bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational spectroscopy and dynamics of small anions in ionic liquid solutions
Authors: Dahl Kevin , Sando Gerald M. , Fox Douglas M. , Sutto Thomas E. , Owrutsky Jeffrey C.
Published: August 2005

Fourier-transform infrared (FTIR) and time-resolved IR spectroscopies have been used to study vibrational band positions, vibrational energy relaxation (VER) rates, and reorientation times of anions in several ionic liquid (IL) solutions. The ILs primarily investigated are based on the 1-butyl-2,3-dimethylimidazolium ([BM2IM]) cation with thiocyanate (NCS−), dicyanamide (N(CN)2−), and tetrafluoroborate (BF4−) anions. Spectroscopic studies are carried out near 2000cm−1 for the CN stretching bands of NCS− and N(CN)2− as the IL anion as well as for NCS−, N(CN)2−, and azide (N3−) anions dissolved in [BM2IM][BF4]. The VER studies of N(CN)2− are reported for the first time. VER of N3−, NCS−, and N(CN)2− is measured in normal solvents, such as N-methylformamide, to compare with the IL solutions. The spectral shifts and VER rates of the anions in IL solution are quite similar to those in polar aprotic, conventional organic solvents, i.e., dimethylsulfoxide, and significantly different than those in methanol, in which there is hydrogen bonding. Similar studies were also carried out for the anions in another IL, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), in which the C2 hydrogen is present. The results for the anions are similar to those in the [BM2IM] containing ILs, in which the C2 hydrogen is methyl substituted. This suggests that substituting this hydrogen has, at most, a minor effect on the degree of hydrogen bonding in the anion-IL solvation interaction based on the infrared spectra and dynamics.
Properties of nearly one-electron molecules. I. An iterative Green function approach to calculating the reaction matrix
Authors: Altunata Serhan N. , Coy Stephen L. , Field Robert W.
Published: August 2005

An ab initio R-matrix method for determining the molecular reaction matrix of scattering theory is introduced. The method makes use of a principal-value Green function to compute the collision channel wave functions for the scattered electron, in combination with the Kohn variational scheme for the evaluation of R-matrix eigenvalues on a spherical boundary surface at short range. This technique permits the size of the bounded volume in the variational calculation to be reduced, making the computations fast and efficient. The reaction matrix is determined in a form that minimizes its energy dependence. Thus the procedure does not require modification or an increase in the computational effort to study the electronic structure and dynamics in Rydberg molecules with extremely polar ion cores. The analysis is specialized to examine the bound-state and free-electron scattering properties of nearly one-electron molecular systems, which are characterized by a Rydberg/scattering electron incident on a closed-shell ion core. However, it is shown that the treatment is compatible with all-electron/ab initio representations of open-shell and nonlinear polyatomic ion cores, emphasizing its generality. The introduced approach is used to calculate the electronic spectrum of the calcium monofluoride molecule, which has the extremely polar (Ca+2F−)+e− closed-shell ion-core configuration. The calculation utilizes an effective single-electron potential determined by M. Arif, C. Jungen, and A. L. Roche [J. Chem. Phys. 106, 4102 (1997)] previously. Close agreement with experimental data is obtained. The results demonstrate the practical utility of this method as a viable alternative to the standard variational approaches.
Properties of nearly one-electron molecules. II. Application to the Rydberg spectrum of CaF
Authors: Altunata Serhan N. , Coy Stephen L. , Field Robert W.
Published: August 2005

The ab initio K matrix method described in the preceding paper (Part I) is applied to the Rydberg electronic structure of calcium monofluoride. The spectroscopic quantum defects for the Σ+2, Π2, Δ2, and Φ2 states of CaF are computed using the effective potential of Arif et al. [M. Arif, Ch. Jungen, and A. L. Roche, J. Chem. Phys. 106, 4102 (1997)]. Satisfactory agreement with the experimental values is obtained. The eigenquantum defects obtained from the reaction matrix for the CaF++e− system are found to be strongly energy dependent. The analysis shows that the main features of the energy-dependent structure in the eigenphases are a consequence of a broad molecular shape resonance. Partial-l (orbital angular momentum) characters of two interacting collision eigenchannels vary rapidly as a function of increasing collision energy. This prominent variation leads to interference structure in the intensities for transitions into the ionization continuum, manifesting nodal points in the total ionization cross section in the continuum above the shape resonance. The usefulness of this structure in the ionization cross section as a direct probe of the l-character of the bound state is discussed. In addition, ab initio results for the photoelectron angular distribution and the anisotropy parameter are presented. These computed results are susceptible to direct experimental verification.
Theoretical study of the structure and optical properties of carbon-doped rutile and anatase titanium oxides
Authors: Kamisaka Hideyuki , Adachi Takahisa , Yamashita Koichi
Published: August 2005

