220 Matching Results

Search Results

Advanced search parameters have been applied.

Time-resolved far-infrared experiments at the National Synchrotron Light Source. Final report

Description: A facility for time-resolved infrared and far-infrared spectroscopy has been built and commissioned at the National Synchrotron Light Source. This facility permits the study of time dependent phenomena over a frequency range from 2-8000cm{sup {minus}1} (0.25 meV-1 eV). Temporal resolution is approximately 200 psec and time dependent phenomena in the time range out to 100 nsec can be investigated.
Date: October 12, 1999
Creator: Tanner, D.B.; Reitze, D.H. & Carr, G.L.
Partner: UNT Libraries Government Documents Department

Response to FCC 98-208 notice of inquiry in the matter of revision of part 15 of the commission's rules regarding ultra-wideband transmission systems

Description: In general, Micropower Impulse Radar (MIR) depends on Ultra-Wideband (UWB) transmission systems. UWB technology can supply innovative new systems and products that have an obvious value for radar and communications uses. Important applications include bridge-deck inspection systems, ground penetrating radar, mine detection, and precise distance resolution for such things as liquid level measurement. Most of these UWB inspection and measurement methods have some unique qualities, which need to be pursued. Therefore, in considering changes to Part 15 the FCC needs to take into account the unique features of UWB technology. MIR is applicable to two general types of UWB systems: radar systems and communications systems. Currently LLNL and its licensees are focusing on radar or radar type systems. LLNL is evaluating MIR for specialized communication systems. MIR is a relatively low power technology. Therefore, MIR systems seem to have a low potential for causing harmful interference to other users of the spectrum since the transmitted signal is spread over a wide bandwidth, which results in a relatively low spectral power density.
Date: December 8, 1998
Creator: Morey, R M
Partner: UNT Libraries Government Documents Department

A Collection of Complex Permittivity and Permeability Measurements

Description: We present the results of measurements of the complex permittivity and permeability over a frequency range of 0.1-5.1 GHz for a range of microwave absorbing materials used in a variety of accelerator applications. We also describe the automated measurement technique which uses swept-frequency S-parameter measurements made on a strip transmission line device loaded with the material under test.
Date: February 1, 1993
Creator: Barry, W.; Byrd, J.; Johnson, J. & Smithwick, J.
Partner: UNT Libraries Government Documents Department

Evaluation of signal processing techniques for the analysis of large civil structures.

Description: Several new methods of determining change in the data signature of a large Cable-Stayed bridge are examined and compared. Two sets of data, one taken in September 1995, and the second in June 2000 are studied. Structural changes are investigated using several techniques; (1) Modal behavior in the .3 to 3 Hz range is investisated using Transmissibility FRFs and the Random Decrement Method, (2) Quasi Periodic behavior in the 3 to 30 Hz frequency range is observed in several tests. Potential causes and characteristics of this behavior are investigated. (3) Some methods of non-linear analysis are applied to the bridge data and changes in behavior are evaluated. Capability and concerns with each method are addressed in conjunction with physical ambient excitation data and its signal properties.
Date: January 1, 2001
Creator: Hunter, N. F. (Norman F.) & Schultze, J. F. (John F.)
Partner: UNT Libraries Government Documents Department

Very High Power THz Radiation Sources

Description: We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. Such sources are ideal for imaging, for high power damage studies and for studies of non-linear phenomena in this spectral range. We describe the source, presenting theoretical calculations and their experimental verification. For clarity, we compare this sources with one based on ultrafast laser techniques.
Date: October 1, 2002
Creator: Carr, G.L.; Martin, Michael C.; McKinney, Wayne R.; Jordan, Kevin; Neil, George R. & Williams, Gwyn P.
Partner: UNT Libraries Government Documents Department

Generation of THz Radiation by Excitation of InAs with a Free Electron Laser

Description: Terahertz (THz) radiation is generated by exciting an un-doped InAs wafer with a femtosecond free-electron laser (FEL) at the Thomas Jefferson National Accelerator Facility. A microwatt level of THz radiation is detected from the unbiased InAs emitter when it is excited with the femtosecond FEL pulses operated at a wavelength of 1.06 {mu}-m and 10 W average power.
Date: January 1, 2001
Creator: Tani, Mashiko; Kono, Shunsuke; Gu, Ping; Sakai, Kiyomi; Usami, Mamoru; Shinn, Michelle D. et al.
Partner: UNT Libraries Government Documents Department

Controlled-source magnetotellurics: source effects

Description: In this paper we evaluate the CSMT impedance in the wavenumber domain, and compare the result with the full EM impedance obtained from the exact solution over the layered earth. Preliminary results show that we can find a pair of wavenumbers that reproduces the full EM impedance over the frequency range affected by source effects. This observation suggests that it is now possible to obtain the electrical resistivity using the low-frequency EM impedance data that can be represented by a pair of wavenumbers, thereby greatly simplifying the computational requirements. The process will involve a non-linear inversion of near-source impedance data for a pair of wavenumbers and a layered-earth resistivity structure.
Date: April 1, 1999
Creator: Smith, T. & Lee, K.H.
Partner: UNT Libraries Government Documents Department

