Beam-plasma interactions
Wavelength, frequency, and growth rate dependence on density, stream velocity, and magnetic field strength
STREAM FUNCTION↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Global Patterns of Lightning Properties Derived by LIS
The Lightning Imaging Sensor LIS aboard the TRMM satellite provides unmatched empirical data of the global lightning distribution (up to approx.35deg S/N) since end of 1997. Climatological flash rate densities derived from LIS are standard references, e.g. for flash rate parameterizations used in GCMs. It is known that flash characteristics are quite variable, and that various quantities (like the flash energy or the NOx production per flash) vary considerably, statistically as well as systematically on regional and seasonal scales. LIS provides information beyond flash counts, in particular radiance and flash footprint. Here we present an analysis of global patterns of various lightning properties derived from LIS, in relation to the number of flashes. These normalized flash characteristics show consistent spatial patterns of regions with "strong" versus regions with "weak" lightning. Most striking is a clear land-ocean contrast, with oceanic flashes being "stronger" than continental flashes. But also over continents, flash strength shows systematic variations. Highest continental values are found over the US, while values over South America and India are quite low. These regional variations cannot be simply parameterized as function of latitude. Information on spatial patterns of mean flash "strength", though rather qualitative up to now, is potentially a valuable input for improving empirical parameterizations based on flash counts (like precipitation or lightning NOx). Further investigation is in progress to come to a more physical and quantitative understanding of the spatial patterns of the different LIS properties. In particular, it has to be checked how far they could be related to established lightning properties (like energy or the fraction of intra-cloud to cloud-to-ground flashes) or to meteorological quantities (like CAPE).
Beirle, S.↗
Structure-dependent binding and activation of perfluorinated compounds on human peroxisome proliferator-activated receptor γ
Perfluorinated compounds (PFCs) have been shown to disrupt lipid metabolism and even induce cancer in rodents through activation of peroxisome proliferator-activated receptors (PPARs). Lines of evidence showed that PPARα was activated by PFCs. However, the information on the binding interactions between PPARγ and PFCs and subsequent alteration of PPARγ activity is still limited and sometimes inconsistent. In the present study, in vitro binding of 16 PFCs to human PPARγ ligand binding domain (hPPARγ-LBD) and their activity on the receptor in cells were investigated. The results showed that the binding affinity was strongly dependent on their carbon number and functional group. For the eleven perfluorinated carboxylic acids (PFCAs), the binding affinity increased with their carbon number from 4 to 11, and then decreased slightly. The binding affinity of the three perfluorinated sulfonic acids (PFSAs) was stronger than their PFCA counterparts. No binding was detected for the two fluorotelomer alcohols (FTOHs). Circular dichroim spectroscopy showed that PFC binding induced distinctive structural change of the receptor. In dual luciferase reporter assays using transiently transfected Hep G2 cells, PFCs acted as hPPARγ agonists, and their potency correlated with their binding affinity with hPPARγ-LBD. Molecular docking showed that PFCs with different chain length bind with the receptor in different geometry, which may contribute to their differences in binding affinity and transcriptional activity. - Highlights: • Binding affinity between PFCs and PPARγ was evaluated for the first time. • The binding strength was dependent on fluorinated carbon chain and functional group. • PFC binding induced distinctive structural change of the receptor. • PFCs could act as hPPARγ agonists in Hep G2 cells.
60 APPLIED LIFE SCIENCES↗
Pressureless sintered beta-prime-Si3N4 solid solution - Fabrication, microstructure, and strength
Pressureless sintering of beta-prime-Si3N4 solid solution was studied as a function of temperature using Si3N4, A1N, and Al2O3 as basic constituents. Y2O3-SiO2 additions were used to promote liquid-phase sintering. The sintered specimens were characterized with respect to density, microstructure, strength, oxidation, and thermal shock resistance. Density greater than 98 percent of theoretical was achieved by pressureless sintering at 1750 C. The microstructure consisted essentially of fine-grained beta-prime-Si3N4 solid solution as the major phase. Modulus of rupture strengths up to 483 M Pa were achieved at moderate temperature (1000 C), but decreased to 228 M Pa at 1380 C. This substantial strength loss was attributed to a 'glassy' grain boundary phase formed during cooling from the sintering temperature. The best oxidation resistance was exhibited by a composition containing 3 mol % Y2O3-SiO2 additives. Water quench thermal shock resistance was equivalent to that of reaction sintered silicon nitride but lower than hot-pressed silicon nitride.