The structure and optical properties of carbon-doped titanium oxides, TiO2, in the rutile and anatase forms have been investigated theoretically from first principles. Two possible doping sites were studied, carbon at an oxygen site (anion doping) and carbon at a titanium site (cation doping). The calculated structures suggest that cation-doped carbon atoms form a carbonate-type structure, whereas anion-doped carbon atoms do not invoke any significant structural change. A density-of-states analysis revealed three in-gap impurity states for anion doping. The optical properties of anion-doped cells qualitatively agree with the experimentally reported visible-light absorbance values. We ascribe part of the absorption to transitions from the valence band to one of the impurity states. These transitions should be able to promote photocatalytic reactions, because electron holes in the valence band are considered to be crucial for this process. Neither in-gap impurity states nor visible-light absorbance were observed in the case of cation doping. The effect of oxygen vacancies was also investigated. Introduction of oxygen vacancies into anion-doped TiO2 populates the impurity states and thus suppresses photocatalysis. The interaction of a doped carbon atom with an oxygen vacancy at a finite spatial separation was also carried out. The possibility of either a carbon-oxygen vacancy pair or higher carbon-oxygen vacancy complex existing is discussed.
Equilibrium spherically curved two-dimensional Lennard-Jones systems
Authors: Voogd J. M. , Sloot P. M. A. , van Dantzig R.
Published: August 2005

To learn about the basic aspects of nanoscale spherical molecular shells during their formation, spherically curved two-dimensional N-particle Lennard-Jones systems are simulated, studying curvature evolution paths at zero temperature. For many N values (N<800) equilibrium configurations are traced as a function of the curvature radius R. Sharp jumps for tiny changes in R between trajectories with major differences in topological structure correspond to avalanche-like transitions. For a typical case, N=25, equilibrium configurations fall on smooth trajectories in state space which can be traced in the E-R plane. The trajectories show up with local energy minima, from which growth in N at steady curvature can develop.
Observation of a sequence of wetting transitions in the binary water+ethylene glycol monobutyl ether mixture
Authors: Wu Chih-Kang , Chen Li-Jen
Published: August 2005

A homemade pendant drop/bubble tensiometer was assembled and applied to perform the surface-interfacial tension measurements for the binary water+ethylene glycol monobutyl ether (C4E1) mixture over the temperature range from 50to128°C at 10bar. The symbol CiEj is the abbreviation of a nonionic polyoxyethylene alcohol CiH2i+1(OCH2CH2)jOH. The wetting behavior of the C4E1-rich phase at the interface separating the gas and the aqueous phases was systematically examined according to the wetting coefficient calculated from the experimental results of surface/interfacial tensions. It was found that the C4E1-rich phase exhibits a sequence of wetting transitions, nonwetting→partial wetting→complete wetting, at the gas-water interface in the water+C4E1 system along with increasing the temperature, consistent with the conjecture of Kahlweit and Busse [J. Chem. Phys. 91, 1339 (1989)]. In addition, the relationship of the mutual solubility and the interfacial tension of the interface separating the C4E1-rich phase and the aqueous phase is discussed.
Heavy hydrides: H2Te ultraviolet photochemistry
Authors: Underwood J. , Chastaing D. , Lee S. , Wittig C.
Published: August 2005

The room-temperature ultraviolet absorption spectrum of H2Te has been recorded. Unlike other group-6 hydrides, it displays a long-wavelength tail that extends to 400 nm. Dissociation dynamics have been examined at photolysis wavelengths of 266 nm (which lies in the main absorption feature) and 355 nm (which lies in the long-wavelength tail) by using high-n Rydberg time-of-flight spectroscopy to obtain center-of-mass translational energy distributions for the channels that yield H atoms. Photodissociation at 355 nm yields TeH(Π1∕22) selectively relative to the TeH(Π3∕22) ground state. This is attributed to the role of the 3A′ state, which has a shallow well at large RH-TeH and correlates to H+TeH(Π1∕22). Note that the Π1∕22 state is analogous to the P1∕22 spin-orbit excited state of atomic iodine, which is isoelectronic with TeH. The 3A′ state is crossed at large R only by 2A″, with which it does not interact. The character of 3A′ at large R is influenced by a strong spin-orbit interaction in the TeH product. Namely, Π1∕22 has a higher degree of spherical symmetry than does Π3∕22 (recall that I(P1∕22) is spherically symmetric), and consequently Π1∕22 is not inclined to form either strongly bonding or antibonding orbitals with the H atom. The 3A′←X transition dipole moment dominates in the long-wavelength region and increases with R. Structure observed in the absorption spectrum in the 380–400 nm region is attributed to vibrations on 3A′. The main absorption feature that is peaked at ∼240nm might arise from several excited surfaces. On the basis of the high degree of laboratory system spatial anisotropy of the fragments from 266 nm photolysis, as well as high-level theoretical studies, the main contribution is believed to be due to the 4A″ surface. The 4A″←X transition dipole moment dominates in the Franck-Condon region, and its polarization is in accord with the experimental observations. An extensive secondary photolysis (i.e., of nascent TeH) is observed at 266 and 355 nm, and the corresponding spectral features are assigned. Analyses of the c.m. translational energy distributions yield bond dissociation energies D0. For H2Te and TeH, these are 65.0±0.1 and 63.8±0.4kcal∕mol, respectively, in good agreement with predictions that use high-level relativistic theory.
Universal scaling laws of diffusion: Application to liquid metals
Authors: Samanta Alok , Musharaf Ali Sk. , Ghosh Swapan K.
Published: August 2005

