bluuebunny/crossref_metadata_2025 huggingface dataset:
Scrape-off layer transport and deposition studies in DIII-D
Authors: Groth M. , Allen S. L. , Boedo J. A. , Brooks N. H. , Elder J. D. , Fenstermacher M. E. , Groebner R. J. , Lasnier C. J. , McLean A. G. , Leonard A. W. , Lisgo S. , Porter G. D. , Rensink M. E. , Rognlien T. D. , Rudakov D. L. , Stangeby P. C. , Wampler W. R. , Watkins J. G. , West W. P. , Whyte D. G.
Published: May 2007

Trace C13H4 injection experiments into the main scrape-off layer (SOL) of low density L-mode and high-density H-mode plasmas have been performed in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] to mimic the transport and deposition of carbon arising from a main chamber sputtering source. These experiments indicated entrainment of the injected carbon in plasma flow in the main SOL, and transport toward the inner divertor. Ex situ surface analysis showed enhanced C13 surface concentration at the corner formed by the divertor floor and the angled target plate of the inner divertor in L-mode; in H-mode high surface concentration was found both at the corner and along the surface bounding the private flux region inboard of the outer strike point. Interpretative modeling was made consistent with these experimental results by imposing a parallel carbon ion flow in the main SOL toward the inner target, and a radial pinch toward the separatrix. Predictive modeling carried out to better understand the underlying plasma transport processes suggests that the deuterium flow in the main SOL is related to the degree of detachment of the inner divertor leg. These simulations show that carbon ions are entrained with the deuteron flow in the main SOL via frictional coupling, but higher charge-state carbon ions may be suspended upstream of the inner divertor X-point region due to balance of the friction force and the ion temperature gradient force.
Disruption of hydrogen bond structure of water near charged electrode surfaces
Authors: Suresh S. J.
Published: May 2007

The understanding of the hydrogen (H) bonded structure of water near charged surfaces is highly relevant in the context of several important areas of research, including electrochemistry, biochemistry, and geology. Past simulation studies have not yielded conclusive answers; while some suggest breakage of H bonds near a charged surface, others argue that H-bonding interactions can stabilize the structure of surface water even in the presence of high electric (E) fields. Recent experiments, on the other hand, suggest a partial breakdown of H-bond structure near a charged electrode. In all these studies, however, the conclusions regarding H bonding were drawn based on the density profile of hydrogen/oxygen atoms near the interface. In the present paper, we investigate this problem using a new theory that explicitly accounts for the influence of E field on the H-bond network of water near the solid-liquid interface. We find that the average number of H bonds per molecule in bulk increases from ∼3.8 at E<105V∕m to ∼3.95 at E=2×109V∕m (suggesting enhancement in H-bond network), while that near the electrode surface decreases from ∼2.8 to a saturation value of ∼2.0 (suggesting weakening of H-bond network).
Carrier transport in Ge nanowire/Si substrate heterojunctions
Authors: Lee E.-K. , Kamenev B. V. , Tsybeskov L. , Sharma S. , Kamins T. I.
Published: May 2007

Low impedance and negligible conductivity temperature dependence are found for micron-long Ge nanowires (NWs) grown on (p+)Si substrates. In contrast, Ge NW/(n+)Si substrate samples exhibit many orders of magnitude higher impedance, an exponential dependence of conductivity on temperature, current instabilities, and negative differential photoconductivity. Our experimental results are explained by a model that considers energy-band alignment and carrier transport in abrupt Ge NW/Si substrate heterojunctions.
Influence of nanocrystal size on optical properties of Si nanocrystals embedded in SiO2 synthesized by Si ion implantation
Authors: Ding L. , Chen T. P. , Liu Y. , Yang M. , Wong J. I. , Liu Y. C. , Trigg A. D. , Zhu F. R. , Tan M. C. , Fung S.
Published: May 2007

Si nanocrystals (nc-Si) with different sizes embedded in SiO2 matrix have been synthesized with various recipes of Si ion implantation. The influence of nanocrystal size on optical properties, including dielectric functions and optical constants, of the nc-Si has been investigated with spectroscopic ellipsometry. The optical properties of the nc-Si are found to be well described by the four-term Forouhi-Bloomer model. A strong dependence of the dielectric functions and optical constants on the nc-Si size is observed. For the imaginary part of the dielectric functions, the magnitude of the main peaks at the transition energies E1 and E2 exhibits a large reduction and a significant redshift in E2 depending on the nc-Si size. A band gap expansion is observed when the nc-Si size is reduced. The band gap expansion with the reduction of nc-Si size is in good agreement with the prediction of first-principles calculations based on quantum confinement.
Nonlinear excitation of geodesic acoustic modes by drift waves
Authors: Chakrabarti N. , Singh R. , Kaw P. K. , Guzdar P. N.
Published: May 2007

In this paper, two mode-coupling analyses for the nonlinear excitation of the geodesic acoustic modes (GAMs) in tokamak plasmas by drift waves are presented. The first approach is a coherent parametric process, which leads to a three-wave resonant interaction. This investigation allows for the drift waves and the GAMs to have comparable scales. The second approach uses the wave-kinetic equations for the drift waves, which then couples to the GAMs. This requires that the GAM scale length be large compared to the wave packet associated with the drift waves. The resonance conditions for these two cases lead to specific predictions of the radial wave number of the excited GAMs.
Inverse scattering problem for time dependent Hartree-Fock equations in the three-body case
Authors: Watanabe Michiyuki
Published: May 2007