Dutta, S.↗
Description of C isotopes within RMF+BCS approach
In the present investigations we have employed relativistic mean-field plus BCS (RMF + BCS) approach to carry out a systematic study for the ground state properties of even-even C Isotopes. One of the prime reason of this study has been to look into the role of low lying states in neutron rich reason near neutron drip line. It is found that irrespective of whether any resonant state exists or not, the occupancy of weakly bound neutron single particle states having low orbital angular momentum, (l = 0 or 1), with a well spread wave function due to the absence or very small strength of centrifugal barrier, helps to cause the occurrence of nuclei with widely extended neutron density. Such nuclei are found to have characteristically very small two-neutron separation energy and large neutron rms radius akin to that observed in weakly bound systems.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Low-velocity impact tests on fibrous composite sandwich structures
The effect of low-velocity projectile impact on the load-carrying ability of the composite sandwich structural components is investigated experimentally, the impact simulating the damage caused by runway debris and the accidental dropping of hand tools during servicing on secondary aircraft structures made with composites. The sandwich-type beam specimens were fabricated with graphite/epoxy face sheets, aluminum honeycomb core, and a steel (back) plate. A four-point beam-loading apparatus was used, and the ultimate strength, ultimate strain, and residual strength of the composites were determined. A faired curve is presented indicating the lower bound of the failure threshold for each of the laminate configurations tested in compression and tension as a function of the projectile impact energy. It is shown that strength degradation due to impact is dependent on the laminate configuration and the fiber/matrix combination. The laminates having more angle plies near the impact surface and unidirectional plies elsewhere seem to show extensive interply and intraply fiber delaminations at failure relative to the laminates with a cross-ply on the impact surface.
Sharma, A. V.↗
Quantum mechanical calculation of the collision-induced absorption spectra of N{sub 2}–N{sub 2} with anisotropic interactions
We present quantum mechanical calculations of the collision-induced absorption spectra of nitrogen molecules, using ab initio dipole moment and potential energy surfaces. Collision-induced spectra are first calculated using the isotropic interaction approximation. Then, we improve upon these results by considering the full anisotropic interaction potential. We also develop the computationally less expensive coupled-states approximation for calculating collision-induced spectra and validate this approximation by comparing the results to numerically exact close-coupling calculations for low energies. Angular localization of the scattering wave functions due to anisotropic interactions affects the line strength at low energies by two orders of magnitude. The effect of anisotropy decreases at higher energy, which validates the isotropic interaction approximation as a high-temperature approximation for calculating collision-induced spectra. Agreement with experimental data is reasonable in the isotropic interaction approximation, and improves when the full anisotropic potential is considered. Calculated absorption coefficients are tabulated for application in atmospheric modeling.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Optical Diagnostic Characterization of High-Power Hall Thruster Wear and Operation
Optical emission spectroscopy is employed to correlate BN insulator erosion with high-power Hall thruster operation. Specifically, actinometry leveraging excited xenon states is used to normalize the emission spectra of ground state boron as a function of thruster operating condition. Trends in the strength of the boron signal are correlated with thruster power, discharge voltage, and discharge current. In addition, the technique is demonstrated on metallic coupons embedded in the walls of the HiVHAc EM thruster. The OES technique captured the overall trend in the erosion of the coupons which boosts credibility in the method since there are no data to which to calibrate the erosion rates of high-power Hall thrusters. The boron signals are shown to trend linearly with discharge voltage for a fixed discharge current as expected. However, the boron signals of the higher-power NASA 300M and NASA 457Mv2 trend with discharge current and show an unexpectedly weak to inverse dependence on discharge voltage. Electron temperatures measured optically in the near-field plume of the thruster agree well with Langmuir probe data. However, the optical technique used to determine Te showed unacceptable sensitivity to the emission intensities. Near-field, single-frequency imaging of the xenon neutrals is also presented as a function of operating condition for the NASA 457 Mv2.
