200 Matching Results

Search Results

Advanced search parameters have been applied.

High-Frequency Limit of Longitudinal Impedance

Description: A method of iterations which takes into account finite widths of resonances is developed and used to calculate the longitudinal impedance for a cylindrical cavity with side pipes. In the high-frequency limit the dependence of the real part of the impedance on the frequency is omega^(-1/2) in agreement with the estimate for the average impedance obtained by G. Do^me.
Date: August 1, 1987
Creator: Heifets, Sam & Heifets, Sam
Partner: UNT Libraries Government Documents Department

Toward a simple molecular understanding of sum frequency generation at air-water interfaces

Description: Second-order vibrational spectroscopies successfully isolate signals from interfaces, but they report on intermolecular structure in a complicated and indirect way. Here we adapt a perspective on vibrational response developed for bulk spectroscopies to explore the microscopic fluctuations to which sum frequency generation (SFG), a popular surface-specific measurement, is most sensitive. We focus exclusively on inhomogeneous broadening of spectral susceptibilities for OH stretching of HOD as a dilute solute in D{sub 2}O. Exploiting a simple connection between vibrational frequency shifts and an electric field variable, we identify several functions of molecular orientation whose averages govern SFG. The frequency-dependence of these quantities is well captured by a pair of averages, involving alignment of OH and OD bonds with the surface normal at corresponding values of the electric field. The approximate form we obtain for SFG susceptibility highlights a dramatic sensitivity to the way a simulated liquid slab is partitioned for calculating second-order response.
Date: January 13, 2009
Creator: Noah-Vanhoucke, Joyce; Smith, Jared D. & Geissler, Phillip L.
Partner: UNT Libraries Government Documents Department

Intracavity Frequency Doubling of a Diode-Pumped, External Cavity, Surface Emitting Semiconductor Laser

Description: The authors present a compact, robust, solid-state blue light (490 nm) source capable of greater than 5 mW of output in a TEM{sub 00} mode. This device is an optically pumped, vertical external-cavity surface-emitting laser (VECSEL) with an intracavity frequency doubling crystal.
Date: April 22, 1999
Creator: Alford, W.J.; Allerman, A.A.; Crawford, M.H. & Raymond, T.D.
Partner: UNT Libraries Government Documents Department

Geometric optimization of the 56 MHz SRF cavity and its frequency table

Description: It is essential to know the frequency of a Superconducting Radio Frequency (SRF) cavity at its 'just being fabricated' stage because frequency is the key parameter in constructing the cavity. In this paper, we report our work on assessing it. We can estimate the frequency change from stage to stage theoretically and/or by simulation. At the operating stage, the frequency can be calculated accurately, and, from this value, we obtain the frequencies at other stages. They are listed in a table that serves to check the processes from stage to stage. Equally important is optimizing the geometric shape of the SRF cavity so that the peak electric-field and peak magnetic-field are as low as possible. It is particularly desirable in the 56MHz SRF cavity of RHIC to maximize the frequency sensitivity of the slow tuner. After undertaking such optimization, our resultant peak electric-field is only 44.1MV/m, and the peak magnetic-field is 1049G at 2.5MV of voltage across the cavity gap. To quench superconductivity in an SRF cavity, it is reported that the limit of the peak magnetic-field is 1800G [1], and that of the peak electric-field is more than l00MV/m for a SRF cavity [2]. Our simulations employed the codes Superfish and Microwave Studio.
Date: October 1, 2008
Creator: Chang,X. & Ben-Zvi, I.
Partner: UNT Libraries Government Documents Department

Evidence for back scattering of near-podal seismic P'P' waves from the 150-220 km zone in Earth's upper mantle