We consider an inverse scattering problem for time dependent Hartree-Fock equations in the three-body case. It will be shown that interaction potentials with simple forms are uniquely determined by the corresponding scattering data. We also give reconstruction formulas.
The effect of size on the quantitative estimation of defect depth in steel structures using lock-in thermography
Authors: Wallbrink C. , Wade S. A. , Jones R.
Published: May 2007

An investigation into the effect of size on the quantitative estimation of defect depth in a steel specimen has been undertaken using lock-in thermography. Phase contrast measurements over circular defects of varying diameter and depth are presented for a range of excitation frequencies. It was found that the diameter of a defect had an appreciable effect on the observed phase angle which consequently has significant implications with regard to estimating defect depth. Phase contrast measurements for a range of defects in a 10mm steel specimen indicate that an excitation frequency of 0.02Hz is the optimal frequency for defect detection. Results obtained with an excitation frequency of 0.02Hz are used to discuss the limitations of determining the size and depth of defects. A finite element analysis was found to have good correlation with experimental data and thus demonstrates potential in providing improved estimates of defect depth.
Computational study of scalar mixing in the field of a gaseous laminar line vortex
Authors: Basu S. , Barber T. J. , Cetegen B. M.
Published: May 2007

A computational study of scalar mixing in a laminar vortex is presented for vortices generated between two gas streams (one seeded and another unseeded) flowing parallel to each other in a rectangular flow channel. An isolated line vortex is initiated by momentarily increasing one of the stream velocities in relation to the other in otherwise equal velocity, co-flowing streams separated upstream by a splitter plate. A detailed parametric study was conducted to determine the effects of vortex strength, convection time, and nonuniform temperature on scalar mixing characteristics. A qualitative relationship was developed between the vortex and the convection Reynolds numbers to obtain a well-defined vortical structure. As it is well-known in the literature on mixing layers, the vortex initiation process creates an abundance of the fluid in the vortex core from the pulsed (or high speed) stream. Spatial mixing statistics are obtained in the vortex interaction domain by determining the scalar concentration probability density functions as well as the mean mixed fluid concentration and its variance. Computational results are found to be in excellent agreement with the experiments conducted in the same configuration by one of the authors. Both computations and experiments suggest that the interfacial area generation as a result of vortex interaction is primarily responsible for mixing augmentation at high vortex Reynolds numbers (Rev≥140). Effects of molecular diffusion become more important for weak vortices and at short convection times. Temperature (or density) ratio between co-flowing streams clearly affects the rate of growth of the vortices and this is consistent with the findings in nonuniform density mixing layers. Nonuniform temperatures result in a decrease of the mean mixed fluid concentration regardless of the stream from which the vortex is generated. The mean mixed fluid concentration in the vortex interaction region scales with the product of vortex Reynolds number and nondimensional convective time scale (or degree of stirring) and inversely with temperature ratio. Empirical correlations were developed for this parameter for vortices generated from either stream.
Local effective potential theory: Nonuniqueness of potential and wave function
Authors: Sahni Viraht , Slamet Marlina , Pan Xiao-Yin
Published: May 2007

In local effective potential energy theories such as the Hohenberg-Kohn-Sham density functional theory (HKS-DFT) and quantal density functional theory (Q-DFT), electronic systems in their ground or excited states are mapped to model systems of noninteracting fermions with equivalent density. From these models, the equivalent total energy and ionization potential are also obtained. This paper concerns (i) the nonuniqueness of the local effective potential energy function of the model system in the mapping from a nondegenerate ground state, (ii) the nonuniqueness of the local effective potential energy function in the mapping from a nondegenerate excited state, and (iii) in the mapping to a model system in an excited state, the nonuniqueness of the model system wave function. According to nondegenerate ground state HKS-DFT, there exists only one local effective potential energy function, obtained as the functional derivative of the unique ground state energy functional, that can generate the ground state density. Since the theorems of ground state HKS-DFT cannot be generalized to nondegenerate excited states, there could exist different local potential energy functions that generate the excited state density. The constrained-search version of HKS-DFT selects one of these functions as the functional derivative of a bidensity energy functional. In this paper, the authors show via Q-DFT that there exist an infinite number of local potential energy functions that can generate both the nondegenerate ground and excited state densities of an interacting system. This is accomplished by constructing model systems in configurations different from those of the interacting system. Further, they prove that the difference between the various potential energy functions lies solely in their correlation-kinetic contributions. The component of these functions due to the Pauli exclusion principle and Coulomb repulsion remains the same. The existence of the different potential energy functions as viewed from the perspective of Q-DFT reaffirms that there can be no equivalent to the ground state HKS-DFT theorems for excited states. Additionally, the lack of such theorems for excited states is attributable to correlation-kinetic effects. Finally, they show that in the mapping to a model system in an excited state, there is a nonuniqueness of the model system wave function. Different wave functions lead to the same density, each thereby satisfying the sole requirement of reproducing the interacting system density. Examples of the nonuniqueness of the potential energy functions for the mapping from both ground and excited states and the nonuniqueness of the wave function are provided for the exactly solvable Hooke’s atom. The work of others is also discussed.
Mechanism of the electro-optic effect in the perovskite-type ferroelectric KNbO3 and LiNbO3
Authors: Meng X. Y. , Wang Z. Z. , Zhu Y. , Chen C. T.
Published: May 2007

