Positive Accelerations Research Articles

On the acceleration sensitivity and its active reduction by edge electrodes in AT-cut quartz resonators.

Incremental piezoelectric equations for small vibrations superposed on initial deformations are presented. The equations are implemented in COMSOL finite element models (FEA). Equations are validated by comparing the results for the force sensitivity coefficient Kf of a circular quartz plate subjected to a pair of diametrical forces with measured data. The model results show a consistent trend with the experimental results, and the relative difference between our FEA results and Ballato's measured result is about 13%. A detailed study of the acceleration sensitivity of a rectangular AT-cut quartz plate is presented. The plate resonator is fixed along one edge as a cantilever. For AT-cut quartz resonators with the crystal digonal X-axis perpendicular to plate X-axis, the in-plane acceleration sensitivity is found to be negligible compared with the out-of-plane (Y-axis) acceleration sensitivity. For AT-cut quartz resonators with the crystal digonal X-axis parallel to plate X-axis, the Y-axis acceleration sensitivity is found to be rectified, that is the fractional change in frequency is positive with respect to both positive and negative Y-axis accelerations. The Y-axis acceleration sensitivity is small in comparison with the in-plane acceleration sensitivity for small body forces. However, for large body forces, the Y-axis acceleration sensitivity dominates because it increases nonlinearly with the Y-axis acceleration. The resonator rectified acceleration sensitivity is confirmed by phase noise measurements. For reduced acceleration sensitivity, two pairs of electrodes along the plate edges reduce the bending of the plate resonator and subsequently reduce acceleration sensitivity. We present a new method using these edge electrodes in which a dc bias field is employed to control the resonant frequency of resonator subjected to g body forces. A dc bias field with an appropriate dc bias voltage could potentially yield a reduction of acceleration sensitivity in Y-axis direction of about two orders of magnitude.

Sea level rise around Korea: Analysis of tide gauge station data with the ensemble empirical mode decomposition method

This study estimates the trend and acceleration of sea level rise (SLR) at the tide gauge stations around Korea as now the data from the stations are recorded for approximately 50 years, which allow us to estimate the acceleration of SLR. We use not only traditional polynomial regression analysis but also the ensemble empirical mode decomposition (EEMD) approach, whose strength is the elimination of long-term variations in sea level data, to process this relatively short-term data. The relative sea level data from the five tide gauge stations around Korea, including Mokpo, Jeju, Busan, Ulsan and Mukho are used in this study. With Jeju showing the highest trend of SLR, all stations exhibit rising trend of sea level regardless of the methods used in this study. Positive accelerations of SLR are found in four out of five stations with the highest acceleration at Mukho. We also compare the results based on the EEMD approach and those based on the regression analysis and find generally consistent results between two. While the trends show the slight differences at the five stations with no tendency toward over- or under-estimation, the accelerations are slightly lower with the EEMD approach than with the regression analysis at all four stations with positive accelerations.

Development of processing methodologies used to form complete driving-cycle dynamometer tests based on urban on-road driving and road gradient data

This work involves the development of ‘real-world’ driving cycles using on-road data from the greater area of Athens, Greece. Two different methodologies of driving-cycle development are presented here, based on the MATLAB code. Driving patterns from various test vehicles were processed to form driving cycles consisting of a specific number of driving periods. The main criterion for the design and acceptance of each method was the correlation of the resulting driving cycles with the corresponding characteristics of the processed road data. Time is an important issue when processing data. Applying the same set of data to both methods, method A needed 5 h to complete the processing compared with 9 s for method B. The corresponding average accuracies were 99.9% and 97.2% respectively. The road gradient was taken into account for the development of the driving cycles. For method A, the road gradient was included in the final result by intervening in the mean positive accelerations and the mean negative accelerations. Those were increased by 11.99% and 16.06% respectively for the Greek Urban Driving Cycle for Motorcycles. For method B, the road gradient was assimilated by a ‘load cycle’ expressed in kilowatts and used in combination with the developed driving cycle, thus forming a complete chassis dynamometer test. The load cycle was produced by calculating the power related to the vehicle’s mass that holds or assists it when driving uphill or downhill. The Greek Urban Driving Cycle for Motorcycles was developed using method A. Its characteristics include the follwoing: a duration of 822 s, an average speed of 28.86 km/h, a stop-time percentage of 12.04 and a positive acceleration of 0.6065 m/s2. Method B was used for the Greek Urban Driving Cycle for passenger cars. Some of its characteristics include the following: a duration of 1175 s, an average speed of 18.67 km/h, a stop-time percentage of 31.66 and a positive acceleration of 0.692 m/s2.

