Peak Vertical Velocities Research Articles

Step type is associated with loading and ankle motion in tap dance.

Tap dance generates forces and joint motions that can lead to injury; however, little is known about the magnitude of load across different tap steps. The purpose of this study was to calculate peak vertical forces, average vertical foot velocities, and maximum/minimum ankle angles produced by tap dancers with different levels of experience performing the toe cannon, heel cannon, flap, and cramp roll. This prospective cross-sectional study included 14 female tap dancers aged ≥18 years with varying tap experience. Participants were recorded by three cameras while performing a choreographed tap combination containing four steps of interest on a force platform. Adjusting for experience and dancer-level clustering, we identified the steps-cramp roll and toe cannon-that had the highest peak vertical ground reaction force, angles, and velocities compared to flap and heel cannon. There was no effect of experience. The results supported our hypothesis and provide new insights into step production. Over time, the larger forces associated with these steps could pose an increased risk of injury to bones and joints when compared to smaller forces, which may suggest the importance of adjusting routines to reduce or avoid injury.

Damage features and dynamic triggering mechanism of the Jianshanying landslide induced by underground mining in Shuicheng County, Guizhou Province, China

Extensive mining of mineral resources in the mountainous areas of southwestern China has caused frequent occurrences of landslides, threatening social and economic development. Therefore, further research on the formation mechanism of such landslides is urgently investigated. Using detailed geological investigations, a numerical simulation, and related theoretical analysis reveal the dynamic triggering mechanism, influencing factors, and mechanical evolution model of the Jianshanying landslide under the coupled action of heavy rainfall and mine blasting vibrations. Results showed the following: First, rainfall of about 5 days, which nearly saturated the slope, and nearly 3 blasting cycles (peak horizontal and vertical velocities of 0.3375 and 0.1573 cm/s, respectively) executed close to it were the main controlling factors inducing the landslide. Second, the macroscopic deformation of the slope manifested obvious subsidence and tipping, and the maximum vertical and horizontal displacements of the slope shoulder reached 13.466 and 2.961 m, respectively. Third, the critical failure of the slope occurred at 15 s in the dynamic analysis, and its subsequent responses involved disintegration and fragmentation, debris flow, scraping of the sliding bed, and self-stabilized accumulation. Finally, its mechanical evolution model was divided into the subsidence stage and the shear-tension stage. These results provide technical support for early identification and risk management of geological hazards in mines in southwestern China.

Postural Responses to Sudden Horizontal Perturbations in Tai Chi Practitioners

Tai Chi has been shown to elicit numerous positive effects on health and well-being. In this study, we examined reactive postural control after sudden unloading horizontal perturbations, which resembled situations encountered during Tai Chi. The study involved 20 participants, 10 in the Tai Chi group (age: 37.4 ± 7.8 years), who had been regularly training the push-hand technique for at least 7 years, and 10 in the control group, consisting of healthy adults (age: 28.8 ± 5.0). Perturbations were applied at three different positions (hips, shoulders, and arms) via the load-release paradigm. Twenty measurements were carried out for each perturbation position. We measured peak vertical and horizontal forces on the ground (expressed percentage of body mass (%BM)), peak center of pressure displacement and peak horizontal and vertical velocities at the knee, hip and shoulder joints. The Tai Chi group exhibited smaller increases in vertical ground reaction forces when perturbations were applied at the hips (11.5 ± 2.1 vs. 19.6 ± 5.5 %BW; p = 0.002) and the arms (14.1 ± 4.2 vs. 23.2 ± 8.4 %BW; p = 0.005). They also responded with higher horizontal force increase after hip perturbation (16.2 ± 3.2 vs. 13.1 ± 2.5 %BW; p < 0.001). Similar findings were found when observing various outcomes related to velocities of vertical movement. The Tai Chi group also showed lower speeds of backward movement of the knee (p = 0.005–0.009) after hip (0.49 ± 0.13 vs. 0.85 ± 0.14 m/s; p = 0.005) and arm perturbations (0.97 ± 0.18 vs. 1.71 ± 0.29 m/s; p = 0.005). Center of pressure displacements were similar between groups. Our study demonstrated that engaging in Tai Chi could be beneficial to reactive postural responses after sudden perturbations in a horizontal direction; however, future interventional studies are needed to directly confirm this. Moreover, because of the age difference between the groups, some confounding effects of age cannot be ruled out.

