Major Axis Of Ellipse Research Articles

Stress Engineering of Magnetization Fluctuation and Noise Spectra in Low-Barrier Nanomagnets Used as Analog and Binary Stochastic Neurons.

A single-domain nanomagnet, shaped like a thin elliptical disk with small eccentricity, has a double-well potential profile with two degenerate energy minima separated by a small barrier of a few kT (k = Boltzmann constant and T = absolute temperature). The two minima correspond to the magnetization pointing along the two mutually anti-parallel directions along the major axis of the ellipse. At room temperature, the magnetization fluctuates randomly between the two minima, mimicking telegraph noise. This makes the nanomagnet act as a "binary" stochastic neuron (BSN) with the neuronal state encoded in the magnetization orientation. If the nanomagnet is magnetostrictive, then the barrier can be depressed further by applying (electrically generated) uniaxial stress along the ellipse's major axis, thereby gradually eroding the double-well shape. When the barrier almost vanishes, the magnetization begins to randomly assume any arbitrary orientation (not just along the major axis), making the nanomagnet act as an "analog" stochastic neuron (ASN). The magnetization fluctuation then begins to increasingly resemble white noise. The full width at half maximum (FWHM) of the noise auto-correlation function decreases with increasing stress, as the fluctuation gradually transforms from telegraph noise to white noise. Consistent with this trend, the noise spectral density exhibits a 1/fβ spectrum (at high frequencies) with β decreasing from 2.00 to 1.88 with increasing stress. Stress can thus not only reconfigure a BSN to an ASN, which has its own applications, but it can also perform "noise engineering", i.e., tune the auto-correlation function and power spectral density, having applications in signal processing.

Bone Density Distribution Pattern in the Lateral Wall of the Femoral Intercondylar Notch: Implications for the Direct Insertion of the Femoral ACL Attachment

Background: The ideal position of the femoral bone tunnel in the anterior cruciate ligament (ACL) is controversial. The functional importance of the ACL fiber varies depending on where it is attached to the femur. Functionally important fibers can cause high mechanical stress on the bone, and the Wolff law predicts that bone mineral density will increase at high mechanical stress sites. Purpose/Hypothesis: The purpose of this study was to use computed tomography imaging to determine the distribution pattern of bone density in the lateral intercondylar wall. It was hypothesized that the high-density area (HDA) of the lateral intercondylar wall would reflect the functional insertion of the ACL as reported in previous anatomic studies. Study Design: Descriptive epidemiology study. Methods: Data from 39 knees without ACL injuries were retrospectively collected. The HDA of the lateral intercondylar wall was defined as the region containing the top 10% of the radiodensity values. The shape of the HDA was approximated as an ellipse, and the quadrant method was used to determine the center of the ellipse. The association between the ratio of the minor axis to the major axis of the ellipse and background characteristics was investigated. Results: According to the quadrant method, the center of the HDA ellipse was 33.6% in the deep-shallow direction and 23.4% in the high-low direction. The center of the ellipse was comparable to the anatomic center of the ACL footprint, as previously reported. The ratio of the minor axis to the major axis of the ellipse was 0.58 (95% CI, 0.54-0.62). There was a significant negative correlation between the ratio of the minor axis to the major axis of the HDA ellipse and the posterior tibial slope ( r = −0.38, P = .02). Conclusion: The center of the HDA ellipse was found to be similar to the anatomic center of the ACL footprint. Considering the mechanical stress responses in bone, the HDA of the lateral intercondylar wall has the potential to represent the ACL insertion, especially functional insertion.

