bluuebunny/crossref_metadata_2025 huggingface dataset:
Aligned single-walled carbon nanotubes by Langmuir–Blodgett technique
Authors: Jia Lu , Zhang Yafei , Li Jinyong , You Chang , Xie Erqing
Published: October 2008

Single-walled carbon nanotubes (SWNTs) were chemically functionalized with amphiphilic octadecylamine after purification. Lower density and highly oriented SWNTs were obtained via Langmuir–Blodgett (LB) technique. A model was introduced to explain the compression-induced alignment. The phase behavior of the spreading monolayer was studied by surface pressure-area isotherms at different temperatures and different compression speeds. The transferred LB films of SWNTs with different mean lengths were investigated by the field emission scanning electron microscopy, showing that SWNTs with average length at 1000–2000 nm have more preference of reorientation upon compression than shorter ones (∼500 nm), while SWNTs that are too long (∼3000 nm) would tangle together and the reorientation is weaker. Multilayers (up to 18 layers) of SWNTs were obtained with high transfer ratios (>0.93) and the UV-vis absorption spectra indicated that the layer-by-layer deposition was successful.
Electron dephasing scattering rate in two-dimensional GaAs/InGaAs heterostructures with embedded InAs quantum dots
Authors: Pagnossin I. R. , Meikap A. K. , Quivy A. A. , Gusev G. M.
Published: October 2008

We report a comprehensive study of weak-localization and electron-electron interaction effects in a GaAs/InGaAs two-dimensional electron system with nearby InAs quantum dots, using measurements of the electrical conductivity with and without magnetic field. Although both the effects introduce temperature dependent corrections to the zero magnetic field conductivity at low temperatures, the magnetic field dependence of conductivity is dominated by the weak-localization correction. We observed that the electron dephasing scattering rate τφ−1, obtained from the magnetoconductivity data, is enhanced by introducing quantum dots in the structure, as expected, and obeys a linear dependence on the temperature and elastic mean free path, which is against the Fermi-liquid model.
Localization and nonlinear transport in single walled carbon nanotube fibers
Authors: Ksenevich V. K. , Odzaev V. B. , Martunas Z. , Seliuta D. , Valusis G. , Galibert J. , Melnikov A. A. , Wieck A. D. , Novitski D. , Kozlov M. E. , Samuilov V. A.
Published: October 2008

Electrical and magnetotransport properties of single walled carbon nanotube (SWCNT) fibers are reported. The dependencies of resistance on temperature can be approximated by the Mott law for three-dimensional variable range hopping (VRH) below 80 K and by typical law for fluctuation induced tunneling model within the range of 80–300 K. Both negative and positive magnetoresistances (MRs) were observed. At low fields, MR is negative. Positive upturn was observed on the MR curves, which shifted to the high field’s values with temperature increase. The upturn field of the MR effect was shifted from 1.5 T at 2 K to a value of about 20 T at 40 K. The value of positive MR varies as exp(B2), which changes to B1/3 at sufficiently high fields as expected for the VRH transport. The model of VRH transport is illustrated by the influence of strong microwave field and terahertz radiation induced photocurrent manifestation at low temperatures.
Enhanced ferroelectric properties of Hf-doped bismuth titanate thin films on STO (111) substrates
Authors: Wang X. P. , Zhu J. , Luo W. B. , Zhang Y. , Li Y. R.
Published: October 2008

Bi 4 Ti 3 O 12 (BIT) and Hf-doped BIT (BTH) thin films have been fabricated on (111) SrTiO3 substrates with SrRuO3 bottom electrodes by pulsed laser deposition, respectively. X-ray photoelectron spectroscopy investigation revealed that Hf doping would strengthen the oxygen covalent bond to B-site ions, which could consolidate the BO6 octahedral structure in BTH. As confirmed by x-ray diffraction scans, including θ-2θ and Φ scans, both films were highly (104) oriented and showed triple-twin situation. Compared to the BIT films, the BTH films have significantly enhanced electrical properties with 3 times larger remanent polarization (2Pr=45.7 μC/cm2), 0.7 times smaller coercive field (2Ec=184 kV/cm), and better fatigue endurance (11.4% degradation). The difference of ionic radius and the strengthened covalency in BO6 octahedral structure are supposed to be the two aspects resulting in the enhancement of 2Pr value. The improved fatigue properties could be believed to result from the high activation energies of oxygen vacancy caused by Hf doping.
Detection of magnetic nanoparticle fusion by magnetic measurements
Authors: Jagodič Marko , Gyergyek Sašo , Jagličić Zvonko , Makovec Darko , Trontelj Zvonko
Published: October 2008

A ferrofluid composed of γ-Fe2O3 nanoparticles of an average diameter of 11 nm dispersed in n-decane was prepared. A series of magnetic measurements was carried out on samples frozen in a magnetic field and in zero magnetic field. The influence of interparticle interactions on the magnetic behavior of ferrofluids is addressed and the potential use of magnetic measurements in estimating the extent of nanoparticle fusion into clusters behaving as superspins is proposed.
Interface structure and anisotropic strain relaxation of nonpolar wurtzite (112¯) and (101¯) orientations: ZnO epilayers grown on sapphire
Authors: Chauveau J.-M. , Vennéguès P. , Laügt M. , Deparis C. , Zuniga-Perez J. , Morhain C.
Published: October 2008