Passive transport of a benthic bivalve (Corbicula fluminea) in large lakes: implications for deepwater establishment of invasive species

Once introduced into a new ecosystem, the benthic bivalve Corbicula fluminea (Asian clam) will spread rapidly through both active and passive transport. In Lake Tahoe, CA-NV, where C. fluminea was introduced in 2002, populations have been found to thrive at shallow depths, where individuals are reproductive, but also at deeper depths where the only possible mechanism of population growth is downslope recruitment. This study used a variety of field and laboratory measurements to parameterize a hydrodynamic drag force model to predict passive clam transport under varying flow conditions. Laboratory results for clam shells ranging from 5 to 20 mm in length under flow conditions from 10 to 25 cm s−1 were used to solve for drag and lift coefficients. Field results are presented during weak stratification (September 2010–March 2011) when cooler water temperatures acted as a potential stressor for buried individuals to rise to the surface and be subjected to flows from which they would otherwise be isolated. During episodic wind events throughout this time period, peak horizontal water velocities of 25 cm s−1 and peak vertical (downwards) water velocities of 4 cm s−1 were measured in which all size classes of adult C. fluminea were potentially transported. Using a fundamental hydrodynamic drag force model approach to predict passive transport, the results of this study can be extended to other bivalve species for a wide array of flow conditions.

Evaluation of cloud‐resolving and limited area model intercomparison simulations using TWP‐ICE observations: 1. Deep convective updraft properties

AbstractTen 3‐D cloud‐resolving model simulations and four 3‐D limited area model simulations of an intense mesoscale convective system observed on 23–24 January 2006 during the Tropical Warm Pool‐International Cloud Experiment (TWP‐ICE) are compared with each other and with observed radar reflectivity fields and dual‐Doppler retrievals of vertical wind speeds in an attempt to explain published results showing a high bias in simulated convective radar reflectivity aloft. This high‐bias results from ice water content being large, which is a product of large, strong convective updrafts, although hydrometeor size distribution assumptions modulate the size of this bias. Making snow mass more realistically proportional to D2 rather than D3 eliminates unrealistically large snow reflectivities over 40 dBZ in some simulations. Graupel, unlike snow, produces high biased reflectivity in all simulations, which is partly a result of parameterized microphysics but also partly a result of overly intense simulated updrafts. Peak vertical velocities in deep convective updrafts are greater than dual‐Doppler‐retrieved values, especially in the upper troposphere. Freezing of liquid condensate, often rain, lofted above the freezing level in simulated updraft cores greatly contributes to these excessive upper tropospheric vertical velocities. The strongest simulated updraft cores are nearly undiluted, with some of the strongest showing supercell characteristics during the multicellular (presquall) stage of the event. Decreasing horizontal grid spacing from 900 to 100 m slightly weakens deep updraft vertical velocity and moderately decreases the amount of condensate aloft but not enough to match observational retrievals. Therefore, overly intense simulated updrafts may additionally be a product of unrealistic interactions between convective dynamics, parameterized microphysics, and large‐scale model forcing that promote different convective strengths than observed.

Prescribed burning of logging slash in the boreal forest of Finland: emissions and effects on meteorological quantities and soil properties