Williams, George J., Jr.↗
Influence of fine-scale B2 precipitation on dynamic compression and wear properties in hypo-eutectic Al0.5CoCrFeNi high-entropy alloy
The near equiatomic high-entropy alloys based on Al, Co, Cr, Fe, Ni have provided a novel microstructural template for alloy design. The face-centered cubic (FCC) matrix strengthened by body-centered cubic (BCC) based ordered B2 precipitates can be used to develop a new generation of precipitation strengthened alloys. The present study focuses on an Al0.5CoCrFeNi hypo-eutectic alloy consisting of an as-solidified FCC+B2 microstructure. Guided by solution thermodynamic modeling, this alloy has been isothermally aged for solid-state precipitation of a high fraction of fine-scale intragranular B2 particles. The dynamic compressive strength, hardness, and sliding wear response of the alloy as a function of B2 phase fraction is examined. The flow stress at 0.02% true strain increased from ~ 670 MPa to ~1350 (102%) MPa, the ultimate compressive strength increased from ~1160 MPa to 1500 MPa (20%), and the wear resistance increased more than 5 times with progressively increasing phase fraction of B2 precipitates.
Gwalani, Bharat↗
Orientation-dependent binding energy of graphene on palladium
Using density functional theory calculations, we show that the binding strength of a graphene monolayer on Pd(111) can vary between physisorption and chemisorption depending on its orientation. By studying the interfacial charge transfer, we have identified a specific four-atom carbon cluster that is responsible for the local bonding of graphene to Pd(111). The areal density of such clusters varies with the in-plane orientation of graphene, causing the binding energy to change accordingly. Similar investigations can also apply to other metal substrates and suggests that physical, chemical, and mechanical properties of graphene may be controlled by changing its orientation.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Change Detection in Constellations of Buried Objects Extracted From Ground-Penetrating Radar Data
Detection of deliberately buried objects in ground-penetrating radar (GPR) data acquired along a path is a clutter-limited problem. Detection-false alarm rate performance can be improved by replacing the detection statistic with a change statistic that incorporates information from previous path traversals. A constellation matching approach is developed for buried-object change detection in GPR data. Network topologies of buried objects detected in GPR data from previous path traversals are maintained in a constellation database. Localized groups of buried objects newly detected on the latest path traversal are matched to the constellation. Buried objects from the latest path traversal whose locations or strengths cannot be reconciled with the constellation are identified as changes. The system has one component that generates constellation databases offline and another component suitable for change detection in real time. It can tolerate paths with significant translational misalignments. The system uses the following: 1) a customized translational relaxation algorithm for point pattern matching that incorporates detection strength and a probabilistic uncertainty model for buried-object location into the objective function and 2) a change statistic that accounts for the magnitude of change relative to predicted detection strength. A constellation database can typically be generated offline from a single path traversal roughly two orders of magnitude faster than the time typically required for a vehicle to travel the extent of the path. Database sizes are typically four to five orders of magnitude smaller than the data sets of GPR signal scans or focused 3-D GPR images that they were generated from. On bumpy dirt roads buried exclusively with nonmetallic objects at various depths, detection-false alarm rate performance is shown to be significantly better for our change statistics than for our detection statistics.
47 OTHER INSTRUMENTATION↗
Transport functions of nitrogen up to 26,000 K
The current field strength characteristic, E(1), and a large number of radial temperature distributions, T(r,I), measured in a 5 mm N2 cascade arc at normal pressure are used to evaluate the transport properties of nitrogen up to 26,000 K. The electrical conductivity sigma (T) and the Coulomb cross section are determined directly from the E(I) and several T(r,I) curves. Between 10,000 and 15,000 K the radiative energy flux for different arc current, the thermal conductivity, and from this the charge exchange cross section are determined in a good approximation utilizing the large number of measured temperature distributions. It turns out, that at the highest measured arc current, i.e., 570 A, in the axial region of the arc about 95% of the supplied energy is carried off by radiation.
Hermann, W.↗
Multifunctional curing agents and their use in improving strength of composites containing carbon fibers embedded in polymeric matrix
A functionalized carbon fiber having covalently bound on its surface a sizing agent containing epoxy groups, at least some of which are engaged in covalent bonds with crosslinking molecules, wherein each of said crosslinking molecules possesses at least two epoxy-reactive groups and at least one free functional group reactive with functional groups of a polymer matrix in which the carbon fiber is to be incorporated, wherein at least a portion of said crosslinking molecules are engaged, via at least two of their epoxy-reactive groups, in crosslinking bonds between at least two epoxy groups of the sizing agent. Composites comprised of these functionalized carbon fibers embedded in a polymeric matrix are also described. Methods for producing the functionalized carbon fibers and composites thereof are also described.
