bluuebunny/crossref_metadata_2025 huggingface dataset:
Complex Interactions of Pollutant and Allergen Exposures and Their Impact on People With Asthma
Authors: Eggleston Peyton A.
Published: February 2009

Pediatric asthma has many causes and can manifest differently in different children and at different times. Understanding the many factors related to the development and exacerbation of asthma is complicated by the complexity of the many environmental exposures related to asthma development and morbidity. Furthermore, the same environmental exposures that may cause increased symptoms at 1 point in time may be protective when the exposure occurs earlier or at high enough levels. We know that environmental exposures such as allergens, irritants, and pollutants are quite complex in their composition; further examination of this complexity may improve our understanding of this complex and highly prevalent disease.
Quality of Care for Childhood Asthma: Estimating Impact and Implications
Authors: Mattke Soeren , Martorell Francisco , Sharma Priya , Malveaux Floyd , Lurie Nicole
Published: February 2009

We conducted a review of 164 relevant publications to consolidate the evidence on gaps in the quality of asthma care, the impact of those gaps, and the costs and benefits of closing those gaps. Researchers used a wide variety of definitions for measures of quality asthma care, clinical and utilization end points, and disease severity. Gaps in care were most evident for pharmacologic treatment, particularly the underuse of inhaled corticosteroids, with median usage rates of 40%; however, in studies with large proportions of black subjects, the inhaled corticosteroid usage rate was only 32%, compared with 51% for nonminority populations. Studies on outcomes focused on emergency department visits, hospital admissions, and missed school days. Because only 6 studies included information on the costs of improving asthma care, no consensus estimates of the cost/benefit ratio for better asthma care could be derived. There was insufficient evidence in the literature for assessment of the impact of gaps in care and the costs of closing those gaps. More economic evaluations of the impact of gaps in asthma care and of interventions to improve asthma control are needed. Future research on gaps in asthma care and their impact must use standardized definitions for key variables such as disease severity and care utilization to allow comparisons across studies and building of an evidence base that is convincing for policy makers and purchasers of care.
Correlation Among Material Quality, Performance and Reliability of High Power and High Frequency AlGaN/GaN HFET
Authors: Nanishi Yasushi
Published: February 2009

Performances of AlGaN/GaN HFETs have much improved recently and very high potential of this hetero- structure for high power and high frequency electronic devices has been verified. Application of new device technologies such as field plate, recessed gate, digital pre-distortion circuit and dual field plate was essential to realize such high device performances both at 2 GHz, 5GHz and 26 GHz. However, practical requirements on the quality and structure of these material systems for production of these devices are still not clear. Extensive studies on correlation among material quality, device performance and reliability were investigated under Japanese NEDO project. Firstly, this paper reviews recent progress of the performances of high power and high frequency AlGaN/GaN HFETs. Then, several interesting results which suggest practical requirements on material quality and structure will be discussed based on our extensive characterization studies in terms of device performances and reliabilities.
Optimizing MIM Device Electrical Properties. Impact of Bottom Electrodes and High K Materials
Authors: Bonvalot Marceline , Vallée Christophe , Gourvest Emmanuel , Jorel Corentin , Gonon Patrice
Published: February 2009

High quality MIM capacitors with improved capacitance density, low leakage currents and linear C(V) behaviour are the object of active research, with potential applications in CMOS, BICMOS and bipolar technologies as filters, analog to digital converters and related radio-frequency operating devices. Several high-k materials (Ta2O5, HfO2, Y2O3, Al2O3-HfTiO, HfON-SiO2) have been put on trial as possible candidates for SiO2 substitution which is required by the aggressive downscaling of electronic devices. Among those, HfO2- based materials seem to offer promising properties, combining a high chemical stability with Si and a high k value. However, HfO2 shows a strong ability to favour charge defects such as oxygen vacancies, which in turn affect the intrinsic properties of devices such as threshold voltage or leakage currents. These oxygen vacancies are actually thought to accumulate in the vicinity of the electrode, thus forming an oxidized interfacial layer and inducing a significant voltage linearity degradation of MIM capacitors.

In this work, it will be shown that this oxide layer thickness can be strongly minimized by using appropriate bottom electrode material. Indeed, high work function materials can efficiently prevent oxygen vacancies charge stocking on their surface. Several MIM devices have been prepared based on HfO2, Al2O3 and SrTiO3 as dielectric materials, and TiN, WSi2.7 and Pt as bottom electrode material. All these devices have been fully characterized in terms of materials properties and electrical behaviour. These results have been analysed and show that a reduced dielectric thickness is preferred to achieve high capacitance density, but is also responsible for voltage linearity degradation. High work function electrode material can help improve this degraded linear behaviour, thanks to the formation of a reduced interfacial oxygen trap layer thickness. Leakage currents seem to be deeply correlated with the morphological state of the dielectric material, an amorphous state being obviously more efficient to prevent current pathways through grain boundaries.