Theoretical analysis and fracture process of elliptical tunnel with symmetric cracks subjected to water pressure and ground stress

The water diversion tunnel played an important role in the allocation of water resources in the water diversion project. In the process of actual use, some cracks or joints at the edge of the tunnel could produce further cracking under the action of internal water pressure and in-situ stress, which was dangerous to the safety of the tunnel. The analytical solution formulas of stress intensity factors (SIFs) of the elliptical tunnel with two cracks were derived by using the complex function method, and the external factors affecting the stability of the elliptical tunnel were analyzed. The failure process of the specimens was analyzed by using the high-speed camera and digital image correlation (DIC) method to obtain the evolution laws of crack initiation behavior and tunnel fracture modes. The results can conclude that both sides of the elliptical tunnel and the crack tip were stress concentration areas. As the inclination angle α of the elliptical tunnel is varied from 0° to 45°, tensile cracks occur at the top and bottom of the elliptical tunnel caused by tensile stress, and the compressive strength is smallest when the elliptical tunnel with α is 45°. As the inclination angle α is 75°, two penetrating cracks appear at the edge of the elliptical tunnel and crack tips. The initiation pressure increases with the inclination angle α. The SIF of mode II rises with the ellipse major semi axis and the crack length.

In-Orchard Sizing of Mango Fruit: 1. Comparison of Machine Vision Based Methods for On-The-Go Estimation

Estimation of fruit size on-tree is useful for yield estimation, harvest timing and market planning. Automation of measurement of fruit size on-tree is possible using RGB-depth (RGB-D) cameras, if partly occluded fruit can be removed from consideration. An RGB-D Time of Flight camera was used in an imaging system that can be driven through an orchard. Three approaches were compared, being: (i) refined bounding box dimensions of a YOLO object detector; (ii) bounding box dimensions of an instance segmentation model (Mask R-CNN) applied to canopy images, and (iii) instance segmentation applied to extracted bounding boxes from a YOLO detection model. YOLO versions 3, 4 and 7 and their tiny variants were compared to an in-house variant, MangoYOLO, for this application, with YOLO v4-tiny adopted. Criteria developed to exclude occluded fruit by filtering based on depth, mask size, ellipse to mask area ratio and difference between refined bounding box height and ellipse major axis. The lowest root mean square error (RMSE) of 4.7 mm and 5.1 mm on the lineal length dimensions of a population (n = 104) of Honey Gold and Keitt varieties of mango fruit, respectively, and the lowest fruit exclusion rate was achieved using method (ii), while the RMSE on estimated fruit weight was 113 g on a population weight range between 180 and 1130 g. An example use is provided, with the method applied to video of an orchard row to produce a weight frequency distribution related to packing tray size.

Manipulated deformation of lipid bilayer vesicles in magnetic fields

ABSTRACTWe have extended the Helfrich’s spontaneous curvature model of the equilibrium vesicle by adding the interaction between magnetic field and the constituent molecules to supply an explaination in principle of the emerging manipulated deformation of a magnetic vesicles such as the reversibly deformation of artificial stomatocyte. The small deformation can be measured by birefringence. Here, we present the derivations of formulas in detailed to reveal the perturbation of deformation ψ under two cases. New features, for example, a ‘phase transition’ of shape will occur with increasing of B from B1∗ to B2∗ for Δχ<0, in which the major axis of ellipse was rotated by 90°, have been revealed. It is worthy for experimenter to demonstrate the ‘phase transition’. The significance of imaginary relation (B1∗<B<B2∗) is also waiting to be uncovered.

Purity of 3D polarization.

Measures of purity for 3D partially polarized fields, and in particular, the separation into circularly and linearly polarized contributions, are reexamined, and a new degree of total linear polarization introduced. Explicit expressions for the characteristic decomposition in terms of coherency matrix elements are presented, including the special case of an intrinsic coherency matrix. Parameterization of the coherency matrix in terms of ellipticity, and the directions of the ellipse normal and major axis are investigated. Phase consistency is discussed. A comprehensive collection of results regarding intrinsic polarization properties is presented.

