Velocity Bias Research Articles

The Wind Profile in the Coastal Boundary Layer: Wind Lidar Measurements and Numerical Modelling

Traditionally it has been difficult to verify mesoscale model wind predictions against observations in the planetary boundary layer (PBL). Here we used measurements from a wind lidar to study the PBL up to 800 m above the surface at a flat coastal site in Denmark during a one month period in autumn. We ran the Weather Research and Forecasting numerical model with two different roughness descriptions over land, two different synoptic forcings and two different PBL schemes at two vertical resolutions and evaluated the wind profile against observations from the wind lidar. The simulated wind profile did not have enough vertical shear in the lower part of the PBL and also had a negative bias higher up in the boundary layer. Near the surface the internal boundary layer and the surface roughness influenced the wind speed, while higher up it was only influenced by the choice of PBL scheme and the synoptic forcing. By replacing the roughness value for the land-use category in the model with a more representative mesoscale roughness, the observed bias in friction velocity was reduced. A higher-order PBL scheme simulated the wind profile from the west with a lower wind-speed bias at the top of the PBL. For easterly winds low-level jets contributed to a negative wind-speed bias around 300 m and were better simulated by the first-order scheme. In all simulations, the wind-profile shape, wind speed and turbulent fluxes were not improved when a higher vertical resolution or different synoptic forcing were used.

Scintillation Measurements of the Solar Wind Velocity in Strong Scattering near the Sun

The multi-antenna scintillation method of measuring the solar-wind velocity has been very effective, particularly near the Sun and at high heliographic latitudes where direct measurements are rare or non-existent. However, scintillation observations inherently involve an LOS integration. Several methods have been used to deal with this problem, but they all require the basic assumption that contributions from different parts of the LOS add linearly. This assumption is valid for weak scintillations where the Born approximation holds, but it is not correct for strong scintillations. In this article we compare simultaneous observations of the same radio source, and therefore the same solar wind, at radio wavelengths of 32 cm and 92 cm. The 32-cm observations at the European Incoherent Scatter Radar (EISCAT) were made in weak-scattering and those at 92 cm at the Solar-Terrestrial Environment Laboratory (STEL) were made in strong-scattering mode. The results showed no significant bias in velocity caused by strong scattering, confirming that the LOS inversion techniques can be extended into the strong-scattering regime.

Performance analysis of advanced GPS receiver technique in radio frequency difficult environment

Global Positioning System (GPS) is widely used in many applications, especially on its position, velocity and timing (PVT) services. In general, a GPS receiver performs accurately and smoothly under open-sky environment. However, under urban canyon and dense foliage environments, a GPS receiver could not provide PVT services adequately due to GPS signal blockage or multipath. As a result, this paper develops and implements an advance GPS receiver technique, the Vector Tracking (VT) technique, to compare its performance with the conventional standard GPS receiver design under radio frequency difficult environments. The VT technique is based on an Extended Kalman Filter (EKF) to track all GPS satellites simultaneously and to estimate the user's position, velocity, and clock bias. The VT technique takes the advantage of the user's dynamic to predict the associated changes in the GPS signal, and it could thus facilitate the GPS receiver to bridge the temporary signal outages. Additionally, the tuning of the EKF is the key performance factor of the VT technique, and two algorithms to estimate the noise covariance, namely the correlation method and the empirical setting method, are discussed in this paper as well. Finally, this paper presents the performance gained from the developed VT technique in comparison to the conventional GPS receiver under various Radio Frequency (RF) difficult environments.

A FIRST APPLICATION OF THE ALCOCK-PACZYNSKI TEST TO STACKED COSMIC VOIDS

We report on the first application of the Alcock-Paczynski test to stacked voids in spectroscopic galaxy redshift surveys.We use voids from the Sutter et al. (2012) void catalog, which was derived from the Sloan Digital Sky Survey Data Release 7 main sample and luminous red galaxy catalogs. The construction of that void catalog removes potential shape measurement bias by using a modified version of the ZOBOV algorithm and by removing voids near survey boundaries and masks. We apply the shape-fitting procedure presented in Lavaux & Wandelt (2012) to ten void stacks out to redshift z=0.36. Combining these measurements, we determine the mean cosmologically induced "stretch" of voids in three redshift bins, with 1-sigma errors of 5-15%. The mean stretch is consistent with unity, providing no indication of a distortion induced by peculiar velocities. While the statistical errors are too large to detect the Alcock-Paczynski effect over our limited redshift range, this proof-of-concept analysis defines procedures that can be applied to larger spectroscopic galaxy surveys at higher redshifts to constrain dark energy using the expected statistical isotropy of structures that are minimally affected by uncertainties in galaxy velocity bias.