Description: The deepest and most inaccessible parts of Earth's interior--the core and core-mantle boundary regions can be studied from compressional waves that turn in the core and are routinely observed following large earthquakes at epicentral distances between 145{sup o} and 180{sup o} (also called P', PKIKP or PKP waves). P'P' (PKPPKP) are P' waves that travel from a hypocenter through the Earth's core, reflect from the free surface and travel back through the core to a recording station on the surface. P'P' waves are sometimes accompanied by precursors, which were reported first in the 1960s as small-amplitude arrivals on seismograms at epicentral distances of about 50{sup o}-70{sup o}. Most prominent of these observed precursors were explained by P'P' waves generated by earthquakes or explosions that did not reach the Earth's surface but were reflected from the underside of first order velocity discontinuities at 410 and 660 km in the upper mantle mantle. Here we report the discovery of hitherto unobserved near-podal P'P' waves (at epicentral distance less than 10{sup o}) and very prominent precursors preceding the main energy by as much as 55 seconds. We interpret these precursors as a back scattered energy from undocumented structure in the upper mantle, in a zone between 150 and 220 km depth beneath Earth's surface. From these observations, we identify a frequency dependence of Q (attenuation quality factor) in the lithosphere that can be modeled by a flat relaxation spectrum below about 0.05-0.1 Hz and increasing with as the first power of frequency above this value, confirming pioneering work by B. Gutenberg.
Date: July 15, 2005
Creator: Tkalcic, H; Flanagan, M P & Cormier, V F
Partner: UNT Libraries Government Documents Department

FY05 LDRD Final Report The Innermost Inner Core: Fact or Artifact?

Description: P'P' (PKPPKP) are P waves that travel from a hypocenter through the Earth's core, reflect from the free surface and travel back through the core to a recording station on the surface. Here we report the observations of hitherto unobserved near-podal P'P' waves (at epicentral distance < 10{sup o}) and very prominent precursors preceding the main energy by as much as 60 s. We interpret these precursors as a back-scattered energy from previously undocumented horizontally connected small-scale heterogeneity in the upper mantle beneath the oceans in a zone between 150 and 220 km depth beneath the Earth's surface. From these observations, we identify a frequency dependence of attenuation quality factor Q in the lithosphere through forward modeling of the observed amplitude spectra of the main and back-scattered P'P' waves. In addition, we did not find that travel times corresponding to very polar paths through the centermost inner core with respect to the rotation axis of Earth are anomalously advanced, which argues for isotropic or at best --weakly-anisotropic center of Earth in the direction parallel with the rotation axis. More systematic sampling near Earth's center and characterization of anisotropy in Earth's center will be a subject of future research efforts.
Date: January 9, 2006
Creator: Tkalcic, H; Flanagan, M P & Mogri, H
Partner: UNT Libraries Government Documents Department

HIGHER MODE FREQUENCY EFFECTS ON RESONANCE IN MACHINERY, STRUCTURES, AND PIPE SYSTEMS

Description: The complexities of resonance in multi-degree of freedom systems (multi-DOF) may be clarified using graphic presentations. Multi-DOF systems represent actual systems, such as beams or springs, where multiple, higher order, natural frequencies occur. Resonance occurs when a cyclic load is applied to a structure, and the frequency of the applied load equals one of the natural frequencies. Both equations and graphic presentations are available in the literature for single degree of freedom (SDOF) systems, which describe the response of spring-mass-damper systems to harmonically applied, or cyclic, loads. Loads may be forces, moments, or forced displacements applied to one end of a structure. Multi-DOF systems are typically described only by equations in the literature, and while equations certainly permit a case by case analysis for specific conditions, graphs provide an overall comprehension not gleaned from single equations. In fact, this collection of graphed equations provides novel results, which describe the interactions between multiple natural frequencies, as well as a comprehensive description of increased vibrations near resonance.
Date: May 2, 2010
Creator: Leishear, R.
Partner: UNT Libraries Government Documents Department

