Showing papers on "Acceleration published in 2004"

Acceleration-based theft detection system for portable electronic devices

Abstract: A theft prevention system for protecting portable electronic devices is disclosed. An acceleration sensor detects the acceleration of a portable electronic device, and a controller analyzes this acceleration to determine whether a theft condition is present. If so, an alarm can be initiated. The theft prevention system can include a filter for attenuating irrelevant acceleration frequencies and isolating those representative of theft, and comparison hardware/software for determining whether the detected acceleration matches a known acceleration profile characteristic of theft. Various parameters of the theft prevention system can also be set by a user through mechanisms such as a graphical user interface.

Relativistic electrons in the outer radiation belt: Differentiating between acceleration mechanisms

Abstract: [1] Many theoretical models have been developed to explain the rapid acceleration to relativistic energies of electrons that form the Earth's radiation belts. However, after decades of research, none of these models has been unambiguously confirmed by comparison to observations. Proposed models can be separated into two types: internal and external source acceleration mechanisms. Internal source acceleration mechanisms accelerate electrons already present in the inner magnetosphere (L < 6.6), while external source acceleration mechanisms transport and accelerate a source population of electrons from the outer to the inner magnetosphere. In principle, the two types of acceleration mechanisms can be differentiated because they imply that different radial gradients of electron phase space density expressed as a function of the three adiabatic invariants will develop. Model predictions can be tested by transforming measured electron flux (given as a function of pitch angle, energy, and position) to phase space density as a function of the three invariants, μ, K, and Φ. The transformation requires adoption of a magnetic field model. Phase space density estimates have, in the past, produced contradictory results because of limited measurements and field model errors. In this study we greatly reduce the uncertainties of previous work and account for the contradictions. We use data principally from the Polar High Sensitivity Telescope energetic detector on the Polar spacecraft and the Tsyganenko and Stern [1996] field model to obtain phase space density. We show how imperfect magnetic field models produce phase space density errors and explore how those errors modify interpretations. On the basis of the analysis we conclude that the data are best explained by models that require acceleration of an internal source of electrons near L* ∼ 5. We also suggest that outward radial diffusion from a phase space density peak near L* ∼ 5 can explain the observed correspondence between flux enhancements at geostationary orbit and increases in ULF wave power.

Electrodynamics and ultimate SNR in parallel MR imaging

Abstract: The purpose of this article is to elucidate inherent limitations to the performance of parallel MRI. The study focuses on the ultimate signal-to-noise ratio (SNR), which refers to the maximum SNR permitted by the electrodynamics of the signal detection process. Using a spherical model object, it is shown that the behavior of the ultimate SNR imposes distinct limits on the acceleration rate in parallel imaging. For low and moderate acceleration, the ultimate SNR performance is nearly optimal, with geometry factors close to 1. However, for high reduction factors beyond a critical value, the ultimate performance deteriorates rapidly, corresponding to exponential growth of the geometry factor. The transition from optimal to deteriorating performance depends on the electrodynamic characteristics of the detected RF fields. In the near-field regime, i.e., for low B0 and small object size, the critical reduction factor is constant and approximately equal to four for 1D acceleration in the sphere. In the far-field wave regime the critical reduction factor is larger and increases both with B0 and object size. Therefore, it is concluded that parallel techniques hold particular promise for human MR imaging at very high field. Magn Reson Med 52:376–390, 2004. © 2004 Wiley-Liss, Inc.

A Study of the Kinematic Evolution of Coronal Mass Ejections

Abstract: We report the kinematic properties of a set of three coronal mass ejections (CMEs) observed with the LASCO (Large Angle and Spectrometric Coronagraph) on the Solar and Heliospheric Observatory (SOHO) spacecraft, which showed characteristics of impulsive, intermediate, and gradual acceleration, respectively. The first CME had a 30 minute long fast acceleration phase during which the average acceleration was about 308 m s-2; this acceleration took place over a distance of about 3.3 R☉ (from 1.3 to 4.6 R☉, height measured from disk center). The CME characterized by intermediate acceleration had a long acceleration phase of about 160 minutes during which the average acceleration was about 131 m s-2; the CME traveled a distance of at least 4.3 R☉, reaching a height of 7.0 R☉ at the end of the acceleration phase. The CME characterized by gradual acceleration had no fast acceleration phase. Instead, it displayed a persistent weak acceleration lasting more than 24 hr with an average acceleration of only 4.0 m s-2 throughout the LASCO field of view (from 1.1 to 30 R☉). This study demonstrates that the final velocity of a CME is determined by a combination of acceleration magnitude and acceleration duration, both of which can vary significantly from event to event. The first two CME events were associated with soft X-ray flares. We found that in the acceleration phase there was close temporal correlation both between the CME velocity and the soft X-ray flux of the flare and between the CME acceleration and derivative of the X-ray flux. These correlations indicate that the CME large-scale acceleration and the flare particle acceleration are strongly coupled physical phenomena occurring in the corona.

