bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic Limitations in Two-and Three-Dimensional Growth
Authors: Man K. L. , Tang W. X. , Huang Hanchen , Altman M. S. 
Published: April 2011

ABSTRACTKinetic limitations related to the Schwoebel-Ehrlich (SE) diffusion barrier are examined in two-(2D) and three-dimensional (3D) growth. It is shown that the realization of step instabilities in 2D growth, possibly caused by the SE barrier, may be hindered by other factors such as step permeability and the relative importance of diffusion and step attachment. Growth shapes of Ag crystallites are also determined that reveal the impact of kinetic limitations. Dramatic changes of growth shape caused by In codeposition suggest that surfactants can modify the 3D SE barrier.
Magnetic nanoparticles for space applications
Authors: Sharma S. K. , Kumar Ravi , Dolia S. N. , Siva Kumar V. V. , Singh Mahavir 
Published: April 2011

ABSTRACTRadiation resistant ferrite materials have potential applications in space station. Mg-Mn spinel ferrite was choosen for this study because of its radiation resistance and potential for use as an insulator in radiation environments. The radiation damage expected in these environments can be quickly and conveniently simulated using ion irradiation. The results of swift heavy ion irradiation induced modifications in the magnetization behavior of the Mg-Mn ferrite nanoparticles have been investigated using 100 MeV Ni8+ ion irradiation. To ensure the singlephase spinel structure of the system powder x-ray diffraction patterns has been performed. The powder samples were irradiated at three different fluences in the range 1×1012-5×1013 ions/cm2. Isothermal dc magnetization studies have been performed using SQUID and vibration sample magnetometer (VSM) on the pristine as well as on the irradiated samples at 20 K and 300 K. With irradiation saturation magnetization remains almost constant with ions irradiation. The coercivity values of the materials decreased about 5% with the fluence 1×1013 ions/cm2 as compare to the pristine nanoparticles. The results have been explained on the basis of the existence of surface defects produced by swift heavy ions, which generate orientational disorder of surface spins. The behavior of saturation magnetization with irradiations makes these nanoparticles suitable for memory devices in the space research.
Polymer Degradation from the Thermal Analysis Point of View
Authors: Artiaga Ramón , Cao Ricardo , Naya Salvador , García Ana 
Published: April 2011

ABSTRACTThis work applies different thermal analysis methods to polymer based materials degradation, studying the degradation process itself and evaluating the degree of material damage as a consequence of chemical degradation by thermal or radiation effects. On the one hand, thermal degradation in varied atmospheres is investigated by means of thermogravimetric analysis (TGA) in dynamic experiments. The authors find that the evolution of the sample mass follows a mixture of logistics models, and these can fit an overall TGA curve. The fitting parameters have important physical meaning related to the kinetics of the different processes involved and to the relative amount of each component in the sample. The method itself entails separating overlapping processes. Other improvements made by the authors are related to reducing the noise and smoothing the TGA and differential scanning calorimetry (DSC) data, particularly when estimating TGA derivatives through logistic regression.Analyzing many materials by means of TGA results in more or less complex traces that do not allow a simple parametric fit like the one described above. Although it reproduces asymptoticity at the beginning and end of the reaction, there are times when many processes overlap, resulting in a complex trace that would need a high number of logistic components to be adequately fitted. However, it is possible to use a local polynomial regression model instead. This is also applicable to DSC traces, whose shapes are totally different from those found in TGA. The authors propose a model based on a nonparametric estimation, where the fit's suitability very much depends on the bandwidth selection, especially where derivatives are concerned. The proposed model gives a satisfactory fitting. It smoothes noise and always provides reliable values, different from those obtained by other methods strongly dependent on user choice.On the other hand, to evaluate the degree of damage by thermal analysis methods, dynamic mechanical analysis (DMA) is applied to polyamides. The glass transition temperature is measured before and after exposure to varying doses of proton radiation, emulating the space environment. Other examples show how exposure over long periods at moderately elevated temperatures results in reduction of some mechanical properties. Additionally, the effect of different nanofillers on styrene-isoprene-styrene block copolymers is evaluated by DMA. A shift in the glass transition temperature seems to be dependent on nanofiller content. The degradation of some materials suitable for space applications, such as polyethylene and polyamide, are also briefly reviewed.
Aerothermal analysis of an advanced hot structure for hypersonic flight tests
Authors: Savino Raffaele , Fumo Mario De Stefano , Marino Giuliano , Tului Mario 
Published: April 2011