Based on the theoretical model published by Chen et al. [Chem. Phys. Lett. 397, 222 (2004)], we present an efficient scheme for studying the mechanism of the electro-optic (EO) effect in perovskite-type ferroelectrics employing the electronic density-functional theory and the generalized gradient approximation. The results show that the main contribution to the EO effect in KNbO3 and LiNbO3 crystals comes from the relative displacements of the central metal ion and oxygen in the NbO6 oxygen octahedron induced by a low frequency applied electric field. These displacements change the band wave functions of the electrons in the crystals through electron-phonon coupling, which then affects the electronic response of the lattice to the incident optical wave (i.e., induces a change of refractive index). Furthermore, the relationship between the microstructure of perovskite-type ferroelectrics and the clamped EO effect and the physical meaning of the parameter βk(ij) published by Chen et al. are explained.
Spin-orbit coupling in O2(v)+O2 collisions. II. Quantum scattering calculations on dimer states involving the XΣg−3, aΔg1, and bΣg+1 states of O2
Authors: Dayou Fabrice , Hernández Marta I. , Campos-Martínez José , Hernández-Lamoneda Ramón
Published: May 2007

The dynamics of collisional deactivation of O2(XΣg−3,v=20–32) by O2(XΣg−3,v′=0) is investigated in detail by means of quantum-mechanical calculations. The theoretical approach involves ab initio potential energy surfaces correlating to the XΣg−3, aΔg1, and bΣg+1 states of O2 and their corresponding spin-orbit couplings [F. Dayou, M. I. Hernández, J. Campos-Martínez, and R. Hernández-Lamoneda, J. Chem. Phys. 123, 074311 (2005)]. Accurate Rydberg-Klein-Rees potentials are included in order to improve the description of the vibrational structure of the fragments. The calculated Boltzmann-averaged depletion probabilities display a dependence with v in good agreement with experimental measurements. The onset of the vibrational-to-electronic (V-E) depletion mechanism is noticeable for v⩾26, and it is due to energy transfer to both aΔg1 and bΣg+1 states of the diatom. For O2(XΣg−3,v=28), a further and sharp increase in the removal probabilities is caused by a near degeneracy with the O2(bΣg+1,v=19) vibrational state. Analysis of the temperature dependence of the Boltzmann-averaged probabilities indicates a transition from the vibrational-to-translational to the V-E energy transfer regime, which can be traced back to the behavior of the inelastic probabilities as functions of kinetic energy. Furthermore, branching ratios for outcomes through the three different electronic states show a strong propensity towards populating a unique vibrational level within each electronic state. These results provide supported evidence that spin-orbit couplings account for a large portion of the “dark channel” reported in total depletion measurements. New insight for further experimental and theoretical investigations is also given.
Relativistic corrections to the non-Born-Oppenheimer energies of the lowest singlet Rydberg states of He3 and He4
Authors: Stanke Monika , Kȩdziera Dariusz , Bubin Sergiy , Adamowicz Ludwik
Published: May 2007

In this work the authors present an approach to calculate the leading-order relativistic corrections for ground and excited states of helium isotopomers. In the calculations they used variational wave functions expanded in terms of explicitly correlated Gaussians obtained without assuming the Born-Oppenheimer approximation.
Adsorption of linear alkanes on Cu(111): Temperature and chain-length dependence of the softened vibrational mode
Authors: Fosser Kari A. , Kang Joo H. , Nuzzo Ralph G. , Wöll Christof
Published: May 2007

The vibrational spectra of linear alkanes, with lengths ranging from n-propane to n-octane, were examined on a copper surface by reflection-absorption infrared spectroscopy. The appearance and frequency of the “soft mode,” a feature routinely seen in studies of saturated hydrocarbons adsorbed on metals, were examined and compared between the different adsorbates. The frequency of the mode was found to be dependent on both the number of methylene units of each alkane as well as specific aspects of the order of the monolayer phase. Studies of monolayer coverages at different temperatures provide insights into the nature of the two-dimensional (2D) melting transitions of these adlayer structures, ones that can be inferred from observed shifts in the soft vibrational modes appearing in the C–H stretching region of the infrared spectrum. These studies support recently reported hypotheses as to the origins of such soft modes: the metal-hydrogen interactions that mediate them and the dynamics that underlay their pronounced temperature dependencies. The present data strongly support a model for the 2D to one-dimensional order-order phase transition arising via a continuous rather than discrete first-order process.
Monte Carlo approach to the decay rate of a metastable system with an arbitrarily shaped barrier
Authors: Bao Jing-Dong , Bi Lei , Jia Ying
Published: May 2007

