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Amplitude of Supersonic Diffuser Flow Pulsations

Description: "A theoretical method for evaluating the stability characteristics and the amplitude and the frequency of pulsation of ram-jet engines without heat addition is presented herein. Experimental verification of the theoretical results are included where data were available. Theory and experiment show that the pulsation amplitude of a high mass-flow-ratio diffuser having no cone surface flow separation increases with decreasing mass flow" (p. 1).
Date: December 16, 1952
Creator: Sterbentz, William H. & Davids, Joseph
Partner: UNT Libraries Government Documents Department

Averaging of Periodic Pressure Pulsations by a Total-Pressure Probe

Description: Note presenting information on the average pressure indicated by a total-pressure probe subjected to a stagnation pressure that alternates periodically between two constant values. Calculated and experimental data are in good agreement and errors are reduced when the probe design is such as to ensure laminar-flow pulsations in the probe at all times.
Date: October 1955
Creator: Johnson, R. C.
Partner: UNT Libraries Government Documents Department

Criterions for prediction and control of ram-jet flow pulsations

Description: Report presenting the results of a theoretical and experimental study of ramjet diffuser flow pulsing, commonly referred to as a buzz condition, with and without combustion. The acoustical resonance properties of ram jets are an important factor in establishing the frequency of diffuser flow pulsations.
Date: May 16, 1951
Creator: Sterbentz, William H. & Evvard, John C.
Partner: UNT Libraries Government Documents Department

Pressure Pulsations on Rigid Airfoils at Transonic Speeds

Description: Report presenting testing to obtain the effects of changes in Mach number, thickness ratio, and angle of attack on the amplitude of the pressure pulsations on several airfoils at transonic speeds. The tests were performed on NACA 65A-series airfoils with thicknesses ranging from 4 to 12 percent chord at a range of Mach numbers and angles of attack. The relations of pressure pulsations to buffeting are also provided.
Date: December 6, 1951
Creator: Humphreys, Milton D.
Partner: UNT Libraries Government Documents Department

The confirmation of the 2.1 ms candidate for PSR1987A and the 1000-hour Arecibo Piggyback ms Pulsar Survey. Final report

Description: The authors objectives included (1) The confirmation of the 2.1 ms candidate for the pulsar (PSR1987A) in Supernova 1987A (SN1987A), and, provided the candidate is real (and if it is real, the authors have successfully tracked its frequency for two years), (2) to determine the nature of its spindown, including whether it is a result of gravitational radiation (GR), inertia transfer associated with differential rotation, changes in the moment of inertia, or the affects of a wide binary system. The authors have decent results to support the supposition that the spindown of this candidate for PSR1987A is indeed due almost entirely to gravitational radiation. The observations with the University of Tasmania 1-m telescope were successful in detecting the 2.1 ms candidate pulsar on at least three occasions. They can conclude that there is now little doubt that SN1987A was the result of a merger of two giant stars which resulted in: (1) The ejection of the three rings during a common-envelope/Roche lobe overflow phase which may have lasted only 300 to 1,000 years some 30,000 years ago, (2) The extreme mixing of the elements during the spiraling in phase of the two {approximately}0.7 solar mass white dwarf cores, (3) The blue supergiant nature of the progenitor star, Sk-69 202, and (4) the formation of a weak-field ms pulsar spinning every 2.1 ms. The importance of this finding is nearly inestimable. The authors now know that neutron stars can sustain or grow oblatenesses of 5 parts in ten million some 5-7 years after their explosive birth, and that pulsars born in such a way can outshine all other compact solar mass type objects by an order of magnitude in nearly pure gravitational radiation. They know now that most weak field ms, pulsars are born in such core mergers, which explains their ...
Date: June 1, 1995
Creator: Middleditch, J. & Kulkarni, S.
Partner: UNT Libraries Government Documents Department

Enhanced Electron Attachment to Highly-Excited Molecules and Its Applications in Pulsed Plasmas