Offshore Wind Farm Footprint on Organic and Mineral Particle Flux to the Bottom

Offshore wind farms (OWFs) are an important source of renewable energy accounting for 2.3% of the European Union's electricity demand. Yet their impact on the environment needs to be assessed. Here, we couple a hydrodynamic (including tides and waves) and sediment transport model with a description of the organic carbon and mineral particle dynamics in the water column and sediments. The model is applied to the Belgian Coastal Zone (BCZ) where OWFs currently occupy 7% of its surface area which is estimated to double in the next 5 years. The impact of OWFs on the environment is represented through the filtration of the water column and fecal pellets production by the blue mussel, the dominant fouling organism. Our model simulations show that the impact of biodeposition on the mud particle sedimentation and on sediment composition is small compared to the fluxes associated with tidal deposition and resuspension and the lateral inputs. In contrast, the total organic carbon (TOC) flux to the sediment is significantly altered inside the OWF perimeters and TOC deposition is increased up to 50% in an area 5 km around the monopiles. Further away, the TOC flux to the bottom decreases with a notable effect up to 30 km away. The major changes are found along the direction of the main residual current and tidal ellipse's major axis. In addition, sub-mesoscale gyres act as retention areas with increased carbon deposition. A future OWF in the BCZ will be located close to gravel beds in a Natura 2000 area, considered as vulnerable habitats and biodiversity hotspots. The different scenarios for this OWF, varying in turbine number and positioning, are compared in terms of impact on the carbon and mineral particle deposition flux in the BCZ and, particularly, to these gravel beds. The scenarios show that the number of turbines has only a slight impact on the TOC deposition flux, unlike their positioning that significantly alters the TOC flux to the gravel beds. The TOC deposition flux exceeds 50%, when the turbines are placed next to the gravel beds; while a limited increase is simulated, when the turbines are located the farthest possible from them.

3D Scanning of the Forearm for Orthosis and HMI Applications.

The rise of rehabilitation robotics has ignited a global investigation into the human machine interface (HMI) between device and user. Previous research on wearable robotics has primarily focused on robotic kinematics and controls but rarely on the actual design of the physical HMI (pHMI). This paper presents a data-driven statistical forearm surface model for designing a forearm orthosis in exoskeleton applications. The forearms of 6 subjects were 3D scanned in a custom-built jig to capture data in extreme pronation and supination poses, creating 3D point clouds of the forearm surface. Resulting data was characterized into a series of ellipses from 20 to 100% of the forearm length. Key ellipse parameters in the model include: normalized major and minor axis length, normalized center point location, tilt angle, and circularity ratio. Single-subject (SS) ellipse parameters were normalized with respect to forearm radiale-stylion (RS) length and circumference and then averaged over the 6 subjects. Averaged parameter profiles were fit with 3rd-order polynomials to create combined-subjects (CS) elliptical models of the forearm. CS models were created in the jig as-is (CS1) and after alignment to ellipse centers at 20 and 100% of the forearm length (CS2). Normalized curve fits of ellipse major and minor axes in model CS2 achieve R2 values ranging from 0.898 to 0.980 indicating a high degree of correlation between cross-sectional size and position along the forearm. Most other parameters showed poor correlation with forearm position (0.005 < R2 < 0.391) with the exception of tilt angle in pronation (0.877) and circularity in supination (0.657). Normalized RMSE of the CS2 ellipse-fit model ranged from 0.21 to 0.64% of forearm circumference and 0.22 to 0.46% of forearm length. The average and peak surface deviation between the scaled CS2 model and individual scans along the forearm varied from 0.56 to 2.86 mm (subject averages) and 3.86 to 7.16 (subject maximums), with the peak deviation occurring between 45 and 50% RS length. The developed equations allow reconstruction of a scalable 3D model that can be sized based on two user measures, RS length and forearm circumference, or based on generic arm measurements taken from existing anthropometric databases.

The Temporal Relationship Between Ecological Pain and Life-Space Mobility in Older Adults With Knee Osteoarthritis: A Smartwatch-Based Demonstration Study.