Vautard, Frederic↗
Asymmetric Yield Function Based on the Stress Invariants for Pressure Sensitive Metals
A general asymmetric yield function is proposed with dependence on the stress invariants for pressure sensitive metals. The pressure sensitivity of the proposed yield function is consistent with the experimental result of Spitzig and Richmond (1984) for steel and aluminum alloys while the asymmetry of the third invariant is preserved to model strength differential (SD) effect of pressure insensitive materials. The proposed yield function is transformed in the space of the stress triaxaility, the von Mises stress and the normalized invariant to theoretically investigate the possible reason of the SD effect. The proposed plasticity model is further extended to characterize the anisotropic behavior of metals both in tension and compression. The extension of the yield function is realized by introducing two distinct fourth-order linear transformation tensors of the stress tensor for the second and third invariants, respectively. The extended yield function reasonably models the evolution of yield surfaces for a zirconium clock-rolled plate during in-plane and through-thickness compression reported by Plunkett et al. (2007). The extended yield function is also applied to describe the orthotropic behavior of a face-centered cubic metal of AA 2008-T4 and two hexagonal close-packed metals of high-purity-titanium and AZ31 magnesium alloy. The orthotropic behavior predicted by the generalized model is compared with experimental results of these metals. The comparison validates that the proposed yield function provides sufficient predictability on SD effect and anisotropic behavior both in tension and compression. When it is necessary to consider r-value anisotropy, the proposed function is efficient to be used with nonassociated flow plasticity by introducing a separate plastic potential for the consideration of r-values as shown in Stoughton & Yoon (2004, 2009).
99 GENERAL AND MISCELLANEOUS↗
Mechanical Properties and Microstructure Investigation of Lead Free Solder
While the electronics industry appears to be focusing on Sn-Ag-Cu as the alloy of choice for lead free electronics assembly, ,the exact composition varies by geographic region, supplier and user. Add to that dissolved copper and silver from the printed circuit board traces and surface finish, and there can be significant variation in the final solder joint composition. A systematic study of the mechanical and microstructural properties of Sn-Ag-Cu alloys with Ag varying from 2wt% to 4wt% and Cu varying from 0.5wt% to lSwt%, was undertaken in this research study. Different sample preparation techniques (water quenched, oil quenched and water quenched followed by reflow) were explored and the resulting microstructure compared to that of a typical reflowed lead free chip scale package (CSP) solder joint. Tensile properties (modulus, 0.2% yield strength and the ultimate tensile strength) and creep behavior of selected alloy compositions (Sn-4Ag-1 X u , Sn-4Ag-OSCu, Sn- 2Ag-1 X u , Sn-2Ag-OSCu, Sn-3.5Ag-O.SCu) were determined for three conditions: as- cast; aged for 100 hours at 125OC; and aged for 250 hours at 125OC. There was no significant difference in Young's Modulus as a function of alloy composition. After an initial decrease in modulus after 100 hours at 125"C, there was an insignificant change with further aging. The distribution of 0.2% strain yield stress and ultimate tensile strength as a function of alloy composition was more significant and decreased with aging time and temperature. The microstructures of these alloys were examined using light and scanning electron microscopy (LM and SEM) respectively and SEM based energy dispersive x-ray spectroscopy (EDS). Fracture surface and cross-section analysis were performed on the specimens after creep testing. The creep testing results and the effect of high temperature aging on mechanical properties is presented for the oil quenched samples. In general the microstructure of oil quenched specimen exhibited a eutectic region of Sn with moderately dispersed Ag3Sn intermetallic, surrounded by a dendritic Sn-rich phase. The SEM images of the fracture surface indicated the presence of a tough shear surface at the initial cavity break area and a break line in the middle of specimen along the failure direction. A hyperbolic-sine creep model was adopted and used to fit the creep experiment data. The effect on the mechanical properties by adding the quaternary element bismuth to the Sn-3.5Ag-0.8Cu alloy was measured and compared with the mechanical properties of the ternary alloys. The results of this research study provide necessary data for the modeling of solder joint reliability for a range of Sn-Ag-Cu compositions and a baseline for evaluating the effects of subsequent quaternary additions.