A path integral Monte Carlo method based on the fast-Fourier transform technique combined with the important sampling method is proposed to calculate the decay rate of a metastable quantum system with an arbitrary shape of a potential barrier. The contribution of all fluctuation actions is included which can be used to check the accuracy of the usual steepest-descent approximation, namely, the perturbation expansion of potential. The analytical approximation is found to produce the decay rate of a particle in a cubic potential being about 20% larger than the Monte Carlo data at the crossover temperature. This disagreement increases with increasing complexity of the potential shape. We also demonstrate via Langevin simulation that the postsaddle potential influences strongly upon the classical escape rate.
Resonance Raman and density functional theory investigation of the photodissociation dynamics of the A-band absorption of (E)-β-nitrostyrene in cyclohexane solution
Authors: Zhang Shu-Qiang , Wang Hui-gang , Pei Ke-Mei , Zheng Xuming , Phillips David Lee
Published: May 2007

Resonance Raman spectra were obtained for (E)-β-nitrostyrene in cyclohexane solution with excitation wavelengths in resonance with the charge transfer (CT)-band absorption spectrum. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion predominantly along the nominal NO2 symmetric stretch mode (ν14), the nominal CC stretch mode (ν8), the nominal benzene ring stretch mode (ν9), accompanied by a smaller amount of motion along the nominal ONO symmetric bend/benzene ring stretch mode (ν34), the nominal CCH in-plane bending mode (ν20), the nominal HCCH in-plane bending mode (ν18), the nominal NO2 asymmetric stretch mode (ν11), the nominal C–N stretch/benzene ring breathing mode (ν27), and the nominal CCC trigonal bending mode (ν25). A preliminary resonance Raman intensity analysis was done and these results for (E)-β-nitrostyrene were compared to results previously reported for several nitrobenzene and trans-stilbene compounds. The differences and similarities between the CT-band resonance Raman spectra and vibrational reorganizational energies for (E)-β-nitrostyrene relative to those for nitrobenzene and trans-stilbene were briefly discussed.
Resonant Raman scattering and surface phonon modes of hollow ZnS microspheres
Authors: Luo Y. Y. , Duan G. T. , Li G. H.
Published: May 2007

The optical properties of hollow ZnS microspheres were studied. The Raman scattering spectra of the hollow ZnS microspheres depend strongly on the excitation power, and at an excitation power of about I0∕10, a strong resonant Raman scattering spectrum with high-order longitudinal optical modes and weak high-order surface optical modes appeared. The weak surface phonons are sensitive to the surrounding medium and are considered to come from the surface defects of the microspheres. The frequency of the weak surface phonon is in agreement with the prediction calculated on the basis of the dielectric continuum approach.
Low-field approach to double resonance in nuclear quadrupole resonance of spin-1 nuclei
Authors: Prescott D. W. , Olmedo O. , Soon S. , Sauer K. L.
Published: May 2007

Using double-resonance conditions, in which the Larmor frequency of a spin-1∕2 nucleus is matched to one of the nuclear quadrupole resonance frequencies of a spin-1 nucleus, the authors demonstrate increased cross relaxation between the two nuclear spin species. They calculate the cross-relaxation rate using the motionally averaged heterogeneous dipole Hamiltonian as a perturbation to the combined quadrupole and Zeeman Hamiltonians. Using this cross-relaxation rate, in addition to hydrogen and nitrogen autorelaxation rates, expressions governing spin-1∕2 and spin-1 spin-lattice relaxation are determined. With ammonium nitrate, containing nitrogen (spin-1) and hydrogen (spin-1∕2), increased nitrogen signal and spin-lattice relaxation are demonstrated, using fields less than 120G. The cross-relaxation rate is also measured and an overall signal/noise improvement by a factor of 2.3±0.1 is attained.
Synchrotron x-ray spectroscopy of Eu∕HNO3 aqueous solutions at high temperatures and pressures and Nb-bearing silicate melt phases coexisting with hydrothermal fluids using a modified hydrothermal diamond anvil cell and rail assembly
Authors: Mayanovic Robert A. , Anderson Alan J. , Bassett William A. , Chou I-Ming
Published: May 2007

A modified hydrothermal diamond anvil cell (HDAC) rail assembly has been constructed for making synchrotron x-ray absorption spectroscopy, x-ray fluorescence, and x-ray mapping measurements on fluids or solid phases in contact with hydrothermal fluids up to ∼900°C and 700MPa. The diamond anvils of the HDAC are modified by laser milling grooves or holes, for the reduction of attenuation of incident and fluorescent x rays and sample cavities. The modified HDAC rail assembly has flexibility in design for measurement of light elements at low concentrations or heavy elements at trace levels in the sample and the capability to probe minute individual phases of a multiphase fluid-based system using focused x-ray microbeam. The supporting rail allows for uniform translation of the HDAC, rotation and tilt stages, and a focusing mirror, which is used to illuminate the sample for visual observation using a microscope, relative to the direction of the incident x-ray beam. A structure study of Eu(III) aqua ion behavior in high-temperature aqueous solutions and a study of Nb partitioning and coordination in a silicate melt in contact with a hydrothermal fluid are described as applications utilizing the modified HDAC rail assembly.
Analytic functions for the three-body potential of the helium trimer
Authors: Røeggen I.
Published: May 2007

