Object Collision Research Articles

PLANETARY COLLISIONS OUTSIDE THE SOLAR SYSTEM: TIME DOMAIN CHARACTERIZATION OF EXTREME DEBRIS DISKS

Luminous debris disks of warm dust in the terrestrial planet zones around solar-like stars are recently found to vary, indicative of ongoing large-scale collisions of rocky objects. We use Spitzer 3.6 and 4.5 {\mu}m time-series observations in 2012 and 2013 (extended to 2014 in one case) to monitor 5 more debris disks with unusually high fractional luminosities ("extreme debris disk"), including P1121 in the open cluster M47 (80 Myr), HD 15407A in the AB Dor moving group (80 Myr), HD 23514 in the Pleiades (120 Myr), HD 145263 in the Upper Sco Association (10 Myr), and the field star BD+20 307 (>1 Gyr). Together with the published results for ID8 in NGC 2547 (35 Myr), this makes the first systematic time-domain investigation of planetary impacts outside the solar system. Significant variations with timescales shorter than a year are detected in five out of the six extreme debris disks we have monitored. However, different systems show diverse sets of characteristics in the time domain, including long-term decay or growth, disk temperature variations, and possible periodicity.

Calibrating the scale of the NRLMSISE00 model during solar maximum using the two line elements dataset

Empirical mass density models for the thermosphere are widely used for object orbit determination and prediction, object collision avoidance, and re-entry analysis. But the error of these empirical models can often reach 15–30% or even larger during highly disturbed periods of the space environment. On the other hand, the mass density of the thermosphere can be derived from the orbit information contained in the two line elements (TLE) dataset. This technique provides an approach for calibrating the empirical model. Here we select TLE data of 36 low Earth orbiters (LEOs) recorded during 2000–2002 (solar maximum). The ratios of the TLE-derived densities to those from the empirical NRLMSISE00 model are calculated and used to calibrate the scale error of the NRLMSISE00 model by applying a linear height-dependent function. The calibration models for the NRLMSISE00 model during 2000–2002 are then obtained by a least squares adjustment procedure. The calibration factors at 250, 400, and 550km from this calibration model are compared to the density ratios obtained by Emmert et al. (2008) who used TLE data from ∼5000 LEOs. The result indicates that the biases between these two independent factors at the 3 altitudes are all within +/−2%, and the standard deviations (STDs) are under 7%. Another 5 LEOs with altitudes ranging from 200 to 500km are also selected to validate the precision of the calibration model. Their density ratios are calculated using the calibration model and the NRLMSISE00 model, respectively. The results demonstrate that by applying this calibration method the relative root mean square (RMS) error of the NRLMSISE00 model can be reduced by about 9%.

Numerical analysis on wave generated by the Qianjiangping landslide in Three Gorges Reservoir, China

The Qianjiangping landslide occurred on July 13, 2003 when water level in the Three Gorges Reservoir in China reached 135 m a.s.l. for about 1 month. Thirteen people on the slope and 11 fishermen on boats in the nearby area were killed by this landslide and its wave. As a typical case, the Qianjiangping landslide is researched extensively, but the wave itself was studied much less. In this paper, a fluid–solid coupling model based on general moving objects (GMO) collision model and renormalisation group (RNG) turbulent model were employed, simplifying the sliding motion of the Qianjiangping landslide as a rigid body circular motion whose validity was verified by comparing with actual survey conditions related. Numerical simulation analysis shows that in the Qianjiangping landslide event, the solid–fluid energy-transferring rate was 5.97 %, while the motion of sliding mass could push and raise water body. The maximum-modelled wave run-up generated by the Qianjiangping landslide was 40.4 m (up to 175.4 m a.s.l.), while the maximal observed one was 39 m. It was the solitary wave, and the wave celerity was 32∼36 m/s or so. The hazardous river length of impulse wave was estimated to be 12.6 km, where wave height was more than 1 m high. The fluid–solid coupling numerical model employed by this paper can provide important reference for wave generated by other landslides around the world. Research of the landslide-generated wave is very significant in landslide hazard reduction and prevention.

Quick numerical evaluation of the probability that an asteroid will collide with a planet

We propose a numerical method for quick evaluation of the probability that an asteroid will collide with a planet. The method is based on linear mappings of an expected moment of a close approach of the asteroid to the planet and the detection of collisions of the virtual objects with the massive body. The standard way for solving the problem of estimating the collision probability consists in simulating the evolution of the uncertainty cloud numerically based on the stepwise integration of virtual orbits. This is naturally associated with huge processor time costs. The proposed method is tested using the examples of the 2011 AG5 and 2007 VK184 asteroids that are presently in the top of the list of the most dangerous celestial objects. The test results show that linear mappings allow one to obtain the estimates of probabilities quicker by several orders than numerical integration of all virtual orbits.