ABSTRACTThis paper deals with the aerothemodynamic analysis of an advanced concept of hot structure to be investigated in the Expert flight test programme.Three-dimensional fluid dynamic computations have been carried out at the flight conditions of the reference Expert trajectory to evaluate the aerothermodynamic field and the thermal loads on the winglet. The physical model includes viscous effects, real gas properties, non equilibrium chemical reactions and surface catalytic effects. The unsteady aerothermal analysis has been carried out considering different thermal boundary conditions (adiabatic wall or thermal coupling with the capsule metallic skin).The results are discussed with particular attention to the temperature distributions in the Ultra High Temperature Ceramics (UHTC) and in the structural support.
Thermoplastic matrix composites for SPACE SOLAR POWER TRUSS (SSP)
Authors: Zhang Hao , Guidanean Koorosh , Nutt Steven 
Published: April 2011

ABSTRACTThermoplastic matrix composites with a low glass transition temperature (Tg) have been developed for the Space Solar Power Truss (SSP). In this application, the truss is folded and packaged for launch, then expanded and deployed in space using a heat source. The present paper describes a resin film infusion process (RFI) used to fabricate laboratory-scale laminate tubes consisting of polyurethane and plain weave carbon fabrics. Subscale (1:5) sample tubes were formed to approximate the real tubes. The performance of the folded and unfolded tubes was measured under compression loading and compared with as-fabricated tubes at 25 and -75°C. Results show that elastic modulus was restored and even increased after bending. Stitched samples were also examined to evaluate the potential for reducing delamination at folds.
Preparation and Characterization of Electrospun Poly(ethylene oxide) (PEO) Nanofibers-reinforced Epoxy Matrix Composites
Authors: Lee Jae-Rock , Park Soo-Jin , Seo Min-Kang , Park Joung-Man 
Published: April 2011

ABSTRACTIn this work, electrospinning was carried out using 12 wt.% poly(ethylene oxide) (PEO) solution under fixed tip-to-collect distance (10 cm) and voltage (15 kV) in order to fabricate nanofibers-reinforced composites. The content of PEO nanofibers was varied from 0 to 10 wt.% in the epoxy (EP) matrix resins. And the PEO powders-impregnated composites were also prepared to compare with physicochemecal properties of nanofibers-reinforced composites. Thermal and mechanical interfacial properties of EP/PEO nanocomposites were characterized by thermogravimetric analysis (TGA) and fracture toughness test, respectively. As a result, the PEO-based nanofibers-reinforced composites showed an improvement of thermal stability parameters (initial decomposed temperature (IDT) and integral procedural decomposition temperature (IPDT)) and fracture toughness factors (KIC and GIC), compared to the composites impregnated with PEO powders. And the thermal and mechanical interfacial properties of the composites were increased with increasing the PEO content, which could be probably attributed to the higher specific surface area and larger aspect ratio of PEO nanofibers, resulting in improving the demand performance of the nanocomposites.
Non-equilibrium Ti-Fe bulk alloys with ultra-high strength and enhanced ductility
Authors: Louzguine-Luzgin Dmitri V. , Louzguina-Luzgina Larissa V. , Kato Hidemi , Inoue Akihisa 
Published: April 2011

ABSTRACTThe high-strength and ductile hypo-, hyper- and eutectic Ti-Fe alloys were formed in the shape of the arc-melted ingots with the dimensions of about 25–40 mm in diameter and 10–15 mm in height. The structure of the samples consists of cubic Pm 3 m TiFe and BCC Im 3 m β-Ti supersaturated solid solution phase. The arc-melted hypereutectic Ti65Fe35 alloy has a dispersed structure consisting of the primary TiFe phase and submicron-size eutectic structure. This alloy exhibits excellent mechanical properties: a Young's modulus of 149 GPa, a high mechanical fracture strength of 2.2 GPa, a 0.2 % yield strength of 1.8 GPa and 6.7 % ductility. The hard round-shaped intermetallic TiFe phase and the supersaturated β-Ti solid solution result in a high strength of the Ti65Fe35 alloy which in addition has much higher ductility compared to that of the nanostructured or glassy alloys. The reasons for the high ductility of the hypereutectic alloy are discussed.
Multifunctional Metal/Polymer Hybrid Fiber for Space and Aerospace Applications
Authors: Lee Jar-Wha , Hart Dale L. , Shinn Elizabeth T. , Cooley Abigail J. , White Edward L. , MacDowell Paul W. , Schomburg Erik , Slenski George A. , Watkins Anthony N. , Yang Robert L. 
Published: April 2011