LUMBO-PELVIC ANGULAR KINEMATICS IN YOUTH BASEBALL PITCHERS AFTER A SIMULATED GAME

BackgroundA growing body of evidence may indicate that the lumbo-pelvic-hip complex (LPHC) has an influence on the function of the scapular and shoulder in overhand throwing athletes. Dysfunction of the...

Study on optimal kinematic synthesis of cam profiles for engine valve trains

Kinematic cam profile synthesis for engine valve trains to satisfy the requirements of a large lift area and small acceleration magnitudes is a multi-objective optimization problem. This paper proposed that its Pareto optimal solution set is constructed with constant acceleration profiles. For the definite design of an engine valve train, its Pareto front is a function of the time durations of the positive and negative accelerations. The relationships of positive acceleration, negative acceleration, and lift area for a constant acceleration cam profile are analyzed, and the results are applied to discuss the characteristics of polynomial cam profiles.

Low-frequency accelerations over-estimate impact-related shock during walking

During gait, a failure to acknowledge the low-frequency component of a segmental acceleration signal will result in an overestimation of impact-related shock and may lead to inappropriately drawn conclusions. The present study was undertaken to investigate the significance of this low-frequency component in two distinctly different modalities of gait: barefoot (BF) and shod (SHOD) walking. Twenty-seven participants performed five walking trials at self-selected speed in each condition. Peak positive accelerations (PPA) at the shank and spine were first derived from the time-domain signal. The raw acceleration signals were then resolved in the frequency-domain and the active (low-frequency) and impact-related components of the power spectrum density (PSD) were quantified. PPA was significantly higher at the shank (P<0.0001) and spine (P=0.0007) in the BF condition. In contrast, no significant differences were apparent between conditions for shank (P=0.979) or spine (P=0.178) impact-related PSD when the low-frequency component was considered. This disparity between approaches was due to a significantly higher active PSD in both signals in the BF condition (P<0.0001; P=0.008, respectively), due to kinematic differences between conditions (P<0.05). These results indicate that the amplitude of the low-frequency component of an acceleration signal during gait is dependent on knee and ankle joint coordination behaviour, and highlight that impact-related shock is more accurately quantified in the frequency-domain following subtraction of this component.

Frequency variations of gravity waves interacting with a time-varying tide

Abstract. Using a nonlinear, 2-D time-dependent numerical model, we simulate the propagation of gravity waves (GWs) in a time-varying tide. Our simulations show that when a GW packet propagates in a time-varying tidal-wind environment, not only its intrinsic frequency but also its ground-based frequency would change significantly. The tidal horizontal-wind acceleration dominates the GW frequency variation. Positive (negative) accelerations induce frequency increases (decreases) with time. More interestingly, tidal-wind acceleration near the critical layers always causes the GW frequency to increase, which may partially explain the observations that high-frequency GW components are more dominant in the middle and upper atmosphere than in the lower atmosphere. The combination of the increased ground-based frequency of propagating GWs in a time-varying tidal-wind field and the transient nature of the critical layer induced by a time-varying tidal zonal wind creates favorable conditions for GWs to penetrate their originally expected critical layers. Consequently, GWs have an impact on the background atmosphere at much higher altitudes than expected, which indicates that the dynamical effects of tidal–GW interactions are more complicated than usually taken into account by GW parameterizations in global models.

Multi-scale dynamical analysis (MSDA) of sea level records versus PDO, AMO, and NAO indexes

Herein I propose a multi-scale dynamical analysis to facilitate the physical interpretation of tide gauge records. The technique uses graphical diagrams. It is applied to six secular-long tide gauge records representative of the world oceans: Sydney, Pacific coast of Australia; Fremantle, Indian Ocean coast of Australia; New York City, Atlantic coast of USA; Honolulu, U.S. state of Hawaii; San Diego, U.S. state of California; and Venice, Mediterranean Sea, Italy. For comparison, an equivalent analysis is applied to the Pacific Decadal Oscillation (PDO) index and to the Atlantic Multidecadal Oscillation (AMO) index. Finally, a global reconstruction of sea level and a reconstruction of the North Atlantic Oscillation (NAO) index are analyzed and compared: both sequences cover about three centuries from 1700 to 2000. The proposed methodology quickly highlights oscillations and teleconnections among the records at the decadal and multidecadal scales. At the secular time scales tide gauge records present relatively small (positive or negative) accelerations, as found in other studies. On the contrary, from the decadal to the secular scales (up to 110-year intervals) the tide gauge accelerations oscillate significantly from positive to negative values mostly following the PDO, AMO and NAO oscillations. In particular, the influence of a large quasi 60-70 year natural oscillation is clearly demonstrated in these records. The multiscale dynamical evolutions of the rate and of the amplitude of the annual seasonal cycle of the chosen six tide gauge records are also studied.

