Ensemble-averaged Data Research Articles

Measurement of Single Macromolecule Orientation by Total Internal Reflection Fluorescence Polarization Microscopy

A new approach is presented for measuring the three-dimensional orientation of individual macromolecules using single molecule fluorescence polarization (SMFP) microscopy. The technique uses the unique polarizations of evanescent waves generated by total internal reflection to excite the dipole moment of individual fluorophores. To evaluate the new SMFP technique, single molecule orientation measurements from sparsely labeled F-actin are compared to ensemble-averaged orientation data from similarly prepared densely labeled F-actin. Standard deviations of the SMFP measurements taken at 40 ms time intervals indicate that the uncertainty for individual measurements of axial and azimuthal angles is ∼10° at 40 ms time resolution. Comparison with ensemble data shows there are no substantial systematic errors associated with the single molecule measurements. In addition to evaluating the technique, the data also provide a new measurement of the torsional rigidity of F-actin. These measurements support the smaller of two values of the torsional rigidity of F-actin previously reported.

Quantization Error and Resolution in Ensemble Averaged Data With Noise

We investigate the properties of ensemble averaged data from a uniform quantizer, when the quantizer input signal is noisy. An expression for the mean-square error (MSE) MSE(/spl sigma/,N) of the ensemble averaged data, accounting for an ensemble of finite length N, and noise RMS /spl sigma/, is obtained. Previously published results for N=1 and N/spl rarr//spl infin/ are recovered. For intermediate N, we show that there is an optimal noise RMS, /spl sigma//sub opt/(N), which minimizes the MSE. Such a minimum point exists regardless of the type of noise probability distribution function. Conditions on /spl sigma/ and N for achieving a smaller MSE than in the noise-free case (/spl Delta//sup 2//12) are discussed. The convergence properties of MSE(/spl sigma/,N) for increasing N, and the effect of applying uniformly distributed dither, is established.

Exciton migration in a polythiophene: Probing the spatial and energy domain by line-dipole Förster-type energy transfer

We study exciton migration in low molecular weight poly[3-(2,5-dioctylphenyl)thiophene] in dilute solution by means of ultrafast spectroscopy and Monte Carlo simulations of resonance energy transfer using the line-dipole Forster approach. The model includes the build-up of polymer chains, site-selective exciton generation, and diffusion through incoherent energy transfer. Time-resolved, ensemble-averaged experimental data are reproduced, namely photoluminescence spectral migration and stimulated emission anisotropy decays measured by streak camera and femtosecond transient absorption spectroscopy under site-selective excitation conditions. Importantly, the relatively simple line-dipole Forster-type approach beyond the point-dipole approximation reproduces both experiments quantitatively. Since explicit chain conformations are used in the model, the simulations yield a descriptive microscopic picture of exciton migration. The effective conjugation length (l(seg)=2.9 nm, 7.4 monomer units) and the disorder of the chains (Omega=0.8) are yielded as the only fitting parameters. We find an extra component that is not covered by our fits in anisotropy decays at early times for high excitation energies. This is interpreted within the context that the effective conjugation is limited by conformational disorder.

Unsteady Boundary Layer Development Due to Wake Passing Effects on a Highly Loaded Linear Compressor Cascade

The effects of wake passing on boundary layer development on a highly loaded linear compressor cascade were investigated in detail on the suction side of a compressor blade. The experiments were performed in the High Speed Cascade Wind Tunnel of the Institut fuer Strahlantriebe at Mach and Reynolds numbers representative for real turbomachinery conditions. The experimental data were acquired using different measurement techniques, such as fast-response Kulite sensors, hot-film array and hot-wire measurements. The incoming wakes clearly influence the unsteady boundary layer development. Early forced transition in the boundary layer is followed in time by calmed regions. Large pressure fluctuations detectable in the ensemble averaged Kulite data reveal the existence of coherent structures in the boundary layer. Distinct velocity variations inside the boundary layer are amplified when approaching the blade surface. The time–mean momentum thickness values are reduced compared to the steady ones and therefore clarify the potential for a loss reduction due to wake passing effects.