All these results will be presented in detail and discussed with regards to different models proposed in the literature to account for these data.
The effect of BCl3 pretreatment on the etching of AlN in Cl2-based plasma
Authors: Xu Xiaoyan , Kuryatkov Vladimir , Borisov Boris , Pandikunta Mahesh , Nikishin Sergey A , Holtz Mark
Published: February 2009

The effect of BCl3 and BCl3/Ar pretreatment on Cl2/Ar and Cl2/Ar/BCl3 dry etching of AlN is investigated using inductively coupled plasma reactive ion etching. The native AlN oxide can be effectively removed by a short exposure to BCl3 or BCl3/Ar plasma. Compared to the chlorine based plasma etching, BCl3/Ar is found to have the highest etch rate for both AlN and its native oxide. Following removal of the native oxide, Cl2/Ar/BCl3 plasma etching with 15% BCl3 fraction results in a high etch rate ˜ 87 nm/min and modest increases in the surface roughness.
Ambient Copper-Copper Thermocompression Bonding using Self Assembled Monolayers
Authors: Ang Xiaofang , Wei Jun , Chen Zhong , Wong Chee Cheong
Published: February 2009

A typical copper-copper thermocompression bonding process is carried out in an ultrahigh vacuum (UHV) or inert environment at a bonding temperature >300°C. The ultraclean environment serves a single purpose – to maintain oxide-free copper surfaces, allowing intimate physical contact between copper atoms. This study investigates the temperature dependence of direct copper bonding from room temperature to 300°C under ambient condition. An anomalous thermal dependence of bond strength occurs between 80°C to 140°C where an increase in bonding temperature within this regime is in fact, detrimental to joint strength. This is interpreted as a thermal competition between oxidation and bond formation. This study also demonstrates that by simply coating the copper surface with a self assembled monolayer of 1-undecanethiol prior to bonding, Cu joints can be successfully formed at close to ambient temperature without a vacuum, yielding joint shear strengths on the order of 70MPa. The densely packed monolayer serves to passivate the copper surface against oxidation under ambient conditions. The ultrathin organic monolayer structure, as compared to a bulk oxide layer, could be easily displaced during the mechanical deformation at the bonding interface which accompanies thermocompression. This method could be an effective simple bonding solution for three-dimensional integrated chips.
Three-Dimensional Integration Technology Based on Self-Assembled Chip-to-Wafer Stacking
Authors: Fukushima Takafumi , Tanaka Tetsu , Koyanagi Mitsumasa
Published: February 2009

We have demonstrated that a number of known good dies (KGDs) can be precisely aligned in batch and stacked on LSI wafers by our chip-to-wafer three-dimensional (3D) integration technology using an innovative self-assembly technique. Compared with conventional robotic pick-and-place chip assembly, the fluidic self-assembly can provide high-throughput chip alignment and bonding, and the resulting self-assembled chips have high alignment accuracy of approximately 0.3 micron on average. Immediately after chip release, the chips are aligned onto the predetermined hydrophilic bonding areas in a short time within 0.1 sec by the surface tension of aqueous liquid used in our self-assembly. By using the self-assembly, a number of KGDs with different chip sizes, different materials and different devices can be stacked in high yield to give highly integrated 3D chips we call the 3D Super Chip.
Level Spectrum of a Single Gated Arsenic Donor in a Three Terminal Geometry
Authors: Lansbergen Gabriel P. , Rahman Rajib , Wellard Cameron J. , Caro Jaap , Woo Insoo , Colleart Nadine , Biesemans Serge , Klimeck Gerhard , Hollenberg Lloyd , Rogge Sven
Published: February 2009

State of the art CMOS devices have been scaled to such dimensions that we need take atomistic approach to understand their operation for nano-electronics. From a bottoms-up perspective, the smallest functional element within a nano-device would be a single (dopant) atom itself. Control and understanding of the eigenenergies and wavefunctions of a single dopant in Si is a key ingredient for device technology beyond-CMOS like quantum-information processing. Here, we will discuss the eigenlevels of a single As donor in a three terminal configuration. The donor is incorporated in the channel of prototype transistors called FinFETs. The measured eigenlevels are shown to consist of levels associated with the donors Coulomb potential, levels associated with a triangular well at the gate interface and hybridized combinations of the two. The theoretical framework in which we describe this system (NEMO-3D) is based on a tight-binding approximation.
Magnetic Transitions in the Double Perovskite Sr2FeRe1-xFexO6(0≤X≤0.5)
Authors: Gao Haitao , Ksenofotov Vadim , Barth Joachim , Panthöefer Martin , Claudia Felser , Tremel Wolfgang
Published: February 2009

The synthesis, structure, and magnetic and transport properties of solid solutions Sr2FeRe1-xFexO6 (0≤x≤0.5) are reported. A structural evolution in the solid solutions from a double perovskite to perovskite is observed with increasing Fe/Re disorder. Except for the metallic parent compound all members of the series are semiconducting. For the Fe-doped samples a change from ferrimagnetic interactions in the parent compound to a complex superposition of ferrimagnetic and antiferromagnetic interactions was observed. The magnetic moment decreases with x, whereas the Curie temperature TC remains unaffected. The magnetic and Mössbauer data suggest Fe to act as a redox-buffer.
Charge-Transfer Properties of Dye-Sensitized Solar Cells via Long-Range-Corrected Density Functional Theory
Authors: Wong Bryan Matthew
Published: February 2009