Multifractal statistics of Lagrangian velocity and acceleration in turbulence

Abstract: The statistical properties of velocity and acceleration fields along the trajectories of fluid particles transported by a fully developed turbulent flow are investigated by means of high resolution direct numerical simulations. We present results for Lagrangian velocity structure functions, the acceleration probability density function, and the acceleration variance conditioned on the instantaneous velocity. These are compared with predictions of the multifractal formalism, and its merits and limitations are discussed.

Magnetic Driving of Relativistic Outflows in Active Galactic Nuclei. I. Interpretation of Parsec-Scale Accelerations

Abstract: There is growing evidence that relativistic jets in active galactic nuclei undergo extended (parsec-scale) acceleration. We argue that, contrary to some suggestions in the literature, this acceleration cannot be purely hydrodynamic. Using exact semianalytic solutions of the relativistic MHD equations, we demonstrate that the parsec-scale acceleration to relativistic speeds inferred in sources such as the radio galaxy NGC 6251 and the quasar 3C 345 can be attributed to magnetic driving. Additional observational implications of this model will be explored in future papers in this series.

Energy-efficient motion planning for mobile robots

Abstract: This paper presents a new approach to find energy-efficient motion plans for mobile robots. Motion planning has two goals: finding the routes and determining the velocities. We model the relationship of motors' speed and their power consumption with polynomials. The velocity of the robot is related to its wheels' velocities by performing a linear transformation. We compare the energy consumption of different routes at different velocities and consider the energy consumed for acceleration and turns. We use experiment-validated simulation to demonstrate up to 51% energy savings for searching an open area.

The effects of knee contact angle on impact forces and accelerations.

Abstract: This article will summarize findings from several studies that together allow: 1) the examination of the effect that knee contact angle has on the severity of the resulting impact, 2) examination of the relationship between vertical ground reaction impact forces and leg impact accelerations, and 3) exploration of the adaptations that occur in response to running during changing environmental conditions. Changing the knee flexion angle at contact can alter the effective mass during activities in which the foot impacts the ground. It has been shown that increasing the knee flexion angle at ground contact can reduce the peak vertical ground reaction impact force, but it can also increase the peak impact acceleration at the leg. Attenuation can be calculated from accelerometers on the leg and the head and combined with the leg acceleration values to give a more accurate impression of the severity of the impact. Lower-extremity joint contact angles can be used to examine the kinematic adaptations that take place in response to changing environmental conditions. One common adaptation that can occur when the internal or external environment is not ideal is an increase in the knee flexion angle at contact. More extended knee contact angles can increase the forces experienced by the body and therefore increase injury potential. Increased knee flexion may give the runner a larger margin for dealing with kinematic errors but this benefit likely has an associated metabolic cost that will reduce performance.

The vertical-to-horizontal response spectral ratio and tentative procedures for developing simplified V/H and vertical design spectra

Abstract: This paper presents the results of a study on the engineering characteristics of vertical ground motion. A ground-motion model for the vertical-to-horizontal ratio (V/H) of peak ground acceleration...

Differentiating between modified gravity and dark energy

Abstract: The nature of the fuel that drives today's cosmic acceleration is an open and tantalizing mystery. We entertain the suggestion that the acceleration is not the manifestation of yet another new ingredient in the cosmic gas tank, but rather a signal of our first real lack of understanding of gravitational physics. By requiring that the underlying gravity theory respect Birkhoff's law, we derive the modified gravitational force law necessary to generate any given cosmology, without reference to the fundamental theory, revealing modifications of gravity at scales typically much smaller than today's horizon. We discuss how, through these modifications, the growth of density perturbations, the late-time integrated Sachs-Wolfe effect, and even solar-system measurements may be sensitive to whether today's cosmic acceleration is generated by dark energy or modified gravitational dynamics, and are subject to imminent observational discrimination. We argue how these conclusions can be more generic, and probably not dependent on the validity of Birkhoff's law.

