Bayesian inference of physiologically meaningful parameters from body sway measurements.

The control of the human body sway by the central nervous system, muscles, and conscious brain is of interest since body sway carries information about the physiological status of a person. Several models have been proposed to describe body sway in an upright standing position, however, due to the statistical intractability of the more realistic models, no formal parameter inference has previously been conducted and the expressive power of such models for real human subjects remains unknown. Using the latest advances in Bayesian statistical inference for intractable models, we fitted a nonlinear control model to posturographic measurements, and we showed that it can accurately predict the sway characteristics of both simulated and real subjects. Our method provides a full statistical characterization of the uncertainty related to all model parameters as quantified by posterior probability density functions, which is useful for comparisons across subjects and test settings. The ability to infer intractable control models from sensor data opens new possibilities for monitoring and predicting body status in health applications.

3D histopathological grading of osteochondral tissue using contrast-enhanced micro-computed tomography.

OBJECTIVE: Histopathological grading of osteochondral (OC) tissue is widely used in osteoarthritis (OA) research, and it is relatively common in post-surgery in vitro diagnostics. However, relying on thin tissue section, this approach includes a number of limitations, such as: (1) destructiveness, (2) sample processing artefacts, (3) 2D section does not represent spatial 3D structure and composition of the tissue, and (4) the final outcome is subjective. To overcome these limitations, we recently developed a contrast-enhanced µCT (CEµCT) imaging technique to visualize the collagenous extracellular matrix (ECM) of articular cartilage (AC). In the present study, we demonstrate that histopathological scoring of OC tissue from CEµCT is feasible. Moreover, we establish a new, semi-quantitative OA µCT grading system for OC tissue. RESULTS: Pathological features were clearly visualized in AC and subchondral bone (SB) with µCT and verified with histology, as demonstrated with image atlases. Comparison of histopathological grades (OARSI or severity (0-3)) across the characterization approaches, CEµCT and histology, excellent (0.92, 95% CI = [0.84, 0.96], n = 30) or fair (0.50, 95% CI = [0.16, 0.74], n = 27) intra-class correlations (ICC), respectively. A new µCT grading system was successfully established which achieved an excellent cross-method (µCT vs histology) reader-to-reader intra-class correlation (0.78, 95% CI = [0.58, 0.89], n = 27). CONCLUSIONS: We demonstrated that histopathological information relevant to OA can reliably be obtained from CEµCT images. This new grading system could be used as a reference for 3D imaging and analysis techniques intended for volumetric evaluation of OA pathology in research and clinical applications.

Temperature and pH dependence of DNA ejection from archaeal lemon-shaped virus His1.

The archaeal virus His1 isolated from a hypersaline environment infects an extremely halophilic archaeon Haloarcula hispanica. His1 features a lemon-shaped capsid, which is so far found only in archaeal viruses. This unique capsid can withstand high salt concentrations, and can transform into a helical tube, which in turn is resistant to extremely harsh conditions. Hypersaline environments exhibit a wide range of temperatures and pH conditions, which present an extra challenge to their inhabitants. We investigated the influence of pH and temperature on DNA ejection from His1 virus using single-molecule fluorescence experiments. The observed number of ejecting viruses is constant in pH 5 to 9, while the ejection process is suppressed at pH below 5. Similarly, the number of ejections within 15-42 °C shows only a minor increase around 25-37 °C. The maximum velocity of single ejected DNA increases with temperature, in qualitative agreement with the continuum model of dsDNA ejection.

Calibration of Fourier domain short coherence interferometer for absolute distance measurements.

We calibrated and determined the measurement uncertainty of a custom-made Fourier domain short coherence interferometer operated in laboratory conditions. We compared the optical thickness of two thickness standards and three coverslips determined with our interferometer to the geometric thickness determined by SEM. Using this calibration data, we derived a calibration function with a 95% confidence level system uncertainty of (5.9×10(-3)r+2.3) µm, where r is the optical distance in µm, across the 240 µm optical measurement range. The confidence limit includes contributions from uncertainties in the optical thickness, geometric thickness, and refractive index measurements as well as uncertainties arising from cosine errors and thermal expansion. The results show feasibility for noncontacting absolute distance characterization with micrometer-level accuracy. This instrument is intended for verifying the alignment of the discs of an accelerating structure in the possible future compact linear collider.