Description: Studies conducted over the past several years have shown that electron attachment to highly-excited states of molecules have extremely large cross sections. We will discuss the implications of this for pulsed discharges used for H<sup>-</sup> generation, material processing, and plasma remediation.
Date: June 27, 1999
Creator: Ding, W. X.; Ma, C. Y.; McCorkle, D. L. & Pinnaduwage, L. A.
Partner: UNT Libraries Government Documents Department

High Amplitude (delta)-Scutis in the Large Magellanic Cloud

Description: The authors present 2323 High-Amplitude {delta}-Scutis (HADS) candidates discovered in the Large Magellanic Cloud (LMC) by the SuperMACHO survey (Rest et al. 2005). Frequency analyses of these candidates reveal that several are multimode pulsators, including 119 whose largest amplitude of pulsation is in the fundamental (F) mode and 19 whose largest amplitude of pulsation is in the first overtone (FO) mode. Using Fourier decomposition of the HADS light curves, they find that the period-luminosity (PL) relation defined by the FO pulsators does not show a clear separation from the PL-relation defined by the F pulsators. This differs from other instability strip pulsators such as type c RR Lyrae. They also present evidence for a larger amplitude, subluminous population of HADS similar to that observed in Fornax (Poretti et al. 2008).
Date: January 25, 2010
Creator: Garg, A; Cook, K H; Nikolaev, S; Huber, M E; Rest, A; Becker, A C et al.
Partner: UNT Libraries Government Documents Department

The Effects of Camber and Leading-Edge-Flap Deflection on the Pressure Pulsations on Thin Rigid Airfoils at Transonic Speeds

Description: Report discussing an investigation into the effects of camber and leading-edge-flap deflection on the pressure pulsations on thin rigid airfoils at a range of Mach numbers. The ideal camber or flap deflection was found to be dependent on Mach number and normal-force coefficient. The results of this testing, which used a 64A006 airfoil, was compared to previous testing using a 65A006 airfoil.
Date: October 27, 1952
Creator: Humphreys, Milton D. & Kent, John D.
Partner: UNT Libraries Government Documents Department

The MACHO Project Sample of Galactic Bulge High-Amplitude Scuti Stars: Pulsation Behavior and Stellar Properties

Description: We have detected 90 objects with periods and lightcurve structure similar to those of field {delta} Scuti stars, using the Massive Compact Halo Object (MACHO) Project database of Galactic bulge photometry. If we assume similar extinction values for all candidates and absolute magnitudes similar to those of other field high-amplitude {delta} Scuti stars (HADS), the majority of these objects lie in or near the Galactic bulge. At least two of these objects are likely foreground {delta} Scuti stars, one of which may be an evolved nonradial pulsator, similar to other evolved, disk-population {delta} Scuti stars. We have analyzed the light curves of these objects and find that they are similar to the light curves of field {delta} Scuti stars and the {delta} Scuti stars found by the Optical Gravitational Lens Experiment (OGLE). However, the amplitude distribution of these sources lies between those of low- and high-amplitude {delta} Scuti stars, which suggests that they may be an intermediate population. We have found nine double-mode HADS with frequency ratios ranging from 0.75 to 0.79, four probable double- and multiple-mode objects, and another four objects with marginal detections of secondary modes. The low frequencies (5-14 cycles d{sup -1}) and the observed period ratios of {approx}0.77 suggest that the majority of these objects are evolved stars pulsating in fundamental or first overtone radial modes.
Date: November 16, 1999
Creator: Bennett, D.P.; Cook, K.H.; Freeman, K.C.; Geha, M.; Griest, K.; Lehner, M.J. et al.
Partner: UNT Libraries Government Documents Department

Pulsating hydrodynamic instability and thermal coupling in an extended Landau/Levich model of liquid-propellant combustion. 2. Viscous analysis

