bluuebunny/crossref_metadata_2025 huggingface dataset:
Search for fourth sound propagation in supersolid He4
Authors: Aoki Y. , Kojima H. , Lin X.
Published: May 2008

A systematic study is carried out to search for fourth sound propagation solid He4 samples below 500mK down to 40mK between 25 and 56bar using the techniques of heat pulse generator and titanium superconducting transition edge bolometer. If solid He4 is endowed with superfluidity below 200mK, as indicated by recent torsional oscillator experiments, theories predict fourth sound propagation in such a supersolid state. If found, fourth sound would provide convincing evidence for superfluidity and a new tool for studying the new phase. The search for a fourth sound-like mode is based on the response of the bolometers to heat pulses traveling through cylindrical samples of solids grown with different crystal qualities. Bolometers with increasing sensitivity are constructed. The heater generator amplitude is reduced to the sensitivity limit to search for any critical velocity effects. The fourth sound velocity is expected to vary as ∝ρs∕ρ. Searches for a signature in the bolometer response with such a characteristic temperature dependence are made. The measured response signal has not so far revealed any signature of a new propagating mode within a temperature excursion of 5μK from the background signal shape. Possible reasons for this negative result are discussed. Prior to the fourth sound search, the temperature dependence of heat pulse propagation was studied as it transformed from “second sound” in the normal solid He4 to transverse ballistic phonon propagation. Our work extends the studies of [V. Narayanamurti and R. C. Dynes, Phys. Rev. B 12, 1731 (1975)] to higher pressures and to lower temperatures. The measured transverse ballistic phonon propagation velocity is found to remain constant (within the 0.3% scatter of the data) below 100mK at all pressures and reveals no indication of an onset of supersolidity. The overall dynamic thermal response of solid to heat input is found to depend strongly on the sample preparation procedure.
Photoresonance and conductivity of surface electrons on liquid He3
Authors: Konstantinov D. , Kono K. , Monarkha Y.
Published: May 2008

Resonance variations of the in-plane conductivity of surface electrons (SEs) over liquid He3 induced by microwave (MW) radiation of a fixed frequency are experimentally and theoretically studied for low temperature scattering regimes (T<0.5K). The system was tuned to resonance by varying the amplitude of the vertical electric field which shifts the positions of SE Rydberg levels. The line-shape change and reversing of the sign of the effect are found to be opposite to those reported previously for weak vertical electric fields. A theoretical analysis of conductivity of the SE system heated due to decay of electrons excited to the second Rydberg level by the MW explains well the line-shape variations observed. It shows also that shifting the MW resonance into the range of weak vertical fields leads to important qualitative changes in the line-shape of SE conductivity which are in agreement with observations reported previously.
Dynamical structure factor of two-dimensional electrons over a helium film
Authors: Venturini P. C. , Studart N. , Rino J. P.
Published: May 2008

The dynamical structure factor of a two-dimensional electrons trapped to a helium film deposited on a solid substrate is determined through molecular dynamics simulations for different film thicknesses and two substrates. The phases of the system varying from the classical Wigner crystal to strong and intermediate- correlated electron liquid as well the influence of the film thickness and substrate are analyzed in the numerical experiments.
Construction of a generalized gradient approximation by restoring the density-gradient expansion and enforcing a tight Lieb–Oxford bound
Authors: Zhao Yan , Truhlar Donald G.
Published: May 2008

Recently, a generalized gradient approximation (GGA) to the density functional, called PBEsol, was optimized (one parameter) against the jellium-surface exchange-correlation energies, and this, in conjunction with changing another parameter to restore the first-principles gradient expansion for exchange, was sufficient to yield accurate lattice constants of solids. Here, we construct a new GGA that has no empirical parameters, that satisfies one more exact constraint than PBEsol, and that performs 20% better for the lattice constants of 18 previously studied solids, although it does not improve on PBEsol for molecular atomization energies (a property that neither functional was designed for). The new GGA is exact through second order, and it is called the second-order generalized gradient approximation (SOGGA). The SOGGA functional also differs from other GGAs in that it enforces a tighter Lieb–Oxford bound. SOGGA and other functionals are compared to a diverse set of lattice constants, bond distances, and energetic quantities for solids and molecules (this includes the first test of the M06-L meta-GGA for solid-state properties). We find that classifying density functionals in terms of the magnitude μ of the second-order coefficient of the density gradient expansion of the exchange functional not only correlates their behavior for predicting lattice constants of solids versus their behavior for predicting small-molecule atomization energies, as pointed out by Perdew and co-workers [Phys. Rev. Lett. 100, 134606 (2008); PerdewPhys. Rev. Lett. 80, 891 (1998)], but also correlates their behavior for cohesive energies of solids, reaction barriers heights, and nonhydrogenic bond distances in small molecules.
Theory of resonance energy transfer involving nanocrystals: The role of high multipoles
Authors: Baer Roi , Rabani Eran
Published: May 2008

