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Some remarks on antenna response in a reverberation chamber

Description: The simple formula, {l_angle}P{sub r}{r_angle}=(E{sub o}{sup 2}/{eta})({lambda}{sup 2}/8{pi}), for the received power of an antenna with a matched load in an over-moded cavity actually holds for an antenna of any shape and size. This can be seen from the close connection between the correlation tensor of the cavity field at two different points and the imaginary part of the free-space dyadic Green's function.
Date: March 15, 2000
Creator: WARNE,LARRY K. & LEE,K.S.H.
Partner: UNT Libraries Government Documents Department

Vibration Testing - Reviewing the State of the Art

Description: Vibration testing has advanced significantly over the past several decades. Comparatively speaking, enormous volumes of acceleration data are now available for virtually every vibration test. This data is readily compressed into frequency response functions and modal models. The modal models are compared with corresponding analytical models. Model updating techniques are used to adjust analytical model parameters to minimize the differences between model and test frequencies and mode shapes. These are very positive developments. Model and testing limitations lie in areas other than the direct recording and translation of acceleration data to modal models. Two major limitations of models are the inability to model damping and the limited degree to which nonlinear behavior is incorporated into model construction and model validation. Much more thorough understanding of damping mechanisms in real structures is required. Currently we know enough to bound the range of damping values for some typical structures. A much more thorough understanding of mechanical joints is required to accurately model structural joints. Some studies now underway offer a beginning to such understanding.
Date: June 23, 1999
Creator: Hunter, N. F.
Partner: UNT Libraries Government Documents Department

Statistical Properties of Antenna Impedance in an Electrically Large Cavity

Description: This paper presents models and measurements of antenna input impedance in resonant cavities at high frequencies.The behavior of input impedance is useful in determining the transmission and reception characteristics of an antenna (as well as the transmission characteristics of certain apertures). Results are presented for both the case where the cavity is undermoded (modes with separate and discrete spectra) as well as the over moded case (modes with overlapping spectra). A modal series is constructed and analyzed to determine the impedance statistical distribution. Both electrically small as well as electrically longer resonant and wall mounted antennas are analyzed. Measurements in a large mode stirred chamber cavity are compared with calculations. Finally a method based on power arguments is given, yielding simple formulas for the impedance distribution.
Date: December 13, 2000
Partner: UNT Libraries Government Documents Department


Description: This research presents a new method to improve analytical model fidelity for non-linear systems. The approach investigates several mechanisms to assist the analyst in updating an analytical model based on experimental data and statistical analysis of parameter effects. The first is a new approach at data reduction called feature extraction. This is an expansion of the ''classic'' update metrics to include specific phenomena or characters of the response that are critical to model application. This is an extension of the familiar linear updating paradigm of utilizing the eigen-parameters or frequency response functions (FRFs) to include such devices as peak acceleration, time of arrival or standard deviation of model error. The next expansion of the updating process is the inclusion of statistical based parameter analysis to quantify the effects of uncertain or significant effect parameters in the construction of a meta-model. This provides indicators of the statistical variation associated with parameters as well as confidence intervals on the coefficients of the resulting meta-model. Also included in this method is the investigation of linear parameter effect screening using a partial factorial variable array for simulation. This is intended to aid the analyst in eliminating from the investigation the parameters that do not have a significant variation effect on the feature metric. Finally an investigation of the model to replicate the measured response variation is examined.
Date: March 1, 2001
Creator: SCHULTZ, J. & AL, ET
Partner: UNT Libraries Government Documents Department

Applications of the Automated SMAC Modal Parameter Extraction Package

Description: An algorithm known as SMAC (Synthesize Modes And Correlate), based on principles of modal filtering, has been in development for a few years. The new capabilities of the automated version are demonstrated on test data from a complex shell/payload system. Examples of extractions from impact and shaker data are shown. The automated algorithm extracts 30 to 50 modes in the bandwidth from each column of the frequency response function matrix. Examples of the synthesized Mode Indicator Functions (MIFs) compared with the actual MIFs show the accuracy of the technique. A data set for one input and 170 accelerometer outputs can typically be reduced in an hour. Application to a test with some complex modes is also demonstrated.
Date: October 29, 1999
Partner: UNT Libraries Government Documents Department

(e,e'N) Reactions

Description: With the advent of a new generation of high energy, high duty cycle electron accelerators, a whole range of new nuclear and subnuclear phenomena can be investigated, in particular through coincidence experiments.This contribution focuses on one and two nucleon emission studies below pion threshold.After a brief review of recent experimental and theoretical work, the study of single nucleon densities through high energy (e,e'N) experiments is discussed.New insights in short-range multihadron phenomena are likely to be obtained through (e,e'p), (e,e'd) and (e,e'2N) reactions.Coincidence experiments, some of them involving polarization measurement, are described to study the free and bound nucleon electromagnetic responses.
Date: January 1, 1987
Creator: Mougey, Jean
Partner: UNT Libraries Government Documents Department