Description: A pulsating form of hydrodynamic instability has recently been shown to arise during liquid-propellant deflagration in those parameter regimes where the pressure-dependent burning rate is characterized by a negative pressure sensitivity. This type of instability can coexist with the classical cellular, or Landau, form of hydrodynamic instability, with the occurrence of either dependent on whether the pressure sensitivity is sufficiently large or small in magnitude. For the inviscid problem, it has been shown that when the burning rate is realistically allowed to depend on temperature as well as pressure, that sufficiently large values of the temperature sensitivity relative to the pressure sensitivity causes the pulsating form of hydrodynamic instability to become dominant. In that regime, steady, planar burning becomes intrinsically unstable to pulsating disturbances whose wavenumbers are sufficiently small. In the present work, this analysis is extended to the fully viscous case, where it is shown that although viscosity is stabilizing for intermediate and larger wavenumber perturbations, the intrinsic pulsating instability for small wavenumbers remains. Under these conditions, liquid-propellant combustion is predicted to be characterized by large unsteady cells along the liquid/gas interface.
Date: January 1, 2000
Creator: Margolis, Stephen B.
Partner: UNT Libraries Government Documents Department

DRIVING G-MODE PULSATIONS IN GAMMA DORADUS VARIABLES

Description: The {gamma} Doradus stars are a newly-discovered class of gravity-mode pulsators which lie just at or beyond the red edge of the {delta} Scuti instability strip. We present the results of calculations which predict pulsation instability of high-order g-modes with periods between 0.4 and 3 days, as observed in these stars. The pulsations are driven by the modulation of radiative flux by convection at the base of a deep envelope convection zone. Pulsation instability is predicted only for models with temperatures at the convection zone base between {approximately}200,000 and {approximately}480,000 K. The estimated shear dissipation due to turbulent viscosity within the convection zone, or in an overshoot region below the convection zone, can be comparable to or even exceed the predicted driving, and is likely to reduce the number of unstable modes, or possibly to quench the instability. Additional refinements in the pulsation modeling are required to determine the outcome. A few Doradus stars have been observed that also pulsate in {delta} Scuti-type p-modes, and at least two others have been identified as chemically peculiar. Since our calculated driving region is relatively deep, Doradus pulsations are not necessarily incompatible with surface abundance peculiarities or with {delta} Scuti p-mode pulsations driven by the H and He-ionization {kappa} effect. Such stars will provide useful observational constraints on the proposed Doradus pulsation mechanism.
Date: October 10, 2000
Creator: GUZIK, J.; KAYE, A. & AL, ET
Partner: UNT Libraries Government Documents Department

Bulge Delta Scuti Stars in the MACHO database

Description: The authors describe the search for {delta} Scuti stars in the MACHO database of bulge fields. Concentrating on a sample of high amplitude {delta} Scutis, they examine the light curves and pulsation modes. They also discuss their spatial distribution and evolutionary status using mean colors and absolute magnitudes.
Date: July 29, 1997
Creator: Minnniti, D; Alcock, C; Alves,D R; Axelrod, T S; Becker, A; Bennett, D P et al.
Partner: UNT Libraries Government Documents Department

Discovery of Pulsed Gamma Rays from the Young Radio Pulsar PSR J1028-5819 with the Fermi Large Area Telescope

Description: Radio pulsar PSR J1028-5819 was recently discovered in a high-frequency search (at 3.1 GHz) in the error circle of the Energetic Gamma-Ray Experiment Telescope (EGRET) source 3EG J1027-5817. The spin-down power of this young pulsar is great enough to make it very likely the counterpart for the EGRET source. We report here the discovery of {gamma}-ray pulsations from PSR J1028-5819 in early observations by the Large Area Telescope (LAT) on the Fermi Gamma-Ray Space Telescope. The {gamma}-ray light curve shows two sharp peaks having phase separation of 0.460 {+-} 0.004, trailing the very narrow radio pulse by 0.200 {+-} 0.003 in phase, very similar to that of other known {gamma}-ray pulsars. The measured {gamma}-ray flux gives an efficiency for the pulsar of {approx}10-20% (for outer magnetosphere beam models). No evidence of a surrounding pulsar wind nebula is seen in the current Fermi data but limits on associated emission are weak because the source lies in a crowded region with high background emission. However, the improved angular resolution afforded by the LAT enables the disentanglement of the previous COS-B and EGRET source detections into at least two distinct sources, one of which is now identified as PSR J1028-5819.
Date: May 15, 2009
Creator: Abdo, Aous A.; Ackermann, M.; Atwood, W.B.; Baldini, L.; Ballet, J.; Barbiellini, Guido et al.
Partner: UNT Libraries Government Documents Department

