Change In Rotation Velocity Research Articles

Modeling small remotely piloted aircraft system to head impact for investigating craniocerebral response

Understanding small remotely piloted aircraft system (sRPAS) to human head impacts is needed to better protect human head during sRPAS ground collision accidents. Recent literature reported cadaveric data on sRPAS to human head impacts, which provided a unique opportunity for developing validated computational models. However, there lacks an understanding of skull stress and brain strain during these impacts. Meanwhile, how slight changes in sRPAS impact setting could affect human head responses remains unknown. Hence, a representative quadcopter style sRPAS finite element (FE) model was developed and applied to a human body model to simulate a total of 45 impacts. Among these 45 simulations, 17 were defined according to cadaveric setting for model validation and the others were conducted to understand the sensitivity of impact angle, impact location, and impacted sRPAS components. Results demonstrated that FE-model-predicted head linear acceleration and rotational velocity agreed with cadaveric data with average predicted linear acceleration 4.5% lower than experimental measurement and average predicted of rotational velocity 2% lower than experimental data. Among validated simulations, high skull stresses and moderate level of brain strains were observed. Also, sensitivity study demonstrated significant effect of impact angle and impact location with 3° variation inducing 30% changes in linear acceleration and 29% changes in rotational velocity. Arm-first impact was found to generate more than two times higher skull stresses and brain strains compared to regular body-shell-first impact.

Signature of geomagnetic superstorm in Earth’s rotation speed

A connection between solar activity and decadal Length of day variations is investigated. Statistical comparison of Length of day with various geomagnetic and Solar activity indices has been done for the last 140 years. A jump in Length of day (LOD) is found at the moment of the geomagnetic storm, the largest one for the last few decades, that happened in late October 2003, the so called Halloween storm. This change in rotational velocity of the Earth can not be explained by any known atmospheric or oceanic influences. Moreover, such jump in LOD is an unique one for the few recent years. It is supposed that this jump can be caused by transfer of angular momentum between Solar wind and the solid Earth. A possible mechanism of such a transfer is proposed.

The influence of impact source on variables associated with strain for impacts in ice hockey

Concussion can occur from a variety of events (falls to ice, collisions etc) in ice hockey, and as a result it is important to identify how these different impact sources affect the relationship between impact kinematics and strain that has been found to be associated to this injury. The purpose of this research was to examine the relationship between kinematic variables and strain in the brain for impact sources that led to concussion in ice hockey. Video of professional ice hockey games was analyzed for impacts that resulted in reported clinically diagnosed concussions. The impacts were reconstructed using physical models/ATDs to determine the impact kinematics and then simulated using finite element modelling to determine maximum principal strain and cumulative strain damage measure. A stepwise linear regression was conducted between linear acceleration, change in linear velocity, rotational acceleration, rotational velocity, and strain response in the brain. The results for the entire dataset was that rotational acceleration had the highest r2 value for MPS (r2 = 0.581) and change in rotational velocity for cumulative strain damage measure (r2 = 450). When the impact source (shoulder, elbow, boards, or ice impacts) was isolated the rotational velocity and acceleration r2 value increased, indicating that when evaluating the relationships between kinematics and strain based metrics the characteristics of the impact is an important factor. These results suggest that rotational measures should be included in future standard methods and helmet innovation and design in ice hockey as they have the highest association with strain in the brain tissues.

Application of hydrophobic micropatterns to centrifugal fluid valve in flow channel