Safe system approach to reducing serious injury risk in motorcyclist collisions with fixed hazards

Collisions with fixed objects in the roadway environment account for a substantial proportion of motorcyclist fatalities. Many studies have identified individual roadway environment and/or motorcyclist characteristics that are associated with the severity of the injury outcome, including the presence of roadside barriers, helmet use, alcohol use and speeding. However, no studies have reported the cumulative benefit of such characteristics on motorcycling safety. The safe system approach recognises that the system must work as a whole to reduce the net injury risk to road users to an acceptable level, including the four system cornerstone areas of roadways, speeds, vehicles and people. The aim of the present paper is to consider these cornerstone areas concomitantly, and quantitatively assess the serious injury risk of motorcyclists in fixed object collisions using this holistic approach. A total of 1006 Australian and 15,727 (weighted) United States motorcyclist-fixed object collisions were collected retrospectively, and the serious injury risks associated with roadside barriers, helmet use, alcohol use and speeding were assessed both individually and concomitantly. The results indicate that if safety efforts are made in each of the safe system cornerstone areas, the combined effect is to substantially reduce the serious injury risk of fixed hazards to motorcyclists. The holistic approach is shown to reduce the serious injury risk considerably more than each of the safety efforts considered individually. These results promote the use of a safe system approach to motorcycling safety.

DUSTY DISKS AROUND CENTRAL STARS OF PLANETARY NEBULAE

Only a few percent of cool, old white dwarfs (WDs) have infrared excesses interpreted as originating in small hot disks due to the infall and destruction of single asteroids that come within the star's Roche limit. Infrared excesses at 24 micron were also found to derive from the immediate vicinity of younger, hot WDs, most of which are still central stars of planetary nebulae (CSPN). The incidence of CSPN with this excess is 18%. The Helix CSPN, with a 24 micron excess, has been suggested to have a disk formed from collisions of Kuiper belt-like objects (KBOs). In this paper, we have analyzed an additional sample of CSPN to look for similar infrared excesses. These CSPN are all members of the PG 1159 class and were chosen because their immediate progenitors are known to often have dusty environments consistent with large dusty disks. We find that, overall, PG 1159 stars do not present such disks more often than other CSPN, although the statistics (5 objects) are poor. We then consider the entire sample of CSPN with infrared excesses, and compare it to the infrared properties of old WDs, as well as cooler post-AGB stars. We conclude with the suggestion that the infrared properties of CSPN more plausibly derive from AGB-formed disks rather than disks formed via the collision of KBOs, although the latter scenario cannot be ruled out. We finally remark that there seems to be an association between CSPN with a 24 micron excess and confirmed or possible binarity of the central star.

Real-time multibody application for tree harvester truck simulator

A real-time simulator for a tree harvester has been developed for training in more effective vehicle and cutter operation and tree management. The equations of motion of the constrained mechanical system of the tree harvester are expressed using a recursive formulation. The hydraulic actuator modelling of the harvester is based on lumped fluid theory, in which the hydraulic circuit is divided into discrete volumes where pressures are assumed to be distributed equally, while pressure wave propagation in pipes and hoses is assumed to be negligible. For modelling purposes, valves are broken up into a number of adjustable restrictors, which can be modelled separately. The contact model used comprises two parts: collision detection and response. Collision detection identifies whether, when and where moving bodies may come in contact. Collision response prevents penetration when contact occurs and identifies how it should behave after collision. A penalty method is used in this study to establish object collision events. The major achievement of this study is combining these three modelling methods in the application of a real-time simulator.

НОВЫЙ АСПЕКТ МОДЕЛИРОВАНИЯ МНОГОЭЛЕМЕНТНОЙ СИСТЕМЫ ОРБИТАЛЬНЫХ ОБЪЕКТОВ

The simplified method of simulation of multiple-unit system of orbit objects is worked out for problems deals with the forecasting of mechanical conflicts (collisions) between its elements. The method is based on simulation of the virtual elements of system injected into viewing – nodes of mechanical conflicts (parts of the trajectoris, being from each other on distance, dangerous to collisions of orbit objects at their possible diflaction from these trajectoris). Figs.: 3. Refs.: 16 titles.