Observations involving broadband impedance modelling

Description: Results for single- and multi-bunch instabilities can be significantly affected by the precise model that is used for the broadband impendance. This paper discusses three aspects of broadband impendance modeling. The first is an observation of the effect that a seemingly minor change in an impedance model has on the single-bunch mode coupling threshold. The second is a successful attempt to construct a model for the high-frequency tails of an r.f cavity. The last is a discussion of requirements for the mathematical form of an impendance which follow from the general properties of impendances.
Date: August 1, 1995
Creator: Berg, J. S.
Partner: UNT Libraries Government Documents Department

Observations of collective effects at the Advanced Light Source

Description: We present a summary of measurements of single beam collective effects in the Advanced Light Source (ALS). We describe measurements of coupled-bunch instabilities, including some recent results using the newly commissioned feedback systems and the results of an initial search for the fast ion instability. Single bunch effects include bunch lengthening, energy spread increase, HOM loss measurements, head-tail damping rates, current dependent tune shifts, and transverse mode coupling instability threshold. The longitudinal measurements are consistent with a broadband impedance {vert_bar}{Zeta}{sub {parallel}}/{eta}{vert_bar}{sub eff} = 0.22{plus_minus}0.07 {Omega} and transverse measurements indicate broadband impedances of {Zeta}{sub y,eff} = 155 k{Omega}/m and Z{sub x,eff} = 58 k{Omega}/m.
Date: October 1, 1995
Creator: Byrd, J.M.; Barry, W.; Corlett, J.N.; Fox, J. & Teytelman, D.
Partner: UNT Libraries Government Documents Department

Development and integration of applique decoupling capacitors

Description: For high-speed integrated circuit applications, it is important to interconnect decoupling capacitors and integrated circuits (ICs) as intimately as possible, to minimize parasitic impedances. This can be achieved by mounting free-standing, thin film capacitors directly onto ICs as part of a chip-scale packaging approach. These applique capacitors utilize a chemically-prepared PLZT dielectric, which is nominally 1 {micro}m thick. The small size and weight of applique capacitors can be used to improve packaging efficiency. Applique capacitors, which are initially fabricated on silicon wafers, have high permittivity ({var_epsilon} {approx_equal} 1,000), low loss (tan{delta} {approx_equal} 0.01) and high breakdown strength (E{sub b} {approx_equal} 1 MV/cm) and leakage resistance ({rho} > 10{sup 14} {Omega}-cm {at} 125 C). Various processes being developed to remove the capacitors from the silicon substrate and reattach them to ICs is described. In addition, a concept for interconnecting the capacitors using a repatterning process is discussed.
Date: October 1, 1996
Creator: Garino, T.J.; Dimos, D. & Lockwood, S.J.
Partner: UNT Libraries Government Documents Department

Force-limited vibration tests aplied to the FORTE` satellite

Description: A force limited random vibration test was conducted on a small satellite called FORTE{prime}. This type of vibration test reduces the over testing that can occur in a conventional vibration test. Two vibration specifications were used in the test: The conventional base acceleration specification, and an interface force specification. The vibration level of the shaker was controlled such that neither the table acceleration nor the force transmitted to the test item exceeded its specification. The effect of limiting the shake table vibration to the force specification was to reduce (or ``notch``) the shaker acceleration near some of the satellite`s resonance frequencies. This paper describes the force limited test conducted for the FORTE{prime} satellite. The satellite and its dynamic properties are discussed, and the concepts of force limiting theory are summarized. The hardware and setup of the test are then described, and the results of the force limited vibration test are discussed.
Date: February 1, 1996
Creator: Stevens, R.R. & Butler, T.A.
Partner: UNT Libraries Government Documents Department