ABSTRACTThe stringent weight and space requirements of advanced space and aerospace systems have lead to a need for stronger, lighter, smaller, and more flexible cable and wiring components. Syscom has fabricated a multifunctional metal/polymer hybrid fiber from a rigid-rod type of polymer, such as poly(p-phenylene benzobisoxazole) (PBO) fiber, for signal transfer and electromagnetic interference (EMI) shielding in wiring and cable applications. The test results indicated that the metal/polymer hybrid PBO fiber exhibited ∼67% the electrical conductivity, ∼73% the weight and ∼200% the tensile strength of a comparable size of beryllium-copper CS95 wire. Additional experimental results of electric current carrying capability, cable shielding performance and atomic oxygen erosion protection will also be discussed.
Materials for High-Energy Radiation Shielding on Extra-Terrestrial Surfaces
Authors: Kiefer R. L. , Chapman J. L. , Boone A. R. , Thibeault S. A. 
Published: April 2011

ABSTRACTPolyethylene and polypropylene were used with simulated lunar regolith to make microcomposites as possible materials for habitat construction on extra-terrestrial surfaces. The polymer powders were used in various mass percents and thoroughly mixed with regolith powder before heating. A heated press or a microwave oven was used to heat the polymer/regolith mixture and form the micro-composite. The resulting materials were characterized by thermal analysis.
Proton Beam Induced Modifications in Multi-Functional Polyethylene-Based Carbon Nanotubes Composites
Authors: Pulikkathara Merlyn. X. , Pena-Paras Laura , McIntosh Daneesh , Chipara Mircea , Wilkins Richard , Barrera Enrique V. , Dye David , Zaleski Jeffrey M. 
Published: April 2011

ABSTRACTThe space applications of composites obtained by dispersing carbon nanotubes within high-density polyethylene are analyzed. Electron spin resonance investigations on proton-irradiated composites are reported. The effect of ionizing radiation of the parameters of electron spin resonance spectra is studied. A radiation-induced increase of the concentration of uncoupled electronic spins delocalized over the conducting domains of carbon nanotubes is reported. It is concluded that radiation-induced modifications in such composites are weak.
Ground-Based Space Radiation Effects Studies on Single-Walled Carbon Nanotube Materials
Authors: Wilkins R. , Pulikkathara M. X. , Khabashesku Valery N. , Barrera E. V. , Vaidyanathan Ranji K. , Thibeault S. A. 
Published: April 2011

ABSTRACTMaterials based on carbon nanotubes hold great promise for a variety of applications relevant to space exploration and the aerospace industry. Materials used for these applications will be subject to hostile environments including increased levels of high-energy particulate radiation. The type, energy range and fluence of the radiation will depend on the environment of the space mission. While it is not feasible to conduct an exhaustive study of the effects of space radiation on the earth's surface, ground-based experiments can be designed to simulate expected radiation environments using sources representing components of the relevant radiation environments. In this paper we present a compilation of results on materials based on singlewalled carbon nanotubes (SWNT) emphasizing nano-composites with raw (non-functionalized) and with 2–5% functionalized SWNTs in a polyethylene matrix. Materials such as these are promising candidates for multi-functional materials with good structural and radiation shielding characteristics. The radiation sources discussed here are relevant to the upper atmosphere (high energy neutrons), low earth orbit (medium energy protons) and interplanetary space (high energy protons and heavy ions). The samples are characterized before and after radiation with Raman spectroscopy which gives information on the structure of the SWNT and state of sidewall functionalization. Based on results from the SWNT papers (“buckypapers”) and the composites made from functionalized and non-functionalized SWNT, our data indicates that structural integrity and any sidewall functionalization of the SWNT in the nano-composite are radiation tolerant to radiation fluences commensurate with expected exposures on long-term spaceflight. More importantly, we find that the chemistry and material science of the processes used to produce the pristine and functionalized SWNT can affect the radiation characteristics of the nano-composites.
Investigation of Resiliency of Carbon Nanotubes and Gallium Nitride Nanocircuits to Simulated Space Radiation
Authors: Jacobs B. W. , Ayres V. M. , Crimp M. A. , Ronningen R. M. , Zeller A. F. , Shaw H. C. , Benavides J. B. , Kogut A. J. , Halpern J. M. , Petkov M. P. 
Published: April 2011

