evident, these findings provide a molecular mechanism for the neuroreparative effects of cytokines and suggest a mechanism of neuroprotection by which promotion of a plastic phenotype results in decreased inflammation and neuronal death.
Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity
Authors: Pan Lijia , Yu Guihua , Zhai Dongyuan , Lee Hye Ryoung , Zhao Wenting , Liu Nian , Wang Huiliang , Tee Benjamin C.-K. , Shi Yi , Cui Yi , Bao Zhenan
Published: May 2012

Conducting polymer hydrogels represent a unique class of materials that synergizes the advantageous features of hydrogels and organic conductors and have been used in many applications such as bioelectronics and energy storage devices. They are often synthesized by polymerizing conductive polymer monomer within a nonconducting hydrogel matrix, resulting in deterioration of their electrical properties. Here, we report a scalable and versatile synthesis of multifunctional polyaniline (PAni) hydrogel with excellent electronic conductivity and electrochemical properties. With high surface area and three-dimensional porous nanostructures, the PAni hydrogels demonstrated potential as high-performance supercapacitor electrodes with high specific capacitance (∼480 F·g
-1
), unprecedented rate capability, and cycling stability (∼83% capacitance retention after 10,000 cycles). The PAni hydrogels can also function as the active component of glucose oxidase sensors with fast response time (∼0.3 s) and superior sensitivity (∼16.7 μA·mM
-1
). The scalable synthesis and excellent electrode performance of the PAni hydrogel make it an attractive candidate for bioelectronics and future-generation energy storage electrodes.