An Algorithm for Estimating Acceleration Magnitude and Impact Location Using Multiple Nonorthogonal Single-Axis Accelerometers

Abstract: Accelerations of the head are the likely cause of concussion injury, but identifying the specific etiology of concussion has been difficult due to the lack of a valid animal or computer model. Contact sports, in which concussions are a rising health care concern, offer a unique research laboratory environment. However, measuring head acceleration in the field has many challenges including the need for large population sampling because of the relatively low incidence of concussions. We report a novel approach for calculating linear acceleration that can be incorporated into a head-mounted system for on-field use during contact sports. The advantages of this approach include the use of single-axis linear accelerometers, which reduce costs, and a nonorthogonal arrangement of the accelerometers, which simplifies the design criteria for a head-mounted and helmet compatible system. The purpose of this study was to describe the algorithm and evaluate its accuracy for measuring linear acceleration magnitude and impact location using computer simulation and experimental tests with various accelerometer configurations. A 10% error in magnitude and a 10 deg error in impact location were achieved using as few as six single-axis accelerometers mounted on a hemispherical headform.

Model predictive control of transitional maneuvers for adaptive cruise control vehicles

Abstract: In this paper, model predictive control (MPC) is used to compute the spacing-control laws for transitional maneuvers (TMs) of vehicles equipped with adaptive cruise control (ACC) systems. A TM is required, for example, to establish a steady-state following distance behind a newly encountered vehicle traveling with a slower velocity. These spacing-control laws are computed by formulating the objective of a TM as an optimal control problem (OCP). The steady-state following distance, collision avoidance, and acceleration limits of the ACC vehicle are incorporated into the OCP as constraints. The spacing-control laws are then obtained by solving this constrained OCP by using a receding-horizon approach, where the acceleration command computed at each sampling instant is a function of the current measurements of range and range rate. A baseline scenario requiring a TM is used to evaluate and compare the performance of the MPC algorithm and the standard constant time gap (CTG) algorithm. The simulation results show that the ACC vehicle is able to perform the TM of the baseline scenario using the MPC spacing-control laws, whereas the ACC vehicle is unable to perform this TM using the CTG spacing-control laws. The success of the MPC spacing-control laws is shown to depend on whether collision avoidance and the acceleration limits of the ACC vehicle are explicitly incorporated into the formulation of the control algorithm.

Attitude sensing system for an automotive vehicle relative to the road

Abstract: A system (18) for controlling a safety system (44) of an automotive vehicle (10) includes a longitudinal acceleration sensor (36), a vehicle speed sensor (20), a lateral acceleration sensor (32), a yaw rate sensor, and a controller (26). The controller (26) determines a reference pitch in response to the longitudinal acceleration signal and the vehicle speed signal and a reference roll angle in response to the yaw rate signal, the wheel speed signal and the lateral acceleration signal. The controller (26) determines a roll stability index and a pitch stability index. The controller (26) determines an adjusted pitch angle in response to the reference pitch angle and the pitch stability index and an adjusted roll angle in response to the reference roll angle and the roll stability index. The controller (26) controls the safety system (44) in response to the adjusted roll angle and the adjusted pitch angle.

Design and Evaluation of an Acceleration Guidance Algorithm for Entry

Abstract: The design and performance evaluation of an entry guidance algorithm for future space transportation vehicles is presented. The guidance concept is to plan and track aerodynamic acceleration. This concept, on which the longitudinal entry guidance for the Space Shuttle Orbiter is based, is extended to integrated longitudinal and lateral guidance. With integrated longitudinal and lateral guidance, more extreme points in the landing footprint can be reached accurately; in particular, the cross-range capability is extended. The guidance algorithm consists of two components: a trajectory planner and a trajectory tracking law. The planner generates reference drag acceleration and heading angle profiles, along with reference state and bank angle profiles. The planner executes onboard and is capable of generating updates as the entry evolves. The tracking law, based on feedback linearization, commands the angles of bank and attack required to follow the reference drag and heading angle profiles. The planner and tracking law are described, along with additional higher level logic included in the algorithm. Extensive simulations for a set of return-from-orbit entries, including ones requiring large cross range, demonstrate that this algorithm consistently achieves the desired target conditions within allowable tolerances and satisfies all other entry constraints.

