1,173 Matching Results

Search Results

Advanced search parameters have been applied.

Turbulence and Temperature Fluctuations Behind a Heated Grid

Description: "In the approximately isotropic velocity and temperature fluctuation fields behind a hot grid, measurements were made of fluctuation levels and of various double and triple correlation functions. The double and triple correlation coefficient functions are of roughly the same spatial extent for the vector and scalar fields. As anticipated from theoretical considerations, the temperature fluctuations die out more slowly than does the turbulence" (p. 1).
Date: August 1958
Creator: Mills, R. R., Jr.; Kistler, A. L.; O'Brien, V. & Corrsin, S.
Partner: UNT Libraries Government Documents Department

An Investigation into the Characteristics and Causes of Monthly and Yearly Price Fluctuations of Spot Cotton at New York, New York, During the Period, 1911-1953

Description: This study endeavors to give an insight into the causes and characteristics of price fluctuations of spot cotton at New York, N.Y., for the period 1911-1953, and to indicate whenever possible the factors which caused the price of cotton to rise or fall during selected periods.
Date: February 1954
Creator: Reynolds, Harry M.
Partner: UNT Libraries

Measurements of Lift Fluctuations Due to Turbulence

Description: Note presenting a study of the fluctuating lift of a rigid wing in turbulent flow and the power spectra of the lift and turbulent fluctuations. Using these measurements, the aerodynamic admittance of the wing was obtained. Results regarding the infinite wing and aspect-ratio effect are provided.
Date: March 1957
Creator: Lamson, P.
Partner: UNT Libraries Government Documents Department

Application of Scattering Theory to the Measurement of Turbulent Density Fluctuations by an Optical Method

Description: "An analysis shows that the scattering of unpolarized plane light waves which penetrate turbulent, transparent gases provides a measure of the average integral scale and intensity of the turbulent density fluctuations. The analysis is based upon the scattering coefficient deduced by Booker and Gordon and, thus, assumes isotropic fluctuations having an exponentially decaying (Markoffian) correlation function. Photometric data taken through turbulent boundary layers in air are found to conform functionally with the analytical prediction" (p. 1).
Date: June 1956
Creator: Stine, Howard A. & Winovich, Warren
Partner: UNT Libraries Government Documents Department

Investigations of Free Turbulent Mixing

Description: Note presenting a discussion of the integral relations for flow of the boundary-layer type. It is shown that the characteristic laws of spread of jets, wakes, and so forth, can be obtained directly for the laminar case and, with the help of dimensional reasoning, for the turbulent case as well. Measurements of the mean velocity, the intensity and scale of the turbulent fluctuations, and of the turbulent shear in a two-dimensional mixing zone are presented.
Date: August 1947
Creator: Liepmann, Hans Wolfgang & Laufer, John
Partner: UNT Libraries Government Documents Department

Preliminary investigation of the pressure fluctuations in the wakes of two-dimensional wings at low angles of attack

Description: Report presenting a measurement of the magnitudes of pressure fluctuations in the turbulent wakes of restrained two-dimensional airfoils at transonic speeds. Measurements indicated that the total-pressure fluctuations occurred only within the wake. Results regarding the magnitude of pressure oscillation in the wake, effect stream-angle fluctuations in the wake, and frequencies of pressure oscillation on the wing and in the wake are provided.
Date: October 30, 1951
Creator: Sorenson, Robert M.; Wyss, John A. & Kyle, James C.
Partner: UNT Libraries Government Documents Department

Effect of ram-jet pressure pulsations on supersonic-diffuser performance

Description: Experimental study of effects of combustion roughness and controlled mechanical oscillations on diffuser operation was conducted on an 8-inch ram jet at Mach number 1.87. Within experimental accuracy, the optimum mean combustion-chamber static pressure occurred when the maximum instantaneous static pressure equalled the optimum steady-flow value and the corresponding decrement in optimum mean static pressure was equal to one-half the total amplitude of the pressure pulsations. A marked attenuation of amplitude of cold-buzz pressure fluctuations was effected over limited range of subcritical diffuser operation by means of properly tuned rotating disk located in combustion chamber.
Date: November 20, 1950
Creator: Connors, James F.
Partner: UNT Libraries Government Documents Department