Optimizing the use of micro-flow channels as fluid control mechanisms is an effective means of increasing the sensitivity and selectivity of biosensors. The purpose of this study was to clarify the effectiveness of periodic structure applied to this type of fluid control mechanism to improve the hydrophobicity. We evaluated the functionality of centrifugal fluid valve with micrometer-sized periodic structure in the micro-flow channel. A disposable compact disc-based chip with centrifugal fluid valve was designed for this evaluation. The hydrophobic properties such as transferred volume ratio of the sample solution and the change in the transferred volume ratio with rotational velocity (slope) of the centrifugal fluid valve were investigated. In this case, parallel pillars showed higher hydrophobicity than cross-shaped pillars. The transferred volume ratio increased by 20% compared to that without a micro-periodic structure when a protein solution with a similar concentration to that in saliva and plasma was used. Additionally, a change in rotational velocity of only 49.3 rpm was sufficient to switch a centrifugal fluid valve with parallel pillars, meaning that it makes it possible to have two critical rotation speeds when the fluid begins to move with a rotational velocity of 100 rpm. It was shown that the static hydrophobicity dominates the switching characteristics in the proposed centrifugal fluid valve. Our study suggests that applying periodic structure to fluid control mechanisms is an effective means of realizing hydrophobic surfaces.

Results from a recent stellar rotation census of B stars

AbstractIn an analysis of the rotational properties of more than 1100 B stars (~660 cluster and ~500 field B stars), we determine the projected rotational velocity (V sin i), effective temperature, gravity, mass, and critical rotation speed for each star. The new data provide us a solid observational base to explore many hot topics in this area: Why do field B stars rotate slower than cluster B stars? How fast do B stars rotate when they are just born? How fast can B stars rotate before they become Be stars? How does the rotation rate of B stars change with time? Does the evolutionary change in rotation velocity lead to the Be phenomenon? Here we report the results of our efforts in searching for answers to these questions based on the latest B star census.

Motion sickness induced by off-vertical axis rotation (OVAR)

We tested the hypothesis that motion sickness is produced by an integration of the disparity between eye velocity and the yaw-axis orientation vector of velocity storage. Disparity was defined as the magnitude of the cross product between these two vectors. OVAR, which is known to produce motion sickness, generates horizontal eye velocity with a bias level related to velocity storage, as well as cyclic modulations due to re-orientation of the head re gravity. On average, the orientation vector is close to the spatial vertical. Thus, disparity can be related to the bias and tilt angle. Motion sickness sensitivity was defined as a ratio of maximum motion sickness score to the number of revolutions, allowing disparity and motion sickness sensitivity to be correlated. Nine subjects were rotated around axes tilted 10 degrees-30 degrees from the spatial vertical at 30 degrees/s-120 degrees/s. Motion sickness sensitivity increased monotonically with increases in the disparity due to changes in rotational velocity and tilt angle. Maximal motion sickness sensitivity and bias (6.8 degrees/s) occurred when rotating at 60 degrees/s about an axis tilted 30 degrees. Modulations in eye velocity during OVAR were unrelated to motion sickness sensitivity. The data were predicted by a model incorporating an estimate of head velocity from otolith activation, which activated velocity storage, followed by an orientation disparity comparator that activated a motion sickness integrator. These results suggest that the sensory-motor conflict that produces motion sickness involves coding of the spatial vertical by the otolith organs and body tilt receptors and processing of eye velocity through velocity storage.

Kinematic modelling of disk galaxies

This is the second of a series of papers in which the kinematics of disk galaxies is studied by analysing spectroscopic data. Making use of the methods presented in Paper I, this work focuses on the large-scale distribution of disk and Dark Matter halo material by analysing the structure of warped galaxies. observations of three disk galaxies showing regular large-scale (“grand-design”) warps are presented and their structure is analysed. The kinematics and geometry of the galaxies are modelled by fitting a tilted-ring model directly to the data cube, thereby avoiding problems due to orbit crowding or beam smearing. The galaxies follow the previously known “rules for the behaviour of warps”. Furthermore, at large radii the disk settles into a relatively coplanar disk that is inclined with respect to the inner one. With increasing radius, the measured rotation velocity shows a rise. In one of the cases, NGC 5204, the rotation curve shows a jump at the transition radius. While the best fits in the other two cases also suggest that such a jump is present, the change in rotation velocity is compatible with a gradual rise. In two cases, the surface density of the warped layer shows a clear drop at the transition radius and decreases only very slowly further out, while this feature is not as clear for UGC 3580. A literature search shows that these properties are shared by a number of other galaxies. In all cases, an additional, slowly rotating gas layer is found to be present. The change in the rotation velocity and the remarkable geometry of the disks together indicate that the radius at which the warp starts marks the transition between two dynamical regimes, an inner one governed by the stellar disk and an outer one determined by the Dark Matter halo.