The excited-state properties in a series of solar cell dyes are investigated with a long-range-corrected (LC) functional which provides a more accurate description of charge-transfer states. Using time-dependent density functional theory (TDDFT), the LC formalism correctly predicts a large increase in the excited-state electric dipole moment of the dyes with respect to that of the ground state, indicating a sizable charge separation associated with the S1 ← S0 excitation. The performance of the LC-TDDFT formalism, illustrated by computing excitation energies, oscillator strengths, and excited-state dipole moments, demonstrates that the LC technique provides a consistent picture of charge-transfer excitations as a function of molecular size. In contrast, the widely-used B3LYP functional severely overestimates excited-state dipole moments and underestimates the experimentally observed excitations, especially for larger dye molecules. The results of the present study emphasize the importance of long-range exchange corrections in TDDFT for investigating the charge-transfer dynamics in solar cell dyes.
Efficient Light Harvesting with LB Films for Application in Crystalline Silicon Solar Cells
Authors: Danos Lefteris , Markvart Tomas
Published: February 2009

We have carried out fluorescence lifetime measurements using time correlated single photon counting (TCSPC) for a cyanine dye near the silicon surface. The measurements have been carried out for both (100) and (111) crystal orientations of the silicon surface, showing the dependence of energy transfer rate as a function of the separation between the dye monolayer and the silicon surface. Langmuir Blodgett fatty acid layers were used to create a multistep structure and a monolayer of a cyanine dye was deposited on top of the stepped structure. Spectroscopic ellipsometry has been used to measure the thickness of the fatty acid steps and provide an accurate estimate of the distance of the dye monolayer to the silicon surface. Time resolved emission spectra and fluorescence decay curves were measured with a single photon picosecond time correlated system. We find that the fluorescence lifetime of the dye monolayer is significantly shortened when present close to the silicon surface signifying efficient energy transfer. The dissipation of the excitation energy near silicon is explained using the classical theory developed for metals and a deviation is observed for distances close to the silicon surface (d<5nm). The model can be reconciled with the observed data by modifying the value of the silicon extinction coefficient which can provide an insight into the energy transfer process in the near field dye-silicon interaction.
A Comparison of Electrochemical Performance of Double Perovskite REBaCo2O5+x Cathodes in Symmetrical Solid Oxide Fuel Cells
Authors: Gong Wenquan , Yadav Manoj , Jacobson Allan J.
Published: February 2009

The segregated vacancies in the A site-ordered oxygen-deficient double perovskites REBaCo2O5+x (RE = La, Pr, Nd, Sm, Eu) (RBCO) are thought to greatly enhance the diffusivity of oxide ions in the bulk of these materials and possibly supply surface defect sites with enhanced reactivity towards molecular oxygen. Some materials in this family of REBaCo2O5+x compounds, such as PrBaCo2O5+x, (PBCO), have already demonstrated high electronic conductivity, rapid oxygen ion diffusion and surface exchange kinetics. Therefore, the family of REBaCo2O5+x compounds were synthesized and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (SOFCs) based on gadolinium doped ceria (CGO) electrolytes. The electrochemical performance of symmetrical cells (REBaCo2O5+x + CGO composite cathodes on the CGO electrolytes) was evaluated by using AC impedance spectroscopy. The area specific resistance (ASR) performance was measured as a function of temperature as well as oxygen partial pressure.
Screening and Fabrication of Half-Heusler Phases for Thermoelectric Applications
Authors: Wunderlich Wilfried , Motoyama Yuichiro
Published: February 2009

Half-Heusler phases have gained recently much interest as thermoelectric materials. Screening of possible systems was performed by drawing their stability region in a three-dimensional Pettifor map. The fabrication of Half-Heusler phases requires three steps, surface activation of the raw material by ball milling, arc-melting of pressed pellets and finally long-term annealing treatment in a vacuum furnace. On doped TiCoSb specimens, Seebeck coefficients of 0.1 mV/K, on NiNbSn 0.16 mV/K were measured, although the microstructure was not yet optimized.
An overview of the ESA-ESRF-ILL collaboration in the framework of the IMPRESS Integrated Project
Authors: Reinhart G. , Iles G.N. , McIntyre G.J. , Fitch A.N. , Jarvis D.J.
Published: February 2009

Three intergovernmental research organizations from the EIROforum collaboration: the European Space Agency (ESA), the European Synchrotron Radiation Facility (ESRF) and the Institut Laue-Langevin (ILL), are cooperating to perform advanced experimental characterization in the field of materials science within the framework of the IMPRESS Integrated Project. This project aims to develop and test two distinct prototype-based intermetallic materials: (i) γ-TiAl turbine blades for aero-engines and stationary gas turbines, and (ii) Raney-type Ni-Al catalytic powder for use in hydrogen fuel cell electrodes and hydrogenation reactions. The opportunity to carry out investigations combining the use of both synchrotron radiation at the ESRF and neutrons at the ILL provides unique experimental data to complement other benchmark experiments performed on the ground and in microgravity. We present an overview of the different synchrotron X-ray and neutron characterization techniques implemented at ESRF and ILL to study the solidification and subsequent processes leading to the final products for these two materials.
Phase Field Simulation of Coarsening Kinetics in Al-Sc and Al-Sc-Zr Alloys
Authors: Zapolsky H. , Boisse J. , Patte R. , Lecoq N.
Published: February 2009

