Critical Deceleration Research Articles

Surrogate safety evaluation of curve sections on an interurban highway under heterogeneous traffic conditions in India

<p class="H1">Road traffic safety is a global concern. Conventionally, road safety evaluation is carried out by analyzing historical crash data, which is a reactive approach to safety analysis. The safety analyst has to wait for sufficient time to accumulate crash data before taking up any safety analysis as a sample of substantial crashes is required for analysis. But in safety analysis with a proactive approach no crash data is required, which is replaced with surrogate “conflicts”, which can be obtained from the new techniques of traffic conflict technique and surrogate safety parameters. Other approaches can be applied in traffic safety evaluation in anticipation of the crash occurrence. The advent of traffic conflict techniques, i.e., use of traffic conflicts in place of crashes and microsimulation methods like modeling of the traffic flow and pattern in traffic streams on a road network, started to apply as a method of analyzing microscopic simulation models and traffic conflict techniques to determine the safety issues in traffic systems and correlate them to the probable incidences of collisions. In this regard, surrogate safety parameters have been used to determine the level of safety on the typical curve sections of an interurban highway namely, Faridabad-Gurgaon four-lane divided highway in Haryana, India. This is accomplished by the use of vehicle trajectory data extracted through microscopic simulation in Verkher in Staedten Simulation (VISSIM) and analysis in Surrogate Safety Assessment Model (SSAM) for the above-referred corridor. Further, efforts have been made to present the intensity of traffic conflicts happening at the curved sections. The surrogate safety measures time to collision (TTC), deceleration rate (DR), and change in velocity (<em>ΔV</em>), as well as conflicting vehicle speed (Max <em>S</em>), are obtained by analysis from the SSAM model for all the curve sections and are validated using the reported crash data on the curve sections of the candidate corridor for 3 years. With the help of statistical elaboration, the critical threshold for TTC with the heterogeneous traffic movement is found 1.6 s, meaning any conflict occurring less than this time would invariably lead to a fatal crash. Similarly, the critical deceleration rate is observed as 0.569 m/s<sup>2</sup>, implying that any conflict with more than this value may lead to a fatal crash. Further, the Delta<em>V</em> values deduced for the study corridor on interurban curve sections catering to heterogeneous traffic movement is 4.1 m/s. Again, any conflict more than this value can turn into a potential crash.</p>

Study of adsorption effect on orientational and relaxation properties of finite polymer chains near the solid surface

To study dynamic properties of a polymer coating, we consider a polymer chain with finite length. We take into account a chain bending rigidity and assume that the chain is located near an adsorbing flat surface of a solid. One part of the chain is fixed on the surface, and the second one remains free. It is supposed that the cause of chain stretching is the internal effective mean (molecular) field formed as a result of intermolecular interactions with free ends of other chains. Kinetic equations based on the Kubo method are obtained to calculate the relaxation time of the segments. The dependences of the long-range orientational order parameter and relaxation time on the adsorption parameter, the mean field coefficient and chain bending rigidity parameters are calculated. It is shown that a first-order phase transition occurs at the critical point, which is associated with a drastic change in the degree of the chain elongation. We discovered the “critical deceleration” effect, which consists in a sharp increase in the relaxation time near the critical point during the formation of surface polymer layers on the surface of a solid.

Spectrum of relaxation times of polarization in thin film ferroelectrics near the phase transition point

The temperature dependences of the spectrum of polarization relaxation times above the temperature of the second-order phase transition of order-disorder type with relaxation Debye mode in a thin ferroelectric film are determined depending on its thickness and the degree of polarization fixation on the film surface. It has been established that the longest of the relaxation times τ1 behaves abnormally, which is unlimitedly increased τ1∼(T−Tf)−1 as the phase transition temperature Tf approaches, causing a critical deceleration of the relaxation processes. Taking into account intrinsic electric fields decreases the relaxation time at other identical film parameters.

Estimating Rear-End Accident Probabilities at Signalized Intersections: A Comparison Study of Intersections With and Without Green Signal Countdown Devices

Objective: Rear-end accidents are the most common accident type at signalized intersections, because the diversity of actions taken increases due to signal change. Green signal countdown devices (GSCDs), which have been widely installed in Asia, are thought to have the potential of improving capacity and reducing accidents, but some negative effects on intersection safety have been observed in practice; for example, an increase in rear-end accidents.Methods: A microscopic modeling approach was applied to estimate rear-end accident probability during the phase transition interval in the study. The rear-end accident probability is determined by the following probabilities: (1) a leading vehicle makes a “stop” decision, which was formulated by using a binary logistic model, and (2) the following vehicle fails to stop in the available stopping distance, which is closely related to the critical deceleration used by the leading vehicle. Based on the field observation carried out at 2 GSCD intersections and 2 NGSCD intersections (i.e., intersections without GSCD devices) along an arterial in Suzhou, the rear-end probabilities at GSCD and NGSCD intersections were calculated using Monte Carlo simulation.Results: The results suggested that, on the one hand, GSCDs caused significantly negative safety effects during the flashing green interval, especially for vehicles in a zone ranging from 15 to 70 m; on the other hand, GSCD devices were helpful in reducing rear-end accidents during the yellow interval, especially in a zone from 0 to 50 m.Conclusions: GSCDs helped shorten indecision zones and reduce rear-end collisions near the stop line during the yellow interval, but they easily resulted in risky car following behavior and much higher rear-end collision probabilities at indecision zones during both flashing green and yellow intervals. GSCDs are recommended to be cautiously installed and education on safe driving behavior should be available.

