bluuebunny/crossref_metadata_2025 huggingface dataset:
Some solutions to the space fractional Schrödinger equation using momentum representation method
Authors: Dong Jianping , Xu Mingyu
Published: July 2007

The space fractional Schrödinger equation with linear potential, delta-function potential, and Coulomb potential is studied under momentum representation using Fourier transformation. By use of Mellin transform and its inverse transform, we obtain the energy levels and wave functions expressed in H function for a particle in linear potential field. The wave function expressed also by the H function and the unique energy level of the bound state for the particle of even parity state in delta-function potential well, which is proved to have no action on the particle of odd parity state, is also obtained. The integral form of the wave functions for a particle in Coulomb potential field is shown and the corresponding energy levels which have been discussed in Laskin’s paper [Phys. Rev. E 66, 056108 (2002)] are proved to satisfy an equality of infinite limit of the H function. All of these results contain the ones of the standard quantum mechanics as their special cases.
Structure of Langmuir and electromagnetic collapsing wave packets in two-dimensional strong plasma turbulence
Authors: Alinejad H. , Robinson P. A. , Cairns I. H. , Skjaeraasen O. , Sobhanian S.
Published: July 2007

Nucleating and collapsing wave packets relevant to electromagnetic strong plasma turbulence are studied theoretically in two dimensions. Model collapsing Langmuir and transverse potentials are constructed as superpositions of approximate eigenstates of a spherically symmetric density well. Electrostatic and electromagnetic potentials containing only components with azimuthal quantum numbers m=0, 1, 2 are found to give a good representation of the electric fields of nucleating collapsing wave packets in turbulence simulations. The length scales of these trapped states are related to the electron thermal speed ve and the length scale of the density well. It is shown analytically that the electromagnetic trapped states change with ve and that for ve≲0.17c they are delocalized, in accord with recent simulations. In this case, the Langmuir mode collapses independently, as in electrostatic plasma turbulence. For ve≳0.17c, the Langmuir and transverse modes remain coupled during collapse, with autocorrelation lengths in a constant ratio. An investigation of energy transfer to packets localized in density wells shows that the strongest power transfer to the nucleating state occurs for Langmuir waves. Energy transitions between different trapped and free states for collapsing wave packets are studied, and the transition rate from trapped Langmuir to free plane electromagnetic waves is calculated and related to the emission of electromagnetic waves at the plasma frequency.
Target ionization by a high current relativistic monoenergetic electron beam
Authors: Debayle A. , Tikhonchuk V. T.
Published: July 2007

The propagation through an insulator of a high-current monoenergetic fast electron beam is investigated in a one-dimensional model. The target ionization provides the charge and current neutralization and enables the beam propagation. The ionization process consists of two stages: (i) the self-consistent electric field ionization of atoms in the beam front and (ii) the collisional ionization of atoms by the return current in the beam body. The ionization in the beam front defines the propagation velocity. The charge neutralization quickly suppresses the electric field behind the beam front and the plasma heating by the return current supports the collisional ionization in the beam body. This constitutes the main mechanism of the energy loss for high beam densities.
Molecular response properties from explicitly time-dependent configuration interaction methods
Authors: Krause Pascal , Klamroth Tillmann , Saalfrank Peter
Published: July 2007

In this paper we report the calculation of molecular electric response properties with the help of explicitly time-dependent configuration interaction (TD-CI) methods. These methods have the advantage of being applicable (within the limitations of the time-dependent Schrödinger equation) to time-dependent perturbations of arbitrary shape and strength. Three variants are used to solve the time-dependent electronic Schrödinger equation, namely, the TD-CIS (inclusion of single excitations only), TD-CISD (inclusion of single and double excitations), and TD-CIS(D) (single excitations and perturbative treatment of double excitations) methods and applied for illustration to small molecules, H2 and H2O. In the calculation, slowly varying off-resonant electric fields are applied to the molecules and linear (polarizabilities) and nonlinear (hyperpolarizabilities, harmonic generation) response properties are determined from the time-dependent dipole moments.
Assessment and formal properties of exchange-correlation functionals constructed from the adiabatic connection
Authors: Cohen Aron J. , Mori-Sánchez Paula , Yang Weitao
Published: July 2007

We examine the development and investigate the performance of exchange-correlation functionals constructed from the adiabatic connection. Our method is based on a direct modeling of the adiabatic connection curve in the coupling-constant space and is very flexible in the models. Several different models are investigated in the construction of new families of exchange-correlation functionals. Also the performance of two of these models (MCY1 and MCY2) is investigated over a wider range of systems and properties, with comparison made to the performance of established functionals. Overall, the adiabatic functionals improve upon widely used hybrid and generalized gradient approximation functionals, particularly in correctly describing one-electron systems and reaction energy barriers.
Response to “Comment on ‘The swimming of animalcules'” [Phys. Fluids 19, 079101 (2007)]
Authors: Felderhof B. U.
Published: July 2007

The proof of the statement that a two-bead structure with constant mobilities cannot swim is incorrect. A general expression for the swimming velocity of a two-bead structure with given periodic relative motion is derived in the form of a line integral. The net torque exerted on the fluid is also expressed as a line integral. It is shown that in the example given by Friedman a net torque is exerted on the fluid. Therefore it is not acceptable as a swimming motion. A more complicated periodic relative motion is constructed for which the net torque vanishes, but which leads to a nonvanishing swimming velocity. A dynamical formulation appears to restrict the possibility of swimming.
Second order explicitly correlated R12 theory revisited: A second quantization framework for treatment of the operators’ partitionings
Authors: Noga Jozef , Kedžuch Stanislav , Šimunek Ján
Published: July 2007

