Knee Angle Estimation with Dynamic Calibration Using Inertial Measurement Units for Running.

The knee flexion angle is an important measurement for studies of the human gait. Running is a common activity with a high risk of knee injury. Studying the running gait in realistic situations is challenging because accurate joint angle measurements typically come from optical motion-capture systems constrained to laboratory settings. This study considers the use of shank and thigh inertial sensors within three different filtering algorithms to estimate the knee flexion angle for running without requiring sensor-to-segment mounting assumptions, body measurements, specific calibration poses, or magnetometers. The objective of this study is to determine the knee flexion angle within running applications using accelerometer and gyroscope information only. Data were collected for a single test participant (21-year-old female) at four different treadmill speeds and used to validate the estimation results for three filter variations with respect to a Vicon optical motion-capture system. The knee flexion angle filtering algorithms resulted in root-mean-square errors of approximately three degrees. The results of this study indicate estimation results that are within acceptable limits of five degrees for clinical gait analysis. Specifically, a complementary filter approach is effective for knee flexion angle estimation in running applications.

Methodology and validation for identifying gait type using machine learning on IMU data.

With the rising popularity of activity tracking, there is a desire to not only count the number of steps a person takes, but also identify the type of step (e.g., walking or running) they are taking. For rehabilitation and athletic training, this difference is important to the prescribed regiment. Fourteen healthy adults walked, jogged and ran on a treadmill at three different constant speeds (1.21, 2.01, 2.68 m/s) for 90 s. An inertial measurement unit (IMU) with accelerometer and gyroscope was affixed to their left ankle. Collected acceleration and angular velocity data were partitioned into individual time-normalised strides. These data were used as features in the artificial neural network (ANN) that classified the type of stride. Several ANN models were tested: using only acceleration, only angular velocity and both. Using primarily acceleration data in the trained ANN yielded the best results (>94% correct stride-type identification) after cross-validation. The ANN models were able to accurately classify the gait type of each stride using a single wearable IMU. The accuracy of the method should improve further as more data is added to the ANN training.

A comprehensive comparison of simple step counting techniques using wrist- and ankle-mounted accelerometer and gyroscope signals.

The goal of this work is to compare the differences between various step counting algorithms using both accelerometer and gyroscope measurements from wrist and ankle-mounted sensors. Participants completed four different conditions on a treadmill while wearing an accelerometer and gyroscope on the wrist and the ankle. Three different step counting techniques were applied to the data from each sensor type and mounting location. It was determined that using gyroscope measurements allowed for better performance than the typically used accelerometers, and that ankle-mounted sensors provided better performance than those mounted on the wrist.

Design and validation of a simple automated optical step counting method for treadmill walking.

BACKGROUND: Reliable step counting is a critical part of locomotion research. Current counting methods can be inaccurate, time consuming, expensive or encumbering to the subject. Here, we present a camera-based optical method for automatically counting steps. METHODS: Fifteen healthy adults walked, jogged and ran on a treadmill at three different constant speeds (1.21, 2.01, 2.68 m/s) and once at varying speed (1.21-2.68 m/s) for 90 s. Subjects had visual marker affixed to their left foot while walking. Video was recorded synchronously at low- and high-resolution during trials. The step count found manually from the video was compared to an automated video analysis system using the two configurations of the optical system. RESULTS: Bland-Altman plots, Intra-class correlation coefficients (ICC) and relative error comparison were used for quantitative assessment of device reliability. Reliability of optical method was high (ICC ≥0.98). CONCLUSIONS: The method produces accurate step count results for the range of speeds tested. They use customisable open-source software and off-the-shelf hardware. The method has a low cost of implementation compared to many consumer products and grants researchers access to the raw sensor data.

Design method for multi-user workstations utilizing anthropometry and preference data.