Hot-Air Balloon Tours: Crash Epidemiology in the United States, 2000-2011

Hot-air balloon tours are FAR Part 91-governed balloon rides conducted for compensation or hire. Part 91, General Aviation, in general involves the least strict federal regulations and accounts for the majority of aviation crashes and fatalities. National Transportation Safety Board reports of hot-air balloon tour crashes in the United States from 2000 through 2011 were read and analyzed. During the 12-yr period, 78 hot-air balloon tours crashed, involving 518 occupants. There were 91 serious injuries and 5 fatalities; 83% of crashes resulted in one or more serious or fatal outcomes. Of the serious injuries characterized, 56% were lower extremity fractures. Most crashes (81%) occurred during landing; 65% involved hard landings. Fixed object collisions contributed to 50% of serious injuries and all 5 fatalities. During landing sequences, gondola dragging, tipping, bouncing, and occupant ejection were associated with poor outcomes. Of the crashes resulting in serious or fatal outcomes, 20% of balloons were significantly damaged or destroyed. The incidence of morbidity and mortality is high among hot-air balloon tour crashes, and the proportion of balloon crashes attributed to paid rides appears to have increased over time. In addition to examining the role of restraint systems, personal protective equipment, and power line emergency procedures in ballooning, injury prevention efforts should target factors such hard landings, object strikes, gondola instability, and occupant ejections, which are associated with balloon injuries and deaths. Crash outcomes may also improve with vehicle engineering that enables balloons themselves to absorb impact forces.

The rising burden of serious thoracic trauma sustained by motorcyclists in road traffic crashes

In many countries increased on-road motorcycling participation has contributed to increased motorcyclist morbidity and mortality over recent decades. Improved helmet technologies and increased helmet wearing rates have contributed to reductions in serious head injuries, to the point where in many regions thoracic injury is now the most frequently occurring serious injury. However, few advances have been made in reducing the severity of motorcyclist thoracic injury. The aim of the present study is to provide needed information regarding serious motorcyclist thoracic trauma, to assist motorcycling groups, road safety advocates and road authorities develop and prioritise counter-measures and ultimately reduce the rising trauma burden. For this purpose, a data collection of linked police-reported and hospital data was established, and considerable attention was given to establishing a weighting procedure to estimate hospital cases not reported to police and fatal cases not admitted to hospital. The resulting data collection of an estimated 19,979 hospitalised motorcyclists is used to provide detailed information on the nature, incidence and risk factors for thoracic trauma. Over the last decade the incidence of motorcyclist serious thoracic injury has more than doubled in the population considered, and by 2011 while motorcycles comprised 3.2% of the registered vehicle fleet, one quarter of road traffic-related serious thoracic trauma cases treated in hospitals were motorcyclists. Motor-vehicle collisions, fixed object collisions and non-collision crashes were fairly evenly represented amongst these cases, while older motorcyclists were over-represented. Several prevention strategies are identified and discussed.

Hierarchical Bounding Sphere FFD-AABB Algorithm for Fast Collision Handing of 3D Deformable Objects on Smart Devices

Due to the recent enriched micro-level hardware and advanced computer software technology, portable yet powerful smart devices draw fervent responses from users and consequently the world’s smart device market has been rapidly expanded. In addition, since smart devices can be used anytime and anywhere using the wireless internet environment, the traditional PC-oriented works are swiftly moving to smart devices. Recently, the demands for representing more realistic 3D deformable objects have been increased for smart device based 3D game, virtual reality, 3D mobile advertisement, augmented reality and so on. However, current smart devices cannot sufficiently process the details of complex 3D object representation and associated physics based animation yet. This paper proposes a new optimized 3D object simulation and collision handling method specifically targeted for smart devices. The proposed hierarchical bounding sphere FFD- AABB (Free Form Deformation -- Axis Aligned Bounding Box) algorithm provides efficient 3D object simulation, since it quickly rejects unnecessary complex collision tasks by executing simple hierarchical bounding sphere distance tests. We have conducted experimental tests under various iOS environments and have performed comparative performance analysis with previous methods. The proposed method shows on average 34% improvement in dynamic simulation and collision handling procedures.