The three-body potential for the ground state of the helium trimer is determined by an extended geminal model. The basis set for the calculation is an uncontracted (19s,7p,6d,5f,4g,2h) set of Gaussian-type functions. Three different types of configurations were considered: (i) equilateral triangles, (ii) linear configurations with R12=R23, and (iii) a set of pseudorandom configurations. The interatomic distances were selected within the interval [3.0,9.0]bohrs. The computed points have been fitted to global potential functions. The fit is characterized by a maximum absolute error equal to 0.69μEh and a mean error equal to −0.018μEh.
Optical amplification in multilayer photorefractive liquid crystal films
Authors: Sun Xiudong , Pei Yanbo , Yao Fengfeng , Zhang Jianlong , Hou Chunfeng
Published: May 2007

Photorefractive two-beam coupling was performed in fullerene C60-doped nematic liquid crystal cell. Photorefractive gain coefficient as high as 1386cm−1 was obtained at an input pump power as weak as 16mW. However, the thin film nature led to a small gain of 16. By the use of several such cells stacked together to increase the overall interaction length, the optical gain was improved greatly, and the pump power to obtain the highest optical gain was reduced. At 1.2V, the highest gain of 141 was obtained for the 40μW signal at an input pump power of 12mW.
Size dependent damping in picosecond dynamics of single nanomagnets
Authors: Barman A. , Wang S. , Maas J. , Hawkins A. R. , Kwon S. , Bokor J. , Liddle A. , Schmidt H.
Published: May 2007

The authors use time-resolved cavity-enhanced magneto-optical Kerr spectroscopy to study the damping of magnetization precession in individual cylindrical nickel nanomagnets. A wide range of shapes (diameters of 5μm–125nm and aspect ratio: 0.03–1.2) is investigated. They observe a pronounced difference in damping between the micro- and nanomagnets. Microscale magnets show large damping at low bias fields, whereas nanomagnets exhibit bias field-independent damping. This behavior is explained by the interaction of in-plane and out-of-plane precession modes in microscale magnets that results in additional dissipative channels. The small and robust damping values on the nanoscale are promising for implementation of controlled precessional switching schemes in nanomagnetic devices.
Sound field inside acoustically levitated spherical drop
Authors: Xie W. J. , Wei B.
Published: May 2007

The sound field inside an acoustically levitated small spherical water drop (radius of 1mm) is studied under different incident sound pressures (amplitude p0=2735–5643Pa). The transmitted pressure ptr in the drop shows a plane standing wave, which varies mainly in the vertical direction, and distributes almost uniformly in the horizontal direction. The maximum of ptr is always located at the lowermost point of the levitated drop. Whereas the secondary maximum appears at the uppermost point if the incident pressure amplitude p0 is higher than an intermediate value (3044Pa), in which there exists a pressure nodal surface in the drop interior. The value of the maximum ptr lies in a narrow range of 2489–3173Pa, which has a lower limit of 2489Pa when p0=3044Pa. The secondary maximum of ptr is rather small and only remarkable at high incident pressures.
Hole mobility of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine investigated by using space-charge-limited currents
Authors: Chu Ta-Ya , Song Ok-Keun
Published: May 2007

The hole mobility of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) at various thicknesses (50–1000nm) has been estimated by using space-charge-limited current measurements. A thin layer of buckminsterfullerene has been used for a quasi-Ohmic contact between NPB and indium tin oxide. The mobility at bulk property dominant thickness is in excellent agreement with the results from time-of-flight method. For the typical thickness of organic light-emitting devices, the hole mobility of NPB, 1.63×10−5cm2∕Vs, at 50nm is smaller than the value 7.64×10−4cm2∕Vs at 1000nm (electric field at 0.1MV∕cm). The authors suggest that the lower mobility is caused by the interfacial trap states.
Growth and properties of Mg-doped In-polar InN films
Authors: Wang Xinqiang , Che Song-Bek , Ishitani Yoshihiro , Yoshikawa Akihiko
Published: May 2007

Mg doping into In-polar InN layers for different Mg fluxes is performed on GaN templates by molecular beam epitaxy, and their electrical and optical properties are investigated. Mg concentration is linearly proportional to Mg-beam flux, indicating that the Mg-sticking coefficient is almost unity. With Mg doping, electron concentration decreases by the effect of carrier compensation, but it begins to increase with further increasing Mg flux because of Mg-related donorlike-defects formation. For the partially carrier-compensated Mg-doped InN, two photoluminescence peaks are observed; one is originated from free-to-acceptor emission with an acceptor activation energy of about 61meV and the other is similar to the conventional band-to-band emission.
Theory of non-Condon emission from the interchain exciton in conjugated polymer aggregates
Authors: Bittner Eric R. , Karabunarliev Stoyan , Herz Laura M.
Published: May 2007

The authors present here a simple analysis that explains the apparent strengthening of electron phonon interaction upon aggregation in conjugated polymer materials. The overall scheme is that of an intermolecular Herzberg-Teller effect whereby sidebands of a forbidden transition are activated by oppositely phased vibrations. The authors show that upon aggregation, the 0-0 emission becomes symmetry forbidden and the apparent redshift and remaining vibronic structure are due to sideband (0-1,0-2, etc.) emission. At higher temperatures, the 0-0 peak is due to thermal population in a higher lying even-parity vibronic state rather than direct emission from the odd-paritied lowest intermolecular vibronic state.
Epitaxial behavior and transport properties of PrBaCo2O5 thin films on (001) SrTiO3
Authors: Yuan Z. , Liu J. , Chen C. L. , Wang C. H. , Luo X. G. , Chen X. H. , Kim G. T. , Huang D. X. , Wang S. S. , Jacobson A. J. , Donner W.
Published: May 2007

