Artykuły w czasopismach na temat „Collisions”
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Chatterjee, A., i A. Ruina. "A New Algebraic Rigid-Body Collision Law Based on Impulse Space Considerations". Journal of Applied Mechanics 65, nr 4 (1.12.1998): 939–51. http://dx.doi.org/10.1115/1.2791938.
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We present a geometric representation of the set of three-dimensional rigid-body collisional impulses that are reasonably permissible by the combination of non-negative post-collision separation rate, non-negative collisional compression impulse, non-negative energy dissipation and the Coulomb friction inequality. The construction is presented for a variety of special collisional situations involving special symmetry or extremes in the mass distribution, the friction coefficient, or the initial conditions. We review a variety of known friction laws and show how they do and do not fit in the permissible region in impulse space as well as comment on other attributes of these laws. We present a few parameterizations of the full permissible region of impulse space. We present a simple generalization to arbitrary three-dimensional point contact collisions of a simple law previously only applicable to objects with contact-inertia eigenvectors aligned with the surface normal and initial relative tangential velocity component (e.g., spheres and disks). This new algebraic collision law has two restitution parameters for general three-dimensional frictional single-point rigid-body collisions. The new law generates a collisional impulse that is a weighted sum of the impulses from a frictionless but nonrebounding collision and from a perfectly sticking, nonrebounding collision. We describe useful properties of our law; show geometrically the set of impulses it can predict for several collisional situations; and compare it with existing laws. For simultaneous collisions we propose that the new algebraic law be used by recursively breaking these collisions into a sequence ordered by the normal approach velocities of potential contact pairs.
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Li, Xiang-Yu, Axel Brandenburg, Gunilla Svensson, Nils E. L. Haugen, Bernhard Mehlig i Igor Rogachevskii. "Effect of Turbulence on Collisional Growth of Cloud Droplets". Journal of the Atmospheric Sciences 75, nr 10 (październik 2018): 3469–87. http://dx.doi.org/10.1175/jas-d-18-0081.1.
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We investigate the effect of turbulence on the collisional growth of micrometer-sized droplets through high-resolution numerical simulations with well-resolved Kolmogorov scales, assuming a collision and coalescence efficiency of unity. The droplet dynamics and collisions are approximated using a superparticle approach. In the absence of gravity, we show that the time evolution of the shape of the droplet-size distribution due to turbulence-induced collisions depends strongly on the turbulent energy-dissipation rate [Formula: see text], but only weakly on the Reynolds number. This can be explained through the [Formula: see text] dependence of the mean collision rate described by the Saffman–Turner collision model. Consistent with the Saffman–Turner collision model and its extensions, the collision rate increases as [Formula: see text] even when coalescence is invoked. The size distribution exhibits power-law behavior with a slope of −3.7 from a maximum at approximately 10 up to about 40 μm. When gravity is invoked, turbulence is found to dominate the time evolution of an initially monodisperse droplet distribution at early times. At later times, however, gravity takes over and dominates the collisional growth. We find that the formation of large droplets is very sensitive to the turbulent energy dissipation rate. This is because turbulence enhances the collisional growth between similar-sized droplets at the early stage of raindrop formation. The mean collision rate grows exponentially, which is consistent with the theoretical prediction of the continuous collisional growth even when turbulence-generated collisions are invoked. This consistency only reflects the mean effect of turbulence on collisional growth.
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Na, Sang-Chul, i Young-Dae Jung. "Screened Collision-Induced Quantum Interference in Collisional Plasmas". Zeitschrift für Naturforschung A 64, nr 3-4 (1.04.2009): 233–36. http://dx.doi.org/10.1515/zna-2009-3-410.
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Abstract The effects of neutral particle collisions on the quantum interference in electron-electron collisions are investigated in collisional plasmas. The effective potential model taking into account the electronneutral particle collision effects is employed in order to obtain the electron-electron collision cross section including the total spin states of the collision system. It is found that the collision effects significantly enhance the cross section. In addition, the collision-induced quantum interference effects are found to be significant in the singlet spin state. It is shown that the quantum interference effects decrease with increasing the thermal energy of the plasma. It is also shown that the quantum interference effects increase with an increase of the collision energy
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Arakawa, Sota, Hidekazu Tanaka i Eiichiro Kokubo. "Impacts of Viscous Dissipation on Collisional Growth and Fragmentation of Dust Aggregates". Astrophysical Journal 933, nr 2 (1.07.2022): 144. http://dx.doi.org/10.3847/1538-4357/ac7460.
