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At least 91 records · Page 5

A cloud physics investigation utilizing Skylab data

The author has identified the following significant results. The Lowtran 2 program, S191 spectral response, and solar spectrum were used to compute the expected absorption by 2.0 micron band for a variety of cloud pressure levels and solar zenith angles. Analysis of the three long wavelength data channels continued in which it was found necessary to impose a minimum radiance criterion. It was also found necessary to modify the computer program to permit the computation of mean values and standard deviations for selected subsets of data on a given tape. A technique for computing the integrated absorption in the A band was devised. The technique normalizes the relative maximum at approximately .78 micron to the solar irradiance curve and then adjusts the relative maximum at approximately .74 micron to fit the solar curve.

Alishouse, J.↗

Development of a high efficiency thin silicon solar cell

One hundred thin (120 microns to 260 microns) silicon-aluminum solar cells were fabricated and tested. Silicon slices were prepared, into which an aluminum alloy was evaporated over a range of temperatures and times. Antireflection coatings of tantalum oxide were applied to the cells. Reflectance of the silicon-aluminum interfaces was correlated to alloy temperature (graphs are shown). Optical measurements of the rear surface-internal reflectance of the cells were performed using a Beckman spectrophotometer. An improved gridline pattern was evaluated and stability tests (thermal cycling tests) were performed. Results show that: (1) a high-index, high-transmittance antireflection coating was obtained; (2) the improved metallization of the cells gave a 60 percent rear surface-internal reflectance, and the cells displayed excellent fill factors and blue response of the spectrum; (3) an improved gridline pattern (5 micron linewidths compared to 13 micron linewidths) resulted in a 1.3 percent improvement in short circuit currents; and (4) the stability tests showed no change in cell properties.

Lindmayer, J.↗

A research program to reduce interior noise in general aviation airplanes

The relevance of KU-FRL test results in predicting (theoretically or semi-empirically) interior noise levels in general aviation aircraft was studied. As a result of this study, it was decided to make a few additions to the program. These additions are: (1) to use three (instead of two) noise sources in the plane wave tube to evaluate the influence of excitation spectrum on panel response, (2) to use theoretical and experimental data obtained in the course of the project to develop more efficient noise reduction materials (or procedures to apply these), or to develop guidelines for the design of such materials for procedures, and (3) to use nonstructural materials in the collection of specimens to be tested in the KU-FRL plane wave tube.

Peschier, T. D.↗

Analysis and identification of subsynchronous vibration for a high pressure parallel flow centrifugal compressor

The summary of a complete analytical design evaluation of an existing parallel flow compressor is presented and a field vibration problem that manifested itself as a subsynchronous vibration that tracked at approximately 2/3 of compressor speed is reviewed. The comparison of predicted and observed peak response speeds, frequency spectrum content, and the performance of the bearing-seal systems are presented as the events of the field problem are reviewed. Conclusions and recommendations are made as to the degree of accuracy of the analytical techniques used to evaluate the compressor design.

Kirk, R. G.↗

WARC and CCIR support for spectrum-orbit planning

Papers prepared for the use of the U.S. delegation to the 1979 World Administrative Radio Conference; papers contributed to the National CCIR study groups on broadcasting satellites and spectrum-orbit utilization; responses to specific requests for technical analyses and evaluations; and papers presented at technical conferences on related topics are presented. Nonlinear optimization methods for finding optimum positions of satellites in the fixed satellite service; the effects of geography on the use of the geostationary orbit; intercontinental orbit sharing; traffic coordination in interfering satellites operating in the fixed satellite service; and domestic fixed and broadcasting satellite systems are covered. A possible channel orbit plan for broadcasting satellite service in the U.S. and Canada; polarization for broadcasting satellite systems; and the communication capacity of the geostationary satellite orbit are also examined.

Sawitz, P. H.↗

Thermo-viscoelastic analysis of composite materials, volume 1

Advanced composite materials, especially graphite/epoxy, are being applied to aircraft structures in order to improve performance and save weight. An important consideration in composite design is the residual strength of a structure containing holes, delaminations, or interlaminar damage when subjected to compressive loads. Recent studies have revealed the importance of viscoelastic effects in polymer-based composites. The viscoelastic effect is particularly significant at elevated temperature/moisture conditions since the matrix material is strongly affected by the environment. The solution of viscoelastic problems in composites was limited to special cases which can be solved by classical lamination theory. A finite element procedure is presented for calculating time-dependent stresses and strains in composite structures with general configurations and complicated boundary conditions. Using this procedure the in-plane and interlaminar stress distributions and histories in notched and unnotched composites were obtained for mechanical and thermal loads. Both two-dimensional and three-dimensional viscoelastic problems are analyzed. The effects of layup orientation and load spectrum on creep response and stress relaxation were also studied.

