bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of Design and Performance of a Cryogenic Mems Micropump Realized with Si-Based Diaphragm Using Combination of Zygo/Wyko Interferometer and Raman Spectroscopy
Authors: Zhao Yi , Ludlow Daryl , Li Biao , Zhang Xin 
Published: April 2011

ABSTRACTThis paper reports work concerning a silicon-based micro pump for use in a cryogenic cooling system. The diaphragm deflection, which is critical for the control of pumping capacity, was accurately derived using a combination of ZYGO and WYKO interferometer. The relationship between the pumping capacity and differential pressure was further achieved. Stress distribution was obtained using Micro Raman spectroscopy. It was found that Young's modulus derived from the maximum deflection increases with decreasing temperature. The compressive stress concentrates at the edge centers; whereas the tensile stress occurs at the diaphragm center. There is a fairly good match between the theoretical predications and experimental observations.
Novel Electro-Optic Ceramic Materials for Microchip and High Power Lasers
Authors: Chen Xuesheng , Li Kewen , Zou Kevin , Zhang Run , Jiang Hua , Ozen Gonul , Bartolo B. Di 
Published: April 2011

ABSTRACTThis paper reports optical studies on transparent electro-optic ceramics, 2%Er:PLZT and 0.5%Er-2.5%Yb:PLZT. Strong photoluminescence was observed in these polycrystalline ceramics in the 1550 nm region when pumped by diode lasers either at ∼970nm or ∼800nm. Efficient green upconversion luminescence was also observed. Co-doping Yb3+ did enhance the Er3+ emission in the 1550nm region when pumped with ∼970 nm diode laser. This work provides important information for developing microchip and high-power ceramic lasers using Er-doped PLZT ceramics.
Mechanical Characterizations of Laser Microwelds for MEMS Packaging
Authors: Han Wei , Pryputniewicz Ryszard J. 
Published: April 2011

ABSTRACTLaser micromachining has proven to be a very powerful and successful tool for precision machining and microfabrication with applications in electronics, MEMS, medical, and biomedical fields. For MEMS fabrication and packaging, several approaches based on localized heating and bonding have been proposed such as localized eutectic bonding, fusion bonding, solder bonding, and chemical vapor deposition (CVD) bonding. However, these approaches are based on resistive heating which requires intimate contact at the electrodes, and this is not preferred for MEMS packaging applications. As a good alternative, laser microwelding has advantages of non contact, low heat distortion, high speed, high precision, and consistent weld integrity. Therefore, it is finding increasing use in MEMS fabrication and packaging applications. In laser microwelding, the material in the HAZ of the workpiece experiences heating, melting, and re-solidifying stages, and the final characterizations of the laser microwelds can be influenced by various factors such as the laser beam properties, the system cooling condition, and the surface roughness/reflectivity of the component. This paper presents characterization of laser microwelds, with emphasis on study of deformation and strength of the microwelds made by a Nd:YAG pulsed laser. Optical interferometry is used to nondestructively record fringe patterns of the shape and deformation of the laser microwelded workpiece before, during, and after the microwelding process, and tensile tests are performed to study strength of the laser microwelds as a function of different welding parameters. Results indicate that quality of the laser microwelds depends on selection of an appropriate set of parameters controlling the microwelding process.
Molecular Modeling Computer Simulations of Organic Polymers: A Novel Computer Simulation Technique to Characterize Nanostructured Materials
Authors: Schulz Sarah G. , Kuhn Hubert , Schmid Günter 
Published: April 2011