The coarsening kinetics of γ’ precipitates in binary and ternary Al3Sc1-xZrx alloys is studied by using the two- and three-dimensional phase-field simulations. Our focus is on the influence of diffusion coefficients of Sc and Zr atoms on the transformation path kinetics from disordered f.c.c. matrix to two phases equilibrium state with γ’ precipitates and f.c.c. disordered matrix. Our simulation results demonstrate that in the case of binary alloys taking into account the concentration dependence of the mobility of atoms decreases the coarsening rate. In the case of ternary alloys we show that the Al3Sc particles precipitate first following by appearance of a Zr-rich shell. Our simulations results are in good agreement with experimental observations.
An Experimentally Validated Micromechanical Model for Elasticity and Strength of Hydroxyapatite Biomaterials
Authors: Fritsch Andreas , Dormieux Luc , Hellmich Christian , Sanahuja Julien
Published: February 2009

Hydroxyapatite biomaterials production has been a major field in biomaterials science and biomechanical engineering. As concerns prediction of their stiffness and strength, we propose to go beyond statistical correlations with porosity or empirical structure-property relationships, as to resolve the material-immanent microstructures governing the overall mechanical behavior. The macroscopic mechanical properties are estimated from the microstructures of the materials and their composition, in a homogenization process based on continuum micromechanics. Thereby, biomaterials are envisioned as porous polycrystals consisting of hydroxyapatite needles and spherical pores. Validation of respective micromechanical models relies on two independent experimental sets: Biomaterial-specific macroscopic (homogenized) stiffness and uniaxial (tensile and compressive) strength predicted from biomaterial-specific porosities, on the basis of biomaterial-independent (‘universal') elastic and strength properties of hydroxyapatite, are compared to corresponding biomaterial-specific experimentally determined (acoustic and mechanical) stiffness and strength values. The good agreement between model predictions and the corresponding experiments underlines the potential of micromechanical modeling in improving biomaterial design, through optimization of key parameters such as porosities or geometries of microstructures, in order to reach desired values for biomaterial stiffness or strength.
Graphened IR Screens: A New Spectroscopic Platform For Bio-Species
Authors: Banerjee Amrita , Moeller Dieter , Grebel Haim
Published: February 2009

Metallo-dielectric screens are periodic structures, which are at resonance with the infrared (IR) wavelength of interest: a standing wave of surface charges is formed at resonance conditions, which enables transmission or, reflection of certain IR bands. Graphene is a monolayer thick crystal of carbon. It is chemically inert and exhibits very large electronic mobility. Recently, we succeeded in fabricating mono and a few-layered suspended graphene on top of these screens. We combined these two unique components in fabricating novel platforms, which enhance IR signals of soft bio-species. Specifically, we used these platforms to examine IR spectra of a model protein, cytochrome c from a bovine heart tissue. Clear Raman signal variation as a function of platform orientation has been demonstrated. Accentuation of the IR absorption spectra was shown as well.
Design of a Biocompatible and Optically-Stable Solution-Phase Substrate for SERS Detection
Authors: Roca Maryuri , Mackie Prescott M. , Hae Amanda J.
Published: February 2009

Detection of important biological molecules using surface-enhanced Raman scattering (SERS) has become widely used because of the highly sensitive and label free approach offered by SERS as well as the low cytotoxic response from some SERS substrates. Gold nanoparticles are commonly used in SERS studies; however, the inherent instability of these metal nanostructures in solution adversely influences the reproducibility and quantitative nature of these measurements. Furthermore, the metal surface often denatures biomolecules upon their direct interaction. To combat this incompatibility and improve optical stability, gold nanoparticles have been encapsulated in silica shells. These Au@SiO2 nanostructures have been used extensively in cellular studies, but their SERS capabilities are generally limited to uses that include silica-entrapped SERS reporter molecules rather than direct SERS detection. This work focuses on combating these limitations via the fabrication of Au@SiO2 nanoparticles with porous silica membranes for the direct detection of target molecules in solution. Gold nanoparticles have been designed and coated with a variety of silica morphologies and subsequently interrogated using extinction spectroscopy and SERS. It will be revealed that these gold nanoparticles entrapped in silica membranes serve as optically stable substrates for the quantitative and direct detection of target molecules. These advances in nanomaterial fabrication are envisioned to impact both fundamental and applied studies in a variety of research areas including catalysis, separations, and spectroscopy.
Identifying the limitation of Oliver and Pharr method in characterizing the viscoelastic-plastic materials with respect to indenter geometry
Authors: Balasundaram Keerthika , Cao Yanping , Raabe Dierk
Published: February 2009

Nanoindentation tests are widely used in recent years to characterize the mechanical properties of viscoelastic-plastic materials like polymers and biomaterials at the micro or nano-scale using the analysis method proposed by Oliver & Pharr (OP). However, recent studies revealed that the mechanical properties of viscoelastic-plastic (polymeric) materials determined using the OP method does not lead to a correct evaluation of Young's modulus. A systematic experimental study is performed with different indenter geometries like spherical and Berkovich geometries using various polymers in order to identify the limitations of the OP method.
Measurement and Analysis of Structural Damping in Silicon Carbide Microresonators
Authors: Prabhakar Sairam , Nabki Frederic , El-Gamal Mourad , Vengallatore Srikar
Published: February 2009

The design of microresonators with high natural frequencies (1 MHz to 1 GHz) and low structural damping is essential for devices used for applications in communications. Here, we report experimental measurements of damping at low pressure and ambient temperature in electrostatically-actuated, metallized silicon carbide microresonators. Comparison of the measured values with the predictions of a model for thermoelastic damping indicates that the contribution of this mechanism to the measured damping ranges from 10% to 50% over a broad frequency range (3 MHz to 30 MHz).
Effects of Aspect Ratio of Micro-sized Photoresist Patterns on Bond Strength between a Si Substrate with AFM Fracture Observation
Authors: Ishiyama Chiemi , Shibata Akinobu , Sone Masato , Higo Yakichi
Published: February 2009