Abstract. A prescribed fire experiment was conducted on 26 June 2009 in Hyytiälä, Finland, to study aerosol and trace gas emissions from prescribed fires of slash fuels and the effects of fire on soil properties in a controlled environment. A 0.8 ha forest near the SMEAR II measurement station (Station for Measuring Ecosystem-Atmosphere Relations) was cut clear; some tree trunks, all tree tops and branches were left on the ground and burned. The amount of burned organic material was ~46.8 tons (i.e., ~60 tons ha−1). The flaming phase lasted 2 h 15 min, the smoldering phase 3 h. Measurements were conducted on the ground with both fixed and mobile instrumentation, and in the air from a research aircraft. In the middle of the burning area, CO2 concentration peaked around 2000–3000 ppm above the baseline, and peak vertical flow velocities were ~9 m s−1, as measured with a 10 Hz 3-D sonic anemometer placed within the burn area. In the mobile measurements the peak particle number concentrations were approximately 1–2 × 106 cm−3 in the plume at a distance of 100–200 m from the burn area. On the ground at the SMEAR II station the geometric mean diameter of the mode with the highest concentration was 80 ± 1 nm during the flaming phase and in the middle of the smoldering phase, but, at the end of the smoldering phase, the largest mode was 122 nm. In the volume size distributions, geometric mean diameter of the largest volume mode was 153 nm during the flaming phase and 300 nm during the smoldering phase. The lowest single-scattering albedo of the ground-level measurements was 0.7 in the flaming-phase plume and ~0.9 in the smoldering phase. Elevated concentrations of several volatile organic compounds (VOC) (including acetonitrile, a biomass burning marker) were observed in the smoke plume at ground level. Measurements at the forest floor (i.e., a richly organic layer of soil and debris, characteristic of forested land) showed that VOC fluxes were generally low and consisted mainly of monoterpenes, and VOC flux peaked after the burning. After one year, the fluxes had nearly stabilized close to the level before the burning. The clear-cutting and burning of slash increased the total long-term CO2 release from the soil, and altered the physical, chemical and biological properties of the soil, such as increased the available nitrogen contents of the soil, which in turn, affected the long-term fluxes of greenhouse gases.

Biomechanics of rising from a chair and walking in pregnant women

The present study aimed to assess the changes in the pattern of rising from a chair and walking forward as pregnancy progressed. Twelve pregnant women and 10 nulliparous women were included in this study. Participants were videotaped with a digital video camera in the sagittal plane, and the coordinates of the markers attached to the subjects were identified using image analysis software. The peak trunk-flexion angle in pregnant women during rising was smaller, but the hip-extension angle during the stance phase was larger than in controls. Also, the peak horizontal and vertical velocities of the center of mass were lower, and appeared earlier, in pregnant women than in controls. During rising, pregnant women dampened the propulsion attributable to increased uterus volume, and they enhanced the forward propulsion at gait initiation. To ensure safe motion, pregnant women should not initiate gait until reaching a stable standing position after rising.

A climatology of lee waves over the UK derived from model forecasts

ABSTRACTA lee wave forecast system has been run operationally at the UK Met Office since 2006. The forecasts are produced by a numerical model for flow over complex terrain (3DVOM) which is run for five separate hilly regions across the UK. These regions cover Dartmoor (southwest England), Snowdonia (north Wales), Cumbria and the Pennines (northern England), the Grampians (Scotland) and the Mourne and Sperrin mountains (Northern Ireland). Examples of verification of the model forecasts against aircraft and satellite observations are presented. Three years of forecast data for these regions have been used to generate a lee wave climatology for the UK. The model predicts large geographical differences, with lee waves occurring least frequently over Dartmoor and most frequently over Snowdonia and the Grampians. Large amplitude waves, with peak vertical velocities exceeding 3 m s−1 at 700 hPa or above, are more common in forecasts for the Grampian region than others. Lee waves occur more frequently in forecasts during winter months than in summer. The most favourable conditions are those in which there is little turning of the lower tropospheric winds and analysis suggests that the waves are typically trapped in the lower troposphere. The influence of the lee waves on the near‐surface flow has also been investigated. Large accelerations and flow deflections can occur beneath the waves. It is suggested that the latter correspond to turbulent lee wave rotors. Preferred locations for this behaviour have been identified in the model forecasts for the Grampians and Pennines.

