bluuebunny/crossref_metadata_2025 huggingface dataset:
High efficiency laser photothermal excitation of microcantilever vibrations in air and liquids
Authors: Kiracofe Daniel , Kobayashi Kei , Labuda Aleksander , Raman Arvind , Yamada Hirofumi
Published: January 2011

Photothermal excitation is a promising means of actuating microscale structures. It is gaining increased interest for its capability to excite atomic force microscopy (AFM) microcantilevers with wide frequency bandwidth in liquid environments yielding clean resonance peaks without spurious resonances. These capabilities are particularly relevant for high speed and high resolution, quantitative AFM. However, photothermal efficiency is low, which means a large amount of laser power is required for a given mechanical response. The high laser power may cause local heating effects, or spill over the cantilever and damage sensitive samples. In this work, it is shown that by simply changing from a probe with a rectangular cross-section to one with a trapezoidal cross-section, the photothermal efficiency of an uncoated silicon cantilever can be increased by more than a order of magnitude, and the efficiency of a coated cantilever can be increased by a factor of 2. This effect is demonstrated experimentally and explained theoretically using thermomechanical analysis. Results are shown for both air and water, and for normal bending and torsional oscillations.
Waveguide biosensor with integrated detector array for tuberculosis testing
Authors: Yan Rongjin , Lynn N. Scott , Kingry Luke C. , Yi Zhangjing , Slayden Richard A. , Dandy David S. , Lear Kevin L.
Published: January 2011

A label-free immunoassay using a local evanescent array coupled (LEAC) biosensor is reported. Complementary metal oxide semiconductor chips with integrated photoconductor arrays are used to detect an antibody to a M. tuberculosis protein antigen, HspX. The metrology limits of the LEAC sensor using dc and ac measurement systems correspond to average film thicknesses of 28 and 14 pm, respectively. Limits of detection are 87 and 108 pm, respectively, for mouse immunoglobulin G antibody patterning and antigen detection.
Diagonalization of infinite transfer matrix of boundary Uq,p(AN−1(1)) face model
Authors: Kojima Takeo
Published: January 2011

We study infinitely many commuting operators TB(z), which we call infinite transfer matrix of boundary Uq,p(AN−1(1)) face model. We diagonalize the infinite transfer matrix TB(z) by using free field realizations of the vertex operators of the elliptic quantum group Uq,p(AN−1(1)).
Studies on oxygen chemical surface exchange and electrical conduction in thin film nanostructured titania at high temperatures and varying oxygen pressure
Authors: Ko Changhyun , Karthikeyan Annamalai , Ramanathan Shriram
Published: January 2011

We report on oxygen surface exchange studies in ∼450-nm-thick nanocrystalline titania films with an average grain size of ∼13 nm by electrical conductivity relaxation along with the conductivity measurements at varying temperatures and oxygen partial pressures (pO2s). By electrochemical impedance spectroscopy technique, the high temperature conductivity was measured in the pO2 range from ∼10−16 to ∼10−6 Pa at temperatures from 973 to 1223 K and activation energy, ΔEa, for conduction was estimated as ∼3.23 eV at pO2 ∼10−11 Pa. Under reducing atmosphere (pO2 < 10−6 Pa), two distinct n-type conduction regimes were observed and corresponding predominant defects are discussed while, at high pO2 regime (pO2 >10−6 Pa), ionic conduction appears dominant leading to a conductivity plateau. The surface relaxation was observed to have two independent time constants likely originating from microstructural effects. The surface exchange coefficients are measured as ∼10−8–10−7 m/s and ∼10−9–10−8 m/s for each contribution with ΔEas of 2.79 and 1.82 eV, respectively, without much pO2 dependence across several orders of pO2 range of ∼10−16–10−6 Pa in the temperature range between 973 and 1223 K. The results are of potential relevance to understanding the near-surface chemical phenomena in nanocrystalline titania which is of great interest for energy and environmental studies.
Dynamic response of phenolic resin and its carbon-nanotube composites to shock wave loading
Authors: Arman B. , An Q. , Luo S. N. , Desai T. G. , Tonks D. L. , Çağın T. , Goddard W. A.
Published: January 2011

We investigate with nonreactive molecular dynamics simulations the dynamic response of phenolic resin and its carbon-nanotube (CNT) composites to shock wave compression. For phenolic resin, our simulations yield shock states in agreement with experiments on similar polymers except the “phase change” observed in experiments, indicating that such phase change is chemical in nature. The elastic–plastic transition is characterized by shear stress relaxation and atomic-level slip, and phenolic resin shows strong strain hardening. Shock loading of the CNT-resin composites is applied parallel or perpendicular to the CNT axis, and the composites demonstrate anisotropy in wave propagation, yield and CNT deformation. The CNTs induce stress concentrations in the composites and may increase the yield strength. Our simulations suggest that the bulk shock response of the composites depends on the volume fraction, length ratio, impact cross-section, and geometry of the CNT components; the short CNTs in current simulations have insignificant effect on the bulk response of resin polymer.
Magnetic domain structure and magnetization reversal in amorphous microwires with circular anisotropy: A micromagnetic approach
Authors: Betancourt I. , Hrkac G. , Schrefl T.
Published: January 2011