A Reverse Driving Control Method for Hydrostatic Double-drum Vibratory Rollers

A reverse driving control method for hydrostatic double-drum vibratory rollers is devised in this paper. Based on the analysis of dynamic characteristics of stopping process, the relationship equation between engine speed and pump displacement is established. To restrict the peak value of engine overspeed within the allowable region, an offline parameter determination approach complied with the requirements of average stopping deceleration is developed. The online control method using the selected parameter is presented. Approaches are derived to determine the two key parameters of the control methods, i.e., the critical deceleration value and the coefficient of relationship equation of the engine friction torque and the engine speed. The control method can also be applied to one type of hydrostatic machinery with their engine throttle position unchangeable in stopping process in addition to the double-drum vibratory roller.

Evaluation of modal damping factor as a diagnostic tool for osteoporosis and its relation with serum osteocalcin and collagen I N-telopeptide for monitoring the efficacy of alendronate in ovariectomized rats

Osteoporosis is a metabolic bone disease characterized by reduced bone mass and deterioration of bone microarchitecture. It results from the shift of the osteoblast–osteoclast activity equilibrium in favor of the later. Although, a number of biochemical markers, such as collagen I N-telopeptide (NTx) and osteocalcin (OC), have been used for monitoring bone remodeling, a new, monitoring, non-invasive method, which is based on the measurement of the dynamic characteristic of bone and is known as modal damping factor (MDF), has not been evaluated as a diagnostic tool for osteoporosis. Bisphosphonates, such as alendronate, have an established role in the treatment of osteoporosis. The aim of the present study was, therefore, to evaluate the effects of alendronate on the levels of MDF, serum NTx and OC on osteoporosis induced by ovariectomy in rats. Furthermore, the effects of alendronate on osteoporosis have been histologically evaluated. Fifteen adult female Wistar rats were bilaterally ovariectomized and osteoporosis was histologically confirmed and by the use of peripheral quantitative computerized tomography (pQCT). MDF was applied to assess the bone structural integrity. The serum levels of NTx (37.4 ± 0.5 nM bone collagen equivalents, BCE) and OC (111.0 ± 8.2 ng/mL) were found to significantly increase following ovariectomy (72.0 ± 2.9 nM BCE and 213.5 ± 12.1 ng/mL, respectively, p < 0.001). As assessed by histology and the levels of NTx and OC in sera, animals treated with alendronate presented a statistically significant deceleration in the progression of the disease in comparison to the no-therapy control group (alendronate group NTx levels: 146.3 ± 8.9 nM BCE versus no-therapy control group NTx levels: 265.3 ± 14.0 nM BCE, p < 0.001, alendronate group OC levels: 205.6 ± 18.2 ng/mL versus no-therapy group OC levels: 353.9 ± 26.1 ng/mL, p < 0.001). Data obtained from the vibration analysis performed illustrated that the change in damping was equal or greater to the change in total and trabecular density, respectively. Damping increased with decreasing bone density, as expected, given that damping accounts for the structural integrity of bone (MDF value before ovariectomy: 0.058 ± 0.003 versus MDF value after ovariectomy: 0.098 ± 0.003, p < 0.001). The higher damping values correspond to more deteriorated structures. In particular, both total and trabecular density were significantly decreased following ovariectomy (total density before ovariectomy: 702.4 ± 19.0 versus total density after ovariectomy: 542.2 ± 12.8, p < 0.001, trabecular density before ovariectomy: 445.3 ± 13.0 versus trabecular density after ovariectomy: 396.7 ± 8.4, p < 0.05). MDF value of the alendronate group (0.07 ± 0.002) was significantly lower ( p < 0.001) as compared to MDF value after ovariectomy (0.098 ± 0.003) and that of the no-therapy group (0.1 ± 0.004, p < 0.001). The administration of alendronate seemed to have no effect on either total or trabecular density, since both parameters continued to decrease (alendronate group total density: 549.4 ± 12.3, alendronate group trabecular density: 368.4 ± 14.7). However, when this was compared to the no-therapy group, a statistically significant difference of total density at the 0.05 level was observed (no-therapy total density: 464.8 ± 9.1). The results of this study suggest that combined measurements of MDF, NTx and OC may be a potential diagnostic tool for osteoporosis and monitoring bone integrity during treatment with bisphosphonates. Furthermore, administration of alendronate showed to offer a critical deceleration in the progression of osteoporosis.

Testing the impact attenuation of loose-fill playground surfaces

Objectives—Our objective was to measure the impact attenuation performance of five types of loose-fill playground surfaces at a variety of drop heights, material depths, and conditions. Methods—In a laboratory setting,...

Droplet impaction with a substrate—The critical condition for detachment

Abstract A new experimental device was developed for the purpose of determining the critical condition associated with the release of an attached droplet from a decelerating substrate. A droplet of known size was located on the test substrate which, in turn, was located on a spring-loaded platform. Upon release of the spring, the substrate impacted into the droplet causing an advancement followed by a receding of the triphase line. Any droplet detachment, as revealed by a high-speed video, was noted. Keeping the deceleration conditions constant, the droplet volume was varied until the critical size for detachment was obtained. A system consisting of a water droplet in contact with a PTFE substrate was examined using substrate decelerations ranging from about 200 to 4000 m s −2 . The critical condition for detachment of “small” droplets followed the simple scaling law, α ∝ D −2 , where α is the critical deceleration and D is the droplet diameter. This result is consistent with that expected from an analysis of the drop-weight model, as used for measuring surface tension. The results are relevant to the more general problem of a free droplet impacting with a substrate.