Baseline adjustment increases accurate interpretation of posturographic sway scores.

Postural steadiness may be quantified using posturographic sway measures. These measures are commonly used to differentiate between a person's baseline balance and balance related to some physiological condition. However, the difference in sway scores between the two conditions may be difficult to detect due to large inter-subject variation. We compared detection accuracy provided by three models that linearly regress a sway measure (mean distance, velocity, or frequency) on the effect of eye closure on balance (eyes open (EO) vs. eyes closed (EC)). In Model 1 the dependent variable is a single sway score (EO or EC), whereas in Models 2 and 3 it is a change score (EO-EO or EC-EO). The independent variable is always the group (group=0: EO or group=1: EC). Model 3 also accounts for the regression to the mean effect (RTM), by considering the baseline value (EO) as a covariate. When differentiating between EO and EC conditions, 94% accuracy can be achieved when using mean velocity as sway measure and either Model 2 or 3. Thus by adjusting for baseline score one increases the accurate interpretation of posturographic sway scores.

Determining collagen distribution in articular cartilage using contrast-enhanced micro-computed tomography.

OBJECTIVE: Collagen distribution within articular cartilage (AC) is typically evaluated from histological sections, e.g., using collagen staining and light microscopy (LM). Unfortunately, all techniques based on histological sections are time-consuming, destructive, and without extraordinary effort, limited to two dimensions. This study investigates whether phosphotungstic acid (PTA) and phosphomolybdic acid (PMA), two collagen-specific markers and X-ray absorbers, could (1) produce contrast for AC X-ray imaging or (2) be used to detect collagen distribution within AC. METHOD: We labeled equine AC samples with PTA or PMA and imaged them with micro-computed tomography (micro-CT) at pre-defined time points 0, 18, 36, 54, 72, 90, 180, 270 h during staining. The micro-CT image intensity was compared with collagen distributions obtained with a reference technique, i.e., Fourier-transform infrared imaging (FTIRI). The labeling time and contrast agent producing highest association (Pearson correlation, Bland-Altman analysis) between FTIRI collagen distribution and micro-CT -determined PTA distribution was selected for human AC. RESULTS: Both, PTA and PMA labeling permitted visualization of AC features using micro-CT in non-calcified cartilage. After labeling the samples for 36 h in PTA, the spatial distribution of X-ray attenuation correlated highly with the collagen distribution determined by FTIRI in both equine (mean ± S.D. of the Pearson correlation coefficients, r = 0.96 ± 0.03, n = 12) and human AC (r = 0.82 ± 0.15, n = 4). CONCLUSIONS: PTA-induced X-ray attenuation is a potential marker for non-destructive detection of AC collagen distributions in 3D. This approach opens new possibilities in development of non-destructive 3D histopathological techniques for characterization of OA.

Traceable methods for vertical scale characterization of dynamic stroboscopic scanning white-light interferometer measurements.

Stroboscopic scanning white-light interferometry (SSWLI) can be used for 3D imaging of oscillating samples. It allows measurement of micrometer to millimeter size samples with nanometer vertical precision. Unlike coherent light source systems the SSWLI can measure unambiguously samples with vertical steps. Traceability of the vertical displacement measurement is important with SSWLI since the height measurement is not related to any specific monochromatic light wavelength. For static measurements SSWLI can be calibrated using, e.g., step height standards, but to characterize dynamic measurements traceable samples with accurate motion are needed due to error sources related to the frequency response of the SSWLI. In the presented method, SSWLI measurements are performed on dynamic transfer standards, which are characterized using a laser interferometer traceable to the SI meter. In this work dynamic SSWLI measurements at subkilohertz to 10.7 kHz frequencies with micrometer range displacement are characterized. The expanded uncertainty (k=2) was 9.6 nm for a measured displacement of 766 nm at 10.7 kHz. The methodology can be used up to the frequency limits of the SSWLI using suitable samples.

The potential utility of high-intensity ultrasound to treat osteoarthritis.