A study on a generalized parametric interpolator with real-time jerk-limited acceleration

Abstract: The impossibility of exact arc length computation for ‘standard’ parametric curves such as Bezier/B-spline curves makes it difficult to generate a feedrate profile with desired accelerations in real-time. This paper presents a new recursive trajectory generation method that estimates an admissible path increment and determines the initiation of the final deceleration stage according to the distance left to travel estimated at every sampling time, resulting in exact feedrate trajectory generation through jerk-limited acceleration profiles for the parametric curves. The proposed approach allows the feedrate profile to be dynamically adjusted according to geometrical path constraints for the curved path. The simulation result has been also provided to illustrate the generation of smooth feedrate profile encompassing a sequence of mixed NC blocks including traditional linear and circular blocks.

Active noise cancellation using MEMS accelerometers for motion-tolerant wearable bio-sensors

Abstract: An active noise cancellation method using a MEMS accelerometer is developed for recovering corrupted wearable sensor signals due to body motion The method is developed for a finger ring PPG sensor, the signal of which is susceptive to the hand motion of the wearer A MEMS accelerometer (ACC) imbedded in the PPG sensor detects the hand acceleration, and is used for recovering the corrupted PPG signal The correlation between the acceleration and the distorted PPG signal is analyzed, and a low-order FIR model relating the signal distortion to the hand acceleration is obtained The model parameters are identified in real time with a recursive least square method Experiments show that the active noise cancellation method can recover ring PPG sensor signals corrupted with 2G of acceleration in the longitudinal direction of the digital artery

Acceleration limiting for a vehicle

Abstract: A method and apparatus to control acceleration of a vehicle equipped with an electrically variable transmission and including a regenerative braking system, each are operably connected to a vehicle driveline. The method and apparatus include determining which one of a preselected shift selector position for the transmission is commanded, and determining operator demand for acceleration, using inputs from throttle pedal and brake pedal. Vehicle acceleration is measured, and magnitude of commanded torque transferred from the electrically variable transmission and the regenerative braking system to the vehicle driveline is controlled based upon the commanded preselected shift selector position, the operator demand for acceleration, and the measured vehicle acceleration.

Vehicle dynamics model for estimating maximum light-duty vehicle acceleration levels

Abstract: A vehicle dynamics model for predicting maximum light-duty vehicle accelerations for use within a microscopic traffic simulation environment is presented and validated. The research also constructs a database of unconstrained vehicle acceleration data for 13 light-duty vehicles and trucks. With the use of the field data, the proposed vehicle dynamics model is validated and compared with a number of state-of-the-art vehicle acceleration models, including the Searle model and the dual-regime, linear decay, and polynomial models. The advantages of the proposed model include its ability to predict vehicle behavior accurately with readily available input parameters and its flexibility in estimating acceleration rates of both large and small vehicles on varied types of terrain.

Six degree-of-freedom micro-machined multi-sensor

Abstract: A six degree-of-freedom micro-machined multi-sensor (100) that provides 3-axes of acceleration sensing, and 3-axes of angular rate sensing, in a single multi-sensor device. The six degree-of-freedom multi-sensor device includes a first multi-sensor substructure (103) providing 2-axes of acceleration sensing and 1-axis of angular rate sensing, and a second multi-sensor substructure (105) providing a third axis of acceleration sensing, and second and third axes of angular rate sensing. The first and second multi-sensor substructures are implemented on respective substrates within the six degree-of-freedom multi-sensor device.

Fast reconnection in relativistic pair plasmas: Analysis of particle acceleration in self-consistent full particle simulations

Abstract: Particle acceleration in collisionless magnetic reconnection is studied in the relativistic regime of an electron-positron plasma. For the first time, the highly dynamic late-time evolution of reconnection is simulated in two dimensions (2D) and the finite size of the acceleration region is resolved in 3D applying a fully electromagnetic relativistic particle-in-cell (PIC) code. The late-time evolution is extremely important with respect to particle acceleration, because thin current sheets show a highly dynamic late-time phase with instabilities evolving in the Alfven velocity vA0 regime. Consequently, since c∼vA0 is valid as a peculiarity of pair plasmas, v×B-contributions become dominant in the accelerating electric field. Most remarkable: Though acceleration regions are highly variable at late times, the power-law shape of the particle energy distribution is smoothed compared to quasi-static reconnection configurations at early times [S. Zenitani and M. Hoshino, Astrophys. J. 562, L63 (2001)]. Spectra...