Elastohydrodynamic theory for wet oblique collisions

This paper presents a model for oblique collisions of spherical particles with a plane surface covered with a thin liquid layer. Elastohydrodynamic theory developed previously for fully immersed collisions [Davis, Serayssol and Hinch 1986 JFM 63 479–497] is modified for the normal component of motion to account for the finite thickness of the liquid layer. The resulting time evolution of the film thickness profile is then used along with sliding lubrication to determine the tangential component of motion. The critical Stokes number (dimensionless ratio of particle inertia and viscous forces), below which no rebound is seen, is predicted in terms of the physical properties of the materials involved in the collision, as described by a compliance parameter representing a dimensionless measure of elastic deformation due to viscous forces. Beyond the critical Stokes number, the normal restitution coefficient is found to increase with the Stokes number and the compliance parameter, asymptoting to the dry restitution coefficient at high Stokes numbers. The lubrication suction resistance during rebound is limited by cavitation. The tangential restitution is independent of the impact angle and is linearly dependent on the ratio of the fluid layer thickness to the sphere radius, in addition to depending on the Stokes number and compliance parameter. The tangential restitution is found to be close to unity and is generally higher for a larger value of the compliance parameter. Moreover, the tangential restitution is seen to increase with the Stokes number at small compliance and decrease with the Stokes number at large compliance. The change in rotational velocity exhibits trends that are the reverse of the tangential restitution. Finally, closed-form expressions have been developed for describing the restitution coefficients and dimensionless change in rotational velocity.

Evaluation of head response to ballistic helmet impacts using the finite element method

Injuries to the head caused by ballistic impacts are not well understood. Ballistic helmets provide good protection, but still, injuries to both the skull and brain occur. Today there is a lack of relevant test procedure to evaluate the efficiency of a ballistic helmet. The purpose of this project was (1) to study how different helmet shell stiffness affects the load levels in the human head during an impact, and (2) to study how different impact angles affects the load levels in the human head. A detailed finite element (FE) model of the human head, in combination with an FE model of a ballistic helmet (the US Personal Armour System Ground Troops’ (PASGT) geometry) was used. The head model has previously been validated against several impact tests on cadavers. The helmet model was validated against data from shooting tests. Focus was aimed on getting a realistic response of the coupling between the helmet and the head and not on modeling the helmet in detail. The studied data from the FE simulations were stress in the cranial bone, strain in the brain tissue, pressure in the brain, change in rotational velocity and translational and rotational acceleration. A parametric study was performed to see the influence of a variation in helmet shell stiffness on the outputs from the model. The effect of different impact angles was also studied. Dynamic helmet shell deflections larger than the initial distance between the shell and the skull should be avoided in order to protect the head from the most injurious threat levels. It is more likely that a fracture of the skull bone occurs if the inside of the helmet shell strikes the skull. Oblique ballistic impacts may in some cases cause higher strains in the brain tissue than pure radial ones.

Injury tolerances for oblique impact helmet testing

The most frequently sustained severe injuries in motorcycle crashes are injuries to the head, and many of these are caused by rotational force. Rotational force is most commonly the result of oblique impacts to the head. Good testing methods for evaluating the effects of such impacts are currently lacking. There is also a need for improving our understanding of the effects of oblique impacts on the human head. Helmet standards currently in use today do not measure rotational effects in test dummy heads. However rotational force to the head results in large shear strains arising in the brain, which has been proposed as a cause of traumatic brain injuries like diffuse axonal injuries (DAI). This paper investigates a number of well-defined impacts, simulated using a detailed finite element (FE) model of the human head, an FE model of the Hybrid III dummy head and an FE model of a helmet. The same simulations were performed on both the FE human head model and the FE Hybrid III head model, both fitted with helmets. Simulations on both these heads were performed to describe the relationship between load levels in the FE Hybrid III head model and strains in the brain tissue in the FE human head model. In this study, the change in rotational velocity and the head injury criterion (HIC) value were chosen as appropriate measurements. It was concluded that both rotational and translational effects are important when predicting the strain levels in the human brain.