Osteoarthritis (OA) is a widespread musculoskeletal disease that reduces quality of life and for which there is no cure. The treatment of OA is challenging since cartilage impedes the local and systemic delivery of therapeutic compounds (TCs). This review identifies high-intensity ultrasound (HIU) as a non-contact technique to modify articular cartilage and subchondral bone. HIU enables new approaches to overcome challenges associated with drug delivery to cartilage and new non-invasive approaches for the treatment of joint disease. Specifically, HIU has the potential to facilitate targeted drug delivery and release deep within cartilage, to repair soft tissue damage, and to physically alter tissue structures including cartilage and bone. The localized, non-invasive ultrasonic delivery of TCs to articular cartilage and subchondral bone appears to be a promising technique in the immediate future.

Evaluation of postural steadiness before and after sedation: comparison of four nonlinear and three conventional measures.

Sedative drugs decrease postural steadiness and increase the risk of injury from falls and accidents. The recovery rate is individual, making it hard to predict the patient's steadiness and hence safe discharge time. 103 outpatients sedated with midazolam and fentanyl were measured posturographically, before (PRE) and after (POST) endoscopy. The ability of conventional and nonlinear sway measures to separate the PRE and POST conditions were compared, and the area under the receiver operating characteristics curve (AUC) was used to quantify the significance of the separation. A nonlinear measure, fuzzy sample entropy, scored the largest AUC (AUCFSE = 0.83, p < 0.0001). While the AUCFSE was not significantly larger than the AUCs of conventional sway measures which offer easy quantification of postural steadiness, nonlinear measures provide more insight into the structure of postural control, which may help understand the effect of sedation on postural steadiness. This study is a step toward developing a tester that indicates a safe discharge time.

DNA ejection from an archaeal virus--a single-molecule approach.

The translocation of genetic material from the viral capsid to the cell is an essential part of the viral infection process. Whether the energetics of this process is driven by the energy stored within the confined nucleic acid or cellular processes pull the genome into the cell has been the subject of discussion. However, in vitro studies of genome ejection have been limited to a few head-tailed bacteriophages with a double-stranded DNA genome. Here we describe a DNA release system that operates in an archaeal virus. This virus infects an archaeon Haloarcula hispanica that was isolated from a hypersaline environment. The DNA-ejection velocity of His1, determined by single-molecule experiments, is comparable to that of bacterial viruses. We found that the ejection process is modulated by the external osmotic pressure (polyethylene glycol (PEG)) and by increased ion (Mg(2+) and Na(+)) concentration. The observed ejection was unidirectional, randomly paused, and incomplete, which suggests that cellular processes are required to complete the DNA transfer.

Circadian amplitude and homeostatic buildup rate in postural control.

Postural control during quiet stance is a common everyday physical activity. Sleepiness is increasingly prevalent in our 24-h society. Yet, little research exists that quantitatively links the fluctuations in sleepiness and postural control. This study quantifies the circadian amplitude and homeostatic buildup rate in postural control. With a force plate we assessed postural control in 12 participants (21-38 years) every 2h during 24h of sustained wakefulness. The sway area was 1.39 ± 0.71 mm(2) at the circadian high around noon, and 4.02 ± 0.67 mm(2) at the circadian low around 6 am (a 189% change, p=0.02). The circadian amplitude of the sway area was therefore 2.63 mm(2). The sway area was 1.92 ± 0.64 mm(2) at the start of the 24-h period and 4.42 ± 0.69 mm(2) at the end of the period (a 130% change, p<0.001). The homeostatic buildup rate of sway area was 0.04 h(-1). The circadian- and homeostatic effects on sway variability, sway velocity, sway frequency and fractal dimension were smaller but still significant. This study found that the circadian amplitude and homeostatic buildup rate are quantifiable from posturographic data, and that they have significant impact on postural control. This finding is important because it means that one could apply the framework of the famous two-process model of sleep regulation (published by Borbély in 1982) to explain the previously reported sleepiness-related changes in postural control.

Stroboscopic supercontinuum white-light interferometer for MEMS characterization.

We used a supercontinuum-based scanning white-light interferometer to characterize the oscillation of a MEMS device. The output of a commercially available supercontinuum light source (FiberWare Ilum II USB) was modulated to achieve stroboscopic operation. By synchronizing the modulation frequency of the source to the sample oscillation, dynamic 3-D profile measurements were recorded. These results were validated against those obtained with a white light LED setup. The measured maximum deflection of a 400×25×4 µm(3) microbridge driven with 0-6.8 V sinusoidal voltage at 10 Hz was 1.42±0.03 µm (supercontinuum), which agreed with the LED measurement. The method shows promise for characterization of high-frequency MEMS devices.