Lin, K. Y.↗

The Influence of Finite-size Sources in Acousto-ultrasonics

This work explores the effects that the finite normal axisymmetric traction loading of an infinite isotropic plate has on wave propagation in acousto-ultrasonics (AU), in which guided waves are created using two normal incidence transducers. Although the work also addresses the effects of the transducer pressure distribution and pulse shape, this thesis concentrates on two main questions: how does the transducer's diameter control the phase velocity and frequency spectrum of the response, and how does the plate thickness relate to the plate's excitability? The mathematics of the time-harmonic solution and the physical principles and the practical considerations for AU wave generation are explained. Transient sources are modeled by the linear superposition of the time-harmonic solutions found using the Hankel transform and they are then compared to experimental data to provide insight into the relation between the size of the transducer and the preferred phase velocity.

Pavlakovic, Brian N.↗

Role of strategic planning in engineering management

Today, more than ever before, engineers are faced with uncertain and sometimes chaotic environments in which to function. The traditional roles of an engineer to design, develop, and streamline a manufacturing process for a product are still valued and relevant. However, the need for an engineer to participate in the process of identifying the product to be developed, the schedule and resources required, and the goal of satisfying the customer, has become paramount to achieving the success of the enterprise. When we include these endeavors in the functions of an engineer, management of 'engineering' takes on a new dimension. In this paper, the ramifications of the changing and increased functions of an engineer and consequent impacts on engineering management are explored. The basic principles which should be invoked in order to embrace the new environment for engineering management are outlined. The ultimate finding of this study is that the enterprise strategic plan should be developed in such a way as to allow engineering management to encompass the full spectrum of the responsibilities of engineers. A consequence of this is that the fundamental elements of the strategic process can best be implemented through a project team or group approach. The paper thus concentrates on three areas: evolving environment, strategic plan, and ways to achieve enterprise success.

Krishen, Kumar↗

Damage Detection and Impact Testing on Laminated and Sandwich Composite Panels

This research investigates health monitoring of sandwich shell composites to determine if the Transmittance Functions (TF) are effective in determining the present of damage. The health monitoring test was conducted on the sandwich plates before and after low velocity impacts using the health monitoring technique given in TFs are a NDE (Nondestructive Evaluation) technique that utilizes the ratios of cross-spectrums to auto-spectrums between two response points on the sandwich composites. The test for transmittance was conducted on the same density foam core throughout the experiment. The test specimens were 17.8 cm by 25.4 cm in dimension. The external sheets (face sheets) were created from graphite/epoxy laminate with dimension of 1.58 mm thick. The polymethacrylide (Rohacell) foam core was 12.7 mm thick. These samples experienced a transformation in the TF that was considered the low velocity impact damage. The low velocity damage was observed in the TFs for the sandwich composites.

Hughes, Derke R.↗

Influence of Population Variation of Physiological Parameters in Computational Models of Space Physiology

The earliest manifestations of Visual Impairment and Intracranial Pressure (VIIP) syndrome become evident after months of spaceflight and include a variety of ophthalmic changes, including posterior globe flattening and distension of the optic nerve sheath. Prevailing evidence links the occurrence of VIIP to the cephalic fluid shift induced by microgravity and the subsequent pressure changes around the optic nerve and eye. Deducing the etiology of VIIP is challenging due to the wide range of physiological parameters that may be influenced by spaceflight and are required to address a realistic spectrum of physiological responses. Here, we report on the application of an efficient approach to interrogating physiological parameter space through computational modeling. Specifically, we assess the influence of uncertainty in input parameters for two models of VIIP syndrome: a lumped-parameter model (LPM) of the cardiovascular and central nervous systems, and a finite-element model (FEM) of the posterior eye, optic nerve head (ONH) and optic nerve sheath. Methods: To investigate the parameter space in each model, we employed Latin hypercube sampling partial rank correlation coefficient (LHSPRCC) strategies. LHS techniques outperform Monte Carlo approaches by enforcing efficient sampling across the entire range of all parameters. The PRCC method estimates the sensitivity of model outputs to these parameters while adjusting for the linear effects of all other inputs. The LPM analysis addressed uncertainties in 42 physiological parameters, such as initial compartmental volume and nominal compartment percentage of total cardiac output in the supine state, while the FEM evaluated the effects on biomechanical strain from uncertainties in 23 material and pressure parameters for the ocular anatomy. Results and Conclusion: The LPM analysis identified several key factors including high sensitivity to the initial fluid distribution. The FEM study found that intraocular pressure and intracranial pressure had dominant impact on the peak strains in the ONH and retro-laminar optic nerve, respectively; optic nerve and lamina cribrosa stiffness were also important. This investigation illustrates the ability of LHSPRCC to identify the most influential physiological parameters, which must therefore be well-characterized to produce the most accurate numerical results.