Global validation of two-channel AVHRR aerosol optical thickness retrievals over the oceans

The paper presents validation results for the aerosol optical thickness derived by applying a two-channel retrieval algorithm to Advanced Very High Resolution Radiometer (AVHRR) radiance data. The satellite retrievals are compared with ship-borne sun-photometer results. The comparison of spatial and temporal statistics of the AVHRR results and the ship measurements shows a strong correlation. The satellite retrieval results obtained with the original algorithm for a wavelength of 0.55μm are systematically higher than the sun-photometer measurements in the cases of low aerosol loads. The ensemble averaged satellite-retrieved optical thickness overestimates the ensemble averaged sun-photometer data by about 11% with a random error of about 0.04. Increasing the diffuse component of the ocean surface reflectance from 0.002 to 0.004 in the AVHRR algorithm produces a better match, with the ensemble-averaged AVHRR-retrieved optical thickness differing by only about 3.6% from the sun-photometer truth and having a small offset of 0.03.

A comparison of Eulerian and Lagrangian schemes for the simulation of an incompressible planar jet

In this investigation solutions have been obtained using an Eulerian time accurate fractional step Direct Numerical Simulation (DNS) scheme for a homogeneous incompressible planar jet and the results compared with those obtained using a Lagrangian Direct Simulation Monte-Carlo (DSMC) method. Comparisons were made of various flow features using plots constructed from instantaneous and ensemble averaged data. Details of the schemes, computational requirements and the accuracy obtained with each of the methods will be presented.

Measurement of the turbulent diffusivity in the near field of variable density jets using conditional velocimetry

Pulsed laser Mie scattering and laser Doppler velocimetry (LDV), both conditioned on the origin of the seed particles, have been successively performed in turbulent jets with variable density. In the early stages of the jet developments, significant differences are measured between the ensemble average LDV data obtained by jet seeding and those obtained by seeding the ambient air. Careful analysis of the marker statistics shows that this difference is a quantitative measure of the turbulent mixing. The good agreement with gradient–diffusion modelling suggests the validity of a general diffusion equation where the velocities involved are expressed in terms of ensemble conditional Favre averages. This operator accounts for all events (including intermittent ones) and for variations in the density of the marked fluid whose velocity is still specified by the binary origin of the marker.

Experimental Investigation of a Transonic Aspirated Compressor

Abstract The experimental investigation of a transonic aspirated stage demonstrating the application of boundary layer aspiration to increase stage work is presented. The stage was designed to produce a pressure ratio of 1.6 at a tip speed of 750ft∕s resulting in a stage work coefficient of 0.88. The primary aspiration requirement for the stage is a bleed fraction 0.5% of the inlet mass flow on the rotor and stator suction surfaces. Additional aspiration totaling 2.8% was also used at shock impingement locations and other locations on the hub and casing walls. Detailed rotor and stator flow field measurements, which include time-accurate and ensemble-averaged data, are presented and compared to three-dimensional viscous computational analyses of the stage. The stage achieved a peak pressure ratio of 1.58 and through-flow efficiency of 90% at the design point. In addition, the stage demonstrated good performance with an aspiration lower than the design requirement, and a significant off-design flow range below that predicted by the computational analysis.

Validity and reliability of diastolic pulse contour analysis (windkessel model) in humans.

The present study assessed (1) the impact of the measurement site (lower versus upper extremity) on the corresponding compliance variables and (2) the overall reliability of diastolic pulse contour (Windkessel-derived) analysis in normal and hypertensive subjects. Arterial tonograms were recorded in the supine position from the radial and posterior tibial arteries in 20 normotensive (116+/-12/68+/-8 mm Hg) and 27 essential hypertensive subjects (160+/-16/94+/-14 mm Hg). Ensemble-averaged data for each subject were fitted to a first-order lumped-parameter model (basic Windkessel) to compute whole-body arterial compliance (C(A)) and to a third-order lumped-parameter model (modified Windkessel) to compute proximal compliance (C(1)) and distal compliance (C(2)). Despite high-fidelity waveforms in each subject, the first-order Windkessel model did not yield interpretable (positive) values for C(A) in 50% of normotensives and 41% of hypertensives, whereas the third-order model failed to yield interpretable C(1) or C(2) results in 15% of normotensives and 41% of hypertensives. No between-site correlations were found for the first-order time constant, 2 of the 3 third-order model curve-fitting constants, or C(A), C(1), or C(2) (P>0.50). Mean values for all 3 compliance variables were higher for the leg than the arm (P<0.05 each). We conclude that differences in Windkessel-derived compliance values in the arm and leg invalidate whole-body model assumptions and suggest a strong influence of regional circulatory properties. The validity and utility of Windkessel-derived variables is further diminished by the absence of between-site correlations and the common occurrence of uninterpretable values in hypertensive subjects.

