bluuebunny/crossref_metadata_2025_split huggingface dataset:
Developing an Application for Refractory Open Cell Metal Foams in Jet Engines
Authors: Azzi Wassim E. , Roberts William L. , Rabiei Afsaneh 
Published: April 2011

ABSTRACTThe thermodynamic efficiency of the Brayton cycle, upon which all gas turbines (aeropropulsion and power generation) are based on scales with the peak operating temperature. However, the peak temperature is limited by the turbine blades and the temperature they can withstand. The highest temperatures in the gas turbine occur in the combustor region but these temperatures are often too high for turbine blades. As a result, the combustion products must be diluted with relatively cooler air from the compressor to reduce the temperature to tolerable levels for the turbine blades. This research suggests placing a ring of high temperature open cell metal foam between the combustors and turbine sections of the jet engine to mix and average the difference in temperatures resulting from the cooling schemes in combustor cans. Temperature mixing effect was tested using a special setup with the application of an infrared camera and streams of hot and cold air passing through the foam. High speed flow pressure drop around Mach 1 (340 m/s) was done on the same foam samples to understand pressure drop in the compressible regime of air. Infrared imaging showed that open cell metal foams successfully mixed and averaged the difference in temperatures of the hot and cold gasses thus creating a more uniform temperature profile while pressure drop testing revealed that open cell metal foams result in minimal pressure drop at high flows especially when the increase in temperature in taken into consideration.
Nondestructive Damage Sensitivity and Reinforcing Effect of Functionalized Carbon Nanotube and Nanofiber/Epoxy Composites Using Electro-Micromechanical Techniques
Authors: Park Joung-Man , Jung Jin-Kyu , Kim Sung-Ju , Kim Dae-Sik , Lee Jae-Rock , Kim Tae-Wook 
Published: April 2011

ABSTRACTNondestructive damage sensing and load transfer mechanisms of thermal treated carbon nanotube (CNT) and nanofiber (CNF)/epoxy composites were investigated using electro-micromechanical technique. Carbon black (CB) was used only for the comparison. Electro-micromechanical techniques were applied to obtain the fiber damage and stress transferring effect of carbon nanocomposites with their contents. Thermal treatment and temperature affected on apparent modulus and electrical properties on nanocomposites due to enhanced inherent properties of each CNMs. Coefficient of variation (COV) of volumetric electrical resistance can be used to obtain the dispersion degree indirectly for various CNMs. Dispersion and surface modification are very important parameters to obtain improved mechanical and electrical properties of CNMs for multifunctional applications. Further optimized functionalization and dispersion conditions will be investigated for the following work continuously.
Synthesis, Characterization, and Modeling of Nanotube Materials with Variable Stiffness Tethers
Authors: Frankland S. J. V. , Herzog M. N. , Odegard G. M. , Gates T. S. , Fay C. C. 
Published: April 2011

ABSTRACTSynthesis, mechanical testing, and modeling have been performed for a carbon nanotube material in which the nanotubes are functionalized with variable stiffness tethers (VST) capable of cross-linking the nanotubes. Tests using nanoindentation indicated a six-fold enhancement in the storage modulus when comparing the base material (the cross-linking agent with no nanotubes) to the composite (functionalized nanotube material) that contained 5.3 wt% of nanotubes. To understand how crosslinking the nanotubes may further alter the stiffness, a model of the system was constructed using nanotubes crosslinked with the VST. The model predicted that for a composite with 5 wt% nanotubes at random orientations, crosslinked with the VST, the bulk Young's modulus was reduced to 30% that of the non-crosslinked equivalent.
InAs Quantum Dot Development for Enhanced InGaAs Space Solar Cells
Authors: Raffaelle R. P. , Sinharoy Samar , William King C. , Bailey S. G. 
Published: April 2011