Bond strength between three dimensional micro-sized cylindrical patterns and Si substrate has been evaluated to clarify the effects of the cylinder length vs. diameter ratio, i.e. the aspect ratio, on the bond strength. Cylindrical shape was employed for avoiding ambiguity of loading point under bend conditions. Multiple cylindrical specimens of an epoxy type photoresist, SU-8 with various lengths were fabricated on a silicon substrate under the same photolithographic condition. Bond strength between micro-sized SU-8 and Si substrate under bend loading mode was measured by a mechanical testing machine for micro-sized materials. The maximum bend moment is 9.6 × 10−6 Nm in average and lineally increases with increasing the aspect ratio. On the other hand, the maximum load, i.e. maximum shear load is 106 mN in average and almost constant with increasing aspect ratio. This result suggests that the shear stress near the interface may cause the initiation of delamination. This phenomenon is discussed with three dimensional fracture observation and quantitative analysis of the line profile around the initiation site by AFM.
Controlling the Wrinkling of the Bilayer Thin Films Electrothermally
Authors: Chintapatla Shravan , Muth John F. , Lunardi Leda M.
Published: February 2009

Wrinkling of thin sheets under strain is a universal phenomenon. The amplitude and period of the wrinkles formed in a thin sheet clamped at both ends are dependent on its strain and material parameters. In our study, wrinkling is observed in microscale for double clamped thin films (L>W>>t) consisting of 200nm deposited low stress silicon nitride bridges fabricated by bulk micromachining. A bilayer system is formed with 30nm aluminum evaporated on to these bridges. At room temperature the bridges are essentially flat. When an electrical current passes through the aluminum layer electrothermal, heating results in thermal expansion that wrinkles the bilayer. In addition we investigated various dimensions of the bridges and their correlation to the amplitude and the number of wrinkles. The observations are compared to existing wrinkling theory.
Investigating the Stress and Crystal Quality of AlN Air-Bridges through Micro-Raman Scattering
Authors: Kuchibhatla Sridhar , Rodak L. E. , Korakakis D.
Published: February 2009

In this work, we report the post-growth investigation of the microstructure and stress in the AlN films grown on patterned amorphous dielectrics through micro-Raman spectroscopy. The surface texture of AlN/SiO2 structures was characterized by randomly oriented crystallites typical of polycrystalline films. Post growth analysis of the AlN/SiO2 structures using micro Raman spectroscopy did not reveal phonon modes corresponding to wurtzite AlN. The presence of randomly oriented crystallites with a possibility of oxidized Al phase in the AlN film could have suppressed the appearance of wurtzite AlN phonon peaks in the Raman spectrum. Profiling the stress and the microstructure of AlN/SiO2 structures across the width of the bridges is thus limited by these factors. AlN structures on SiO2 when subjected to wet etching in buffered HF (10:1) showed a clear change in texture. Micro-raman spectroscopy on the etched areas revealed wurtzite AlN like phonon modes. The appearance of wurtzite AlN modes can be attributed to the removal of oxidized Al phase in the AlN film after wet etching.
Micro Tensile Tests on Aluminium Thin Films: Tensile Device and In Situ Observations
Authors: Ignat Michel T. , Lay Sabine , Roussel d'Herbey Francine , Seguineau Cedric , Malhaire Christophe , Lafontan Xavier , Desmarres Jean Michel , Brida Sebastiano
Published: February 2009

The results of micromechanical tensile experiments performed on thin aluminum samples are presented and discussed. The micro tensile test system and the design of the samples, based on finite element modeling (FEM), and their production by micromachining are briefly described. Some examples of the stress strain curves are presented. The Young's modulus and critical parameters (flow and rupture stress and strains) are reported. The micro structural changes induced by the tensile experiment were observed during and after the testing by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The results of micromechanical tensile experiments performed on thin aluminum samples are presented and discussed. The micro tensile test system and the design of the samples, based on finite element modeling (FEM), and their production by micromachining are briefly described. Some examples of the stress strain curves are presented. The Young's modulus and critical parameters (flow and rupture stress and strains) are reported. The micro structural changes induced by the tensile experiment were observed during and after the testing by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
Poly(3-hexythiophene)/multi-walled carbon nanotube composites: electrochemical and optical characterization
Authors: Calado Hállen D. R. , Valadares Marcelo , Musumeci Anthony W. , Waclawik Eric R. , Cury Luiz A. , Silva Glaura Goulart
Published: February 2009

Carbon nanotubes (CNT) / conjugated polymer composites have been used for the preparation of thin film-modified electrodes. Thin, short, multi-walled CNT (MWNT) (purity higher than 95%) was completely coated by regioregular poly(3-hexylthiophene) (P3HT) through precipitation of a mixture of both in the non-solvent methanol. This work reports the electrochemical and optical characterization of P3HT and composites after dissolution in xylene and spin casting of films with thickness <1 micrometer. Cyclic voltammetry showed that all samples were characterized by a semi-reversible behavior. The samples with 0% and 2% of MWNT, for instance, present anodic peak potential at +0.67 and +0.68V respectively when cycling at 100 mV/s. Optical properties, such as optical absorption and photoluminescence (PL), have been investigated. The samples showed maximum of absorption at ˜530 nm and intense PL in the orange. PL spectra of nanocomposites exhibited a new band at lower energy characteristic of a structure with higher conjugation length when compared to P3HT.
Annealing of Nanocrystalline Silicon Micro-bridges with Electrical Stress
Authors: Bakan Gokhan , Cywar Adam , Boztug Cicek , Akbulut Mustafa Bilal , Silva Helena , Gokirmak Ali
Published: February 2009