Natural oscillations and trends in long-term tide gauge records from the Pacific

Recognition of climate patterns is needed to characterise and understand the various climate mechanisms that culminate in the behaviour of the atmosphere or the ocean. The analysis of the periodic patterns in the oscillating sea levels is an important step in determining the presence or absence of non-periodic accelerating behaviours due to global warming or other effects. This is true for periodic patterns with a multi-decadal scale. Fast periodic (sub-decadal) patterns would not matter much if one is looking at long range accelerations. The analysis of high quality tide gauge records of the Pacific spanning more than 100 yr permits to evidence the multi-decadal oscillations of sea levels and their influence on the sea level rate of rise that may be computed by a linear fitting with different time windows. Without at least 65-70 yr of recorded data, the computed sea level rate of rise differs considerably from the actual long-term sea level rate of rise. These high quality long-term tide gauges show a non-accelerating oscillating behaviour with different periodicities in different locations. This result is consistent with a picture of locally and globally oscillating sea levels without any major sign of sharp positive accelerations at the present time.

Theoretical study of a mixed pump in startup process

In this paper, based on the angular momentum conservation and energy conservation, analytical equation was build to calculate the transient head of a mixed pump. From the theoretical analysis, the transient head was composed of a steady term and an unsteady term which was determined by angular acceleration and flow rate acceleration. The equation showed that an angular acceleration term would increase the total head for positive angular accelerations while flow rate acceleration would decrease the total head for positive flow rate accelerations. The theoretical transient head was calculated and compared to the numerical head. They were in good agreement. Factors affected the computational accuracy of the theoretical transient head were analyzed and improvements were proposed. Transient head was also compared with quasi-steady head. At the beginning of the starting period, an angular acceleration term contributed most of the total head. With time went on (t=0.5s-1.0s), with the great increase of flow rate, the total head was significantly smaller than the steady head in the same rotate speed and flow rate. The result showed that in mild transient conditions the quasi-steady head could be used to replace the transient head.

On the Interplanetary Coronal Mass Ejection Shocks in the Vicinity of the Earth

We studied the relation between the near-Earth signatures of the interplanetary coronal mass ejections (ICMEs) shocks such as sudden storms commencement (SSC), and their counterparts of coronal mass ejections (CMEs) observed near-Sun by solar and heliospheric observatory (SOHO)/large angle and spectrometric coronagraph (LASCO) coronagraph during 1996–2008. Our result showed that there is a good correlation between the travel time of the ICMEs shocks and their associated radial speeds. Also we have separated the ICME shocks into two groups according to their effective acceleration and deceleration. The results showed that the faster ICME shocks (with negative accelerations which decelerated by solar wind plasma) are more correlated to their associated travel time than those with positive accelerations.

Dashboard Videos

Last school year, I had a web link emailed to me entitled “A Dashboard Physics Lesson.”1 The link, created and posted by Dale Basier on his Lab Out Loud blog, illustrates video of a car's speedometer synchronized with video of the road. These two separate video streams are compiled into one video that students can watch and analyze. After seeing this website and video, I decided to create my own dashboard videos to show to my high school physics students. I have produced and synchronized 12 separate dashboard videos, each about 10 minutes in length, driving around the city of Lawrence, KS, and Douglas County, and posted them to a website.2 Each video reflects different types of driving: both positive and negative accelerations and constant speeds. As shown in Fig. 1, I was able to capture speed, distance, and miles per gallon from my dashboard instrumentation. By linking this with a stopwatch, each of these quantities can be graphed with respect to time. I anticipate and hope that teachers will find these useful in their own classrooms, i.e., having physics students watch the videos and create their own motion maps (distance-time, speed-time) for study.

