bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Blood Compatible Alpha-lipoic acid Coated Stent with a Good Adhesive by Low Temperature Plasma Polymerization
Authors: Song Sun-Jung , Kim Kyoung Seok , Cho Dong Lyun , Jeong Myung Ho
Published: June 2009

Neointimal hyperplasia is a main cause for in-stent restenosis after stent-implantation and is triggered by inflammatory response to foreign materials. It can be inhibited if the stent is modified to have good blood compatibility by coating drug compounds. Low temperature plasma polymerization of 1, 2-diaminocyclohexane was performed to prepare more adhesive polymeric thin film onto the metallic stent. Then, the chemical grafting of α-lipoic acid (ALA) was carried out to improve blood compatibility of stent. Drugs containing carboxylic groups can be chemically grafted through the formation of amide bond in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide methiodide onto the DACH deposited stent surface. ALA grafted film showed good mechanical stability and blood compatibility.
Microstructures of Electron Beam Melted (EBM) Biomaterial Ti-6Al-4V
Authors: Safdar Adnan , Wei Liu-Ying
Published: June 2009

Ti-6Al-4V alloy is an attractive biomaterial. The current work evaluates the microstructures of the solid and net-shape Ti-6Al-4V alloy produced by Electron Beam Melting (EBM) system using SEM/EDX and optical microscope. The microstructures are influenced by the cooling rate, processing parameters of the EBM system and re-heating of the existing layer during the melting of subsequent layers. Layer structure and columnar grains have been observed, with growing direction parallel to the built direction. The interior of these grains consists of alternating α / β phases. The β phase in the colonies resembles rod shape embedded in the α platelet. Along the grain boundaries more or less continuous α layers were observed. In comparison to solid samples uneven surfaces and pores were seen in the net shape structure. Microhardness evaluation of the EBM produced alloys was also carried out and compared with conventionally produced alloys.
Rapid chemical vapor sensing and micro gas chromatography detection using optofluidic ring resonators
Authors: Sun Yuze , Shopova Siyka I. , White Ian M. , Zhu Hongying , Frye-Mason Greg , Ja Shiou-jyh , Thompson Aaron , Fan Xudong
Published: June 2009

We develop rapid chemical vapor sensors and micro gas chromatography (μGC) analyzers based on the optofluidic ring resonator (OFRR). An OFRR is a micro-sized thin-walled glass capillary; the circular cross-section of the capillary acts as an optical ring resonator while the whispering gallery modes or circulating waveguide modes (WGMs) supported by the ring resonator interact with the vapor samples passing through the capillary. The OFRR interior surface is coated with a vapor-sensitive polymer. The analyte and polymer interaction causes the polymer refractive index (RI) and the thickness to change, which is detected as a WGM spectral shift. Owing to the excellent fluidics, the OFRR vapor sensor exhibits sub-second detection and recovery time with a flow rate of 1 mL/min. On-column separation and detection in the OFRR based μGC system is also demonstrated, showing efficient separation of vapor mixtures and presenting highly reproducible retention time for the individual analyte. Compared to the conventional GC system, the OFRR μGC has the advantage of small size, rapid response, and high selectivity over a short length of column.
Enzymatic Biosensors with Integrated Thin Film a-Si:H Photodiodes
Authors: Pereira Ana Teresa , Chu Virginia , Prazeres Duarte M. F. , Conde Joao P.
Published: June 2009

A microfabricated amorphous silicon photodiode is used to detect chemiluminescent and colorimetric horseradish peroxidase (HRP) enzymatic reactions. Detections limits of 1 nM and 1 pM of HRP are obtained for chemiluminescent and colorimetric measurements, respectively, with the reactions carried out in solution volume of 50 μL in polystyrene microwells. Surface-adsorbed HRP can be detected with a limit of 1 fmol.cm-2 by both detection methods. Immunoassays were performed using HRP-labeled antibodies and the detection of specific antibody-antigen molecular recognition is demonstrated both in the plastic well and inside a microfluidic channel. The application of the a-Si:H/HRP system is extended by coupling HRP with oxidase enzyme systems for glucose detection and a sensitivity of 0.1 mmol/L was achieved.
Layer Cross-Fading at Organic/Organic Interfaces in OVPD-Processed Red Phosphorescent Organic Light Emitting Diodes as a New Concept to Increase Current and Luminous Efficacy
Authors: Lindla Florian , Boesing Manuel , Zimmermann Christoph , Jessen Frank , van Gemmern Philipp , Bertram Dietrich , Keiper Dietmar , Meyer Nico , Heuken M. , Kalisch Holger , Jansen Rolf H.
Published: June 2009

The current and luminous efficacy of a red phosphorescent organic light emitting diode (OLED) with sharp interfaces between each of the organic layers can be increased from 18.8 cd/A and 14.1 lm/W (at 1,000 cd/m2) to 36.5 cd/A (+94%, 18% EQE) and 33.7 lm/W (+139%) by the introduction of a layer cross-fading zone at the hole transport layer (HTL) to emission layer (EL) interface. Layer cross-fading describes a procedure of linearly decreasing the fraction in growth rate of an organic layer during deposition over a certain thickness while simultaneously increasing the fraction in growth rate of the following layer. For OLED processing and layer cross-fading organic vapor phase deposition (OVPD) is used. The typical observation of a roll-off in current efficacy of phosphorescent OLED to higher luminance can be reduced significantly. An interpenetrating network of a prevailing hole and a prevailing electron conducting material is created in the cross-fading zone. This broadens the recombination zone and furthermore lowers the driving voltage. The concept of layer cross-fading to increase the efficacies is suggested to be useful in multi-colored OLED stacks as well.
Synthesis and Optical properties of Perylene Bisimide Incorporated Low Bandgap Polymers for Photovoltaics
Authors: Vajiravelu Sivamurugan , valiyaveettil suresh
Published: June 2009