A theory for the fluorescence resonance energy transfer (FRET) between a pair of semiconducting nanocrystal quantum dots is developed. Two types of donor-acceptor couplings for the FRET rate are described: dipole-dipole (d-d) and the dipole-quadrupole (d-q) couplings. The theory builds on a simple effective mass model that is used to relate the FRET rate to measureable quantities such as the nanocrystal size, fundamental gap, effective mass, exciton radius, and optical permittivity. We discuss the relative contribution to the FRET rate of the different multipole terms, the role of strong to weak confinement limits, and the effects of nanocrystal sizes.
The potential energy curves of low-lying electronic states of S2O
Authors: Han Huixian , Suo Bingbing , Jiang Zhenyi , Wang Yubin , Wen Zhenyi
Published: May 2008

Potential energy curves (PECs) of the symmetric and asymmetric bent S2O molecules are constructed using the configuration-based multireference second order perturbation theory and multireference configuration interaction with single and double excitations. Based on the PECs, the equilibrium structures of the ground state and several low-lying excited states, as well as the vertical and adiabatic transition energies, are obtained. Furthermore, avoided crossings and intersections displayed on the PECs are studied. The dissociation of states for the asymmetric bent S2O, especially the predissociative of the excited C̃A′1 state, is also discussed in detail. According to our calculations, the predissociation limit of C̃A′1 is found to be located in the vicinity of 26 or 25 (reckoning in the zero-point energy revision) S–S stretching vibration level, which is in good agreement with the available experimental data.
Anomalous structural and mechanical properties of solids confined in quasi-one-dimensional strips
Authors: Chaudhuri Debasish , Sengupta Surajit
Published: May 2008

We show using computer simulations and mean field theory that a system of particles in two dimensions, when laterally confined by a pair of parallel hard walls within a quasi-one-dimensional channel, possesses several anomalous structural and mechanical properties not observed in the bulk. Depending on the density ρ and the distance between the walls Ly, the system shows structural characteristics analogous to a weakly modulated liquid, a strongly modulated smectic, a triangular solid, or a buckled phase. At fixed ρ, a change in Ly leads to many re-entrant discontinuous transitions involving changes in the number of layers parallel to the confining walls depending crucially on the commensurability of interlayer spacing with Ly. The solid shows resistance to elongation but not to shear. When strained beyond the elastic limit, it fails undergoing plastic deformation but surprisingly, as the strain is reversed, the material completely recovers and returns to its original undeformed state. We obtain the phase diagram from mean field theory and finite size simulations and discuss the effect of fluctuations.
Effects of pressure and temperature on the carrier transports in organic crystal: A first-principles study
Authors: Wang L. J. , Li Q. K. , Shuai Z.
Published: May 2008

By employing density-functional theory coupled with Holstein–Peierls model, we investigate the pressure and temperature dependence of the hole and electron mobilities in naphthalene single crystal from atmospheric pressure up to 2.1GPa (at room temperature) and from 5to296K (at ambient pressure). It is found that the pressure reduces the electron-phonon coupling strength and enhances the mobilities. Importantly, we point out that only when temperature-dependent structure modifications are taken into account can one better describe the temperature-dependent transport behavior. Especially, the band to hopping crossover transition temperature for the electron transport in the c′-axis is calculated to be around 153K, which is close to the experimental result of between 100 and 150K. If this temperature-dependent structure modifications were neglected, the transition temperature would be only about 23K, as previously obtained [L. J. Wang et al., J. Chem. Phys. 127, 044506 (2007)].
Maximum Caliber: A variational approach applied to two-state dynamics
Authors: Stock Gerhard , Ghosh Kingshuk , Dill Ken A.
Published: May 2008

We show how to apply a general theoretical approach to nonequilibrium statistical mechanics, called Maximum Caliber, originally suggested by E. T. Jaynes [Annu. Rev. Phys. Chem. 31, 579 (1980)], to a problem of two-state dynamics. Maximum Caliber is a variational principle for dynamics in the same spirit that Maximum Entropy is a variational principle for equilibrium statistical mechanics. The central idea is to compute a dynamical partition function, a sum of weights over all microscopic paths, rather than over microstates. We illustrate the method on the simple problem of two-state dynamics, A↔B, first for a single particle, then for M particles. Maximum Caliber gives a unified framework for deriving all the relevant dynamical properties, including the microtrajectories and all the moments of the time-dependent probability density. While it can readily be used to derive the traditional master equation and the Langevin results, it goes beyond them in also giving trajectory information. For example, we derive the Langevin noise distribution rather than assuming it. As a general approach to solving nonequilibrium statistical mechanics dynamical problems, Maximum Caliber has some advantages: (1) It is partition-function-based, so we can draw insights from similarities to equilibrium statistical mechanics. (2) It is trajectory-based, so it gives more dynamical information than population-based approaches like master equations; this is particularly important for few-particle and single-molecule systems. (3) It gives an unambiguous way to relate flows to forces, which has traditionally posed challenges. (4) Like Maximum Entropy, it may be useful for data analysis, specifically for time-dependent phenomena.
In situ transmission electron microscopy study on the crystallization of GeTe binary alloy
Authors: Kim Eun Tae , Lee Jeong Yong , Kim Yong Tae
Published: May 2008

