Measurement of the temperature of the resting rotor in analytical ultracentrifugation

Accurate measurements of rotor temperature are critical for the interpretation of hydrodynamic parameters in analytical ultracentrifugation. We have recently developed methods for a more accurate determination of the temperature of a spinning rotor using iButton temperature loggers. Here we report that the temperature measured with the iButton on the counterbalance of a resting rotor, following thermal equilibration under high vacuum, closely corresponded to the temperature of the spinning rotor with a precision better than 0.2 °C. This strategy offers an inexpensive and straightforward approach to monitor the accuracy of the temperature calibration and determine corrective temperature offsets.     

Transport Phenomena in Zonal Centrifuge Rotors: I. Velocity and Shear-Stress Distributions of Fluid During Acceleration

An analysis is presented for the evaluation of velocity components and shear-stress distributions of fluid in zonal centrifuge rotors during acceleration. Analytical expressions for the distribution of tangential and radial velocity components and the tangential shear-stress and the radial shear-stress distributions of fluid are obtained for the transient case. Characteristics of each distribution for a typical density gradient liquid in a zonal centrifuge rotor are computed from the relations derived, and are presented as figures. An unusual phenomenon—the tangential velocity of the gradient exceeding the velocity of the rotor during a particular period of acceleration—is demonstrated.     

Temperature effects on snapping performance in the common snapper Chelydra serpentina (Reptilia, Testudines)

Studies on the effect of temperature on whole-animal performance traits other than locomotion are rare. Here we investigate the effects of temperature on the performance of the turtle feeding apparatus in a defensive context. We measured bite force and the kinematics of snapping in the Common Snapping Turtle (Chelydra serpentina) over a wide range of body temperatures. Bite force performance was thermally insensitive over the broad range of temperatures typically experienced by these turtles in nature. In contrast, neck extension (velocity, acceleration, and deceleration) and jaw movements (velocity, acceleration, and deceleration) showed clear temperature dependence with peak acceleration and deceleration capacity increasing with increasing temperatures. Our results regarding the temperature dependence of defensive behavior are reflected by the ecology and overall behavior of this species. These data illustrate the necessity for carefully controlling T(b) when carrying out behavioral and functional studies on turtles as temperature affects the velocity, acceleration, and deceleration of jaw and neck extension movements. More generally, these data add to the limited but increasing number of studies showing that temperature may have important effects on feeding and defensive performance in ectotherms.     

A simple method for computing sprint acceleration kinetics from running velocity data: Replication study with improved design

Measuring the ground reaction forces (GRF) underlying sprint acceleration is important to understanding the performance of such a common task. Until recently direct measurements of GRF during sprinting were limited to a few steps per trial, but a simple method (SM) was developed to estimate GRF across an entire acceleration. The SM utilizes displacement- or velocity-time data and basic computations applied to the runner’s center of mass and was validated against compiled force plate (FP) measurements; however, this validation used multiple-trials to generate a single acceleration profile, and consequently fatigue and error may have introduced noise into the analyses. In this study, we replicated the original validation by comparing the main sprint kinetics and force-velocity-power variables (e.g. GRF and its horizontal and vertical components, mechanical power output, ratio of horizontal component to resultant GRF) between synchronized FP data from a single sprinting acceleration and SM data derived from running velocity measured with a 100 Hz laser. These analyses were made possible thanks to a newly developed 50-m FP system providing seamless GRF data during a single sprint acceleration. Sixteen trained male sprinters performed two all-out 60-m sprints. We observed good agreement between the two methods for kinetic variables (e.g. grand average bias of 4.71%, range 0.696 ± 0.540–8.26 ± 5.51%), and high inter-trial reliability (grand average standard error of measurement of 2.50% for FP and 2.36% for the SM). This replication study clearly shows that when implemented correctly, this method accurately estimates sprint acceleration kinetics.     

Fluctuations in acceleration during voluntary contractions lead to greater impairment of movement accuracy in old adults.