Cued task‐specific training is better than exercise in improving sit‐to‐stand in patients with Parkinson's disease: A randomized controlled trial

We examined whether 4 weeks of audio-visual (AV) cued task-specific training could enhance sit-to-stand (STS) and whether the treatment effects could outlast the treatment period by 2 weeks. Fifty-two subjects with PD completed the study. They were randomly allocated to receive 4 weeks of AV cued task-specific training, conventional exercise (Ex), or no treatment (control). Each subject was assessed before, at the end of 2 and 4 weeks of treatment, and 2 weeks after treatment ended. After 2 weeks of training, the AV group significantly increased the peak horizontal velocity (by 13%, P<0.01) when compared with the Ex group. After 4 weeks of training, AV group increased both peak horizontal and vertical velocities, respectively by 18% and 51%, and reduced the time taken to complete STS by 25%. These improvements were greater than those of the Ex group, who showed 8% (nonsignificant between-group) and 20% (P<0.05 between-group) increases respectively for peak horizontal and vertical velocities, and 10% decrease in movement time (P<0.05). Worth-noting is the improvements in AV group could be carried over to 2 weeks after treatment ended. These findings provided concrete evidence for the use of AV cued task-specific training to reeducate STS in patients with PD.

Shoulder joint loading in the high performance flat and kick tennis serves

Objective:To quantify and compare the full body kinematics and shoulder joint kinetics during the high-performance tennis flat (FS) and kick serves (KS).Methods:A 12-camera 250 Hz, Vicon motion analysis system recorded...

Centre of mass motion during stair negotiation in young and older men

The aim of this study was to compare centre of mass (COM) motion and its separation from centre of pressure (COP) as 13 young men (aged 23–36 years) and 15 healthy, community dwelling older men (aged 73–84 years) ascended and descended a three step staircase at a controlled cadence of approximately 90 steps/min. Centre of mass was obtained from whole body motion analysis, and simultaneously, COP was obtained using force plates built into the steps. The following variables were investigated: medio-lateral COM range of motion; peak antero-posterior and medio-lateral COM–COP separation; and peak antero-posterior, medio-lateral, and vertical COM velocities. No significant differences in these variables between young men and older men were present during ascent or descent. It was concluded that frontal plane dynamic stability during stair negotiation is well maintained in healthy older men, and that healthy older men do not exhibit an altered strategy in traversing the COM in the plane of progression during stair negotiation.

The speed of sit-to-stand can be modulated in Parkinson's disease

Objective: To evaluate whether Parkinsonian patients could modify the speed of a sit-to-stand (STS) task to the same extent as that of healthy subjects. Methods: Twenty Parkinsonian patients and 20 control subjects were instructed to stand up at a natural and fast speed. Kinematic data and kinetic data were recorded. Results: Parkinsonian patients were significantly slower than healthy individuals during STS at a natural speed. When required to perform STS task at a fast speed, these patients could increase both peak horizontal and vertical velocities of the task, by significantly increasing hip and ankle dorsiflexion torques and the rate of torque production, just as the control subjects did. In fact, no difference was found for the percentage changes in both peak velocities and movement time between the two groups, though similar between-group differences during STS at a natural speed still existed at a fast speed. Conclusions: Parkinsonian patients had problems in generating adequate lower limb joint torques and in the rate of torque production when performing STS at a natural speed. However, these patients were capable of increasing the speed of their STS with the same percentage changes as those of healthy subjects. Significance: The capability of Parkinsonian patients for increasing movement speed gives new insights to rehabilitation strategy.

Audiovisual cues can enhance sit-to-stand in patients with Parkinson's disease.

We investigated whether preparatory signals, in the form of audiovisual cues, could enhance the performance of sit-to-stand (STS) in Parkinson's disease (PD) patients. Fifteen patients and fifteen control subjects similar in age, gender, weight, and height were examined. All subjects were instructed to carry out STS under self-initiated and cue-initiated conditions. A PEAK Motion Analysis System and two force plates were synchronized to record kinematic and kinetic data. In patients with PD, the addition of audiovisual cues was found to increase hip flexion and knee extension torques and decrease the time-to-peak joint torques, as well as increase peak horizontal and vertical velocities of the body center of mass and decrease the time taken to complete STS. Consequently, the performance of STS in these patients approached that of control subjects. In fact, during cue-initiated STS, no difference was found between the patient and control groups for the time-to-peak of all joint torques, the peak horizontal and vertical velocities, and the time taken to complete STS. Our findings thus demonstrated that audiovisual cues were effective in enhancing STS in patients with PD. These feed-forward signals could have enhanced the defective motor preparatory phase, thus leading to improved performance of the STS task. These findings provide a scientific basis for the use of audiovisual signals to enhance STS performance in patients with PD.