Microstructural properties of GeTe thin films were investigated by an in situ heating method within a high voltage electron microscope (HVEM). The results confirm that the transformation from an amorphous state to a fcc crystalline state yields a GeTe binary alloy with a ring-shaped amorphous structure. The fcc structured GeTe transforms into a GeTe orthorhombic structure during the experiment. The crystallization behavior of the GeTe orthorhombic structure in the HVEM is quite different from thermal crystallization. Our observation of real-time structural change confirms that the relaxed amorphous structure participates in the crystallization process in the electron beam irradiation condition.
Ion thermalization using pressure transients in a quadrupole ion trap coupled to a vacuum matrix-assisted laser desorption ionization source and a reflectron time-of-flight mass analyzer
Authors: Papanastasiou D. , Belgacem O. , Sudakov M. , Raptakis E.
Published: May 2008

Efficient trapping and detection of intact peptide ions is demonstrated in a quadrupole ion trap (QIT) coupled to an external vacuum matrix-assisted laser desorption ionization (MALDI) source. Deactivation of metastable ions generated by MALDI is achieved in a pressure transient environment inside the QIT established by pulsing gas to access the higher pressures required for fast thermalization, without affecting vacuum conditions in the ion source and time-of-flight (TOF) mass analyzer. Pressure transients are experimentally determined and a threshold of ∼10mTorr is identified where internally excited ions, which commonly observed to dissociate upon injection in a QIT, are stabilized. Fragment-free spectra are presented for a set of peptides by using 2,5-dihydroxybenzoic acid (DHB) as a matrix, and significantly reduced fragmentation is observed by using a-cyano-4-hydroxycinnamic acid (CHCA). Intact peptide spectra of a protein tryptic digest are also recorded with CHCA. The process of translational cooling for externally injected ions in a dynamic pressure environment is visualized by using ion trajectory simulations that employ hard sphere collisions. Statistical theory of dynamic equilibrium of ions stored in rf fields is applied to our QIT to characterize a translationally thermalized ion cloud, to explain observed ejection efficiency into the TOF mass analyzer, and to further discuss collisional deactivation of metastable ions.
Effect of frequency and temperature on microwave-induced magnetoresistance oscillations in two-dimensional electron systems
Authors: Iñarrea Jesús
Published: May 2008

Experimental results on microwave-induced magnetoresistance oscillations in two-dimensional electron systems show a similar behavior regarding temperature and microwave frequency. It is found that these oscillations tend to quench when frequency or temperature increases, approaching magnetoresistance to the response of the dark system. In this work, we show that this experimental behavior can be addressed on the same theoretical basis. Microwave radiation forces the electron orbits to move back and forth being damped by interaction with the lattice. We show that this damping dramatically depends on microwave frequency and also on temperature.
Understanding of transmission in the range of high-order photonic bands in thin opal film
Authors: Romanov S. G. , Bardosova M. , Povey I. M. , Pemble M. E. , Sotomayor Torres C. M.
Published: May 2008

Diffraction in the face centered cubic lattice cannot explain some minima observed in the transmission spectra of self-assembled opal films. Here, we compared them with minima observed in the transmission spectra of a hexagonal close packed monolayer of spheres of the same diameter. The identity of the sphere packing on the surface of the opal film and in the sphere monolayer was demonstrated by the light diffraction at the sample surfaces. It was shown that excitation of surface propagating modes in the opal film is responsible for the formation of additional minima in opal film transmission.
Heteroepitaxial growth of GaAs on (100) Ge/Si using migration enhanced epitaxy
Authors: Tanoto H. , Yoon S. F. , Loke W. K. , Chen K. P. , Fitzgerald E. A. , Dohrman C. , Narayanan B.
Published: May 2008

In this paper, heteroepitaxial growth of GaAs on nominal (100) Ge/Si substrate was investigated. The root-mean square surface roughness of the sample where the first few monolayers of the GaAs were nucleated by migration enhanced epitaxy (MEE) is four times smaller compared to the sample without such a process, indicating better surface planarity. From the (004) x-ray diffraction rocking curve measurement, the full width at half maximum of the GaAs layer nucleated by MEE is 40% lower compared to that of the GaAs layer without such a process, indicating better crystal quality. Furthermore, it was found that the sample where the GaAs layer was nucleated by MEE experienced early relaxation. As the MEE process promotes two-dimensional growth, the GaAs layer where nucleation was initiated by such a process has fewer islandlike formations. This leads to a pseudomorphically grown GaAs layer, which experiences higher strain compared to the GaAs layer with more islandlike formations, where most relaxation occurs on the free surface of the islands. Therefore, for the same layer thickness, the GaAs layer on (100) Ge/Si substrate where nucleation was initiated by MEE relaxed first.
Green phosphorescent light-emitting diodes from polymer doped with iridium complex
Authors: Lee Seung-Joon , Park Jin Su , Song Myungkwan , Yoon Kyung-Jin , Kim Young Inn , Jin Sung-Ho , Seo Hoe-Joo
Published: May 2008