Borehole seismic monitoring of seismic stimulation at OccidentalPermian Ltd's -- South Wason Clear Fork Unit

Description: Seismic stimulation is a proposed enhanced oil recovery(EOR) technique which uses seismic energy to increase oil production. Aspart of an integrated research effort (theory, lab and field studies),LBNL has been measuring the seismic amplitude of various stimulationsources in various oil fields (Majer, et al., 2006, Roberts,et al.,2001, Daley et al., 1999). The amplitude of the seismic waves generatedby a stimulation source is an important parameter for increased oilmobility in both theoretical models and laboratory core studies. Theseismic amplitude, typically in units of seismic strain, can be measuredin-situ by use of a borehole seismometer (geophone). Measuring thedistribution of amplitudes within a reservoir could allow improved designof stimulation source deployment. In March, 2007, we provided in-fieldmonitoring of two stimulation sources operating in Occidental (Oxy)Permian Ltd's South Wasson Clear Fork (SWCU) unit, located near DenverCity, Tx. The stimulation source is a downhole fluid pulsation devicedeveloped by Applied Seismic Research Corp. (ASR). Our monitoring used aborehole wall-locking 3-component geophone operating in two nearbywells.
Date: April 30, 2007
Creator: Daley, Tom & Majer, Ernie
Partner: UNT Libraries Government Documents Department

A proposed pulsation driving mechanism for [gamma] doradus variable stars

Description: We propose a pulsation driving mechanism for {gamma} Doradus variable stars. This mechanism requires that the local convective timescale at the base of the envelope convection zone be comparable to or longer than the pulsation period. This mechanism explains both the red and blue edges of the {gamma} Dor instability strip. We predict that some cadidate {gamma} Dor stars summarized by Handler (1999) may actually be too hot or too cool to be {gamma} Dor variables.
Date: January 1, 2001
Creator: Kaye, A. B. (Anthony B.); Bradley, P. A. (Paul A.); Cox, Arthur N.; Neuforge, C. M. (Corinne M.) & Guzik, J. A. (Joyce Ann)
Partner: UNT Libraries Government Documents Department

Start-to-end global imaging as a sunward propagating, SAPS-associated giant undulation event

Description: We present high-time resolution global imaging of a sunward propagating giant undulation event from start to finish. The event occurred on November 24, 2001 during a very disturbed storm interval. The giant undulations began to develop at around 13UT and persisted for approximately 2 hours. The sunward propagation speed was on the order of 0.6 km/s (relative to SM coordinate system). The undulations had a wavelength of {approx} 750 km, amplitudes of {approx} 890 km and produced ULF pulsations on the ground with a period of {approx} 1108s. We show that the undulations were associated with SAPs flows that were caused by the proton plasma sheet penetrating substantially farther Earthward than the electron plasma sheet on the duskside. The observations appear to be consistent with the development of a shear flow and/or ballooning type of instability at the plasmapause driven by intense SAPS-associated shear flows.
Date: January 1, 2009
Creator: Henderson, Michael G; Donovan, Eric F; Foster, John C; Mann, Ian R; Immel, Thomas J; Mende, Stephen B et al.
Partner: UNT Libraries Government Documents Department