The purpose of the study was to assess the effect of movement velocity on the relation between fluctuations in acceleration and the ability to achieve a target velocity during voluntary contractions performed by young (29.5 +/- 4.3 yr) and old (74.9 +/- 6.2 yr) adults. Subjects performed concentric and eccentric contractions with the first dorsal interosseus muscle while lifting a submaximal load (15% of maximum) at six movement velocities (0.03-1.16 rad/s). Fluctuations in acceleration, the accuracy of matching the target velocity, and electromyographic (EMG) activity were determined from three trials for each contraction type and movement velocity. The fluctuations in acceleration increased with movement velocity for both concentric and eccentric contractions, but they were greatest during fast eccentric contractions ( approximately 135%) when there was stronger modulation of acceleration in the 5- to 10-Hz bandwidth. Nonetheless, EMG amplitude for first dorsal interosseus increased with movement velocity only for concentric and not eccentric contractions. Consistent with the minimum variance theory, movement accuracy was related to the fluctuations in acceleration for both types of contractions in all subjects. For a given level of fluctuations in acceleration, however, old subjects were three times less accurate than young subjects. Although the EMG amplitude at each speed was similar for young and old adults, only the young adults modulated the power in the EMG spectrum with speed. Thus the fluctuations in acceleration during voluntary contractions had a more pronounced effect on movement accuracy for old adults compared with young adults, probably due to factors that influenced the frequency-domain characteristics of the EMG.     

Characterization of the separation properties of the beckman elutriator system

The role of fluid flow in the elutriation process was visualized by pumping dye solution through the Beckman JE-6 elutriator rotor. Three major fluid flow disturbances were observed in the separation chambers, namely; jet-streaming, ripple flow, and whirl flow. In order to evaluate the effects of these non-ideal fluid flow patterns on the separation of homogeneous populations of particles or cells, 12–35 μm diameter latex spheres and 9L rat brain tumor cells were fractionated with the Beckman elutriator system. The elutriator system was evaluated on the basis of: (1) recovery, (2) elution loss during loading, (3) homogeneity of the size distributions, and (4) the relationship of the median volume of eluted particles or cells to the rotor speed and the collection fluid velocity. Both a conventional collection method (two 40-mL fractions at each collection rotor speed) and a long collection method (10–15 40-mL fractions at several collection rotor speeds) were compared to determine if collection procedures could compensate for some of the difficulties caused by the non-ideal fluid flow patterns. Although more than 90% of the particles or cells were always recovered, about 5% eluted during the loading procedure. Neither collection method altered this phenomenon. The collected populations, but this was accompanied by a reduction in cell yield. The median particle or cell volume of each fraction agreed with that expected under ideal fluid flow conditions except at high and low rotor speeds when the conventional collection method was used.     

Bayesian calibration of the Unified budburst model in six temperate tree species

Numerous phenology models developed to predict the budburst date of trees have been merged into one Unified model (Chuine, 2000, J. Theor. Biol. 207, 337–347). In this study, we tested a simplified version of the Unified model (Unichill model) on six woody species. Budburst and temperature data were available for five sites across Belgium from 1957 to 1995. We calibrated the Unichill model using a Bayesian calibration procedure, which reduced the uncertainty of the parameter coefficients and quantified the prediction uncertainty. The model performance differed among species. For two species (chestnut and black locust), the model showed good performance when tested against independent data not used for calibration. For the four other species (beech, oak, birch, ash), the model performed poorly. Model performance improved substantially for most species when using site-specific parameter coefficients instead of across-site parameter coefficients. This suggested that budburst is influenced by local environment and/or genetic differences among populations. Chestnut, black locust and birch were found to be temperature-driven species, and we therefore analyzed the sensitivity of budburst date to forcing temperature in those three species. Model results showed that budburst advanced with increasing temperature for 1–3 days °C⁻¹, which agreed with the observed trends. In synthesis, our results suggest that the Unichill model can be successfully applied to chestnut and black locust (with both across-site and site-specific calibration) and to birch (with site-specific calibration). For other species, temperature is not the only determinant of budburst and additional influencing factors will need to be included in the model.     