biomechanics↗

Significant and Variable Linear Polarization During the Prompt Optical Flash of GRB 160625B

Measurement of polarized light provides a direct probe of magnetic fields in collimated outflows (jets) of relativistic plasma from accreting stellar-mass black holes at cosmological distances. These outflows power brief and intense flashes of prompt gamma-rays known as Gamma Ray Bursts (GRBs), followed by longer-lived afterglow radiation detected across the electromagnetic spectrum. Rapid-response polarimetric observations of newly discovered GRBs have probed the initial afterglow phase. Linear polarization degrees as high as Π∼30% are detected minutes after the end of the prompt GRB emission, consistent with a stable, globally ordered magnetic field permeating the jet at large distances from the central source. In contrast, optical and gamma-ray observations during the prompt phase led to discordant and often controversial results, and no definitive conclusions on the origin of the prompt radiation or the configuration of the magnetic field could be derived. Here we report the detection of linear polarization of a prompt optical flash that accompanied the extremely energetic and long-lived prompt gamma-ray emission from GRB 160625B. Our measurements probe the structure of the magnetic field at an early stage of the GRB jet, closer to the central source, and show that the prompt GRB phase is produced via fast cooling synchrotron radiation in a large-scale magnetic field advected from the central black hole and distorted from dissipation processes within the jet.

High-energy astrophysics↗

Significant and Variable Linear Polarization During the Prompt Optical Flash of GRB 160625B

Measurement of polarized light provides a direct probe of magnetic fields in collimated outflows (jets) of relativistic plasma from accreting stellar-mass black holes at cosmological distances. These outflows power brief and intense flashes of prompt gamma-rays known as Gamma Ray Bursts (GRBs), followed by longer-lived afterglow radiation detected across the electromagnetic spectrum. Rapid-response polarimetric observations of newly discovered GRBs have probed the initial afterglow phase. Linear polarization degrees as high as Π∼30% are detected minutes after the end of the prompt GRB emission, consistent with a stable, globally ordered magnetic field permeating the jet at large distances from the central source. In contrast, optical and gamma-ray observations during the prompt phase led to discordant and often controversial results, and no definitive conclusions on the origin of the prompt radiation or the configuration of the magnetic field could be derived. Here we report the detection of linear polarization of a prompt optical flash that accompanied the extremely energetic and long-lived prompt gamma-ray emission from GRB 160625B. Our measurements probe the structure of the magnetic field at an early stage of the GRB jet, closer to the central source, and show that the prompt GRB phase is produced via fast cooling synchrotron radiation in a large-scale magnetic field advected from the central black hole and distorted from dissipation processes within the jet.

High-energy astrophysics↗

Resolving Wave-Particle Duality Could Accelerate the Mass Production of Quantum Computers