Phased-array vector velocity estimation using transverse oscillations

A method for estimating the 2-D vector velocity of blood using a phased-array transducer is presented. The approach is based on the transverse oscillation (TO) method. The purposes of this work are to expand the TO method to a phased-array geometry and to broaden the potential clinical applicability of the method. A phased-array transducer has a smaller footprint and a larger field of view than a linear array, and is therefore more suited for, e.g., cardiac imaging. The method relies on suitable TO fields, and a beamforming strategy employing diverging TO beams is proposed. The implementation of the TO method using a phased-array transducer for vector velocity estimation is evaluated through simulation and flow-rig measurements are acquired using an experimental scanner. The vast number of calculations needed to perform flow simulations makes the optimization of the TO fields a cumbersome process. Therefore, three performance metrics are proposed. They are calculated based on the complex TO spectrum of the combined TO fields. It is hypothesized that the performance metrics are related to the performance of the velocity estimates. The simulations show that the squared correlation values range from 0.79 to 0.92, indicating a correlation between the performance metrics of the TO spectrum and the velocity estimates. Because these performance metrics are much more readily computed, the TO fields can be optimized faster for improved velocity estimation of both simulations and measurements. For simulations of a parabolic flow at a depth of 10 cm, a relative (to the peak velocity) bias and standard deviation of 4% and 8%, respectively, are obtained. Overall, the simulations show that the TO method implemented on a phased-array transducer is robust with relative standard deviations around 10% in most cases. The flow-rig measurements show similar results. At a depth of 9.5 cm using 32 emissions per estimate, the relative standard deviation is 9% and the relative bias is -9%. At the center of the vessel, the velocity magnitude is estimated to be 0.25 ± 0.023 m/s, compared with an expected peak velocity magnitude of 0.25 m/s, and the beam-to-flow angle is calculated to be 89.3° ± 0.77°, compared with an expected angle value between 89° and 90°. For steering angles up to ±20° degrees, the relative standard deviation is less than 20%. The results also show that a 64-element transducer implementation is feasible, but with a poorer performance compared with a 128-element transducer. The simulation and experimental results demonstrate that the TO method is suitable for use in conjunction with a phased-array transducer, and that 2-D vector velocity estimation is possible down to a depth of 15 cm.

Influence of particle properties on the wall region in packed capillaries

Analytical columns (4.6mm i.d.) packed with core–shell particles have shown a significantly reduced eddy dispersion contribution to band broadening compared to conventional fully porous particles. It has been speculated if this is caused by the narrow particle size distribution (PSD) of the core–shell particles, as an intrinsic advantage, or by an improved packing structure that specifically reduces the transcolumn velocity biases caused by wall effects. A recent simulation study has pointed against the former proposition [A. Daneyko et al., Anal. Chem. 83 (2011) 3903]. It is more likely that the slurry packing process for core–shell particles results in bed morphologies with reduced wall effects compared to the fully porous particles with a wide PSD. To access the latter proposition experimentally we slurry packed capillary columns (100μm i.d.) with different fully porous (wide PSDs) and core–shell (narrow PSDs) particles and imaged their bed structures three-dimensionally using confocal laser scanning microscopy. This allowed us to resolve and analyze the bed morphology in these columns locally on all length scales contributing to eddy dispersion. On the transcolumn scale we observed a systematic difference between core–shell and fully porous particles: In the vicinity of the column wall the core–shell particles packed denser (closer to the bulk packing densities) and with a higher regularity than the fully porous particles. The bulk regions of all packings were effectively indistinguishable. This provides experimental evidence that the reduced eddy dispersion contribution with core–shell packings should be attributed to a higher transcolumn homogeneity rather than to an improved bed morphology on smaller length scales, e.g., to a reduced short-range disorder.

