Low-motion fMRI data can be obtained in pediatric participants undergoing a 60-minute scan protocol

Performing functional magnetic resonance imaging (fMRI) scans of children can be a difficult task, as participants tend to move while being scanned. Head motion represents a significant confound in fMRI connectivity analyses. One approach to limit motion has been to use shorter MRI protocols, though this reduces the reliability of results. Hence, there is a need to implement methods to achieve high-quality, low-motion data while not sacrificing data quantity. Here we show that by using a mock scan protocol prior to a scan, in conjunction with other in-scan steps (weighted blanket and incentive system), it is possible to achieve low-motion fMRI data in pediatric participants (age range: 7–17 years old) undergoing a 60 min MRI session. We also observe that motion is low during the MRI protocol in a separate replication group of participants, including some with autism spectrum disorder. Collectively, the results indicate it is possible to conduct long scan protocols in difficult-to-scan populations and still achieve high-quality data, thus potentially allowing more reliable fMRI findings.

Velocity of Transmission of Electrical Force and Aberration of Electric Field

An electron of rest mass mo and charge –e moving with velocity v at angle θ to an electric field of intensity E and magnitude E, is subject to aberration of electrid field, as a result of relativity (c – v) of velocity between the electric force, transmitted with velodity of light c of magnitude c and the electron moving with velocity v. The accelerating force, at time t, in accordance with Newton’s second law of motion, put as F = - (eE/c) (c – v) = m (dv/dt), is less than the electrostatic force–eE, the difference being the radiation reaction force. At the velocity of light F become zero and the electron continues to move with speed c as a limit. Motion of the electron with constant mass m and its radiation power are treated under acceleration with θ=0 or deceleration with θ=π radians or at constant speed v, in a circle of radiua r, with θ=π/2 radians. It is shown that circular motion of an electron round a central force of attraction, as in the Rutherford’s nuclear model of the hydrogen atom, is without radiation.

Evaluating Foot Kinematics Using Magnetic Resonance Imaging: From Maximum Plantar Flexion, Inversion, and Internal Rotation to Maximum Dorsiflexion, Eversion, and External Rotation

The foot consists of many small bones with complicated joints that guide and limit motion. A variety of invasive and noninvasive means [mechanical, X-ray stereophotogrammetry, electromagnetic sensors, retro-reflective motion analysis, computer tomography (CT), and magnetic resonance imaging (MRI)] have been used to quantify foot bone motion. In the current study we used a foot plate with an electromagnetic sensor to determine an individual subject’s foot end range of motion (ROM) from maximum plantar flexion, internal rotation, and inversion to maximum plantar flexion, inversion, and internal rotation to maximum dorsiflexion, eversion, and external rotation. We then used a custom built MRI-compatible device to hold each subject’s foot during scanning in eight unique positions determined from the end ROM data. The scan data were processed using software that allowed the bones to be segmented with the foot in the neutral position and the bones in the other seven positions to be registered to their base positions with minimal user intervention. Bone to bone motion was quantified using finite helical axes (FHA). FHA for the talocrural, talocalcaneal, and talonavicular joints compared well to published studies, which used a variety of technologies and input motions. This study describes a method for quantifying foot bone motion from maximum plantar flexion, inversion, and internal rotation to maximum dorsiflexion, eversion, and external rotation with relatively little user processing time.

Segmental variation in the activity and function of the equine longissimus dorsi muscle during walk and trot