We demonstrate efficient organic light-emitting diodes by using a phosphorescent host/guest system consisting of a recently developed green electrophosphorescent molecule, bis[(4,6-difluorophenyl)-8-methylpyridinato-N,C2′)iridium pyrazinate [(dfmppy)2Irprz], as the guest and a blend of poly(N-vinylcarbazole) (PVK) with 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as the host and different cathode structures such as a triple layer of BAlq∕LiF∕Al and a bilayer of CsF∕Al. The electrophosphorescence emission was characteristic of (dfmppy)2Irprz, with its maximum at 563nm with Commission International de L’Eclairage coordinates of (0.43, 0.53). The device with 0.5wt% of (dfmppy)2Irprz in PVK/PBD (60:40wt%) with a CsF (2nm)∕Al bilayer exhibited an external quantum efficiency of 6.2%, luminescence efficiency of 17.3cd∕A, luminous power efficiency of 24.2lm∕W, and maximum brightness of 10220cd∕m2.
Detection of chloride ions using an integrated Ag∕AgCl electrode with AlGaN∕GaN high electron mobility transistors
Authors: Hung S. C. , Wang Y. L. , Hicks B. , Pearton S. J. , Dennis D. M. , Ren F. , Johnson J. W. , Rajagopal P. , Roberts J. C. , Piner E. L. , Linthicum K. J. , Chi G. C.
Published: May 2008

Al Ga N ∕ Ga N high electron mobility transistors (HEMTs) with an Ag∕AgCl gate exhibit significant changes in channel conductance upon exposing the gate region to various concentrations of chloride (Cl−) ion. The Ag∕AgCl gate electrode, prepared by potentiostatic anodization, changes electrical potential when it encounters Cl− ions. This gate potential changes lead to a change of surface charge in the gate region of the HEMT, inducing a higher positive charge on the AlGaN surface, and increasing the piezoinduced charge density in the HEMT channel. These anions create an image positive charge on the Ag gate metal for the required neutrality, thus increasing the drain current of the HEMT. The HEMT source-drain current was highly dependent on Cl− ion concentration. The limit of detection achieved was 1×10−8M using a 20×50μm2 gate sensing area.
Cutoff effect of light transmission through structured metal films
Authors: Liu Shi-qiang , Wang Qian-jin , Yin Xiao-gang , Huang Cheng-ping , Zhu Yong-yuan
Published: May 2008

The optical transmission spectra of structured metal films, which were fabricated by depositing a thin metal layer on the perforated metal surface, have been experimentally studied in this paper. They exhibit an extraordinary cutoff effect at certain wavelength, beyond which no efficient light transmission can be achieved. A systematic study reveals that the cutoff wavelength is dependent on the lattice period but not on the hole shape or size, making a difference to the cutoff of waveguide. To understand the effect, a qualitative explanation has been proposed.
Transversely tapered hybrid electro-optic polymer/sol-gel Mach–Zehnder waveguide modulators
Authors: Enami Y. , Mathine D. , DeRose C. T. , Norwood R. A. , Luo J. , Jen A. K.-Y. , Peyghambarian N.
Published: May 2008

We show results of a proposed hybrid modulator structure that reduces both the optical loss and half wave voltage (Vπ). A sol-gel waveguide core transversely sandwiched between two Mach–Zehnder arms of electro-optic (EO) polymer cores enables an adiabatic transverse transition between the sol-gel and the EO polymer cores without the need for Y branches. The undercladding thickness is reduced to 3.7μm with negligible further optical loss from the bottom electrode. EO modulation with Vπ of 1.8V at 1550nm is demonstrated using a guest-host EO polymer, with an optical insertion loss of 13.7dB in the transverse magnetic mode.
Enhancement of charge and energy storage in sol-gel derived pure and La-modified PbZrO3 thin films
Authors: Parui Jayanta , Krupanidhi S. B.
Published: May 2008

Antiferroelectric lanthanum-modified PbZrO3 thin films with La contents between 0 and 6at.% have been deposited on Pt(111)∕Ti∕SiO2∕Si substrate by sol-gel route. On the extent of La-modification, maximum polarization (Pmax) and recoverable energy density (W) have been enhanced followed by their subsequent reduction. A maximum Pmax (∼0.54C∕m2 at ∼60MV∕m) as well as a maximum W (∼14.9J∕cc at ∼60MV∕m) have been achieved on 5% La modification. Both Pmax and W have been found to be strongly dependent on La-induced crystallographic orientations.
Low-noise wideband ultrasound detection using polymer microring resonators
Authors: Huang Sheng-Wen , Chen Sung-Liang , Ling Tao , Maxwell Adam , O’Donnell Matthew , Guo L. Jay , Ashkenazi Shai
Published: May 2008

Polymer microring resonators for low-noise, wideband ultrasound detection are presented. Using a nanoimprinting technique, we fabricated polymer microring resonators with a quality factor of 6000 resulting in high sensitivity to ultrasound. A noise-equivalent pressure of 0.23kPa over 1–75MHz and a detection bandwidth of over 90MHz at −3dB were measured. These results demonstrate the potential of polymer microring resonators for high-frequency ultrasound and photoacoustic imaging. For a typical photoacoustic imaging test case, the high sensitivity demonstrated in these devices would increase imaging depth by a factor of 3 compared to state-of-the-art polyvinylidene fluoride detectors.
Carrier-envelope phase stabilization by controlling compressor grating separation
Authors: Li Chengquan , Mashiko Hiroki , Wang He , Moon Eric , Gilbertson Steve , Chang Zenghu
Published: May 2008