Nanocrystalline silicon (nc-Si) micro-bridges are melted and crystallized through Joule heating by applying high-amplitude short duration voltage pulses. Full crystallization of nc-Si bridges is achieved by adjusting the voltage-pulse amplitude and duration. If the applied pulse cannot deliver enough energy to the bridges, only surface texture modification is observed. On the contrary, if the pulse is not terminated after the entire bridge melts, molten silicon diffuses on to the contact pads and the bridge tapers in the middle. Melting of the bridges can be monitored through current-time (I-t) and voltage-time (V-t) measurements during the electrical stress. Conductance of the bridges is enhanced after the electrical stress.
Luminescence characterization of InGaN/GaN vertical heterostructures grown on GaN nanocolumns
Authors: Armitage Robert
Published: February 2009

The photoluminescence of MBE-grown InGaN/GaN vertical heterostructures on c-axis oriented GaN nanocolumns is investigated. Nanocolumnar InGaN heterostructures exhibit luminescence efficiencies greater than 20% for peak emission wavelengths as long as 540 nm. Compared to otherwise identical InGaN samples with larger median column diameters, the luminescence is blue-shifted and exhibits reduced efficiency for diameters less than about 50 nm. Growth of InGaN on GaN columns with a broad distribution of diameters results in broad-band photoluminescence that appears white to the eye and has efficiency as high as 23%.
Monitoring Organic Thin Film Growth In Aqueous Solution In-situ With A Combined Quartz Crystal Microbalance and Ellipsometry
Authors: Sarkar Amitabha , Viitala Tapani , Hofmann Tino , Tiwald Tom E. , Woollam John A. , Kjerstad Ann , Laderian Bahar , Schubert Mathias
Published: February 2009

The change of the visible light ellipsometric parameters and mechanical harmonic frequencies of a hydrophobic gold surface attached to a quartz crystal are measured in aqueous solution during deposition of synperonic polymer thin film. The ellipsometry data reveal the amount of polymer mass attached to the surface, while the mechanical resonance shifts are caused by the total mass attached to the surface. Analysis of the combined ellipsometry and quartz crystal microbalance data reveal that the polymer thin film has a high water content, and we determine in-situ, for the first time, the porosity, or the water content, of a polymer thin film in aqueous solution.
In vitro susceptibility testing of dermatophytes isolated in Goiania, Brazil, against five antifungal agents by broth microdilution method
Authors: Araújo Crystiane Rodrigues , Miranda Karla Carvalho , Fernandes Orionalda de Fatima Lisboa , Soares Ailton José , Silva Maria do Rosário Rodrigues
Published: February 2009

The antifungal activities of fluconazole, itraconazole, ketoconazole, terbinafine and griseofulvin were tested by broth microdilution technique, against 60 dermatophytes isolated from nail or skin specimens from Goiania city patients, Brazil. In this study, the microtiter plates were incubated at 28 ºC allowing a reading of the minimal inhibitory concentration (MIC) after four days of incubation for Trichophyton mentagrophytes and five days for T. rubrum and Microsporum canis. Most of the dermatophytes had uniform patterns of susceptibility to the antifungal agents tested. Low MIC values as 0.03 µg/mL were found for 33.3%, 31.6% and 15% of isolates for itraconazole, ketoconazole and terbinafine, respectively.
Endobronchial leiomyoma: an unusual non-defining neoplasm in a patient with AIDS
Authors: Metta Humberto , Corti Marcelo , Redini Liliana , Dure Roberto , Campitelli Ana M. , Narbaitz Marina
Published: February 2009

Smooth muscle neoplasms are more frequent in human immunodeficiency infected children than in HIV seropositive adults. Endobronchial leiomyoma is a rare benign tumor in HIV infected adult patients. Epstein-Barr virus (EBV) has been implicated in the pathogenesis of these tumors. Here we describe an adult patient with HIV infection with atelectasis of the left upper pulmonary lobe as the first clinical expression of an intrabronchial leiomyoma. In this case, we can not show the association with EBV. Our report suggests that smooth muscle tumors as leiomyoma should be included in the differential diagnosis of endobronchial masses in AIDS patients.
Anisotropia no estudo da variabilidade espacial de algumas variáveis químicas do solo
Authors: Guedes Luciana Pagliosa Carvalho , Uribe-Opazo Miguel Angel , Johann Jerry Adriany , Souza Eduardo Godoy de
Published: February 2009