ABSTRACTThe majority of high-efficiency space solar cells being produced today are based on multi-junction devices of lattice-matched III-V materials. An alternative which has been receiving an increasing amount of attention is the lattice mis-matched or metamorphic approach to multi-junction cell development. In the metamorphic triple junction cell under development by ERI and its partners, the InGaAs junction (bottom cell) of the three-cell stack is the current limiting entity, due to the current matching which must be maintained through the device. This limitation may be addressed through the incorporation of InAs quantum dot array into the depletion region of an InGaAs cell. The InAs quantum dots in the InGaAs cell will provide sub-gap absorption and thus improve its short circuit current. This cell could then be integrated into the three-cell stack to achieve a space solar cell whose efficiency exceeds current state-of-the-art standards. A theoretical estimate predicts that a InGaAlP(1.95eV)/InGaAsP(1.35 eV)/InGaAs(1.2 eV) triple junction cell incorporating quantum dots to improve the bottom cell current would have an efficiency exceeding 40%. In addition, theoretical estimates have demonstrated that the use of quantum dot structures may also hold other cell benefits such as improved temperature coefficients and better radiation tolerance, which are especially important for utilization in space. As a first step towards achieving that goal, we have initiated the development of InAs quantum dots on lattice-mismatched InGaAs (1.2 eV bandgap) grown epitaxially on GaAs by metallorganic vapor phase epitaxy (MOVPE). These quantum dots have been characterized via photoluminescence (PL) and atomic force microscopy (AFM). A correlation exists between the quantum dot size and resulting optical band structure and can be controlled via the synthesis parameters. Quantum dots were incorporated into prototype InGaAs devices. A comparison of the resulting photovoltaic efficiency under simulated 1 sun intensity and air mass zero (AM0) illumination and spectral response demonstrated that an improvement in the long-wavelength photoconversion efficiency was achieved through the incorporation of the InAs quantum dots.
Computer Simulation of Displacement Damage in Silicon Carbide
Authors: Devanathan R. , Gao F. , Weber W. J. 
Published: April 2011

ABSTRACTWe have performed molecular dynamics simulation of displacement events on silicon and carbon sublattices in silicon carbide for displacement doses ranging from 0.005 to 0.5 displacements per atom. Our results indicate that the displacement threshold energy is about 21 eV for C and 35 eV for Si, and amorphization can occur by accumulation of displacement damage regardless of whether Si or C is displaced. In addition, we have simulated defect production in high-energy cascades as a function of the primary knock-on atom energy and observed features that are different from the case of damage accumulation in Si. These systematic studies shed light on the phenomenon of non-ionizing energy loss that is relevant to understanding space radiation effects in semiconductor devices.
Assessment of Shielding Material Performance for Deep Space Missions
Authors: Mansur L. K. , Frame B. J. , Gallego N. C. , Guetersloh S. B. , Johnson J. O. , Klett J. W. , Townsend L. W. 
Published: April 2011

ABSTRACTRadiation doses from galactic cosmic rays (GCR) are a significant issue for spacecraft crew exposures in deep space. We report initial work to evaluate a range of materials for GCR shielding. Earlier work has shown that conventional spacecraft materials, aluminum and higher atomic number structural alloys, provide relatively little shielding and, under certain conditions, may increase radiation risk. Materials containing high proportions of hydrogen and other low atomic mass nuclei provide improved GCR shielding. Polyethylene (PE) is generally considered a good performance benchmark shield material. However, PE shielding occupies volume and adds mass to the spacecraft. In this work we investigate several materials that are shown to provide shielding similar to PE, but which could furnish additional spacecraft functions, possibly eliminating the need for materials currently used for structural support or thermal management. Carbon forms that can incorporate a large mass of hydrogen, as well as polymers and polymer composites are being explored. Calculations of shielding effectiveness in GCR spectra have been carried out. Experiments to measure shielding properties recently have been completed at the NASA Space Radiation Laboratory (NSRL) located at Brookhaven National Laboratory (BNL) using high energy beans of O16. In this paper we report preliminary shielding results.
Raman Spectroscopy of Graphitic Foams
Authors: Barros Eduardo B. , Demir Nasser S. , Souza Filho Antonio G. , Filho Josué Medes , Jorio Ado , Dresselhaus Gene , Dresselhaus Mildred S. 
Published: April 2011