This work focuses on the universal scaling laws, which relate scaled diffusivity to excess entropy in fluids and their mixtures. The derivation of the new scaling law for diffusivity proposed recently [A. Samanta, Sk. M. Ali, and S. K. Ghosh, Phys. Rev. Lett. 92, 145901 (2004)] is discussed in details highlighting the nature of approximations involved. Also the applicability of the scaling law is extended to a new class of liquids, viz., liquid metals. The results calculated based on the scaling laws are shown to be in very good agreement with the simulation results for liquid Rb and Cs metals along the liquid-vapor coexistence curve corresponding to a wide variation of temperature and density. The new universal scaling law discussed here is superior to the earlier empirically proposed scaling laws and provides a very simple route to calculate a dynamical quantity such as diffusivity from an equilibrium property such as the radial distribution function.
Waves on radial film flows
Authors: Cholemari Murali R. , Arakeri Jaywant H.
Published: August 2005

We study the stability of surface waves on the radial film flow created by a vertical cylindrical water jet striking a horizontal plate. In such flows, surface waves have been found to be unstable and can cause transition to turbulence. This surface-wave-induced transition is different from the well-known Tollmien–Schlichting wave-induced transition. The present study aims at understanding the instability and the transition process. We do a temporal stability analysis by assuming the flow to be locally two-dimensional but including spatial variations to first order in the basic flow. The waves are found to be dispersive, mostly unstable, and faster than the mean flow. Spatial variation is the major destabilizing factor. Experiments are done to test the results of the linear stability analysis and to document the wave breakup and transition. Comparison between theory and experiments is fairly good and indicates the adequacy of the model.
Classical molecular-dynamics simulation of the hydroxyl radical in water
Authors: Campo Mario G. , Grigera J. Raul
Published: August 2005

We have studied the hydration and diffusion of the hydroxyl radical OH0 in water using classical molecular dynamics. We report the atomic radial distribution functions, hydrogen-bond distributions, angular distribution functions, and lifetimes of the hydration structures. The most frequent hydration structure in the OH0 has one water molecule bound to the OH0 oxygen (57% of the time), and one water molecule bound to the OH0 hydrogen (88% of the time). In the hydrogen bonds between the OH0 and the water that surrounds it the OH0 acts mainly as proton donor. These hydrogen bonds take place in a low percentage, indicating little adaptability of the molecule to the structure of the solvent. All hydration structures of the OH0 have shorter lifetimes than those corresponding to the hydration structures of the water molecule. The value of the diffusion coefficient of the OH0 obtained from the simulation was 7.1×10−9m2s−1, which is higher than those of the water and the OH−.
Initial-value problem for three-dimensional disturbances in a compressible boundary layer
Authors: Forgoston Eric , Tumin Anatoli
Published: August 2005

An initial-value problem is formulated for a three-dimensional wave packet in a compressible boundary layer flow. The problem is solved using a Laplace transform with respect to time and Fourier transforms with respect to the streamwise and spanwise coordinates. The solution can be presented as a sum of modes consisting of continuous and discrete spectra of temporal stability theory. Two discrete modes, known as mode S and mode F, are of interest in high-speed flows since they may be involved in a laminar-turbulent transition scenario. The continuous and discrete spectrum are analyzed numerically for a hypersonic flow with Mach number M=5.6. The following features are revealed: (1) The synchronism of mode S with acoustic waves at a streamwise wave number α→0 is primarily two-dimensional; (2) at high angles of disturbance propagation, mode F is no longer synchronized with entropy and vorticity waves; (3) at high angles of disturbance propagation, the synchronism between mode S and mode F is not accompanied by a mode S instability, and at even higher angles of disturbance propagation, mode S and mode F are not synchronized.
Table-top water window transmission x-ray microscopy: Review of the key issues, and conceptual design of an instrument for biology
Authors: Adam Jean-François , Moy Jean-Pierre , Susini Jean
Published: August 2005

As it has been beautifully demonstrated in synchrotron facilities, water window transmission x-ray microscopy (WW-TXM) has a great potential for high resolution three dimensional (3D) tomographic imaging of frozen cells, without the cumbersome staining and slicing preparation needed by electron microscopy. However, the existing instruments do not exactly meet the expectations of cell biologists in terms of performance and accessibility: 3D images of entire cells grown on a flat substrate with details in the 50–80nm range are necessary for structural cell studies. Functional imaging is also a key issue. Specific molecular probes are widely used to achieve molecular imaging in optical and electron microscopy. The same demand applies to x-ray microscopy. Immediate availability of the observation technique within the biology laboratory is as important as its performance. Therefore, WW-TXM will develop on a wider scale only when table-top instruments become available. We present a detailed analysis of such a microscope. The source is clearly the key element. Laser created plasmas of carbon or nitrogen are a proven but expensive solution. Cerenkov emission in vanadium has been demonstrated as a potential monochromatic source, but we emphasize severe obstacles: huge thermal load and radiation protection. We show that oxygenKα line excitation by an electron beam is a realistic alternative. Being a purely monochromatic source, it would allow the use of a high efficiency mirror condenser, while laser plasmas imply spectral selection with the associated losses. We then describe the main elements of an affordable laboratory microscope, supported by numerical simulations and preliminary experimental work. We also show that functionalized quantum dots, currently used in fluorescence microscopy, are equally detectable with soft x-rays and would allow a dual modality observation. Finally, the expected performance of this prototype is discussed and confronted by the requirements of cell biology.
Ab initio study of a biradical radiationless decay channel of the lowest excited electronic state of cytosine and its derivatives
Authors: Zgierski Marek Z. , Patchkovskii Serguei , Lim Edward C.
Published: August 2005