Muscle function depends in part on the interplay between its activity and its length within the stretch-shortening cycle. The longissimus dorsi is a large epaxial muscle running along the thoracic and lumbar regions of the equine back. Due to its anatomical positioning, the longissimus dorsi has the capability of contributing to many functions: developing bending moments in the dorsoventral and lateral (coupled to axial rotation) directions and also providing stiffness to limit motion in these directions. We hypothesize that the exact function of the longissimus dorsi will vary along the back and between gaits as the relation between activity and motion of the back changes. Electromyograms (EMG) were recorded at walk (inclined and level) and trot (on the level) on a treadmill from the longissimus dorsi at muscle segments T14, T16, T18 and L2. Back motion was additionally measured using a fibre-optic goniometer. Co-contractions of the muscle between its left and right sides were quantified using correlation analysis. A greater dominance of unilateral activity was found at more cranial segments and for level walking, suggesting a greater role of the longissimus dorsi in developing lateral bending moments. Timing of the EMG varied between muscle segments relative to the gait cycle, the locomotor condition tested and the flexion–extension cycle of the back. This supports the hypothesis that the function of the longissimus dorsi changes along the back and between gaits.

Design and Development of Passive and Active Force Feedback Systems Using Magnetorheological Fluids

Recently, haptic devices have been in use to increase the effectiveness of human-machine interfaces. On the forefront of this technology are passive, force-feedback controllers that resist or even limit motion. This motion control can be the result of a manipulator coming into contact with an object in either the virtual or physical world. Thus, an end-user can get both visual and tactile feedback on system operations. Furthermore, an active force-feedback controller can not only resist motion, but also create a reactive force that the user can sense. This active force-feedback is essential for delicate operations, such as telerobotic surgery, where a doctor needs to feel the difference between a spongy muscle and a hard bone. However, such haptic devices need to be simple and fast, so that they will not interfere with the existing system dynamics. A promising solution employs magnetorheological (MR) fluids in an active force-feedback controller. MR fluids feature a rheological change that is brought about when micron-sized particles within the fluid are exposed to a magnetic field. This change happens within milliseconds and can be used to create resistance quickly and easily. MR fluids can also be combined in a motor driven clutch mechanism to provide active resistance to the user with a force proportional to what the manipulator is experiencing. This paper will show the model development, design, construction, and control implementation of passive and active force-feedback devices.

Hydrodynamics and Thermodynamics of Newtonian Stars

We investigated spherically symmetric solution for nonrelativistic cosmological fluid equations and thermodynamic equation of state for Newtonian stars. It was shown that the assumption of a polytropic state equation, P 0 = κ ρ 0 γ , at the center of the star only suffices to integrate the equations explicitly. Our exact solution yields many fruitful results such as stellar stability, spherical oscillation and collapses of stars. Pressure, temperature, and density profiles inside stars were obtained. Central densities, pressures and temperatures of the Newtonian stars such as Sun, Jupiter and Saturn were also calculated. Analytical results show that stars with γ ≤ 4/3 are unstable so that they are collapsing or they may expand forever. On the other hand, stars with γ > 4/3 are stables so that they could undergo spherical oscillation. The upper bound value of white dwarf mass obtained turns out to be close to the Chandrasekhar limit. Motion of the Universe was also discussed within the framework of Newtonian mechanics.

Limit motion of an Ornstein–Uhlenbeck particle on the equilibrium manifold of a force field

In this paper we consider a position–velocity Ornstein-Uhlenbeck process in an external gradient force field pushing it toward a smoothly imbedded submanifold of . The force is chosen so that is asymptotically stable for the associated deterministic flow. We examine the asymptotic behavior of the system when the force intensity diverges together with the diffusion and the damping coefficients, with appropriate speed. We prove that, under some natural conditions on the initial data, the sequence of position processes is relatively compact, any limit process is constrained on , and satisfies an explicit stochastic differential equation which, for compact , has a unique solution.

Limit motion of an Ornstein–Uhlenbeck particle on the equilibrium manifold of a force field

In this paper we consider a position–velocity Ornstein-Uhlenbeck process in an external gradient force field pushing it toward a smoothly imbedded submanifold of . The force is chosen so that is asymptotically stable for the associated deterministic flow. We examine the asymptotic behavior of the system when the force intensity diverges together with the diffusion and the damping coefficients, with appropriate speed. We prove that, under some natural conditions on the initial data, the sequence of position processes is relatively compact, any limit process is constrained on , and satisfies an explicit stochastic differential equation which, for compact , has a unique solution.