On the flow field about an electrophoretic particle

The flow field about an electrophoretic body is theoretically investigated by analytical methods. An effective boundary condition for the electric potential at particle surface is derived. This condition, which generalizes the one obtained by Levich [Physicochemical Hydrodynamics (Prentice-Hall, Englewood Cliffs, 1962), Chap. 9, p. 475], captures the effect of (convective and electromigratory) surface current in the Debye layer and is valid as far as it is legitimate to neglect ion-concentration gradient in the bulk liquid. Conditions for negligible concentration gradients are also presented and discussed. The effect of surface current determines a deviation from Morrison's “classical” theory, which predicts irrotational flow-field for any particle shape with electrophoretic velocity given by the well-known Smoluchowski formula and always directed along the applied electric field. It is shown here that in the presence of the above effect the irrotationality of the flow field is not preserved if the particle surface has non-uniform curvature. However, irrotational flow-field still subsists for a sphere and a cylinder and is analytically determined in terms of a new non-dimensional parameter, referred to as the electrophoretic number. The case of spheroidal objects is also examined in detail. In this case the flow field, though not strictly irrotational, is shown to be nearly approximated by an irrotational flow-field, which is also determined over wide ranges of electrophoretic number and spheroid aspect ratio. The quality of this approximation is expressed as a relative error on the Helmholtz-Smoluchowski condition and numerically evaluated both in longitudinal and transverse configuration. The limiting cases of spheroid degenerating into a needle and a disk are also addressed. In all above cases the respective mobilities deviate from Smoluchowski's formula and depend on the electrophoretic number. An important effect of surface ion-transport in the double layer is anisotropy of electrophoretic mobility for non-spherical objects. That always bears a bias of the electrophoretic velocity with respect to the applied electric field when the latter is not collinear with a symmetry axis of the body. For a cylinder, bias is always toward the axis. For a spheroid, it is generally toward the polar axis; however, bias toward the equatorial axis is predicted for moderately oblate spheroids. In general, the bias angle is remarkable, which is of potential consequence in technical applications of electrophoresis. Comparison of results of the present theory with experimental work from the literature is presented and discussed.

Theoretical and experimental impact of the bed aspect ratio on the axial dispersion coefficient of columns packed with 2.5 μm particles

The impact of the ratio of the column diameter to the average particle size (or bed aspect ratio) on the column performance was investigated from theoretical and experimental viewpoints. The experiments were conducted for two series of 100mm long columns, 2.1, 3.0, and 4.6mm in diameter, packed with 2.5μm fully porous particles of Bridge Ethylene Hybrid (BEH) for one series and Charged Surface Hybrid (CSH) for the other. The heights equivalent to a theoretical plate (HETP) of two low molecular weight compounds, uracil (non-retained, k=0) and naphthalene (retained, k=2.5), were determined from the true moments of the recorded peak profiles. The results showed a systematic decrease of the column performance for uracil at high flow velocities with decreasing column inner diameter, in agreement with the theoretical predictions of the variation of the trans-column eddy dispersion HETP term with decreasing bed aspect ratio. This result is consistent with the increasing volume fraction of the wall region of the column, in which the average linear velocity of the mobile phase over a distance of 5 particle diameters from the column wall is about 10% larger than in the bulk center of the column (infinite diameter column). For the retained compound, the discrepancies are levelled out due to the longer average residence time and larger particle diffusivities of retained compounds, which allow a more efficient relaxation of the radial concentration gradients. Further improvements of the performance of the larger I.D. columns (3.0 and 4.6mm I.D.) may be achieved by decreasing the harmful effect of this trans-column velocity bias by injecting and/or collecting the sample molecules in a wide central zone of the column. For 2.1mm I.D. columns, this approach would prove useful only when HPLC instruments providing a lower extra-column band broadening contribution will become available. Finally, the further minimization of the trans-column eddy dispersion HETP term and the design of new, better inlet/outlet column endfitting/frit assemblies requires newer and more accurate models of eddy dispersion in packed columns than those previously provided by Gunn and Giddings and the numerical calculation of band profiles using original functions to account for the distribution and collection of the sample molecules at the inlet and outlet of the column.