BackgroundOlder adults who experience pain are more likely to reduce their community and life-space mobility (ie, the usual range of places in an environment in which a person engages). However, there is significant day-to-day variability in pain experiences that offer unique insights into the consequences on life-space mobility, which are not well understood. This variability is complex and cannot be captured with traditional recall-based pain surveys. As a solution, ecological momentary assessments record repeated pain experiences throughout the day in the natural environment.ObjectiveThe aim of this study was to examine the temporal association between ecological momentary assessments of pain and GPS metrics in older adults with symptomatic knee osteoarthritis by using a smartwatch platform called Real-time Online Assessment and Mobility Monitor.MethodsParticipants (n=19, mean 73.1 years, SD 4.8; female: 13/19, 68%; male: 6/19, 32%) wore a smartwatch for a mean period of 13.16 days (SD 2.94). Participants were prompted in their natural environment about their pain intensity (range 0-10) at random time windows in the morning, afternoon, and evening. GPS coordinates were collected at 15-minute intervals and aggregated each day into excursion, ellipsoid, clustering, and trip frequency features. Pain intensity ratings were averaged across time windows for each day. A random effects model was used to investigate the within and between-person effects.ResultsThe daily mean pain intensities reported by participants ranged between 0 and 8 with 40% reporting intensities ≥2. The within-person associations between pain intensity and GPS features were more likely to be statistically significant than those observed between persons. Within-person pain intensity was significantly associated with excursion size, and others (excursion span, total distance, and ellipse major axis) showed a statistical trend (excursion span: P=.08; total distance: P=.07; ellipse major axis: P=.07). Each point increase in the mean pain intensity was associated with a 3.06 km decrease in excursion size, 2.89 km decrease in excursion span, 5.71 km decrease total distance travelled per day, 31.4 km2 decrease in ellipse area, 0.47 km decrease ellipse minor axis, and 3.64 km decrease in ellipse major axis. While not statistically significant, the point estimates for number of clusters (P=.73), frequency of trips (P=.81), and homestay (P=.15) were positively associated with pain intensity, and entropy (P=.99) was negatively associated with pain intensity.ConclusionsIn this demonstration study, higher intensity knee pain in older adults was associated with lower life-space mobility. Results demonstrate that a custom-designed smartwatch platform is effective at simultaneously collecting rich information about ecological pain and life-space mobility. Such smart tools are expected to be important for remote health interventions that harness the variability in pain symptoms while understanding their impact on life-space mobility.

A calculation method of sliding friction coefficient on tooth surface for helical gear pair based on loaded tooth contact analysis and elastohydrodynamic lubrication theory

The sliding friction coefficient on tooth surface is related to power loss, carry capacity and transmission performance of gear. Reasonable transmission analysis of gear pair is the premise of accurate calculation of sliding friction coefficient on tooth surface. However, for helical gear pair, the line contact without considering machining error/installation error/modification of gear is usually adopted to replace the major axis of ellipse caused by contact load. Therefore, in this paper, contact path on tooth surface, length of contact line, load distribution on tooth surface and loaded transmission errors are accurately calculated by loaded tooth contact analysis (LTCA). Combing with elastohydrodynamic lubrication (EHL) theory, a calculation method of sliding friction coefficient on tooth surface for helical gear pair is proposed.

Two dimensional in-vitro phenotyping of root system architecture using Poly Ethylene Glycol in backcross inbred lines harboring drought tolerant QTLs of rice (Oryza sativa L.)

The present investigation was made to validate the effect and expression of multiple drought QTLs from Apo in the background of high yielding drought susceptible variety IR 64 under two dimensional in-vitro root architecture studies. The genotype CB 229 (DTY2.2, DTY3.1 and DTY8.1) recorded a higher network bushiness, network width, specific root length and network distribution of roots under PEG treatment (stress) and in network area CB 193-3 outperformed than CB 229. This clearly shows that introgression of multiple drought QTLs in various combination in the same genetic background enhances different level of expression of QTLs and tolerance to varied intensity of drought. Under field screening for drought, CB 229 out performed in both spikelet fertility percentage and yield than the remaining BILs. The traits viz., major ellipse axis, maximum number of roots, network bushiness, specific root length, network convex area and network width are positively correlated with spikelet fertility percentage and single plant yield under drought experiment. Principal component analysis accounted for 78.47 per cent of variability among root traits in PC1 and was loaded with all the traits observed under in-vitro condition. Hence, an understanding on complex nature of QTL expression associated with root system architecture under in-vitro stress in rice may help the breeder to develop new cultivars with enhanced level of tolerance against water limited situations in near future.