Wang, Qing↗
Redox-Induced Structural Reorganization Dictates Kinetics of Cobalt(III) Hydride Formation via Proton-Coupled Electron Transfer
Two-electron, one-proton reactions of a family of [CoCp(dxpe)(NCCH 3 )] 2+ complexes (Cp = cyclopentadienyl, dxpe = 1,2-bis(di(aryl/alkyl)phosphino)ethane) form the corresponding hydride species [HCoCp(dxpe)] + through a stepwise proton-coupled electron transfer process. For three [CoCp(dxpe)(NCCH 3 )] 2+ complexes (dxpe = dppe (1,2-bis(diphenylphosphino)ethane), depe (1,2-bis(diethylphosphino)ethane), and dcpe (1,2-bis(dicyclohexylphosphino)ethane)), peak shift analysis was employed to quantify apparent proton transfer rate constants from cyclic voltammograms recorded with acids ranging 22 pK a units. The apparent proton transfer rate constants correlate with the strength of the proton source for weak acids, but these apparent proton transfer rate constants curiously plateau (k pl ) as the reaction becomes increasingly exergonic. The absolute apparent proton transfer rate constants across both these regions correlate with the steric bulk of the chelating diphosphine ligand, with bulkier ligands leading to slower kinetics (k plateau,depe = 3.5 x 10 7 M -1 s -1 , k plateau,dppe = 1.7 x 10 7 M -1 s -1 , k plateau,dcpe = 7.1 x 10 4 M -1 s -1 ). Mechanistic studies were conducted to identify the cause of the aberrant $k_PT^{app}$–ΔpK a trends. When the deuterated acids are employed, deuterium incorporation in the Cp ring is observed, indicating protonation of the CoCp(dxpe) species to form the corresponding hydride proceeds via initial ligand protonation. Digital simulations of cyclic voltammograms show ligand loss accompanying initial reduction gates subsequent PCET activity at higher driving forces. Together, these experiments reveal the details of the reaction mechanism: reduction of the Co(III) species is followed by dissociation of the bound acetonitrile ligand, subsequent reduction of the unligated Co(II) species to form a Co(I) species is followed by protonation, which occurs at the Cp ring, followed by tautomerization to generate the stable Co(III)-hydride product [HCoCp(dxpe)] + . Analysis as a function of chelating disphosphine ligand, solvent, and acid strength reveals that the ligand dissociation equilibrium is directly influenced by the steric bulk of the phosphine ligands and gates protonation, giving rise to the plateau of apparent proton transfer rate constant with strong acids. The complexity of the reaction mechanism underpinning hydride formation, encompassing dynamic behavior of the entire ligand set, highlights the critical need to understand elementary reaction steps in proton-coupled electron transfer reactions.
14 SOLAR ENERGY↗
An Elongated Tetrakaidecahedron Model for Open-Celled Foams
A micro-mechanics model for non-isotropic, open-celled foams is developed using an elongated tetrakaidecahedron (Kelvin model) as the repeating unit cell. The micro-mechanics model employs an elongated Kelvin model geometry which is more general than that employed by previous authors. Assuming the cell edges possess axial and bending rigidity, the mechanics of deformation of the elongated tetrakaidecahedron lead to a set of equations for the Young's modulus, Poisson's ratio and strength of the foam in the principal material directions. These equations are written as a function of the cell edge lengths and cross-section properties, the inclination angle and the strength and stiffness of the solid material. The model is applied to predict the strength and stiffness of several polymeric foams. Good agreement is observed between the model results and the experimental measurements.
Sullivan, Roy M.↗
In Situ Poling and Imidization of Amorphous Piezoelectric Polyimides
An amorphous piezoelectric polyimide containing polar functional groups has been developed using a combination of experimental and molecular modeling for potential use in high temperature applications. This amorphous polyimide, (Beta-CN)APB/ODPA, has exhibited good thermal stability and piezoelectric response at temperatures up to 150C. Density functional calculations predicted that a partially cured amic acid (open imide ring) possesses a dipole moment four times larger than the fully imidized closed ring. In situ poling and imidization of the partially cured (Beta-CN)APB/ODPA, was studied in an attempt to maximize the degree of dipolar orientation and the resultant piezoelectric response. A positive corona poling was used to minimize localized arcing during poling and to allow use of higher poling fields without dielectric breakdown. The dielectric relaxation strength, remanent polarization, and piezoelectric response were evaluated as a function of the poling profile. The partially cured, corona poled polymers exhibited higher dielectric relaxation strength (delta varepsilon), remanent polarization (Pr) and piezoelectric strain coefficient (d33) than the fully cured, conventionally poled ones.
Park, Cheol↗