Magnetic Hydrogen Atmosphere Models and the Neutron Star RX J1856.5-3754

Description: RX J1856.5-3754 is one of the brightest nearby isolated neutron stars, and considerable observational resources have been devoted to it. However, current models are unable to satisfactorily explain the data. We show that our latest models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a condensed surface can fit the entire spectrum, from X-rays to optical, of RX J1856.5-3754, within the uncertainties. In our simplest model, the best-fit parameters are an interstellar column density N{sub H} {approx} 1 x 10{sup 20} cm{sup -2} and an emitting area with R{sup {infinity}} {approx} 17 km (assuming a distance to RX J1856.5-3754 of 140 pc), temperature T{sup {infinity}} {approx} 4.3 x 10{sup 5} K, gravitational redshift z{sub g} {approx} 0.22, atmospheric hydrogen column y{sub H} {approx} 1 g cm{sup -2}, and magnetic field B {approx} (3-4) x 10{sup 12} G; the values for the temperature and magnetic field indicate an effective average over the surface. We also calculate a more realistic model, which accounts for magnetic field and temperature variations over the neutron star surface as well as general relativistic effects, to determine pulsations; we find there exist viewing geometries that produce pulsations near the currently observed limits. The origin of the thin atmospheres required to fit the data is an important question, and we briefly discuss mechanisms for producing these atmospheres. Our model thus represents the most self-consistent picture to date for explaining all the observations of RX J1856.5-3754.
Date: December 8, 2006
Creator: Ho, Wynn C.G.; /MIT, MKI /KIPAC, Menlo Park; Kaplan, David L.; /MIT, MKI; Chang, Philip; /UC, Berkeley, Astron. Dept. /UC, Santa Barbara et al.
Partner: UNT Libraries Government Documents Department

The Fermi Gamma Ray Space Telescope discovers the Pulsar in the Young Galactic Supernova-Remnant CTA 1

Description: Energetic young pulsars and expanding blast waves (supernova remnants, SNRs) are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 ms, a period derivative of 3.614 x 10{sup -13} s s{sup -1}. Its characteristic age of 10{sup 4} years is comparable to that estimated for the SNR. It is conjectured that most unidentified Galactic gamma ray sources associated with star-forming regions and SNRs are such young pulsars.
Date: May 15, 2009
Creator: Abdo, Aous A.; Ackermann, M.; Atwood, W.B.; Baldini, L.; Ballet, J.; Barbiellini, G. et al.
Partner: UNT Libraries Government Documents Department

TECHNOLOGIES TO ENHANCE THE OPERATION OF EXISTING NATURAL GAS COMPESSION INFRASTRUCTURE

Description: This quarterly report documents work performed under Tasks 15, 16, and 18 through 23 of the project entitled: ''Technologies to Enhance the Operation of Existing Natural Gas Compression Infrastructure''. The project objective is to develop and substantiate methods for operating integral engine/compressors in gas pipeline service, which reduce fuel consumption, increase capacity, and enhance mechanical integrity. The report presents results of design analysis performed on the TCVC10 engine/compressor installed at Dominion's Groveport Compressor Station to develop options and guide decisions for reducing pulsations and enhancing compressor system efficiency and capacity. The report further presents progress on modifying and testing the laboratory GMVH6 at SwRI for correcting air imbalance.
Date: January 24, 2006
Creator: Smalley, Anthony J.; Harris, Ralph E.; Bourn, Gary D. & Deffenbaugh, Danny M.
Partner: UNT Libraries Government Documents Department

Variable Red Giants--The MACHO View

Description: The authors present a study of the MACHO red variable population in the Large Magellanic Cloud. This study reveals six period-luminosity relations among the red variable population. Only two of these were known prior to MACHO. The results are consistent with Mira pulsation in the fundamental mode. A sequence comprising 26% of the red variable population can not be explained by pulsation. They propose a dust {kappa}-mechanism in the circumstellar environment is responsible for the long period variation of these objects. The luminosity function of the variables shows a sharp edge at the tip of the red giant branch (TRGB). This is the first clear indication of a population of variable stars within the immediate vicinity of the TRGB. The results indicate this population amounts to 8% of the RGB population near the TRGB.
Date: January 3, 2003
Creator: Keller, S C & Cook, K H
Partner: UNT Libraries Government Documents Department

Investigation of the mechanism in RIJKE pulse combustors with tangential air and fuel injection. Progress report, August 1, 1992--January 31, 1993

