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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

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

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

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

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

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


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

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

Negative differential mobility of weakly driven particles in models of glass formers

Description: We study the response of probe particles to weak constant driving in kinetically constrained models of glassy systems, and show that the probe's response can be non-monotonic and give rise to negative differential mobility: increasing the applied force can reduce the probe's drift velocity in the force direction. Other significant non-linear effects are also demonstrated, such as the enhancement with increasing force of the probe's fluctuations away from the average path, a phenomenon known in other contexts as giant diffusivity. We show that these results can be explained analytically by a continuous-time random walk approximation where there is decoupling between persistence and exchange times for local displacements of the probe. This decoupling is due to dynamic heterogeneity in the glassy system, which also leads to bimodal distributions of probe particle displacements. We discuss the relevance of our results to experiments.
Date: April 1, 2008
Creator: Jack, Robert L.; Kelsey, David; Garrahan, Juan P. & Chandler, David
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

Fluctuations and Gibbs-Thomson Law - the Simple Physics.

Description: Crystals of slightly soluble materials should be subject of relatively weak attachment/detachment fluctuations on their faces so that steps on that faces have low kink density. These steps are parallel to the most close packed lattice rows and form polygons on a crystal surface. The process responsible for implementation of the classical Gibbs-Thomson law (GTL) for the polygonal step (in two dimensions, 2D) is kink exchange between the step corners. For the 3D crystallites, this mechanism includes step exchange. If these mechanisms do not operate because of slow fluctuations the GTL is not applicable. Physics of these processes and conditions for the GTL applicability are discussed on a simple qualitative level.
Date: September 15, 2006
Creator: Chernov, A A; De Yoreo, J J & Rashkovich, L N
Partner: UNT Libraries Government Documents Department

Initial Eccentricity in Deformed 197Au+197Au and 238U+238U Collisions at RHIC

Description: Initial eccentricity and eccentricity fluctuations of the interaction volume created in relativistic collisions of deformed {sup 197}Au and {sup 238}U nuclei are studied using optical and Monte-Carlo (MC) Glauber simulations. It is found that the non-sphericity noticeably influences the average eccentricity in central collisions and eccentricity fluctuations are enhanced due to deformation. Quantitative results are obtained for Au+Au and U+U collisions at energy {radical}s{sub NN} = 200 GeV.
Date: July 7, 2010
Creator: Filip, Peter; Lednicky, Richard; Masui, Hiroshi & Xu, Nu
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

Transonic wind-tunnel investigation of static-pressure fluctuations in duct of a scale inlet model of a supersonic fighter-bomber airplane

Description: Report presenting a transonic investigation of the static-pressure fluctuations in the left duct of a scale inlet model of a supersonic fighter-bomber airplane. The amplitude and frequency of pressure fluctuations were measured using an electrical pressure gage mounted on the diffuser wall at several Mach numbers and mass-flow ratios. Results regarding amplitude characteristics of pressure fluctuations, power-spectral analyses, and flow distortions at compressor face are provided.
Date: August 6, 1957
Creator: Brooks, Joseph D.
Partner: UNT Libraries Government Documents Department

Measurement and Analysis of Turbulent Flow Containing Periodic Flow Fluctuations

Description: Memorandum presenting techniques for the measurement of the energy spectrum of flow fluctuations in both axial and lateral flow directions. A simple spectrum analysis is presented by which quantitative distinction may be made between turbulence and the flow disturbances associated with sound waves in ducts. Results regarding the measurement and analysis of turbulent-flow fields containing random and periodic flow fluctuations, effect of random sound disturbances on turbulence spectrum, and effect of combustion on combustor approach-stream spectrum are provided.
Date: August 19, 1953
Creator: Mickelsen, William R. & Laurence, James C.
Partner: UNT Libraries Government Documents Department

Measurements of the Motion of Plasma Filaments in a Plasma Ball

Description: Measurements were made of the motion of the filamentary structures in a plasma ball using high speed cameras and other optical detectors. These filaments traverse the ball radially at ~106 cm/sec at the driving frequency of ~26 kHz, and drift upward through the ball at ~1 cm/sec. Varying the applied high voltage and frequency caused the number, length, and diameter of the filaments to change. A custom plasma ball was constructed to observe the effects of varying gas pressure and species on the filament structures.
Date: January 26, 2010
Creator: M. Campanell, J. Laird, T. Provost, S. Vasquez, S.J. Zweben
Partner: UNT Libraries Government Documents Department

Ion charge state fluctuations in vacuum arcs

Description: Ion charge state distributions of cathodic vacuum arcs have been investigated using a modified time-of-flight method. Experiments have been done in double gate and burst gate mode, allowing us to study both systematic and stochastic changes of ion charge state distributions with a time resolution down to 100 ns. In the double gate method, two ion charge spectra are recorded with a well-defined time between measurements. The elements Mg, Bi, and Cu were selected for tests, representing metals of very different properties. For all elements it was found that large stochastic changes occur even at the limit of resolution. This is in agreement with fast changing arc properties observed elsewhere. Correlation of results for short times between measurements was found but it is argued that this is due to velocity mixing rather than due to cathode processes. The burst mode of time-of-flight measurements revealed the systematic time evolution of ion charge states within a single arc discharge, as opposed to previous measurements that relied on data averaged over many pulses. The technique shows the decay of the mean ion charge state as well as the level of material-dependent fluctuations.
Date: December 14, 2004
Creator: Anders, Andre; Fukuda, Kentaro & Yushkov, Georgy Yu
Partner: UNT Libraries Government Documents Department

The Remarkable Similarity Between the Scaling of Kurtosis with Squared Skewness for TORPEX Density Fluctuations and Sea-surface Temperature Fluctuations

Description: The striking similarity between the statistics of plasma density fluctuations in the TORPEX device [B. Labit et al., Phys. Rev. Lett. 98, 255002 (2007)] and sea-surface temperature fluctuations [Po Sura and P. D. Sardeshmukh, J. Phys. Oceanogr. 38, 638 (2007)] (SS) is discussed. A nonlinear Langevin theory due to SS is generalized to include linear wave propagation. An interpretation of the nonlinear Langevin equation based on statistical closure theory is proposed.
Date: February 28, 2008
Creator: Krommes, John A.
Partner: UNT Libraries Government Documents Department

Study of Turbulent Fluctuations Driven by the Electron Temperature Gradient in the National Spherical Torus Experiment

Description: Various theories and numerical simulations support the conjecture that the ubiquitous problem of anomalous electron transport in tokamaks may arise from a short-scale turbulence driven by the electron temperature gradient. To check whether this turbulence is present in plasmas of the National Spherical Torus Experiment (NSTX), measurements of turbulent fluctuations were performed with coherent scattering of electromagnetic waves. Results from plasmas heated by high harmonic fast waves (HHFW) show the existence of density fluctuations in the range of wave numbers k⊥ρe=0.1-0.4, corresponding to a turbulence scale length of the order of the collisionless skin depth. Experimental observations and agreement with numerical results from the linear gyro-kinetic GS2 code indicate that the observed turbulence is driven by the electron temperature gradient. These turbulent fluctuations were not observed at the location of an internal transport barrier driven by a negative magnetic shear.
Date: March 26, 2009
Creator: Mazzucato, E.; Bell, R. E.; Ethier, S.; Hosea, J. C.; Kaye, S. M.; LeBlanc, B. P. et al.
Partner: UNT Libraries Government Documents Department