A theoretical model for the ultrafast S1→S0 internal conversion of cytosine is presented, in which a state switch from the initially prepared π1π* state to the out-of-plane deformed excited state of biradical character controls the rate of the S1(π1π*) decay. This mechanism successfully accounts for the dramatically longer S1 lifetimes of 5-fluorocytosine and N-acetylcytosine relative to cytosine. The replacement of the C5 hydrogen atom by a methyl group is predicted to lead to a substantial, but not dramatic, increase in the S1 lifetime, also consistent with experiment. It is this ability to correctly predict the substituent effects that distinguishes the present model from the previously proposed mechanisms.
Stretching of material lines in shock-accelerated gaseous flows
Authors: Kumar S. , Orlicz G. , Tomkins C. , Goodenough C. , Prestridge K. , Vorobieff P. , Benjamin R.
Published: August 2005

A Mach 1.2 planar shock wave impulsively accelerates one of five different configurations of heavy-gas (SF6) cylinders surrounded by lighter gas (air), producing one or more pairs of interacting vortex columns. The interaction of the columns is investigated with planar laser-induced fluorescence in the plane normal to the axes of the cylinders. For the first time, we experimentally measure the early time stretching rate (in the first 220μs after shock interaction before the development of secondary instabilities) of material lines in shock-accelerated gaseous flows resulting from the Richtmyer-Meshkov instability at Reynolds number ∼25000 and Schmidt number ∼1. The early time specific stretching rate exponent associated with the stretching of material lines is measured in these five configurations and compared with the numerical computations of Yang et al. [AIAA J. 31, 854 (1993)] in some similar configurations and time range. The stretching rate is found to depend on the configuration and orientation of the gaseous cylinders, as these affect the refraction of the shock and thus vorticity deposition. Integral scale measurements fail to discriminate between the various configurations over the same time range, however, suggesting that integral measures are insufficient to characterize early time mixing in these flows.
Numerical simulation of the generation mechanism of axisymmetric supersonic jet screech tones
Authors: Li X. D. , Gao J. H.
Published: August 2005

In this paper an axisymmetric computational aeroacoustic procedure is developed to investigate the generation mechanism of axisymmetric supersonic jet screech tones. The axisymmetric Navier-Stokes equations and the two equations standard k-ϵ turbulence model modified by Turpin and Troyes [“Validation of a two-equation turbulence model for axisymmetric reacting and non-reaction flows,” AIAA Paper No. 2000-3463 (2000)] are solved in the generalized curvilinear coordinate system. A generalized wall function is applied in the nozzle exit wall region. The dispersion-relation-preserving scheme is applied for space discretization. The 2N storage low-dissipation and low-dispersion Runge-Kutta scheme is employed for time integration. Much attention is paid to far-field boundary conditions and turbulence model. The underexpanded axisymmetric supersonic jet screech tones are simulated over the Mach number from 1.05 to 1.2. Numerical results are presented and compared with the experimental data by other researchers. The simulated wavelengths of A0, A1, A2, and B modes and part of simulated amplitudes agree very well with the measurement data by Ponton and Seiner [“The effects of nozzle exit lip thickness on plume resonance,” J. Sound Vib. 154, 531 (1992)]. In particular, the phenomena of modes jumping have been captured correctly although the numerical procedure has to be improved to predict the amplitudes of supersonic jet screech tones more accurately. Furthermore, the phenomena of shock motions are analyzed. The predicted splitting and combination of shock cells are similar with the experimental observations of Panda [“Shock oscillation in underexpanded screeching jets,” J. Fluid. Mech. 363, 173 (1998)]. Finally, the receptivity process is numerically studied and analyzed. It is shown that the receptivity zone is associated with the initial thin shear layer, and the incoming and reflected sound waves.
Free-standing protein films for dynamic mode detection of cations binding
Authors: Saya Daisuke , Coleman Anthony W. , Lazar Adina N. , Bergaud Christian , Nicu Liviu
Published: August 2005

This letter reports on the investigation of the mechano-chemical effect of cross-linked dried free-standing alpha-lactalbumin (α-lactalbumin) thin films induced by different cation, calcium, magnesium, and potassium binding. The protein membranes were fabricated by drying droplets of an α-lactalbumin solution on top of silicon through-wafer holes obtained by deep reactive ion etching. Then the membranes were consecutively exposed to solutions of the cations in HEPES buffer solution while their resonant frequencies were measured by full-field surface stroboscopic white light interferometry. Tests on more than 30 free-standing protein films showed more significant conformational changes of the α-lactalbumin after immersion in a calcium solution than those observed after immersion in magnesium and potassium solutions. These results demonstrate, the real potential of free-standing protein films to be used as resonant biosensors for multiple cation detection.
Defocused imaging of quantum-dot angular distribution of radiation
Authors: Patra Digambara , Gregor Ingo , Enderlein Jörg , Sauer Markus
Published: August 2005

We have applied defocused imaging of single fluorescent quantum dots to study the angular distribution of their emission. It is found that quantum dots exhibit an angular distribution best described by a superposition of emission of three perpendicular dipoles. A theory of the defocused images of such emitters is presented and compared with the measurements. Furthermore, it is shown that standard fluorescence anisotropy measurements are not able to uncover such complex emission behavior.
Design of two-dimensional/three-dimensional composite porous alumina by colloidal crystal templating and subsequent anodization
Authors: Asoh Hidetaka , Ono Sachiko
Published: August 2005