Description: This report summarizes the accomplishments of DOE Contract No. DE-AS04-85AL31881. This three year investigation started in August 1989 and its objective was to elucidate the mechanisms that control the driving of pulsations in the liquid fuel burning, Rijke type, pulse combustor developed under a preceding DOE contracts. It was demonstrated in that contract that the developed Rijke type pulse combustor can burn a variety of light and heavy liquid fuel oils with high combustion efficiencies while using low excess air, which produces high thermal efficiencies. Since the elucidation of the driving mechanism in the Rijke pulse combustor required the use of optical diagnostics (e.g., radiation measurements), it was decided to perform these investigations in a Rijke pulse combustor that burned propane instead of a liquid fuel in order to avoid difficulties that are often encountered due to the presence of liquid droplets in the combustion region. Consequently, an effort was made to develop a Rijke pulse combustor that is similar to the one developed in the preceding program and demonstrated similar performance characteristics. Such a pulse combustor was developed in the early phases of this program. The developed experimental setup was provided with capabilities for measuring steady combustor temperature distributions, the characteristics of the excited pressure oscillations, the exhaust flow composition, the characteristics of the flow field and the reaction rates. This pulse combustor consists of a cylindrical tube that is attached to a decoupling chamber at each end. Fuel and air are supplied via a tangential air/fuel injection system that is located at a distance of L/4 from the combustor entrance, where L is the combustor length. Part of the combustor tube, where combustion occurs, is water cooled. This section is also equipped with flat quartz windows to permit optical diagnostics.
Date: February 1, 1993
Creator: Zinn, B.T.; Jagoda, J.I.; Daniel, B.R. & Bai, T.
Partner: UNT Libraries Government Documents Department

Investigation of mineral transformations and ash deposition during staged combustion. Quarterly technical progress report, October 1, 1996--December 31, 1996

Description: The key issues addressed this quarter were related to operational problems in the coal feed system, namely, the inability to accurately measure all of air entering the system, and plugging of coal in the feed lines due to poor entrainment. Both of these problems caused unacceptable uncertainty and/or fluctuations in the operating conditions and therefore required solutions. The coal entrainment problem was solved by installing a new educator designed for entraining solids in gas streams. All of the air entering the reactor now flows through the educator, either as motive air or through the suction air inlet. This ensures that the coal is entrained at relatively high velocity, so that it will flow to the reactor without forming slugs in the lines. A new feeder shroud was also installed with an air jet directed towards the auger to sweep off the tip in order to reduce pulsations when feeding coal. The problems associated with accurately metering the air have been somewhat more difficult to resolve. New strategies for completely closing the system have been tested and look promising. A new flowmeter was also purchased with cost sharing funds to directly measure the air flow rate of the two phase stream (after the coal injection point). If the system can be operated without leaks, then the changes will provide two independent measurements of the air flow to ensure accuracy. If the system cannot be sealed, the new flowmeter will still provide reliable measurement of the air flow and permit proper operation of the combustor. Consequently, we feel that the problems have been resolved and we look forward to a productive next quarter.
Date: February 13, 1997
Creator: Harb, J.N.
Partner: UNT Libraries Government Documents Department

RR Lyrae stars in the MACHO database

Description: The MACHO Project has catalogued {approximately} 8000 RR Lyrae stars in the Large Magellanic Cloud, {approximately} 180 in the Galactic bulge, and {approximately} 50 in the Sgr dwarf galaxy. These variables are excellent distance indicators, and are used as tools to study the structure of the Large Magellanic Cloud and the bulge. The large datasets also probe uncommon pulsation modes. A number of double-mode RR Lyrae stars (RRd) are found in the Large Magellanic Cloud sample. These stars provide important clues for understanding the formation and evolution of the inner Galaxy, the Large Magellanic Cloud and the Sgr dwarf galaxy. A large number of second overtone pulsators (RRe) are found in the LMC and bulge. Finally, the RR Lyrae belonging to the Sgr dwarf yield an accurate distance to this galaxy. Their presence also alerts us of the very interesting possibility of distant sources for bulge microlensing effects. 49 refs., 7 figs., 1 tab.
Date: October 1, 1996
Creator: Minniti, D.; Alcock, C; Alves, D. R.; Axelrod, T. S.; Bennett, D. P.; Cook, K. H. et al.
Partner: UNT Libraries Government Documents Department