ABSTRACTTo better understand the very high thermal conductivity to weight ratio of the graphitic foams recently developed at the Oak Ridge National Laboratory, a Raman spectroscopy study was performed. It was also shown that the Raman scattering can be useful for the characterization of the graphitic foam, being able to evaluate the quality of the samples with respect to the density and location of lattice defects.
Spectroscopic Investigations on the Effect of Proton Bombardment of Polyimide
Authors: Edwards David L , de Groh Kim K , Nehls Mary , Miller Sharon K , Banks Bruce , Stephens Chris , Artiaga Ramon , Benson Roberto , Balascuta S. , Zaleski Jeffrey M. , Chipara Mircea 
Published: April 2011

ABSTRACTThe effect of the radiation component of the space environment on polyimide films is reviewed. Experimental data obtained by electron spin resonance and dynamical mechanical analysis proved that the ionizing radiation generates free radicals with a long lifetime through a dominant chain scission mechanism. The radiation-induced shift of the glass transition of polyimide towards lower values confirms the decrease of the average molecular mass of the polymer during irradiation. The importance of polyimide for space exploration is critically analyzed.
TEM Studies of Protective Al Coatings on Kapton H
Authors: Yang Judith C. , Xu Huiping , Li Long , Waters Deborah , Banks Bruce 
Published: April 2011

ABSTRACTPolymeric materials undergo rapid erosion when exposed to the harsh low-earth-orbit (LEO) environment. Coatings can reduce the erosion rate of polyimide Kapton from atomic oxygen (AO) attack. Specifically, we are investigating how thin Al coatings can protect Kapton. Protective Al layers with variations in layer thickness and growth conditions were deposited on Kapton H. The quality of these protective coatings were evaluated by mass loss measurement and compared to Kapton alone and the SiO2 coating, where dramatically decreased erosion rate was noted. To understand how these coatings protect Kapton as well as how the AO interacts with the coatings, we are investigating the microstructure of these coated materials by plane view and cross-sectional transmission electron microscopy (TEM) methods. To understand the AO degradation mechanism, we attempted to correlate the mass loss with growth conditions and microstructures. We noted a slight improvement in erosion resistance of the Al coating due to the presence of the dendrimer, but a major improvement when the Al coating is deposited under ultrahigh vacuum conditions.
New Materials on the Renaissance Artists' Palette
Authors: Berrie Barbara H. , Matthew Louisa C. 
Published: April 2011

ABSTRACTIn the light of new documentary information regarding the range of materials available to sixteenth century artists, cross sections from paintings were re-examined using scanning electron microscopy - energy dispersive spectrometry. Among a variety of new materials, colored glassy pigments were found including diverse yellow glassy particles, specifically lead silicate and a glass colored by lead antimonate. These are the “yellow smalts” described in Renaissance writings on artists’ materials.
A Study of the Materials of Pontormo's “Portrait of Alessandro de' Medici”
Authors: Sutherland Ken , Price Beth A. , Passeri Irma , Tucker Mark 
Published: April 2011

ABSTRACTIn studies of the materials of old master paintings, the characterization of thin and degraded layers often presents unusual challenges for routinely used methods of analysis. This paper discusses analyses performed as part of a study of the materials and techniques of Pontormo's “Portrait of Alessandro de’ Medici” (1534–5) carried out during a recent cleaning and restoration of the painting. Pontormo built up the portrait using a complex sequence of preparation, drawing and paint layers, the analysis of which was complicated further in some areas by the presence of degraded materials on the paint surface. The materials used for the various stages of preparation and painting were characterized by gas chromatography/mass spectrometry (GCMS), Fourier transform infrared microspectroscopy (FTIR) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The focus of this paper will be the particular approaches taken to the characterization of the preparation layers and degraded surface materials.
Laser Cleaning of Fifteenth and Early Sixteenth Century A.D. Wax Votive Images from St. Peter's Cathedral, Exeter, England
Authors: Moreno Teresa 
Published: April 2011