The unique two-dimensional/three-dimensional composite porous alumina structure, which consisted of the outer inverse opal structure and the inner parallel channel array structure formed on an Al substrate, has been fabricated using a combination process involving colloidal crystal templating and subsequent multistep anodization. The pore periodicity and film thickness of the sophisticated porous structure presented here can be easily controlled by changing the diameter of spherical colloidal particles used as templates and adjusting the anodization conditions, such as voltage and time. The resulting porous materials can potentially find applications as catalytic supports, separation media, optical devices, and sensors.
High-performance, tensile-strained Ge p-i-n photodetectors on a Si platform
Authors: Liu Jifeng , Michel Jurgen , Giziewicz Wojciech , Pan Dong , Wada Kazumi , Cannon Douglas D. , Jongthammanurak Samerkhae , Danielson David T. , Kimerling Lionel C. , Chen Jian , Ilday F. Ömer , Kärtner Franz X. , Yasaitis John
Published: August 2005

We demonstrate a high-performance, tensile-strained Ge p-i-n photodetector on Si platform with an extended detection spectrum of 650–1605 nm and a 3 dB bandwidth of 8.5 GHz measured at λ=1040nm. The full bandwidth of the photodetector is achieved at a low reverse bias of 1 V, compatible with the low driving voltage requirements of Si ultralarge-scale integrated circuits. Due to the direct bandgap shrinkage induced by a 0.20% tensile strain in the Ge layer, the device covers the entire C band and a large part of the L band in telecommunications. The responsivities of the device at 850, 980, 1310, 1550, and 1605 nm are 0.55, 0.68, 0.87, 0.56, and 0.11A∕W, respectively, without antireflection coating. The internal quantum efficiency in the wavelength range of 650–1340 nm is over 90%. The entire device was fabricated using materials and processing that can be implemented in a standard Si complementary metal oxide semiconductor (CMOS) process flow. With high speed, a broad detection spectrum and compatibility with Si CMOS technology, this device is attractive for applications in both telecommunications and integrated optical interconnects.
Growth of highly resistive BiMnO3 films
Authors: Eerenstein W. , Morrison F. D. , Scott J. F. , Mathur N. D.
Published: August 2005

Bi Mn O 3 (010) films (100nm) were grown epitaxially on SrTiO3 (001) and 0.2at.% Nb-doped SrTiO3 (001) substrates using pulsed laser deposition. The microstructure, electrical, and magnetic properties, and indeed the formation of the correct phase, were found to be very sensitive to growth parameters. This optimization has resulted in highly resistive BiMnO3 films and thus enabled room-temperature dielectric measurements: We obtained a resistivity of 5×107Ωcm, and an effective (i.e. thickness dependent) dielectric constant of 1400. These findings pave the way for magnetoelectric measurements and further optimization.
Spectral conversion of InGaN ultraviolet microarray light-emitting diodes using fluorene-based red-, green-, blue-, and white-light-emitting polymer overlayer films
Authors: Heliotis G. , Stavrinou P. N. , Bradley D. D. C. , Gu E. , Griffin C. , Jeon C. W. , Dawson M. D.
Published: August 2005

We report the fabrication of hybrid organic/inorganic semiconductor light-emitting devices that operate across the entire visible spectrum. The devices are based on a series of blue-, green-, and red-light-emitting polyfluorene materials that convert the emission from an array of micron-sized ultraviolet InGaN light-emitting diodes. We also demonstrate white-light-emitting versions of these hybrid devices by employing single films of carefully adjusted polyfluorene blends in which cascade energy transfer occurs between the constituent materials. The spectral and operating characteristics of the devices are described in detail. Such organic emission layer/inorganic light-emitting diode (LED) array based devices may provide a promising route to the fabrication of low-cost full-color microdisplays and other instrumentation devices.
Correlation between dielectric anisotropy and positive or zero transverse piezoelectric coefficients in perovskite ferroelectric single crystals
Authors: Davis Matthew , Damjanovic Dragan , Setter Nava
Published: August 2005

The transverse piezoelectric coefficient (d31⋆) has been calculated for tetragonal barium titanate (BT) and lead titanate (PT) cut along nonpolar axes, over a range of temperatures, using the phenomenological Landau-Ginzburg-Devonshire theory. It is shown that negative values of d31⋆ are favored when the transverse dielectric susceptibility η11 and shear coefficient d15 are large, such that polarization rotation is more significant than the collinear piezoelectric effect. This occurs in tetragonal BT close to its ferroelectric-ferroelectric phase transition to an orthorhombic phase. In PT, however, where no phase transition occurs, d15 is small and polarization “extension” due to d33 dominates: small or positive values of d31⋆ become prominent. This extends a previous result found for polycrystalline modified PT ceramics.
Growth habits and defects in ZnO nanowires grown on GaN/sapphire substrates
Authors: Levin Igor , Davydov Albert , Nikoobakht Babak , Sanford Norman , Mogilevsky Pavel
Published: August 2005