The effects of temperature and diet on age grading and population age structure determination in Drosophila

The age structure of natural population is of interest in physiological, life history and ecological studies but it is often difficult to determine. One methodological problem is that samples may need to be invasively sampled preventing subsequent taxonomic curation. A second problem is that it can be very expensive to accurately determine the age structure of given population because large sample sizes are often necessary. In this study, we test the effects of temperature (17 °C, 23 °C and 26 °C) and diet (standard cornmeal and low calorie diet) on the accuracy of the non-invasive, inexpensive and high throughput near-infrared spectroscopy (NIRS) technique to determine the age of Drosophila flies. Composite and simplified calibration models were developed for each sex. Independent sets for each temperature and diet treatments with flies not involved in calibration model were then used to validate the accuracy of the calibration models. The composite NIRS calibration model was generated by including flies reared under all temperatures and diets. This approach permits rapid age measurement and age structure determination in large population of flies as less than or equal to 9 days, or more than 9 days old with 85–97% and 64–99% accuracy, respectively. The simplified calibration models were generated by including flies reared at 23 °C on standard diet. Low accuracy rates were observed when simplified calibration models were used to identify (a) Drosophila reared at 17 °C and 26 °C and (b) 23 °C with low calorie diet. These results strongly suggest that appropriate calibration models need to be developed in the laboratory before this technique can be reliably used in field. These calibration models should include the major environmental variables that change across space and time in the particular natural population to be studied.     

Lightweight low-profile nine-accelerometer package to obtain head angular accelerations in short-duration impacts

Despite recognizing the importance of angular acceleration in brain injury, computations using data from experimental studies with biological models such as human cadavers have met with varying degrees of success. In this study, a lightweight and a low-profile version of the nine-accelerometer system was developed for applications in head injury evaluations and impact biomechanics tests. The triangular pyramidal nine-accelerometer package (PNAP) is precision-machined out of standard aluminum, is lightweight (65 g), and has a low profile (82 mm base width, 35 mm vertex height). The PNAP assures accurate orthogonal characteristics because all nine accelerometers are pre-aligned and attached before mounting on a human cadaver preparation. The feasibility of using the PNAP in human cadaver head studies is demonstrated by subjecting a specimen to an impact velocity of 8.1 m/s and the resultant angular acceleration peaked at 17 krad/s2. The accuracy and the high fidelity of the PNAP device at high and low angular acceleration levels were demonstrated by comparing the PNAP-derived angular acceleration data with separate tests using the internal nine-accelerometer head of the Hybrid III anthropomorphic test device. Mounting of the PNAP on a biological specimen such as a human cadaver head should yield very accurate angular acceleration data.     

Behavioral classification of low‐frequency acceleration and temperature data from a free‐ranging small mammal

The miniaturization and affordability of new technology is driving a biologging revolution in wildlife ecology with use of animal‐borne data logging devices. Among many new biologging technologies, accelerometers are emerging as key tools for continuously recording animal behavior. Yet a critical, but under‐acknowledged consideration in biologging is the trade‐off between sampling rate and sampling duration, created by battery‐ (or memory‐) related sampling constraints. This is especially acute among small animals, causing most researchers to sample at high rates for very limited durations. Here, we show that high accuracy in behavioral classification is achievable when pairing low‐frequency acceleration recordings with temperature. We conducted 84 hr of direct behavioral observations on 67 free‐ranging red squirrels (200–300 g) that were fitted with accelerometers (2 g) recording tri‐axial acceleration and temperature at 1 Hz. We then used a random forest algorithm and a manually created decision tree, with variable sampling window lengths, to associate observed behavior with logger recorded acceleration and temperature. Finally, we assessed the accuracy of these different classifications using an additional 60 hr of behavioral observations, not used in the initial classification. The accuracy of the manually created decision tree classification using observational data varied from 70.6% to 91.6% depending on the complexity of the tree, with increasing accuracy as complexity decreased. Short duration behavior like running had lower accuracy than long‐duration behavior like feeding. The random forest algorithm offered similarly high overall accuracy, but the manual decision tree afforded the flexibility to create a hierarchical tree, and to adjust sampling window length for behavioral states with varying durations. Low frequency biologging of acceleration and temperature allows accurate behavioral classification of small animals over multi‐month sampling durations. Nevertheless, low sampling rates impose several important limitations, especially related to assessing the classification accuracy of short duration behavior.     