Second order R12 theory is presented and derived alternatively using the second quantized hole-particle formalism. We have shown that in order to ensure the strong orthogonality between the R12 and the conventional part of the wave function, the explicit use of projection operators can be easily avoided by an appropriate partitioning of the involved operators to parts which are fully describable within the computational orbital basis and complementary parts that involve imaginary orbitals from the complete orbital basis. Various Hamiltonian splittings are discussed and computationally investigated for a set of nine molecules and their atomization energies. If no generalized Brillouin condition is assumed, with all relevant partitionings the one-particle contribution arising in the explicitly correlated part of the first order wave function has to be considered and has a significant role when smaller atomic orbital basis sets are used. The most appropriate Hamiltonian splitting results if one follows the conventional perturbation theory for a general non-Hartree-Fock reference. Then, no couplings between the R12 part and the conventional part arise within the first order wave function. The computationally most favorable splitting when the whole complementary part of the Hamiltonian is treated as a perturbation fails badly. These conclusions also apply to MP2-F12 approaches with different correlation factors.
Isotropic-nematic phase transition in athermal solutions of rod-coil diblock copolymers
Authors: Jiang Tao , Wu Jianzhong
Published: July 2007

We present a hybrid method to investigate the isotropic-nematic (I-N) transition in athermal solutions of rod-coil copolymers. This method incorporates the scaled-particle theory for semiflexible chains with two-chain Monte Carlo simulation for the osmotic second virial coefficient and for the angle-dependent excluded volume. We compare the theoretical prediction with Monte Carlo simulations for fused rod-coil copolymers and find good agreement for both the equation of state and the orientational order parameter. The theory is also used to examine the effects of the bond length, the chain length, and the chain composition on orientational ordering in athermal solutions of rod-coil block copolymers. It predicts I-N transition in rod-coil copolymers with fixed rod length but a variable flexible tail in good agreement with experiments.
Surface-depletion controlled gas sensing of ZnO nanorods grown at room temperature
Authors: Li C. C. , Du Z. F. , Li L. M. , Yu H. C. , Wan Q. , Wang T. H.
Published: July 2007

The authors report on surface-depletion controlled gas sensing ZnO nanorods. These nanorods were synthesized through a simple wet chemical route at room temperature. The diameter of nanorods is about 15nm, which is close to two times of the Debye length of ZnO. In contrast to the previous report, the sensing is surface-depletion controlled rather than contact controlled and the sensitivity is up to 29.7 against 100ppm ethanol. Such high sensitivity is due to an almost complete depletion of the rods in air, which is confirmed from photoluminescence spectrum and x-ray photoelectron spectroscopy. The gas sensing mechanism controlled by surface depletion provides another approach to realize high-performance gas sensors.
Fine structure and chemical shifts in nonresonant inelastic x-ray scattering from Li-intercalated graphite
Authors: Balasubramanian M. , Johnson C. S. , Cross J. O. , Seidler G. T. , Fister T. T. , Stern E. A. , Hamner C. , Mariager S. O.
Published: July 2007

The authors report measurements of hard x-ray nonresonant inelastic x-ray scattering (IXS) from the Li and C 1s electrons of fully staged LiC6 Li-intercalated graphite prepared by both chemical and electrochemical methods. They find that the Li 1s orbital shifts to higher energies relative to Li metal. Relative to graphite, the C 1s IXS for LiC6 shows a shift for the σ-orbital threshold to lower energies, but no shift for the π* resonance. The findings provide bulk-sensitive evidence for substantial charge transfer from the Li intercalant to the carbon host and establish important groundwork for future in situ electrochemical studies.
Frequency-dependent refractive index of one-dimensionally structured thick metal film
Authors: Shin Young-Min , So Jin-Kyu , Won Jong-Hyo , Park Gun-Sik
Published: July 2007

The authors have studied the frequency-dependent dielectric response of thick metal film one-dimensionally perforated by a subwavelength slit waveguide array. Our theoretical approach based on a three-dimensional homogenization of the periodic metallic structure shows that an effective refractive index chromatically varying due to TE waveguide mode formation gives rise to dense Fabry-Pérot resonance population near the cutoff, which leads to an energy level continuum in the transmission spectrum. Finite difference time domain simulation numerically demonstrates the transmission spectrum and spatial field distributions of even and odd resonance modes.
Three-dimensional Monte Carlo simulations of intracellular diffusion and reaction of signaling proteins
Authors: Zhdanov Vladimir P.
Published: July 2007

We show that the Monte Carlo technique makes it possible to perform three-dimensional simulations of intracellular protein-mediated signal transduction with realistic ratio of the rates of protein diffusion and association with genes. Specifically, we illustrate that in the simplest case when the protein degradation and phosphorylation/dephosphorylationthe are negligible the distribution of the first passage time for this process is close to exponential provided that the number of target genes is between 1 and 100.
Reflection-free complex absorbing potential for electronic structure calculations: Feshbach-type autoionization resonances of molecules
Authors: Sajeev Y. , Moiseyev Nimrod
Published: July 2007

The reflection-free complex absorbing potential (RF-CAP) method has been already applied to the study of the autoionization resonance of helium [Sajeev et al., Chem. Phys. 329, 307 (2006)]. The present work introduces a systematic way for implementing RF-CAP for the electronic structure calculations using Gaussian basis sets for molecules. As a test case study we applied the RF-CAP method to the lowest Σg+1 and Σu+1 Feshbach-type autoionization resonances of hydrogen molecule. Since thin RF-CAP absorbs fast electrons much better than the slow ones, a weak dc field has been added to the RF-CAP in the peripheral region of the molecule.
Development of solitons in composite right- and left-handed transmission lines periodically loaded with Schottky varactors
Authors: Narahara Koichi , Nakamichi Toru , Suemitsu Tetsuya , Otsuji Taiichi , Sano Eiichi
Published: July 2007