Herein we report on the synthesis of perylene diimide (PDI) based P1 and P2 conjugated polymers via Suzuki polymerization. The chemical structure of the polymers was elucidated using GPC, 1H, 13C NMR and elemental analysis. The absorption spectra of polymers were in the visible region from 250 – 800 nm in solution and in solid state. The optical band gap was (Egopt) found to be between 1.60 – 1.83 eV in solid state.
Reduced Contact Resistances in Organic Transistors with Secondary Gates on Source and Drain Electrodes
Authors: Nakayama Kengo , Uemura Takafumi , Uno M. , Takeya Jun
Published: June 2009

Secondary-gate electrodes are introduced in organic thin-film transistors to reduce carrier-injection barriers into air-stable organic semiconductors. The additional gate electrodes buried in the gate insulators under the source and drain electrodes form “carrier-rich regions” in the vicinity of source and drain electrodes with the application of sufficiently high local electric fields. Fabricating the structure with dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene, known for its excellent air-stability, it turned out that the contact resistance is drastically reduced especially when operated at low gate voltage in the main channel. The result demonstrates carrier injection with a minimized potential barrier realizing that from the same semiconductor material in the absence of peculiar interfacial trap levels at metal-to-semiconductor junctions.
Formation of Ohmic Carrier Injection at Anode/organic Interfaces and Carrier Transport Mechanisms of Organic Thin Films
Authors: Matsushima Toshinori , Jin Guang-He , Kanai Yoshihiro , Yokota Tomoyuki , Kitada Seiki , Kishi Toshiyuki , Murata Hideyuki
Published: June 2009

We have shown that hole mobilities of a wide variety of organic thin films can be estimated using a steady-state space-charge-limited current (SCLC) technique due to formation of Ohmic hole injection by introducing a very thin hole-injection layer of molybdenum oxide (MoO3) between an indium tin oxide anode layer and an organic hole-transport layer. Organic hole-transport materials used to estimate hole mobilities are 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA), 4,4′,4″-tris(N-2-naphthyl-N-phenyl-amino)triphenylamine (2-TNATA), rubrene, N,N′-di(m-tolyl)-N,N′-diphenylbenzidine (TPD), and N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD). These materials are found to have electric-field-dependent hole mobilities. While field dependence parameters (β) estimated from SCLCs are almost similar to those estimated using a widely used time-of-flight (TOF) technique, zero field SCLC mobilities (μ0) are about one order of magnitude lower than zero field TOF mobilities.
Accurate and Simultaneous Determination of Carrier Density and Mobility in Organic Semi-conducting Materials
Authors: Shum Kai , Chen Zhuo , Xue Chenming , Jin Shi
Published: June 2009

How to accurately determine carrier mobility and density in organic semiconducting materials is a very important subject for their optoelectronic applications including light-emitting diodes, solar cells, and thin film field-effect transistors. In this work, we report on a unique data analysis procedure for space-charge limited currents to simultaneously obtain the carrier density and mobility in semiconducting organic-materials. This procedure has been used for a few newly synthesized perylene tetracarboxylic diimide (PDI) derivatives with tunable π-stack structures without altering the electronic characteristic of individual molecules. How π-stack structural variation and residual carrier density affect electron transport performance will be discussed.
Ultra-Low energy Ion Implantation of Si into HfO2-based layers for Non Volatile Memory Applications
Authors: Coulon Pierre-Eugène , Chan Shin Yu Kristel , Schamm Sylvie , Ben Assayag Gerard , Pécassou Béatrice , Slaoui Abdelilah , Bhabani Sahu , Carrada Marzia , Lhostis Sandrine , Bonafos Caroline
Published: June 2009

The fabrication of NCs is carried out using an innovative method, ultra-low energy (≤5 keV) ion implantation (ULE-II) into thin (6-9 nm) HfO2–based layers in order to form after subsequent annealing a controlled 2D array of Si NCs. The implantation of Si into HfO2 leads to the formation of SiO2–rich regions at the projected range due to the oxidation of the implanted Si atoms. This anomalous oxidation that takes place at room temperature is mainly due to humidity penetration in damaged layers. Different solutions are investigated here in order to avoid this oxidation process and stabilize the Si-phase. Finally, unexpected structures as HfO2 NCs embedded with SiO2 matrix are obtained and show interesting memory characteristics. Interestingly, a large memory window of 1.18 V has been achieved at relatively low sweeping voltage of ± 6 V for these samples, indicating their utility for low operating voltage memory device.
Localized Silicon Nanocrystals Fabricated by Stencil Masked Low Energy Ion Implantation: Effect of the Stencil Aperture Size on the Implanted Dose
Authors: Diaz Regis , Dumas Carine , Grisolia Jeremie , Ondarçuhu Thierry , Schamm Sylvie , Arbouet Arnaud , Paillard Vincent , BenAssayag Gerard , Normand Pascal , Brugger Juergen
Published: June 2009