What role would the pores related to brittle minerals play in the process of oil migration and oil & water two-phase imbibition?

This study aimed to investigate the geometry distinction of the pores formed by brittle minerals in shale oil reservoir and dig out its significance in hydrocarbon migration and exploitation.14050 pores related to brittle minerals in typical shale oil reservoir samples are selected as the research objects, high-resolution field emission scanning electron microscopy (FE-SEM), imbibition test, Nuclear Magnetic Resonance(NMR), high-resolution image technique, construction of new parameters, statistics and analysis of large numbers and other means are used to discover this issue.Results firstly show that the development of pores in the two directions (Angle between two directions is 90 degrees or approximately 90 degrees) are complementary and promote each other. Reversely, the data points begin to be scattered, which means that the development of the pore in the above two directions begins to “lose stability”, rather than promote each other all the time. This could prove that the rectangle (width, height), Legendre ellipse (major axis and major axis) and maximum and minimum Feret diameter of pores can all be used as the effective criteria for the development of pore shape related to brittle minerals. Sufficient evidences could prove that the pores related to brittle minerals contribute to oil and gas migration and oil & water imbibition.The conclusion of this study will provide an important theoretical basis for clarifying the oil occurrence mechanism of shale oil reservoir and looking for the geological and engineering dessert from the microscopic viewpoint.

Spectral and Polarization Characteristics of the Light Passing through a Cholesteric Photonic Crystal

Combined optical studies of a cholesteric photonic crystal are performed: the transmission spectra and the rotation of the plane of polarization of light (RPPL) spectra of the crystal are recorded, and the polarization characteristics of the light having passed through the photonic crystal are measured. The RPPL spectra have specific features related to the presence of a photonic quasi-band gap. The photonic density of states and its transformation with the photonic crystal temperature and thickness are determined. The ellipticity (ratio of the minor to the major axis of ellipse) of the light having passed through the sample is maximal at the center of the band gap and decreases when the distance from the band gap increases. At the center of the photonic quasi-band gap, the ellipticity increases with increasing photonic crystal thickness L and decreasing temperature, and it is close to a circular one in samples with L > 5 μm. The results obtained are compared with the existing theories, the analytical expressions derived from the Maxwell equations, and the results of numerical calculations performed by the 4 × 4 Berreman matrix method

An Angle-Independent Cross-Sectional Doppler Method for Flow Estimation in the Common Carotid Artery.

The Doppler ultrasound is the most common technique for noninvasive quantification of blood flow, which, in turn, is of major clinical importance for the assessment of the cardiovascular condition. In this article, a method is proposed in which the vessel is imaged in the short axis, which has the advantage of capturing the whole flow profile while measuring the vessel area simultaneously. This view is easier to obtain than the longitudinal image that is currently used in flow velocity estimation, reducing operator dependence. However, the Doppler angle in cross-sectional images is unknown since the vessel wall can no longer be used to estimate the flow direction. The proposed method to estimate the Doppler angle in these images is based on the elliptical intersection between a cylindrical vessel and the ultrasound plane. The parameters of this ellipse (major axis, minor axis, and rotation) are used to estimate the Doppler angle by solving a least-squares problem. Theoretical feasibility was shown in a geometrical model, after which the Doppler angle was estimated in simulated ultrasound images generated in Field II, yielding a mean error within 4°. In vitro, across 15 short-axis measurements with a wide variety of Doppler angles, errors in the flow estimates were below 10%, and in vivo, the average velocities in systole obtained from longitudinal ( v=69.1 cm/s) and cross-sectional ( v=66.5 cm/s) acquisitions were in agreement. Further research is required to validate these results on a larger population.

Effects of Exoskeleton Gait Training on Balance, Load Distribution, and Functional Status in Stroke: A Randomized Controlled Trial.