Controller strategy for a 6 DOF piezoelectric translation stage

Description: A controller for the third generation, 6 degree-of-freedom (DOF) piezoelectric translation stage shown in Figure 1 is presented. This was tested by monitoring all six coordinate motions using an orthogonal array of six, high-resolution capacitance gages. The full 6 DOF matrix transformations and controller block diagrams for this system have been measured and the system operated under closed loop control. Results of early experiments to determine the 21 open loop response functions as well as preliminary results showing the closed loop response for the 3 linear translations are presented in this abstract. The ultimate goal of this project is to incorporate this 6 DOF stage within a long range X-Y scanning system for nanometer pick-and-place capability over an area of 50 x 50 mm. The control strategy and early results from this system will be presented.
Date: March 22, 2006
Creator: Buice, E S; Yang, H; Smith, S T; Hocken, R J; Trumper, D L; Otten, D et al.
Partner: UNT Libraries Government Documents Department

Damage detection using frequency domain ARX models and extreme value statistics

Description: Structural health monitoring (SHM) is fast becoming a field of great importance as engineers seek for new ways to ensure the safety of structures throughout their designed lifetime. Current methods for analyzing the dynamic response of structures often use standard frequency response functions to model linear system input/output relationships. However, these functions do not account for the nonlinear response of a system, which damage often introduces. In this study, an auto-regressive model with exogenous inputs (ARX) in the frequency domain is used to extract damage sensitive features, explicitly considering the nonlinear effect in the frequency domain. Furthermore, because of the non-Gaussian nature of the extracted features, extreme value statistics (EVS) is employed to develop a robust damage classifier. The applicability of the ARX model combined with EVS to nonlinear damage detection is demonstrated using vibration data obtained from a laboratory experiment of a three-story building model.
Date: January 1, 2002
Creator: Fasel, T. R. (Timothy R.); Sohn, H. (Hoon) & Farrar, C. R. (Charles R.)
Partner: UNT Libraries Government Documents Department


Description: At low energies certain one dimensional Mott insulators can be described in terms of an exactly solvable quantum field theory, the U(1) Thirring model. Using exact results derived from integrability we determine dynamical properties like the frequency dependent optical conductivity and the single-particle Green's function. We discuss the effects of a small temperature and the effects on interchain tunneling in a model of infinitely many weakly coupled chains.
Date: January 14, 2004
Creator: ESSLER,F. H. L. TSVELIK,A. M.
Partner: UNT Libraries Government Documents Department

On the long-time behavior of ferroelectric systems

Description: In this note we investigate a new model for the behavior of ferroelectric materials. This model is analogous to one used in [1] to describe the dynamics of elastic materials which exhibit phase changes.
Date: July 16, 2003
Creator: Greenberg, J. M.; MacCamy, R. C. & Coffman, C. V.
Partner: UNT Libraries Government Documents Department


Description: The Sextant Test of the Relativistic Heavy Ion Collider (RHIC) was an important step towards its completion. One sixth of the two RHIC accelerators was fully commissioned. Gold ion beam was injected and transported through one sextant of one of the two rings. The betatron phase advance per cell was measured by recording differences in the horizontal and vertical positions of the beam at the end of the sextant due to a sequence of correction dipole kicks along the beam line. Measurement results show excellent agreement with predicted values, confirming that production measurements of the integral functions of the quadrupoles were very accurate, and that the polarity of all elements (correction dipoles, quadrupoles, dipoles etc.) was correct.
Date: June 26, 1998
Creator: TRBOJEVIC, D.
Partner: UNT Libraries Government Documents Department

Consideration on Isochronal Anneal Technique: From Measurement to Physics

Description: The isochronal anneal technique used to predict isothermal anneal behavior of MOS devices is analyzed as a function of experimental parameters. The effects of detrapping of trapped holes and compensating electrons are discussed.
Date: March 9, 1999
Creator: Flament, O.; Fleetwood, D.M.; Leray, J.L. & Paillet, P.
Partner: UNT Libraries Government Documents Department

An Investigation into the Response of a Micro Electro Mechanical Compound Pivot Mirror Using Finite Element Modeling