In this work we present a numerical investigation on the magnetic domain formation and magnetization reversal mechanism in submillimeter (250 μm length) amorphous microwires with negative magnetostriction by means of micromagnetic calculations. The formation of circular magnetic domains surrounding an axially, multidomain-oriented central nucleus was observed for the micromagnetic model representing the amorphous microwire. The magnetization reversal described by micromagnetic computations is consistent with a combined nucleation-propagation-rotational mechanism for the magnetization reversal after the saturated state.
Photoelectron spectroscopic studies of 5-halouracil anions
Authors: Radisic Dunja , Ko Yeon Jae , Nilles John M. , Stokes Sarah T. , Sevilla Michael D. , Rak Janusz , Bowen Kit H.
Published: January 2011

The parent negative ions of 5-chlorouracil, UCl− and 5-fluorouracil, UF− have been studied using anion photoelectron spectroscopy in order to investigate the electrophilic properties of their corresponding neutral halouracils. The vertical detachment energies (VDE) of these anions and the adiabatic electron affinities (EA) of their neutral molecular counterparts are reported. These results are in good agreement with the results of previously published theoretical calculations. The VDE values for both UCl− and UF− and the EA values for their neutral molecular counterparts are much greater than the corresponding values for both anionic and neutral forms of canonical uracil and thymine. These results are consistent with the observation that DNA is more sensitive to radiation damage when thymine is replaced by halouracil. While we also attempted to prepare the parent anion of 5-bromouracil, UBr−, we did not observe it, the mass spectrum exhibiting only Br− fragments, i.e., 5-bromouracil apparently underwent dissociative electron attachment. This observation is consistent with a previous assessment, suggesting that 5-bromouracil is the best radio-sensitizer among these three halo-nucleobases.
A metal-metal Fabry–Pérot cavity photoconductor for efficient GaAs terahertz photomixers
Authors: Peytavit E. , Coinon C. , Lampin J.-F.
Published: January 2011

The low responsivity of the low-temperature-grown GaAs based planar photoconductors used in the photomixing experiments can be improved by using a metal-metal Fabry–Pérot cavity. This resonant cavity photoconductor exhibits a dc-responsivity above 0.1 A/W and current density higher than 50 kA/cm2 with a low-temperature-grown-GaAs epitaxial layer presenting a subpicosecond carrier lifetime. Based on these results, up to 100 μW output power at 1 THz could be expected if this photoconductor is used in a photomixing experiment with a resonant antenna.
Chirality-dependent domain wall pinning in a multinotched planar nanowire and chirality preservation using transverse magnetic fields
Authors: Eastwood D. S. , King J. A. , Bogart L. K. , Cramman H. , Atkinson D.
Published: January 2011

Chirality-dependent pinning of magnetic domain walls (DWs) has been observed in a planar Ni81Fe19 nanowire with two spatially separated notches on opposite edges of the wire. Using focused magneto-optical Kerr effect measurements of field-driven magnetization reversal we show that several different metastable remanent magnetization states can be formed reproducibly, and that the application of a component of magnetic field transverse to the wire axis maintains the chirality of DW as it interacts with both notches and overcomes the problems of chirality loss due to Walker breakdown.
Magnetotransport properties of lattice-matched In0.18Al0.82N/AlN/GaN heterostructures
Authors: Miao Z. L. , Tang N. , Xu F. J. , Cen L. B. , Han K. , Song J. , Huang C. C. , Yu T. J. , Yang Z. J. , Wang X. Q. , Zhang G. Y. , Shen B. , Wei K. , Huang J. , Liu X. Y.
Published: January 2011

Magnetotransport properties of the two-dimensional electron gas (2DEG) in lattice-matched In0.18Al0.82N/AlN/GaN heterostructures have been studied at low temperatures and high magnetic fields. The double subband occupancy of the 2DEG in the triangular quantum well at the heterointerface is observed. The 2DEG density is determined to be 2.09×1013 cm−2 and the energy separation between the first and the second subbands is 191 meV. Both of them are significantly higher than those in AlxGa1−xN/AlN/GaN heterostructures owing to the stronger spontaneous polarization effect. The evident difference of the quantum scattering times in the two subbands of the 2DEG indicates that the interface roughness scattering plays an important role in the transport properties of the 2DEG in InxAl1−xN/AlN/GaN heterostructures.
Ultrafast relaxation and absorption saturation at near exciton resonance in a thin ZnO epilayer
Authors: Ou Po-Chi , Liu Wei-Rein , Ton Ho-Jei , Lin Ja-Hon , Hsieh Wen-Feng
Published: January 2011

We observed ultrafast free exciton thermalization time of 700–900 fs and obtained the magnitude of maximal differential absorption to be 1.8×104 cm−1 with the pumping fluence of 10 μJ/cm2 by measuring transient differential transmission in a thin ZnO epitaxial layer at room temperature. The largest induced transparency occurs near exciton resonance associated with absorption saturation by comparing the excitation from the above band-gap to band-tail states. The pumping dependent transient absorption reveals transition of excitonic relaxation from exciton-phonon scattering to exciton-exciton scattering or to an electron-hole plasma.
Magnetic vortex formation and gyrotropic mode in nanodisks
Authors: Toscano D. , Leonel S. A. , Dias R. A. , Coura P. Z. , Rocha J. C. S. , Costa B. V.
Published: January 2011