The interface properties between nonpolar ZnO and sapphire have been studied using high resolution transmission electron microscopy. Two nonpolar orientations are investigated: a- and m-orientations corresponding to [112¯0] and [101¯0] crystallographic directions. After the definition of the epitaxial relationships and the resulting initial lattice mismatch, we show that nonpolar ZnO can be grown on sapphire with perfectly flat interfaces. Geometrical misfit dislocations are observed at the interface ZnO/sapphire and their density gives the residual strain in the layer. A strong anisotropy in the strain relaxation is found along the two perpendicular in-plane directions. This anisotropy may be explained in terms of initial anisotropic mismatch yielding different relaxation processes. A domain matching epitaxy is observed in m- and a-oriented layers for mismatches larger than 9% while a lattice matching epitaxy, in which the relaxation is driven by nucleation and glide of dislocations, is observed in a-oriented ZnO along the [0001] in-plane direction. In order to explain the observed relaxation the activated slip systems are calculated for both nonpolar orientations as a function of the in-plane stress due to the anisotropic mismatch. There is a major difference from the polar orientations. Low energy prismatic slip systems can be effective for plastic relaxation in the nonpolar orientations because they are no longer parallel to the growth direction, which is the case of c-oriented layers, nor to the applied stress. Our results can be directly extended to other nonpolar wurtzite structures such as III-nitrides.
Experimental evidence of tetrahedral interstitial and bond-centered Er in Ge
Authors: Decoster S. , De Vries B. , Wahl U. , Correia J. G. , Vantomme A.
Published: October 2008

We report on an emission channeling study of the lattice site location of implanted Er in Ge together with its thermal stability. We found direct experimental evidence of Er atoms located on the tetrahedral (T) interstitial site and on the bond-centered (BC) site, with a maximum total occupancy after annealing at 400°C. Whereas Er is expected to occupy the T site in a diamond crystal structure, the observation of BC Er in Ge is more surprising and believed to be related to the Er-vacancy defect in the split-vacancy complex configuration.
The vacancy in silicon: A critical evaluation of experimental and theoretical results
Authors: Bracht Hartmut , Chroneos Alexander
Published: October 2008

Recent experimental studies of Shimizu et al. [Phys. Rev. Lett. 98, 095901 (2007)] revealed an activation enthalpy of 3.6 eV for the vacancy contribution to Si self-diffusion. Although this value seems to be in accurate agreement with recent theoretical results, it is at variance with experiments on vacancy-mediated dopant diffusion in Si. In the present study we review results from electronic structure calculations and conclude that the calculations are consistent with an activation enthalpy of 4.5–4.6 eV rather than 3.6 eV for the vacancy contribution to self-diffusion. Moreover, our calculations predict activation enthalpies of 4.45 and 3.81 eV for the vacancy-mediated diffusion of phosphorus and antimony, respectively, in good agreement with the most recent experimental results.
Effect of laminar velocity profile variation on mixing in microfluidic devices: The sigma micromixer
Authors: Yakhshi Tafti Ehsan , Kumar Ranganathan , Cho Hyoung J.
Published: October 2008

The effect of the laminar velocity profile and its variation on mixing phenomena at the reduced scale is studied. It is shown that the diffusive mass flux between two miscible streams, flowing laminar in a microchannel, is enhanced if the velocity at their diffusion interface is increased. Based on this idea, an in-plane passive micromixing concept is proposed and implemented in a working device (sigma micromixer). This mixer shows considerable mixing performance by periodically varying the flow velocity profile, such that the maximum of the profile coincides with the transversely progressing diffusion fronts repeatedly throughout the mixing channel.
Fishtail effect and the vortex phase diagram of single crystal Ba0.6K0.4Fe2As2
Authors: Yang Huan , Luo Huiqian , Wang Zhaosheng , Wen Hai-Hu
Published: October 2008

By measuring the magnetization hysteresis loops of superconducting Ba0.6K0.4Fe2As2 single crystals, we obtained the high upper critical field and large current carrying ability, which point to optimistic applications. The fishtail (or second peak) effect is also found in the material, and the position of the vortex pinning force shows a maximum at 1∕3 of the reduced field, being consistent with the picture of vortex pinning by small size normal cores in the sample. Together with the resistive measurements, for the first time the vortex phase diagram is obtained for superconductor Ba0.6K0.4Fe2As2.
Enhancing electron transport in Si:P delta-doped devices by rapid thermal anneal
Authors: Goh K. E. J. , Augarten Y. , Oberbeck L. , Simmons M. Y.
Published: October 2008

We address the use of rapid thermal anneal (RTA) to enhance electron mobility and phase coherent transport in Si:P δ-doped devices encapsulated by low temperature Si molecular beam epitaxy while minimizing dopant diffusion. RTA temperatures of 500–700°C were applied to δ-doped layers encapsulated at 250°C. From 4.2K magnetotransport measurements, we find that the improved crystal quality after RTA increases the mobility/mean free path by ∼40% and the phase coherence length by ∼25%. Our results suggest that the initial capping layer has near optimal crystal quality and transport improvement achieved by a RTA is limited.
Phase field modeling of magnetization processes in growth twinned Terfenol-D crystals
Authors: Huang Yongxin Y. , Jin Yongmei M.
Published: October 2008

Phase field micromagnetic microelastic modeling is used to simulate magnetization processes in growth twinned Terfenol-D crystals under external magnetic field applied along the [112¯] growth direction. The simulations reveal complex domain microstructure evolution involving both magnetization rotation and domain wall motion. It is found that domains strongly interact across the (111) growth twin boundaries. The competitions among magnetostatic, elastic, and magnetocrystalline anisotropy energies are analyzed, which explains the underlying domain mechanisms responsible for the experimentally observed magnetostriction jump effect in growth twinned Terfenol-D crystals.
Super Schrödinger algebra in AdS/CFT
Authors: Sakaguchi Makoto , Yoshida Kentaroh
Published: October 2008