The characteristics of composite right- and left-handed (CRLH) transmission lines periodically loaded with Schottky varactors are discussed in relation to the development of solitons. CRLH lines are highly dispersive and thus, when appropriately designed, compensate the effect of nonlinearity introduced by the Schottky varactors to support solitons. The reductive perturbation method applied to the transmission equation of nonlinear CRLH lines leads to the observation that the nonlinear Schrödinger equation governs the wave property at long wavelengths. The condition of the Schottky CRLH lines for the development of solitons, together with several results of the numerical finite-difference time-domain calculations, is discussed.
Phase transitions and corresponding magnetic entropy changes in Ni2Mn0.75Cu0.25−xCoxGa Heusler alloys
Authors: Khan Mahmud , Dubenko Igor , Stadler Shane , Ali Naushad
Published: July 2007

Detailed studies of room temperature crystal structures, phase transitions, and related magnetic entropy changes (ΔSm) in shape memory alloys Ni2Mn0.75Cu0.25−xCoxGa (x=0.0, 0.01, 0.02,0.025 0.03, 0.05) have been carried out by x-ray diffraction, magnetization, and thermal expansion measurements in magnetic fields of up to 5 T and in a temperature interval of 5–400 K. The high temperature austenitic cubic phase passes through a magnetic transition to ferromagnetic state and a structural transition to martensitic phase at the same temperature for all samples of the Ni2Mn0.75Cu0.25−xCoxGa system. The first order magnetostructural transition temperature increases from 308 to 345 K with increasing Co concentration. All of the alloys in the Ni2Mn0.75Cu0.25−xCoxGa system were found to possess large magnetic entropy changes. The maxima in the magnetic entropy changes ranged from ΔSmmax=−48 J/kg K to −64 J/kg K in a temperature range of 308–345 K.
Determination of complex transmissivity using x-ray in-line holography and two-beam interferometry
Authors: Kohmura Yoshiki , Sakurai Tatsuyuki , Ishikawa Tetsuya , Takeuchi Akihisa , Suzuki Yoshio , Goto Shunji
Published: July 2007

A method for quantitative measurement of the complex transmissivity of samples is presented where in-line holography and additional shearing interferograms, at a fixed sample-detector distance, are used. The wave field at the detector plane is completely determined and the exit-face wave field of the sample is reconstructed by deconvolution. The principle of experiment and the results of imaging of various samples are described.
Charge-order breaking and ferromagnetism in La0.4Ca0.6MnO3 nanoparticles
Authors: Lu C. L. , Dong S. , Wang K. F. , Gao F. , Li P. L. , Lv L. Y. , Liu J.-M.
Published: July 2007

La 0.4 Ca 0.6 Mn O 3 nanoparticles of grain size as small as ∼20nm are prepared and their magnetic behaviors are investigated in order to understand the size effect of the charge ordering in manganites. The highly stable charge-ordered state can be significantly suppressed upon reduction of the grain size down to nanometer scale, while the ferromagnetism is enhanced. The magnetic phase separation due to the competition between ferromagnetic state and charge-ordered state as well as the surface spin disordering is responsible for the spin-glass-like state at low temperature.
High strength ultrafine/nanostructured aluminum produced by back pressure equal channel angular processing
Authors: Xu W. , Honma T. , Wu X. , Ringer S. P. , Xia K.
Published: July 2007

High strength ultrafine/nanograined aluminum materials with ultimate strength up to 740MPa and Vickers microhardness up to 2285MPa were produced using back pressure equal channel angular processing of ultrafine-sized aluminum powder at 400°C. Microstructure analyses revealed that the attained high strength and microhardness were derived from the presence of nanosized aluminum and γ-alumina grains (5–10nm) as well as residual amorphous alumina. The interaction between the severe shear deformation and the preexisting amorphous alumina, concurrent oxidation, and amorphous to γ-alumina transition was considered to be responsible for the formation of such a refined and complex nanostructure.
Rotating sample holder at low temperature
Authors: Pasternak Sebastien , Perrin Florian , Ciatto Gianluca , Palancher Hervé , Steinmann Ricardo
Published: July 2007

A low temperature rotary device (cryoturbine) for use in extended x-ray-absorption fine structure measurements in fluorescence mode has been designed and manufactured. The instrument works at a temperature close to liquid Nitrogen and can reach frequencies up to 100Hz with good stability. The rotation speed is measured with a light-emitting diode driven in stroboscopic mode by a simple electronic circuit.
Enhancement of thermoelectric figure of merit of AgTlTe by tuning the carrier concentration
Authors: Kurosaki Ken , Goto Keita , Muta Hiroaki , Yamanaka Shinsuke
Published: July 2007

The authors tried to enhance the thermoelectric figure of merit of AgTlTe with extremely low thermal conductivity by controlling the carrier concentration. Pd- or Cu-doped AgTlTe was prepared and characterized. Pd did not dissolve in AgTlTe, whereas Cu fully dissolved up to x=0.4 in Ag1−xCuxTlTe. The effect of Cu doping was investigated by measuring the thermoelectric properties of polycrystalline Ag1−xCuxTlTe (x=0−0.4) from room temperature to slightly below the melting temperature. Cu doping resulted in a net increase in the hole concentration of AgTlTe. Cu doping improved the power factor of AgTlTe while keeping the thermal conductivity extremely low, leading to an enhancement of the thermoelectric figure of merit.
High-temperature Hall measurements of lanthanide based ternary intermetallics
Authors: Sekimoto Takeyuki , Kurosaki Ken , Muta Hiroaki , Yamanaka Shinsuke
Published: July 2007