Consolidation of Modal Parameters from Several Extraction Sets

Description: Experienced experimentalists have gone through the process of attempting to identify a final set of modal parameters from several different sets of extracted parameters. Usually, this is done by visually examining the mode shapes. With the advent of automated modal parameter extraction algorithms such as SMAC (Synthesize Modes and Correlate), very accurate extractions can be made to high frequencies. However, this process may generate several hundred modes that then must be consolidated into a final set of modal information. This has motivated the authors to generate a set of tools to speed the process of consolidating modal parameters by mathematical (instead of visual) means. These tools help quickly identify the best modal parameter extraction associated with several extractions of the same mode. The tools also indicate how many different modes have been extracted in a nominal frequency range and from which references. The mathematics are presented to achieve the best modal extraction of multiple modes at the same nominal frequency. Improvements in the SMAC graphical user interface and database are discussed that speed and improve the entire extraction process.
Date: October 24, 2000
Creator: MAYES,RANDALL L. & KLENKE,SCOTT E.
Partner: UNT Libraries Government Documents Department

Magnetic Probe Construction using Thick-film Technology

Description: Thick-film technology has been successfully adapted for the design and fabrication of magnetic probes of a new type suitable for use in the simultaneous ultra-high vacuum and high-temperature environment of a nuclear fusion device. The maximum usable temperature is expected to be around 900 degrees C. This new probe has a specific sensitivity (coupling area per unit volume) an order of magnitude higher than a conventional coil. The new probe in one implementation is capable of simultaneously measuring magnetic field in three orthogonal directions about a single spatial point and in two frequency ranges. Low-frequency coils have a measured coupling area of 296-323 cm squared and a frequency response of about 300 kHz. High-frequency coils have a design coupling area of 12-15 cm squared.
Date: February 2, 2001
Creator: Takahashi, H.; Sakakibara, S.; Kubota, Y. & and Yamada, H.
Partner: UNT Libraries Government Documents Department

Dynamic modulus estimation and structural vibration analysis.

Description: Often the dynamic elastic modulus of a material with frequency dependent properties is difficult to estimate. These uncertainties are compounded in any structural vibration analysis using the material properties. Here, different experimental techniques are used to estimate the properties of a particular elastomeric material over a broad frequency range. Once the properties are determined, various structures incorporating the elastomer are analyzed by an interactive finite element method to determine natural frequencies and mode shapes. Then, the finite element results are correlated with results obtained by experimental modal analysis.
Date: November 18, 1998
Creator: Gupta, A.
Partner: UNT Libraries Government Documents Department

Observation of Compressional Alfven Modes during Neutral Beam Heating on the National Spherical Torus Experiment

Description: Neutral-beam-driven compressional Alfven eigenmodes (CAE) at frequencies below the ion cyclotron frequency have been observed and identified for the first time in the National Spherical Torus Experiment (NSTX). The modes are observed as a broad spectrum of nearly equally spaced peaks in the frequency range from approximately 0.2 to approximately 1.2 omega(subscript ''ci''). The frequency has a scaling with toroidal field and plasma density consistent with Alfven waves. The modes have been observed with high bandwidth magnetic pick-up coils and with a reflectometer.
Date: October 3, 2001
Creator: Fredrickson, E.D.; Gorelenkov, N.; Cheng, C.Z.; Bell, R.; Darrow, D.; Johnson, D. et al.
Partner: UNT Libraries Government Documents Department

Extensional wave attenuation and velocity in partially-saturated sand in the sonic frequency range

Description: Extensional wave attenuation and velocity measurements on a high permeability Monterey sand were performed over a range of gas saturations for imbibition and degassing conditions. These measurements were conducted using extensional wave pulse propagation and resonance over a 1 - 9 kHz frequency range for a hydrostatic confining pressure of 8.3 MPa. Analysis of the extensional wave data and the corresponding X-ray CT images of the gas saturation show strong attenuation resulting from the presence of the gas (QE dropped from 300 for the dry sand to 30 for the partially-saturated sand), with larger attenuation at a given saturation resulting from heterogeneous gas distributions. The extensional wave velocities are in agreement with Gassmann theory for the test with near-homogeneous gas saturation and with a patchy saturation model for the test with heterogeneous gas saturation. These results show that partially-saturated sands under moderate confining pressure can produce strong intrinsic attenuation for extensional waves.
Date: June 17, 2002
Creator: Liu, Z.; Rector, J.W.; Nihei, K.T.; Tomutsa, L.; Myer, L.R. & Nakagawa, S.
Partner: UNT Libraries Government Documents Department