Past efforts have been made to design single-user workstations to accommodate users' anthropometric and preference distributions. However, there is a lack of methods for designing workstations for group interaction. This paper introduces a method for sizing workstations to allow for a personal work area for each user and a shared space for adjacent users. We first create a virtual population with the same anthropometric and preference distributions as an intended demographic of college-aged students. Members of the virtual population are randomly paired to test if their extended reaches overlap but their normal reaches do not. This process is repeated in a Monte Carlo simulation to estimate the total percentage of groups in the population that will be accommodated for a workstation size. We apply our method to two test cases: in the first, we size polygonal workstations for two populations and, in the second, we dimension circular workstations for different group sizes.

Both coordination and symmetry of arm swing are reduced in Parkinson's disease.

OBJECTIVE: A recent study reporting significantly reduced symmetry in arm swing amplitude in early Parkinson's disease (PD), as measured during single strides in a gait laboratory, led to this investigation of arm swing symmetry and coordination over many strides using wearable accelerometers in PD. METHODS: Forearm accelerations were recorded while eight early PD subjects and eight Controls performed 8-min walking trials. Arm swing asymmetry (ASA), maximal cross-correlation (MXC), and instantaneous relative phase (IRP) of bilateral arm swing were compared between PD and Controls. Correlations between arm swing measurements (ASA and MXC) and Unified PD Rating Scale (UPDRS) scores were estimated. RESULTS: PD subjects demonstrated significantly higher ASA (p=0.002) and lower MXC (p<0.001) than Controls. The IRP probability distribution for PD was significantly different than Controls (p<0.001), with an angular standard deviation of 67.2° for PD and 50.6° for Controls. Among PD subjects, ASA was significantly correlated with the UPDRS score for the limbs (R(2)=0.58, p=0.049), whereas MXC was significantly correlated with the tremor subscore of the limbs (R(2)=0.64, p=0.031). DISCUSSION: The study confirms previously reported higher arm swing asymmetry in PD but also shows there is significantly lower MXC and greater IRP variability, suggesting that reduction in bilateral arm coordination may contribute to clinically observed asymmetry in PD. The differential correlation of clinical measures of motor disability with measurements of arm swing during gait is intriguing and deserves further investigation.

Molecular recognition of trigonal oxyanions using a ditopic salt receptor: evidence for anisotropic shielding surface around nitrate anion.

A ditopic, macrobicyclic receptor with adjacent anion and cation binding sites is able to extract a range of monovalent salts into chloroform solution. The structures of the receptor complexed with KAcO, LiNO(3), NaNO(3), KNO(3), and NaNO(2) are characterized in solution by NMR spectroscopy and in the solid state by X-ray crystallography. The sodium and potassium salts are bound to the receptor as contact ion-pairs, with the metal cation located in the receptor's crown ether ring and the trigonal oxyanion hydrogen bonded to the receptor NH residues. The solid-state structure of the LiNO(3) complex has a bridging water molecule between the cation and anion. In all solid-state structures, the trigonal oxyanion is not located symmetrically inside the receptor cavity. It appears that anion orientation is controlled by a complex interplay of steric factors, coordination bonding to the metal cation, and hydrogen bonding with the receptor NH residues. An important feature with this latter effect is the fact that hydrogen bonds directed toward the oxygen lone pairs on a trigonal oxyanion are stronger than hydrogen bonds to the pi-electrons. In solution, the (1)H NMR spectra of the nitrate and nitrite salt complexes are noteworthy because several receptor signals, including the NH protons, undergo unusual upfield movements in chemical shift upon complexation. This is a reflection of the diamagnetic anisotropy of these trigonal oxyanions. The magnetic shielding surface for the NO(3)(-) anion is calculated using density functional theory and shown to have a shielding region directly above the central nitrogen.

Bronsted acid-promoted olefin aziridination and formal anti-aminohydroxylation.

A straightforward synthesis of aziridines is reported from an electron-rich azide (alkyl or aryl azide), electron-deficient olefin, and triflic acid in cold acetonitrile. The only coproduct of the reaction is dinitrogen (N2). Active ester substrates bearing a nucleophilic carbonyl engage the putative protonated aziridine intermediate to produce the product of olefin aminohydroxylation in which the nitrogen is benzyl protected and the oxygen is acylated. The possibility that a triazoline need not be an intermediate in aziridine production is advanced.

Selective solid-liquid extraction of lithium halide salts using a ditopic macrobicyclic receptor.