The authors performed high-temperature Hall measurements on hexagonal LaPdSb and GdPdSb and cubic ErPdSb, GdPdBi, and ErPdBi to investigate the difference among the thermoelectric properties. The thermal excitation of carriers and T−3∕2 dependence of carrier mobility due to acoustic phonon scattering were observed. For the cubic compounds, the carrier concentration rather than the effective mass affects the magnitude of the thermoelectric power. High carrier mobility due to the long carrier relaxation time in spite of the large effective mass is realized in hexagonal LaPdSb, leading to the quite high power factor (=S2∕ρ; S: thermoelectric power, ρ: electrical resistivity).
Secondary magnetic phases in (Ga,Mn)As determined by x-ray magnetic circular dichroism
Authors: Edmonds K. W. , Freeman A. A. , Farley N. R. S. , Wang K. Y. , Campion R. P. , Gallagher B. L. , Foxon C. T. , van der Laan G. , Arenholz E.
Published: July 2007

We have studied the magnetic and electronic properties of (Ga,Mn)As ferromagnetic semiconductor layers containing low concentrations of room temperature magnetic MnAs precipitates, using x-ray magnetic circular dichroism in x-ray absorption spectroscopy. Measurements below and above the Curie temperature of the (Ga,Mn)As show localized multiplet structures and broad metallic-like line shapes, respectively. By applying magnetic fields below the coercivity of the (Ga,Mn)As layer, the magnetization reversal behavior of the ferromagnetic semiconductor and the MnAs precipitates can be resolved and are found to be independent of each other.
Laser-induced exfoliation of amorphous carbon layer on an individual multiwall carbon nanotube
Authors: Singh G. , Rice P. , Hurst K. E. , Lehman J. H. , Mahajan R. L.
Published: July 2007

Pulsed laser treatment of an individual multiwall carbon nanotube induced selective exfoliation of the amorphous carbon contamination layer. The multiwall carbon nanotube (MWCNT) was exposed to a 248nm excimer laser. After the treatment, transmission electron microscopy images show that the amorphous layer has expanded and separated from the crystalline MWCNT walls. This interesting observation has implications for laser cleaning and possible thinning of MWCNTs to reduce the radial dimensions.
Modified Eshelby tensor modeling for elastic property prediction of carbon nanotube reinforced ceramic nanocomposites
Authors: Chen Yao , Balani Kantesh , Agarwal Arvind
Published: July 2007

A modified model using the Eshelby equivalent tensor is developed to evaluate overall elastic properties of carbon nanotube (CNT) reinforced aluminum oxide nanocomposites. This model accounts for the effect of carbon nanotube geometry and porosity on the effective elastic modulus. Experimental results are compared with the computed predictions. Computed results show higher elastic modulus values, which are attributed to the perfect bonding between the reinforcement and the matrix. It is concluded that the modified Eshelby model can predict the elastic property of CNT reinforced ceramic nanocomposites.
Thermal emittance measurements for electron beams produced from bulk and superlattice negative electron affinity photocathodes
Authors: Yamamoto Naoto , Yamamoto Masahiro , Kuwahara Makoto , Sakai Ryosuke , Morino Takanori , Tamagaki Kuniaki , Mano Atsushi , Utsu Akira , Okumi Shouji , Nakanishi Tsutomu , Kuriki Masao , Bo Chen , Ujihara Toru , Takeda Yoshikazu
Published: July 2007

Extremely low emittance electron beams are required for next generation accelerators. GaAs semiconductor photocathodes with negative electron affinity (NEA) surfaces have an intrinsic advantage for generating such low emittance beams and the thermal emittance as low as 0.1 π mm mrad is expected in ideal case. The thermal emittance of photoelectrons was measured for two different NEA photocathodes: a bulk-GaAs photocathode and a GaAs-GaAsP superlattice strained photocathode. The normalized root-mean-sqare emittances for the beam radius of 1.0 mm were as low as 0.20−0.29±0.02 and 0.15±0.02 π mm mrad, respectively. A comparison of these results shows that the superlattice photocathode minimizes the thermal emittance for photon excitation energies higher than the band gap energy.
Materials and electrical characterization of molecular beam deposited CeO2 and CeO2/HfO2 bilayers on germanium
Authors: Brunco D. P. , Dimoulas A. , Boukos N. , Houssa M. , Conard T. , Martens K. , Zhao C. , Bellenger F. , Caymax M. , Meuris M. , Heyns M. M.
Published: July 2007

Properties of CeO2 and CeO2/HfO2 bilayers grown by molecular beam deposition on in situ prepared, oxide-free Ge(100) surfaces are reported here. Deposition is achieved by a simultaneous flux of electron-beam evaporated metal (Ce or Hf) and of remote plasma generated atomic oxygen. These conditions result in an interfacial layer (IL) between the cubic CeO2 and Ge substrate. Electron energy loss spectroscopy shows that this IL is comprised of Ge and O and a small amount of Ce, and x-ray photoelectron spectroscopy suggests that the Ge is in a mix of 2+ and 3+ oxidation states. A comparison of capacitance, conductance, and leakage data shows a higher quality dielectric for 225 °C deposition than for room temperature. However, CeO2-only deposition results in an unacceptably high leakage current due to the small CeO2 band gap, which is remedied by the use of CeO2/HfO2 bilayers. Using the Nicollian–Goetzberger method, interface trap densities in the mid 1011 eV−1 cm−2 are obtained for CeO2/HfO2 gate stacks on both n- and p-Ge.
Scanning photovoltage microscopy of potential modulations in carbon nanotubes
Authors: Freitag Marcus , Tsang James C. , Bol Ageeth , Avouris Phaedon , Yuan Dongning , Liu Jie
Published: July 2007