In this paper, we develop a new method based on ultra-low-energy ion implantation through a stencil mask to locally fabricate Si nanocrystals in an ultrathin silica layer. We perform a 1 keV Si implantation with doses of 5×1015 Si+/cm2, 7.5×1015 Si+/cm2 and 1×1016 Si+/cm2 in a 7 nm thick silicon oxide layer through stencil mask apertures ranging from 1μm up to 5 μm. After the mask removal the samples are furnace annealed at a temperature of 1050°C for 90 min under N2 atmosphere. The samples are then characterized by mapping the implanted and non-implanted areas by atomic force microscopy and photoluminescence spectroscopy. The intensity and the wavelength of the PL peak are found to depend on the implanted NCs cell size. A slight blue shift from 730 nm up to 720 nm is observed with decreasing cell size. Simultaneously, the PL intensity decreases and the signal vanishes for submicron features (which should contain 102 to 103 NCs). AFM microcopy performed on the implanted regions shows that the well-known oxide swelling usually observed after NCs synthesis decreases from 3.5 nm down to 0 as the cell size decreases. This result demonstrates that the effective implanted dose clearly decreases with the size of the cells. This effect is probably due to an electrostatic charging of the Si3N4 membrane despite the metallization treatments applied to the mask surface.
A Simulation Model of Resistive Switching in Electrochemical Metallization Memory Cells (ECM)
Authors: Menzel Stephan , Klopstra Bart , Kügeler Carsten , Böttger Ulrich , Staikov Georgi , Waser Rainer
Published: June 2009

The storage principal of the Electrochemical Metallization Memory Cell is based on change of cell resistance induced by electro-chemical driven growth and rupture of a cupric or silver filament in an insulating matrix. This kind of switching was found in several materials as AgGeSe, CuGeS, silicon oxide or tungsten oxide [1].

During write operation copper or silver is oxidized at the corresponding electrode and copper or silver ions are driven out of the copper or silver anode into the insulating matrix due to the applied field, whereas the insulating matrix serves as solid electrolyte. The silver or copper ions migrate towards the cathode. At the cathode electrochemical reduction occurs, and deposition of metallic copper or silver takes place. Fast diffusion paths in the solid electrolyte matrix or preferred nucleation sites (seeds) at the boundary lead to filamentary growth. This growing cupric or silver dendrite finally reaches the anode and switches the device to a low resistance state.

Based on this switching mechanism a FEM simulation model was set up. To simplify the model space charges due to silver or copper migration are neglected. It is further assumed, that the conductivity in the solid electrolyte is only ionic. Hence, it is sufficient to solve the well-known Laplace equation to address the electric properties as well as ion migration. A “Level Set” method is used to track the boundary of the growing filament. The velocity of this boundary is proportional to the ionic current density calculated by Laplace equation. Based on this model simulations are applied to cell structures with multiple fast diffusion paths and seeds. Simulation results show that just one filament reaches the anode.

In a second step, Butler-Vollmer boundary conditions are introduced. This nonlinearity leads to an exponential dependence between switching time and switching voltage. As switching voltage increases, switching time decreases.

A simulation model capable of simulating ECM memory cells is presented. The model enables to simulate the behaviour of different cell geometries or different materials as solid electrolyte. Furthermore it gives deeper insight into the switching mechanism.

This work was supported by the European project EMMA “Emerging Materials for Mass storage Architectures” (FP6-033751).
Ultraviolet Photoresponse of Pure and Al doped ZnO Polycrystalline Thin Films by Inkjet Printing
Authors: Wu Yan , Tamaki Takahiko , Voit Wolfgang , Belova Lyubov M. , Rao K. V.
Published: June 2009

Pure ZnO, and Al doped ZnO, 120 -300 nm thin films on glass substrates, were synthesized by inkjet printing technique using zinc and aluminum acetate solution as precursors and a two stage heat treatment process to obtain polycrystalline hexagonal wurtzite structure with the mean grain size of 25 and 30 nm respectively. All films exhibit a transmittance above 85-90% in the visible wavelength range below 700 nm. In the Al doped films the UV absorption spectra show a strong absorption onset below 380nm followed by shoulders centered around 325 nm depending on the film thickness. The electrical conductivity of Al doped ZnO thin films is larger by two orders of magnitude than that for pure ZnO films while the photoconductivity increases by about three orders of magnitude under UV irradiation. The photoresponse of the films with UV irradiation in terms of the rise and decay times in the frequency range from 5 to 500 Hz is also presented and discussed.
Optimization of Ce Content in CexLa1-xF3 Colloidal Nanocrystals for Gamma Radiation Detection
Authors: Withers Nathan J , Sankar Krishnaprasad , Plumley John B , Akins Brian A , Memon Tosifa A , Rivera Antonio C , Smolyakov Gennady , Osiński Marek
Published: June 2009

We report on experimental investigations of CexLa1-xF3 colloidal nanocrystals (CNCs) and their properties in function of Ce content. The CNCs were characterized by TEM, energy-dispersive X-ray spectroscopy (EDS), steady-state UV-VIS optical absorption and photoluminescence (PL) spectroscopy, and by PL lifetime measurements. We also report on observations of scintillation from the cerium-doped lanthanum fluoride CNC material in experiments on radiation detection.
The Influence of the Composition Ratio on CZTS-based Thin Film Solar Cells
Authors: Katagiri Hironori , Jimbo Kazuo , Tahara Masami , Araki Hideaki , Oishi Koichiro
Published: June 2009

Cu2ZnSnS4 (CZTS) thin films were fabricated by using three RF co-sputtering continued with sulfurization method. The new type of thin film solar cells using CZTS as an absorber consists of buffer-layer and window-layer on CZTS films that were fabricated on a Mo-coated Soda Lime Glass (SLG) substrate. It was confirmed that CZTS solar cells with high conversion efficiency existed in a relatively narrow composition region. In this paper, the fabrication method of CZTS-based thin film solar cells in our laboratory was stated briefly and the influence of the composition ratio on the photovoltaic properties were presented. Furthermore, the properties of a genuine non-toxic solar cell using a Cd-free buffer-layer were introduced.
Structural Properties of CdTe Thin Films for Solar Cell Applications Deposited on Flexible Foil Substrates
Authors: Palekis Vasilios , Hodges Deidra Ranel , Morel Don L , Stefanakos Lee , Ferekides Chris S
Published: June 2009