Description: This report is a presentation of modeling and simulation work for analyzing three designs of Micro Electro Mechanical (MEM) Compound Pivot Mirrors (CPM). These CPMs were made at Sandia National Laboratories using the SUMMiT{trademark} process. At 75 volts and above, initial experimental analysis of fabricated mirrors showed tilt angles of up to 7.5 degrees for one design, and 5 degrees for the other two. Nevertheless, geometric design models predicted higher tilt angles. Therefore, a detailed study was conducted to explain why lower tilt angles occurred and if design modifications could be made to produce higher tilt angles at lower voltages. This study showed that the spring stiffnesses of the CPMs were too great to allow for desired levels of rotation at lower levels of voltage. To produce these lower stiffnesses, a redesign is needed.
Date: January 1, 2002
Partner: UNT Libraries Government Documents Department

Analysis of the bi-modal nature of solar wind-magnetosphere coupling

Description: It has been shown that the optimal linear prediction filter relating the solar wind electric field and the geomagnetic activity, as measured by the AL index, is both bi-modal and dependent on the level of activity in the magnetosphere. Further studies truncated the prediction filter to a five parameter model containing two low-pass filtered delta functions of arbitrary amplitude and delay time. The present study elaborates on the nature of the bi-modal response by using the five parameter model to quantify the effects of the level of geomagnetic activity on each of the modes of the filter individually. The authors find that at all levels of activity, the second mode, occurring at approximately one hour, is relatively unchanged. The first mode, however, has a one parameter dependence on the level of activity in the magnetosphere. The amplitude of the first mode is shown to have a significant increase with respect to activity.
Date: May 1, 1997
Creator: Smith, J. P. & Horton, W.
Partner: UNT Libraries Government Documents Department

A thematic approach to system safety

Description: Sandia National Laboratories has refined a process for developing inherently safer system designs, based on methods used by the Laboratories to design detonation safety into nuclear weapons. The process was created when the Laboratories realized that standard engineering practices did not provide the level of safety assurance necessary for nuclear weapon operations, with their potential for catastrophic accidents. A systematic approach, which relies on mutually supportive design principles integrated through fundamental physical principles, was developed to ensure a predictably safe system response under a variety of operational and accident based stresses. Robust, safe system designs result from this thematic approach to safety, minimizing the number of safety critical features. This safety assurance process has two profound benefits: the process avoids the need to understand or limit the ultimate intensity of off normal environments and it avoids the requirement to analyze and test a bewildering and virtually infinite array of accident environment scenarios (e.g., directional threats, sequencing of environments, time races, etc.) to demonstrate conformance to all safety requirements.
Date: December 1, 1997
Creator: Ekman, M.E.; Werner, P.W.; Covan, J.M. & D`Antonio, P.E.
Partner: UNT Libraries Government Documents Department

Dynamical Behavior of Multi-Robot Systems Using Lattice Gas Automata

Description: Recent attention has been given to the deployment of an adaptable sensor array realized by multi-robotic systems. Our group has been studying the collective behavior of autonomous, multi-agent systems and their applications in the area of remote-sensing and emerging threats. To accomplish such tasks, an interdisciplinary research effort at Sandia National Laboratories are conducting tests in the fields of sensor technology, robotics, and multi-robotic and multi-agents architectures. Our goal is to coordinate a constellation of point sensors that optimizes spatial coverage and multivariate signal analysis using unmanned robotic vehicles (e.g., RATLERs, Robotic All-ten-sin Lunar Exploration Rover-class vehicles). Overall design methodology is to evolve complex collective behaviors realized through simple interaction (kinetic) physics and artificial intelligence to enable real-time operational responses to emerging threats. This paper focuses on our recent work understanding the dynamics of many-body systems using the physics-based hydrodynamic model of lattice gas automata. Three design features are investigated. One, for single-speed robots, a hexagonal nearest-neighbor interaction topology is necessary to preserve standard hydrodynamic flow. Two, adaptability, defined by the swarm's deformation rate, can be controlled through the hydrodynamic viscosity term, which, in turn, is defined by the local robotic interaction rules. Three, due to the inherent non-linearity of the dynamical equations describing large ensembles, development of stability criteria ensuring convergence to equilibrium states is developed by scaling information flow rates relative to a swarm's hydrodynamic flow rate. An initial test case simulates a swarm of twenty-five robots that maneuvers past an obstacle while following a moving target. A genetic algorithm optimizes applied nearest-neighbor forces in each of five spatial regions distributed over the simulation domain. Armed with knowledge, the swarm adapts by changing state in order to avoid the obstacle. Simulation results are qualitatively similar to lattice gas.
Date: March 11, 1999
Creator: Cameron, S.M.; Robinett, R.; Stantz, K.M.; Trahan, M.W. & Wagner, J.S.
Partner: UNT Libraries Government Documents Department

Effect of Substrate Composition on the Piezoelectric Response of Reactively Sputtered AlN Thin Films