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Abstract Understanding the collisional behavior of dust aggregates consisting of submicron-sized grains is essential to unveiling how planetesimals formed in protoplanetary disks. It is known that the collisional behavior of individual dust particles strongly depends on the strength of viscous dissipation force; however, impacts of viscous dissipation on the collisional behavior of dust aggregates have not been studied in detail, especially for the cases of oblique collisions. Here we investigated the impacts of viscous dissipation on the collisional behavior of dust aggregates. We performed numerical simulations of collisions between two equal-mass dust aggregates with various collision velocities and impact parameters. We also changed the strength of viscous dissipation force systematically. We found that the threshold collision velocity for the fragmentation of dust aggregates barely depends on the strength of viscous dissipation force when we consider oblique collisions. In contrast, the size distribution of fragments changes significantly when the viscous dissipation force is considered. We obtained the empirical fitting formulae for the size distribution of fragments for the case of strong dissipation, which would be useful to study the evolution of size and spatial distributions of dust aggregates in protoplanetary disks.
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ZENIT, R., M. L. HUNT i C. E. BRENNEN. "Collisional particle pressure measurements in solid–liquid flows". Journal of Fluid Mechanics 353 (25.12.1997): 261–83. http://dx.doi.org/10.1017/s0022112097007647.
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Experiments were conducted to measure the collisional particle pressure in both cocurrent and countercurrent flows of liquid–solid mixtures. The collisional particle pressure, or granular pressure, is the additional pressure exerted on the containing walls of a particulate system due to the particle collisions. The present experiments involve both a liquid-fluidized bed using glass, plastic or steel spheres and a vertical gravity-driven flow using glass spheres. The particle pressure was measured using a high-frequency-response flush-mounted pressure transducer. Detailed recordings were made of many different particle collisions with the active face of this transducer. The solids fraction of the flowing mixtures was measured using an impedance volume fraction meter. Results show that the magnitude of the measured particle pressure increases from low concentrations (<10% solid volume fraction), reaches a maximum for intermediate values of solid fraction (30–40%), and decreases again for more concentrated mixtures (>40%). The measured collisional particle pressure appears to scale with the particle dynamic pressure based on the particle density and terminal velocity. Results were obtained and compared for a range of particle sizes, as well as for two different test section diameters.In addition, a detailed analysis of the collisions was performed that included the probability density functions for the collision duration and collision impulse. Two distinct contributions to the collisional particle pressure were identified: one contribution from direct contact of particles with the pressure transducer, and the second one resulting from particle collisions in the bulk that are transmitted through the liquid to the pressure transducer.
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Chen, Sisi, Man-Kong Yau, Peter Bartello i Lulin Xue. "Bridging the condensation–collision size gap: a direct numerical simulation of continuous droplet growth in turbulent clouds". Atmospheric Chemistry and Physics 18, nr 10 (25.05.2018): 7251–62. http://dx.doi.org/10.5194/acp-18-7251-2018.
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Abstract. In most previous direct numerical simulation (DNS) studies on droplet growth in turbulence, condensational growth and collisional growth were treated separately. Studies in recent decades have postulated that small-scale turbulence may accelerate droplet collisions when droplets are still small when condensational growth is effective. This implies that both processes should be considered simultaneously to unveil the full history of droplet growth and rain formation. This paper introduces the first direct numerical simulation approach to explicitly study the continuous droplet growth by condensation and collisions inside an adiabatic ascending cloud parcel. Results from the condensation-only, collision-only, and condensation–collision experiments are compared to examine the contribution to the broadening of droplet size distribution (DSD) by the individual process and by the combined processes. Simulations of different turbulent intensities are conducted to investigate the impact of turbulence on each process and on the condensation-induced collisions. The results show that the condensational process promotes the collisions in a turbulent environment and reduces the collisions when in still air, indicating a positive impact of condensation on turbulent collisions. This work suggests the necessity of including both processes simultaneously when studying droplet–turbulence interaction to quantify the turbulence effect on the evolution of cloud droplet spectrum and rain formation.