Molecular dynamic simulation of structural, mobility effects between dilute aqueous CH3CN solution and crosslinked PAA

Using molecular simulations we have investigated the diversity of the mobility of water molecules in a three-component system of crosslinked PAA/water/acetonitrile affected by local structural inhomogeneities. We examine quantitative analysis concepts for the extraction of local structure and dynamics properties in anisotropic fluids from molecular dynamics simulations. By calculation of local translational and reorientational correlation functions on trajectories of individual molecules in equivalent local environments, it is possible to extract local reorientational and translational diffusion quantities. In our simulated liquid mixtures, we classify the environments of different centres like crosslinkers, side chains, pores and water regions in the complex structure. We get insight into the local molecular dynamics of water molecules from the calculation of local reorientational relaxation times and diffusion coefficients from the slope of the mean square displacements of the water molecules in the specific local environments. In addition, we calculate a distance dependent curve for the reorientational mobility of the water molecules on the PAA/water interface. Finally, we extract dynamical information by linking the ensemble-averaged diffusion data from the simulations to stimulated spin-echo experiments with pulsed magnetic field gradients to study time dependent local self-diffusion processes of the water solution in swollen crosslinked polyacrylamide gels.

Development and Assessment of Hot‐Film Sensor Technique for the Multistage Turbomachinery Environment

The slanted hot-film technique has been successfully modified and adapted for flow measurement in the complex and hostile environment encountered in multistage turbomachinery. The sources of probe and prong vibrations and methods of eliminating them are discussed. The incorporation of compressibility corrections and improvements in calibration techniques developed are discussed. The procedure is validated against the data from a five-hole probe. Suggestions are made for improving the accuracy of measurement. The ensemble-averaged data is resolved into time average, blade periodic, blade aperiodic, and non-deterministic velocity components. This is used to model the turbomachinery flow field. The flow is found to be highly complex with appreciable secondary flow in the casing region, and large flow unsteadiness in the suction-casing corner region.

Molecular dynamics simulation of structural, mobility effects between dilute aqueous CH3CN solution and crosslinked PAA : Part 2. Dynamics

Using molecular simulations we have investigated the diversity of the mobility of water molecules in a three-component system of crosslinked PAA/water/acetonitrile affected by local structural inhomogeneities. We examine quantitative analysis concepts for the extraction of local structure and dynamics properties in anisotropic fluids from molecular dynamics simulations. By calculation of local translational and reorientational correlation functions on trajectories of individual molecules in equivalent local environments, it is possible to extract local reorientational and translational diffusion quantities. In our simulated liquid mixtures, we classify the environments of different centres like crosslinkers, side chains, pores and water regions in the complex structure. We get insight into the local molecular dynamics of water molecules from the calculation of local reorientational relaxation times and diffusion coefficients from the slope of the mean square displacements of the water molecules in the specific local environments. In addition, we calculate a distance dependent curve for the reorientational mobility of the water molecules on the PAA/water interface. Finally, we extract dynamical information by linking the ensemble-averaged diffusion data from the simulations to stimulated spin-echo experiments with pulsed magnetic field gradients to study time dependent local self-diffusion processes of the water solution in swollen crosslinked polyacrylamide gels.

The Influence of Rotor Detuning on Rotor-Stator Interaction Generated Acoustic Response