We use the locally generated photovoltage in carbon nanotubes to image potential modulations produced by defects. The correlation with spatially resolved spectroscopy of the disorder-enhanced Raman band allows us to locate the defects and to determine their effect on band bending. The defects produce local potential maxima, which are consistent with trapped electrons near the tube. An offset photovoltage is generated when the laser populates metastable traps in the oxide. Previously uncharged defects can thus be imaged. To demonstrate the versatility of the technique, we show that tube-tube junction at the base of nanotube loops can be electronically characterized.
Evolution of boron-interstitial clusters in crystalline Si studied by transmission electron microscopy
Authors: Boninelli S. , Mirabella S. , Bruno E. , Priolo F. , Cristiano F. , Claverie A. , De Salvador D. , Bisognin G. , Napolitani E.
Published: July 2007

The thermal evolution of large boron-interstitials clusters (BICs) in crystalline Si has been studied by transmission electron microscopy (TEM). After ion implantation (20keV and 1×1014Si∕cm2) and annealing (815°C and 5min), large clusters (6–8nm) have been observed in correspondence of a narrow, highly doped Si:B layer (2×1020B∕cm3). Under prolonged annealing, such clusters dissolve, progressively shrinking their mean size below the TEM detection limit. The time evolution of such a BIC shrinking is fully compatible with the slow path dissolution kinetics recently published. These data suggest the identification of the slow dissolving BICs with the large observed clusters.
First principles studies of ideal strength and bonding nature of AlN polymorphs in comparison to TiN
Authors: Zhang R. F. , Sheng S. H. , Veprek S.
Published: July 2007

The stress-strain relationships under tensile and shear loads and bonding nature of fcc (rocksalt)-, hcp (wurtzite)-AlN, and fcc (rocksalt)-TiN are calculated by first principles method. Compared to fcc-TiN, fcc-AlN shows similar anisotropy of tensile strengths, but lower shear strength is found in both AlN polymorphs. Based on the calculated electronic density of states, bonding nature for both AlN polymorphs is discussed. The hardness enhancement in TiN∕AlN heterostructures and nanocomposites cannot be attributed to the difference of the ideal strength and bonding nature between fcc-AlN and hcp-AlN, but to the formation of semicoherent fcc-TiN/fcc-AlN interface.
Correlation between fragility and glass-forming ability/plasticity in metallic glass-forming alloys
Authors: Park E. S. , Na J. H. , Kim D. H.
Published: July 2007

In the present study, the authors draw attention to the relationship among fragility index (m), glass-forming ability (GFA), and plasticity in various metallic glass-forming alloys (MGAs), and show that the m value is closely related to both characteristics. In particular, m can be formulated with ν (Poisson’s ratio): ν=−0.179+0.312logm, which means that high m as well as large ν values might be regarded as indicators of the MGAs ductility. As an example, it can be rationalized that the lowest m value (21.5 at 5K∕min) of Ca65Mg15Zn20 supports both outstanding GFA and extreme brittleness.
Enhanced Pockels effect in GaN∕AlxGa1−xN superlattice measured by polarization-maintaining fiber Mach-Zehnder interferometer
Authors: Chen P. , Tu X. G. , Li S. P. , Li J. C. , Lin W. , Chen H. Y. , Liu D. Y. , Kang J. Y. , Zuo Y. H. , Zhao L. , Chen S. W. , Yu Y. D. , Yu J. Z. , Wang Q. M.
Published: July 2007

Six-period 4nm GaN∕10nm AlxGa1−xN superlattices with different Al mole fractions x were prepared on (0001) sapphire substrates by low-temperature metal-organic chemical vapor deposition. The linear electro-optic (Pockels) effect was studied by a polarization-maintaining fiber-optical Mach-Zehnder interferometer system with an incident light wavelength of 1.55μm. The measured electro-optic coefficients, γ13=5.60±0.18pm∕V, γ33=19.24±1.21pm∕V (for sample 1, x=0.3), and γ13=3.09±0.48pm∕V, γ33=8.94±0.36pm∕V (for sample 2, x=0.1), respectively, are about ten times larger than those of GaN bulk material. The enhancement effect in GaN∕AlxGa1−xN superlattice can be attributed to the large built-in field at the interfaces, depending on the mole fraction of Al.
FRET imaging in living maize cells reveals that plasma membrane aquaporins interact to regulate their subcellular localization
Authors: Zelazny Enric , Borst Jan Willem , Muylaert Mélanie , Batoko Henri , Hemminga Marcus A. , Chaumont François
Published: July 2007