Switching of movement direction is central to parkinsonian bradykinesia in sit-to-stand.

Patients with Parkinson's disease (PD) are known to manifest slowness in movements. We sought to identify the particular kinematic and kinetic disorders that contribute to the slowness in performing sit-to-stand in these patients. Two inter-related studies were carried out. In the first study, 20 patients with PD and 20 control subjects were instructed to perform sit-to-stand at a natural speed. In the second study, 15 control subjects were instructed to simulate the slower speed of sit-to-stand of the patients identified in the first study. Kinematic and kinetic data were recorded by a PEAK motion analysis system and two force platforms. The results showed that patients with PD generated smaller peak horizontal and vertical velocities during the task. They took a longer time to complete each individual phase as well as the whole movement of sit-to-stand. Patients also produced smaller peak hip flexion and ankle dorsiflexion joint torques and had prolonged time-to-peak torques from sit-to-stand onset. When control subjects simulated the patients' speed of sit-to-stand, there was no difference in all the kinematic and kinetic data between groups. The only exception was that they exhibited a shorter transition time between peak horizontal velocity (flexion phase) and seat-off (extension phase) than the patients. This study demonstrated that the slowness of PD patients during sit-to-stand at a natural speed could be attributed to inadequate peak hip flexion and ankle dorsiflexion torques, a prolonged torque production, as well as a difficulty in switching from the flexion to extension direction during sit-to-stand. As the latter difficulty persisted when the control subjects performed the task at a speed similar to that of the patients, our findings suggest that a fundamental problem of patients with Parkinson's disease could be a switch between movement directions.

Attenuation Characteristics of Peak Ground Motions in the 1995 Hyogo-ken Nanbu Earthquake.

The peak horizontal acceleration and velocity of observed records from the 1995 Hyogo-ken Nanbu earthquake are compared with those predicted from empirical attenuation relations that were derived to be applicable to near-source areas. We found that the observed peak values matched well the empirical attenuation relations. The observed peak vertical accelerations were about half the peak horizontal accelerations when less than 100 cm/s/s. But, the observed peak vertical accelerations tended to be more than half the horizontal ones beyond 100 cm/s/s, and at some sites on soft soil, the peak vertical accelerations were greater than the peak horizontal accelerations. On the other hand, most of the observed peak vertical velocities were about 40% of the peak horizontal velocities independent of the peak amplitudes. At Port Island in Kobe City, remarkable non-linear behavior of soft soil was observed in the vertical array records. The high-frequency shear waves decreased due to liquefaction and the peak horizontal accelerations decayed at the surface. On the contrary, vertical ground motion was amplified by the strong contrast of P-wave velocity in the surface soils. This fact may be one of the causes for greater peak vertical acceleration than peak horizontal acceleration.

The ELDORA/ASTRAIA Airborne Doppler Weather Radar: High-Resolution Observations from TOGA COARE

