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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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At least 1,369 records · Page 76
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DOE OSTI2018

Oscillation, Rotation, and Wandering of Solutions to Linear Differential Systems

For solutions of a linear system on the semi-axis, we introduce a series of Lyapunov exponents that describe the oscillation, rotation, and wandering properties of these solutions. In the case of systems with constant matrices, these exponents are closely related to the imaginary parts of the eigenvalues. We examine the problem on the existence of a similar relationship in the case of piecewise constant of arbitrary systems.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Two-Step Estimation in a Heteroscedastic Linear Regression Model

We study the problem of estimating a parameter in some heteroscedastic linear regression model in the case where the regressors consist of all order statistics based on the sample of identically distributed not necessarily independent observations with finite second moment. It is assumed that the random errors depend on the parameter and distributions of the corresponding regressors. We propose a two-step procedure for finding explicit asymptotically normal estimators.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Evaluation of the Index and Singular Points of Linear Differential-Algebraic Equations of Higher Order

We study linear systems of ordinary differential equations of higher order with an identically singular matrix at the higher derivative of the required vector-valued function in the domain of definition. We give definitions of the index and singular points for these systems, formulate the conditions of solvability, and deduce a formula for the general solution. The algorithms for finding the index and singular points are presented.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Application of the p-Adic Topology on ℤ to the Problem of Finding Solutions in Integers of an Implicit Linear Difference Equation

We study solutions in integers of an implicit linear inhomogeneous first order difference equation bx{sub n+1} = ax{sub n} + f{sub n}. Based on the p-adic topology on the ring of integers, we obtain a criterion for the existence of solutions and show that for a = 1 a typical (in the natural topological sense) equation has no integer solutions.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Linear Oscillations of Thin Plates with Corners and Cracks

We study linear oscillations of a thin plate in a bounded domain G ⊂ ℝ{sup 2} with finitely many corner points at the boundary ∂G. The time t runs the real axis. The boundary conditions are related to the rigidly fixed or free boundary of the plate. We describe the asymptotics of a solution to the problem near the corner points.

42 ENGINEERING↗
DOE OSTI2019

Explicit Equations for Exterior Square of the General Linear Group

Several explicit systems of equations defining the exterior square of the general linear group ⋀{sup 2} GL{sub n} as affine group scheme are presented. Algebraic ingredients of the equations, so called exterior numbers, are translated to the language of weight diagrams corresponding to a Lie group of type A{sub n−1} in the representation with the highest weight ϖ{sub 2}.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Compatibility of mesophase pitch and linear low-density polyethylene for low-cost carbon fiber

Mesophase pitch and linear low-density polyethylene (LLDPE) were blended by shear mixing and extruded producing precursor fibers which were then converted to carbon fibers (CFs). LLDPE additives agglomerate within the isotropic spheres rather than uniformly dispersing throughout the entire matrix. The blends possess different thermal properties and precursor tensile properties evident by two-phase tensile stress nature not present in precursor fibers produced from pure pitch. The resultant CFs were oxidized at 280 °C for 4 h and carbonized at 1000 °C for 15 min. This process created pitch CFs with a tensile strength of 1.23 GPa and a Young’s modulus of 99 GPa. All CFs produced from blends of pitch and LLDPE possessed a tensile strength of 0.63 GPa and less. These CFs showed a microstructure slightly different from the pure pitch CFs with fractured CF cross sections revealing voids present in all blended CFs due to burnt off LLDPE stemming from carbonization. Further study into compatibilizers and new conversion processes is required to successfully blend LLDPE with mesophase pitch for the purpose of producing a new low-cost CF.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Suppression of four-wave mixing in a 22 × 10 Gbps dense wavelength division multiplexed system by linearly chirped fiber Bragg gratings

A scheme comprising two linearly chirped fiber Bragg gratings (LCFBGs) is proposed to suppress four-wave mixing (FWM) effects in a 22×10 Gbps dense wavelength division multiplexed (DWDM) system employing dispersion shifted fiber with 0.2 nm channel spacing. The FWM reduction in our proposed scheme has been studied by varying the input signal power per channel from − 2 to + 10 dBm. The parameters of LCFBGs are optimized to obtain a maximum quality factor for all 22 channels. The proposed method is effective even at high input power (10 dBm) and provides a simple, cost effective way to improve the transmission performance in DWDM system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Optical soliton solutions, explicit power series solutions and linear stability analysis of the quintic derivative nonlinear Schrödinger equation