We discuss (extended) super-Schrödinger algebras obtained as subalgebras of the superconformal algebra psu(2,2∣4). The Schrödinger algebra with two spatial dimensions can be embedded into so(4,2). In the superconformal case the embedded algebra may be enhanced to the so-called super-Schrödinger algebra. In fact, we find an extended super-Schrödinger subalgebra of psu(2,2∣4). It contains 24 supercharges (i.e., 3/4 of the original supersymmetries) and the generators of so(6), as well as the generators of the original Schrödinger algebra. In particular, the 24 supercharges come from 16 rigid supersymmetries and half of 16 superconformal ones. Moreover, this superalgebra contains a smaller super-Schrödinger subalgebra, which is a supersymmetric extension of the original Schrödinger algebra and so(6) by eight supercharges (half of 16 rigid supersymmetries). It is still a subalgebra even if there are no so(6) generators. We also discuss super-Schrödinger subalgebras of the superconformal algebras, osp(8∣4) and osp(8∗∣4), and find super Schrödinger subalgebras in the same way.
Hopf bifurcation control in a congestion control model via dynamic delayed feedback
Authors: Guo Songtao , Feng Gang , Liao Xiaofeng , Liu Qun
Published: October 2008

A typical objective of bifurcation control is to delay the onset of undesirable bifurcation. In this paper, the problem of Hopf bifurcation control in a second-order congestion control model is considered. In particular, a suitable Hopf bifurcation is created at a desired location with preferred properties and a dynamic delayed feedback controller is developed for the creation of the Hopf bifurcation. With this controller, one can increase the critical value of the communication delay, and thus guarantee a stationary data sending rate for larger delay. Furthermore, explicit formulae to determine the period and the direction of periodic solutions bifurcating from the equilibrium are obtained by applying perturbation approach. Finally, numerical simulation results are presented to show that the dynamic delayed feedback controller is efficient in controlling Hopf bifurcation.
Common-emitter and common-base small-signal operation of the transistor laser
Authors: Faraji B. , Shi W. , Pulfrey D. L. , Chrostowski L.
Published: October 2008

We derive analytic expressions for the transistor laser in the common-emitter and common-base configuration and compare the performance of the transistor in these two modes of operation. We show that the common-base operation results in a wide-band, small-signal modulation response. This effect is due to reduced carrier lifetime in the base. The bandwidth equalization and the suppression of the relaxation oscillation frequency are shown. A bandwidth of 48 GHz is predicted for a vertical cavity laser biased at 10Ith.
Optically reconfigurable patterning for control of the propagation characteristics of a planar waveguide
Authors: Wang Y. , Klittnick A. , Clark N. A. , Keller P.
Published: October 2008

We demonstrate an easily fabricated all-optical and freely reconfigurable method of controlling the propagating characteristics of the optic path within a planar waveguide with low insertion losses by employing the optical patterning of the refractive index of an erasable and rewriteable photosensitive liquid crystal polymer cladding layer.
Ferromagnetic resonance signature of metallic Co clusters in ferromagnetic ZnCoO thin films
Authors: von Bardeleben H. J. , Jedrecy N. , Cantin J. L.
Published: October 2008

Highly Co-doped Zn0.7Co0.3O thin films that can be reproducibly grown ferromagnetic by pulsed laser deposition have been investigated by optical absorption and ferromagnetic resonance spectroscopy (FMR). The saturation magnetization depends strongly on the O2 content during the growth, the highest value being obtained for the lowest oxygen pressure conditions. Whereas the optical absorption spectra confirm the incorporation of Co as CoZn2+ in ZnO, the FMR spectra prove the additional presence of randomly oriented metallic Co nanoparticles. The angular variation in the FMR spectra allows us to determine in the most ferromagnetic film the effective magnetization, 4πM∼800 G at 300 K and the g factor, g=2.18, which is that of metallic Co. The fraction of the two species CoZn2+ and Co metal is estimated to be ∼3:1
Shape dependence of nonlinear optical behaviors of nanostructured silver and their silica gel glass composites
Authors: Zheng Chan , Du Yuhong , Feng Miao , Zhan Hongbing
Published: October 2008

Nanostructured Ag in shapes of nanoplate, nanowire, and nanoparticle, as well as their silica gel glass composites have been prepared and characterized. Nonlinear optical (NLO) properties were measured at 532 and 1064 nm using open aperture z-scan technique and studied from the view of shape effect. NLO behaviors of the nanostructured Ag are found to be shape dependent in suspensions at both the investigated wavelengths, although they originate differently. Comparing to the mother suspensions, the Ag/silica gel glass nanocomposites present rather dissimilar NLO behaviors, which is quite interesting for further studies.
Stress-induced and thermoelastic properties of Ni–Fe–Al melt-spun ribbon
Authors: Chernenko V. A. , Kanth B. Rajini , Mukhopadhyay P. K. , Kaul S. N. , Villa E. , Gambardella A. , Besseghini S.
Published: October 2008