Position estimation and object collision detection of a tendon-driven actuator based on a polytopic observer synthesis

This paper proposes a multi-model based approach that estimates joint position and collision detection of a lightweight electric actuator dedicated to manipulation tasks. Taking advantage of an optimized back-drivable mechatronic design, the use of proprioceptive measures at the motor level enables the estimation of the unmeasured terminal position of the mechanical motor-to-joint transmission and force contact disturbance. A polytopic formulation is introduced based on an accurate model of the mechatronic transmission. Then, a multi-model observer-based estimator is synthesized using root-clustering for exteroceptive variables estimation without additional position/force sensor. The approach is experimentally validated with a single degree-of-freedom manipulator.

The multimessenger picture of compact object encounters: binary mergers versus dynamical collisions

We explore the multimessenger signatures of encounters between two neutron stars (ns2) and between a neutron star and a stellar mass black hole (nsbh). We focus on the differences between gravitational-wave-driven binary mergers and dynamical collisions that occur, for example, in globular clusters. Our discussion is based on Newtonian hydrodynamics simulations that incorporate a nuclear equation of state and a multiflavour neutrino treatment. For both types of encounters we compare the gravitational wave and neutrino emission properties. We also calculate the rates at which nearly unbound mass is delivered back to the central remnant in a ballistic-fallback-plus-viscous-disc model and we analyse the properties of the dynamically ejected matter. Last but not least we address the electromagnetic transients that accompany each type of encounter. We find that dynamical collisions are at least as promising as binary mergers for producing (short) gamma-ray bursts, but they also share the same possible caveats in terms of baryonic pollution. All encounter remnants produce peak neutrino luminosities of at least ∼1053 erg s−1, some of the collision cases exceed this value by more than an order of magnitude. The canonical ns2 merger case ejects more than 1 per cent of a solar mass of extremely neutron-rich (Ye ∼ 0.03) material, an amount that is consistent with double neutron star mergers being a major source of r-process in the galaxy. nsbh collisions eject very large amounts of matter (∼0.15 M⊙) which seriously constrains their admissible occurrence rates. The compact object collision rate (sum of ns2 and nsbh) must therefore be less, likely much less, than 10 per cent of the ns2merger rate. The radioactively decaying ejecta produce optical–ultraviolet ‘macronova’ which, for the canonical merger case, peak after ∼0.4 d with a luminosity of ∼5 × 1041 erg s−1. ns2 (nsbh) collisions reach up to two (four) times larger peak luminosities. The dynamic ejecta deposit a kinetic energy comparable to a supernova in the ambient medium. The canonical merger case releases approximately 2 × 1050 erg, the most extreme (but likely rare) cases deposit kinetic energies of up to 1052 erg. The deceleration of this mildly relativistic material by the ambient medium produces long lasting radio flares. A canonical ns2 merger at the detection horizon of advanced LIGO/Virgo produces a radio flare that peaks on a time-scale of 1 yr with a flux of ∼0.1 mJy at 1.4 GHz. Collisions eject more material at higher velocities and therefore produce brighter and longer lasting flares.

Supermassive Black Holes, the Early Universe, and Gamma-Ray Bursts

Observational evidence reveals that supermassive black holes reside at the center of most galaxies up to the furthest observable redshifts. The tight M-σ relation suggests a close operative feedback between the growth of supermassive black holes and the growth of the galactic bulge. Models describing the formation scenarios of seeding black holes and their growth are reviewed. In each of these models, the prevailing environments in the primordial-galactic disks, including the gas dynamics, cooling processes, and metallic enrichment are explored. It is shown that the galactic disk parameters set constraints on the channel of formation of the seeding black holes and their growth. Primordial black holes from the inflationary era, their formation, possible interaction, and constraints on their observations are discussed. Gamma-ray bursts resulting either from the collapse of massive stars, or from the collision of compact objects are explored. The abundance of these violent events in the early universe suggests a possible connection with galaxy formation.

Objects Collision Detection in Virtual Scene

An algorithm of two stages collision detection is presented for moving objectives in virtual scene. Firstly, AABB bounding box was used to test the intersection of interesting objects in coarse detection stage. Then combining space projection with Z-buffer algorithm, the potential intersecting objects in previous step were tested in precision detection stage, thus we can obtain objects collision data information and complete object collision detection. Finally experimental results show that the algorithm is more efficiency than traditional bounding box detection, the improved technology can realize further accurate collision detection.