Gravity and large-scale nonlocal bias

The relationship between galaxy and matter overdensities, bias, is most often assumed to be local. This is however unstable under time evolution, we provide proofs under several sets of assumptions. In the simplest model galaxies are created locally and linearly biased at a single time, and subsequently move with the matter (no velocity bias) conserving their comoving number density (no merging). We show that, after this formation time, the bias becomes unavoidably non-local and non-linear at large scales. We identify the non-local gravitationally induced fields in which the galaxy overdensity can be expanded, showing that they can be constructed out of the invariants of the deformation tensor (Galileons). In addition, we show that this result persists if we include an arbitrary evolution of the comoving number density of tracers. We then include velocity bias, and show that new contributions appear, a dipole field being the signature at second order. We test these predictions by studying the dependence of halo overdensities in cells of fixed matter density: measurements in simulations show that departures from the mean bias relation are strongly correlated with the non-local gravitationally induced fields identified by our formalism. The effects on non-local bias seen in the simulations are most important for the most biased halos, as expected from our predictions. The non-locality seen in the simulations is not fully captured by assuming local bias in Lagrangian space. Accounting for these effects when modeling galaxy bias is essential for correctly describing the dependence on triangle shape of the galaxy bispectrum, and hence constraining cosmological parameters and primordial non-Gaussianity. We show that using our formalism we remove an important systematic in the determination of bias parameters from the galaxy bispectrum, particularly for luminous galaxies. (abridged)

The relation between subauroral polarization streams, westward ion fluxes, and zonal wind: Seasonal and hemispheric variations

We investigate the seasonal variation of the relation between SAPS (subauroral polarization streams) peak ion velocity and zonal wind velocity with coordinated DMSP and CHAMP satellite observations in both hemispheres, separately for Kp < 4 and Kp ≥ 4 geomagnetic conditions. Both SAPS and westward zonal wind peak almost at the same latitude. However, SAPS and zonal wind peak velocities show significantly different seasonal variations. SAPS peak velocities are larger in winter as compared to summer, while zonal wind peak velocities have opposite behavior, larger in summer and smaller in winter, which is valid in both hemispheres and for both geomagnetic activity levels. We reveal, for the first time, that SAPS peak westward ion fluxes, the product of SAPS ion velocity and ion density, exhibit similar seasonal variation as the zonal wind. The results indicate that the effect of SAPS on the zonal wind depends strongly on local ion densities. A linear relationship between SAPS ion fluxes and zonal wind is derived for both hemispheres, which is practically independent of geomagnetic activity. The scaling factor between ion flux and wind velocity is about the same in both hemispheres. Conversely, the background westward wind velocity (bias value in linear equation) is by about 100 m/s higher in the Northern than in the Southern Hemisphere. We attribute this difference to the effect of the large offset between geographic and magnetic poles in the Southern Hemisphere.

The spatial and velocity bias of linear density peaks and protohaloes in the Λ cold dark matter cosmology

We use high resolution N-body simulations to investigate the Lagrangian bias of cold dark matter haloes within the LCDM cosmology. Our analysis focuses on "proto-haloes", which we identify in the simulation initial conditions with the subsets of particles belonging to individual redshift-zero haloes. We then calculate the number-density and velocity-divergence fields of proto-haloes and estimate their auto spectral densities. We also measure the corresponding cross spectral densities with the linear matter distribution. We use our results to test a Lagrangian-bias model presented by Desjacques and Sheth which is based on the assumption that haloes form out of local density maxima of a specific height. Our comparison validates the predicted functional form for the scale-dependence of the bias for both the density and velocity fields. We also show that the bias coefficients are accurately predicted for the velocity divergence. On the contrary, the theoretical values for the density bias parameters do not accurately match the numerical results as a function of halo mass. This is likely due to the simplistic assumptions that relate virialized haloes to density peaks of a given height in the model. We also detect appreciable stochasticity for the Lagrangian density bias, even on very large scales. These are not included in the model at leading order but correspond to higher order corrections.