Invited article: Electric solar wind sail: toward test missions.

The electric solar wind sail (E-sail) is a space propulsion concept that uses the natural solar wind dynamic pressure for producing spacecraft thrust. In its baseline form, the E-sail consists of a number of long, thin, conducting, and centrifugally stretched tethers, which are kept in a high positive potential by an onboard electron gun. The concept gains its efficiency from the fact that the effective sail area, i.e., the potential structure of the tethers, can be millions of times larger than the physical area of the thin tethers wires, which offsets the fact that the dynamic pressure of the solar wind is very weak. Indeed, according to the most recent published estimates, an E-sail of 1 N thrust and 100 kg mass could be built in the rather near future, providing a revolutionary level of propulsive performance (specific acceleration) for travel in the solar system. Here we give a review of the ongoing technical development work of the E-sail, covering tether construction, overall mechanical design alternatives, guidance and navigation strategies, and dynamical and orbital simulations.

Quantifying time awake posturographically.

Although sleepiness is a major risk factor in traffic and occupational accidents, convenient, quantitative, and commercial sleepiness testing is lacking. The issue is relevant to policymakers concerned with legislation for, and surveillance of, traffic- and occupational safety. This work suggested and examined posturographic sleepiness testing for instrumentation purposes. In 63 subjects--for whom we tested balance with a force platform during sustained waking for maximum 36 h--sustained waking impaired the balance. The sustained waking explained 60% of the diurnal balance variations, whereas the time of day explained 40% of the balance variations. The first finding -that balance depends on the subject's time awake (TA)- allowed to posturographically estimate the subjects' TA with 86% accuracy and 97% precision. Results also show that balance scores tested at 13:30 hours serve as a threshold to detect excessive sleepiness. This work provides guidelines for a posturographic sleepiness tester.

Model-based posturographic sleepiness monitor tested on 20 subjects.

A previous posturographic force platform study verified that human balance deteriorates as a function of time awake (TA). It found that TA can be estimated with +/-2.5 h accuracy using 30 s trial length. For a fast, reliable and convenient sleepiness monitor even better TA estimation accuracy and shorter trial length is needed. We continued this quest by modeling the quiet stance test situation with a single-link inverted pendulum model (SLIPM). The center-of-mass (COM) trace in the AP (anterior-posterior) direction was calculated from the measured center-of-pressure (COP) trace. The sway angle theta, ankle torque tau and the horizontal force F acting on the COM were calculated from the SLIP equations--each analyzed with 13 different sway measures, i.e. variables that correlate with TA. The effect of circadian rhythm was separated from the sway measures. Twenty subjects' sway measures were analyzed. The SLIPM-based posturographic averaged TA estimation accuracy improved to +/-2.3 h. The trial length could be shortened to 21 s.

Preliminary study of ultrasonic structural quality control of Swiss-type cheese.

There is demand for a new nondestructive cheese-structure analysis method for Swiss-type cheese. Such a method would provide the cheese-making industry the means to enhance process control and quality assurance. This paper presents a feasibility study on ultrasonic monitoring of the structural quality of Swiss cheese by using a single-transducer 2-MHz longitudinal mode pulse-echo setup. A volumetric ultrasonic image of a cheese sample featuring gas holes (cheese-eyes) and defects (cracks) in the scan area is presented. The image is compared with an optical reference image constructed from dissection images of the same sample. The results show that the ultrasonic method is capable of monitoring the gas-solid structure of the cheese during the ripening process. Moreover, the method can be used to detect and to characterize cheese-eyes and cracks in ripened cheese. Industrial application demands were taken into account when conducting the measurements.

Measurement of the effect of high-power ultrasound on wetting of paper.

High-power ultrasound has been known to promote penetration of liquids into porous materials. This work presents results of experimental investigations of the influence of 40 kHz high-power ultrasound on wetting processes of papers. Wetting was monitored by the measurement of the attenuation of 0.5-9 MHz ultrasound transmitted through the immersed sample. The samples were sized papers with contact angles 40 degrees, 70 degrees and 110 degrees, and the immersion liquids were isopropanol-water mixtures of 0-100% isopropanol concentration. The investigation showed that application of high-power ultrasound resulted in faster sorption processes. However, the absolute reduction in time to reach the stationary state was not very great.