Spatial and Temporal Control of Hyperthermia Using Real Time Ultrasonic Thermal Strain Imaging with Motion Compensation,Phantom Study

Mild hyperthermia has been successfully employed to induce reversible physiological changes that can directly treat cancer and enhance local drug delivery. In this approach, temperature monitoring is essential to avoid undesirable biological effects that result from thermal damage. For thermal therapies, Magnetic Resonance Imaging (MRI) has been employed to control real-time Focused Ultrasound (FUS) therapies. However, combined ultrasound imaging and therapy systems offer the benefits of simple, low-cost devices that can be broadly applied. To facilitate such technology, ultrasound thermometry has potential to reliably monitor temperature. Control of mild hyperthermia was previously achieved using a proportional-integral-derivative (PID) controller based on thermocouple measurements. Despite accurate temporal control of heating, this method is limited by the single position at which the temperature is measured. Ultrasound thermometry techniques based on exploiting the thermal dependence of acoustic parameters (such as longitudinal velocity) can be extended to create thermal maps and allow an accurate monitoring of temperature with good spatial resolution. However, in vivo applications of this technique have not been fully developed due to the high sensitivity to tissue motion. Here, we propose a motion compensation method based on the acquisition of multiple reference frames prior to treatment. The technique was tested in the presence of 2-D and 3-D physiological-scale motion and was found to provide effective real-time temperature monitoring. PID control of mild hyperthermia in presence of motion was then tested with ultrasound thermometry as feedback and temperature was maintained within 0.3°C of the requested value.     

Inertial sensor based method for identifying spherical joint center of rotation

The miniaturized wireless inertial measurement unit (IMU) technology and algorithms presented herein promote rapid and accurate predictions of the center-of-rotation (CoR) for ball/spherical joints. The algorithm improves upon existing IMU-based methods by directly utilizing the measured acceleration and angular velocity provided by the IMU to deduce the CoR in lieu of relying on error-prone velocity and position estimates. Results demonstrate that this new method resolves the position of the CoR to within a 3 mm sphere of the true CoR determined by a precision coordinate measuring machine. Such accuracy may render this method attractive for broad use in field, laboratory and clinical settings requiring non-invasive and rapid estimates of joint CoR.     

A Multilaboratory Comparison of Calibration Accuracy and the Performance of External References in Analytical Ultracentrifugation

Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies.     

Two distinct visual motion mechanisms for smooth pursuit: evidence from individual differences

Smooth-pursuit eye velocity to a moving target is more accurate after an initial catch-up saccade than before, an enhancement that is poorly understood. We present an individual-differences-based method for identifying mechanisms underlying a physiological response and use it to test whether visual motion signals driving pursuit differ pre- and postsaccade. Correlating moment-to-moment measurements of pursuit over time with two psychophysical measures of speed estimation during fixation, we find two independent associations across individuals. Presaccadic pursuit acceleration is predicted by the precision of low-level (motion-energy-based) speed estimation, and postsaccadic pursuit precision is predicted by the precision of high-level (position-tracking) speed estimation. These results provide evidence that a low-level motion signal influences presaccadic acceleration and an independent high-level motion signal influences postsaccadic precision, thus presenting a plausible mechanism for postsaccadic enhancement of pursuit.     