Description: Deposition parameters were found to have a marked effect on piezoelectric response of reactive radio frequency (RF) sputtered AlN thin films. The authors observed peizoelectric response values ranging from {minus}3.5 to +4.2 pm/V for 1 {micro}m thick AlN films deposited onto Ti/Ru electrode stacks. An investigation of the effects of deposition parameters, in particular the nature of the Ru/AlN interface, was conducted. The lag time between deposition of adjacent thin film layers appeared to have the greatest affect on the value of the piezoelectric response. This suggests that chemical reaction occurring on the Ru thin film surface is responsible for changing an important thin film property such as dipole orientation within the overlying AlN thin film.
Date: April 21, 1999
Creator: Clem, P.G.; Dimos, D.B.; Gonzales, D.M.; Ruffner, J.A. & Tuttle, B.A.
Partner: UNT Libraries Government Documents Department

Impact response of preloaded structures with revolute joints

Description: Many structural components designed to support static loads must also demonstrate the ability to withstand low probability events that can produce impact loading. For some constructs the structure is not only subjected to the initial impact, but is also subjected to rebound impacts as well. In some designs, support structures must be moved in and out of position as part of normal operations. These structures often employ revolute joints to allow the motions. In addition, functional requirements may require that a significant preload exist within the structure during normal operating conditions. This paper present the methodology needed for simulating the impact response of preloaded structures with revolute joints. A three-dimensional revolute joint is presented for use in explicit time integration analysis of problems with severe impacts. The computational engine used for the transient solution of preloaded structures is discussed. These developments are used in the analysis of a preloaded platen subjected to drop loads. The resulting transient response of the system is presented.
Date: September 1, 1997
Creator: Kulak, R.F. & Pfeiffer, P.A.
Partner: UNT Libraries Government Documents Department

Initial commissioning results from the APS loss monitor system

Description: The design of the beam loss monitor system for the Argonne National Laboratory Advanced Photon Source is based on using a number of air dielectric coaxial cables as long ionization chambers. Results to date show that the loss monitor is useful in helping to determine the cause of injection losses and losses large enough to limit circulating currents in the storage ring to short lifetimes. Sensitivities ranging from 13 to 240 pC of charge collected in the injector BTS (booster-to-storage-ring) loss monitor per picocoulomb of loss have been measured, depending on the loss location. These results have been used to predict that the storage ring loss monitor leakage current limit of 10 pA per cable should allow detection of losses resulting in beam lifetimes of 100 hours or less with 100 mA stored beam. Significant DC bias levels associated with the presence of stored beam have been observed. These large bias levels are most likely caused by the loss monitor responding to hard x-ray synchrotron radiation. No such response to synchrotron radiation was observed during earlier tests at SSRL. However, the loss monitor response to average stored beam current in APS has provided a reasonable alternative to the DC current transformer (DCCT) for measuring beam lifetimes.
Date: October 1, 1996
Creator: Patterson, D.R.
Partner: UNT Libraries Government Documents Department

Shock certification of replacement subsystems and components in the presence of uncertainty

Description: In this paper a methodology for analytically estimating the response of replacement components in a system subjected to worst-case hostile shocks is presented. This methodology does not require the use of system testing but uses previously compiled shock data and inverse dynamic analysis to estimate component shock response. In the past component shock responses were determined from numerous system tests; however, with limitations on system testing, an alternate methodology for determining component response is required. Such a methodology is discussed. This methodology is mathematically complex in that two inverse problems, and a forward problem, must be solved for a permutation of models representing variabilities in dynamics. Two conclusions were deduced as a result of this work. First, the present methodology produces overly conservative results. Second, the specification of system variability is critical to the prediction of component response.
Date: May 8, 2000
Partner: UNT Libraries Government Documents Department

Spectral Resolution for Five-Element, Filtered, X-Ray Detector (XRD) Arrays Using the Methods of Backus and Gilbert

Description: The generalized method of Backus and Gilbert (BG) is described and applied to the inverse problem of obtaining spectra from a 5-channel, filtered array of x-ray detectors (XRD's). This diagnostic is routinely fielded on the Z facility at Sandia National Laboratories to study soft x-ray photons ({le}2300 eV), emitted by high density Z-pinch plasmas. The BG method defines spectral resolution limits on the system of response functions that are in good agreement with the unfold method currently in use. The resolution so defined is independent of the source spectrum. For noise-free, simulated data the BG approximating function is also in reasonable agreement with the source spectrum (150 eV black-body) and the unfold. This function may be used as an initial trial function for iterative methods or a regularization model.
Date: January 17, 2000
Partner: UNT Libraries Government Documents Department