ABSTRACTHeavy ion irradiations of single and multi walled carbon nanotubes and total ionization dose of gallium nitride nanowires were investigated. Post irradiation analyses of samples were performed with transmission and scanning electron microscopy, atomic force microscopy and micro Raman spectroscopy.
Conducting and Antistatic Composites for Space Applications
Authors: Chipara Mircea , Sankar Jagannathan , Notinger Petre , Panaitescu Denis , Hui David , Aldica Gheorghe V. , Chipara Magdalena D. , Lau Kin-tak 
Published: April 2011

ABSTRACTThe percolative dependence of the DC conductivity on the volume concentration of fillers for composites obtained by dispersing conducting particles into polymeric matrices is studied in detail. An empirical Boltzmann like dependence is proposed for the modeling of the dependence of DC conductivity versus filler concentration. This expression allows for a more accurate determination of the percolation threshold in the case of broad percolations. It is shown that the loading of the polymeric matrices with conducting fillers produces percolative-like changes of various physical properties (such as the reciprocal of the tensile strength and the reciprocal of the double integral of the resonance spectrum). Experimental mechanical, electrical, and electron spin resonance data on polyvinylchloride-carbon, polyvinylchloride-polyaniline, and polyethylene-polyaniline composites are reported.
Preventive Surface Treatment of Silicone Materials for Outgassing and Contamination Reduction in Space Application
Authors: Iskanderova Z. , Kleiman J. , Ng R. , Gudimenko Y. , Kaute D. A. 
Published: April 2011

ABSTRACTContaminating films on spacecraft sensitive materials surfaces in many cases consist primarily of products resulting from the interaction of atomic oxygen with silicones. Necessity of a drastic reduction of the outgassing of volatiles and the following contamination has thus become a challenging problem. The effective surface conversion of space related organosilicone materials to oxide-based protective sub-surface layers under ground-based OpenAir™ plasma pre-treatment has been researched. Oxygen plasma asher testing and complementary surface analysis techniques have been used to assess the surface composition, bounding states and atomic oxygen resistance of the treated materials. It was shown that the application of this approach may essentially simplify the technological development to reduce or prevent contamination caused by silicone-coated space materials and structures.
Properties and Improved Space Survivability of POSS (Polyhedral Oligomeric Silsesquioxane) Polyimides
Authors: Tomczak Sandra J. , Marchant Darrell , Svejda Steve , Minton Timothy K. , Brunsvold Amy L. , Gouzman Irina , Grossman Eitan , Schatz George C. , Troya Diego , Sun LiPeng , Gonzalez Rene I. 
Published: April 2011

ABSTRACTKapton polyimide (PI) is widely used on the exterior of spacecraft as a thermal insulator. Atomic oxygen (AO) in lower earth orbit (LEO) causes severe degradation in Kapton resulting in reduced spacecraft lifetimes. One solution is to coat the polymer surface with SiO2 since this coating is known to impart remarkable oxidation resistance. Imperfections in the SiO2 application process and micrometeoroid / debris impact in orbit damage the SiO2 coating, leading to erosion of Kapton.A self passivating, self healing silica layer protecting underlying Kapton upon exposure to AO may result from the nanodispersion of silicon and oxygen within the polymer matrix. Polyhedral oligomeric silsesquioxane (POSS) is composed of an inorganic cage structure with a 2:3 Si:O ratio surrounded by tailorable organic groups and is a possible delivery system for nanodispersed silica. A POSS dianiline was copolymerized with pyromellitic dianhydride and 4, 4′-oxydianiline resulting in POSS Kapton Polyimide. The glass transition temperature (Tg) of 5 to 25 weight % POSS Polyimide was determined to be slightly lower, 5 – 10 %, than that of unmodified polyimides (414 °C). Furthermore the room temperature modulus of polyimide is unaffected by POSS, and the modulus at temperatures greater than the Tg of the polyimide is doubled by the incorporation of 20 wt % POSS.To simulate LEO conditions, POSS PI films underwent exposure to a hyperthermal O-atom beam. Surface analysis of exposed and unexposed films conducted with X-ray photoelectron spectroscopy, atomic force microscopy, and surface profilometry support the formation of a SiO2 self healing passivation layer upon AO exposure. This is exemplified by erosion rates of 10 and 20 weight % POSS PI samples which were 3.7 and 0.98 percent, respectively, of the erosion rate for Kapton H at a fluence of 8.5 × 1020 O atoms cm-2. This data corresponds to an erosion yield for 10 wt % POSS PI of 4.8 % of Kapton H. In a separate exposure, at a fluence of 7.33 × 1020 O atoms cm-2, 25 wt % POSS Polyimide showed the erosion yield of about 1.1 % of that of Kapton H. Also, recently at a lower fluence of 2.03 × 1020 O atoms cm-2, in going from 20 to 25 wt % POSS PI the erosion was decreased by a factor of 2 with an erosion yield too minor to be measured for 25 wt % POSS PI.
Increased Ordering in the Amorphous SiOx due to Hyperthermal Atomic Oxygen.
Authors: Kisa Maja , Stratton William G. , Minton Timothy K. , Benthem Klaus van , Pennycook Steve J. , Voyles Paul M. , Chen Xidong , Li Long , Yang Judith C. 
Published: April 2011