Gait analysis using gravitational acceleration measured by wearable sensors

A novel method for measuring human gait posture using wearable sensor units is proposed. The sensor units consist of a tri-axial acceleration sensor and three gyro sensors aligned on three axes. The acceleration and angular velocity during walking were measured with seven sensor units worn on the abdomen and the lower limb segments (both thighs, shanks and feet). The three-dimensional positions of each joint are calculated from each segment length and joint angle. Joint angle can be estimated mechanically from the gravitational acceleration along the anterior axis of the segment. However, the acceleration data during walking includes three major components; translational acceleration, gravitational acceleration and external noise. Therefore, an optimization analysis was represented to separate only the gravitational acceleration from the acceleration data. Because the cyclic patterns of acceleration data can be found during constant walking, a FFT analysis was applied to obtain some characteristic frequencies in it. A pattern of gravitational acceleration was assumed using some parts of these characteristic frequencies. Every joint position was calculated from the pattern under the condition of physiological motion range of each joint. An optimized pattern of the gravitational acceleration was selected as a solution of an inverse problem. Gaits of three healthy volunteers were measured by walking for 20 s on a flat floor. As a result, the acceleration data of every segment was measured simultaneously. The characteristic three-dimensional walking could be shown by the expression using a stick figure model. In addition, the trajectories of the knee joint in the horizontal plane could be checked by visual imaging on a PC. Therefore, this method provides important quantitive information for gait diagnosis.     

Prediction Models Discriminating between Nonlocomotive and Locomotive Activities in Children Using a Triaxial Accelerometer with a Gravity-removal Physical Activity Classification Algorithm

The aims of our study were to examine whether a gravity-removal physical activity classification algorithm (GRPACA) is applicable for discrimination between nonlocomotive and locomotive activities for various physical activities (PAs) of children and to prove that this approach improves the estimation accuracy of a prediction model for children using an accelerometer. Japanese children (42 boys and 26 girls) attending primary school were invited to participate in this study. We used a triaxial accelerometer with a sampling interval of 32 Hz and within a measurement range of ±6 G. Participants were asked to perform 6 nonlocomotive and 5 locomotive activities. We measured raw synthetic acceleration with the triaxial accelerometer and monitored oxygen consumption and carbon dioxide production during each activity with the Douglas bag method. In addition, the resting metabolic rate (RMR) was measured with the subject sitting on a chair to calculate metabolic equivalents (METs). When the ratio of unfiltered synthetic acceleration (USA) and filtered synthetic acceleration (FSA) was 1.12, the rate of correct discrimination between nonlocomotive and locomotive activities was excellent, at 99.1% on average. As a result, a strong linear relationship was found for both nonlocomotive (METs = 0.013×synthetic acceleration +1.220, R² = 0.772) and locomotive (METs = 0.005×synthetic acceleration +0.944, R² = 0.880) activities, except for climbing down and up. The mean differences between the values predicted by our model and measured METs were −0.50 to 0.23 for moderate to vigorous intensity (>3.5 METs) PAs like running, ball throwing and washing the floor, which were regarded as unpredictable PAs. In addition, the difference was within 0.25 METs for sedentary to mild moderate PAs (<3.5 METs). Our specific calibration model that discriminates between nonlocomotive and locomotive activities for children can be useful to evaluate the sedentary to vigorous PAs intensity of both nonlocomotive and locomotive activities.     

Use of microspheres in measurement of regional blood flows during +GZ stress

The use of the radiolabeled microsphere technique for the study of the effects of +GZ acceleration on regional blood flow is examined. A theoretical analysis of the limits of this technique in a high acceleration environment is presented. Chronically implanted, electromagnetic, aortic flow probes were used to determine the relationship between aortic blood flow velocity and +GZ acceleration in conscious adult miniature swine. It was found that conscious straining adult miniature swine, with the assistance of an inflated anti-G suit, are able to compensate quite well to acceleration levels less than or equal to +7 GZ. Exposure to +9 GZ often resulted in unstable cardiovascular states involving relative bradycardia, often progressing to asystole, declining aortic blood pressure, and markedly diminished cardiac outputs approaching zero. It was found that, if aortic pressure and heart rate attain a relatively steady state during acceleration, and if heart level mean aortic pressure is greater than or equal to 100 Torr, the application of the microsphere technique during +GZ acceleration is theoretically valid. This hypothesis was tested using the microsphere technique (9.0 +/- 0.8 microns diam) in conscious miniature swine during exposure to +GZ acceleration. It is concluded that within the defined limits the radiolabeled microsphere technique is as accurate for use during acceleration studies as it is for use in routine laboratory studies.     