RELATIVISTIC JETS IN THE RADIO REFERENCE FRAME IMAGE DATABASE. II. BLAZAR JET ACCELERATIONS FROM THE FIRST 10 YEARS OF DATA (1994-2003)

(Abridged) We analyze blazar jet apparent speeds and accelerations from the RDV series of astrometric and geodetic VLBI experiments. From these experiments, we have produced and analyzed 2753 global VLBI images of 68 sources at 8 GHz with a median beam size of 0.9 milliarcseconds (mas), and a median of 43 epochs per source. From this sample, we analyze the motions of 225 jet components in 66 sources. The distribution of the fastest measured apparent speed in each source has a median of 8.3c and a maximum of 44c. Sources in the 2FGL Fermi LAT catalog display higher apparent speeds than those that have not been detected. On average, components farther from the core in a given source have significantly higher apparent speeds than components closer to the core. We measure accelerations of components in orthogonal directions parallel and perpendicular to their average velocity vector. Parallel accelerations have significantly larger magnitudes than perpendicular accelerations, implying observed accelerations are predominantly due to changes in the Lorentz factor (bulk or pattern) rather than projection effects from jet bending. Positive parallel accelerations are significantly more common than negative ones, so the Lorentz factor (bulk or pattern)tends to increase on the scales observed here. Observed parallel accelerations correspond to modest source frame increases in the bulk or pattern Lorentz factor.

A Versatile Acceleration-Based Cam Profile for Single-Dwell Applications Requiring Cam-Follower Clearance During Dwell

Presented in this paper is an asymmetric acceleration-derived cam motion program suitable for single-dwell cam-follower systems with clearance between the cam and follower during dwell. Asymmetric rise and fall is included as this is desirable in certain manufacturing operations and machines that require a quick rise or fall. The motion program for the cam-follower actuation is derived from the follower acceleration so that designers can control the ratio of the magnitudes of positive and negative accelerations. This provides cam designers more control over the cam-follower interface force and therefore more control over factors such as cam wear and the potentially destructive phenomenon known as “follower jump.” The motion program used to close and open the clearance gap is derived from a velocity function, allowing more control of follower inertia during the important clearance closing event. The motion program is presented in closed-form, suitable for implementation in standard engineering equation-solving software.

A cyclic behavior of CME accelerations for accelerating and decelerating events

We investigate the cyclic evolutionary behavior of CME accelerations for accelerating and decelerating CME events in cycle 23 from 1997 January to 2007 December. It is found that the absolute values of semiannual mean accelerations of both accelerating and decelerating CME events roughly wax and wane in a cycle, delaying the sunspot cycle in time phase. We also investigate the semiannual number of CMEs with positive and negative acceleration and find that there are more decelerating CME events than accelerating CME events during the maximum period of a cycle (about three years), but there are more accelerating CME events than decelerating CME events during the rest of the time interval of the cycle. Our results seem to suggest that the different driving mechanisms may be acting accelerate and decelerate CME events: for accelerating CME events, the propelling force (Fp) statistically seems to play a significant role in pushing CMEs outward; for decelerating CME events, the drag (Fd) statistically seems to play a more effective role in determining CME kinematic evolution in the outer corona. During the maximum period of a cycle, because of the V2 dependence, Fd is generally stronger; because of the magnetic field dependence, Fp is also generally stronger. Thus, the absolute values of both the negative and positive accelerations are generally larger during that time. Because of the V2 dependence, Fd may be more effective during the maximum period of a cycle. Hence, there are more decelerating CME events than accelerating CME events during that time. During the minimum time interval of a cycle, CMEs have relatively small speeds, and Fp may be more effective. Therefore, there are more accelerating CME events than decelerating CME events during that time.

Polymer microoptoelectromechanical systems: Accelerometers and variable optical attenuators

This paper presents the design, fabrication and characterization of polymer microoptoelectromechanical systems (MOEMS). An optical accelerometer and a variable optical attenuator (VOA) based on SU-8 are presented. Both devices consist on a quad-beam polymer structure and can be fabricated with a simple technology, requiring only two photolithographic steps. Self-alignment structures for fast and accurate fiber optic positioning have also been implemented in both devices. The accelerometer working principle consists on a misalignment between the three waveguides, which comprise the structure, as acceleration is applied. Experimental optical sensitivities of 13.1dB/g for negative and 17.5dB/g for positive accelerations, and a high repeatability in an uncontrolled atmosphere are observed. Using the same devices and taking advantage of the high thermal expansion (CTE) of the SU-8, it is possible to obtain a low-power consumption VOA. Experimental results show an attenuation of 20dB for a power consumption of 12mW.