The superparamagnetic limit imposes a restriction on how far the miniaturization of electronic devices can reach. Recently it was shown that magnetic thin films with nanoscale dimensions can exhibit a vortex as its ground state. The vortex can lower its energy by developing an out-of-plane magnetization perpendicular to the plane of the film, the z direction, which can be “up” or “down.” Because the vortex structure is very stable this twofold degeneracy opens up the possibility of using a magnetic nanodisk as a bit of memory in electronic devices. The manipulation of the vortex and a way to control the core magnetization is a subject of paramount importance. Recent results have suggested that the polarity of a vortex core could be switched by applying a pulsed magnetic field in the plane of the disk. Another important effect induced by an external magnetic field due to the component out-of-plane in vortex-core is the gyrotropic mode. The gyrotropic mode is the elliptical movement around the disk center executed by the vortex-core under the influence of a magnetic field. In the present work we used numerical simulations to study the ground state as well as the dynamical behavior of magnetic vortices in thin nanodisks. We have considered a model where the magnetic moments interact through exchange (−J∑S⃗i⋅S⃗j) and dipolar potentials {D∑[S⃗i⋅S⃗j−3(S⃗i⋅r̂ij)×(S⃗j⋅r̂ij)]/rij3}. We have investigated the conditions for the formation of the vortex-core with and without an out-of-plane magnetization as a function of the strength of the dipole interaction D and of the size and thickness of the magnetic nanodisk. Our results were consistent with the existence of two vortex phases separated by a crossover line [(Dc−D)α]. We have observed that Dc does not depend on the radius of nanodisk but depends on its thickness. The exponent α was found to be α≈0.55(2). The gyrotropic motion is studied by applying an external magnetic field parallel to the plane of the magnetic nanodisk. Our results show that there is a minimum value for the modulus of the out-of-plane vortex-core magnetization, from which we can excite the gyrotropic mode. This minimum value depends on the thickness of the nanodisk. This result suggest that an experimental way to improve the stability of the process of switching may be through the thickness control. We also observed that the gyrotropic mode frequency increases with the aspect ratio, which is in qualitatively accordance with theoretical and experimental results. Finally, we present theoretical results for Permalloy nanodisks obtained from our model, which are also in good agreement with experimental results.
Electromagnetic properties of resonant magnetoplasmonic core-shell nanostructures
Authors: Essone Mezeme M. , Lasquellec S. , Brosseau C.
Published: January 2011

We present a numerical model we have created and verified to characterize the frequency dependence of the effective magnetic permeability and permittivity of a core-shell (CS) nanostructure composed of a magnetic core and a plasmonic shell with well-controlled dimensions for different geometries and polarizations. Two principal ingredients in our model are as follows: (i) we consider two-dimensional (or cross sections of infinite three-dimensional parallel, infinitely long, identical, cylinders, where the properties and characteristics are invariant along the perpendicular cross sectional plane) three-phase heterostructure, and (ii) while strictly valid only in a dc situation, our analysis can be extended to treat electric fields that oscillate with time provided that the wavelengths associated with the fields are much larger than the microstructure dimension in order that the homogeneous (effective medium) representation of the composite structure makes sense. Such nanostructures simultaneously possess both magnetic gyromagnetic resonance and plasmonic resonance (PLR) resonances. To illustrate the effects of shape anisotropy of the CS structure, we analyze several possible shell shapes involving sharp edges and tips. Geometric parameters of the CS nanostructures and excitation polarized parallel and perpendicular to the antenna axis permit to finely tune the PLR. Changing the internal geometry of the nanostructure not only shifts its resonance frequencies but can also strongly modify the relative magnitudes of the electric field enhancement, independently of nanoparticle shape. The model sets the foundation of quantitatively determining the spatial confinement of the electric field in regions ≈20 nm in linear dimension. Because of its resonant nature, we found nanolocalized terahertz fields corresponding to large electric field enhancement two orders of magnitude higher in amplitude than the excitation optical field. The simulations in this paper are important because magnetoplasmonic CS nanostructures are currently being explored as candidates for resonant optical nanoantennas for biosensing applications.
Exciton formation as a rate limiting step for charge recombination in disordered organic molecules or polymers
Authors: Preezant Yevgeni , Tessler Nir
Published: January 2011

The exciton formation (direct charge recombination) is studied and quantified as a function of material physical-properties such as the exciton binding energy, the exciton lifetime, and the mechanism causing the electronic disorder. By using a model that is an extension of a charge transport model [Y. Preezant and N. Tessler, Phys. Rev. B 74, 235202 (2006)] we are able to compare the direct exciton formation rate with the one predicted by the Langevin model. Using reasonable material parameters we find that in many cases the overall balance between free charge carrier and excitons is significantly affected by the exciton formation rate with its values being significantly low compared to the Langevin rate. We also find that in order to describe the complete recombination process it is important to introduce an intermediate state which we term exciton-precursor. This is in contrast to the common practice of using the Langevin model which embeds the assumption that the exciton formation rate is negligibly fast. The relations found between the physical-properties and the recombination rate can explain why certain materials exhibit Langevin rate while others exhibit significantly suppressed rates. This would eventually lead to the design of new materials better suited for either photocells or light-emitting diodes.
Development and application of a continuous measurement system for radon exhalation rate
Authors: Hosoda Masahiro , Ishikawa Tetsuo , Sorimachi Atsuyuki , Tokonami Shinji , Uchida Shigeo
Published: January 2011