A ditopic salt receptor that is known to bind and extract solid NaCl, KCl, NaBr, and KBr into organic solution as their contact ion pairs is now shown by NMR and X-ray crystallography to bind and extract solid LiCl and LiBr as water-separated ion pairs. The receptor can transport these salts from an aqueous phase through a liquid organic membrane with a cation selectivity of K+ > Na+ > Li+. However, the selectivity order is strongly reversed when the receptor extracts solid alkali metal chlorides and bromides into organic solution. For a three-component mixture of solid LiCl, NaCl, and KCl, the ratio of salts extracted and complexed to the receptor in CDCl3 was 94:4:2, respectively. The same strong lithium selectivity was also observed in the case of a three-component mixture of solid LiBr, NaBr, and KBr where the ratio of extracted salts was 92:5:3. This observation is attributed to the unusually high solubility of lithium salts in organic solvents. The study suggests that ditopic receptors with an ability to extract solid salts as associated ion pairs may have application in separation processes.

Transport of alkali halides through a liquid organic membrane containing a ditopic salt-binding receptor.

A ditopic receptor is shown to have an impressive ability to recognize and extract the ion pairs of various alkali halides into organic solution. X-ray diffraction analysis indicates that the salts are bound in the solid state as contact ion pairs. Transport experiments, using a supported liquid membrane and high salt concentration in the source phase, show that the ditopic receptor can transport alkali halide salts up to 10-fold faster than a monotopic cation or anion receptor and 2-fold faster than a binary mixture of cation and anion receptors. All transport systems exhibit the same qualitative order of ion selectivity; that is, for a constant anion, the cation selectivity order is K+ > Na+ > Li+, and for a constant cation, the anion transport selectivity order is I- > Br- > Cl-. The data suggest that with a ditopic receptor, the polarity of the receptor-salt complex can be lowered if the salt is bound as an associated ion pair, which leads to a faster diffusion through the membrane and a higher maximal flux.

Molecular recognition of alkylammonium contact ion-pairs using a ditopic receptor.

A ditopic, macrobicyclic receptor with adjacent anion and cation binding sites is able to distinguish between various monoalkylammonium salts by binding them as contact ion-pairs. The affinity for linear n-propylammonium chloride is at least 2 orders of magnitude greater than that for n-propylammonium acetate, n-propylammonium p-toluenesulfonate, and branched isopropylammonium chloride. An X-ray structure of the receptor complexed with methylammonium chloride illuminates the basis of the molecular recognition.

Facilitated transport of sodium or potassium chloride across vesicle membranes using a ditopic salt-binding macrobicycle.

A synthetic receptor, with an ability to bind sodium or potassium chloride as a contact ion-pair, is shown to effectively transport either salt across vesicle membranes. Significant transport is observed even when the transporter: phospholipid ratio is as low as 1:2500. Chloride efflux from unilamellar vesicles is monitored using a chloride selective electrode. Mechanistic studies indicate that the facilitated efflux is due to the uncomplexed transporter diffusing into the vesicle and the transporter-salt complex diffusing out. Vesicle influx experiments are also reported, where the facilitated influx of chloride and sodium ions into vesicles is observed directly by 35Cl and 23Na NMR, respectively.

Templated conversion of a crown ether-containing macrobicycle into [2]rotaxanes.

A crown ether-containing macrobicycle was used as the wheel component in a templated synthesis of a [2]rotaxane with an acetal-containing axle. The molecular structures of the macrobicycle and the [2]rotaxane were characterized by NMR spectroscopy and X-ray crystallography. The chloride-binding ability of the macrobicycle, either free in solution or when it is part of a [2]rotaxane, is quite weak as determined by NMR titration experiments. A second analogous [2]rotaxane, with a longer axle, was synthesized, and its solvent-dependent co-conformation was characterized by 2D NMR spectroscopy. The position of the wheel along the axle can be controlled by the solvent polarity, however, attempts to use metal cations such as Na(+), K(+), Ba(2+), and Ag(+) to switch the wheel position in polar solvents were unsuccessful.