The ELDORA/ASTRAIA (Electra Doppler Radar/Analyese Stereoscopic par Impulsions Aeroporte) airborne Doppler weather radar was recently placed in service by the National Center for Atmospheric Research and the Centre d'étude des Environnements Terrestre et Planetaires in France. After a multiyear development effort, the radar saw its first field tests in the TOGA COARE (Tropical Oceans–Global Atmosphere Coupled Ocean–Atmosphere Response Experiment) field program during January and February 1993. The ELDORA/ASTRAIA radar (herein referred to as ELDORA) is designed to provide high-resolution measurements of the air motion and rainfall characteristics of very large storms, storms that are frequently too large or too remote to be adequately observed by ground-based radars. This paper discusses the measurement requirements and the design goals of the radar and concludes with an evaluation of the performance of the system using data from TOGA COARE. The performance evaluation includes data from two cases. First, observations of a mesoscale convective system on 9 February 1993 are used to compare the data quality of the ELDORA radar with the National Oceanic and Atmospheric Administration P-3 airborne Doppler radars. The large-scale storm structure and airflow from ELDORA are seen to compare quite well with analyses using data from the P-3 radars. The major differences observed between the ELDORA and P-3 radar analyses were due to the higher resolution of the ELDORA data and due to the different domains observed by the individual radars, a result of the selection of flight track past the storm for each aircraft. In a second example, the high-resolution capabilities of ELDORA are evaluated using observations of a shear-parallel mesoscale convective system (MCS) that occurred on 18 February 1993. This MCS line was characterized by shear-parallel clusters of small convective cells, clusters that were moving quickly with the low-level winds. High-resolution analysis of these data provided a clear picture of the small scale of the storm vertical velocity structure associated with individual convective cells. The peak vertical velocities measured in the high-resolution analysis were also increased above low-resolution analysis values, in many areas by 50%–100%. This case exemplifies the need for high-resolution measurement and analysis of convective transport, even if the goal is to measure and parameterize the large-scale effects of storms. The paper concludes with a discussion of completion of the remaining ELDORA design goals and planned near-term upgrades to the system. These upgrades include an implementation of dual–pulse repetition frequency and development of real-time, in-flight dual-Doppler analysis capability.

Present‐day Antarctic ice mass changes and crustal motion

The peak vertical velocities predicted by three realistic, but contrasting, present‐day scenarios of Antarctic ice sheet mass balance are found to be of the order of several mm/a. One scenario predicts local uplift rates in excess of 5 mm/a. These rates are small compared to the peak Antarctic vertical velocities of the ICE‐3G glacial rebound model, which are in excess of 20 mm/a. If the Holocene Antarctic deglaciation history portrayed in ICE‐3G is realistic, and if regional upper mantle viscosity is not an order of magnitude below 1021 Pa·s, then a vast geographical region in West Antarctica is uplifting at a rate that could be detected by a future Global Positioning System (GPS) campaign. While present‐day scenarios predict small vertical crustal velocities, their overall continent‐ocean mass exchange is large enough to account for a substantial portion of the observed secular polar motion and time‐varying zonal gravity field .

A statistical model for ground motion produced by earthquakes at local and regional distances

AbstractTo adapt random process theory techniques for statistical estimation of peak ground motion to more realistic earth models, we constrain the parameters of duration, geometrical spreading, and spectral shape by modeling the main ground motion as being the result of major contributions by the direct S wave and supercritically reflected S waves. The results of our modeling are constrained to be consistent with values from full-wave synthetics for the test models. The combination of estimation theory and theoretical amplitude spectrum of the main ground motion within the ergodic window successfully predicts the mean peak vertical ground displacements, velocities, and accelerations of the 1982 Miramichi earthquakes in New Brunswick, Canada. In addition, upon considering the effects of source depth and crustal structure for the November 25, 1988, Saguenay earthquake (M = 5.8) in Québec, Canada, the predicted mean peak horizontal ground accelerations match the observed data very well. The effects of source depth and crustal structure on the peak ground motion are complicated for different source sizes and at different epicentral distance ranges.

Current response at the shelf break to transient wind forcing

An analysis of current meter and hydrographic data collected from an array of moorings situated at the shelf break off Nova Scotia is presented. In particular, the focus is on the ocean response to moderate (10 to 20m s−1) transient winds of two or more days duration blowing parallel to the local bathymetry. Under these conditions, upwelling occurs at the shelf break from depths of 400 m and with peak vertical velocities of about 2 mm s−1. The upwelling appears to be confined to within 10 km of the slope. Acceleration, Coriolis, and pressure‐gradient terms are important for the along‐ and cross‐slope momentum balances. Local topographic variations contribute to the anomalously large bottom currents on the shoreward side of the shelf break. Both coastal sea level and the shelf break circulation respond coherently to synoptic wind forcing, but quantitative agreement with two‐layer shelf models is poor.