A continuous measurement system, with a ventilation-type accumulation chamber, was developed for radon exhalation rate determination. A reasonable sampling flow rate for the measurement system was determined by comparing the values obtained by the system with those obtained by a grab sampling method. The sampling flow rate of passage through the scintillation cell from the accumulation chamber was varied from 0.05 to 2.0 l min−1. The difference in pressure between the inside and outside of the accumulation chamber increased as the sampling flow rate became large, and the estimated radon exhalation rate also increased with the sampling flow rate. From these results, a reasonable sampling flow rate was estimated to be less than 0.2 l min−1.
Anisotropic field-effect hole mobility of liquid crystalline conjugated polymer layers formed on photoaligned polyimide films
Authors: Sakamoto Kenji , Yasuda Takeshi , Miki Kazushi , Chikamatsu Masayuki , Azumi Reiko
Published: January 2011

We have fabricated organic field-effect transistors (OFETs) with a highly oriented active layer of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2), which was formed with the help of a photoaligned polyimide film. Photoalignment is an attractive technique for integrating OFETs with aligned active layers on the same substrate, because of its potential capability of two-dimensional alignment patterning. The F8T2 layer formed on the photoaligned polyimide film showed an absorption dichroic ratio greater than 15 after annealing at 285 °C. Top-gate/bottom-contact-type OFETs with a parylene gate insulating layer exhibited an enhanced hole mobility (0.016 cm2 V−1 s−1) along the alignment direction of the F8T2 backbone structure and a suppressed one (0.002 cm2 V−1 s−1) along the perpendicular direction. This result shows that the photoaligned polyimide film is an attractive alignment layer for fabricating and integrating OFETs with aligned active layers. Current-direction-dependent bias stress effect was observed for those OFETs; when the current flowed parallel to the alignment direction of the F8T2 backbone structures, a larger negative threshold voltage shift was observed. This anisotropic bias stress effect was discussed on the basis of a microstructure model of aligned F8T2 films.
Influence of oxygen partial pressure on surface tension and its temperature coefficient of molten iron
Authors: Ozawa S. , Suzuki S. , Hibiya T. , Fukuyama H.
Published: January 2011

Influences of oxygen partial pressure, PO2, of ambient atmosphere and temperature on surface tension and its temperature coefficient for molten iron were experimentally investigated by an oscillating droplet method using an electromagnetic levitation furnace. We successfully measured the surface tension of molten iron over a very wide temperature range of 780 K including undercooling condition in a well controlled PO2 atmosphere. When PO2 is fixed at 10−2 Pa at the inlet of the chamber, a “boomerang shape” temperature dependence of surface tension was experimentally observed; surface tension increased and then decreased with increasing temperature. The pure surface tension of molten iron was deduced from the negative temperature coefficient in the boomerang shape temperature dependence. When the surface tension was measured under the H2-containing gas atmosphere, surface tension did not show a linear relationship against temperature. The temperature dependence of the surface tension shows anomalous kink at around 1850 K due to competition between the temperature dependence of PO2 and that of the equilibrium constant of oxygen adsorption.
Reassessment of the impedance spectra and dielectric responses of undoped and CaSiO3-doped CaCu3Ti4O12
Authors: Fang Tsang-Tse , Chung Han-Yang
Published: January 2011

The impedance and dielectric relaxation spectra of undoped and CaSiO3-doped CaCu3Ti4O12 (CCTO) have been reassessed by rigorous theoretical fittings and simulations; and the related physical elements are substantially identified. The extended Maxwell–Wagner (MW) two-layer condenser model has been proposed, which clarifies the nature of the plateaus appearing in the dielectric relaxation spectra of CCTO. The plateaus essentially consist of a hybrid of two of the concerned physical elements, assumed in the established equivalent circuit. The temperature dependence of the low-frequency plateaus of CaSiO3-doped CCTO with In–Ga electrode is further interpreted underlying this extended model. New defect structure and reactions have been proposed to plausibly interpret the semiconductivity of the grain interiors and the insulation of grain boundaries of CCTO.
ZnS nanocrystals decorated single-walled carbon nanotube based chemiresistive label-free DNA sensor
Authors: Rajesh  , Das Basanta K. , Srinives Sira , Mulchandani Ashok
Published: January 2011

We fabricated ZnS nanocrystals decorated single-walled carbon nanotube (SWNT) based chemiresistive sensor for DNA. Since the charge transfer in the hybrid nanostructures is considered to be responsible for many of their unique properties, the role of ZnS nanocrystals toward its performance in DNA sensor was delineated. It was found that the free carboxyl groups surrounding the ZnS nanocrystals allowed large loading of single strand DNA (ssDNA) probe that provided an ease of hybridization with target complementary c-ssDNA resulting in large electron transfer to SWNT. Thus it provided a significant improvement in sensitivity toward c-ssDNA as compared to bare SWNT based DNA sensor.
Theoretical model for k−3 spectra in dispersed multiphase flows
Authors: Risso Frédéric
Published: January 2011

The spectrum of a signal consisting of a sum of localized random bursts can exhibit, under certain conditions, an intermediate subrange evolving as the power −3 of the wavenumber k. These bursts should have a smooth and regular pattern, their strength and size should be statistically independent, and their size should be uniformly distributed between two finite wavelengths. This is probably the explanation for the k−3 subrange that is commonly observed in the velocity spectra of bubble-induced turbulence, which results from the interaction of the localized velocity disturbances caused by the bubbles.
NiO-like single layer formed on a Ni/Cu(001) thin film revealed by the depth-resolved x-ray absorption spectroscopy
Authors: Amemiya Kenta , Sakamaki Masako
Published: January 2011