Self-stressing structures for wafer-level oxide breakdown to 200 MHz

Description: We have demonstrated for the first time high frequency (210 MHz) oxide breakdown at the wafer-level using on-chip, self-stressing test structures. This is the highest frequency oxide breakdown that has been reported. We used these structures to characterize the variation in oxide breakdown with frequency (from 1 Hz to over 200 MHz) and duty cycle (from 10% to 90%). Since the stress frequency, duty cycle and temperature are controlled by DC signals in these structures, we used conventional DC wafer-level equipment without any special modifications (such as high frequency cabling). This self-stressing structure significantly reduces the cost of performing realistic high frequency oxide breakdown experiments necessary for developing reliability models and building-in-reliability.
Date: February 1, 1995
Creator: Snyder, E.S.; Tanner, D.M.; Bowles, M.R.; Swanson, S.E.; Anderson, C.H. & Perry, J.P.
Partner: UNT Libraries Government Documents Department

Localized wave pulses in the keyport experiment

Description: Localized wave (LW) pulses were produced using a standard Navy array in the anechoic tank at Navy Underwater Weapons Center (NUWC) Keyport. The LW pulses used were the MPS pulse first derived by Ziolkowski, and a new type of pulse based on a superposition of Gaussian beam modes. This new type is motivated by a desire to make a comparison of the MPS pulse with another broad band pulse built from solutions to the wave equation. The superposed Gaussian pulse can be described by parameters which are analogous to those describing the MPS pulse. We compare the directivity patternsand the axial energy decay between the pulses. We find the behavior of the pulses to be similar so that the superposed Gaussian could be another candidate in the class of low diffractive pulses known as localized waves.
Date: February 17, 1998
Creator: Chambers, D.H. & Lewis, D.K.
Partner: UNT Libraries Government Documents Department

Characterization and equalization of the AC responses of the corrector magnets for the APS local orbit feedback system

Description: Local feedback for the APS storage ring uses local bumps to control the position and angle of the positron beam through each x-ray source point. Induced eddy currents in the aluminum vacuum chamber dominate the AC characteristics of the corrector magnetic fields. Small differences in the geometries at each magnet location change the eddy current effects and result in bump closure errors which must be reduced in order to minimize the coupling between each of the many local loops and the global control loop. By a combination of flux-damping coils, flux-shielding copper sheets, and a set of steel laminations for end-flux clamping, the differences of the eddy current effects between two corrector magnets were reduced from 0.18 Gm/A to 0.035 Gm/A in the frequency span of 0.1-100 Hz.
Date: August 1, 1997
Creator: Doose, C. & Kim, S.H.
Partner: UNT Libraries Government Documents Department

Analysis and application of microwave radiation from the damping manifolds of the SLAC Damped Detuned Structures (DDS)

Description: The power spectrum emerging from the damping manifolds of a DDS provides valuable quasi-local information on the displacement of a drive beam from the axis of individual cells, where the displacement may be due to beam offset, small cell misalignment, or a combination of the two. The degree of localization and the indexing of frequency to cell number is determined directly from the spectral function theory. Examples for specific DDS designs will be presented. These relations can be used to determine geometrical misalignment patterns.
Date: May 1, 1997
Creator: Jones, R.M.; Seidel, M. & Miller, R.H.
Partner: UNT Libraries Government Documents Department

Tune modulation due to synchrotron oscillations and chromaticity, and the dynamic aperture

Description: A tracking study was done of the effects of a tune modulations, due to synchrotron oscillations and the tune dependence on momentum (chromaticity), on the dynamic aperture. The studies were done using several RHIC lattices and tracking runs of about 1 {times} 10{sup 6} turns. The dynamic aperture was found to decrease roughly linearly with the amplitude of the tune modulation. Lower order non-linear resonances, like the 1/3 and 1/4 resonance are not crossed because of the tune modulation. Three different cases were studied, corresponding to RHIC lattices with different {beta}*, and with different synchrotron oscillation amplitudes. In each case, the tune modulation amplitude was varied by changing the chromaticity. In each case, roughly the same result, was found. The result found here for the effect of a tune modulation due to chromaticity may be compared with the result found for the effect of a tune modulation due to a gradient ripple in the quadrupoles. The effect of a tune modulation due to a gradient ripple appears to be about 4 times stronger than the effect of a tune modulation due to chromaticity and synchrotron oscillations.
Date: May 1, 1995
Creator: Parzen, G.
Partner: UNT Libraries Government Documents Department