ABSTRACTWe had studied the effects of hyperthermal (5.1eV) atomic oxygen (AO) on the structural characteristics of the silica layer and Si/SiOx interface formed by the oxidation of Si-single crystal by a variety of microcharacterization techniques. A laser detonation source was used to produce atomic oxygen with 5.1eV kinetic energy. High Resolution Transmission Electron Microscopy (HRTEM) and Selected Area Electron Diffraction (SAED) demonstrated that the silica layer formed on Si(100) by atomic oxygen is thicker, more homogeneous, and less amorphous, compared to the oxide layer created by molecular oxygen (MO). High spatial resolution Electron Energy Loss Spectroscopy (EELS) study confirmed that the Si/SiOx interface created by atomic oxygen is abrupt containing no suboxides as opposed to the broad interface with transitional states formed by molecular oxygen. SAED technique was used to observe sharper diffraction rings present in the diffraction pattern of Si(100) oxidized by reactive atomic oxygen as opposed to the diffused haloes present in the diffraction pattern of Si(100) oxidized by molecular oxygen. Radial Distribution Function (RDF) analyses were performed on the SAED patterns of Si(100) oxidized in atomic and molecular oxygen, indicating that a more ordered oxide is formed by atomic oxygen. Initial Fluctuation Electron Microscopy (FEM) results confirmed an increased medium range ordering in SiOx formed by atomic oxygen when compared to the non-regular arrangement present in the amorphous oxide formed by the oxidation of Si(100) in molecular oxygen.
An Investigation of the Chemical Changes of Artists' Acrylic Paint Films When Exposed to Water
Authors: Ploeger R. , Murray A. , Hesp S. , Scalarone D. 
Published: April 2011

ABSTRACTThis paper addresses some of the conservation concerns of artists' acrylic paints by investigating the chemical changes of the paint films caused during a one-hour exposure to water experiments and the rate at which some of the changes occur. Three different acrylic paint films were investigated. Real-time capillary rise, conductivity measurements and thermo-mechanical analysis (TMA) gave an indication of the rate at which these changes occurred. Much of the measurable leaching occurred within the first 20 minutes of the paint film being exposed to water, while the most rapid leaching occurred within the first five minutes, before approaching an equilibrium state. All physical and visual changes in colour, gloss, dimension, mass and surface morphology (using atomic force microscopy, AFM) were monitored. A decrease in size and mass indicated that material had been permanently removed from the paint films. Gloss and colour measurements, as well as AFM images, also showed evidence of changes caused by the exposure to water.
Using ICP-MS to Detect Inorganic Elements in Organic Materials: A New Tool to Identify Mordants or Dyes on Ancient Textiles
Authors: Dussubieux Laure , Ballard Mary W. 
Published: April 2011

ABSTRACTThe feasibility of determining metallic elements used as mordants or dyes with inorganic constituents was tested using inductively coupled plasma – mass spectrometry (ICP-MS). For this purpose, modern, historic and archaeological samples were investigated. Mordants containing copper, iron, tin, aluminium or uranium were successfully identified as well as an organic dye with a substitutional bromine.