An Overview on Base Real-Time Shadow Techniques in Virtual Environments

Shadows are elegant to create a realistic scene in virtual environments variety type of shadow techniques encourage us to prepare an overview on all base shadow techniques. Non real-time and real-time techniques are big subdivision of shadow generation. In non real-time techniques ray tracing, ray casting and radiosity are well known and are described deeply. Radiosity is implemented to create very realistic shadow on non real-time scene. Although traditional radiosity algorithm is difficult to implement, we have proposed a simple one. The proposed pseudo code is easier to understand and implement. Ray tracing is used to prevent of collision of movement objects. Projection shadow, shadow volume and shadow mapping are used to create real-time shadow in virtual environments. We have used projection shadow for some objects are static and have shadow on flat surface. Shadow volume is used to create accurate shadow with sharp outline. Shadow mapping that is the base of most recently techniques is reconstructed. The reconstruct algorithm gives some new idea to propose another algorithm based on shadow mapping.

Visual impressions of causality: Effects of manipulating the direction of the target object's motion in a collision event

Stimuli in which a moving object (A) contacts a stationary one (B) and the latter then moves off tend to give rise to visual impressions of causality. In two experiments the angle of Object B's path of motion to that of Object A was manipulated, and in one of these the point of contact of Object A with Object B was also manipulated. The ampliation hypothesis (Michotte, 1963) predicts that the causal impression should be strongest when Object B continues Object A's direction of motion, regardless of point of contact. In fact the causal impression was strongest when the angle of Object B's motion matched the angle that would actually occur for the point of contact in the stimulus. This supports a hypothesis that the causal impression is a product of experience with real object collisions.

Evaluation of Tensile Strength on Repaired Composite Adhesive Bonded Joint

The present work is to study the tensile strength behavior of the repaired material on low velocity impact damaged GFRP laminate using various repair techniques and prediction of their strength through the experimental investigation. While the servicing life of aircraft structures were damaged by the impact damages such as foreign objects collision, mishandlings of tools etc. During the Impact event the laminate were going to cause deformations such as matrix cracking, fiber breaking, and delamination within the laminate. Practically, the damages in composites are unpredictable about their growth where it was using to predict through the ultrasonic A-scan technique. The test specimen made of bi-directional glass fiber and epoxy resin had an impact with a low velocity impact facility. The extent of damage is determined using ultrasonic scanning and the damaged layers were removed using grinding technique. The removed damaged region was repaired using single bonded lap and double bonded lap repair techniques were used to restore the structural integrity of the laminate. These repaired specimens were uniaxially loaded in INSTRON universal testing machine and the behaviors of adhesively bonded patches were studied using load versus displacement graph. From the observed experiments, the failure loads were compared with the strength of undamaged specimen. Using the obtained parameters the optimized repair technique was proposed. Ultimately this work can be used to improve the safety of composite structures while extending their period of service.

Obstacle Detection using Stereo Imaging to Assist the Navigation of Visually Impaired People

Assistive technology enables people to achieve independence when performing daily tasks and it enhances their overall quality of life. Visual information is the basis for most navigational tasks, so visually impaired individuals are at disadvantage due to the lack of sufficient information about their surrounding environment. With recent advances in inclusive technology it is possible to extend the support given to people with visual disabilities in terms of their mobility. In this context we propose and describe the Blavigator project, whose global objective is to assist visually impaired people in their navigation on indoor and outdoor environments. This paper is focused mainly on the Computer Vision module of the Blavigator prototype. We propose an object collision detection algorithm based on disparity images. The proposed algorithm uses a 2D Ensemble Empirical Mode Decomposition image optimization algorithm and a two layer disparity image segmentation to detect nearby objects.

Are supermassive black holes shrouded by ‘super-Oort’ clouds of comets and asteroids?

The last decade has seen a dramatic confirmation that in situ star formation is possible inside the inner parsec of the Milky Way. Here we suggest that giant planets, solid terrestrial-like planets, comets and asteroids may also form in these environments, and that this may have observational implications for active galactic nuclei (AGN). Like in debris discs around main-sequence stars, collisions of large solid objects should initiate strong fragmentation cascades. The smallest particles in such a cascade – the microscopic dust – may provide a significant opacity. We put a number of observational and physical constraints on AGN obscuring tori resulting from such fragmentation cascades. We find that tori fed by fragmenting asteroids disappear at both low and high AGN luminosities. At high luminosities, L∼LEdd, where LEdd is the Eddington limit, the AGN radiation pressure blows out the microscopic dust too rapidly. At low luminosities, on the other hand, the AGN discs may avoid gravitational fragmentation into stars and solids. We also note that these fragmentation cascades may be responsible for astrophysically ‘large’ dust particles of m sizes that were postulated by some authors to explain unusual absorption properties of the AGN tori.