ABSTRACTA rare collection of cast votive images (ex-votos) made of beeswax were found in the 1940s behind the cresting of a screen above the tomb of Bishop Edmund Lacey in the Cathedral Church of St. Peter in Exeter, England. Some of these fragmentary, aged and brittle waxes, dating to the late fifteenth to early sixteenth centuries A.D., served as the basis to further test the cleaning of dirt and accretions using a Q-switched Nd:YAG laser. Because of the low melting point of the wax, observations made of the effects on the wax substrate due to heat emitted from the laser were critical to establish the efficacy of the cleaning method. Preliminary optical microscopy was used to establish a typology of the waxes based on their condition, color, and nature of the weathering phenomena. Several techniques were used to characterize the waxes and the surface deposits, including gas chromatography-mass spectroscopy (GC-MS), energy-dispersive x-ray fluorescence (EDXRF) and scanning electron microscopy (SEM-EDS), in addition to simple tests of melting point and hardness that served to help understand the nature, condition and treatment of the waxes [1].
The Development of Ultra-cool Melt Adhesives for Mounting Resin-Coated (RC) Photographic Papers.
Authors: McGlinchey Chris , Yuan Bing 
Published: April 2011

ABSTRACTThe development of an adhesive that is a hybrid between a pressure sensitive adhesive and a heat seal adhesive is described. The goal of this project, which is a joint collaboration between the Museum of Modern Art and the Polymer Research Institute, is to develop a preservation quality adhesive for application to RC print photographs. RC prints are clad in polyethylene, a low surface energy (LSE) polymer that requires special consideration when devising an adhesive to adhere to it. In arriving at a formula for this purpose research has focused on a combination of hydrocarbon-based polymers and low molecular weight oligomers. In addition, this work addresses other aspects such as activation conditions and joint design, factors critical to developing an adhesive that has the potential to satisfy the stringent criteria of a material acceptable to conservation applications.
Producing New Stone Consolidants for the Conservation of Monumental Stones
Authors: Mosquera María J. , de los Santos D.M. , Montes A. 
Published: April 2011

ABSTRACTA customary procedure in the protection of monumental buildings is the consolidation of decaying stone by the application of commercial products containing tetraethoxysilane (TEOS). These products polymerize within the porous structure of the decaying stone, significantly increasing the cohesion of the material. However, TEOS-based consolidants suffer practical drawbacks, such as cracking of the network during the drying phase, and significant blocking of the rock pores. These limitations are related to the growth of a dense microporous network of the xerogel inside the stone material, which is typical from TEOS sols. Therefore, the purpose of this work is to increase porosity of the product by including colloidal particles in the starting sol.We prepared a colloid-polymer composite gel using TEOS and a commercial silica colloid. The percentage by weight of silica colloid particles to total silica was 54%. Ethanol and dibutyltindilaurate (DBLT) were chosen as solvent and catalyst, respectively. This catalyst promotes the gelation at a neutral pH, preventing stone decay related to acid or basic catalysis. We characterized the properties playing a key role in consolidation. Data were compared with those obtained using a popular commercial product: Tegovakon V 100 produced by Goldsmith.In spite of the colloidal particle addition, sols exhibited viscosity values close to those of the commercial products, as a consequence of their dispersion in ethanol. A gelation time similar to that of commercial consolidants was maintained, whereas the contained sol was stable over a period of up to six months. Concerning textural parameters, the addition of colloid permitted to obtain a crack-free, mesoporous material structure. This generated a crack-free material whereas the gel from Tegovakon V 100 exhibited cracking.We also evaluated the consolidant efficacy on a biocalcareous stone, one of the most common monumental building stone employed in the southwest of Spain. Three key parameters -penetration depth in the rock, mechanical properties and water vapour diffusivity- were measured. Stone permeation was similar to that from the commercial product. Notably, a significant improvement of compression strength of the stone was observed. Reduction in vapour diffusivity of the treated stone was slightly lower for our gel than for the commercial consolidant.
Estimation of Firing Temperature and Compositional Variability of Archaeological Pottery by Differential Scanning Calorimetry
Authors: Giordana A. , Peacock E. , McCarthy M. , Guilbeau K. , Jacobs P. , Seger J.D. , Ramsey W.G. 
Published: April 2011