Cadmium telluride (CdTe) is a leading thin film photovoltaic (PV) material due to its near ideal band gap of 1.45 eV and its high optical absorption coefficient. The typical CdTe thin film solar cell is of the superstrate configuration where a window layer (CdS), the absorber (CdTe), and a back contact are deposited onto a glass slide coated with a transparent electrode. Substrate CdTe solar cells where the above listed films are deposited in reverse order are not common. In this study, the growth of CdTe thin films deposited on foil substrates by the close-spaced sublimation (CSS) has been investigated for the purpose of fabricating substrate based CdTe solar cells. The CdTe films were deposited at substrate temperatures (TSUB) in the range of 300 to 600°C, and source temperatures (TSRC) in the 600 to 650°C range. The effect of the substrate-source temperature variations on the growth rate, film structure and morphology were studied using XRD and SEM. It was found that for low substrate temperature and as the growth rate increases, grain size was the same but the films appeared to be more uniform and more densely packed with less or no pinholes. The growth rate increased as the source temperature increased. The substrate temperature clearly influences the grain growth and the preferred orientation. As the substrate temperature increased the growth rate decreased and the grain size varied from 2 to 6 μm. XRD analysis showed that with the increase in substrate temperature film orientation changes from preferential along the (111) direction to a mix of (111) (220) and (311).
Interdiffusion of Bi and Sb in Superlattices Built from Blocks of Bi2Te3, Sb2Te3 and TiTe2
Authors: Mortensen Clay D. , Johnson David
Published: June 2009

The reaction kinetics of [(Ti-Te)]x[(Sb-Te)]y, [(Bi-Te)]x[(Sb-Te)]y, [(Ti-Te)]w[(Bi-Te)]x and [(Ti-Te)]w[(Bi-Te)]x[(Ti-Te)]y[(Sb-Te)]z precursors as a function of annealing temperature and time was probed using x-ray diffraction techniques to define the parameters required to form superlattice structures. [(TiTe2)1.36]x[Sb2Te3]y and [(TiTe2)1.36]x[Bi2Te3]y superlattices were observed to form while [(Bi-Te)]x[(Sb-Te)]y precursors yielded only Bi2-xSbxTe3 alloys. This behavior was correlated with the immiscibility/miscibility of the constituents of the targeted superlattices. For the three component system, Bi and Sb were observed to interdiffuse through the Ti-Te layer over the range of Ti-Te thicknesses explored, resulting in formation of (BixSb1-x)2Te3 alloys within the superlattice structure. When the Bi2Te3 and Sb2Te3 thicknesses were equal, symmetric [{(TiTe2)}1.36]w[(Bi0.5Sb0.5)2Te3]y superlattices were formed.
Enhancement of Thermoelectric Figure-of-Merit by a Nanostructure Approach
Authors: Ren Zhifeng , Poudel Bed , Ma Yi , Lan Yucheng , Minnich Austin , Muto Andy , Yang Jian , Yu Bo , Yan Xiao , Wang Dezhi , Liu Junming , Dresselhaus Mildred , Chen Gang
Published: June 2009

The dimensionless thermoelectric figure-of-merit (ZT) in bulk materials has remained about 1 for many years. Here we show that a significant ZT improvement can be achieved in nanocrystalline bulk materials. These nanocrystalline bulk materials were made by hot-pressing nanopowders that are ball-milled from either crystalline ingots or elements. Electrical transport measurements, coupled with microstructure studies and modeling, show that the ZT improvement is the result of low thermal conductivity caused by the increased phonon scattering by grain boundaries and defects. More importantly, the nanostructure approach has been demonstrated in a few thermoelectric material systems, proving its generosity. The approach can be easily scaled up to multiple tons. Thermal stability studies have shown that the nanostructures are stable at the application temperature for an extended period of time. It is expected that such enhanced materials will make the existing cooling and power generation systems more efficient.
Size Effects on the Thermal Properties of Self-assembled Ge Quantum Dots in Single-crystal Silicon
Authors: Gillet Jean-Numa
Published: June 2009

Superlattices with an ultra-low thermal conductivity were extensively studied to design thermoelectric materials. However, since they are made up of superposed materials showing lattice mismatches, they often show cracks and dislocations. Therefore, it is challenging to fabricate superlattices with a thermoelectric figure of merit ZT higher than unity. Moreover, like nanowires, they decrease heat transport in only one main direction. Self-assembly from epitaxial layers on a Si substrate is a major bottom-up technology to fabricate 3D Ge quantum-dot (QD) arrays in Si, which have been used for 3D quantum-device applications. Using the model of the atomic-scale 3D phononic crystal, we showed that 3D high-density arrays of self-assembled Ge QDs in Si can also show an ultra-low thermal conductivity in 3D, which can be several orders of magnitude lower than that of bulk Si. As a result, they can be considered to design novel 3D thermoelectric devices showing CMOS compatibility. In an example QD crystal, the thermal conductivity can be decreased below only 0.2 W/m/K. The main objective of this paper is to show the size dependence of the thermal conductivity versus the supercell lattice parameter d. For a constant QD-crystal filling ratio x = 12.5 at%, a decrease of the thermal conductivity is observed for an increasing d. This analysis enables us to predict that the optimal d-value will be of the order of 11 nm for the given filling ratio. At this optimum, the thermal conductivity decreases to the global minimum value of 0.9 W/m/K. The presented results are a first step towards the optimal design of thermoelectric devices with a maximal ZT obtained by global optimization of the size parameters.
Rectifying Polarity Switch of Pt/TiO2-x/Pt
Authors: Zhong Ni , Shima Hisashi , Akinaga Hiro
Published: June 2009