Previously, we demonstrated the stabilization of the carrier-envelope (CE) phase of the laser pulses from a chirped pulse amplifier by controlling the effective grating separation in the stretcher. In this work, we show that the CE phase can also be stabilized to ∼230mrad by controlling the grating separation in a compressor. The cutoff frequency of the piezoelectric transducer mounted grating for the phase stabilization system was found to be higher than 60Hz.
Lifetime and diffusion length of photogenerated minority carriers in single-crystalline n-type β-FeSi2 bulk
Authors: Ootsuka Teruhisa , Suemasu Takashi , Chen Jun , Sekiguchi Takashi , Hara Yoshiaki
Published: May 2008

We have evaluated the lifetime and diffusion length of photogenerated minority carriers (holes) in single-crystalline n-type β-FeSi2 bulk grown by chemical vapor transport. The diffusion length measured by optical-beam-induced current agreed well with that measured by electron-beam-induced current, that is, 51 and 38μm, respectively, for samples annealed at 800°C for 8h. The decay curve of photoconductivity obtained by 1.31 and 1.55μm light pulses was well fitted by assuming a carrier lifetime of approximately a few microseconds. The mobility of photogenerated minority carriers was estimated to be approximately 200–360cm2∕Vs from the measured lifetime and diffusion length.
Slow Bloch modes for enhancing the absorption of light in thin films for photovoltaic cells
Authors: Duché David , Escoubas Ludovic , Simon Jean-Jacques , Torchio Philippe , Vervisch Wilfried , Flory François
Published: May 2008

This paper deals with the improvement of “light harvesting” in photovoltaic cells by using photonic nanostructures. We theoretically study a poly-3-hexylthiophene/[6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PCBM) thin film periodically nanostructured in order to increase its absorption. The periodic nanostructuration allows “slow Bloch modes” (group velocity close to zero) to be coupled inside the material. The P3HT/PCBM photonic crystal parameters are adjusted to maximize the density of Bloch modes and obtain flat dispersion curves. The light-matter interaction is thus strongly enhanced, which results in a 35.6% increase of absorption in the 600–700nm spectral range.
Resonant Raman scattering probe of alloying effect in ZnMgO thin films
Authors: Kong J. F. , Shen W. Z. , Zhang Y. W. , Yang C. , Li X. M.
Published: May 2008

We have presented a detailed resonant Raman scattering investigation for the alloying effect in hexagonal Zn1−xMgxO (x⩽0.323) thin films grown by pulsed laser deposition. Alloy-induced longitudinal optical (LO) phonon resonance effect has been achieved from the Raman peak shift, lineshape, and intensity through changing the Mg composition and temperature to tune the ZnMgO bandgap. By the aid of theoretical analysis combining with the extrinsic Fröhlich interaction mediated via a localized exciton, we demonstrate the pronounced outgoing resonance behavior for the LO phonons in ZnMgO, where the localized exciton due to alloy disorder dominates the resonance processes.
Electric field control of the magnetic state in BiFeO3 single crystals
Authors: Lee Seoungsu , Ratcliff W. , Cheong S-W. , Kiryukhin V.
Published: May 2008

Single crystals of multiferroic BiFeO3 were investigated using neutron scattering. Application of an electric field reversibly switches ferroelastic domains, inducing changes in the magnetic structure which follows rotation of the structural domains. In addition, electric fields can be used to control the populations of the equivalent magnetic domains within a single ferroelastic domain, possibly via field-induced strain.
Experimental demonstration of relativistic magnetron with modified output configuration
Authors: Daimon M. , Itoh K. , Imada G. , Jiang W.
Published: May 2008

A modified configuration of relativistic magnetron with diffraction output has been investigated experimentally by using repetitive pulsed power generator “ETIGO-IV” (400kV, 13kA, 120ns, 1Hz). The purpose is to verify the improved microwave conversion efficiency predicted by numerical simulations [M. Daimon and W. Jiang, Appl. Phys. Lett. 91, 191503 (2007)]. The experiments have concentrated on comparison between the output microwave powers obtained by using the modified and the conventional configurations of relativistic magnetron. The results have been in general agreement with that obtained by the simulations.
Effect of the barrier composition on the polarization fields in near UV InGaN light emitting diodes
Authors: Knauer A. , Wenzel H. , Kolbe T. , Einfeldt S. , Weyers M. , Kneissl M. , Tränkle G.
Published: May 2008

The electroluminescence from near ultraviolet (UV) light emitting diodes containing InGaN multiple quantum wells (MQWs) with GaN, AlGaN, and InAlGaN barriers was investigated. Based on band-structure calculations the observed wavelength shift in the peak emission with increasing injection current is attributed to the screening of the polarization fields and to band gap renormalization. InGaN MQWs with almost zero net polarization have been realized. No blueshift in the emission spectra of these devices was observed over the entire current range.
Cdk5-mediated regulation of the PIKE-A-Akt pathway and glioblastoma cell invasion
Authors: Liu Ren , Tian Bo , Gearing Marla , Hunter Stephen , Ye Keqiang , Mao Zixu
Published: May 2008