Zea mays
plasma membrane intrinsic proteins (ZmPIPs) fall into two groups, ZmPIP1s and ZmPIP2s, that exhibit different water channel activities when expressed in
Xenopus
oocytes. ZmPIP1s are inactive, whereas ZmPIP2s induce a marked increase in the membrane osmotic water permeability coefficient,
P
f
. We previously showed that, in
Xenopus
oocytes, ZmPIP1;2 and ZmPIP2;1 interact to increase the cell
P
f
. Here, we report the localization and interaction of ZmPIP1s and ZmPIP2s in living maize cells. ZmPIPs were fused to monomeric yellow fluorescent protein and/or monomeric cyan fluorescent protein and expressed transiently in maize mesophyll protoplasts. When expressed alone, ZmPIP1 fusion proteins were retained in the endoplasmic reticulum, whereas ZmPIP2s were found in the plasma membrane. Interestingly, when coexpressed with ZmPIP2s, ZmPIP1s were relocalized to the plasma membrane. Using FRET/fluorescence lifetime imaging microscopy, we demonstrated that this relocalization results from interaction between ZmPIP1s and ZmPIP2s. Immunoprecipitation experiments provided additional evidence for the association of ZmPIP1;2 and ZmPIP2;1 in maize roots and suspension cells. These data suggest that PIP1–PIP2 interaction is required for
in planta
PIP1 trafficking to the plasma membrane to modulate plasma membrane permeability.
Chimpanzee locomotor energetics and the origin of human bipedalism
Authors: Sockol Michael D. , Raichlen David A. , Pontzer Herman
Published: July 2007

Bipedal walking is evident in the earliest hominins [Zollikofer CPE, Ponce de Leon MS, Lieberman DE, Guy F, Pilbeam D,
et al.
(2005)
Nature
434:755–759], but why our unique two-legged gait evolved remains unknown. Here, we analyze walking energetics and biomechanics for adult chimpanzees and humans to investigate the long-standing hypothesis that bipedalism reduced the energy cost of walking compared with our ape-like ancestors [Rodman PS, McHenry HM (1980)
Am J Phys Anthropol
52:103–106]. Consistent with previous work on juvenile chimpanzees [Taylor CR, Rowntree VJ (1973)
Science
179:186–187], we find that bipedal and quadrupedal walking costs are not significantly different in our sample of adult chimpanzees. However, a more detailed analysis reveals significant differences in bipedal and quadrupedal cost in most individuals, which are masked when subjects are examined as a group. Furthermore, human walking is ≈75% less costly than both quadrupedal and bipedal walking in chimpanzees. Variation in cost between bipedal and quadrupedal walking, as well as between chimpanzees and humans, is well explained by biomechanical differences in anatomy and gait, with the decreased cost of human walking attributable to our more extended hip and a longer hindlimb. Analyses of these features in early fossil hominins, coupled with analyses of bipedal walking in chimpanzees, indicate that bipedalism in early, ape-like hominins could indeed have been less costly than quadrupedal knucklewalking.
Desensitization of soluble guanylyl cyclase, the NO receptor, by S-nitrosylation
Authors: Sayed Nazish , Baskaran Padmamalini , Ma Xiaolei , van den Akker Focco , Beuve Annie
Published: July 2007

The molecular mechanism of desensitization of soluble guanylyl cyclase (sGC), the NO receptor, has long remained unresolved. Posttranslational modification and redox state have been postulated to affect sGC sensitivity to NO but evidence has been lacking. We now show that sGC can be S-nitrosylated in primary aortic smooth muscle cells by
S
-nitrosocysteine (CSNO), an S-nitrosylating agent, in human umbilical vein endothelial cells after vascular endothelial growth factor treatment and in isolated aorta after sustained exposure to acetylcholine. Importantly, we show that S-nitrosylation of sGC results in decreased responsiveness to NO characterized by loss of NO-stimulated sGC activity. Desensitization of sGC is concentration- and time-dependent on exposure to CSNO, and sensitivity of sGC to NO can be restored and its S-nitrosylation prevented with cellular increase of thiols. We confirm
in vitro
with semipurified sGC that S-nitrosylation directly causes desensitization, suggesting that other cellular factors are not required. Two potential S-nitrosylated cysteines in the α- and β-subunits of sGC were identified by MS. Replacement of these cysteines, C243 in α and C122 in β, created mutants that were mostly resistant to desensitization. Structural analysis of the region near β-C122 in the homologous
Nostoc
H-NOX crystal structure indicates that this residue is in the vicinity of the heme and its S-nitrosylation could dampen NO activation by affecting the positions of key residues interacting with the heme. This study suggests that S-nitrosylation of sGC is a means by which memory of NO exposure is kept in smooth muscle cells and could be a mechanism of NO tolerance.
Common molecular signature in SOD1 for both sporadic and familial amyotrophic lateral sclerosis
Authors: Gruzman Arie , Wood William L. , Alpert Evgenia , Prasad M. Dharma , Miller Robert G. , Rothstein Jeffery D. , Bowser Robert , Hamilton Ronald , Wood Troy D. , Cleveland Don W. , Lingappa Vishwanath R. , Liu Jian
Published: July 2007

Amyotrophic lateral sclerosis (ALS) is a devastating motor neuron degenerative disease whose etiology and pathogenesis remain poorly understood. Most cases of ALS (≈90%) are sporadic (SALS), occurring in the absence of genetic associations. Approximately 20% of familial ALS (FALS) cases are due to known mutations in the copper, zinc superoxide dismutase (SOD1) gene. Molecular evidence for a common pathogenesis of SALS and FALS has remained elusive. Here we use covalent chemical modification to reveal an attribute of spinal cord SOD1 common to both SOD1-linked FALS and SALS, but not present in normal or disease-affected tissues from other neurodegenerative diseases, including Alzheimer's, Parkinson's, and Huntington's diseases and spinal muscular atrophy, a non-ALS motor neuron disease. Biotinylation reveals a 32-kDa, covalently cross-linked SOD1-containing protein species produced not only in FALS caused by SOD1 mutation, but also in SALS. These studies use chemical modification as a novel tool for the detection of a disease-associated biomarker. Our results identify a shared molecular event involving a known target gene and suggest a common step in the pathogenesis between SALS and FALS.
Aquaporin 9 is the major pathway for glycerol uptake by mouse erythrocytes, with implications for malarial virulence
Authors: Liu Yangjian , Promeneur Dominique , Rojek Aleksandra , Kumar Nirbhay , Frøkiær Jørgen , Nielsen Søren , King Landon S. , Agre Peter , Carbrey Jennifer M.
Published: July 2007