Current-voltage (I-V) characteristic of Pt/TiO2-x/Pt has been investigated. The Pt/TiO2-x/Pt devices in the initial state exhibit a rectifying I-V behavior. By applying a pulse voltage, the rectifying polarity could be switched to an opposite direction. The mechanism of the rectifying polarity switch is proposed as the local drift of defects, such as oxygen vacancies (VO), due to applying pulse voltage. It is found that the required pulse voltage height for the polarity switch (Vswitch) exhibits much dependence on the operation temperature and width of applied pulse voltage. With an increase of the pulse voltage width or the measurement temperature (T), Vswitch exhibits a decrease with increase of T. These results suggest that the rectifying polarity switch in the Pt/TiO2-x/Pt is attributed to a thermal and dynamic dependence process, which agree well with the localized migration of VO induced by applied pulse voltage.
Synthesis and Characterization of Flowerlike ZnO Nanoneedle Arrays on Si (100)
Authors: Yang Boqian , Feng Xianping
Published: June 2009

Flowerlike ZnO nanoneedle arrays have been synthesized on Si (100) substrates by pulsed laser deposition techniques. The tips of the nanoneedles are ˜ 20- 50 nm in diameter and their roots are as thick as ˜ 50- 100 nm. The nanoneedle arrays grow preferentially along the [0001] direction. Raman spectroscopy shows three first order optical normal modes which confirm wurtzite structure of ZnO nanoneedles. In the low frequency zone, additive modes (92, 122, 163, and 275 cm-1) are observed and can be attributed to zone boundary phonons. ZnO nanoneedle arrays exhibit a strong UV luminescence emission, and two strong peaks at 3.258 eV and 3.288 eV are observed.
Tailoring TMR Ratios by Ultrathin Magnetic Interlayers: A First-principles Investigation of Fe/MgO/Fe
Authors: Bose Peter , Zahn Peter , Henk Juergen , Mertig Ingrid
Published: June 2009

For spintronic device applications, large and in particular tunable tunnel magnetoresistance (TMR) ratios are inevitable. Fully crystalline and epitaxially grown Fe/MgO/Fe magnetic tunnel junctions (MTJs) are well suited for this purpose and, thus, are being intensively studied [1]. However, due to imperfect interfaces it is difficult to obtain sufficiently large TMR ratios that fulfill industrial demands (e.g. [2]).

A new means to increase TMR ratios is the insertion of ultra-thin metallic buffer layers at one or at both of the Fe/MgO interfaces. With regard to their magnetic and electronic properties as well as their small lattice mismatch to Fe(001), Co and Cr spacer are being preferably investigated.

We report on a systematic first-principles study of the effect of Co and Cr buffers (with thicknesses up to 6 ML) in Fe/MgO/Fe magnetic tunnel junctions (MTJs) on the spin-dependent conductance. The results of the transport calculations reveal options to specifically tune the TMR ratio. Symmetric junctions, i.e. with Co buffers at both interfaces, exhibit for some thicknesses much larger TMR ratios in comparison to those obtained for Fe-only electrodes. Further, antiferromagnetic Cr films at a single interface introduce TMR oscillations with a period of 2 ML, a feature which provides another degree of freedom in device applications. The comparison of our results with experimental findings shows agreement and highlights the importance of interfaces for the TMR effect.
Quantitative Electron Diffraction for Crystal Structure Determination
Authors: Oleynikov Peter , Grüner Daniel , Zhang Daliang , Sun Junliang , Zou Xiaodong , Hovmöller Sven
Published: June 2009

We present a quantitative investigation of data quality using electron precession, compared to standard selected-area electron diffraction (SAED). Data can be collected on a CCD camera and automatically extracted by computer. The critical question of data quality is addressed – can electron diffraction data compete with X-ray diffraction data in terms of resolution, completeness and quality of intensities?
Comparison of two Metal Ion Implantation Techniques for Fabrication of Gold and Titanium Based Compliant Electrodes on Polydimethylsiloxane
Authors: Niklaus Muhamed , Rosset Samuel , Dubois Philippe , Shea Herbert R.
Published: June 2009

This study contrasts the implantation of 25 μm thick Polydimethylsiloxane (PDMS) membranes with titanium and gold ions at 10 keV and 35 keV for doses from 1×1015at/cm2to 2.5×1016at/cm2implanted with two different techniques: Filtered Cathodic Vacuum Arc (FCVA) and Low Energy Broad Ion Beam (LEI). The influence of the ion energy, ion type, and implantation tool on the Young’s modulus (E), resistivity and structural properties (nanocluster size and location, surface roughness) of PDMS membranes is reported. At a dose of 2.5×1016at/cm2and an energy of 10 keV, which for FCVA yields sheet resistance of less than 200 Ω/square, the initial value of E (0.85 MPa) increases much less for FCVA than for LEI. For gold we obtain E of 5 MPa (FCAV) compared to 86 MPa (LEI) and for titanium 0.94 MPa (FCVA) compared to 57 MPa (LEI). Resistivity measurements show better durability for LEI than for FCVA implanted samples and better time stability for gold than for titanium.
Design of Architectured Sandwich Core Materials using Topological Optimization Methods
Authors: Laszczyk Laurent , Dendievel Rémy , Bouaziz Olivier , Bréchet Yves , Parry Guillaume
Published: June 2009