ABSTRACTDigital Scanning Calorimetry (DSC), a thermal characterization technique, can be used to rapidly obtain a rough upper estimate of the firing temperature of archaeological pottery as well as an indication of its composition. The technique involves heating a small sample (10–20 mg) of ground ceramic above the vitrification temperature, cooling and reheating. The curves of the two heating cycles are then compared. The validity of the technique was evaluated by a blind test in which 35 tiles fired at different temperatures were analyzed without knowing their firing point, and by analysis of archaeological pottery samples assumed to be local or imported based upon stylistic criteria.
Ferromagnetism in Fe-doped β-Ga2O3 Prepared by a Solid State Reaction
Authors: Hojo Hajime , Fujita Koji , Tanaka Katsuhisa , Hirao Kazuyuki 
Published: April 2011

ABSTRACTPolycrystalline β-Ga2O3 doped with Fe3+, (Ga1−x Fex)2O3 (x=0.02, 0.05, 0.08 and 0.1), has been prepared by a solid-state reaction. Ferromagnetic ordering is observed at room temperature for samples prepared by β-Ga2O3 and Fe(NO3)3·9H2O and sintered at low temperatures below 900 °C, while the sintering at temperatures above 900 °C leads to the paramagnetic behavior. X-ray diffraction analysis for the samples sintered at 500 °C reveals that the single phase of β-Ga2O3 can be obtained up to x=0.08 without traces of secondary phase or other impurity. Magnetization as a function of temperature shows superparamagnetic or cluster spin-glass behavior, indicating that long-range ferromagnetic ordering does not exist in the present systems. It is suggested that the inhomogeneous distribution of Fe3+ is responsible for the ferromagnetic behavior.
Water-Dispersible FePt Nanoparticles Having ω-Mercapto-α-carboxylic Acid Ligands
Authors: Mabry Janis K. , Tackett Laura Beth , Bargaria Hitesh , Sun Xiangcheng , Ada Earl T. , Shamsuzzoha Mohammad , Sun Kai , Wang Lu-min , Johnson Duane T. , Nikles David E. 
Published: April 2011

ABSTRACTFePt nanoparticles, ∼ 2nm in diameter, were prepared by the polyol reduction of platinum(II) acetylacetonate and iron(III) acetylacetonate in the presence of oleyl amine and oleic acid surfactants. The particles were dispersed in hexane and the dispersion added to a solution of 11-mercaptoundecanoic acid in cyclohexanone. As the 11-mercaptoundecanoic acid ligands replaced the oleic acid ligands, the particles precipitated. The particles could be dispersed in basic water, made basic either with sodium hydroxide or ammonium hydroxide. X-ray photoelectron spectra showed a peak near 164 eV, sulfur (2p) confirming the presence of the thiol ligand. Similarly, the oleic acid ligands were replaced with either 3-mercaptopropionic acid or 16-mercaptohexadecanoic acid to give FePt particles that could be dispersed in water. Dispersions made with FePt nanoparticles having 11-mercaptoundeacnoic acid ligands and ammonium counter ions were dried on TEM grids to give highly ordered films consisting of close-packed arrays of FePt nanoparticles. When the counter ion was sodium, the particles tended to aggregate, instead of forming ordered arrays.
A Novel Fabrication Technique for Interacting Ferromagnetic-metal Nanoparticle Systems: Fine-tuning of Particle Diameter and Interparticle Spacing
Authors: Tomita Satoshi , Akamatsu Kensuke , Shinkai Hiroyuki , Ikeda Shingo , Nawafune Hidemi , Mitsumata Chiharu , Kashiwagi Takanari , Hagiwara Masayuki 
Published: April 2011

ABSTRACTMetallic Ni nanoparticles were embedded in polyimide (PI) films by applying a chemical surface modification technique. The technique consists of a simple alkali treatment of the PI films, an ion exchange reaction, and thermal annealing. The transmission electron microscopic studies showed that the initial alkali treatment time determined the diameter (d) of Ni nanoparticles formed by the annealing at 300 °C.With increasing the annealing time, the thickness of the composite layers containing Ni nanoparticles decreased while the d was almost constant. The shrinkage of the composite layer led to a decrease in the spacing (r) among Ni nanoparticles. The d and r can thus be fine-tuned independently. Electron magnetic resonance study clearly indicated that the tuning of d and r enable us to control the magnetic dipolar interaction in the Ni nanoparticle systems. The present technique opens a new way to realize tailor-made nanomagnetic structures.