Highly conductive PrBaCo2O5.5+δ thin films were grown on (001) SrTiO3 by pulsed laser deposition. Microstructural studies from synchrotron x-ray diffraction and transmission electron microscopy reveal that the as-grown PrBaCo2O5.5+δ films are a-axis oriented with excellent single crystallinity. Two domain structures with c axes in the plane directions parallel to the substrate surface were found with an atomic sharp interface. Transport property and isothermal magnetoresistance measurements for both as-grown and post-annealing were done to understand the physical properties of the films. An abnormal positive magnetoresistance effect was observed in the postannealed films, which suggests that the spins in the system are polarized easier.
Raman scattering by thin film nanomosaic rutile TiO2
Authors: Aita Carolyn Rubin
Published: May 2007

Thin TiO2 films with rutile short-range atomic order grown at room temperature have a nanostructure of rectangular domains based on a faulted rutile structure. Raman scattering by nanomosaic rutile in single layer TiO2 and TiO2–Al2O3 nanolaminate films is reported here. In all architectures, the Eg phonon mode frequency is similar to bulk but the A1g mode frequency is significantly blueshifted. These results are different from published Raman scattering spectra of other nanocrystalline rutile TiO2. A model for nanomosaic rutile is presented in which TiO6 octahedra in the faulted regions are severely distorted with a lengthened equatorial Ti–O bond and a shortened apical Ti–O bond. The observed A1g mode blueshift is a consequence of the shortened apical bond.
Effect of electromigration in the anodic Al interconnect on melting of flip chip solder joints
Authors: Ouyang Fan-Yi , Tu K. N. , Kao Chin-Li , Lai Yi-Shao
Published: May 2007

Melting of eutectic SnPb flip chip solder joints has been observed to occur frequently in dc electromigration tested with current density above 1.5×104A∕cm2 at an ambient temperature of 100°C. It has been found that it is not due to the Joule heating of the solder bump itself, but rather due to the Joule heating of the on-chip Al interconnects. The current density in the Al approaches 2×106A∕cm2 and electromigration has especially generated voids at the anode of the Al. The damage has greatly increased the resistance of the Al, which produces the heat needed to melt the solder joint. The results of electrothermal coupling analysis show that when the resistance of the Al line changed threefold, the solder bump melted.
Integrating demography and fire management: an example from Florida scrub
Authors: Menges Eric S.
Published: May 2007

In this work, I have used life-history and demographic data to define fire return intervals for several types of Florida scrub, a xeric shrubland where fire is the dominant ecological disturbance but where fire suppression is a major issue. The datasets combine chronosequence and longitudinal approaches at community and population levels. Resprouting shrubs, which dominate most types of Florida scrub, recover rapidly after fires (although their limits under frequent fires are not well known) and also increasingly dominate long-unburned areas. These dominant shrubs can prosper over a range of fire return intervals. Obligate-seeding scrub plants, which often have persistent seed banks, can be eliminated by frequent fire but often decline with infrequent fire. Population viability analyses of habitat specialists offer more precision in suggesting ranges of appropriate fire return intervals. For two types of Florida scrub (rosemary scrub and oak–hickory scrub), plant-population viability analyses narrow the interval and suggest more frequent fires than do previous recommendations, at intervals of 15–30 and 5–12 years, respectively. Variation in fire regimes in time and space (pyrodiversity) is recommended as a bet-hedging fire-management strategy and to allow co-existence of species with disparate life histories.
Hierarchies of cause: understanding rarity in an endemic shrub Verticordia staminosa (Myrtaceae) with a highly restricted distribution
Authors: Yates Colin J. , Ladd Philip G. , Coates David J. , McArthur Shelley
Published: May 2007

Verticordia staminosa C.Gardner & A.C.George subsp. staminosa is an extremely rare shrub occurring as an isolated population of ~1200 plants on a granite outcrop in the semi-arid agricultural region of Western Australia, separated from its closest relative V. staminosa subsp. cylindracea by 400 km. We aimed to determine a hierarchy of causes for explaining the extremely restricted distribution of subsp. staminosa, and to determine the genetic relationships among populations within both subspecies. We measured allozyme variation in all known populations of the two subspecies. There were exceptionally high levels of genetic divergence between subsp. staminosa and subsp. cylindracea, including an apparent duplication of the gene encoding phosphoglucomutase, leading to an additional gene in subsp. cylindracea. These findings combined with UPGMA analysis indicate a very long period of historical separation, perhaps originating in the early Pleistocene. Genetic variation was partitioned mostly between rather than within populations, with very low levels of genetic variation within populations of both subspecies. For subsp. staminosa we quantified seed production for three consecutive years and demography for five consecutive years. We used transition matrix models to describe the shrub’s population dynamics and stochastic simulations to explicitly compare the effects of low rainfall and disturbance on population viability. Verticordia staminosa subsp. staminosa produces large numbers of seeds each year and has flower to fruit ratios greater than reported for related rare and common congeners. Seedling recruitment occurs in most years, with pulses in the wettest years. The mean finite population growth rate was 1.031. Elasticity analyses showed that population growth rate was more sensitive to stasis of established plants than to seedling recruitment. Population viability declined with lower rainfall and increased fire-related mortality of adult plants. Rarity in subsp. staminosa is best explained by evolutionary history and the interaction of climate change and disturbances such as fire that kill plants. Climatic fluctuations since the late Pliocene might have led to stochastic extinction episodes of populations on other granite outcrops, resulting in the currently restricted distribution. We discuss the implications of our findings for management of the species.
Biological survey and setting priorities for flora conservation in Western Australia
Authors: Keighery Greg J. , Gibson Neil , van Leeuwen Stephen , Lyons Michael N. , Patrick Sue
Published: May 2007