Robustness of the tuning of fly visual interneurons to rotatory optic flow.

The sophisticated receptive field organization of motion-sensitive tangential cells in the visual system of the blowfly Calliphora vicina matches the structure of particular optic flow fields. Hypotheses on the tuning of particular tangential cells to rotatory self-motion are based on local motion measurements. So far, tangential cells have never been tested with global optic flow stimuli. Therefore we measured the responses of an identifiable neuron, the V1 tangential cell, to wide-field motion stimuli mimicking optic flow fields similar to those the fly encounters during particular self-motions. The stimuli were generated by a "planetarium-projector," casting a pattern of moving light dots on a large spherical projection screen. We determined the tuning curves of the V1-cell to optic flow fields as induced by the animal during 1) rotation about horizontally aligned body axes, 2) upward/downward translation, and 3) a combination of both components. We found that the V1-cell does not respond as specifically to self-rotations, as had been concluded from its receptive field organization. The neuron responds strongly to upward translation and its tuning to rotations is much coarser than expected. The discrepancies between the responses to global optic flow and the predictions based on the receptive field organization are likely due to nonlinear integration properties of tangential neurons. Response parameters like orientation, shape, and width of the tuning curve are largely unaffected by changes in rotation velocity or a superposition of rotational and translational optic flow.

THE MONITORING AND CONTROL OF AN ARM CRANK SYSTEM USING FUZZY LOGIC FOR MULTI-HANDICAPPED YOUTHS WITH MENTAL RETARDATION

In this paper, we try to cope with National Special School in Taoyuan in order to fit the special requirements for multi-handicapped youths with mental retardation using current high technology, such as microcomputer control, sensing technology, and fuzzy logic control. The prototype device of this paper is focused on designing an arm crank system using a fuzzy logic controller (FLC) to exercise for the upper limb. The rotation velocity of this system was controlled via adjusting the electric current of the brake in order to increase the training motivation. Hence, a FLC was designed into this system in comparison with a manual control by an expert (i.e., physical therapist). Fifteen multi-handicapped youth with mental retardation were treated using the manual control as a control group, and another fifteen youths were treated using FLC as an experimental group. The root mean square deviation (RMSD) of the change of rotation velocity of arm crank was no significant difference (p > 0.05) using Student t test analysis. It means that FLC can be replaced the manual control by the qualified physical therapist. Therefore, it can be seen as a demonstration of feasibility of the applicability of this FLC for monitoring and control the velocity of the arm crank. But, it still needs a longer series of multi-handicapped youths with mental retardation, perhaps to refine the rule-bases, and certainly to see how widely they are applicable.

A high-resolution vacuum ultraviolet spectrometer for plasma spectroscopy

A high-resolution spectrometer for the wavelength range 40-200 nm was adapted to a high-speed photo-electric detection system. A wavelength range of 3 nm can be measured up to every 0.2 ms with a resolution of 0.0012 nm and a wavelength accuracy of 0.0001 nm. The system is used for plasma spectroscopy at the Rijnhuizen Tokamak Project. Temperature measurements were performed with a resolution of 0.1 eV and changes in rotation velocity of were observed.