Experimental investigation of pressure fluctuations in 3.6 inch ram jet at Mach number 1.92

Description: Report presenting an experimental study of the pressure fluctuations at the combustion-chamber inlets of a ramjet operating a Mach number of 1.92 in the supersonic tunnel. Results are presented for two burner configurations of different operating characteristics to indicate trends in pressure magnitude, frequency, and wave form. Results regarding the perforated conical flame holder, regenerative-type burner, and diffuser total-pressure recovery are provided.
Date: October 13, 1949
Creator: Connors, James F. & Schroeder, Albert H.
Partner: UNT Libraries Government Documents Department

Preliminary Measurements of Turbulence and Temperature Fluctuations Behind a Heated Grid

Description: "Preliminary measurements have been made of velocity and temperature fluctuations in the flow behind a heated grid in a uniform airstream. Temperature correlation shows a reasonable degree of isotropy, and the temperature fluctuations die out at large distances more slowly than the turbulence, as has been predicted theoretically under some strongly simplifying postulates" (p. 1).
Date: June 10, 1954
Creator: Kistler, A. L.; O'Brien, V. & Corrsin, S.
Partner: UNT Libraries Government Documents Department

Wall Pressure Fluctuations in a Turbulent Boundary Layer

Description: Note presenting an investigation of sound generation that is generated by turbulence on a solid surface. Suitable equipment has been developed to measure the fluctuating wall pressure in the turbulent boundary layer. Results regarding the response of the transducer in a laminar and turbulent boundary layer, power-spectrum measurements, and mean-square pressure measurements are provided.
Date: March 1958
Creator: Willmarth, William W.
Partner: UNT Libraries Government Documents Department

A Method for Estimating the Effect of Turbulent Velocity Fluctuations in the Boundary Layer on Diffuser Total-Pressure-Loss Measurements

Description: Note presenting a method for estimating the effect of turbulent velocity fluctuations on diffuser total-pressure-loss measurements. When the longitudinal velocity fluctuations are large, as evidenced by discrepancies between the inlet and exit weight flows, the method compensates for the discrepancies by adjusting the boundary-layer profile.
Date: January 1954
Creator: Persh, Jerome & Bailey, Bruce M.
Partner: UNT Libraries Government Documents Department

Far-from-equilibrium measurements of thermodynamic length

Description: Thermodynamic length is a path function that generalizes the notion of length to the surface of thermodynamic states. Here, we show how to measure thermodynamic length in far-from-equilibrium experiments using the work fluctuation relations. For these microscopic systems, it proves necessary to define the thermodynamic length in terms of the Fisher information. Consequently, the thermodynamic length can be directly related to the magnitude of fluctuations about equilibrium. The work fluctuation relations link the work and the free energy change during an external perturbation on a system. We use this result to determine equilibrium averages at intermediate points of the protocol in which the system is out-of-equilibrium. This allows us to extend Bennett's method to determine the potential of mean force, as well as the thermodynamic length, in single molecule experiments.
Date: November 5, 2008
Creator: Feng, Edward H. & Crooks, Gavin E.
Partner: UNT Libraries Government Documents Department

Periodic Heat Transfer at Small Pressure Fluctuations

Description: "The effect of cyclic gas pressure variations on the periodic heat transfer at a flat wall is theoretically analyzed and the differential equation describing the process and its solution for relatively. Small pressure fluctuations developed, thus explaining the periodic heat cycle between gas and wall surface. The processes for pure harmonic pressure and temperature oscillations, respectively, in the gas space are described by means of a constant heat transfer coefficient and the equally constant phase angle between the appearance of the maximum values of the pressure and heat flow most conveniently expressed mathematically in the form of a complex heat transfer coefficient" (p. 1).
Date: September 1943
Creator: Pfriem, H.
Partner: UNT Libraries Government Documents Department