Lattice parameters, elastic modulus, internal friction, superelasticity, and shape memory effect are studied in the vicinity of martensitic transformation (MT) exhibited by the Ni55Fe20Al25 melt-spun ribbon. In comparison to the melt-spun ribbons of other ferromagnetic shape memory alloys, Ni–Fe–Al ribbon has abnormally low elastic modulus, a record-breaking strength (>350 MPa), and large recoverable strain (up to 5%) due to both the superelastic and ordinary shape memory effects. The critical stress versus temperature phase diagram consists of two straight lines, indicating the formation of different stress-induced martensitic phases. The structural and thermodynamic results proved to be self-consistent.
Early stages of collapsing pentacene crystal by Au
Authors: Ihm Kyuwook , Chung Sukmin , Kang Tai-Hee , Cheong Sang-Wook
Published: October 2008

The characteristic feature of metal contacts with gold on organics is deterioration of the organic crystals during the contact formation. The unveiled key challenge is to probe dynamic details of the microscopic evolution of the organic crystal when the atomic Au is introduced. Here, we report how the collapse of the pentacene crystal is initiated even by a few Au atoms. Our results indicate that the gentle decoupling of intra and intermolecular π-π interactions causes the localization of the lowest unoccupied molecular orbital as well as the removal of cohesive forces between molecules, leading to the subsequent crystal collapse.
Highly efficient low-voltage cathodoluminescence of LaF3:Ln3+ (Ln=Eu3+,Ce3+,Tb3+) spherical particles
Authors: Wang Zhen-Ling , Chan H. L. W. , Li Hiu-Ling , Hao J. H.
Published: October 2008

Spherical particles of rare-earth doped LaF3 are synthesized through refluxing in glycerol/water media. The low-voltage cathodoluminescence of LaF3:Eu due to D50→F71 and D50→F72 transitions was found to be sensitive to the site that Eu3+ ions occupied. The luminous efficiency of LaF3:Ce3+, Tb3+ with green emission is improved from 1.53 to 2.02 lm/W compared with LaF3:Tb3+, due to the energy transfer processes from Ce3+ to Tb3+ ions. Our results suggest that the obtained spherical particles of rare-earth doped LaF3 are promising as highly efficient low-voltage cathodoluminescent phosphors, which have received considerably less attention.
Thin pentacene interlayer for polymer bulk-heterojunction solar cell
Authors: Kim Ju-Hyung , Huh Sung-Yoon , Kim Tae-il , Lee Hong H.
Published: October 2008

We demonstrate that introducing a thin pentacene layer between metal cathode and photoactive layer results in a better than 50% improvement in the power conversion efficiency of polymer bulk-heterojunction solar cell when compared with the cell without the interlayer. An additional path for electron transfer provided by the thin pentacene layer appears to be mainly responsible for the improvement along with the increase in the open circuit voltage that occurs with increasing pentacene thickness. The concepts of utilizing additional charge transfer route and exploiting possible change in open circuit voltage with the inserted layer could widen avenues for enhancing the device performance.
Current controlled random-access memory based on magnetic vortex handedness
Authors: Bohlens Stellan , Krüger Benjamin , Drews André , Bolte Markus , Meier Guido , Pfannkuche Daniela
Published: October 2008

The theoretical foundation for a nonvolatile memory device based on magnetic vortices is presented. We propose a realization of a vortex random-access memory (VRAM) containing vortex cells that are controlled by alternating currents only. The proposed scheme allows to transfer the vortex into an unambiguous binary state regardless of its initial state within a subnanosecond time scale. The vortex handedness defined as the product of chirality and polarization as a bit representation allows direct mechanisms for reading and writing the bit information. The VRAM is stable at room temperature.
Thermal decomposition products in arc evaporated TiAlN/TiN multilayers
Authors: Knutsson A. , Johansson M. P. , Persson P. O. Å. , Hultman L. , Odén M.
Published: October 2008

Cubic metastable Ti0.34Al0.66N/TiN multilayers were grown by reactive arc evaporation using Ti33–Al67 and Ti cathodes in a N2 atmosphere. X-ray diffractometry and high resolution transmission electron microscopy revealed that metastable c-Ti0.34Al0.66N partly decomposes after annealing at 900 °C into c-TiN rich and c-AlN rich phases with retained lattice coherency. Elemental mapping by energy dispersive x-ray spectroscopy showed a homogenous distribution of Ti and Al in the as-deposited 25 nm Ti0.34Al0.66N layers. The annealed Ti0.34Al0.66N layers exhibited coherent 5 nm domains with high Al content surrounded by a high Ti content matrix. This nanostructure formation is discussed in terms of spinodal decomposition.
Fiber laser pumped high average power single-cycle terahertz pulse source
Authors: Hoffmann Matthias C. , Yeh Ka-Lo , Hwang Harold Y. , Sosnowski Thomas S. , Prall Bradley S. , Hebling János , Nelson Keith A.
Published: October 2008

Near single-cycle terahertz pulse generation from lithium niobate crystal by optical rectification of pulses from an Yb:fiber laser/amplifier system was investigated. The pump laser supplied 250 fs duration pulses with 14 μJ energy at up to 1 MHz repetition rate. The terahertz pulse energy and average power exceeded 0.25 nJ and 0.25 mW, respectively. The average power was more than ten times higher than corresponding values achieved by using GaP as the nonlinear crystal under similar pumping conditions.
Transparent Al–Zn–Sn–O thin film transistors prepared at low temperature
Authors: Cho Doo-Hee , Yang Shinhyuk , Byun Chunwon , Shin Jaeheon , Ryu Min Ki , Park Sang-Hee Ko , Hwang Chi-Sun , Chung Sung Mook , Cheong Woo-Seok , Yoon Sung Min , Chu Hye-Yong
Published: October 2008