Localized wave generation with a standard underwater array

Description: Recent work at the Navy Underwater Weapons Center Keyport test facility showed that existing Navy field equipment could generate Localized Waves. Results of angular scans show a narrowed beam pattern and lowered side lobes relative to standard beams. Results of axial range scans show evidence or an extended near field. Frequency analysis shows that the main beam is a decade wide while the surviving grating lobes are narrow band width, high frequency.
Date: February 17, 1998
Creator: Lewis, D.K.; Chambers, D.H.; Mullin, C.S. & Ziolkowski, R.W.
Partner: UNT Libraries Government Documents Department

ANALYTIC PROPERTIES OF THE LONGITUDINAL BEAM TRANSFER FUNCTION.

Description: The frequency dependence of the longitudinal beam transfer function (BTF) in a storage ring, when expressed in a basis of azimuthal harmonics of the line density, is the Fourier transform of a causal function that depends on the radio-frequency potential well in which the bunch moves. The effect of all synchrotron harmonics are included in this function, which is derived from Krinsky and Wang's expression for the BTF expressed in the same basis (S. Krinsky and J.-M. Wang, Part. Accel. 17, 109-139 (1985)). Analytic properties of the terms of the BTF expressed in a series of synchrotron harmonics, which are approximately Shaposhnikova's BTF matrix elements (E. Shaposhnikova, CERN Report No. SL-94-19-RF (1994)), are studied through the large-argument asymptotics of corresponding causal functions.
Date: June 18, 2001
Creator: TOWNE, N.
Partner: UNT Libraries Government Documents Department

The Synthesis of Structural Responses Using Experimentally Measured Frequency Response Functions and Field Test Data

Description: This paper presents an analysis technique used to generate the structural response at locations not measured during the ejection of a captive-carried store. The ejection shock event is complicated by the fact that forces may be imparted to the store at eight distinct locations. The technique derives forcing functions by combining the initial field test data for a limited number of measurement locations with Frequency Response Functions (FRFs) measured using a traditional modal-type impact (tap) test at the same locations. The derived forcing functions were then used with tap test FRFs measured at additional locations of interest to produce the desired response data.
Date: November 17, 2000
Creator: CAP,JEROME S. & NELSON,CURTIS F.
Partner: UNT Libraries Government Documents Department

FREQUENCY AND DIFFUSION MAPS FOR THE SNS RING.

Description: Using a single particle dynamics approach: the major magnetic non-linearities of the SNS accumulator ring are studied. Frequency maps are employed in order to display the global dynamics of the beam, for several working points. By means of diffusion maps the major resonances are explored and their bandwidth is estimated. The global tune diffusion coefficient is finally used to compare and choose the best working point.
Date: June 18, 2001
Creator: PAPAPHILIPPOU,Y.
Partner: UNT Libraries Government Documents Department

MEASURING NONLINEAR MOMENTUM COMPACTION IN RHIC.

Description: The chromatic nonlinearity parameter, {alpha}{sub 1}, has a strong impact on longitudinal dynamics in the vicinity of transition [1,2,3]. Measurements of the synchrotron frequency as a function of radius are used to constrain the value of {alpha}{sub 1}.
Date: June 18, 2001
Creator: BLASKIEWICZ,M.; BRENNAN,J.M.; CAMERON,P.; DREES,A.; KEWISH,J.; ROSER,T. et al.
Partner: UNT Libraries Government Documents Department

Force Reduction Factors for the Structural Design and Evaluation of Facilities Containing Nuclear and Hazardous Materials

Description: This report examines significant contributions to inelastic behavior of common building systems and develops frequency dependent force reduction factors that may be used with the results from linear elastic analyses models.
Date: July 26, 2001
Creator: Mertz, G.E.
Partner: UNT Libraries Government Documents Department