The formation of a 1-ML-thick NiO-like layer on a 5.5 ML Ni ultrathin film by Ni deposition on oxygen precovered Cu(001) is revealed by the depth-resolved x-ray absorption spectroscopy, and its magnetic properties are investigated. The surface layer exhibits a NiO-like x-ray absorption spectrum, while the underlying layers show a typical spectrum for a metallic Ni film. An uncompensated spin moment is observed in the NiO-like layer, which is antiparallel to the spin moment in the underlying Ni layers. These results demonstrate a potential to fabricate a sharp interface between ferromagnetic and antiferromagnetic materials.
Communication: Universal Markovian reduction of Brownian particle dynamics
Authors: Martinazzo R. , Vacchini B. , Hughes K. H. , Burghardt I.
Published: January 2011

Non-Markovian processes can often be turned Markovian by enlarging the set of variables. Here we show, by an explicit construction, how this can be done for the dynamics of a Brownian particle obeying the generalized Langevin equation. Given an arbitrary bath spectral density \documentclass[12pt]{minimal}\begin{document}$J_{0}$\end{document}J0, we introduce an orthogonal transformation of the bath variables into effective modes, leading stepwise to a semi-infinite chain with nearest-neighbor interactions. The transformation is uniquely determined by \documentclass[12pt]{minimal}\begin{document}$J_{0}$\end{document}J0 and defines a sequence \documentclass[12pt]{minimal}\begin{document}$\lbrace J_{n}\rbrace _{n\in \mathbb {N}}$\end{document}{Jn}n∈N of residual spectral densities describing the interaction of the terminal chain mode, at each step, with the remaining bath. We derive a simple one-term recurrence relation for this sequence and show that its limit is the quasi-Ohmic expression provided by the Rubin model of dissipation. Numerical calculations show that, irrespective of the details of \documentclass[12pt]{minimal}\begin{document}$J_{0}$\end{document}J0, convergence is fast enough to be useful in practice for an effective Ohmic reduction of the dissipative dynamics.
Electrokinetic instability: The sharp interface limit
Authors: Patankar Neelesh A.
Published: January 2011

An instability between two miscible liquid regions of identical mechanical properties but different electrical conductivities stressed by an external electric field parallel to the interface is studied. The problem is of interest due to its applications to mixing in microchannels. It is shown that the problem can be modeled by considering a sharp interface and an appropriate jump condition for the electrical conductivity. The transport of the electrical conductivity is governed by a diffusive equation. An infinite domain case and a shallow channel case are considered. It is shown that any velocity perturbation at the interface leads to a varying electrical conductivity in its vicinity due to the electromechanical coupling in the jump condition for the electrical conductivity. This in turns leads to a bulk charge density that gives a body force in the fluid equations. The body force generates a cellular motion that results in the instability. The results compare favorably with the experimental data and the numerical analysis for the diffuse interface case by Chen et al. [J. Fluid Mech. 524, 263 (2005)]. The critical condition for the instability is given in terms of a nondimensional parameter PΣ, which is a product of the Péclet number and another nondimensional parameter that depends on the conductivity ratio of the two liquids.
Active microcantilevers based on piezoresistive ferromagnetic thin films
Authors: Bhaskaran Harish , Li Mo , Garcia-Sanchez Daniel , Zhao Peng , Takeuchi Ichiro , Tang Hong X.
Published: January 2011

We report the piezoresistivity in magnetic thin films of Fe0.7Ga0.3 and their use for fabricating self-transducing microcantilevers. The actuation occurs as a consequence of both the ferromagnetic and magnetostrictive properties of Fe0.7Ga0.3 thin films, while the deflection readout is achieved by exploiting the piezoresistivity of these films. This self-sensing self-actuating micromechanical system involves a very simple bilayer structure, which eliminates the need for the more complex piezoelectric stack that is commonly used in active cantilevers. Thus, it potentially opens opportunities for remotely actuated cantilever-based sensors.
Exploiting optical near fields for phase change memories
Authors: Leiprecht P. , Kühler P. , Longo M. , Leiderer P. , Afonso C. N. , Siegel J.
Published: January 2011

We apply a recently developed technique based on optical near fields to achieve reversible phase switching in Ge2Sb2Te5 films. By placing dielectric microspheres at the film surface and exposing them to pulsed laser light, a complex intensity distribution due to the optical near field can be created at the film surface. We demonstrate writing and erasing operations of patterns through phase switching. Spheres can be removed after an operation by optical near fields without ablation. Data erasure is achieved with and without near fields. The erasure method used can be determined from the result and erased information can be retrieved although being inverted. Three distinct material states are identified within patterns, showing clear contrast and sharp borders between them, thus opening the possibility of three-level data storage. Our results suggest that optical near fields are a promising candidate for developing strategies in data storage, encryption, and multiplexing.
Temperature contour maps at the strain-induced martensitic transition of a Cu–Zn–Al shape-memory single crystal
Authors: Vives Eduard , Burrows Susan , Edwards Rachel S. , Dixon Steve , Mañosa Lluís , Planes Antoni , Romero Ricardo
Published: January 2011