Background: As a result of stroke, patients have problems with locomotion and transfers, which lead to frequent falls. Recovery after stroke is a major goal of rehabilitation, but it is difficult to choose which treatment method is most beneficial for stroke survivors. Recently, powered robotic exoskeletons are used in treatment to maximize the neural recovery of patients after stroke, but there are no studies evaluating the changes in balance among patients rehabilitated with an exoskeleton.Purpose: The aim of this study was to evaluate the effects of Ekso GT exoskeleton-assisted gait training on balance, load distribution, and functional status of patients after ischemic stroke.Methods: The outcomes are based on 44 patients aged 55–85 years after ischemic stroke who were previously randomly assigned into two groups: experimental (with Ekso GT rehabilitation) and control (with classical rehabilitation). At baseline and after 4 weeks of treatment, the patients were evaluated on balance, load distribution, and functional status using, respectively a stabilometric platform, the Barthel Index, and the Rivermead Mobility Index.Results: In the experimental group, balance improved regarding the variables describing sway area as ellipse major and minor axes. In the control group, improvement was noted in sway velocity. After the therapy, total load distribution on feet in both groups showed a small and insignificant tendency toward reduction in the amount of uninvolved limb loading. In the control group, significant load transfer from the backfoot to the forefoot was noted. Both forms of rehabilitation caused significant changes in functional status.Conclusions: Both training with the use of the Ekso GT exoskeleton and classical physiotherapy lead to functional improvement of patients after ischemic stroke. However, in the experimental group, improvement was observed in a larger number of categories, which may suggest potentially greater impact of treatment with the exoskeleton on functional status. Also, both forms of rehabilitation caused significant changes in balance, but we have noted some trends indicating that treatment with exoskeleton may be more beneficial for some patients. The load transfer from the backfoot to the forefoot observed in the control group was an unfavorable phenomenon. We suggest that the Ekso GT exoskeleton may be a promising tool in the rehabilitation of patients after stroke.Trial registration: Trial ID ACTRN12616000148471

Femtosecond filament emergence between π-shifted beamlets in air.

By rotating the four-section π-shifted phase plate in the transverse plane relatively to the axes of the elliptical beam of 800-nm, 1.1-mJ, 35-fs pulse propagating in air, we switch between the regime of four parallel plasma channels and the regime of spatial symmetry breakup followed by on-axis plasma channel formation identified on the burnt paper images of the beam. Relaxation of the π-phase shift for 45° phase plate rotation is demonstrated explicitly in 3D+time carrier wave resolved numerical simulations yielding the initial step-like phase distribution degradation along the plasma region. This degradation becomes negligible as the angle between the ellipse major axis and the π-phase break line decreases to 15°.

Numerical Simulation of Strength, Deformation, and Failure Characteristics of Rock with Fissure Hole Defect

Using discrete element software, namely, particle flow code as two‐dimensional program (PFC2D), two types of models were established: vertical fissure hole combination and horizontal fissure hole combination with ratios of major and minor axis of ellipse being 1, 1.2, 1.5, 2, and 3, which corresponded to a total of ten samples. The failure mode, mechanical behavior, and stress state before and after crack generation in elliptical hole crack combination models with different ratios of major and minor axis were analyzed. The crack development, stress field evolution, and acoustic emission characteristics of the vertical fissure model and horizontal fissure model were studied at the optimized ratio of major and minor axis of ellipse being 1.5. The results showed that elliptical hole fissure with different ratios of major and minor axis resulted in the decrease in the strength and elastic modulus of rock and increase in the peak strain of rock. The effect of the horizontal fissure model on the peak strength, peak strain, and elastic modulus of rock was found to be greater than that of the vertical fissure hole model. Ellipses with different ratios of major and minor axis in various models slightly influenced the rock failure modes, and their failure modes corresponded to tensile shear failure and tensile failure. Before crack formation, the tensile stress concentration areas of each model were, respectively, distributed at the upper and lower ends of the vertical fissure and the major axis of ellipse, and the compressive stress concentration areas were distributed at both ends of the major axis of ellipse and the fissure in the horizontal direction. After the model failed, the compressive stress concentration areas of the vertical fissure model and the horizontal fissure model transferred to the left upper part and the right upper part of the model along the left end of the hole and the right end of the fissure, respectively. When the ratio of major and minor axis of ellipse was 1.5, cracks in the vertical model and the horizontal model of fissure developed along the axial direction at the ends of cracks and holes, respectively, and then secondary cracks were generated at the ends of left and right sides. The maximum compressive stress in each stage of the vertical fissure model was greater than that of the horizontal fissure model, and when the model was damaged, its stress release was more.