We have fabricated transparent bottom gate thin film transistors (TFTs) using Al-doped zinc tin oxide (AZTO) as active layers. The AZTO active layer was deposited by rf magnetron sputtering at room temperature. The AZTO TFT showed good TFT performance without postannealing. The field effect mobility and the subthreshold swing were improved by postannealing below 180 °C. The AZTO TFT exhibited a field effect mobility (μFET) of 10.1 cm2/V s, a turn-on voltage (Von) of 0.4 V, a subthreshold swing (S/S) of 0.6 V/decade, and an on/off ratio (Ion/Ioff) of 109.
Quantum effects on the formation of negative hydrogen ion by polarization electron capture in partially ionized dense hydrogen plasmas
Authors: Jung Young-Dae , Kato Daiji
Published: October 2008

The quantum effects on the formation of the negative hydrogen ion (H−) by the polarization electron capture process are investigated in partially ionized dense hydrogen plasmas. It is shown that the quantum effect strongly suppresses the electron capture radius as well as the cross section for the formation of the negative hydrogen ion. In addition, it has been found that the electron capture position is receded from the center of the projectile in decreasing the quantum effect of the plasma.
Simulation of high angle annular dark field scanning transmission electron microscopy images of large nanostructures
Authors: Pizarro J. , Galindo P. L. , Guerrero E. , Yáñez A. , Guerrero M. P. , Rosenauer A. , Sales D. L. , Molina S. I.
Published: October 2008

High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) is a powerful tool to quantify size, shape, position, and composition of nano-objects with the assessment of image simulation. Due to the high computational requirements needed, nowadays it can only be applied to a few unit cells in standard computers. To overpass this limitation, a parallel software (SICSTEM) has been developed. This software can afford HAADF-STEM image simulations of nanostructures composed of several hundred thousand atoms in manageable time. The usefulness of this tool is exemplified by simulating a HAADF-STEM image of an InAs nanowire.
Photonic crystals with SiO2–Ag “post-cap” nanostructure coatings for surface enhanced Raman spectroscopy
Authors: Kim Seok-min , Zhang Wei , Cunningham Brian T.
Published: October 2008

We demonstrate that the resonant near fields of a large-area replica molded photonic crystal (PC) slab can efficiently couple light from a laser to SiO2–Ag “post-cap” nanostructures deposited on the PC surface by a glancing angle evaporation technique for achieving high surface enhanced Raman spectroscopy (SERS) enhancement factor. To examine the feasibility of the PC-SERS substrate, the simulated electric field around individual Ag particles and the measured Raman spectrum of trans-1,2-bis(4pyridyl)ethane on the PC-SERS substrate were compared with those from an ordinary glass substrate coated with the same SiO2–Ag nanostructures.
Growth and observation of micro-organic crystals in two-dimensional glass nanovolume cell
Authors: Kobayashi Kaya , Koyama Hiroko , Ishikura Kodai , Mitsui Toshiyuki
Published: October 2008

A simple type of glass cell to control the organic crystal growth in microsize by electrochemical method is presented. We fabricated growth cells with electrodes patterned by photolithograph and nanoliter volume. They have several merits for growth of organic conductors in microsize, including confined growth volume, observable growth space, rapid growth cycle relative to conventional methods, and compatibility with existing microfabrication techniques. The real time observation of the crystal growth was performed. The results are discussed in terms of the growth mechanism, suggesting a possibility of another microscopic view of crystal growth.
Cavity-enhanced stimulated emission cross section in polymer microlasers
Authors: Djiango Martin , Kobayashi Takeyuki , Blau Werner J.
Published: October 2008

We report a cavity quantum electrodynamic enhancement of stimulated emission in polymer microlasers. The enhancement of the stimulated emission cross section is shown through the demonstration of laser action in the 40μm diameter cylindrical microcavities whose total molecular population density is below that theoretically required for the onset of lasing. The lower bound of the enhancement factor is estimated to be 3.9 based on the noncavity value of the stimulated emission cross section and the measured cavity quality factor.
Spin bias measurement based on a quantum point contact
Authors: Xing Yanxia , Sun Qing-feng , Wang Jian
Published: October 2008

Electron charge transport through a quantum point contact (QPC) driven by an asymmetric spin bias (SB) is studied. A large charge current is induced when the transmission coefficient of the QPC jumps from one integer plateau to the next. Furthermore, for an open external circuit, the induced charge bias instead of the charge current is found to be quite large. It provides an efficient and practical way to detect SB by using a very simple device, a QPC or a STM tip. In addition, with the aid of magnetic field, polarization direction of the SB can also be determined.
Shallow trench isolation liners and their role in reducing lattice strains
Authors: Floresca Herman C. , Wang J. G. , Kim M. J. , Smythe J. A.
Published: October 2008

Three spin-on dielectric (SOD) shallow trench isolation (STI) structures were studied: nitride liner, nitride liner with anisotropic amorphous silicon (a-Si) bottom fill, and nitride liner with thin conformal a-Si. All samples received the same SOD material conditions and final thermal oxidation. Convergent beam electron diffraction determined the induced STI strain and has been shown to accurately measure strain on 60nm active areas. The results revealed effects that the liners have in balancing stress induced by volume shrinkage of the SOD. The conformal a-Si liner decreased the shear force that causes dislocations that form at the bottom corners of STI structures.
C
-axis persistent current and Cooper-pair tunneling through intrinsic Josephson junctions in a ring-shaped YBa2Cu3O7−δ film
Authors: Mansour A. I. , Saber M. M. , Chow K. H. , Jung J.
Published: October 2008