Sandwich structures are especially interesting when multiple functionalities (such as stiffness and thermal insulation) are required. Properties of these structures are strongly dependent on the general geometry of the sandwich, but also on the detailed patterns of matter partitioning within the core. Therefore it seems possible to tailor the core pattern in order to obtain the desired properties. But multi-functional specifications and the infinite number of possible shapes, leads to non-trivial selection and/or optimization problems.
In this context of “material by design”, we propose a numerical approach, based on structural optimization techniques, to find the core pattern that leads to the best performances for a given set of conflicting specifications. The distribution of matter is defined thanks to a level-set function, and the convergence toward the optimized pattern is performed through the evolution of this function on a fixed grid. It is shown that the solutions of optimization are strongly dependent on the formulation of the problem, which have to be chosen with respect to the physics.
A first application of this approach is presented for the design of sandwich core materials, in order to obtain the best compromise between flexural stiffness and relative density. The influence of both the initialization (starting geometry) and the formulation of the optimization problem are detailed.
Multifunctional One-dimensional Phononic Crystal Structures Exploiting Interfacial Acoustic Waves
Authors: To Albert C , Lee Bong Jae
Published: June 2009

The present study demonstrates that interfacial acoustic waves can be excited at the interface between two phononic crystals. The interfacial wave existing between two phononic crystals is the counterpart of the surface electromagnetic wave existing between two photonic crystals. While past works on phononic crystals exploit the unique bandgap phenomenon in periodic structures, the present work employs the Bloch wave in the stop band to excite interfacial waves that propagate along the interface and decay away from the interface. As a result, the proposed structure can be used as a wave filter as well as a thermal barrier. In wave filter design, for instance, the incident mechanical wave energy can be guided by the interfacial wave to the lateral direction; thus, its propagation into the depth is inhibited. Similarly, in thermal barrier design, incident phonons can be coupled with the interfacial acoustic wave, and the heat will be localized and eventually dissipated at the interface between two phononic crystals. Consequently, the thermal conductivity in the direction normal to the layers can be greatly reduced. The advantage of using two phononic crystals is that the interfacial wave can be excited even at normal incidence, which is critical in many engineering applications. Since the proposed concept is based on a one-dimensional periodic structure, the analysis, design, and fabrication are relatively simple compared to other higher dimensional material designs.
Modelling the Mechanical and Thermal Properties of Cellular Materials from the Knowledge of their Architecture
Authors: Maire Eric , Caty O. , Bouchet R. , Loretz M. , Adrien J.
Published: June 2009

This paper shows different examples where the architecture of cellular materials has been determined exactly using 3D X ray computed tomography. The images were then subsequently used to generate FE meshes reproducing the architecture as exactly as possible. The FE meshes where in turn used to simulate the mechanical (monotonous and fatigue compression) and the thermal (radiative properties) behavior of the studied materials.
Triple-Shape Capability of Thermo-sensitive Nanocomposites from Multiphase Polymer Networks and Magnetic Nanoparticles
Authors: Uttamchand Narendra Kumar , Kratz Karl , Behl Marc , Lendlein Andreas
Published: June 2009

Thermo-sensitive multiphase polymer networks with triple-shape capability have been recently introduced as a new class of active polymers that can change on demand from a first shape A to a second shape B and from there to a permanent shape C. Such multiphase polymer networks consist of covalent cross-links that determine shape C and at least two phase-segregated domains with distinct thermal transitions Ttrans,A and Ttrans,B , that are associated to shape A and B. In general the application of a two step programming or a one step programming procedure is required for creation of triple-shape functionality. In this study we report about a series of CLEGC nanocomposites consisting of silica coated nanoparticles (SNP) incorporated in a multiphase graft polymer network matrix from crystallisable poly(ε-caprolactone) diisocyanatoethyl methacrylate (PCLDIMA) and poly(ethylene glycol) monomethyl ether monomethacrylate (PEGMA) forming crystallisable side chains. These CLEGC nanocomposites were designed to enabling non contact activation of triple-shape effect in alternating magnetic field. Composites with variable PCLDIMA content ranging from 30 wt-% and 70 wt-% and different SNP amounts (0 wt-%, 2.5 wt-%, 5 wt-% and 10 wt-%) were realized by thermally induced polymerization. The thermal and mechanical properties of the CLEG nanocomposites were explored by means of DSC, DMTA and tensile tests. The triple-shape properties were quantified in cyclic, thermomechanical experiments, which consisted of a two step programming procedure and a recovery module under stress-free conditions for recovery of shapes B and C.
While the thermal properties and the Young’s modulus of the investigated polymer networks were found to be independent from the incorporated amount of SNP, the elongation at break (εB) decreases with increasing nanoparticle content. All investigated composites exhibit excellent triple-shape properties showing a well separated two step shape recovery process.
Microfluidic Manifolds with High Dynamic Range in Structural Dimensions Replicated in Thermoplastic Materials
Authors: Becker Holger , Beckert Erik , Gärtner Claudia
Published: June 2009