The D0 solenoid NMR magnetometer

Description: A field monitoring system for the 2 Tesla Solenoid of the D0 detector is described. It is comprised of a very small NMR probe cabled to a DSP based signal processing board. The design magnetic field range is from 1.0 to 2.2 Tesla, corresponding to an RF frequency range of 42.57 to 93.67 MHz. The desired an accuracy is one part in 10{sup 5}. To minimize material in the interaction region of the D0 detector, the overall thickness of the NMR probe is 4 mm, including its mounting plate, and its width is 10 mm. To minimize cable mass, 4mm diameter IMR-100A cables are used for transmitting the RF signals from a nearby patch panel 25 meters to each of four probes mounted within the bore of the solenoid. RG213U cables 45 meters long are used to send the RF from the movable counting house to the patch panel. With this setup, the detector signal voltage at the moving counting room is in the range of 250-400 mV.
Date: November 20, 2002
Creator: Sten Uldall Hansen Terry Kiper, Tom Regan, John Lofgren et al.
Partner: UNT Libraries Government Documents Department

Compressional Alfvin Eigenmode Dispersion in Low Aspect Ratio Plasmas

Description: Recent observations of new fast ion beam driven instabilities in MHz frequency range in National Spherical Torus experiments (NSTX) are suggested to be Compressional Alfvin Eigenmodes (CAEs). A new theory of CAEs applicable to low aspect ratio toroidal plasmas is developed based on the ballooning representation for the poloidal dependence of the perturbed quantities. In agreement with observations, the analytical theory predicts that CAEs are discrete modes with frequencies correlated with the characteristic Alfvin velocity of the plasma. Plasma equilibrium structure is essential to determine accurately the dispersion of CAEs. The mode structure is localized in both the minor radius and the poloidal directions on the low magnetic field side.
Date: January 29, 2002
Creator: Gorelenkov, N.N.; Cheng, C.Z. & Fredrickson, E.
Partner: UNT Libraries Government Documents Department

Extensional wave attenuation and velocity in partially saturated sand in the sonic frequency range

Description: Extensional wave attenuation and velocity measurements on a high permeability Monterey sand were performed over a range of gas saturations for imbibition and degassing conditions. These measurements were conducted using extensional wave pulse propagation and resonance over a 1-9 kHz frequency range for a hydrostatic confining pressure of 8.3 MPa. Analysis of the extensional wave data and the corresponding X-ray CT images of the gas saturation show strong attenuation resulting from the presence of the gas (Q{sub E} dropped from 300 for the dry sand to 30 for the partially-saturated sand), with larger attenuation at a given saturation resulting from heterogeneous gas distributions. The extensional wave velocities are in agreement with Gassmann theory for the test with near-homogeneous gas saturation and with a patchy saturation model for the test with heterogeneous gas saturation. These results show that partially-saturated sands under moderate confining pressure can produce strong intrinsic attenuation for extensional waves.
Date: August 10, 2001
Creator: Liu, Z.; Rector, J.W.; Nihei, K.T.; Tomutsa, L.; Myer, L.R. & Nakagawa, S.
Partner: UNT Libraries Government Documents Department

SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

Description: In fully-saturated rock and at ultrasonic frequencies, the microscopic squirt flow induced between the stiff and soft parts of the pore space by an elastic wave is responsible for velocity-frequency dispersion and attenuation. In the seismic frequency range, it is the macroscopic cross-flow between the stiffer and softer parts of the rock. We use the latter hypothesis to introduce simple approximate equations for velocity-frequency dispersion and attenuation in a fully water saturated reservoir. The equations are based on the assumption that in heterogeneous rock and at a very low frequency, the effective elastic modulus of the fully-saturated rock can be estimated by applying a fluid substitution procedure to the averaged (upscaled) dry frame whose effective porosity is the mean porosity and the effective elastic modulus is the Backus-average (geometric mean) of the individual dry-frame elastic moduli of parts of the rock. At a higher frequency, the effective elastic modulus of the saturated rock is the Backus-average of the individual fully-saturated-rock elastic moduli of parts of the rock. The difference between the effective elastic modulus calculated separately by these two methods determines the velocity-frequency dispersion. The corresponding attenuation is calculated from this dispersion by using (e.g.) the standard linear solid attenuation model.
Date: July 1, 2002
Creator: Walls, Joel; Taner, M.T.; Mavko, Gary & Dvorkin, Jack
Partner: UNT Libraries Government Documents Department