We report the direct experimental observation of the temperature dependence of the persistent current Icj due to tunneling Cooper pairs along the c-axis intrinsic Josephson junctions integrated into YBa2Cu3O7−δ ring-shaped thin films. The measured Icj exhibits a linear temperature dependence over a wide range of temperatures well below Tc. Similar behavior was observed in different samples, confirming the reproducibility of the fabrication technique and the reliability of the results.
Epitaxial growth of MgO and Fe∕MgO∕Fe magnetic tunnel junctions on (100)-Si by molecular beam epitaxy
Authors: Miao G. X. , Chang J. Y. , van Veenhuizen M. J. , Thiel K. , Seibt M. , Eilers G. , Münzenberg M. , Moodera J. S.
Published: October 2008

Epitaxial growth of MgO barrier on Si is of technological importance due to the symmetry filtering effect of the MgO barrier in conjunction with bcc-ferromagnets. We study the epitaxial growth of MgO on (100)-Si by molecular beam epitaxy. MgO matches Si with 4:3 cell ratio, which renders Fe to be 45° rotated relative to Si, in sharp contrast to the direct epitaxial growth of Fe on Si. The compressive strains from Si lead to the formation of small angle grain boundaries in MgO below 5nm, and also affect the transport characteristics of Fe∕MgO∕Fe magnetic tunnel junctions formed on top.
Leakage mechanisms of self-assembled (BiFeO3)0.5:(Sm2O3)0.5 nanocomposite films
Authors: Yang H. , Wang H. , Zou G. F. , Jain M. , Suvorova N. A. , Feldmann D. M. , Dowden P. C. , DePaula R. F. , MacManus-Driscoll J. L. , Taylor A. J. , Jia Q. X.
Published: October 2008

Nanocomposite (BiFeO3)0.5:(Sm2O3)0.5 films were deposited on (001) oriented Nb-doped SrTiO3 substrates by pulsed laser deposition. The leakage current density versus electric field characteristics were investigated and compared with those of as-deposited and annealed pure BiFeO3 (BFO) thin films. The dominant leakage mechanisms of nanocomposite films were space-charge-limited current and Poole–Frenkle emission for positive and negative biases, respectively. The leakage current density of nanocomposite films was reduced three orders of magnitude in comparison with the as-deposited pure BFO films. The less oxygen vacancies in the BFO phase in the nanocomposite is believed to contribute to the leakage reduction.
Room temperature anomalous Hall effect in Co doped ZnO thin films in the semiconductor regime
Authors: Hsu H. S. , Lin C. P. , Chou H. , Huang J. C. A.
Published: October 2008

Observation of the room temperature (RT) anomalous Hall effect (AHE) and ferromagnetism in semiconducting like (carrier concentration ∼1019cm−3) Co-doped ZnO samples is reported. These small AHE signals match quantitatively with the magnetic hysteresis and can be correspondent to the intrinsic diluted magnetic oxide (DMO) effect with spin polarized carriers. The contribution to the DMO effect depends on the types of carriers and how they incorporated into the electric conduction, magnetic coupling, and the coupling between them. These findings can provide useful information in the study of the origin of RT ferromagnetism in ZnO-based DMO and for further application in spintronics.
High efficiency blue phosphorescent organic light-emitting device
Authors: Chopra Neetu , Lee Jaewon , Zheng Ying , Eom Sang-Hyun , Xue Jiangeng , So Franky
Published: October 2008

We have demonstrated a substantial enhancement in the efficiency of iridium (III) bis[(4,6-di-fluorophenyl)-pyridinate-N,C2′]picolinate based blue phosphorescent organic light-emitting devices (PHOLEDs). The efficiencies of PHOLEDs with conventional electron transport materials are low due to their low electron mobilities as well low triplet energies. High triplet energy electron transporting material with high electron mobility was used as a hole blocker to achieve efficient exciton confinement and good charge balance in the device thereby achieving a high current efficiency of 49cd∕A and an external quantum efficiency of 23%.
Effect of carcass suspension and cooking method on the palatability of three beef muscles as assessed by Korean and Australian consumers
Authors: Park B. Y. , Hwang I. H. , Cho S. H. , Yoo Y. M. , Kim J. H. , Lee J. M. , Polkinghorne R. , Thompson J. M.
Published: October 2008

A total of 36 steer carcasses (18 slaughtered in Australia and 18 slaughtered in Korea), where one side had been suspended by the hip (tenderstretch) and the other by the Achilles tendon were used to provide sensory and shear force samples from the Mm. triceps brachii, longissimus lumborum and semimembranosus. Sensory samples were cooked using grill (25 mm thick) and barbeque (BBQ, 4 mm thick) methods and served to 360 untrained Australian and 720 untrained Korean consumers. Australian consumers sensory tested grill and BBQ samples from Australian carcasses (216 samples), while Korean consumers sensory tested grill and BBQ samples from both Australian and Korean carcasses (a total of 432 samples). The three-way interaction between carcass suspension, cooking method and muscle was significant (P < 0.05) for tenderness, overall liking and a composite palatability score (MQ4), where the combination of BBQ cooking and hip suspension resulted in large increases in sensory scores for the M. semimembranosus. Variation in sensory scores and shear force are discussed in the context of possible interactions with cooking temperature. There was a significant (P < 0.05) first order interaction between consumer group and muscle for juiciness score. Consumer effects were significant (P < 0.05) for all sensory scores, being largest for juiciness (~8 sensory units), like flavour and overall liking (both ~6 sensory units) and MQ4 (~5 sensory units) scores, with the smallest effect on tenderness (~2 sensory units).
A brief note on diacritics
Authors: Kurzon Dennis
Published: October 2008