Bias, redshift space distortions and primordial nongaussianity of nonlinear transformations: application to Ly-α forest

On large scales a nonlinear transformation of matter density field can be viewed as a biased tracer of the density field itself. A nonlinear transformation also modifies the redshift space distortions in the same limit, giving rise to a velocity bias. In models with primordial nongaussianity a nonlinear transformation generates a scale dependent bias on large scales. We derive analytic expressions for the large scale bias,the velocity bias and the redshift space distortion (RSD) parameter β, as well as the scale dependent biasfrom primordial nongaussianity for a general nonlinear transformation. These biases can be expressed entirely in terms of the one point distribution function (PDF) of the final field and the parameters of the transformation. The analysis shows that one can view the large scale bias different from unity and primordial nongaussianity bias as a consequence of converting higher order correlations in densityinto 2-point correlations of its nonlinear transform. Our analysis allows one to devise nonlinear transformations with nearly arbitrary bias properties, which can be used to increase the signal in the large scale clustering limit. We apply the results to the ionizing equilibrium model of Lyman-α forest, in which Lyman-α flux F is related to the density perturbation δ via a nonlinear transformation. Velocity bias can be expressed as an average over the Lyman-α flux PDF. At z = 2.4 we predict the velocity bias of -0.1, compared to the observed value of −0.13±0.03. Bias and primordial nongaussianity bias depend on the parameters of the transformation. Measurements of bias can thus be used to constrain these parameters, and for reasonable values of the ionizing background intensity we can match the predictions to observations. Matching to the observed values we predict the ratio of primordial nongaussianity bias to bias to have the opposite sign and lower magnitude than the corresponding values for the highly biased galaxies, but this depends on the model parameters and can also vanish or change the sign.

A Methodologic Approach for Normalizing Angular Work and Velocity During Isotonic and Isokinetic Eccentric Training

Resistance exercise training commonly is performed against a constant external load (isotonic) or at a constant velocity (isokinetic). Researchers comparing the effectiveness of isotonic and isokinetic resistance-training protocols need to equalize the mechanical stimulus (work and velocity) applied. To examine whether the standardization protocol could be adjusted and applied to an eccentric training program. Controlled laboratory study. Controlled research laboratory. Twenty-one sport science male students (age = 20.6 ± 1.5 years, height = 178.0 ± 4.0 cm, mass = 74.5 ± 9.1 kg). Participants performed 9 weeks of isotonic (n = 11) or isokinetic (n = 10) eccentric training of knee extensors that was designed so they would perform the same amount of angular work at the same mean angular velocity. Angular work and angular velocity. The isotonic and isokinetic groups performed the same total amount of work (-185.2 ± 6.5 kJ and -184.4 ± 8.6 kJ, respectively) at the same angular velocity (21 ± 1°/s and 22°/s, respectively) with the same number of repetitions (8.0 and 8.0, respectively). Bland-Altman analysis showed that work (bias = 2.4%) and angular velocity (bias = 0.2%) were equalized over 9 weeks between the modes of training. The procedure developed allows angular work and velocity to be standardized over 9 weeks of isotonic and isokinetic eccentric training of the knee extensors. This method could be useful in future studies in which researchers compare neuromuscular adaptations induced by each type of training mode with respect to rehabilitating patients after musculoskeletal injury.

Inertial Navigation Aiding by Stationary Updates

Sensor-aided inertial navigation has successfully been used for decades for localization of a roving body. When the rover is known to be stationary, artificial “stationary” measurements (i.e., zero velocity and/or zero angular rate) may be imposed. This corrects the velocity, attitude, and inertial measurement unit (IMU) biases, which decreases the rate of drift of the position and attitude. Implementation requires reliable automated tests to detect periods when the vehicle is stationary. Due to cost concerns, methods that use sensors that are already on the vehicle are preferred. This paper reviews existing stationary detection methods and proposes a new frequency domain approach, using only IMU data, to detect stationarity, with specifications and analysis for land vehicles. The performance of this new approach is evaluated in both theory and practice. In addition, this paper presents analytic and numeric evaluations of the observability of the inertial navigation system (INS) error states with stationary updates. Improvements in localization performance in an INS with stationary detection and aiding is shown experimentally.