Human and rodent erythrocytes are known to be highly permeable to glycerol. Aquaglyceroporin aquaporin (AQP)3 is the major glycerol channel in human and rat erythrocytes. However, AQP3 expression has not been observed in mouse erythrocytes. Here we report the presence of an aquaglyceroporin, AQP9, in mouse erythrocytes. AQP9 levels rise as reticulocytes mature into erythrocytes and as neonatal pups develop into adult mice. Mice bearing targeted disruption of both alleles encoding AQP9 have erythrocytes that appear morphologically normal. Compared with WT cells, erythrocytes from AQP9-null mice are defective in rapid glycerol transport across the cell membrane when measured by osmotic lysis, [
14
C]glycerol uptake, or stopped-flow light scattering. In contrast, the water and urea permeabilities are intact. Although the physiological role of glycerol in the normal function of erythrocytes is not clear, plasma glycerol is an important substrate for lipid biosynthesis of intraerythrocytic malarial parasites. AQP9-null mice at the age of 4 months infected with
Plasmodium berghei
survive longer during the initial phase of infection compared with WT mice. We conclude that AQP9 is the major glycerol channel in mouse erythrocytes and suggest that this transport pathway may contribute to the virulence of intraerythrocytic stages of malarial infection.
The dawn of dominance by the mature domain in tRNA splicing
Authors: Tocchini-Valentini Giuseppe D. , Fruscoloni Paolo , Tocchini-Valentini Glauco P.
Published: July 2007

The relationship between enzyme architecture and substrate specificity among archaeal pre-tRNA splicing endonucleases has been investigated more deeply, by using biochemical assays and model building. The enzyme from
Archeoglobus fulgidus
(AF) is particularly interesting: it cleaves the bulge–helix–bulge target without requiring the mature tRNA domain, but, when the target is a bulge–helix–loop, the mature domain is required. A model of AF based on its electrostatic potential shows three polar patches interacting with the pre-tRNA substrate. A simple deletion mutant of the AF endonuclease lacking two of the three polar patches no longer cleaves the bulge–helix–loop substrate with or without the mature domain. This single deletion shows a possible path for the evolution of eukaryal splicing endonucleases from the archaeal enzyme.
Anin situmethod for the study of strain broadening using synchrotron X-ray diffraction
Authors: Tang C. C. , Lynch P. A. , Cheary R. W. , Clark S. M.
Published: July 2007

A tensonometer for stretching metal foils has been constructed for the study of strain broadening in X-ray diffraction line profiles. This device, which is designed for use on powder diffractometers and was tested on Station 2.3 at Daresbury Laboratory, allowsin situmeasurements to be performed on samples under stress. It can be used for data collection in either transmission or reflection modes using either symmetric or asymmetric diffraction geometries. As a test case, measurements were carried out on an 18 µm-thick copper foil experiencing strain levels of up to 5% using both symmetric reflection and symmetric transmission diffraction. All the diffraction profiles displayed peak broadening and asymmetry which increased with strain. The measured profiles were analysed by the fundamental-parameters approach using theTOPASpeak-fitting software. All the observed broadened profiles were modelled by convoluting a refineable diffraction profile, representing the dislocation and crystallite size broadening, with a fixed instrumental profile predetermined using high-quality LaB6reference powder. The deconvolution process yielded `pure' sample integral breadths and asymmetry results which displayed a strong dependence on applied strain and increased almost linearly with applied strain. Assuming crystallite size broadening in combination with dislocation broadening arising from f.c.c.a/2〈110〉{111} dislocations, the variation of mechanical property with strain has been extracted. The observation of both peak asymmetry and broadening has been interpreted as a manifestation of a cellular structure with cell walls and cell interiors possessing high and low dislocation densities.
Dislocation effects in powder diffraction
Authors: Leoni Matteo , Martinez-Garcia Jorge , Scardi Paolo
Published: July 2007

Owing to the lack of proper models, mainly for the strain broadening component due to dislocations, full exploitation of whole powder pattern modelling for the microstructural analysis of materials has been limited so far to high-symmetry lattices. An extension of the dislocation-induced broadening model, valid for any lattice symmetry, is proposed here. Dislocation effects are modelled through the description of the dislocation contrast factor in terms of a crystallographic invariant whose terms can be either calculated when the material constants and slip systems are known (allowing a dislocation density to be refined) or refined on the experimental data for an effective estimation of dislocation effects.
Revision and extension of the standard laboratory technique for X-ray diffraction measurement of residual stress gradients
Authors: Azanza Ricardo Cristy L. , D'Incau Mirco , Scardi Paolo
Published: July 2007

A new procedure is proposed to determine sub-surface residual stress gradients by laboratory X-ray diffraction measurements at different depths using a chemical layer-removal technique. The standard correction algorithm for stress relaxation due to layer removal is improved by including corrections for X-ray absorption, and by the addition of constraints imposed by the mechanical equilibrium conditions. Besides correcting the data,i.e.providing more reliable through-thickness residual stress trends, the proposed procedure also provides an elastically compatible and plausible estimate of the residual stress inside the component, well beyond the measured region. The application of the model is illustrated for a set of Al-alloy components shot-peened at different Almen intensities. Results are compared with those given by `blind hole drilling', which is an independent and partly destructive method.
A single-crystal time-of-flight neutron diffractometer at a spallation neutron source
Authors: Takahashi Miwako , Ohshima Ken-ichi , Arai Masatoshi
Published: July 2007