Beam Energy and System Size Dependence of Dynamical Net Charge Fluctuations

Description: We present measurements of net charge fluctuations in Au + Au collisions at {radical}s{sub NN} = 19.6, 62.4, 130, and 200 GeV, Cu + Cu collisions at {radical}s{sub NN} = 62.4, 200 GeV, and p + p collisions at {radical}s = 200 GeV using the dynamical net charge fluctuations measure {nu}{sub {+-},dyn}. We observe that the dynamical fluctuations are non-zero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate 1/N{sub ch} scaling, but display approximate 1/N{sub part} scaling. We also study the azimuthal and rapidity dependence of the net charge correlation strength and observe strong dependence on the azimuthal angular range and pseudorapidity widths integrated to measure the correlation.
Date: July 21, 2008
Creator: Coll, STAR
Partner: UNT Libraries Government Documents Department

Effect of flow fluctuations and nonflow on elliptic flow methods

Description: We discuss how the different estimates of elliptic flow are influenced by flow fluctuations and nonflow effects. It is explained why the event-plane method yields estimates between the two-particle correlation methods and the multiparticle correlation methods. It is argued that nonflow effects and fluctuations cannot be disentangled without other assumptions. However, we provide equations where, with reasonable assumptions about fluctuations and nonflow, all measured values of elliptic flow converge to a unique mean v_2,PP elliptic flow in the participant plane and, with a Gaussian assumption on eccentricity fluctuations, can be converted to the mean v_2,RP in the reaction plane. Thus, the 20percent spread in observed elliptic flow measurements from different analysis methods is no longer mysterious.
Date: April 16, 2009
Creator: Ollitrault, Jean-Yves; Poskanzer, Arthur M. & Voloshin, Sergei A.
Partner: UNT Libraries Government Documents Department

Microwave Imaging Reflectometer for TEXTOR

Description: Understanding the behavior of fluctuations in magnetically confined plasmas is essential to the advancement of turbulence-based transport physics. Though microwave reflectometry has proven to be an extremely useful and sensitive tool for measuring small density fluctuations in some circumstances, this technique has been shown to have limited viability for large amplitude, high kq fluctuations and/or core measurements. To this end, a new instrument based on 2-D imaging reflectometry has been developed to measure density fluctuations over an extended plasma region in the TEXTOR tokamak. This technique is made possible by collecting an extended spectrum of reflected waves with large-aperture imaging optics. Details of the imaging reflectometry concept, as well as technical details of the TEXTOR instrument will be presented. Data from roof-of-principle experiments on TEXTOR using a prototype system is presented, as well as results from a systematic off-line study of the advantages and limitations of the imaging reflectometer.
Date: July 9, 2002
Creator: Munsat, T.; Mazzucato, E.; Park, H.; Deng, B.H.; Domier, C.W.; N.C. Luhmann, Jr. et al.
Partner: UNT Libraries Government Documents Department


Description: The goal of the research supported by DOE-FG02-01ER45939 was to synthesize a number of experimental and theoretical approaches to understand the relationship between morphological fluctuations, the electrical response and the reliability (failure) of metallic nanostructures. The primary focus of our work was the study of metallic nanowires which we regard as prototypical of nanoscale interconnects. Our research plan has been to link together these materials properties and behaviors by understanding the phenomenon of, and the effects of electromigration at nanometer length scales. The thrust of our research has been founded on the concept that, for nanostructures where the surface-to-volume ratio is necessarily high, surface diffusion is the dominant mass transport mechanism that governs the fluctuations, electrical properties and failure modes of nanostructures. Our approach has been to develop experimental methods that permit the direct imaging of the electromagnetic distributions within nanostructures, their structural fluctuations and their electrical response. This experimental research is complemented by a parallel theoretical and computational program that describes the temporal evolution of nanostructures in response to current flow.
Date: July 31, 2006
Creator: Rous, Philip J.; Williams, Ellen D. & Fuhrer, Michael S.
Partner: UNT Libraries Government Documents Department

Pressure Fluctuations in a Common-Rail Fuel Injection System

Description: This report presents the results of an investigation to determine experimentally the instantaneous pressures at the discharge orifice of a common-rail fuel injection system in which the timing valve and cut-off valve were at some distance from the automatic fuel injection valve, and also to determine the methods by which the pressure fluctuations could be controlled. The results show that pressure wave phenomena occur between the high-pressure reservoir and the discharge orifice, but that these pressure waves can be controlled so as to be advantageous to the injection of the fuel. The results also give data applicable to the design of such an injection system for a high-speed compression-ignition engine.
Date: May 20, 1930
Creator: Rothrock, A. M.
Partner: UNT Libraries Government Documents Department