Isoform A of phosphatidylinositol 3-kinase enhancer (PIKE-A) is a newly identified prooncogenic factor that has been implicated in cancer cell growth. How PIKE-A activity is regulated in response to growth signal is poorly understood. Here, we demonstrate that cyclin dependent kinase 5 (Cdk5), a protein known to function mainly in postmitotic neurons, directly phosphorylates PIKE-A at Ser-279 in its GTPase domain in glioblastoma cells. This phosphorylation event stimulates PIKE-A GTPase activity and the activity of its downstream effector Akt. Growth signal activates Cdk5 and results in a Cdk5-dependent accumulation of phosphorylated PIKE-A and activation of Akt in the nucleus. Furthermore, PIKE-A phosphorylation and Cdk5 are increased in human glioblastoma specimens. Phosphorylation of PIKE-A by Cdk5 mediates growth factor-induced migration and invasion of human glioblastoma cells. Together, these findings identify PIKE as the first Cdk5 target in cancer cells, revealing a previously undescribed regulatory mechanism that mediates growth signal-induced activation of PIKE-A/Akt and tumor invasion.
Body pedagogies, P/policy, health and gender
Authors: Evans John , Rich Emma , Allwood Rachel , Davies Brian
Published: May 2008

Schools within a ‘knowledge economy’ nurture and endorse particular ‘corporeal orientations’, that is to say, ascribe value, meaning and potential to ‘the body’ (particular bodies) in time, place and space. Such processes reflect wider (national and global) socio‐economic trends. In contemporary culture, these processes increasingly celebrate particular virtues—‘flexible identities’, the manifest aspects of ‘performance’ and ‘corporeal perfection’ (usually defined as ‘the slender ideal’). Calling on the voices of a number of young women (aged 11–18) the article illustrates how these processes can intersect to seriously damage some people's health, perhaps especially those of young women and girls. The analyses suggest that the expectations of a ‘knowledge economy’ relating to the body and health enter the school system through two forms of P/policy: ‘formal’, state‐sanctioned, usually legislated education Policy; and ‘informal’, mainly medical and health institution‐based, state ‘approved’ but non‐legislated, pseudo policy initiatives often merely reflecting expectations and pressures laundered through the popular media. Together, these P/policies define not only formal education but increasingly encode other aspects of school life, in effect, making ‘pedagogy’ everyone's concern, everywhere. The article highlights the relentless and inescapable nature of pedagogical activity in the Totally Pedagogised Micro Societies (TPMS) which schools have become.
Perceiving the Present and a Systematization of Illusions
Authors: Changizi Mark A. , Hsieh Andrew , Nijhawan Romi , Kanai Ryota , Shimojo Shinsuke
Published: May 2008

Over the history of the study of visual perception there has been great success at discovering countless visual illusions. There has been less success in organizing the overwhelming variety of illusions into empirical generalizations (much less explaining them all via a unifying theory). Here, this article shows that it is possible to systematically organize more than 50 kinds of illusion into a 7 × 4 matrix of 28 classes. In particular, this article demonstrates that (1) smaller sizes, (2) slower speeds, (3) greater luminance contrast, (4) farther distance, (5) lower eccentricity, (6) greater proximity to the vanishing point, and (7) greater proximity to the focus of expansion all tend to have similar perceptual effects, namely, to (A) increase perceived size, (B) increase perceived speed, (C) decrease perceived luminance contrast, and (D) decrease perceived distance. The detection of these empirical regularities was motivated by a hypothesis, called “perceiving the present,” that the visual system possesses mechanisms for compensating neural delay during forward motion. This article shows how this hypothesis predicts the empirical regularity.
Voices of young people with a history of specific language impairment (SLI) in the first year of post‐16 education
Authors: Palikara Olympia , Lindsay Geoff , Dockrell Julie E.
Published: May 2008

Background: Giving young people more and better opportunities to have their voices heard is a key feature of current educational policy and research internationally and in the UK.

Aims: To examine the views of young people with a history of specific language impairment (SLI) as they entered post‐16 education.

Methods & Procedures: A total of 54 students identified as having SLI at 8 years of age were followed up through primary and secondary school to post‐16 destinations. Most had been educated in mainstream schools. The young people were interviewed individually in relation to their perceptions of their special educational needs, their views on service provision, the role of family and friends as support systems, and their aspirations and barriers to future education at the early stages of post‐16 education, training and work.

Outcomes & Results: The young people were able to offer accurate accounts of their history of special educational needs and to explore issues related to their development. Most young people were aware of the specific difficulties they experienced and had positive views about the support offered to them during their schooling. All the young people had at least one person in their family or friendship circle to whom they could talk about their joys and concerns, and friendships were an important and positive element in their lives. Additionally, most had a positive view of their post‐16 courses, with comparable numbers hoping to undertake further study or training, or to go into work. They also had optimistic hopes for their futures five years ahead.

Conclusions: The current study has demonstrated that young people with a history of SLI have an awareness of their difficulties and of the impact that these needs have on different aspects of their lives. They were also able to provide valuable views of service provision, both in terms of evaluating the support they received and suggesting ways of improving it. Ascertaining the views of younger children with SLI and including them in decision‐making about their education and lives should be an important aspect of the role of those professionals working with this group of children. The study supports the importance of gaining the views of young people with SLI not only as a matter of rights, but also for the practical benefits that can ensue.
THE AMBIGUITY OF EUROPE:
Authors: Jenkins Richard
Published: May 2008