Single proof mass, 3 axis mems transducer

Abstract: A transducer is provided herein which comprises an unbalanced proof mass (51), and which is adapted to sense acceleration in at least two mutually orthogonal directions. The proof mass (51) has first (65) and second (67) opposing sides that are of unequal mass.

IMM object tracking for high dynamic driving maneuvers

Abstract: Classical object tracking approaches use a Kalman-filter with a single dynamic model which is therefore optimised to a single driving maneuver. In contrast the interacting multiple model (IMM) filter allows for several parallel models which are combined to a weighted estimate. Choosing models for different driving modes, such as constant speed, acceleration and strong acceleration changes, the object state estimation can be optimised for highly dynamic driving maneuvers. The paper describes the analysis of Stop&Go situations and the systematic parametrisation of the IMM method based on these statistics. The evaluation of the IMM approach is presented based on real sensor measurements of laser scanners, a radar and a video image processing unit.

Mobile terminals and methods for determining a location based on acceleration information

Abstract: An acceleration measurement circuit is calibrated based on wireless communication signals ( eg . GPS signals, satellite signals, cellular signals, wide area network signals, wireless local area network signals, etc, … ) that are received by a mobile terminal. A location of the mobile terminal is then determined using the calibrated acceleration measurement circuit; therefore the calibration of the acceleration measurement circuit impoves its accuracy and as a consequence the determination of the location is improved. In a different embodiment, the location of the mobile terminal is determined by combining a first location ( estimated using wireless communication signals, e.g. GPS signals ) and a second location (calculated based on acceleration infromation used to calculate distance a mobile terminal has traveled from the 7 first location ).

Three-Dimensional Structure of the Lagrangian Acceleration in Turbulent Flows

Abstract: We report experimental results on the three-dimensional Lagrangian acceleration in highly turbulent flows. Tracer particles are tracked optically using four silicon strip detectors from high energy physics that provide high temporal and spatial resolution. The components of the acceleration are shown to be statistically dependent. The probability density function of the acceleration magnitude is comparable to a log-normal distribution. Assuming isotropy, a log-normal distribution of the magnitude can account for the observed dependency of the components. The time dynamics of the acceleration components is found to be typical of the dissipation scales, whereas the magnitude evolves over longer times, possibly close to the integral time scale.

Charged particle accelerator

Abstract: The present invention provides a charged particle accelerator comprising a charged particle generating apparatus, a bending magnet, accelerating means and a vacuum duct, wherein first and second acceleration periods ( 22 ), ( 23 ) are provided, accelerating electric field of the accelerating means is applied from the start time ( 25 ) of the first acceleration period ( 22 ) until the end time of the second acceleration period ( 23 ), and bending magnetic field is applied at a fixed value during the first accelerating period while, during the second acceleration period, it is applied so as to increase until the end time of the second acceleration period. Accordingly, there is provided a compact and high power charged particle accelerator which can perform large-current acceleration.

Handheld portable automatic emergency alert system and method

Abstract: In one embodiment, an automated emergency alert system includes a handheld portable communication device operable to initiate communication over a wireless telecommunications network, a dynamic sensor operable to generate an acceleration profile for the device, and a memory operable to store one or more predefined acceleration profiles each associated with an emergency event. The system also includes one or more processors collectively operable to (1) receive from the dynamic sensor an acceleration profile for the device; (2) access one or more of the stored predefined acceleration profiles; (3) compare the received acceleration profile to the one or more stored predefined acceleration profiles to determine if the acceleration profile substantially matches a predefined acceleration profile; and (4) if it is determined that the acceleration profile substantially matches a stored predefined acceleration profile, initiate a communication using the network to one or more emergency call centers to notify the call center that the emergency event has occurred.

Acceleration disturbance detection subsystem for use with disk drives

Abstract: A disk drive comprising a first sensor mounted on a nominally stationary portion of the disk drive and adapted to detect acceleration disturbances of the disk drive. The disk drive further comprising: a dual-function subsystem having a first circuit adapted to provide a write-inhibit signal and a second circuit adapted to provide a feed-forward basis signal, the dual-function subsystem adapted to receive a first sensor signal from the first sensor and to provide (a) the write-inhibit signal based on the received first sensor signal and a first threshold value, and (b) the feed-forward basis signal based on the received first sensor signal.