Growth habits and defects in epitaxial ZnO nanowires grown from Au catalyst on (00.1) GaN/sapphire substrate using the vapor-liquid-solid (VLS) technique were studied using electron microscopy and x-ray diffraction. The results revealed presence of both horizontal (crawling-like) and vertical nanowires having similar orientation relationship to the substrate (00.1)ZnO‖(00.1)GaN, [11.0]ZnO‖[11.0]GaN. The crawling-like growth precedes the vertical growth, and the coalescence and overgrowth of the crawling nanowires produce a highly defective layer which separates the substrate and vertical nanorods. Transmission electron microscopy revealed a high density of planar defects in this interfacial layer. A significant density of stacking faults residing on the (0001) planes was also observed in the shorter vertical nanorods. The crawling nanowires are under residual compressive strain, whereas the vertical nanorods grow strain-free.
The Results of Making a City More Compact: Neighbours' Interpretation of Urban Infill
Authors: Vallance Suzanne , Perkins Harvey C , Moore Kevin
Published: August 2005

The quest for more sustainable urban forms has added renewed vigour to urban planning, with various types of urban infill and intensification becoming increasingly popular with local authorities. These approaches seek to achieve environmental and social objectives but, despite the supposed advantages of a more consolidated urban form, infill housing as a strategy for growth management is not always well received by local residents and it remains a contentious issue. In this paper the authors report on an enquiry into neighbours' interpretations of, and responses to, infill housing in Christchurch, New Zealand.
Investigating the Effectiveness of the Least-Angle Strategy for Wayfinding in Unknown Street Networks
Authors: Hochmair Hartwig H
Published: August 2005

In this paper the wayfinding criterion always to ‘proceed in the direction of the target’, which is the core of the least-angle strategy, is examined. Although human route-selection behavior is much more complex than this, results of empirical studies presented in the literature suggest that preference for most direct direction plays an important role in human route choice within street networks. The least-angle strategy can be applied once the navigator knows the direction of the destination, and is therefore an appropriate temporary heuristic for situations where the navigator lacks more detailed information about the environment. To assess the effectiveness of the least-angle strategy in urban environments, an agent simulation has been performed on the urban street networks of two cities for three different modes of transportation—pedestrian, bicycle, and car. The results of the simulation are analyzed.
How to Simulate the Universe in a Computer
Authors: Knebe Alexander
Published: August 2005

In this contribution a broad overview of the methodologies of cosmological N-body simulations and a short introduction explaining the general idea behind such simulations is presented. After explaining how to set up the initial conditions using a set of N particles two (diverse) techniques are presented for evolving these particles forward in time under the influence of their self-gravity. One technique (tree codes) is solely based upon a sophistication of the direct particle–particle summation whereas the other method relies on the continuous (de-)construction of arbitrarily shaped grids and is realized in adaptive mesh refinement codes.
Are We There Yet? The Road to Gravitational Wave Detection
Authors: McClelland David E.
Published: August 2005

Giant laser interferometers are currently ‘listening’ for gravitational waves but are they sensitive enough? I briefly review the status of the global effort to detect gravity waves and overview Australia's role.
Correcting the Influence of an Asymmetric Line Spread Function in 2-Degree Field Spectrograph Data
Authors: Martin Nicolas F. , Ibata Rodrigo A. , Conn Blair C. , Irwin Mike J. , Lewis Geraint F.
Published: August 2005

We investigate the role of asymmetries in the line spread function of the 2-degree field (2dF) spectrograph and the variations in these asymmetries with the CCD, the plate, the time of observation, and the fibre. A data-reduction pipeline is developed that takes these deformations into account for the calibration and cross-correlation of the spectra. We show that, using the emission lines of calibration lamp observations, we can fit the line spread function with the sum of two Gaussian functions representing the theoretical signal and a perturbation of the system. This model is then used to calibrate the spectra and generate templates by downgrading high-resolution spectra. Thus, we can cross-correlate the observed spectra with templates degraded in the same way. Our reduction pipeline is tested on real observations and provides a significant improvement in the accuracy of the radial velocities obtained. In particular, the systematic errors that were as high as ∼20 km s−1 when applying the AAO reduction package 2DFDR are now reduced to ∼5 km s−1. Even though the 2dF spectrograph is to be decommissioned at the end of 2005, the analysis of archival data and previous studies could be improved by the reduction procedure we propose here.
Temporal and spatial expression of hexose transporters in developing tomato (Lycopersicon esculentum) fruit
Authors: Dibley Stephen J. , Gear Michael L. , Yang Xiao , Rosche Elke G. , Offler Christina E. , McCurdy David W. , Patrick John W.
Published: August 2005

Correlative physiological evidence suggests that membrane transport into storage parenchyma cells is a key step in determining hexose levels accumulated in tomato (Lycopersicon esculentum Mill.) fruit (Ruan et al. 1997). Expression of three previously identified hexose transporter genes (LeHT1, 2 and 3) demonstrated that LeHT3, and to a lesser extent LeHT1, are the predominant transporters expressed in young fruit (10 d after anthesis; DAA). Expression of both transporters dropped sharply until 24 DAA, after which only LeHT3 expression remained at detectable levels through to fruit ripening. LeHT2 was not expressed substantially until the onset of fruit ripening. For fruit at both 10 and 30 DAA, LeHT3 transcripts were detected in storage parenchyma cells of the outer pericarp tissue, but not in vascular bundles or the first layer of parenchyma cells surrounding these bundles. In contrast to LeHT gene expression, hexose transporter protein levels were maximal between 20 and 30 DAA, which corresponded to the period of highest hexose accumulation. The delayed appearance of transporter protein is consistent with some form of post-transcriptional regulation. Based on these analyses, LeHT3 appears to be responsible for the rapid hexose accumulation in developing tomato fruit.
Variation in growth responses to availability of water in Cistus albidus populations from different habitats
Authors: Grant Olga M. , Incoll Lynton D. , McNeilly Tom
Published: August 2005