An estimate of collisional beam scattering during final focus in NDCX-II

Description: The final focus of NDCX-II contains a region with quite high plasma density. We estimate here how much collisional scatter we expect from transit through this plasma. A separate question, not explored here, is how much scatter there might be off of collective fluctuations in the neutralizing plasma, including those driven by the passage of the beam.
Date: March 23, 2010
Creator: Cohen, R.H.
Partner: UNT Libraries Government Documents Department

Scaling Behavior of the First Arrival Time of a Random-Walking Magnetic Domain

Description: We report a universal scaling behavior of the first arrival time of a traveling magnetic domain wall into a finite space-time observation window of a magneto-optical microscope enabling direct visualization of a Barkhausen avalanche in real time. The first arrival time of the traveling magnetic domain wall exhibits a nontrivial fluctuation and its statistical distribution is described by universal power-law scaling with scaling exponents of 1.34 {+-} 0.07 for CoCr and CoCrPt films, despite their quite different domain evolution patterns. Numerical simulation of the first arrival time with an assumption that the magnetic domain wall traveled as a random walker well matches our experimentally observed scaling behavior, providing an experimental support for the random-walking model of traveling magnetic domain walls.
Date: February 4, 2008
Creator: Im, M.-Y.; Lee, S.-H.; Kim, D.-H.; Fischer, P. & Shin, S.-C.
Partner: UNT Libraries Government Documents Department

On the work distribution for the adiabatic compression of a diluteclassical gas

Description: We consider the adiabatic and quasi-static compression of adilute classical gas, confined in a piston and initially equilibratedwith a heat bath. We find that the work performed during this process isdescribed statistically by a gamma distribution. We use this result toshow that the model satisfies the non-equilibrium work and fluctuationtheorems, but not the fluctation-dissipation relation. We discuss therare but dominant realizations that contribute most to the exponentialaverage of the work, and relate our results to potentially universal workdistributions.
Date: February 23, 2006
Creator: Crooks, Gavin E. & Jarzynski, Christopher
Partner: UNT Libraries Government Documents Department

An Overview of Raster Scanning for ICF-Class Laser Optics

Description: Recent work has shown that the damage resistance of both ICF-class (1600 cm') DKDP tripler crystals and SiO{sub 2} components (lenses, gratings and debris shields) benefits from laser raster scanning using pulsed lasers in the 350 nm range. For laser raster scanning to be a viable optical improvement tool for these large optics, damage improvement must be optimized while maintaining scan times of less than 8 hours/optic. In this paper we examine raster scanning with small beams from tabletop laser systems. We show that 120 Watts of average power is required for a tabletop scanning system at one optic/day. Next, we develop equations for total scan time for square and round top hat beams and round and rectangular Gaussian beams. We also consider the effect of packing geometry (square vs. hexagonal), examine the deviations from uniform coverage with each scan geometry and show that hexagonal packing yields lower scan times but is less efficient in coverage than square geometry. We also show that multiple passes at low packing densities are temporally equivalent to a single pass with higher packing density, and discuss the advantages of each method. In addition, we show that the differences between hexagonal and square scan geometries are negated when pointing errors and fluence fluctuations from the laser are considered.
Date: October 30, 2002
Creator: Runkel, M J & Nostrand, M
Partner: UNT Libraries Government Documents Department

Comment regarding"On the Crooks fluctuation theorem and the Jarzynski equality" [J. Chem. Phys. 129, 091101 (2008)]and"Nonequilibrium fluctuation-dissipation theorem of Brownian dynamics" [J. Chem. Phys. 129, 144113 (2008)]

Description: The incongruous"unexpected inapplicability of the [Crook's fluctuation theorem]" is due to an inexplicable, inappropriate use of inconsistent expressions. The girding is secure.
Date: March 4, 2009
Creator: Crooks, Gavin E
Partner: UNT Libraries Government Documents Department