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Szabó, Dániel, Ágnes Gömöry, Krisztina Ludányi, Károly Vékey i László Drahos. "Very Low-Pressure CID Experiments: High Energy Transfer and Fragmentation Pattern at the Single Collision Regime". Molecules 29, nr 1 (30.12.2023): 211. http://dx.doi.org/10.3390/molecules29010211.
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We have performed CID experiments on a triple quadrupole instrument, lowering the collision gas pressure by 50 times compared to its conventional value. The results show that at very low-collision gas pressure, single collisions dominate the spectra. Indirectly, these results suggest that under conventional conditions, 20–50 collisions may be typical in CID experiments. The results show a marked difference between low- and high-pressure CID spectra, the latter being characterized in terms of ‘slow heating’ and predominance of consecutive reactions. The results indicate that under single collision conditions, the collisional energy transfer efficiency is very high: nearly 100% of the center of mass kinetic energy is converted to internal energy.
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Hasegawa, Yukihiko, Takeru K. Suzuki, Hidekazu Tanaka, Hiroshi Kobayashi i Koji Wada. "Collisional Growth and Fragmentation of Dust Aggregates. II. Mass Distribution of Icy Fragments". Astrophysical Journal 944, nr 1 (1.02.2023): 38. http://dx.doi.org/10.3847/1538-4357/acadda.
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Abstract By performing N-body simulations, we investigated the fundamental processes of collisions between dust aggregates composed of submicron-sized icy dust monomers. We examined the mass distribution of fragments in the collisional outcomes in a wide range of the mass ratio and the collision velocity between colliding dust aggregates. We derived analytic expressions of the mass distribution of large remnants and small fragments by numerical fitting to the simulation results. Our analytic formulae for masses of the large remnants can reproduce the contribution of mass transfer from a large target to a small projectile, which occurs for a mass ratio of ≳3 and is shown in a previous study. We found that the power-law index of the cumulative mass distribution of the small fragments is independent of the mass ratio and only weakly dependent on the collision velocity. On the other hand, the mass fraction of fragments of individual dust monomers decreases with an increasing total mass of colliding aggregates for a fixed mass ratio. This tendency implies that multiple hierarchical disruptive collisions (i.e., collisions between fragments, and collisions between fragments of fragments) are required for producing a large number of individual dust monomers via collisional fragmentation. Our fragment model suggests that the total geometric cross section integrated over the fragments is estimated to be about the same order as the geometric cross section of the target.
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Mioc, V., i C. Blaga. "Binary collisions in popovici’s photogravitational model". Serbian Astronomical Journal, nr 165 (2002): 9–16. http://dx.doi.org/10.2298/saj0265009m.
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The dynamics of bodies under the combined action of the gravitational attraction and the radiative repelling force has large and deep implications in astronomy. In the 1920s, the Romanian astronomer Constantin Popovici proposed a modified photogravitational law (considered by other scientists too). This paper deals with the collisions of the two-body problem associated with Popovici?s model. Resorting to McGehee-type transformations of the second kind, we obtain regular equations of motion and define the collision manifold. The flow on this boundary manifold is wholly described. This allows to point out some important qualitative features of the collisional motion: existence of the black-hole effect, gradientlikeness of the flow on the collision manifold, regularizability of collisions under certain conditions. Some questions, coming from the comparison of Levi-Civita?s regularizing transformations and McGehee?s ones, are formulated.
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Chtab, Anna, i Mikhael Gorokhovski. "Large-Eddy Simulation With Simplified Collisional Microdynamics in a High Reynolds Number Particle-Laden Channel Flow". Journal of Fluids Engineering 129, nr 5 (25.10.2006): 613–20. http://dx.doi.org/10.1115/1.2717619.