We study temperature changes at the reverse strain-induced martensitic transformation in a Cu–Zn–Al single crystal. Infrared thermal imaging reveals a markedly inhomogeneous temperature distribution. The evolution of the contour temperature maps enables information to be extracted on the kinetics of the interface motion.
Vertical cavity surface emitting laser action of an all monolithic ZnO-based microcavity
Authors: Kalusniak S. , Sadofev S. , Halm S. , Henneberger F.
Published: January 2011

We report on room temperature laser action of an all monolithic ZnO-based vertical cavity surface emitting laser (VCSEL) under optical pumping. The VCSEL structure consists of a 2λ microcavity containing eight ZnO/Zn0.92Mg0.08O quantum wells embedded in epitaxially grown Zn0.92Mg0.08O/Zn0.65Mg0.35O distributed Bragg reflectors (DBRs). As a prerequisite, design and growth of high reflectivity DBRs based on ZnO and (Zn,Mg)O for optical devices operating in the ultraviolet and blue-green spectral ranges are discussed.
Effects of graphite particles on ion transport in a zeolite Y
Authors: Lu Weiyi , Chow Brian J. , Kim Taewan , Han Aijie , Qiao Yu
Published: January 2011

We report an experimental result that the effective ion transport pressure in nanopores of a zeolite Y is strongly affected by the graphite particles outside. This phenomenon may be related to the electrification of zeolite-graphite interface, which is negligible for large pores but can be greatly amplified by the small nanopore size.
Suppression of donor-vacancy clusters in germanium by concurrent annealing and irradiation
Authors: Schneider S. , Bracht H.
Published: January 2011

Diffusion of phosphorous and arsenic in germanium under in situ proton irradiation has been performed and analyzed with secondary ion mass spectrometry. Dopant profiles corresponding to proton-exposed regions exhibit a higher penetration depth and more pronounced box shape than profiles of nonexposed regions. Continuum theoretical simulations reveal that diffusion under irradiation is much less affected by inactive donor-vacancy clusters than diffusion under annealing only. The suppression of donor-vacancy clusters is caused by interstitials in supersaturation and vacancy concentrations close to thermal equilibrium. Concurrent annealing and irradiation have the potential to attain high active doping levels in Ge.
Liquid-gated electric-double-layer transistor on layered metal dichalcogenide, SnS2
Authors: Yuan H. T. , Toh M. , Morimoto K. , Tan W. , Wei F. , Shimotani H. , Kloc Ch. , Iwasa Y.
Published: January 2011

With ionic liquid (IL) gating in electric-double-layer transistors (EDLTs), we report field effect operation and electronic state modulation in a layered material of SnS2, demonstrating that the EDLT is applicable to modifying the electronic properties of metal dichalcogenides. The IL-gated SnS2 EDLTs allow us to realize high performance transistor operation and to achieve interfacial carrier accumulation to a level as high as 5.4×1014 cm−2, as quantitatively estimated from the Hall effect. A considerable decrease of the activation energy in temperature-dependent sheet resistance implies that liquid gating is an effective way to tune the electronic states of metal dichalcogenides at EDL interfaces.
Macroporous photonic crystal-based vapor detectors created by doctor blade coating
Authors: Yang Hongta , Jiang Peng
Published: January 2011

We report the achievement of rapid and reversible vapor detection by using 3D macroporous photonic crystals created by a continuous and scalable bottom-up technology. Capillary condensation of a condensable vapor in the interconnected macropores with ∼74% porosity leads to the increase of the effective refractive index of the diffractive medium, resulting in the redshift of the optical stop bands. The wavelength shift is linearly proportional to the vapor partial pressure for a spectrum of vapors. Optical simulation and theoretical prediction based on Kelvin equation suggest that a liquid film is formed on the walls of the macropores during vapor condensation.
Metal-insulator transition and electrically driven memristive characteristics of SmNiO3 thin films
Authors: Ha Sieu D. , Aydogdu Gulgun H. , Ramanathan Shriram
Published: January 2011

The correlated oxide SmNiO3 (SNO) exhibits an insulator to metal transition (MIT) at 130 °C in bulk form. We report on synthesis and electron transport in SNO films deposited on LaAlO3 (LAO) and Si single crystals. X-ray diffraction studies show that compressively strained single-phase SNO grows epitaxially on LAO while on Si, mixed oxide phases are observed. MIT is observed in resistance-temperature measurements in films grown on both substrates, with charge transport in-plane for LAO/SNO films and out-of-plane for Si/SNO films. Electrically driven memristive behavior is realized in LAO/SNO films, suggesting that SNO may be relevant for neuromorphic devices.
Establishing reference genes for use in real-time quantitative PCR analysis of early equine embryos
Authors: Paris Damien B. B. P. , Kuijk Ewart W. , Roelen Bernard A. J. , Stout Tom A. E.
Published: January 2011