Measurement of the eddy dispersion term in chromatographic columns. II. Application to new prototypes of 2.3 and 3.2 mm I.D. monolithic silica columns

The mass transfer mechanisms in silica monolithic columns of the second generation were investigated, using four research samples (two 2.3mm×50mm and two 3.2mm×50mm silica rods) provided by their manufacturer. The heights equivalent to a theoretical plate (HETP) of these columns were measured in a range of mobile phase velocities, following a meticulous experimental protocol. The coefficients of the van Deemter equation (longitudinal diffusion term B/uS, skeleton/eluent mass transfer resistance term CuS, and eddy diffusion term A) were determined. The protocol includes using the peak parking method (to determine the longitudinal diffusion term), an accurate model of effective diffusion in silica monolithic structures (to determine the skeleton/eluent mass transfer resistance term), and an accurate method to measure the column HETP and determine the eddy diffusion term. The results show that the minimum plate heights of these new monolithic columns ranges between 4 and 5μm, three to four times lower than those observed for monolithic columns of the first generation. A detailed analysis of the eddy diffusion term demonstrates that this improvement in column efficiency is partly explained by the reduction of the domain size (the sum of the skeleton and throughpore sizes, −40%) but mostly by an increase of the radial homogeneity of the monolithic rods. The columns of this second generation exhibit residual trans-column relative velocity biases as low a 1.4% (instead of 3% for previous columns), a value which is comparable to those observed in 4.6mm I.D. columns packed with sub-3μm core–shell particles, with which they might become competitive.

Investigation of Hydraulic Characteristics of a Volute-type Discharge Passage based on CFD

The internal flow patterns of a volute-type discharge passage were investigated in a mixed-flow pumping system based on CFD by using the RNGturbulence model to close the time-averaged Navier-Stokes equations. According to the numerical analysis of the internal flow, the hydraulic characteristics of the volute-type discharge passage and the velocity distribution features in several key cross sections were analyzed and quantitatively calculated in terms of velocity distribution uniformity and bias angle. The computed results show that the internal flow field is very complicated involving flow separation and vortex in some regions and the velocity distribution is uneven. The uniformity curves of axial velocities in the outlet cross-section of the volute and the outlet cross-section of the passage are protruding ones while the bias angle curves in the same cross-sections are concave ones, both of them reaching their maximum or minimum value respectively at the flow rate corresponding to the best efficiency point of the pumping system. The hydraulic loss of the volute-type discharge passage varies with the discharge and reaches its minimum when the pumping system efficiency approaches its highest. When the pumping system operates under off-design condition on the large flow rate side, the hydraulic loss of the passage tends to increase rapidly causing the pumping system efficiency to drop sharply. Therefore, appropriate regulation methods should be adopted to adjust the pump operating condition to ensure the pumping system working within high efficiency zone.

Measurement of the eddy dispersion term in chromatographic columns: III. Application to new prototypes of 4.6 mm I.D. monolithic columns

We investigated the mass transfer mechanism in four research prototypes of silica monolithic columns of the second generation provided by their manufacturer (Merck KGaA, Darmstadt, Germany). The heights equivalent to a theoretical plate (HETP) of these columns were measured. The different contributions to the total HETP (longitudinal diffusion term B/uS, skeleton/eluent mass transfer resistance term CuS, and eddy diffusion term A) were determined experimentally for a non-retained (uracil) and for a retained (naphthalene) compound. We used the peak parking method to determine the longitudinal diffusion term, a recently developed accurate model of effective diffusion in silica monolithic structures to determine the skeleton/eluent mass transfer resistance term, and an accurate method of measurement of the total column HETP to determine the eddy diffusion term. The results show that the minimum plate heights of these monolithic column prototypes range between 6 and 7μm for retained analytes, three times lower than those observed for monolithic columns of the first generation. A detailed analysis of the eddy diffusion term demonstrates that the improvement observed in the column efficiency is explained in part by the 40% reduction of the domain size (which provides thinner half-height peak width) but mostly by a two-fold decrease of the radial velocity bias across the silica rods (which provides more symmetrical peaks). Yet, the rods in these columns exhibit a residual radial heterogeneity leading to a minimum HETP of only 10μm for non-retained compounds.