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Computing high Reynolds number channel flows laden by heavy solid particles requires excessive CPU resources to calculate interparticle collisions. Since the frequency of these collisions is high, the kinematic details of each elementary collision may not be essential when calculating particle statistics. In this paper, the dynamics of a particle with a phase trajectory that is discontinuous (due to collisions) is simulated using a hypothetical “noncolliding” particle moving along a trajectory smoothed over interparticle collisions. The statistical temperature of this particle is assumed to be in equilibrium with the statistical “temperature” of the resolved turbulence. This simplified microdynamic is introduced into ballistic calculations of particles within the framework of the “two-way” LES approach. The simulation was conducted specifically to compare the velocity statistics of the hypothetical particle with statistics yielded by measurements in the gas∕particle channel flow and by the LES∕particle approach where binary collisions were simulated. This paper shows that, by assuming the universality of collisional microdynamics, one may predict the experimental observation and the results of detailed simulations without requiring supplementary CPU resources to compute the binary collisions.
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Brisset, J., T. Miletich, J. Metzger, A. Rascon, A. Dove i J. Colwell. "Multi-particle collisions in microgravity: Coefficient of restitution and sticking threshold for systems of mm-sized particles". Astronomy & Astrophysics 631 (16.10.2019): A35. http://dx.doi.org/10.1051/0004-6361/201936228.
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Context. The current model of planet formation lacks a good understanding of the growth of dust particles inside the protoplanetary disk beyond mm sizes. A similar collisional regime exists in dense planetary rings. In order to investigate the low-velocity collisions between this type of particles, the NanoRocks experiment was flown on the International Space Station (ISS) between September 2014 and March 2016. We present the results of this experiment. Aims. The objectives of our data analysis are the quantification of the damping of energy in systems of multiple particles in the 0.1–1 mm size range while they are in the bouncing regime, and the study of the formation of clusters through sticking collisions between particles. Methods. We developed statistical methods for the analysis of the large quantity of collision data collected by the experiment. We measured the average motion of particles, the moment of clustering, and the cluster size formed. In addition, we ran simple numerical simulations in order to validate our measurements. Results. We computed the average coefficient of restitution (COR) of collisions and find values ranging from 0.55 for systems including a population of fine grains to 0.94 for systems of denser particles. We also measured the sticking threshold velocities and find values around 1 cm s−1, consistent with the current dust collision models based on independently collected experimental data. Conclusions. Our findings have the following implications that can be useful for the simulation of particles in PPDs and planetary rings: (1) The average COR of collisions between same-sized free-floating particles at low speeds (<2 cm s−1) is not dependent on the collision velocity; (2) The simplified approach of using a constant COR value will accurately reproduce the average behavior of a particle system during collisional cooling; (3) At speeds below 5 mm s−1, the influence of particle rotation becomes apparent on the collision behavior; (4) Current dust collision models predicting sticking thresholds are robust.
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Weng, Jinxian, i Guorong Li. "Economic Loss Analysis of Fishing Boat Collisions Considering Spatial-Temporal Interaction Effects". Journal of Navigation 73, nr 5 (31.03.2020): 1069–86. http://dx.doi.org/10.1017/s037346332000017x.
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Considering unobserved spatial-temporal interaction effects, this study proposes a Bayesian spatial-temporal interaction model for predicting economic loss from fishing boat collisions using 10-year (2004–2014) collision records from six different areas in the waters of Fujian, China. Results show strong spatial heterogeneity and correlation effects in fishing boat collisions, while the economic loss from boat collisions gradually decreases with the time trend. Collision time, collision location, visibility and the involvement of LNG/LPG/chemical-carrying ships show similar marginal effects on the economic loss for the two collision types: fishing boat collisions and collisions involving no fishing boats. Navigational status and the involvement of cargo ships exhibit much bigger effects in fishing boat collisions compared with collisions involving no fishing boat. Unlike collisions involving no fishing boat, fishing boat collisions are associated with reduced economic loss in poor weather conditions characterised by strong wind/waves because in Fujian waters additional safety measures are adopted for fishing boats in such conditions. The proposed model is useful for policymakers in adopting safety enhancement strategies to decrease the economic loss resulting from fishing boat collisions.
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Chatterjee, A., i A. Ruina. "Two Interpretations of Rigidity in Rigid-Body Collisions". Journal of Applied Mechanics 65, nr 4 (1.12.1998): 894–900. http://dx.doi.org/10.1115/1.2791929.