ABSTRACTThe understanding and prediction of complex nanostructured self-assemblies such as colloidal suspensions, micelles, immiscible mixtures, microemulsions, etc., represent a challenge for conventional methods of simulation due to the presence of different time scales in their dynamics.We have recently successfully applied a novel computer simulations technique, Dissipative Particle Dynamics (DPD), to model the behavior of diblockcopolymers at the water/oil interface. With the use of a simple model we have performed simulations of polymer/water/oil systems at different concentrations.We present the results of nanoscale “coarse-grained” simulations with DPD. DPD is a mesoscale simulation technique that has been introduced in order to simulate three-dimensional structures of organic polymer aggregates.In DPD the polymer is modeled using particles which are interacting by conservative, dissipative and random forces. Particles are not regarded as molecules but rather as droplets or nanoclusters of molecules.We have successfully applied this technique to simulate the three-dimensional structures of microemulsions, e.g. the bicontinuous phase of a surfactant in water and oil, in domains of less than 100 nm. The different structures of the polymer/water/oil system were effectively characterized with DPD and are in remarkable agreement with the experiment.The DPD method proofed to be a reliable tool to get a better understanding of the nanostructure of self-assemblies and is therefore applicable to support the often complicated experiments or even to obtain experimentally unavai1able data.
Porous carbon nanoturf using anodized alumina templating
Authors: Rajagopalan Ramakrishnan , Dronavajjala Krishna , Foley Henry C. 
Published: April 2011

ABSTRACTThis paper reports the development of porous carbon nanoturfs using alumina templating method. The nanoporous carbon has a pore size of 4 -5 Å. The length of the pillars in the carbon nanoturf was a function of temperature. It was shown that the pyrolysis of the polymer precursor reduces the dimensions of the polymer only in axial direction as compared to radial direction when it is formed inside the nanochannels.
Controlled Assembly of Carbon Nanotube Fibrils by Dielectrophoresis
Authors: Tang J. , Yang G. , Zhang J. , Geng H. Z. , Gao B. , Velev O. , Qin L.-C. , Zhou O. 
Published: April 2011

ABSTRACTAlthough advances have been made in the synthesis of raw carbon nanotube (CNT) materials, the lack of efficient processes for assembly and integration of CNTs into functional forms has hindered the development of CNT-based devices. Here we report a dielectrophorestic method to manipulate, align and assemble CNTs into one-dimensional nanostructures using an alternating-current electric field. Pre-formed CNTs dispersed in water are assembled into micro-electrodes and sub-micron diameter fibrils with variable lengths from 1 μm to over 1 cm. The CNTs within the fibril are bonded by van der Waals forces and are aligned along the fibril axis. This method affords fine control of the fibril length and is capable of parallel fabrication of multiple fibrils using the same material source. The short CNT fibrils can potentially be used as probes for scanning probe microscopes and the long ones as electrodes or conducting nanowires.
Nano-Structured Polymer Coatings for Ultraviolet Protection
Authors: Katangur Phaneshwar , Warner Steven B , Patra Prabir K , Kim Yong K , Mhetre Shamal K , Dhanote Autumn 
Published: April 2011

ABSTRACTPolymer materials such as Kevlar that are susceptible to UV degradation may be protected by appropriate coatings. We are using zinc oxide and titanium dioxide nanoparticles with an average particle size ranging from 25 to 70 nm. Five weight percent nanoparticles were dispersed in acrylic coatings, the dispersion is assisted by addition of a non-ionic surfactant, mechanical stirring and ultrasonication. The UV protective mechanism of nanoparticle-embedded coatings is theoretically explained using Mie theory. We estimated the minimum thickness of a 5 weight % nanoparticle-embedded coatings that is required to prevent the UV radiation from reaching the base of the substrate. Results obtained from nanoparticle-embedded acrylic-coated Kevlar fabric and neat acrylic-coated Kevlar fabric after exposure to UV radiation in QUV weatherometer show that the nanoparticle coating offers protection. UV-visible spectroscopy was used to obtain quantitative results.
Synthesis of Porous Ceramics Through Directional Solidification and Freeze-Drying
Authors: Kisa Predrag , Fisher Patrick , Olszewski Al , Nettleship Ian , Eror Nicholas G. 
Published: April 2011

ABSTRACTThis study investigated the microstructural characteristics of directionally solidified freeze-dried silica sols. Porous structures were formed by depositing silica sol on silicon (100) single crystals. The deposited sols were unidirectionaly solidified by placing the silicon substrate on a copper block immersed in liquid nitrogen and then subsequently freeze-dried. Freeze drying removal of ice crystals created three-dimensional pore channels ranging from 3 to10 micrometers in diameter aggregated in grain like colonies 50–100 micrometers in diameter. Pore size, spacing, colony size and microstructure were determined using optical microscopy (OM) and scanning electron microscopy (SEM) while the structure of the amorphous SiO2 was characterized by X-ray diffraction (XRD). The microstructure results are compared and contrasted with silica aerogel obtained through conventional processing using supercritical CO2.
Thermally activated phenomena observed by atomic force microscopy
Authors: Gnecco Enrico , Riedo Elisa , Bennewitz Roland , Meyer Ernst , Brune Harald 
Published: April 2011