In this paper, the quintic derivative nonlinear Schrödinger equation is investigated into two main aspects. Firstly, a series of solutions of this equation are derived. More specifically, the singular solitons and dark solitons are obtained by using the ansatz method. The explicit power series solutions for the equation has also been constructed by employing power series method. Secondly, linear stability analysis is applied to estimate the stability of the equation. Finally, all solutions are presented via 3-dimensional plots with choices some special parameters to show the dynamic characteristics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

A 7.4 kHz, 20-bit image encoder with a CMOS linear image sensor

This paper presents a unique CMOS linear image sensor for reading the pseudo-random code on the slit disc, focusing on the two aspects of low noise and readout rate. Each pixel is equipped with an exclusive integral readout circuit, and the shape of the pixel also matches the slit disc, making the output signal consistent by up to 99%. After subdivision, the absolute angle data can be captured with an angular resolution of 16 bits and a maximum speed of 7.4 kHz. In addition, decoding and subdivision methods are suitable for high-speed, inexpensive encoder systems.

42 ENGINEERING↗
DOE OSTI2018

Residual Strain Analysis in Linear Friction Welds of Similar and Dissimilar Titanium Alloys Using Energy Dispersive X-ray Diffraction

Residual strains in linear friction welds (LFW) of similar, Ti-6Al-4V (Ti64) welded to Ti-6Al-4V, and dissimilar, Ti-6Al-4V welded to Ti-5Al-5V-5Mo-3Cr (Ti5553), titanium alloys have been characterized using energy-dispersive X-ray diffraction. For each type of LFW, one sample was chosen in the as-welded (AW) condition and another sample was selected after a post-weld heat treatment (HT). Residual strains have been separately studied in the alpha and beta phases of the material, and five components (three axial and two shear) have been reported in each case. In-plane axial components of the residual strains show a smooth and symmetric behavior about the weld center for the Ti64-Ti64 LFW samples in the AW condition, whereas these components in the Ti64-Ti5553 LFW sample show a symmetric trend with jump discontinuities. Such jump discontinuities, observed in both the AW and HT conditions of the Ti64-Ti5553 samples, suggest different strain-free lattice parameters in the weld region and the parent material, whereas the results from the Ti64-Ti64 LFW samples in both AW and HT conditions suggest nearly uniform strain-free lattice parameters throughout the weld region. Finally, the observed trends in the in-plane axial residual strain components have been rationalized by the corresponding microstructural changes and variations across the weld region via backscatter electron (BSE) images.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Nonuniformity in Mechanical Properties of Linear Friction Welded Mild Steel Joint

Mild steel was successfully joined by linear friction welding. Grain size at peripheral region was coarser than that at the other zones of the weld interface, which had no significant effect on microhardness. The local tensile properties were considerably decreased when oxides or lack of bonding appeared at the interface. Ductile fracture dominated the fracture mode for all joints. Variation in local tensile properties could be relieved under a medium friction pressure, a relatively high amplitude with a sufficient friction time. It was attributed to the facts that plastic metal layer of joint became uniform to some extent and interfacial defects were eliminated. The standard deviation of plastic metal layer thickness (χ{sub p}) could be used to describe the combined effects of welding parameters on joint integral performance. It was found that the standard deviation of plastic metal layer thickness showed a strong inverse correlation with the joint integral performance. Well-formed and defect-free joints exhibiting 90% of the base metal tensile strength could be produced when processing at a frequency of 20 Hz with a friction pressure of 103 MPa or 155 MPa, an amplitude of 2.5 mm and a friction time of at least 4 s.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A Miniaturized Linear Wire Ion Trap with Electron Ionization and Single Photon Ionization Sources

A linear wire ion trap (LWIT) with both electron ionization (EI) and single photon ionization (SPI) sources was built. The SPI was provided by a vacuum ultraviolet (VUV) lamp with the ability to softly ionize organic compounds. The VUV lamp was driven by a pulse amplifier, which was controlled by a pulse generator, to avoid the detection of photons during ion detection. Sample gas was introduced through a leak valve, and the pressure in the system is shown to affect the signal-to-noise ratio and resolving power. Under optimized conditions, the limit of detection (LOD) for benzene was 80 ppbv using SPI, better than the LOD using EI (137 ppbv). System performance was demonstrated by distinguishing compounds in different classes from gasoline. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