Quantum computers, hypothesized in 1980s, use concepts of superposition and entanglement phenomena. Although theoretical propositions and associated search algorithms for accurate measurements are being generated, the development of practical quantum computers themselves are advancing very slowly requiring enormous time and investments. The underlying concepts of a quantum computer are not new to the optical domain. However, the crucial enabling concepts of Entanglement and Superposition Principle are remaining clouded under the unresolved postulates, Wave-Particle Duality (WPD), and Wave Packet Reduction (WPR), implicating incompleteness in the interpretations of the mathematical formalism behind Quantum Mechanics. The WPD debate started during late1600 between Newton and Huygens. Young’s resolution of WPD through his double-slit experiment in 1802 was effectively overturned by Einstein’s interpretation of photoelectric effect as due to “indivisible light quanta”. However, Einstein disowned his “light quanta” postulate shortly before his death in1955, even though it had earned him the Nobel Prize. We resolve WPD by synthesizing Newton’s and Maxwell’s concepts and assume atoms do emit quanta but propagate as time-finite exponential pulses. This assumption also resolves WPR for light-matter interaction with the assumption that Schrodinger’s ψ represents atom’s internal dipolar amplitude stimulations. This over-turns Born’s interpretation that ψ only represents the abstract mathematical probability amplitude, rather than the physical “internal amplitude stimulation” of the quantum entity. However, our concept of atomic pulse emission forces us to re-derive the expression for the N-slit grating-spectrometer response since the classical derivation uses CW light, which does not exist. This pulsespectrometric response function strengthens our postulate since the grating response to the exponential pulse appears to be the convolution of a Lorentzian spectrum with the classical CW response function of the grating. The Fourier Transform of an exponential function is Lorentzian and QM predicts spontaneous emission line width to be Lorentzian. Then, conceptually one can extend the grating-expression (with N=2) to get the double-slit pattern. This approach preserves the classical causality that each of the two slits, like the N-signals out of a grating, are physically real and jointly stimulate the quantum detector array at the far field to generate the “Local” cosine fringes. The detector array executes the square modulus operation on its imposed dipolar amplitude stimulation and absorbs the necessary energy to fill up their quantum cups. Hence the double-slit pattern must also be “Local”, just as the N-slit grating spectrum is generated locally at the exit spectral-plane of the spectrometer. This removes the need to believe that “single photons” mysteriously generate the double slit pattern. Quantum computers, hypothesized in 1980s, use concepts of superposition and entanglement phenomena. Although theoretical propositions and associated search algorithms for accurate measurements are being generated, the development of practical quantum computers themselves are advancing very slowly requiring enormous time and investments. The underlying concepts of a quantum computer are not new to the optical domain. However, the crucial enabling concepts of Entanglement and Superposition Principle are remaining clouded under the unresolved postulates, Wave-Particle Duality (WPD), and Wave Packet Reduction (WPR), implicating incompleteness in the interpretations of the mathematical formalism behind Quantum Mechanics. The WPD debate started during late1600 between Newton and Huygens. Young’s resolution of WPD through his double-slit experiment in 1802 was effectively overturned by Einstein’s interpretation of photoelectric effect as due to “indivisible light quanta”. However, Einstein disowned his “light quanta” postulate shortly before his death in1955, even though it had earned him the Nobel Prize. We resolve WPD by synthesizing Newton’s and Maxwell’s concepts and assume atoms do emit quanta but propagate as time-finite exponential pulses. This assumption also resolves WPR for light-matter interaction with the assumption that Schrodinger’s ψ represents atom’s internal dipolar amplitude stimulations. This over-turns Born’s interpretation that ψ only represents the abstract mathematical probability amplitude, rather than the physical “internal amplitude stimulation” of the quantum entity. However, our concept of atomic pulse emission forces us to re-derive the expression for the N-slit grating-spectrometer response since the classical derivation uses CW light, which does not exist. This pulsespectrometric response function strengthens our postulate since the grating response to the exponential pulse appears to be the convolution of a Lorentzian spectrum with the classical CW response function of the grating. The Fourier Transform of an exponential function is Lorentzian and QM predicts spontaneous emission line width to be Lorentzian. Then, conceptually one can extend the grating-expression (with N=2) to get the double-slit pattern. This approach preserves the classical causality that each of the two slits, like the N-signals out of a grating, are physically real and jointly stimulate the quantum detector array at the far field to generate the “Local” cosine fringes. The detector array executes the square modulus operation on its imposed dipolar amplitude stimulation and absorbs the necessary energy to fill up their quantum cups. Hence the double-slit pattern must also be “Local”, just as the N-slit grating spectrum is generated locally at the exit spectral-plane of the spectrometer. This removes the need to believe that “single photons” mysteriously generate the double slit pattern.