Biological survey has been an integral component of conservation planning in Western Australia for >30 years, providing baseline data for reserve selection and the management of biodiversity at the genetic, species and community levels. Flora surveys are particularly important, given the diverse and poorly documented nature of the state’s vascular flora. Surveys have been conducted at the following four scales: regional, subregional, local and individual species. At all scales, flora surveys have provided detail on individual taxon distribution, have identified previously unknown or unrecognised taxa, have located presumed extinct taxa and have substantially contributed to information on the distribution of threatened flora. Regional-scale surveys normally involve multidisciplinary teams studying a broad selection of the biota. These combined plot-based data are used to develop a ‘classify-then-model’ approach to assessment of comprehensiveness, adequacy and representativeness of the regional conservation reserve system. These regional models describe the broad-scale patterning of common taxa but their utility in reflecting patterns in naturally rare or highly restricted taxa is uncertain. Results from recent surveys show poor correlations between floristic patterning and other components of the biota.
Recent advances in restoration ecology, with a focus on the Banksia woodland and the smoke germination tool
Authors: Rokich Deanna P. , Dixon Kingsley W.
Published: May 2007

This paper details some of the recent research findings concerning restoration needs of the Banksia woodland in Western Australia, including the importance of, and recent advances in, smoke-technology research. Research has enabled testing of a wide spectrum of restoration technologies that enhance plant replacement at sites via treatments of the topsoil seedbank, broadcast seed and seedlings. By the use of smoke technology, which in some systems produces a 48-fold increase in the total number of germinants and a 3-fold increase in the number of species at restoration sites, improved species replacement is a very real possibility in Banksia woodland. At the same time, some commonly employed practices in restoration are a cause for concern, including the application of a herbicide widely used to control a priority Banksia-woodland weed and fire-suppressing agents used to assist fire management. These findings may have broader implications for restoration programs.
Rietveld-based mineralogical quantitation of deferrified oxisol clays
Authors: Alves M. E. , Mascarenhas Y. P. , French D. H. , Vaz C. P. M.
Published: May 2007

Although the mineralogical quantitative analysis of the soil clay fraction can provide useful information for the improvement of soil management practices, the quantitation of all clay components normally requires a combination of different analytical techniques, which makes this determination expensive and time-consuming. One alternative for more expeditious mineralogical quantitations consists of using the Rietveld method for the treatment of X-ray diffraction (XRD) data. In this study we evaluate the accuracy of the mineralogical quantitative analyses of oxisol deferrified clays carried out with the application of the Rietveld method to XRD data obtained for both non-spray- and spray-dried samples. Linear regression analyses were carried out for comparing the XRD-Rietveld results with those calculated from X-ray fluorescence spectroscopy (XRF) data. Correspondence was observed between the XRD-Rietveld and XRF-derived data, confirming the potential utility of the Rietveld method for soil clay mineralogical quantitative analysis. Although sample preparation by using the spray drying procedure tended to improve XRD mineralogical quantitation, accurate results can be also achieved when this procedure is not available in the XRD laboratory.
Persistent improvements in the structure and hydraulic conductivity of a Ferrosol due to liming
Authors: Kirkham J. M. , Rowe B. A. , Doyle R. B.
Published: May 2007

Changes in the soil structure and hydraulic conductivity of an Acidic Red Ferrosol were measured in a long-term (1968–2003) fertiliser experiment on pasture in north-western Tasmania, Australia. Studies were initiated following observations of both softer soil surface and cracking on plots that had received 15 t/ha of ground agricultural limestone. Liming decreased penetration resistance and increased hydraulic conductivity. These structural improvements were associated with increased mean dry aggregate size, a small increase in wet aggregate stability, higher exchangeable calcium levels, and increased plant growth, but a 9% decrease in total soil organic carbon in the surface 50 mm. This decrease in organic carbon was not associated with deterioration in soil structure, as may have been anticipated. This was probably because total organic C was still 82 g/kg on unlimed plots. Decreases in soil penetration resistance due to liming increased the likelihood of pugging from livestock but may improve ease of tillage.
This research demonstrates that liming can improve the structure of a well-aggregated Ferrosol as well as its previously reported effects of increasing soil pH and yields of pasture and barley despite decreasing organic C.
A genome-wide RNA interference screen identifies putative chromatin regulators essential for E2F repression
Authors: Lu Jianrong , Ruhf Marie-Laure , Perrimon Norbert , Leder Philip
Published: May 2007