Real-time quantitative PCR (qPCR) is invaluable for investigating changes in gene expression during early development, since it can be performed on the limited quantities of mRNA contained in individual embryos. However, the reliability of this method depends on the use of validated stably expressed reference genes for accurate data normalisation. The aim of the present study was to identify and validate a set of reference genes suitable for studying gene expression during equine embryo development. The stable expression of four carefully selected reference genes and one developmentally regulated gene was examined by qPCR in equine in vivo embryos from morula to expanded blastocyst stage. SRP14, RPL4 and PGK1 were identified by geNorm analysis as stably expressed reference genes suitable for data normalisation. RPL13A expression was less stable and changed significantly during the period of development examined, rendering it unsuitable as a reference gene. As anticipated, CDX2 expression increased significantly during embryo development, supporting its possible role in trophectoderm specification in the horse. In summary, it was demonstrated that evidence-based selection of potential reference genes can reduce the number needed to validate stable expression in an experimental system; this is particularly useful when dealing with tissues that yield small amounts of mRNA. SRP14, RPL4 and PGK1 are stable reference genes suitable for normalising expression for genes of interest during in vivo morula to expanded blastocyst development of horse embryos.
Betamethasone, progesterone and RU-486 (mifepristone) exert similar effects on connexin expression in trophoblast-derived HTR-8/SVneo cells
Authors: Cervellati F. , Pavan B. , Lunghi L. , Manni E. , Fabbri E. , Mascoli C. , Biondi C. , Patella A. , Vesce F.
Published: January 2011

Connexins (Cx) are membrane proteins able to influence cell trophoblast responses, such as proliferation, differentiation, migration and invasiveness. Likewise, glucocorticoids are also known to modulate many factors involved in implantation, including trophoblast gap-junction intercellular communication, although their influence on pregnancy is controversial. In order to investigate the effects of betamethasone, a synthetic glucocorticoid, on Cx and glucocorticoid receptor (GR) expression and localisation, as well as on cell proliferation, the extravillous trophoblast-derived HTR-8/SVneo cell line was used as a model. The results, confirmed by means of immunofluorescence, demonstrate that betamethasone selectively modifies GR and Cx expression, enhancing the GRα isoform without affecting GRβ, and inhibiting Cx40 expression whilst increasing that of Cx43 and Cx45. Furthermore, betamethasone was shown to exert an inhibitory action on cell proliferation. In this model the abortion drug RU-486 (mifepristone), reported to be a GR antagonist, did not counteract this effect of betamethasone. On the contrary, it induced responses similar to those of the hormone. Knowing that RU-486 is also a potent progesterone-receptor antagonist, the effect of progesterone alone and in combination with the drug on Cx expression and cell proliferation was then tested. Progesterone showed the same effect as betamethasone on Cx expression, but it did not affect proliferation. Based on these results, neither the abortion effects of RU-486 nor the protective action of betamethasone and progesterone are exerted by modulation of Cx. RU-486 did not antagonise the progesterone effect, suggesting that its abortive action does not involve alteration of trophoblast Cx expression.
Postnatal hypothalamic - pituitary - adrenal function in sheep is influenced by age and sex, but not by prenatal growth restriction
Authors: Wallace Jacqueline M. , Milne John S. , Green Lucy R. , Aitken Raymond P.
Published: January 2011

The relationship between impaired fetal nutrient supply and postnatal hypothalamic–pituitary–adrenal (HPA) function was examined in ovine models of prenatal growth restriction (GR) caused by small placental size (SP) or by maternal undernutrition (UN). Adrenocorticotrophin (ACTH) and cortisol responses following corticotrophin-releasing hormone (CRH) plus arginine vasopressin (AVP) challenge were examined at 9, 18 and 24 months in growth-restricted (GR-SP) and normal birthweight (control) females (Experiment 1), and at 6 months in growth-restricted (GR-SP, GR-UN) and normal weight males and females (Experiment 2). In Experiment 1, GR-SP offspring were born early, were 40% lighter at birth and had higher fractional weight gains to weaning than control offspring. Baseline ACTH and cortisol were independent of GR and cortisol decreased with age. GR did not affect the HPA response to CRH + AVP challenge at any stage, but ACTH increased with age. In Experiment 2, birthweight was greater in control offspring than in GR-UN offspring, which had a higher birthweight again compared with GR-SP offspring. Only the latter group was born early and exhibited rapid catch-up growth to weaning. Neither nutritional route to GR altered HPA function at 6 months. Males grew faster than females and HPA responses after stimulation were lower in males. Together, the results of these studies demonstrate that postnatal HPA function in sheep is influenced by age and sex, but not by GR.
Effects of supplemental progesterone on the development, metabolism and blastocyst cell number of bovine embryos produced in vitro
Authors: Larson Jamie E. , Krisher Rebecca L. , Lamb G. Cliff
Published: January 2011

The objectives of the present experiment were to determine whether supplementation with progesterone (LO, 1 ng mL–1 or HI, 100 ng mL–1) during either the first (Culture-1, Day 1 to 3) or second (Culture-2, Day 4 to 7) phase of culture of in vitro-produced embryos alters embryo development, embryo metabolism or blastocyst cell number. The percentage of oocytes that cleaved, the percentage of cleaved embryos that developed to the morula stage or greater, the blastocyst stage or greater or the hatched blastocyst stage were similar among treatments. Quantities of glucose metabolised per blastocyst per hour were similar, but when metabolic data was normalised for numbers of cells in each blastocyst, the LO treatment during Culture-2 metabolised more glucose (P = 0.03) compared with all other treatments. Embryos receiving LO progesterone tended to have greater (P = 0.085) metabolism of glucose compared with embryos receiving HI progesterone. Quantities of pyruvate oxidised per blastocyst per hour, and per cell, were similar among treatments. The number of cells per blastocyst in the control group was increased (P = 0.039) compared with cells in progesterone-treated groups. In conclusion, supplementation with progesterone during the culture of in vitro-produced embryos does not appear to improve embryo characteristics.
Progesterone as the driving regulatory force behind serum FSH concentrations and antral follicular development in cycling ewes
Authors: Baby Tanya E. , Bartlewski Pawel M.
Published: January 2011