Rayleigh Damping Modelling to Assess Viscous Behaviour in Actuated Breast Tissue

Breast cancer is a significant health problem worldwide. Emerging non-invasive methods assess tumor presence by its impact on breast tissue mechanics. This paper outlines a method to identify equivalent viscous damping in breast tissue and fit a model based on the Rayleigh damping (RD) model. Surface motion information of actuated breast tissue was captured using the Digital Image Elasto Tomography (DIET) system. The viscous damping was calculated for over 14,000 reference points using an ellipse fitted to the force-displacement hysteresis loop response data to calculate work done. A damping model based on RD is suggested and fit to median filtered data of viscous damping constant plotted against the major ellipse axis. This successfully described the trend for all 29 breasts (14 cancerous, 15 healthy) with average R2 values ranging from 0.79-0.88. One model coefficient, ‘a’, proportional to local mass, showed reasonable consistency among the subjects and decreased with increasing frequency. No significant difference in this ‘a’ coefficient between healthy and cancerous breasts showed indication of diagnostic potential. However, consistent values across all breasts suggest it is a fundamental tissue property. Further suggestions to normalise the major axis by frequency demonstrate the potential for the model to be developed to describe viscous behaviour of breast tissue in the form of storage and loss modulus.

Performance Analysis and Structure Optimization of a Nautilus Isometric Spiral Wind Turbine

Background: This paper proposes a Nautilus isometric spiral vertical axis wind turbine, which is a new structure, and its aerodynamic performance and power generation performance need to be analyzed. Methods: A 3D model of the wind turbine was built and its aerodynamic performance was analyzed. Then the wind turbine power generation and grid-connected simulation platform was built by MATLAB/SIMULINK, and its power generation performance and subsequent grid connection were studied. Results: The basic parameters of the wind turbine were obtained. In order to improve efficiency, parameters such as pressure, torque, wind energy utilization rate and relative velocity of wind turbines with different blade numbers and different sizes were compared. In addition, by building a simulation platform for the power generation control system, the power generation characteristics and grid connection characteristic curves of the generator were obtained. Conclusions: When the number of blades is three and the ratio between the ellipse major axis and minor axis of the blade inlet is 0.76, the best efficiency of the wind turbine can be obtained. Application of the power generation control system used in this paper can achieve grid-connected operation of this wind turbine. It also confirmed that the Nautilus isometric spiral wind turbine has good performance and is worthy of in-depth research.

The Concurrent Control of Motion and Contact Force in the Presence of Predictable Disturbances.

The simultaneous control of force and motion is important in everyday activities when humans interact with objects. While many studies have analyzed the control of movement within a perturbing force field, few have investigated its dual aspects of controlling a contact force in nonisometric conditions. The mechanism by which the central nervous system controls forces during movements is still unclear, and it can be elucidated by estimating the mechanical properties of the arm during tasks with concurrent motion and contact force goals. We investigate how arm mechanics change when a force control task is accomplished during low-frequency positional perturbations of the arm. Contrary to many force regulation algorithms implemented in robotics, where contact impedance is decreased to reduce force fluctuations in response to position disturbances, we observed a steady increase of arm endpoint stiffness as the task progressed. Based on this evidence, we propose a theoretical framework suggesting that an internal model of the perturbing trajectory is formed. We observed that force regulation in the presence of predictable positional disturbances is implemented using a position control strategy together with the modulation of the endpoint stiffness magnitude, where the direction of the endpoint stiffness ellipse's major axis is oriented toward the desired force.