A single-crystal diffractometer using the time-of-flight (TOF) Laue technique had been operated for studies of structural and magnetic disorder and phase transitions in alloys and magnetic materials at the pulsed spallation neutron source facility of the KEK Neutron Science Laboratory (KENS). In various sample environments, the diffractometer has demonstrated its usefulness in measurements of diffuse scattering for studying local structures, and in surveys of reciprocal space for studying phase transitions and incommensurate structures under the conditions of varying temperature and magnetic field. Particular emphasis is placed on the fact that though the instrument did not receive high-flux neutrons for long wavelengths suitable for the studies of magnetic scattering, it gave good results on the observations of magnetic diffuse scattering and superlattice reflections. Remarks and future tasks of the TOF Laue technique are discussed in relation to the asymmetric pulse shape, separation of the inelastic scattering, and dependence of data correction on the sample quality.
High-temperature structural evolution of hexagonal multiferroic YMnO3and YbMnO3
Authors: Jeong Il-Kyoung , Hur N. , Proffen Th.
Published: July 2007

Neutron powder diffraction studies on the structural evolution of hexagonal multiferroic YMnO3and YbMnO3from 1000 K to 1400 K, and from 1000 K to 1350 K, respectively, are presented. The temperature evolution of diffraction patterns suggests that YMnO3undergoes a phase transition to a non-polar structure above 1200 K, while YbMnO3remains ferroelectric up to 1350 K. Detailed structural parameters were obtained as a function of temperature from Rietveld refinements. Based on this result, the distinct differences in temperature behaviour between YMnO3and YbMnO3, and the origin of the ferroelectricity in these hexagonal multiferroics are discussed.
Modelling of diffraction from fibre texture gradients in thin polycrystalline films
Authors: Birkholz M.
Published: July 2007

Crystallographic textures in thin polycrystalline films typically exhibit a rotational symmetry,i.e.they occur as a fibre texture with the texture pole being orientated in the direction of the substrate normal. As a further characteristic of thin-film textures, it was often observed that the degree of preferred orientation increases with increasing thickness. It is shown in this work how a fibre texture gradient may be modelled in kinematical X-ray diffraction and which effects it has on the intensity mapping of theIHKLreflection, when theHKLpole is the fibre axis. A general expression forIHKLis derived for a depth-dependent fibre texture that is based on the finite Laplace transform of the texture distribution. The concept is outlined for the cosnψ function to model the tilt-angle dependence of intensity, with the parameterndenoting the degree of texture. It is found that the measured intensity distribution sensitively depends on the ratio of texture gradient over X-ray attenuation coefficient. For particular cases, it is found that the maximum intensity may occur for non-zero tilt angles and thus arise at a different tilt angle from the pole of the fibre texture.
Advances in space-group determination from powder diffraction data
Authors: Altomare Angela , Camalli Mercedes , Cuocci Corrado , Giacovazzo Carmelo , Moliterni Anna Grazia Giuseppina , Rizzi Rosanna
Published: July 2007

The space-group determination process by powder diffraction data is not straightforward. The low accuracy of the reflection intensities may invalidate the calculation of the probability associated to each extinction group that is compatible with the crystal system determined in the indexation step. Here the combination of thezstatistics with two new algorithms is reported: the first checks the quality of each 2θ interval in order to omit doubtfulzestimates from the calculations; the second creates a list of reflections with peaks that weakly overlap with any other peak, in order to check if any of them violates the extinction rules of the extinction symbol. The new approach has been applied to a large set of test structures and proved to be much more efficient than the procedure based only on thezstatistics.
Temperature phase changes in solid bicyclo[3.3.1]nonane-2,6-dione and bicyclo[3.3.1]nonane-3,7-dione from powder X-ray diffraction data
Authors: Brunelli Michela , Neumann Marcus A. , Fitch Andrew N. , Mora Asiloé J.
Published: July 2007

The crystal structures of bicyclo[3.3.1]nonane-2,6-dione and bicyclo[3.3.1]nonane-3,7-dione have been solved by direct methods and by direct-space simulated annealing, respectively, from powder synchrotron X-ray diffraction data. Both compounds have a transition to a face-centred-cubic orientationally disordered phase (phase I) near 363 K, as shown by differential scanning calorimetry and powder diffraction measurements. Phase II of bicyclo[3.3.1]nonane-2,6-dione, which occurs below 363 K, is monoclinic, space groupC2/c, witha= 7.38042 (4),b= 10.38220 (5),c= 9.75092 (5) Å and β = 95.359 (1)° at 80 K. Phase II of bicyclo[3.3.1]nonane-3,7-dione, which occurs below 365 K, is tetragonal, space groupP41212, witha= 6.8558 (1) andc= 16.9375 (1) Å at 100 K. This phase coexists in a biphasic mixture with a minor monoclinic phase II′ [a= 11.450 (6),b = 20.583 (1),c= 6.3779 (3) Å, β = 94.7555 (5)°, at 100 K] detected in the sample, which impeded indexing with standard programs. The crystal structures of phases II were solved by direct methods and by direct-space simulated annealing, employing powder synchrotron X-ray diffraction data of increased instrumental intensity and resolution from the ID31 beamline at the ESRF, and novel indexing algorithms.Ab initiomolecular orbital calculations on the two systems are reported. In the solid state, the molecules pack in chair–chair conformation; molecular structures and packing are discussed.