Increasingly complex bimanual multi-frequency coordination patterns are equally easy to perform with on-line relative velocity feedback

An experiment was conducted to determine whether multi-frequency continuous bimanual circling movements of varying difficulty (1:2, 2:3, 3:4, and 4:5) could be effectively performed following relatively little practice when on-line continuous relative velocity feedback is provided. The between-subjects results indicate extremely effective bimanual multi-frequency performance for all coordination patterns with relatively stable and continuous movements of both limbs. The findings suggest that the previous performance effects using Lissajous feedback with reciprocal movement can be extended to circling movements using on-line relative velocity feedback. Contrary to the long-held position that these coordination patterns result in increasing difficulty, we failed to find systematic relative velocity error, variability, or bias differences between the participants performing the various multi-frequency coordination patterns. Indeed, coordination error, variability, and biases were remarkably low for each of the tasks. The results clearly indicate the ease with which participants are able to produce bimanual coordination patterns typically considered difficult if not impossible when salient visual information is provided that allows the participants to detect and correct their coordination errors.

Evaluation of Tricuspid and Pulmonary Valves Using Epicardial and Transesophageal Echocardiography—A Comparative Study

To compare measurements obtained by transesophageal echocardiography (TEE) and epicardial echocardiography (EE) for evaluation of the tricuspid valve (TV) and pulmonary valve (PV). Prospective observational. University hospital. Patients undergoing elective coronary artery bypass grafting with or without aortic valve replacement. After routine intraoperative TEE, EE was performed to compare measurements obtained by the 2 methods. After institutional review board approval, 25 patients >18 years old were recruited. Biases with EE versus TEE for E and A waves were 11.9 cm/second (95% confidence interval [CI], 48.2 to -24.4) and 6.8 cm/second (95% CI, 28 to -15), respectively, and for E/A ratio was 0.08 (95% CI, 1.2 to -1). Pulmonary velocity bias was 57.94 cm/second (95% CI, 192.9 to -76.98), with higher values using EE. Bias for pulmonary trunk diameter was -0.31 cm (95% CI, 1.5 to -2.1). For quality of images, means were 2.4 (standard deviation [SD], 1.0) for EE and 2.3 (SD, 0.57) with TEE for TV and 2.4 (SD, 1.0) with EE and 2.5 (SD, 1.0) with TEE for PV. For the number of leaflets visualized, means were 2.2 (SD, 1.0) with EE and 2.5 (SD, 0.5) with TEE for TV and 2.5 (SD, 0.5) for EE and 1.3 (SD, 1.1) with TEE for PV. There was good agreement for Doppler measurements across TVs; however, measurements across PVs were significantly higher with EE versus TEE. TV Doppler measurements were difficult to acquire even for surgeons experienced in epiaortic scanning.

Kinetic investigation of narrow-bore columns packed with prototype sub-2 μm superficially porous particles with various shell thickness

The recent successful breakthrough of sub-3 μm shell particles in HPLC has triggered considerable research efforts toward the design of new brands of core-shell particles. We investigated the mass transfer mechanism of a few analytes in narrow-bore columns packed with prototype 1.7 μm shell particles, made of 1.0, 1.2, and 1.4 μm solid nonporous cores surrounded by porous shells 350, 250, and 150 nm thick, respectively. Three probe solutes, uracil, naphthalene, and insulin, were chosen to assess the kinetic performance of these columns. Inverse size exclusion chromatography, peak parking experiments, and the numerical integration of the experimental peak profiles were carried out in order to measure the external, internal, and total column porosities, the true bulk diffusion coefficients of these analytes, the height equivalent to a theoretical plate, the longitudinal diffusion term, and the trans-particle mass transfer resistance term. The residual eddy diffusion term was measured by difference. The results show the existence of important trans-column velocity biases (7%) possibly due to the presence of particle multiplets in the slurry mixture used during the packing process. Our results illustrates some of the difficulties encountered by scientists preparing and packing shell particles into narrow-bore columns.