Quantum Computer↗

Short-wavelength electrostatic waves in the earth's magnetosheath

Recent observations with the ISEE-1 spacecraft have found electric field emissions in the dayside magnetosheath whose frequency spectrum is modulated at twice the spacecraft spin period. The upper frequency cut-off in the frequency-time spectrum of the emissions has a characteristic parabola shape or festoon shape. The low frequency cutoff ranges from 100 Hz to 400 Hz, while the high frequency limit ranges from about 1 kHz to 4 kHz. The bandwidth is found to minimize for antenna orientations parallel to the wave vectors. The wave vector does not appear to be related to either the local magnetic field direction of the plasma flow velocity. The spacecraft observed frequency spectrum results from the spacecraft antenna response to the Doppler shifted wave vector spectrum which exists in the plasma. Imposed constraints on the plasma restframe wave vectors and frequencies indicate that the emissions occur within the frequency range from about 150 Hz to 1 kHz, with wavelengths between about 30 meters and 600 meters. These constraints strongly suggest that the festoon-shaped emissions are ion-acoustic waves. The small group velocity and k direction of the ion-acoustic mode are consistent with wave generation upstream at the bow shock and convection downstream to locations within the outer dayside magnetosheath.

Gallagher, D. L.↗

Method of Detecting System Function by Measuring Frequency Response

Real time battery impedance spectrum is acquired using one time record, Compensated Synchronous Detection (CSD). This parallel method enables battery diagnostics. The excitation current to a test battery is a sum of equal amplitude sin waves of a few frequencies spread over range of interest. The time profile of this signal has duration that is a few periods of the lowest frequency. The voltage response of the battery, average deleted, is the impedance of the battery in the time domain. Since the excitation frequencies are known, synchronous detection processes the time record and each component, both magnitude and phase, is obtained. For compensation, the components, except the one of interest, are reassembled in the time domain. The resulting signal is subtracted from the original signal and the component of interest is synchronously detected. This process is repeated for each component.

Morrison, John L.↗

Impact response analyses

General-purpose computer program establishes dynamic response of two impacting elastic bodies, each containing linear or nonlinear impact attenuation mechanism. Program can be used for analysis of broad spectrum of impact motion response investigations.

Bodley, C. S.↗

Advanced-to-Revolutionary Space Technology Options - The Responsibly Imaginable

Paper summarizes a spectrum of low TRL, high risk technologies and systems approaches which could massively change the cost and safety of space exploration/exploitation/industrialization. These technologies and approaches could be studied in a triage fashion, the method of evaluation wherein several prospective solutions are investigated in parallel to address the innate risk of each, with resources concentrated on the more successful as more is learned. Technology areas addressed include Fabrication, Materials, Energetics, Communications, Propulsion, Radiation Protection, ISRU and LEO access. Overall and conceptually it should be possible with serious research to enable human space exploration beyond LEO both safe and affordable with a design process having sizable positive margins. Revolutionary goals require, generally, revolutionary technologies. By far, Revolutionary Energetics is the most important, has the most leverage, of any advanced technology for space exploration applications.

Bushnell, Dennis M.↗

Altered Innate and Lymphocytic Immune Responses in Mouse Splenocytes Post-Flight

Space flight is known to affect immune responses of astronauts and animals, decreasing lymphocytic responses to mitogenic stimuli, delayed typed hypersensitivity reactions, and T-cell activation. Despite changes in immune suppression, there are no reports of consistent adverse clinical events post flight. To further investigate the spectrum of affected immune responses, murine splenocytes were stimulated immediately post-shuttle flight (14 days on STS-135) with T-cell stimulators or toll-like receptor agonists. Comparisons were made to ground control splenocytes from age-matched mice. Cell phenotypes were assessed, as well as activation markers and associated cytokine production. The CD4+ population decreased with no concurrent decrease in CD8+ cells from shuttle mice post flight compared to ground controls. Regarding antigen presenting cell populations, the number of CD11c+ cells were slightly elevated post flight, compared to ground controls, with increased MHC Class I expression (I-A(sup b)) and no change in Class II expression (H-2K(sup b)). CD86+ populations were also significantly diminished. However, the decreased markers did not correlate with activity. Stimulation of splenocytes post flight showed significant increase in bead uptake, increased Class I expression, increased TNF-alpha and IL-6 production in response to TLR-2 (zymosan) and TLR-4 (LPS) agonists. While most activated (ConA or anti-CD3/anti-CD28) CD4+ cells showed markedly diminished responses (reduced IL-2 production), non-specific T cell responses to superantigen (SEA/SEB) increased post flight as determined by expression of early activation markers. Production of additional cytokines was also dysregulated postflight. Overall, persistent immune changes during space flight could represent unique clinical risks for exploration class missions. The consequences of pathogenic encounter remain an important concern that should be addressed.

Hwang, ShenAn↗