In a turbomachine, the stator row is excited by the upstream rotor and responds at multiples of rotor blade pass frequency, resulting in a discrete blade pass frequency tone. Rotor detuning, i.e., unequal circumferential rotor blade spacing, decreases this fundamental tone by breaking the fundamental periodicity of blade passing. However, the stator row responds at additional multiples of rotor shaft pass frequency. This paper is directed at investigating the influence of rotor detuning on discrete frequency acoustic response. Complete data were acquired including acoustic mode and stator vane unsteady surface pressure data. Microphones in a circumferential array upstream of the rotor and stator are sampled simultaneously over one rotor revolution, and an ensemble averaged data set is acquired. A dual transform is then utilized to determine the acoustic pressure amplitude as a function of frequency and spatial mode. The stator vane acoustic response is also calculated from unsteady stator vane surface pressure measurements, and the spectrum of the acoustic response is compared with data from the circumferential microphone array. Rotor detuning is shown to have a significant effect on the discrete frequency noise. Although the stator when forced by the detuned rotor responded at more frequencies, there is an overall reduction in the total intensity level for a range of rotor speeds. Nomenclature Symbol Description ax freestream speed of sound c stator chord I acoustic intensity EL intensity level k reduced frequency k = coc/W k axial wave number kg tangential wave number Ic ... criticalNyquistmode 1 ^ an eigenvalue M axial mean flow Mach number n rotor harmonic N number of microphones number of rotor blades number of stator vanes p acoustic pressure P spatial transform of acoustic pressure s stator pitch spacing SPL sound pressure level r radial coordinate Uoo mean axial velocity Ujj axial acoustic velocity v stator index, v = 0,1,..., NVmes W Freestream velocity in two dimensions x axial direction z blade chord coordinate a mean stator angle-of-attack ctyp Two dimensional axial wave number P Two dimensional tangential wave number s level of detuning Tw unsteady bound vorticity complex magnitude 6 circumferential coordinate r^jj tuned rotor tangential spacing freestream density freestream density frequency co = nNBIadesQ rotor circular frequency pressure pattern phase speed axial coordinate A6,

Simulations of bypass transition

Bypass transition in an initially laminar boundary layer beneath free-stream turbulence is simulated numerically. New perspectives on this phenomenon are obtained from the numerical flow fields. Transition precursors consist of long backward jets contained in the fluctuating u-velocity field; they flow backwards relative to the local mean velocity. The jets extend into the upper portion of the boundary layer, where they interact with free-stream eddies. In some locations a free-stream perturbation to the jet shear layer develops into a patch of irregular motion – a sort of turbulent spot. The spot spreads longitudinally and laterally, and ultimately merges into the downstream turbulent boundary layer. Merging spots maintain the upstream edge of the turbulent region. The jets, themselves, are produced by low-frequency components of the free-stream turbulence that penetrate into the laminar boundary layer. Backward jets are a component of laminar region streaks.A method to construct turbulent inflow from Orr–Sommerfeld continuous modes is described. The free-stream turbulent intensity was chosen to correspond with the experiment by Roach &amp; Brierly (1990). Ensemble-averaged numerical data are shown to be in good agreement with laboratory measurements.

Periodic Transition on an Axial Compressor Stator: Incidence and Clocking Effects: Part II—Transition Onset Predictions

Transition onset observations from a 1.5-stage axial compressor outlet stator presented in Part I of this paper are compared with the predictions of conventional transition correlations applied in a quasi-steady manner. The viscous/inviscid interaction code MISES is used to predict the blade surface pressure distributions and boundary layer development. The temporal variation in transition onset is then predicted using ensemble-averaged free-stream turbulence data from the compressor measurements. This simple procedure captures most significant features of the complex transition process on the compressor, and is clearly superior to fixed transition models based on long-term average free-stream turbulence levels. Parallel computations for both natural and bypass transition modes indicate that the natural transition mode tends to dominate on the compressor. This is at variance with turbine airfoil experience, where bypass transition is clearly more important. Comparison of prediction and experiment highlights the significance of leading edge potential flow interactions in promoting periodic wake-induced transition. Viscous/inviscid interactions in the neighborhood of transition can also have an important influence on boundary layer stability and separation phenomena.

Optical determination of field angular correlation for transmission through three-dimensional turbid media

A method is presented for measuring the correlation between the optical fields scattered in different directions by an arbitrary three-dimensional turbid medium. The field angular correlation function is obtained by processing ensemble average intensity data, which are recorded experimentally by a single-channel Shack–Hartmann wave-front sensor. Some general properties of scattered light are expressed in terms of the field angular correlation function, and the correlation function is measured for transmission through a suspension of microspheres under nonballistic transport conditions.