Seeds of Cistus albidus L. plants from three populations that are exposed to differing temperature and precipitation in Almería province of south-east Spain, were collected and grown together in a factorial experiment with two irrigation treatments. The aim was to determine whether populations from different habitats differed when exposed to common conditions, or differed in the plasticity of their response to availability of water. Significant differences in growth of branches and in leaf dimensions were found between treatments, indicating phenotypic plasticity. There was also significant variation between populations in growth of branches and leaf dimensions, with a population from a location that is intermediate in terms of precipitation and temperature showing the greatest growth of branches and production of leaves under the well-watered treatment. This population is from a semi-arid climate, where precipitation is unpredictable, and selection may have occurred to favour rapid growth when water is available. This population had the narrowest leaves under both treatments, and the lowest leaf mass in the well-watered treatment. It also maintained the same mass per leaf under the two treatments, whereas the others showed an increased mass of leaves with increased availability of water. Thus, populations differed both in their manner of allocating resources and their response to availability of water.
Stable osmotica in Eucalyptus spathulata — responses to salt and water deficit stress
Authors: Merchant Andrew , Adams Mark
Published: August 2005

Salt and water deficit stress elicited contrasting responses in seedlings of Eucalyptus spathulata (Hook.). Under salt stress, seedlings reduced osmotic potential by accumulating large quantities of inorganic ions in leaf tissues. Sodium concentrations reached 350 mm on a leaf water basis and total cellular osmolality reached ∼2000 mm. Under water deficit stress, maximum sodium concentrations were around 50 mm in leaf water and seedlings reduced osmotic potential through increasing concentrations of a range of constitutive solutes up to a total cellular osmolality of ∼1200 mm. We postulate that measured concentrations of the cyclic polyol, quercitol, of up to 200 mm leaf water, are the likely means of balancing accumulation of inorganic ions. Under the common assumption of localisation of inorganic ions to the vacuole and organic balancing solutes to the cytoplasm, the concentrations of cyclitol, and other carbohydrates were more than sufficient to balance osmotic potential across the tonoplast membrane. Results confirm other recent studies that suggest a range of putative roles for cyclitols in tissues and these are discussed in the larger context of plant responses to salt and water deficit stress.
Primary root growth: a biophysical model of auxin-related control
Authors: Chavarría-Krauser Andrés , Jäger Willi , Schurr Ulrich
Published: August 2005

Plant hormones control many aspects of plant development and play an important role in root growth. Many plant reactions, such as gravitropism and hydrotropism, rely on growth as a driving motor and hormones as signals. Thus, modelling the effects of hormones on expanding root tips is an essential step in understanding plant roots. Here we achieve a connection between root growth and hormone distribution by extending a model of root tip growth, which describes the tip as a string of dividing and expanding cells. In contrast to a former model, a biophysical growth equation relates the cell wall extensibility, the osmotic potential and the yield threshold to the relative growth rate. This equation is used in combination with a refined hormone model including active auxin transport. The model assumes that the wall extensibility is determined by the concentration of a wall enzyme, whose production and degradation are assumed to be controlled by auxin and cytokinin. Investigation of the effects of auxin on the relative growth rate distribution thus becomes possible. Solving the equations numerically allows us to test the reaction of the model to changes in auxin production. Results are validated with measurements found in literature.
Direct recognition by
αβ
cytolytic T cells of Hfe, a MHC class Ib molecule without antigen-presenting function
Authors: Rohrlich Pierre S. , Fazilleau Nicolas , Ginhoux Florent , Firat Hüseyin , Michel Frédérique , Cochet Madeleine , Laham Nihay , Roth Marie Paule , Pascolo Steve , Nato Faridabano , Coppin Hélène , Charneau Pierre , Danos Olivier , Acuto Oreste , Ehrlich Rachel , Kanellopoulos Jean , Lemonnier François A.
Published: August 2005

Crystallographic analysis of human Hfe has documented an overall structure similar to classical (class Ia) MHC molecules with a peptide binding groove deprived of ligand. Thus, to address the question of whether αβ T cells could recognize MHC molecules independently of bound ligands, we studied human and mouse Hfe interactions with T lymphocytes. We provide formal evidence of direct cytolytic recognition of human Hfe by mouse αβ T cell receptors (TCR) in HLA-A
*
0201 transgenic mice and that this interaction results in ZAP-70 phosphorylation. Furthermore, direct recognition of mouse Hfe molecules by cytotoxic T lymphocytes (CTLs) was demonstrated in DBA/2 Hfe knockout mice. These CTLs express predominantly two T cell antigen receptor α variable gene segments (AV6.1 and AV6.6). Interestingly, in wild-type mice we identified a subset of CD8
+
T cells positively selected by Hfe that expresses the AV6.1/AV6.6 gene segments. T cell antigen receptor recognition of MHC molecules independently of bound ligand has potential general implications in alloreactivity and identifies in the Hfe case a cognitive link supporting the concept that the immune system could be involved in the control of iron metabolism.
An isoform-specific allele of
Drosophila N-cadherin
disrupts a late step of R7 targeting
Authors: Nern Aljoscha , Nguyen Louis-Vu T. , Herman Tory , Prakash Saurabh , Clandinin Thomas R. , Zipursky S. Lawrence
Published: August 2005