This short note relates to remarks made by Peter Daniels in his 2006 article ‘On beyond alphabets’ on diacritics which he defines as markers that have a consistent phonological function in the particular script. From examples taken from French, Czech and other languages using the roman script, it is shown that the principal function of diacritics is to set up contrasts among various graphemes. This is extrapolated to the Arabic and Perso-Arabic scripts, where it is shown that the dots above and below graphemes are in effect diacritics.
POPE—a tool to aid high-throughput phylogenetic analysis
Authors: Juliusdottir Thorhildur , Pettersson Fredrik , Copley Richard R.
Published: October 2008

Summary: POPE (Phylogeny, Ortholog and Paralog Extractor) provides an integrated platform for automatic ortholog identification. Intermediate steps can be visualized, modified and analyzed in order to assess and improve the underlying quality of orthology and paralogy assignments.

Availability: POPE is available for download from the website: http://www.well.ox.ac.uk/~tota/pope.

Contact:  tota@well.ox.ac.uk
Motions of the running horse and cheetah revisited: fundamental mechanics of the transverse and rotary gallop
Authors: Bertram John E.A. , Gutmann Anne
Published: October 2008

Mammals use two distinct gallops referred to as the transverse (where landing and take-off are contralateral) and rotary (where landing and take-off are ipsilateral). These two gallops are used by a variety of mammals, but the transverse gallop is epitomized by the horse and the rotary gallop by the cheetah. In this paper, we argue that the fundamental difference between these gaits is determined by which set of limbs, fore or hind, initiates the transition of the centre of mass from a downward–forward to upward–forward trajectory that occurs between the main ballistic (non-contact) portions of the stride when the animal makes contact with the ground. The impulse-mediated directional transition is a key feature of locomotion on limbs and is one of the major sources of momentum and kinetic energy loss, and a main reason why active work must be added to maintain speed in locomotion. Our analysis shows that the equine gallop transition is initiated by a hindlimb contact and occurs in a manner in some ways analogous to the skipping of a stone on a water surface. By contrast, the cheetah gallop transition is initiated by a forelimb contact, and the mechanics appear to have much in common with the human bipedal run. Many mammals use both types of gallop, and the transition strategies that we describe form points on a continuum linked even to functionally symmetrical running gaits such as the tölt and amble.
Cheater genotypes in the parthenogenetic antPristomyrmex punctatus
Authors: Dobata Shigeto , Sasaki Tomonori , Mori Hideaki , Hasegawa Eisuke , Shimada Masakazu , Tsuji Kazuki
Published: October 2008

Cooperation is subject to cheating strategies that exploit the benefits of cooperation without paying the fair costs, and it has been a major goal of evolutionary biology to explain the origin and maintenance of cooperation against such cheaters. Here, we report that cheater genotypes indeed coexist in field colonies of a social insect, the parthenogenetic antPristomyrmex punctatus. The life history of this species is exceptional, in that there is no reproductive division of labour: all females fulfil both reproduction and cooperative tasks. Previous studies reported sporadic occurrence of larger individuals when compared with their nest-mates. These larger ants lay more eggs and hardly take part in cooperative tasks, resulting in lower fitness of the whole colony. Population genetic analysis showed that at least some of these large-bodied individuals form a genetically distinct lineage, isolated from cooperators by parthenogenesis. A phylogenetic study confirmed that this cheater lineage originated intraspecifically. Coexistence of cheaters and cooperators in this species provides a good model system to investigate the evolution of cooperation in nature.
Ruptured Jejunal Diverticulum Due to a Single-Band Small Bowel Obstruction
Authors: Durai Rajaraman , Sinha Ashish , Khan Mihir , Hoque Happy , Kerwat Rajab
Published: October 2008

Jejunal diverticulosis is rare and often goes unnoticed until complications occur. The diverticula are true, acquired diverticula and often asymptomatic. Jejunal diverticulosis can be associated with diverticulosis of the duodenum, ileum, and colon. Here we describe a patient with known severe diverticular disease of the large bowel, who presented acutely with abdominal pain and signs of generalised peritonitis. Laparotomy showed ruptured jejunal diverticulosis with a single band over the terminal ileum, causing small bowel obstruction. Spontaneous perforation of a jejunal diverticulum is rare and is usually an intraoperative finding. One should exclude a precipitating cause, such as coexisting distal obstruction, stricture, or a foreign body.
Implementation of a Positive Youth Development Program in a Chinese Context: The Role of Policy, Program, People, Process, and Place
Authors: Shek Daniel T. L. , Sun Rachel C. F.
Published: October 2008

In this paper, a case study is presented based on one school, conducted to examine the factors that influenced the process and quality of implementation of the Tier 1 Program of the Project P.A.T.H.S. Through interviews with the school contact person and focus group interviews with the instructors, an integration of the findings showed that several factors related to the program, people, process, policy, and place (5 “P”s) facilitated the implementation process of the Tier 1 Program in the school. Obstacles and difficulties with reference to the 5 “P”s that affected the quality of implementation were also identified. Overall, the quality of program implementation in the school was good, and the program was well received by the program implementers. Implications of the present findings for future program implementation with reference to school administrative arrangements and implementation issues are discussed.
School-Related Factors in the Implementation of a Positive Youth Development Project in Hong Kong
Authors: Shek Daniel T. L. , Chak Yammy L. Y. , Chan Candace W. Y.
Published: October 2008