Regulation of chromatin structure is critical in many fundamental cellular processes. Previous studies have suggested that the Rb tumor suppressor may recruit multiple chromatin regulatory proteins to repress E2F, a key regulator of cell proliferation and differentiation. Taking advantage of the evolutionary conservation of the E2F pathway, we have conducted a genome-wide RNAi screen in cultured
Drosophila
cells for genes required for repression of E2F activity. Among the genes identified are components of the putative Domino chromatin remodeling complex, as well as the Polycomb Group (PcG) protein-like fly tumor suppressor, L3mbt, and the related CG16975/dSfmbt. These factors are recruited to E2F-responsive promoters through physical association with E2F and are required for repression of endogenous E2F target genes. Surprisingly, their inhibitory activities on E2F appear to be independent of Rb. In
Drosophila
,
domino
mutation enhances cell proliferation induced by E2F overexpression and suppresses a loss-of-function
cyclin E
mutation. These findings suggest that potential chromatin regulation mediated by Domino and PcG-like factors plays an important role in controlling E2F activity and cell growth.
Mixture models and exploratory analysis in networks
Authors: Newman M. E. J. , Leicht E. A.
Published: May 2007

Networks are widely used in the biological, physical, and social sciences as a concise mathematical representation of the topology of systems of interacting components. Understanding the structure of these networks is one of the outstanding challenges in the study of complex systems. Here we describe a general technique for detecting structural features in large-scale network data that works by dividing the nodes of a network into classes such that the members of each class have similar patterns of connection to other nodes. Using the machinery of probabilistic mixture models and the expectation–maximization algorithm, we show that it is possible to detect, without prior knowledge of what we are looking for, a very broad range of types of structure in networks. We give a number of examples demonstrating how the method can be used to shed light on the properties of real-world networks, including social and information networks.
A sperm-specific Na
+
/H
+
exchanger (sNHE) is critical for expression and
in vivo
bicarbonate regulation of the soluble adenylyl cyclase (sAC)
Authors: Wang Dan , Hu Jie , Bobulescu I. Alexandru , Quill Timothy A. , McLeroy Paul , Moe Orson W. , Garbers David L.
Published: May 2007

We previously identified a sperm-specific Na
+
/H
+
exchanger (sNHE) principally localized to the flagellum. Disruption of the
sNHE
gene in mice resulted in absolute male infertility associated with a complete loss of sperm motility. Here, we show that the sNHE-null spermatozoa fail to develop the cAMP-dependent protein tyrosine phosphorylation that coincides with the functional maturation occurring upon incubation in capacitating conditions
in vitro
. Both the sperm motility defect and the lack of induced protein tyrosine phosphorylation are rescued by the addition of cell-permeable cAMP analogs, suggesting that cAMP metabolism is impaired in spermatozoa lacking sNHE. Our analyses of the bicarbonate-dependent soluble adenylyl cyclase (sAC) signaling pathway in sNHE-null sperm cells reveal that sNHE is required for the expression of full-length sAC, and that it is important for the bicarbonate stimulation of sAC activity in spermatozoa. Furthermore, both codependent expression and coimmunoprecipitation experiments indicate that sNHE and sAC associate with each other. Thus, these two proteins appear to be components of a signaling complex at the sperm flagellar plasma membrane. We propose that the formation of this complex efficiently modulates intracellular pH and bicarbonate levels through the rapid and effective control of sAC and sNHE activities to facilitate sperm motility regulation.
Inhibitor of growth 4 (ING4) is up-regulated by a low K intake and suppresses renal outer medullary K channels (ROMK) by MAPK stimulation
Authors: Zhang Xin , Lin Dao-Hong , Jin Yan , Wang Ke-Sheng , Zhang Yan , Babilonia Elisa , Wang ZhiJian , Wang Zhiqin , Giebisch Gerhard , Han Ze-Guang , Wang Wen-Hui
Published: May 2007

Dietary K intake plays an important role in the regulation of renal K secretion: a high K intake stimulates whereas low K intake suppresses renal K secretion. Our previous studies demonstrated that the Src family protein-tyrosine kinase and mitogen-activated protein kinase (MAPK) are involved in mediating the effect of low K intake on renal K channels and K secretion. However, the molecular mechanism by which low K intake stimulates MAPK is not completely understood. Here we show that inhibitor of growth 4 (ING4), a protein with a highly conserved plant homeodomain finger motif, is involved in mediating the effect of low K intake on MAPK. K restriction stimulates the expression of ING4 in the kidney and superoxide anions, and its related products are involved in mediating the effect of low K intake on ING4 expression. We used HEK293 cells to express ING4 and observed that expression of ING4 increased the phosphorylation of p38 and ERK MAPK, whereas down-regulation of ING4 with small interfering RNA decreased the phosphorylation of p38 and ERK. Immunocytochemistry showed that ING4 was expressed in the renal outer medullary potassium (ROMK)-positive tubules. Moreover, ING4 decreased K currents in
Xenopus
oocytes injected with ROMK channel cRNA. This inhibitory effect was reversed by blocking p38 and ERK MAPK. These data provide evidence for the role of ING4 in mediating the effect of low K intake on ROMK channel activity by stimulation of p38 and ERK MAPK.