No estudo do mapeamento da fertilidade do solo, pelas técnicas de geoestatística, algumas características estruturais da variabilidade espacial devem ser consideradas, tais como continuidade espacial e ausência de anisotropia. Neste contexto, o presente trabalho apresenta uma análise da anisotropia no estudo da variabilidade espacial das variáveis químicas do solo: ferro (Fe), acidez potencial (H + Al), matéria orgânica (MO) e Mn, de um conjunto de dados de 128 parcelas sem manejo químico localizado, espacialmente referenciados, estudados entre 1998 e 2002, em um Latossolo Vermelho distroférrico, em Cascavel-PR. A identificação da anisotropia foi realizada por meio da construção de semivariogramas direcionais com modelos ajustados, e a correção da anisotropia realizou-se por meio de transformações lineares e de modelos combinados. Em seguida, utilizou-se um modelo ajustado ao semivariograma omnidirecional para construção de mapas temáticos de variabilidade das variáveis estudadas. Observou-se a existência de anisotropia geométrica para a variável H + Al. Já as variáveis MO, Mn e Fe mostraram a presença de anisotropia combinada, sendo corrigida inicialmente a anisotropia geométrica e, posteriormente, a anisotropia zonal. Por meio do estudo da anisotropia, foi possível eliminar as direções privilegiadas, melhorando assim o ajuste dos semivariogramas e produzindo mapas temáticos das variáveis químicas estudadas com maior acurácia.
Assessment of the soil compaction of two ultisols caused by logging operations
Authors: Dias Junior Moacir de Souza , Silva Sérgio Ricardo , Santos Nadívio Souza dos , Araujo-Junior Cezar Francisco
Published: February 2009

The impact of wood loads on bulk density and preconsolidation pressure and of harvester and forwarder traffic on rut depth, bulk density and preconsolidation pressure of two Ultisols were examined in this study. Our objective was to quantify the threshold beyond which significant soil compaction and rutting would occur. This study was carried out in the county of Eunápolis, state of Bahia, Brazil, (16 º 23 ' 17 '' S and 39 º 10 ' 06 '' W; altitude 80 m asl) in two Ultisols (PAd2 and PAd3) with different texture classes, in experimental areas with eucalypt plantation. The study involved measurements at the wood load site and machine driving at specific locations in the forest during logging operations. The treatments consisted of one harvester pass and, 8, 16 and 40 passes of a fully loaded forwarder. Thresholds were established based on the rut depth and percentage of preconsolidation pressure values in the region of additional soil compaction defined in the bearing capacity model. The percentage of soil samples with values of preconsolidation pressure in the region of additional soil compaction indicated a greater susceptibility of PAd3 than of PAd2 to soil compaction. The threshold levels established here based on preconsolidation pressure and rut depth indicated that no more than eight forwarder passes should be allowed in loading operations in order to minimize soil compaction.
Reversibilidade de fósforo não-lábil em solos submetidos à redução microbiana e química: II - extrações sucessivas do fósforo pela resina de troca aniônica
Authors: Fernández R. Iván Ernesto , Novais Roberto Ferreira , Nunes Flancer Novais , Ker João Carlos
Published: February 2009

A formação de P não-lábil a partir de formas lábeis, adsorvidas aos oxihidróxidos de Fe e Al, é razão para o baixo efeito residual da fertilização fosfatada em solos tropicais. A reversibilidade do P não-lábil para formas lábeis nesses solos pode ser favorecida pela redução do Fe3+ e, ou, pela diminuição da atividade dos oxihidróxidos de Fe e Al. Neste trabalho, objetivou-se avaliar a adsorção e dessorção de P, sua transformação em não-lábil e reversibilidade dessa forma em amostras de solos submetidas à redução microbiana ou química. Para isso, amostras de 11 solos foram homogeneizadas com 300 mg kg-1 de P na forma de NaH2PO4 em solução, incubadas por 30 dias e, então, submetidas a dez extrações sucessivas de P com resina de troca aniônica (RTA) (tratamento sem redução). Em seguida, outras amostras dos solos foram submetidas à ambiente redutor em solução de sacarose 0,1 mol L-1 com posterior aplicação da doses de P (300 mg kg-1) e as dez extrações sucessivas de P (tratamento redução microbiana). Depois, outras amostras foram reduzidas/complexadas com oxalato de amônio (Ox) ou com citrato-ditionito-bicarbonato (CDB), e os solos/resíduos receberam a mesma dose de P dos experimentos anteriores. Foram então incubados por 30 dias e submetidos às extrações sucessivas com RTA (tratamento redução química). A capacidade máxima de adsorção de P (CMAP) dos solos mostrou-se mais dependente da goethita (com 70,8 % de contribuição para seu valor) do que da gibbsita (com contribuição de 29,2 %). A correlação negativa entre os teores de P obtidos na segunda extração com a RTA, nos solos em condição natural, sem redução, e os teores de gibbsita sugere que este, e não a goethita, é o oxihidróxido responsável pela maior restrição à dessorção do P. Os valores de CMAP, estimados por meio do P remanescente (P-rem), mostraram, nas amostras submetidas ao tratamento com redução microbiana, pequena alteração para o grupo dos solos menos oxídicos, com menor CMAP. Todavia, nos solos mais oxídicos, com maior CMAP, o efeito prévio da sacarose foi o aumenta do P-rem (diminuição da CMAP) 10 vezes em relação aos solos para o tratamento sem redução. Entretanto, a redução gerada pela sacarose não alterou a dessorção do P anteriormente adsorvido. A expectativa de que ocorreria significativa reversibilidade de P não-lábil com a redução microbiana ou química dos solos não se concretizou, demonstrando a grande estabilidade dessas formas.
Volatilização de amônia, lixiviação de nitrogênio e produtividade de milho em resposta à aplicação de misturas de uréia com sulfato de amônio ou com gesso agrícola
Authors: Lara Cabezas Waldo Alejandro Ruben , Souza Marcos André
Published: February 2009