A Very Deep Spectrum of the Diffuse Ionized Gas in NGC 891

A deep long-slit spectrum of the diffuse ionized gas (DIG) in the edge-on spiral galaxy NGC 891 has been obtained. The slit crosses the plane at a galactocentric radius of 5 kpc and covers DIG on both the east and west sides of the galaxy. The primary motivation was to attempt to detect the recombination line He I λ5876, the strength of which relative to Hα provides a direct constraint on the hardness of the ionizing spectrum. In the DIG of the Milky Way, this line ratio has turned out to be surprisingly low (Reynolds & Tufte; Heiles et al.), implying an ionizing spectrum much softer than had been inferred from the more readily observable forbidden lines, such as [N II] λ6583 and [S II] λ6717. The He I line has been detected in NGC 891 to a height of about 1.5 kpc from the plane—well into the diffuse gas layer. In the DIG, He I/Hα ≈ 0.034, implying that helium is about 70% ionized and that the ionizing spectrum is significantly harder than in the Reynolds layer. The spectrum also allows very detailed mapping of the [N II] λ6583/Hα ratio as a function of height off the plane. This ratio reaches peak values of about 1.4 at heights of z = 2 kpc on the east side of the plane and z = 4 kpc on the west side. Beyond this height on the east side, the ratio clearly declines again, falling to about 1.0 at z = 4 kpc. Previous modeling indicates that such high values of [N II] λ6583/Hα require an ionizing spectrum significantly harder than that indicated by the He I/Hα ratio. Hence, despite the higher values of He I/Hα, the same dilemma exists as in the Reynolds layer case. These results suggest that we do not understand the heating and ionization of the diffuse gas well enough. A determination of the gas temperature would help, but the nondetection of the line [N II] λ5755 allows only upper limits to be set: 13,000 K on the east side and 10,000 K on the west side. Both the [N II] and Hα lines are detected beyond z = 5 kpc; thus, the DIG layer extends much further than indicated by previous narrowband images. A model of the electron density distribution consisting of two components with scale heights of about 1 kpc and 5-6 kpc provides a good fit to the Hα emission profile. The very extended component was also seen in the image of Rand, Kulkarni, & Hester, but the inferred scale height is now larger. Apart from the known effects of dust absorption on the velocity centroids at low z, there is a smooth gradient in velocity centroids with increasing z above the dust lane in the sense that they become closer to the systemic velocity, changing by about 30 km s-1 from z = 1 kpc to z = 4.5 kpc. We postulate that the effect is due in part to a decreasing rotation speed and an outward radial migration of gas with z. An illustrative model suggests that the rotation speed at z = 4.5 kpc may be about 20 km s-1 slower than in the disk, although other effects could change this estimate. Such a change in rotation velocity is expected in galactic fountain models, but some simple experiments with stellar orbits show that the flow in a fountain may be more complicated than previously thought.

Synthesis and Characterization of Ru ‐ Ti4 O 7 Microelectrode Arrays

A synthesis is described for Ru microelectrode arrays within a conductive ceramic matrix. Data obtained by x‐ray diffractometry and scanning electron microscopy are consistent with the existence of heterogeneous mixtures of Ru particles (ca. 0.8 μm diam) within the matrices. No mixed metal oxides or other new compounds are detected. Rotated disk electrodes (RDEs) constructed from the materials are compared on the basis of their voltammetric response for the oxidations of I− to and in 0.10M . These results are rationalized on the basis of microelectrode arrays, i.e., elevated current densities and diminished sensitivity to changes in rotational velocity compared with solid Ru RDE. An RDE constructed from containing ca. 0.5% Ru by volume exhibits virtually zero dependence on rotational velocity for the oxidation of I− to and, therefore, this material functions as an ideal microelectrode array.

Rotation and the Evolution of the Mass-Accreting Component in Close Binary Systems

When mass is transferred between the two components in a close binary system, the matter falling towards the secondary star can gain a considerable amount of angular momentum. Eventually a ring or disk around this star is formed. The star can increase its angular momentum by accreting part (or the whole) of this matter. We have examined the ensuing changes in rotational velocity of the mass-accreting star. A simplified calculation (assuming accretion from a ring, rigid rotation of the star, and taking the stellar radius as well as its radius of gyration constant) shows that the star reaches its break-up velocity after increasing its original mass by only a few percent.