ABSTRACTThermal effects may affect the velocity dependence of friction on the nanoscale in different ways. In a dry environment the stick-slip motion of a nanotip sliding across a crystalline surface is modified by thermal vibrations, which leads to a logarithmic increase of friction with the sliding velocity at very low speeds (v < 10 μm/s). At higher speeds the role of thermal activation is negligible, and friction becomes velocity-independent. An analytical expression, which explains both regimes of friction vs. velocity, is introduced. In a humid environment the situation is complicated by water capillaries formed between tip and surface, which act as obstacles for thermally activated jumps. Depending on the wettability of the surface, different tendencies in the velocity dependence are observed.
Sliding-induced non-equilibrium in confined systems
Authors: Müser Martin H. 
Published: April 2011

ABSTRACTWhen two solids are in relative sliding motion, the intervening layer separating the two surfaces (for example the boundary lubricant) is typically far from thermal equilibrium. With the help of a generic model reflecting the boundary lubricant, it will be shown that it is often not possible to characterize a sliding contact by means of a single effective temperature. The reason is that the probability distribution (PD) of microscopic variables differs in a characteristic fashion from equilibrium PDs. Non-equilibrium velocity PDs are not Gaussian but tend to be exponential, thus favoring rare events. Leaving dynamic equilibrium by non-uniform sliding conditions leads to yet additional effects, in particular to enhanced dissipation. This is shown in a model describing rubbing polymer brushes in good solvent conditions. Shortly after returning the sliding velocity, the brush interdigitation is distinctly larger than during steady-state sliding. Based on this observation, predictions can be made at what amplitude the loss is maximum for a given driving frequency.
Exploring Reaction Pathways of Single-Molecule Interactions through the Manipulation and Tracking of a Potential-Confined Microsphere in Three Dimensions
Authors: Wong Wesley P. , Heinrich Volkmar , Evans Evan 
Published: April 2011

ABSTRACTWeak non-covalent interactions between single molecules govern many aspects of microscopic biological structure and function, e.g. cell adhesion, protein folding, molecular motors and mechanical enzymes. The dynamics of a weak biomolecular bond are suitably characterized by the kinetic transport of molecular states over an effective energy landscape defined along one or more optimal reaction pathways. Motivated by earlier developments [1,2], we present a novel method to quantify subtle features of weak chemical transitions by analyzing the 3D Brownian fluctuations of a functionalized microsphere held near a reactive substrate. A weak optical-trapping potential is used to confine motion of the bead to a nanoscale domain, and to apply a controlled bias field to the interaction. Stochastic interruptions in the monitored bead dynamics report formation and release of single molecular bonds. In addition, variations in the motion of a bead linked to the substrate via a biomolecule (a protein or nucleic acid) signal conformational changes in the molecule, such as the folding/unfolding of protein domains or the unzipping of DNA. Thus, energy landscapes of complex biomolecular interactions are mapped by identifying distinct fluctuation regimes in the 3D motion of a test microsphere, and by quantifying the rates of transition between these regimes as mediated by the applied confining potential.The 3D motion of the bead is tracked using a reflection interference technique combined with high-speed video microscopy. The position of the bead is measured over 100 times per second with a lateral resolution of ∼3–5 nm and a vertical resolution of ∼1–2 nm. Crucial to the interpretation of results, a Brownian Dynamics simulation has been developed to relate the statistics of bead displacements to molecular-scale kinetics of chemical interactions and structural transitions. The experimental approach is designed to enlarge the scope of current techniques (e.g. dynamic force spectroscopy [3]) to encompass near-equilibrium forward/reverse transitions of weak-complex interactions with multiple binding configurations and more than one transition pathway.
Effect of Different Layer Thicknesses and Boundary Conditions of Confined Liquid Crystal on Dynamics of Director Relaxation: Dynamic Light Scattering Investigations
Authors: Basu Sarmistha , Aliev Fouad M. 
Published: April 2011