This paper takes its starting point in the public discourse, of politicians and academics, that suggests that Europe, specifically the European Union, is suffering from a ‘crisis of identity’. This is believed to stem from the recent enlargements, the pending ‘problem of Turkey’, and disarray over the European Constitution. This issue is addressed in two ways: first, through an exploration of the main current models and meanings of ‘Europe’, and second, applying an anthropological approach to identity, through examining the relationship between models and meanings of ‘Europe’ and local, regional, ethnic and national identities. In the first place, this suggests that there is not, and cannot be, agreement over the shape and meaning of ‘Europe’. There is, rather, rooted in histories, geographies, politics, and cultures, a range of different Europes, which only coincide imperfectly, at best. In the second place, Europe is always viewed from local, regional, ethnic and national points of view. Each approach converges on the same conclusion: there can never be a clear-cut, consensual unified model of Europe. This is a normal situation, not a crisis, and, if anything, is one of the strengths of the European Union project.
CROSS-STATE MOBILITY IN THE EU
Authors: Recchi Ettore
Published: May 2008

The first part of this paper describes the small but constant expansion of the cross-state mobile population within the EU in the two decades preceding the 2004 enlargement. This expansion is puzzling in the light of the economic growth and the income convergence of member states over the same period. While the level of geographical mobility within the EU is frequently held to be ‘low’, data show that it should have been even lower given the rise of prosperity and the decline of income differentials in the EU15. In fact, it is argued that pro-mobility policies and the rise of non-labour migration have countered the diminishing appeal of intra-EU mobility that might be expected on the basis of purely economic conditions. The second part of the paper discusses the rationales and reasons of mobility. A distinction is drawn between observers’ and social actors’ views of the benefits of free movement. While the former usually put an emphasis on economic rewards, the latter are more likely to stress emotional and identity-linked returns. Survey data on Western European citizens who have resettled in another EU member state are revealing of the multifaceted causes and consequences of geographical mobility. In particular, these data show that identification with Europe and support for EU institutions in the mobile population are strikingly higher than among the general population. While it is true that cross-state mobility can entail economic benefits raising productivity and innovation, its political dividends are possibly even clearer.
qpcR: an R package for sigmoidal model selection in quantitative real-time polymerase chain reaction analysis
Authors: Ritz Christian , Spiess Andrej-Nikolai
Published: May 2008

Summary: The qpcR library is an add-on to the free R statistical environment performing sigmoidal model selection in real-time quantitative polymerase chain reaction (PCR) data analysis. Additionally, the package implements the most commonly used algorithms for real-time PCR data analysis and is capable of extensive statistical comparison for the selection and evaluation of the different models based on several measures of goodness of fit.

Availability:  www.dr-spiess.de/qpcR.html.

Contact:  a.spiess@uke.uni-hamburg.de

Supplementary Information: Statistical evaluations of the implemented methods can be found at www.dr-spiess.de under ‘Supplemental Data’.
PhyloWidget: web-based visualizations for the tree of life
Authors: Jordan Gregory E. , Piel William H.
Published: May 2008

Summary: PhyloWidget is a web-based tool for the visualization and manipulation of phylogenetic tree data. It can be accessed online or downloaded as a standalone application. A simple URL-based API allows databases to easily link to and customize PhyloWidget for interactively viewing medium- to large-sized trees.

Availability: PhyloWidget is available for online use or download at http://www.phylowidget.org/. Its source code is released under the GNU General Public License.

Contact:  phylowidget@treebase.org
Effects of Soil Type, Source of Silicon, and Rate of Silicon Source on Development of Gray Leaf Spot of Perennial Ryegrass Turf
Authors: Nanayakkara U. N. , Uddin W. , Datnoff L. E.
Published: May 2008

Silicon amendments have been proven effective in controlling fungal diseases of various crops. However, effects of silicon amendments on gray leaf spot (Magnaporthe oryzae) of perennial ryegrass are not known. Studies were conducted in controlled-environment chambers and microplots where perennial ryegrass pots were buried among perennial ryegrass turf to determine the effects of silicon amendments on gray leaf spot development. Plants were grown in two soil types: peat:sand mix (soil Si = 5.2 mg/liter) and Hagerstown silt loam (soil Si = 70 mg/liter). Both soil types were amended with two sources of silicon—wollastonite and calcium silicate slag—at 0, 0.5, 1, 2, 5, and 10 metric tons/ha and 0, 0.6, 1.2, 2.4, 6, and 12 metric tons/ha, respectively. Nine-week-old perennial ryegrass was inoculated with M. oryzae. Gray leaf spot incidence and severity were assessed 2 weeks after inoculation. Gray leaf spot incidence and severity of perennial ryegrass significantly decreased by different rates of wollastonite and calcium silicate slag applied to both soils under both experimental conditions. Tissue silicon content increased consistently with increasing amount of silicon in the soils, while disease incidence decreased consistently with increasing tissue silicon content in all four soil and source combinations under both experimental conditions. These findings suggest that silicon amendments may be utilized in integrated gray leaf spot management programs on perennial ryegrass.
Integrating Plant Essential Oils and Kaolin for the Sustainable Management of Thrips and Tomato Spotted Wilt on Tomato
Authors: Reitz Stuart R. , Maiorino Giuseppina , Olson Steve , Sprenkel Richard , Crescenzi Aniello , Momol M. Timur
Published: May 2008