Non-equilibrium trajectory dynamics and the kinematics of gliding in a flying snake

Given sufficient space, it is possible for gliding animals to reach an equilibrium state with no net forces acting on the body. In contrast, every gliding trajectory must begin with a non-steady component, and the relative importance of this phase is not well understood. Of any terrestrial animal glider, snakes exhibit the greatest active movements, which may affect their trajectory dynamics. Our primary aim was to determine the characteristics of snake gliding during the transition to equilibrium, quantifying changes in velocity, acceleration, and body orientation in the late phase of a glide sequence. We launched 'flying' snakes (Chrysopelea paradisi) from a 15 m tower and recorded the mid-to-end portion of trajectories with four videocameras to reconstruct the snake's body position with mm to cm accuracy. Additionally, we developed a simple analytical model of gliding assuming only steady-state forces of lift, drag and weight acting on the body and used it to explore effects of wing loading, lift-to-drag ratio, and initial velocity on trajectory dynamics. Despite the vertical space provided to transition to steady-state gliding, snakes did not exhibit equilibrium gliding and in fact displayed a net positive acceleration in the vertical axis, an effect also predicted by the analytical model.     

Is Your System Calibrated? MRI Gradient System Calibration for Pre-Clinical,High-Resolution Imaging

High-field, pre-clinical MRI systems are widely used to characterise tissue structure and volume in small animals, using high resolution imaging. Both applications rely heavily on the consistent, accurate calibration of imaging gradients, yet such calibrations are typically only performed during maintenance sessions by equipment manufacturers, and potentially with acceptance limits that are inadequate for phenotyping. To overcome this difficulty, we present a protocol for gradient calibration quality assurance testing, based on a 3D-printed, open source, structural phantom that can be customised to the dimensions of individual scanners and RF coils. In trials on a 9.4 T system, the gradient scaling errors were reduced by an order of magnitude, and displacements of greater than 100 µm, caused by gradient non-linearity, were corrected using a post-processing technique. The step-by-step protocol can be integrated into routine pre-clinical MRI quality assurance to measure and correct for these errors. We suggest that this type of quality assurance is essential for robust pre-clinical MRI experiments that rely on accurate imaging gradients, including small animal phenotyping and diffusion MR.     

An application of the plaster dissolution method for quantifying water velocity in the shallow hyporheic zone of an Appalachian stream system

1. A method for quantifying interstitial water velocity based on the dissolution rate of plaster of Paris standards was developed as part of a study of vertical, longitudinal (1–4 order sites) and seasonal variation in the biotic and physical characteristics of the shallow hyporheic zone (0–30 cm) of a headwater stream system in West Virginia, U.S.A.
2. A calibration model was developed using a water velocity simulation tank to relate mass loss of plaster standards to water velocity and temperature. The model was then used to calculate water velocity through artificial substrata embedded in the shallow hyporheic zone of four stream reaches based on in situ mass loss of plaster standards.
3. Water velocity in the hyporheic zone increased with stream order, was highest in early spring and winter during high stream base flows, and decreased with depth into the substratum. There was a strong interaction between depth and season: during periods of high stream discharge, water velocity through the upper level of the shallow hyporheic zone (0–10 cm into the substrate) increased disproportionately more than velocity at greater depths. Mean interstitial velocity in March ranged from 0 cm s^–1 in the lowest level (20–30 cm) to 3.5 cm s^–1 at the upper level (0–10 cm) at the first‐order site, and from 2.5 cm s^–1 (20–30 cm) to 9.5 cm s^–1 (0–10 cm s^–1) at the fourth‐order site. Gradients in stream discharge and sediment permeability accounted for treatment effects.
4. Use of calibrated data improved the ability to resolve among‐season differences in interstitial water movement over the use of uncalibrated mass loss data. For some applications of the plaster standard method, empirical calibration may not be necessary.