ABSTRACTDynamic light scattering (DLS) has been used to study the influence of boundary conditions (planar-axial and homeotropic-radial) and layer thickness of liquid crystal (8CB) confined to cylindrical pores on phase transitions and relaxation of director orientational fluctuations. For confined 8CB in the nematic phase two well-defined relaxation processes were observed for both axial and radial orientations of the liquid crystal. The first relaxation is qualitatively associated with bulk-like nematic director fluctuations. The second relaxation (with relaxation time slower than the first one) is most likely due to the fluctuations in the layers nearest the wall surface. In samples with radial boundary conditions, we observed the onset of smectic-A phase order formation on the pore wall even though the rest of the liquid crystal could be in the nematic phase. The influence of pore wall-liquid crystal interactions on the properties of the confined 8CB was stronger for radial boundary conditions of confined liquid crystal, than in the case of axial orientation‥ The separation between the first and the second (slow) process was clearer for thinner layers and the amplitude of the slow process was greater for thinner layers. This suggests that the slow process was related to surface relaxation of director fluctuations.
Terahertz Radiation Spectroscopy on Chloroform Confined in Porous Silica Glasses
Authors: Yamamoto Kohji , Satoh Taku , Okuno Hiroaki , Tominaga Kiesuke , Saito Shinji , Loughnane Brain J. , Scodinu Alessandra , Fourkas John T. 
Published: April 2011

ABSTRACTTerahertz (THz) time-domain spectroscopy (TDS) has been used to study far infrared absorption spectra of chloroform confined within nanoporous glasses of various pore sizes. Intermolecular interactions and dynamics in the confined system are discussed.
Retention of Liquids Above Microporous Membranes
Authors: Charkoudian John , Thom Volkmar 
Published: April 2011

ABSTRACTThe ability of membranes to retain fluids without leaking in devices such as high throughput multiwell plates was examined as a function of membrane polymer, surface modification, and liquid surface tension. Microporous membranes (200–800nm) act as arrays of millions of imperfect microcapillaries. Extrusion and leaking requires pressure plus coalescence of microdroplets. For unmodified membranes, the liquid hold up height (pressure) is critically dependent on liquid surface tension, rising rapidly when the contact angle prevents droplet spreading and coalescence. Topography, as measured by AFM, also plays a role in ease of coalescence. Surface modification has a large impact on hold up pressure and its dependence on liquid surface tension.
Comparison between Adsorption in Pores of a Simple Geometry and Realistic Models of Porous Materials
Authors: Coasne B. , Pikunic J. P. , Pellenq R. J. -M. , Gubbins K. E. 
Published: April 2011

ABSTRACTWe study, by means of Grand Canonical Monte Carlo simulations, the effect of disorder in pore morphology and topology on adsorption of simple fluids at 77 K. We consider the case of microporous carbons and mesoporous silicas. For both systems, we found that morphological and topological disorder affects the adsorption isotherm. Consequently, we show that complex porous networks cannot be modeled as a collection of unconnected pores of simple geometry. In the case of microporous carbons, the isosteric heat of adsorption for disordered systems differs significantly from that obtained for an assembly of unconnected slit pores. In contrast, the isosteric heat of adsorption for the disordered mesoporous silica sample compares reasonably well with that observed for a silica material having regular cylindrical pores.
Raman-Active Nanostructured Materials for Use as Novel Stress-Sensitive Polymeric Coatings
Authors: Halary Jérôme , Stanford John L. , Lovell Peter A. , Young Robert J. 
Published: April 2011

ABSTRACTNanocomposites and nanostructured polymers with unique opto-mechanical properties have been developed as smart coatings for use in a novel, high resolution, and non-contact strain-measuring application. Remote polarized Raman spectroscopy has been used to monitor optical strain sensitivity of deformed coatings (deformation micromechanics), and determine local strains on the micron scale directly from stress/strain induced Raman band shifts.The research is aimed at providing a novel high-resolution non-contact technique for the determination of surface stresses and strains in a wide variety of engineering components used in both laboratory and in-the-field (external) applications.
Meso-to-Nano-scopic Polycrystal/Composite Strengthening
Authors: Armstrong R. W. , Conrad H. , Nabarro F. R. N. 
Published: April 2011