Drosophila
N-cadherin is required for the formation of precise patterns of connections in the fly brain. Alternative splicing is predicted to give rise to 12 N-cadherin isoforms. We identified an
N-cadherin
allele,

N-cad
18Astop

, that eliminates the six isoforms containing alternative exon 18A and demonstrate that it strongly disrupts the connections of R7 photoreceptor neurons. During the first half of pupal development, N-cadherin is required for R7 growth cones to terminate within a temporary target layer in the medulla. N-cadherin isoforms containing exon 18B are sufficient for this initial targeting. By contrast, 18A isoforms are preferentially expressed in R7 during the second half of pupal development and are necessary for R7 to terminate in the appropriate synaptic layer in the medulla neuropil. Transgene rescue experiments suggest that differences in isoform expression, rather than biochemical differences between isoforms, underlie the 18A isoform requirement in R7 neurons.
Tuning genetic control through promoter engineering
Authors: Alper Hal , Fischer Curt , Nevoigt Elke , Stephanopoulos Gregory
Published: August 2005

Gene function is typically evaluated by sampling the continuum of gene expression at only a few discrete points corresponding to gene knockout or overexpression. We argue that this characterization is incomplete and present a library of engineered promoters of varying strengths obtained through mutagenesis of a constitutive promoter. A multifaceted characterization of the library, especially at the single-cell level to ensure homogeneity, permitted quantitative assessment correlating the effect of gene expression levels to improved growth and product formation phenotypes in
Escherichia coli
. Integration of these promoters into the chromosome can allow for a quantitative accurate assessment of genetic control. To this end, we used the characterized library of promoters to assess the impact of phosphoenolpyruvate carboxylase levels on growth yield and deoxy-xylulose-P synthase levels on lycopene production. The multifaceted characterization of promoter strength enabled identification of optimal expression levels for
ppc
and
dxs
, which maximized the desired phenotype. Additionally, in a strain preengineered to produce lycopene, the response to deoxy-xylulose-P synthase levels was linear at all levels tested, indicative of a rate-limiting step, unlike the parental strain, which exhibited an optimum expression level, illustrating that optimal gene expression levels are variable and dependent on the genetic background of the strain. This promoter library concept is illustrated as being generalizable to eukaryotic organisms (
Saccharomyces cerevisiae
) and thus constitutes an integral platform for functional genomics, synthetic biology, and metabolic engineering endeavors.
Toward the development of peptide nanofilaments and nanoropes as smart materials
Authors: Wagner Daniel E. , Phillips Charles L. , Ali Wasif M. , Nybakken Grant E. , Crawford Emily D. , Schwab Alexander D. , Smith Walter F. , Fairman Robert
Published: August 2005

Protein design studies using coiled coils have illustrated the potential of engineering simple peptides to self-associate into polymers and networks. Although basic aspects of self-assembly in protein systems have been demonstrated, it remains a major challenge to create materials whose large-scale structures are well determined from design of local protein–protein interactions. Here, we show the design and characterization of a helical peptide, which uses phased hydrophobic interactions to drive assembly into nanofilaments and fibrils (“nanoropes”). Using the hydrophobic effect to drive self-assembly circumvents problems of uncontrolled self-assembly seen in previous approaches that used electrostatics as a mode for self-assembly. The nanostructures designed here are characterized by biophysical methods including analytical ultracentrifugation, dynamic light scattering, and circular dichroism to measure their solution properties, and atomic force microscopy to study their behavior on surfaces. Additionally, the assembly of such structures can be predictably regulated by using various environmental factors, such as pH, salt, other molecular crowding reagents, and specifically designed “capping” peptides. This ability to regulate self-assembly is a critical feature in creating smart peptide biomaterials.
Primary sequence independence for prion formation
Authors: Ross Eric D. , Edskes Herman K. , Terry Michael J. , Wickner Reed B.
Published: August 2005

Many proteins can adopt self-propagating β-sheet-rich structures, termed amyloid fibrils. The [URE3] and [PSI
+
] prions of
Saccharomyces cerevisiae
are infectious amyloid forms of the proteins Ure2p and Sup35p, respectively. Ure2p forms prions primarily as a result of its sequence composition, as versions of Ure2p with the prion domain amino acids shuffled are still able to form prions. Here we show that prion induction by both Ure2p and Ure2-21p, one of the scrambled versions of Ure2p, is clearly dependent on the length of the inducing fragment. For Ure2-21p, no single sequence is found in all of the inducing fragments, highlighting the sequence independence of prion formation. Furthermore, the sequence of the Sup35p prion domain can also be randomized without blocking prion formation. Indeed, a single shuffled sequence could give rise to several prion variants. These results suggest that [PSI
+
] formation is driven primarily by the amino acid composition of the Sup35p prion domain, and that the Sup35p oligopeptide repeats are not required for prion maintenance.