In this paper, we present the manufacturing process of a polymer microfluidic device which is currently being used to investigate wetting properties of nanostructured microchannels replicated in hydrophobic thermoplastic materials like cyclo-olefin co-polymer (COC), polypropylene (PP) or polymethylmetacrylate (PMMA). These devices feature large structural dynamics (feature sizes between 200 μm and 200 nm). The mold insert necessary was fabricated using a combination of precision machining with single-point diamond turning (SPDT).
Potencial fungitóxico do óleo essencial de Piper hispidinervum (pimenta longa) sobre os fungos fitopatogênicos Bipolaris sorokiniana, Fusarium oxysporum e Colletotrichum gloeosporioides
Authors: Zacaroni Lidiany Mendonça , Cardoso Maria Graças , Souza Paulo Estevão , Pimentel Flavio Araujo , Guimarães Luiz Gustavo de Lima , Salgado Ana Paula Soares Pinto
Published: June 2009

O objetivo deste trabalho foi avaliar a atividade fungicida in vitro do óleo essencial das folhas de Piper hispidinervum sobre Bipolaris sorokiniana, Fusarium oxysporum e Colletotrichum gloeosporioides. Para os ensaios biológicos, empregou-se o teste bioanalítico in vitro utilizando as concentrações de 100, 200, 500, 1000, 1500 e 2000 µg.mL-1 do óleo essencial. Estas foram incorporadas no meio de cultura BDA (batata-dextrose-ágar) para avaliação do crescimento ou inibição micelial. O delineamento estatístico utilizado foi o inteiramente casualizado, com quatro repetições. Na concentração de 200 µg.mL-1, observou-se uma inibição total do fitopatógeno Bipolaris sorokiniana enquanto que, para o Fusarium oxysporum e o Colletotrichum gloeosporioides esta ocorreu na concentração de 1000 µg.mL-1.
Debt renegotiation with incomplete contract
Authors: Jorge Neto Paulo de Melo
Published: June 2009

A debt contract usually does not include a provision about renegotiation. The right to seize the borrower’s asset and the rules of this process are usually stipulated in the contract. Such a promise not to renegotiate is not credible since renegotiation can mitigate the dead-weight loss of liquidating insolvent borrowers. Once the initial contract may not consider the renegotiation procedure and renegotiation may occur, this paper investigates why a complete contract is not offered. It shows that the lender does not need to stipulate the renegotiation procedure on the initial contract because he is indifferent about committing or not to the terms of a contract. This indicates that a complete contract gives the lender the same expected return as an incomplete contract, in which the renegotiation process is determined after the occurrence of default.
Um algoritmo de planos-de-corte para o número cromático fracionário de um grafo
Authors: Campêlo Manoel , Campos Victor A. , Corrêa Ricardo C.
Published: June 2009

O número cromático fracionário χF(G) de um grafo G é um conhecido limite inferior para seu número cromático χ(G). Experimentos relatados na literatura mostram que usar χF(G), em lugar do tamanho da clique máxima, pode ser muito mais eficiente para orientar a busca em um algoritmo tipo branch-and-bound para determinação de χ(G). Uma dificuldade, porém, é tratar o modelo linear conhecido para χF(G), o qual apresenta um número exponencial de variáveis e demanda um caro processo de geração de colunas. Neste trabalho, examinamos uma formulação alternativa para obter um limite inferior para χF(G) que possui um número de variáveis linear no tamanho do grafo, porém um número exponencial de restrições. Utilizamos o método de planos-de-corte para lidar com esse inconveniente. Algumas heurísticas de separação são propostas, e experimentos computacionais mostram que valores muito próximos de χF(G), em muitos casos iguais, são encontrados em tempo inferior à implementação com geração de colunas.
The influence of lidocaine and racemic bupivacaine on neuromuscular blockade produced by rocuronium: a study in rat phrenic nerve-diaphragm preparation
Authors: Carvalho Vanessa Henriques , Braga Angélica de Fátima de Assunção , Braga Franklin Sarmento da Silva , Loyola Yolanda Christina S. , Araújo Daniele Ribeiro de , Mantovani Mario
Published: June 2009

PURPOSE: To evaluate in vitro lidocaine and racemic bupivacaine effects in neuromuscular transmission and in neuromuscular blockade produced by rocuronium. METHODS: Rats were distributed in 5 groups (n = 5) in agreement with the studied drugs: lidocaine, racemic bupivacaine, rocuronium, separately (Groups I, II, III); rocuronium in preparations exposed to local anesthetics (Groups IV, V). The concentrations used were: 20 µg/mL, 5 µg/mL and 4 µg/mL, for lidocaine, bupivacaine and rocuronium, respectively. It was evaluated: 1) amplitude of diaphragm muscle response to indirect stimulation, before and 60 minutes after separately addition of lidocaine, racemic bupivacaine and rocuronium and the association of local anesthetics - rocuronium; 2) membrane potentials (MP) and miniature end-plate potentials (MEPP). RESULTS: Lidocaine and bupivacaine separately didn't alter the amplitude of muscle response and MP. In preparations previously exposed to lidocaine and racemic bupivacaine, the rocuronium blockade was significantly larger (90.10 ± 9.15% and 100%, respectively), in relation to the produced by rocuronium separately (73.12 ± 9.89%). Lidocaine caused an increase in the frequency of MEPP, being followed by blockade; racemic bupivacaine produced decrease being followed by blockade. CONCLUSIONS: Local anesthetics potentiated the blockade caused by rocuronium. The alterations of MEPP identify presynaptic action.
The impact of different shift work schedules on the levels of anxiety and stress in workers in a petrochemicals company
Authors: Almondes Katie Moraes de , Araújo John Fontenele
Published: June 2009