Thrips-vectored Tomato spotted wilt virus is one of the most devastating pest complexes affecting tomato in the southern United States and elsewhere. Field trials were conducted over 2 years to determine the effects of volatile plant essential oils and kaolin-based particle films on the incidence of tomato spotted wilt and population dynamics of Frankliniella spp. thrips. The essential oils, geraniol (a monoterpene constituent of various plant essential oils), lemongrass (Cymbopogon flexuosus) oil, and tea tree (Melaleuca alternifolii) oil, were compared with a standard insecticide treatment and an untreated control. All treatments were applied with and without kaolin, in a 5 × 2 factorial design. Although the treatments did not clearly affect the abundance of vector species, there were treatment differences in the incidence of tomato spotted wilt. When combined with kaolin, the three essential oils reduced tomato spotted wilt incidence by 32 to 51% in 2005 and by 6 to 25% in 2006 compared with the control. In both years, tea tree oil plus kaolin reduced tomato spotted wilt as well as the standard insecticide treatments. Overall, kaolin significantly increased yield by over 26% compared to treatments without kaolin. When applied with kaolin, the three essential oils produced yields similar to the insecticide standard. Therefore, naturally occurring products, such as essential oils and kaolin, could be used successfully to reduce insecticide use on tomatoes.
Improving Fungicide-Based Management of Ray Blight Disease in Tasmanian Pyrethrum Fields
Authors: Pethybridge Sarah J. , Hay Frank S. , Groom Tim , Wilson Calum R.
Published: May 2008

Ray blight disease, caused by Phoma ligulicola var. inoxydablis, is a serious threat to the Tasmanian pyrethrum industry. The management of this disease relies upon the strategic application of fungicides in early spring. A range of fungicides were assessed for their efficacy in controlling ray blight disease in Tasmanian pyrethrum fields, and the primary objective of this study was to increase fungicide options available to growers in different resistance groups. Fungicides were assessed under in vitro conditions, within five replicated-plot field trials over three seasons (2004 to 2006) and in single-plot trials over eight fields in 2005. In each of the field trials, regular assessments of disease intensity (defoliation severity and the incidence of stems with ray blight), stem height, and the number of flowers produced on each stem were made using stems as the primary sampling unit. Canopy reflectance at 830 nm and the Difference Vegetative Index, measured using a handheld multispectral radiometer, also were used to compare fungicide effects on green leaf area. The effect of fungicides on the dry weight of flowers, pyrethrin content within the flowers, flower maturity, and pyrethrin yield were determined. Under in vitro conditions, boscalid reduced both conidial germination and mycelial growth at concentrations of at least 0.16 μg/ml. In field trials 1 and 2 (in 2004), the premixed formulation of pyraclostrobin + boscalid (Pristine) increased pyrethrin yield by an average of 79% compared with nontreated plots over the two locations. Furthermore, in single-plot trials, pyraclostrobin + boscalid increased pyrethrin yield by 134 and 60% compared with the industry-recommended protocol (single application of azoxystrobin at 150 g a.i./ha [Amistar WG] and two additional applications of a tank mixture of difenoconazole at 125 g a.i./ha [Score] and chlorothalonil at 1,008 liters a.i./ha [Bravo 720] at 14- to 21-day intervals) and nontreated plots, respectively. In field trials 3 (in 2005) and 4 and 5 (in 2006), similar yield benefits also were produced by applying pyraclostrobin (Cabrio SC) or boscalid (Filan) alone or in combination with chlorothalonil (Bravo 720) at 1.4 liters of product per hectare, regardless of the rates of pyraclostrobin (250 and 125 g a.i./ha) and boscalid (500 and 250 g a.i./ha) used. These data were used to recommend the incorporation of boscalid to improve the fungicide-based management of ray blight disease. This decreases the number of applications of both strobilurin and triazole fungicides which have been used extensively for the management of ray blight and other diseases in Tasmanian pyrethrum fields and are prone to fungicide resistance development.
Application of a Preliminary Screen to Select Locally Adapted Resistant Rootstock and Soil Amendment for Integrated Management of Tomato Bacterial Wilt in Taiwan
Authors: Lin Chih-Hung , Hsu Shih-Tien , Tzeng Kuo-Ching , Wang Jaw-Fen
Published: May 2008

Host plant resistance and soil amendment (SA) have not been used extensively to manage tomato bacterial wilt caused by Ralstonia solanacearum due to their variable effects over locations. A preliminary screen was developed to increase the chances of identifying successful control measures under diverse conditions. Isolates from three production areas in Taiwan were collected and their virulence evaluated on tomato. Soil samples from four field sites were collected to evaluate ability to suppress the pathogen of SAs consisting of urea or slaked lime alone or combined at 30°C. The mixture of urea and slaked lime showed the best suppressive effect in three tested soils and was used in subsequent field experiments. Resistant eggplant (EG203) and tomato (Hawaii 7996) rootstocks, selected based on stable resistance against representative strains at the seedling stage, significantly reduced disease incidence in field experiments. EG203 grafted plants exhibited 0 to 2.8% wilted plants compared with 24.4 to 92.9% wilted nongrafted plants. Integrated use of Hawaii 7996 as the rootstock and SA provided significantly greater control of wilt than use of Hawaii 7996 as rootstock alone in only one of the four locations, whereas SA did not provide significant control effect when EG203 was used as the rootstock.