Ovarian antral follicles in sheep grow in an orderly succession, producing typically three to four follicular waves per 17-day oestrous cycle. Each wave is preceded by a transient increase in circulating FSH concentrations. The mechanism controlling the number of recurrent FSH peaks and emerging follicular waves remains unknown. During the ewe’s oestrous cycle, the time between the first two FSH peaks and days of wave emergence is longer than the intervals separating the ensuing FSH peaks and follicular waves. The prolonged interpeak and interwave interval occurs early in the luteal phase when low levels of progesterone are secreted by developing, or not fully functional, corpora lutea (CL). The purpose of the present study was to determine the effect of varying progesterone (P4) levels on circulating concentrations of FSH and antral follicular development in sheep. Exogenous P4 (15 mg per ewe, i.m.) was administered twice daily to six cycling Rideau Arcott × Dorset ewes from Day 0 (ovulation) to Day 4 (the mean duration of the interwave interval); six animals served as controls. Follicular growth was monitored in all animals by daily transrectal ultrasonography (Days 0–9). Jugular blood samples were drawn twice a day from Day 0 to Day 4 and then daily until Day 9 to measure systemic concentrations of P4, FSH and 17β-oestradiol (E2). The first FSH peak after ovulation was detected on Days 1.5 ± 0.2 and 4.2 ± 0.2 in treated and control ewes, respectively (P < 0.05). The next FSH peak(s) occurred on Day 3.9 ± 0.3 in the treated group and on Day 6.4 ± 0.5 in the control group. Consequently, the treated group had, on average, three follicular waves emerging on Days 0, 3 and 6, whereas the control group had two waves emerging on Days 0 and 5. Mean serum E2 concentrations were greater (P < 0.05) in control compared with treated ewes on Days 1.3, 2.3, 3.3, 4.0 and 4.3 after ovulation. In summary, creation of mid-luteal phase levels of P4 in metoestrus shortened the time to the first post-ovulatory FSH peak in ewes, resulting in the emergence of one more follicular wave compared with control ewes during the same time frame. Therefore, P4 appears to be a key endocrine signal governing the control of periodic increases in serum FSH concentrations and the number of follicular waves in cycling sheep.
Avian embryonic development does not change the stable isotope composition of the calcite eggshell
Authors: Maurer G. , Portugal S. J. , Boomer I. , Cassey P.
Published: January 2011

The avian embryo resorbs most of the calcium for bone formation from the calcite eggshell but the exact mechanisms of the resorption are unknown. The present study tested whether this process results in variable fractionation of the oxygen and carbon isotopes in shell calcium carbonate, which could provide a detailed insight into the temporal and spatial use of the eggshell by the developing embryo. Despite the uncertainty regarding changes in stable isotope composition of the eggshell across developmental stages or regions of the shell, eggshells are a popular resource for the analysis of historic and extant trophic relationships. To clarify how the stable isotope composition varies with embryonic development, the δ13C and δ18O content of the carbonate fraction in shells of black-headed gull (Larus ridibundus) eggs were sampled at four different stages of embryonic development and at five eggshell regions. No consistent relationship between the stable isotope composition of the eggshell and embryonic development, shell region or maculation was observed, although shell thickness decreased with development in all shell regions. By contrast, individual eggs differed significantly in isotope composition. These results establish that eggshells can be used to investigate a species’ carbon and oxygen sources, regardless of the egg’s developmental stage.
In utero cell transfer between porcine littermates
Authors: McConico Andrea , Butters Kim , Lien Karen , Knudsen Bruce , Wu Xiaosheng , Platt Jeffrey L. , Ogle Brenda M.
Published: January 2011

Trafficking of cells between mother and fetus during the course of normal pregnancy is well documented. Similarly, cells are known to travel between twins that share either a placenta (i.e. monozygotic) or associated chorion (i.e. monochorionic). Transferred cells are thought to be channelled via the vessels of the placenta or vascular connections established via the chorion and the long-term presence of these cells (i.e. microchimerism) can have important consequences for immune system function and reparative capacity of the host. Whether cells can be transferred between twins with separate placentas and separate chorions (i.e. no vascular connections between placentas) has not been investigated nor have the biological consequences of such a transfer. In the present study, we tested the possibility of this type of cell transfer by injecting human cord blood-derived cells into a portion of the littermates of swine and probing for human cells in the blood and tissues of unmanipulated littermates. Human cells were detected in the blood of 78% of unmanipulated littermates. Human cells were also detected in various tissues of the unmanipulated littermates, including kidney (56%), spleen (33%), thymus (11%) and heart (22%). Human cells were maintained in the blood until the piglets were sacrificed (8 months after birth), suggesting the establishment of long-term microchimerism. Our findings show that the transfer of cells between fetuses with separate placentas and separate chorions is significant and thus such twins may be subject to the same consequences of microchimerism as monozygotic or monochorionic counterparts.