A adubação em cobertura na cultura de milho, assim como de outras culturas anuais, deve incluir N e S para acrescentar qualidade protéica à produção de grãos. Este trabalho foi desenvolvido na safra 2004/2005, na cultura de milho, na Fazenda Floresta do Lobo - Pinusplan, BR 050, km 93, município de Uberlândia (MG). O estudo foi realizado em Latossolo Vermelho ácrico típico fase Cerrado subcaducifólio muito argiloso (720 g kg-1), objetivando: quantificar as perdas por volatilização de N-NH3 provenientes de algumas das misturas de grânulos utilizadas em cobertura nitrogenada na cultura de milho; determinar a distribuição, até 60 cm de profundidade de solo, do N-mineral (NH4+ e NO3-) e S-SO4(2-) após 37 e 51 dias da aplicação dos adubos em cobertura; e avaliar o efeito na produtividade de milho da aplicação de misturas de grânulos, com diferentes granulometrias e relações N:S, em relação à aplicação exclusiva, em cobertura nitrogenada, de uréia (U) e sulfato de amônio (SA). Foram instalados 11 tratamentos de adubação N:S:K em cobertura, no estádio de 5-6 folhas, em dose de 90 kg ha-1 de N, nas formas exclusivas de U e SA, em misturas físicas de U+SA granulado (U+SAgr), U+SA farelado (U+SAfa), U+Gesso granulado (U+Gesso gr) e U+Gesso em pó (U+Gesso pó), em delineamento de blocos casualizados. As perdas gasosas de N-NH3 foram em ordem decrescente, em relação ao N aplicado: U 76,8 %; U+SA Gr 37,9 %; U+SAfa 27,7 % e SAfa 7,8 %. Os teores de N-amônio e N-nitrato no solo, após 37 dias da aplicação das misturas, mostraram-se similares à testemunha (menos N), evidenciando que o N fornecido via fertilizante foi em parte absorvido pela cultura, nitrificado, lixiviado e, ou, adsorvido em maior profundidade. Aos 51 dias após a aplicação das misturas, o teor de N-mineral total do solo, estava mais evidente nas camadas de 20 a 40 cm de profundidade, indicando lixiviação de N das camadas mais superficiais. Nos tratamentos com aplicação de apenas U ou SA, essa tendência foi mais atenuada. Quanto ao S-sulfato, a camada mais superficial apresentou os menores teores em todos os tratamentos, diminuindo ainda mais na camada de 0 a 10 cm, após os 37 e 51 dias da aplicação dos fertilizantes. Os teores de S-sulfato continuaram expressivos nas camadas mais profundas. No estádio de florescimento, a análise de nutrientes na folha oposta à espiga não mostrou diferença significativa na relação N:S, assim como na parte aérea da planta. As maiores produtividades foram alcançadas pelos tratamentos de U+SAfa e U+Gesso gr, respectivamente: 10.285 kg ha-1 e 10.241 kg ha-1 de grãos. Os tratamentos com maiores produtividades ocorreram com a aplicação da U em mistura com SAfa, SAgr e Gesso gr, nas relações N:S entre 2,75 e 4,0. Esses resultados permitem concluir que a aplicação de S em cobertura pode ser realizada misturando-se U com SA ou U com Gesso gr, embora esta última tenha apresentado perdas de NH3 mais significativas.
Antecipação da adubação de semeadura do milho em dois sistemas de manejo do solo
Authors: Bertolini Erick Vinicius , Gamero Carlos Antonio , Salata Ariane da Cunha , Piffer Cassio Roberto
Published: February 2009

Cada sistema de manejo do solo é trabalhado de maneira própria, alterando de forma diferenciada suas propriedades químicas, físicas e biológicas, podendo requerer modificações nas recomendações e no manejo da adubação. Com a finalidade de avaliar o desempenho de três cultivares de milho em relação à adubação realizada em pré-semeadura, comparada à adubação na semeadura, em dois sistemas de manejo do solo, foi realizado este estudo. O experimento foi conduzido na Faculdade de Ciências Agronômicas da UNESP, campus de Botucatu-SP, no período de novembro de 2003 a maio de 2004, em Nitossolo Vermelho distroférrico. O delineamento experimental utilizado foi o de blocos ao acaso com parcelas subsubdivididas e quatro repetições. As parcelas foram constituídas pelos sistemas de manejo do solo (plantio direto e preparo reduzido com escarificação); as subparcelas, pelas épocas de adubação (adubação de pré-semeadura na superfície do solo, realizada 22 dias antes da semeadura do milho, e adubação feita junto com a semeadura do milho, sendo os fertilizantes incorporados ao solo); e as subsubparcelas, pelos cultivares de milho (DKB 333B, CO 32 e AL Bandeirante), totalizando 12 tratamentos. Os dados de produtividade, componentes de produção e teores de N, P e K no tecido foliar foram submetidos à análise de variância e às análises multivariadas de agrupamentos e de componentes principais. Os sistemas de manejo do solo não influíram no desempenho da cultura do milho, tampouco as épocas de adubação. As diferenças observadas nos componentes de produção e no desempenho da cultura do milho foram decorrentes, principalmente, da divergência genética dos cultivares de milho.