Logistic Regression Applied to Seismic Discrimination

Description: The usefulness of logistic discrimination was examined in an effort to learn how it performs in a regional seismic setting. Logistic discrimination provides an easily understood method, works with user-defined models and few assumptions about the population distributions, and handles both continuous and discrete data. Seismic event measurements from a data set compiled by Los Alamos National Laboratory (LANL) of Chinese events recorded at station WMQ were used in this demonstration study. PNNL applied logistic regression techniques to the data. All possible combinations of the Lg and Pg measurements were tried, and a best-fit logistic model was created. The best combination of Lg and Pg frequencies for predicting the source of a seismic event (earthquake or explosion) used Lg{sub 3.0-6.0} and Pg{sub 3.0-6.0} as the predictor variables. A cross-validation test was run, which showed that this model was able to correctly predict 99.7% earthquakes and 98.0% explosions for this given data set. Two other models were identified that used Pg and Lg measurements from the 1.5 to 3.0 Hz frequency range. Although these other models did a good job of correctly predicting the earthquakes, they were not as effective at predicting the explosions. Two possible biases were discovered which affect the predicted probabilities for each outcome. The first bias was due to this being a case-controlled study. The sampling fractions caused a bias in the probabilities that were calculated using the models. The second bias is caused by a change in the proportions for each event. If at a later date the proportions (a priori probabilities) of explosions versus earthquakes change, this would cause a bias in the predicted probability for an event. When using logistic regression, the user needs to be aware of the possible biases and what affect they will have on the predicted probabilities.
Date: October 8, 1998
Creator: Amindan, BG & Hagedorn, DN
Partner: UNT Libraries Government Documents Department

Use of Frequency Response Metrics to Assess the Planning and Operating Requirements for Reliable Integration of Variable Renewable Generation

Description: An interconnected electric power system is a complex system that must be operated within a safe frequency range in order to reliably maintain the instantaneous balance between generation and load. This is accomplished by ensuring that adequate resources are available to respond to expected and unexpected imbalances and restoring frequency to its scheduled value in order to ensure uninterrupted electric service to customers. Electrical systems must be flexible enough to reliably operate under a variety of"change" scenarios. System planners and operators must understand how other parts of the system change in response to the initial change, and need tools to manage such changes to ensure reliable operation within the scheduled frequency range. This report presents a systematic approach to identifying metrics that are useful for operating and planning a reliable system with increased amounts of variable renewable generation which builds on existing industry practices for frequency control after unexpected loss of a large amount of generation. The report introduces a set of metrics or tools for measuring the adequacy of frequency response within an interconnection. Based on the concept of the frequency nadir, these metrics take advantage of new information gathering and processing capabilities that system operators are developing for wide-area situational awareness. Primary frequency response is the leading metric that will be used by this report to assess the adequacy of primary frequency control reserves necessary to ensure reliable operation. It measures what is needed to arrest frequency decline (i.e., to establish frequency nadir) at a frequency higher than the highest set point for under-frequency load shedding within an interconnection. These metrics can be used to guide the reliable operation of an interconnection under changing circumstances.
Date: December 20, 2010
Creator: Eto, Joseph H.; Undrill, John; Mackin, Peter; Daschmans, Ron; Williams, Ben; Haney, Brian et al.
Partner: UNT Libraries Government Documents Department

Quantum optics mini-program on fast light, slow light, and metamaterials.

Description: The topic of electromagnetic propagation in dielectric media has been enlivened in the past decade by a number of remarkable experimental results showing the technical ability to control the speed of light propagation in exotic ways. Light pulses have been observed travelling faster than c, or slowed by many orders of magnitude, or even stopped completely. All of thcse results require careful interpretation, and a variety of theoretical interpretations have been proposed and/or published, not all agreeing with each other. At the same time, in a lower frequency range than optical, rapid development of so-called meta-materials or double-negative materials has occurred. These materials are characterized by electric permittivity and magnetic permeability with very unconventional values, both quantities negative in some cases. Such unusual properties, especially when leading to a negative value for the group velocity, clearly indicate another possibility for control of light. Such materials are being improved rapidly, but independent of their implementation in the laboratory, their theoretical properties have led to dramatic predictions such as the existence of a perfect lens, Le., a finite lens (actually even planar-flat rather than parabolic) that can deliver an ideally sharp focus unaffected by diffractive effects. There are strong contentions currently being published that such predictions are erroneous
Date: January 1, 2002
Creator: Milonni, Peter W.
Partner: UNT Libraries Government Documents Department

Proposal to upgrade the MIPP data acquisition system

Description: The MIPP TPC is the largest contributor to the MIPP event size by far. Its readout system and electronics were designed in the 1990's and limit it to a readout rate of 60 Hz in simple events and {approx} 20 Hz in complicated events. With the readout chips designed for the ALICE collaboration at the LHC, we propose a low cost effective scheme of upgrading the MIPP data acquisition speed to 3000 Hz.
Date: March 1, 2005
Creator: Baker, W.; Carey, D.; Johnstone, C.; Kostin, M.; Meyer, H.; Raja, R. et al.
Partner: UNT Libraries Government Documents Department