Individual and focus group interviews were conducted to identify school-related factors that influence the process and quality of implementation of the Tier 1 Program of the Project P.A.T.H.S. in Hong Kong. Results of this case study approach showed that the program implementation quality was generally high. Factors that facilitate the implementation of the program were identified, including administrative support from the school and social work agency, presence of dedicated teachers, positive perceptions of the program among teachers, the teachers' self-disclosure, effective continuous assessment, and excellent co-teaching mode. Difficulties encountered by the school in the process of implementation were also observed. Based on the present findings, school-related process variables that facilitate or impede the implementation of positive youth development programs in the Chinese context are discussed.
A Case Study on the Implementation of a Positive Youth Development Program (Project P.A.T.H.S.) in a Changing Education Policy Environment
Authors: Lee Tak Yan
Published: October 2008

This investigation of the implementation of a positive youth development program (Project P.A.T.H.S.) was part of a large study undertaken comprehensively to explore how effective the Tier 1 Program was in practice and how the results can shed light on future developments. Case studies on randomly selected schools were conducted in order to examine the factors that influence the process and quality of implementation of the Tier 1 Program of the Project P.A.T.H.S. Through interviews with the school contact person and focus group interviews with the teachers, an integration of the findings of these studies showed that five factors related to the program, people, process, policy, and place (5 “P”s) facilitated the implementation process of the Tier 1 Program in the school. Based on the integrated findings of a randomly selected school, it was found that the school made use of the changes in the educational policy environment to facilitate school policy and structural changes, to pave the way for the success of the implementation of a new and “unfamiliar” curriculum. Overall, the quality of program implementation in the school was good and the program was well received by the program implementers. Implications of the present findings for future program implementation with reference to school administrative arrangements and implementation issues are also discussed.
What Makes a Good Program? A Case Study of a School Admitting High Academic Achievers
Authors: Lam Ching Man
Published: October 2008

This paper reports the results of a qualitative study that explored the administration and implementation of the Tier 1 Program (Secondary 1 Curriculum) of the Project P.A.T.H.S. The case study method was used to explore perceptions of the teachers and the project coordinator of program effectiveness, and to identify various factors for program success. A school admitting high academic achievers was selected, and site visits, as well as individual and focus group interviews, were conducted with the program coordinator, social worker, and course teachers. The results suggested that clear vision and program goals, high quality of curriculum, helpful leadership, positive teacher attitude, and strong administrative support are factors for program success. Analyzing the data enables the researchers to understand the characteristics of a successful program as well as the interplay among factors for producing success.
Positive School and Classroom Environment: Precursors of Successful Implementation of Positive Youth Development Programs
Authors: Sun Rachel C. F. , Shek Daniel T. L. , Siu Andrew M. H.
Published: October 2008

This case study was based on a school where the Tier 1 Program of the Project P.A.T.H.S. was integrated into the formal curriculum. In this case study, an interview with the school principal, vice-principal, and social worker was conducted in order to understand their perceptions of administrative arrangements and issues in the school, implementation characteristics, program effectiveness, program success, and overall impression. Results showed that several positive school and classroom attributes were conducive to program success, including positive school culture and belief in students' potentials, an inviting school environment, an encouraging classroom environment, high involvement of school administrative personnel, and systematic program arrangement.
Implementation Quality of a Positive Youth Development Program: Cross-Case Analyses Based on Seven Cases in Hong Kong
Authors: Shek Daniel T. L. , Sun Rachel C. F.
Published: October 2008

Cross-case analyses of factors that influence the process and implementation quality of the Tier 1 Program of the Project P.A.T.H.S. based on seven cases were carried out. Systematic and integrative analyses revealed several conclusions. First, several factors related to policy, people, program, process, and place (5 “P”s) were conducive to the successful implementation of the Tier 1 Program in the schools. Second, there were obstacles and difficulties with reference to the 5 “P”s that impeded the quality of implementation. Third, policy support and people (especially commitment and passion of the principals, senior school administrators, and program implementers) are two main groups of factors that influence the quality of program implementation. Fourth, although there were different arrangements for program implementation, incorporation of the Tier 1 Program into the formal curriculum was a sound and viable strategy. Fifth, implementation of the Tier 1 Program in schools that admitted students with high or low academic achievement was viable. Sixth, the program was generally perceived positively by the program participants and implementers. Finally, the program implementers perceived the program to be beneficial to the program participants.
Detection of Heteromers Formed by Cannabinoid CB1, Dopamine D2, and Adenosine A2AG-Protein-Coupled Receptors by Combining Bimolecular Fluorescence Complementation and Bioluminescence Energy Transfer
Authors: Navarro Gemma , Carriba Paulina , Gandí Jorge , Ciruela Francisco , Casadó Vicent , Cortés Antoni , Mallol Josefa , Canela Enric I. , Lluis Carmen , Franco Rafael
Published: October 2008

Functional interactions in signaling occur between dopamine D2(D2R) and cannabinoid CB1(CB1R) receptors, between CB1R and adenosine A2A(A2AR) receptors, and between D2R and A2AR. Furthermore, direct molecular interactions have been reported for the pairs CB1R-D2R, A2AR-D2R, and CB1R-A2AR. Here a combination of bimolecular fluorescence complementation and bioluminescence energy transfer techniques was used to identify the occurrence of D2R-CB1R-A2AR hetero-oligomers in living cells.