This study evaluated anxiety and stress in workers under different shift work conditions. The sample comprised 239 workers, with an average age of 42.6, standard deviation = 5.7 years, divided into fixed daytime working (n=52) and different working shifts (n=187). Documentation: Free and informed consent form; ID's; State-Trait Anxiety Inventory; Lipp's Stress Symptom Inventory for Adults. We used the t-test for independent samples, ANOVA, Pearson's correlation and the two-sample Comparison of proportions Test. Results showed that shift workers had higher State-Trait Anxiety scores than fixed daytime workers (t=-4.994; p=0.0001; t=-2.816; p=0.005, respectively). Both samples exhibited stress, but there were no statistically significant differences between the groups (t=-1.052; p=0.294). Shift work schedules caused more situational and dispositional anxiety, but did not significantly increase stress levels when compared to fixed daytime working.
Reavaliando o Bem Sex-Role Inventory
Authors: Hernandez José Augusto Evangelho
Published: June 2009

O objetivo deste estudo foi avaliar a estrutura do Bem Sex Role Inventory respondido por uma amostra não probabilística de homens e mulheres brasileiras. Mais de uma década após a última revisão brasileira do inventário, um novo exame faz-se necessário, devido à forte influência cultural sobre seus itens. A escala foi aplicada junto a 922 sujeitos, recrutados em diversos locais de Porto Alegre (RS) e região metropolitana. Foi realizada uma avaliação da estrutura da escala usando a técnica estatística análise fatorial. Além disso, foi examinada a fidedignidade do instrumento. Os resultados obtidos foram comparados com os estudos anteriores. Em geral, apareceram evidências que dão forte apoio à versão verificada e, desta forma, habilitam-na para ser usada na pesquisa psicológica.
A falta da falta e o objeto da angústia
Authors: Pisetta Maria Angélica Augusto de Mello
Published: June 2009

Pretende-se, com este artigo, discutir a especificidade do objeto da angústia, declarado como inexistente por Freud. Com a formulação teórica estabelecida por Lacan em 1962/1963 de um objeto conceitual que escapa a toda significação e apreensão imaginária, essa discussão tomou novos contornos. Trata-se do conceito de objeto a, um objeto constituído de pura falta, decorrente de uma insatisfação. Este texto desenvolveu-se a partir da concepção da perda do objeto de satisfação, citada por Freud como mítica. Intenta-se também aproximar o conceito de objeto a dos conceitos de "estranho" e "familiar", relacionados por Freud em 1919 ao conceito da angústia, considerando-se a declaração lacaniana da proximidade do que é familiar na vivência deste conceito.
Estimação de estados harmônicos usando estratégias evolutivas
Authors: Arruda E. F. , Kagan N.
Published: June 2009

O objetivo deste trabalho é apresentar uma nova metodologia para estimar a distorção harmônica em um sistema elétrico, a partir de medições em locais específicos. O algoritmo desenvolvido se baseia em Estratégias Evolutivas. Esta técnica compreende um ramo de desenvolvimento dos Algoritmos Evolutivos, no qual se inserem os Algoritmos Genéticos. As vantagens no uso desta técnica residem nas facilidades de modelagem e em encontrar uma solução para problemas complexos. A maioria das técnicas encontradas na literatura para solução deste problema utiliza sincronização das medições por meio de métodos de alta tecnologia como GPS. O algoritmo proposto visa sincronizar os dados de forma offline por meio das informações do fluxo de carga para a freqüência fundamental, o que o torna muito mais econômico para compor um sistema de monitoramento de qualidade de energia. O algoritmo foi aplicado em uma rede de teste cujos dados foram extraídos do IEEE.
Brinquedo terapêutico: estratégia de alívio da dor e tensão durante o curativo cirúrgico em crianças
Authors: Kiche Mariana Toni , Almeida Fabiane de Amorim
Published: June 2009

OBJETIVO: Comparar as reações manifestadas pela criança durante o curativo realizado antes e após o preparo emocional com o brinquedo terapêutico instrucional (BTI). MÉTODOS: A amostra constituiu-se de 34 crianças internadas para cirurgia em um hospital público pediátrico da cidade de São Paulo. Os comportamentos da criança e a avaliação da dor foram considerados durante o curativo em dois momentos: antes e após o brinquedo terapêutico. RESULTADOS: Comportamentos indicativos de maior adaptação e aceitação ao procedimento tornaram-se mais freqüentes após o brinquedo, ao contrario daqueles que indicavam menor adaptação e aceitação. Os escores de dor também diminuíram após o brinquedo terapêutico. CONCLUSÃO: O brinquedo terapêutico se evidenciou como estratégia efetiva na redução do medo, da tensão e da dor da criança durante o curativo.
Adaptação cultural de instrumento que avalia atividades do trabalho e sua relação com sintomas osteomusculares
Authors: Coluci Marina Zambon Orpinelli , Alexandre Neusa Maria Costa
Published: June 2009

OBJETIVO: Traduzir e adaptar culturalmente o questionário Work-related activities that may contribute to job-related pain and/or injury para o português falado no Brasil e verificar a validade de conteúdo desta nova versão. MÉTODOS: A adaptação cultural seguiu normas internacionalmente aceitas com as etapas de tradução, síntese, retro-tradução, avaliação por um comitê de especialistas e pré-teste. Esta versão do instrumento foi aplicada em 40 trabalhadores. RESULTADOS: O procedimento de adaptação cultural foi realizado com sucesso. O comitê de especialistas verificou a validade de conteúdo e realizou algumas modificações. No pré-teste, 7,5% dos indivíduos indicaram sugestões para um item do questionário e 17,5% demonstraram dificuldades no entendimento da instrução. Informações adicionais foram incluídas para tornar o instrumento final mais compreensível. CONCLUSÕES: A versão brasileira deste instrumento foi obtida com sucesso.