Application of Two-Dimensional Laser-Induced Fuel Tracer Fluorescence for Ion Current Evaluation

An experiment is performed under well-controlled conditions to evaluate the prospects for fuel-to-air equivalence ratio determination by ion current measurements. To this end, two-dimensional laser-induced fluorescence (2D LIF) is utilized to acquire the true, cycle-resolved equivalence ratio conditions in the vicinity of the electrode gap. The experiment is conducted in an optically accessible combustion cell of constant volume, where methane doped with a fluorescent tracer, acetone, is injected into quiescent air and ignited by an electrical discharge. Different degrees of fuel homogeneity are achieved by varying the air/fuel mixing time prior to ignition. Apart from the local equivalence ratio, the following parameters are measured: the ion current, the combustion chamber pressure and the global equivalence ratio, which is derived from the oxygen content of the exhaust gases and is used for calibration of the 2D LIF data. After data extraction, the ion current and equivalence ratio parameters are examined for interrelations, both as ensemble averages and as individuals. A significant correlation is identified between the local equivalence ratio at the electrode gap and the ignition delay, which is defined as the time delay from spark initiation to the occurrence of a detectable second ion current peak. However, the ignition delay data alone can not be used for unambiguous determination of the local equivalence ratio, since the ignition delay exhibits a minimum for approximately stoichiometric conditions at the electrode gap. Further evaluation reveals that integrated portions of the ion current signal, i.e., the electrical charge, scale with the local equivalence ratio for lean/stoichiometric mixtures. At homogeneous and quiescent conditions, high levels of correlation are found for both ensemble averaged and cycle-resolved data. The presence of strong fuel inhomogeneities, and a simultaneously distinct flow field, however, generally reduces the correlation considerably. Nevertheless, applying the ion current diagnostics to a particular device, mapping the relevant operating conditions and acquiring a specific “fingerprint” behavior of the ion current parameters, can enable practical use of this technique.

Development of wall surface tangent DPIV measurement techniques for arterial branch models.

Experimental techniques for measuring unsteady flow in a glass arterial bifurcation model have been developed to aid in quantifying three-dimensional wall shear fluctuations associated with arterial disease. The unique feature of the current technique is the use of a "curved" laser sheet, which was everywhere tangent to the inner wall of a daughter tube in an arterial bifurcation model. Surface tangent velocity vector field measurements were made to demonstrate the potential of this technique. Ensemble-averaged data showing weak secondary flows as well as statistical distributions of flow angles are presented. Measurements of this type may be used to estimate mean and instantaneous wall shear magnitude and direction, data that are necessary for understanding the importance of circumferential motions on arterial disease.

Constrained least-squares estimation in deconvolution from wave-front sensing

We address the optimal processing of astronomical images using the deconvolution from wave-front sensing technique (DWFS). A constrained least-squares (CLS) solution which incorporates ensemble average DWFS data is derived using Lagrange minimization. The new estimator requires DWFS data, noise statistics, OTF statistics, and a constraint. The constraint can be chosen such that the algorithm selects a conventional regularization constant automatically. No ad hoc parameter tuning is necessary. The algorithm uses an iterative Newton-Raphson minimization to determine the optimal Lagrange multiplier. Computer simulation of a 1 m telescope imaging through atmospheric turbulence is used to test the estimation scheme. CLS object estimates are compared with those processed via manual tuning of the regularization constant. The CLS algorithm provides images with comparable resolution and is computationally inexpensive, converging to a solution in less than 10 iterations.

Mean Stator Loading Effect on the Acoustic Response of a Rotating Cascade

Discrete-frequency tones generated by unsteady blade row interactions are of particular concern in the design of advanced turbine engines. With a rotor ‐ stator mounted in a duct, only certain specie c spatial modes are generated by the rotor ‐ stator interaction, where the generated modes are a function of the number of rotor blades and stator vanes. In addition, only some of these modes propagate to the far e eld, with the rest decaying before reaching the far e eld. Thus, it is only those spatial modes that propagate to the far e eld that represent the discrete-frequency noise received by an observer. This paper’ s aim is to determine the ine uence of steady stator loading on the acoustic response of an annular cascade. To accomplish this, the existence of the propagating modes generated by a rotor ‐ stator interaction must e rst be verie ed. Microphones placed in an axial plane in the outer annulus of the inlet of the Purdue Annular Cascade Research Facility are sampled simultaneously over one rotor revolution, and an ensemble-averaged data set is acquired. With the microphone signals treated as a function of time and space, dual Fourier transforms are utilized to determine the magnitude of the spatial modes at multiples of blade pass frequency. The wave equation is used to predict the propagation characteristics of these modes in the inlet duct. The two predicted propagating modes were found to have signie cantly higher amplitudes than modes that were predicted to decay, or were not to be generated by the rotor ‐ stator interaction, and steady stator loading had a profound ine uence on acoustic response of the cascade. The acoustic response at blade pass and twice blade pass frequency increased by more than 20 dB for angles of attack ranging from 220 to 25 deg.