Nonlinear oscillations and collapse of elongated bubbles subject to weak viscous effects: Effect of internal overpressure

The details of nonlinear oscillations and collapse of elongated bubbles, subject to large internal overpressure, are studied by a boundary integral method. Weak viscous effects on the liquid side are accounted for by integrating the equations of motion across the boundary layer that is formed adjacent to the interface. For relatively large bubbles with initial radius R0 on the order of millimeters, PSt=PSt′∕(2σ∕R0)∼300 and Oh=μ∕(σR0ρ)1∕2∼200, and an almost spherical initial shape, S∼1, Rayleigh-Taylor instability prevails and the bubble breaks up as a result of growth of higher modes and the development of regions of very small radius of curvature; σ, ρ, μ, and PSt′ denote the surface tension, density, viscosity, and dimensional static pressure in the host liquid while S is the ratio between the length of the minor semiaxis of the bubble, taken as an axisymmetric ellipsoid, and its equivalent radius R0. For finite initial elongations, 0.5⩽S&amp;lt;1, the bubble collapses either via two jets that counterpropagate along the axis of symmetry and eventually coalesce at the equatorial plane, or in the form of a sink flow approaching the center of the bubble along the equatorial plane. This pattern persists for the above range of initial elongations examined and large internal overpressure amplitudes, εB⩾1, irrespective of Oh. It is largely due to the phase in the growth of the second Legendre mode during the after-bounce of the oscillating bubble, during which it acquires large enough positive accelerations for collapse to take place. For smaller bubbles with initial radius on the order of micrometers, PSt∼4 and Oh∼20, and small initial elongations, 0.75&amp;lt;S⩽1, viscosity counteracts P2 growth and subsequent jet motion, thus giving rise to a critical value of Oh−1 below which the bubble eventually returns to its equilibrium spherical shape, whereas above it collapse via jet impact or sink flow is obtained. For moderate elongations, 0.5⩽S⩽0.75, and large overpressures, εB⩾0.2, jet propagation and impact along the axis of symmetry prevails irrespective of Oh. For very large elongations, S&amp;lt;0.5, and above a certain threshold value of Oh the counterpropagating jets pinch the contracting bubble sidewalls in an off-centered fashion.

Observations of streamer formation in sprites

Sprites have been recorded at 10,000 fps with 50 μs image exposure time. At this time resolution it is possible to resolve the temporal development of streamer tips. The recordings show that sprites start with a streamer head forming at an altitude near 80 km. The streamer head moves rapidly downwards while brightening, and ∼300 μs after streamer passage longer lasting emissions ensues. This is essentially the C‐sprite. In some events upward moving streamer heads are also observed, in which case we have a carrot‐sprite. The streamer speeds vary between 106 and 107 m/s. Both positive and negative accelerations, of magnitude 105 – 1010 m/s2, were observed. Upward streamers, when present, always start later and from a lower altitude than downward streamers, and they start from existing structure in the sprite.

The effect of caffeine on handwriting movements in skilled writers

In laboratory tasks, caffeine has been shown to improve psychomotor performance. The aim of the present experiment was to assess the effects of caffeine on a skilled everyday life task in habitual caffeine consumers. The assessment of handwriting movements of 20 adults was performed following the administration of 0mg/kg (placebo), 1.5mg/kg, 3.0mg/kg or 4.5mg/kg of caffeine. A digitising tablet was used for the assessment of fine motor movements. Participants were asked to perform a simple writing task. Kinematic analysis of handwriting movements showed that, in comparison to placebo administration, high doses of caffeine (i.e., 4.5mg/kg) can produce improvements in handwriting as indicated by more fluent handwriting movements as well as an increase in maximum velocity and maximum positive and negative accelerations. The results suggest that higher doses of caffeine can enhance psychomotor performance.

Chronology of the push pull effect on nonhuman primates—shift of the arterial pressure threshold

Fighter pilots are frequently exposed to high Gz acceleration which may induce in-flight loss of consciousness (G-LOC). One factor reducing tolerance to accelerations is a previous exposure to negative accelerations. This phenomenon, which happens during the first few seconds after the onset of the positive plateau, is called the push pull effect. Our goal was to validate a non human primate model in order to study push pull physiological mechanisms and possible changes in arterial pressure, which may occur after the first ten seconds of the positive acceleration plateau. Eight rhesus monkeys were centrifuged in profile runs, including positive Gz accelerations (+1.4, +2 and +3 Gz) with or without previous negative Gz acceleration (-2 and -3 Gz vs. +1.4 Gz). Heart rate, blood pressure and esophageal pressure were recorded during the entire centrifugation run. Results showed that the push pull effect was observed in the non human primate model. Moreover, the reduced tolerance to acceleration lingered longer than that during the first ten seconds after exposure to +Gz acceleration. It was found that, after the fourteenth second, mean blood arterial pressure stabilizes at a lower value, when the positive acceleration is preceded by a negative acceleration (15.8 kPa for -1 Gz and 15.5 for -2 Gz vs. 16.9 for 1.4 Gz). The chronology of the push pull effect seems to involve two periods. One has a short time span. The other one has a longer time span and could be induced by shift of pressure threshold, coming from exposure to previous negative acceleration.