ABSTRACTA great challenge associated with current investigations of the structural strength properties of nanometrically-scaled polycrystals and/or composite materials relates to quantitative description of the continuous transition in mechanical behaviors occurring when going over to such materials from those microstructural, and larger, scale material deformation properties seemingly well-understood and modeled during the research investigations of the previous century [1]. The consideration relates to whether the same dislocation generation/interaction mechanisms operating within the grain volumes of a conventional microstructured material, say, as compared in the same case for local deformations, dislocation or otherwise, at the grain boundary regions, are either additionally restricted from operation, or enhanced, for nanostructured materials. The deduced indication is that there should be a relatively smooth mechanical property transition, if any change at all, to be demonstrated here on the basis of available experimental and theoretical modeling results. The predicted smooth transition in behavior, however, may be upset, possibly, by failure to achieve the demanding quality control predictably needed for the combined considerations of: (1) structural characterization; (2) mechanical testing methods; and, (3) model computations, so as to allow quantification of the finer-scaled material behaviors. The combined property behavior is illustrated by application of effective low temperature grain boundary strengthening models at larger grain (or particle) sizes, then, transitioning to effective grain size weakening at the smallest grain sizes, with such weakening thought to occur because of otherwise normal high temperature diffusional or grain boundary weakening mechanisms being promoted somehow to become controlling in the practical “thought-to-be” low temperature regime.
Phase Mixture Models for Metallic Materials with Submicrometer Grain Size
Authors: Estrin Yuri , Kim Hyoung Seop , Bush Mark 
Published: April 2011

ABSTRACTPhase mixture models describing the mechanical properties of submicrometer grained metals are presented. In this approach, grain boundaries or cell walls are treated as a separate phase. Two cases are considered: the mechanical response of an ultrafine grained material and the process of grain refinement by equal channel angular pressing. Model predictions with regard to the evolution of the microstructure, strength and texture are verified for Cu.
Raman Investigation of Fullerene [60] Under hydrostatic Pressure
Authors: El-Ashry Mostafa , Amer Maher , Maguire John F. 
Published: April 2011

ABSTRACTWe report the results of a study of adsorption of small molecules on the surface of buckminsterfullerene, C60. The pressure dependence of the Raman spectrum was investigated over the range 0–10 GPa in methanol-water mixtures that were used as the pressure transmitting fluid (PTF) in a diamond anvil cell. It is found that the spectral shift and its pressure derivative are sensitive to both the applied pressure and to the composition of the PTF. These observations are consistent with an explanation that involves preferential adsorption onto the surface of the C60. In particular, the notion of C60 collapse needs not be invoked to explain the observations.
The Irradiated Microstructure of Ferritic-Martensitic Steel T91 and 9Cr-ODS
Authors: Gan J. , Allen T. R. , Cole J. I. , Ukai S. , Shutthanandan S. , Thevuthasan S. 
Published: April 2011

ABSTRACTA ferritic steel T91 and an oxide dispersion strengthened (ODS) martensitic steel 9Cr-ODS were irradiated with 5 MeV Ni ions at 500°C at a dose rate of 1.38×10-3 dpa/s to doses of 5, 50 and 150 dpa. Both alloys are iron-based with 9Cr and have been designed for use in higher temperature energy systems. However, the radiation effects on these two alloys are not well characterized. For T91, the irradiated microstructure was dominated by tangled dislocation and precipitates, similar to the unirradiated condition except the presence of large dislocation loops of type a<100>. The microstructure of alloy 9Cr-ODS for both the unirradiated and irradiated cases was dominated by dense dislocations, precipitates and yttrium oxides particles and no dislocation loops were observed. The average size of yttrium oxides particles slightly decreased with dose from 11.8 nm for the unirradiated to 9.1 nm at 150 dpa. No voids were detected for both alloys up to a dose of 150 dpa.