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We distinguish between, and discuss the applicability of, two levels of rigidity in rigid-body collision modeling. For rigidity in the strong force-response sense, collisional contact deformations must be highly localized. The bodies then move according to second-order rigid-body mechanics during the collision. Incremental collision laws and most collision models using continuum mechanics for the contact region depend on force-response rigidity. For rigidity in the weaker impulse-response sense, the deformations need not be localized but displacements during the collision need to be small everywhere. Only the time-integrated rigid-body equations, involving before-collision and after-collision velocities, then need apply. Although a force-response rigid body is also impulse-response rigid the converse is not true. Algebraic collision laws depend only on impulse-response rigidity. Elastic vibration models of collisions are also generally consistent with impulse-response rigidity.
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Struck-Marcell, Curtis. "Caustic Waves in Galaxy Disks Produced in Collisions with Low Mass Companions". International Astronomical Union Colloquium 124 (1990): 743–47. http://dx.doi.org/10.1017/s0252921100005911.
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At this meeting much attention has been focussed on interactions and mergers between roughly equal mass galaxies. On the contrary, I will begin by mentioning a few justifications for studying collisions with relatively low mass companions, specifically, less than about one third of the mass of the target galaxy. The first is simply that such collisions are likely to be common, given that the galaxy luminosity function is broad. The second reason is that such collisions have evidently been less well studied than collisions between nearly equal partners. However, there are a few important exceptions to this generalization, including the sinking satellite problem (e.g. Quinn and Goodman 1986), and the collisional model for the formation of shell galaxies in which a companion of negligible mass is completely disrupted(e.g. Dupraz and Combes 1986, Hernquist and Quinn 1988). The third, and potentially most important reason, is that the effects of a collision with a low-mass companion are less extreme (at least from the big galaxy’s point of view!). Thus, these effects are closer to the theorist’s ideal of a “small perturbation”. This is important for both conceptually understanding the effects of the collision, and for justifying the use of approximate numerical techniques (e.g. restricted three-body) to study them.
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Castro, William HM. "Correlation between Exposure to Bomechanical Stress and Whiplash Associated Disorders (WAD)". Pain Research and Management 8, nr 2 (2003): 76–78. http://dx.doi.org/10.1155/2003/425714.
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One of the most discussed questions in WAD is: can an injury of the cervical spine occur in low velocity collisions? Before this question can be answered, the term 'low velocity' and the kind of collisions must first be defined. From the study of Meyer et al. (1994) it is known that the speed change due to collision, Dv, is a suitable parameter to express the biomechanical stress acting on a person in a car collision. This study also showed that from a biomechanical point of view, a bumper car collision is comparable to a normal car collision. In the case of a rear-end collision, Meyer et al. found that the biomechanical stress acting on persons exposed to bumper car collisions (Dv) at a fun fair in Germany can be as high as 15 km/h. In literature, one case could be found of an 8-year-old girl with 'whiplash' after being exposed to a bumper car collision at a fun fair (Kamieth 1990). In the Netherlands, a 13-year survey of persons who were admitted to emergency units of hospitals by the 'Consument en Veiligheid' foundation, showed 14 persons with WAD complaints after being exposed to bumper car collisions at a fun fair. In comparison to the enormous amounts of bumper car collisions, these figures are negligible. With regard to these data, one could argue that low velocity collisions can be defined as those where Dv is below 15 km/h. However, it should be noted that the kind of collision is important. From the work of Becke et al. (1999) and Becke and Castro (2000), we know that in side collisions with a Dv of just 3 km/h, head contact with the side window of the car is possible; it can be expected that in such cases the cervical spine will also be exposed to some biomechanical stress (notice however, that not every head contact is automatically equal to an injury of the cervical spine!). In conclusion, before using expressions like 'low velocity collisions', its definition with regard to Dv as well as the kind of collision, has to be discussed. With regard to the most common collisions that causes WAD, rear-end collisions, low velocity collisions can arguably be defined as collisions where Dv is below 15 km/h (this is for clarity, and does not mean that those collisions can not cause symptoms; this will be discussed later!).
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Bavcevic, Zeljko, i Vincent Harinam. "Targeting Fatal Traffic Collision Risk from Prior Non-Fatal Collisions in Toronto". Cambridge Journal of Evidence-Based Policing 4, nr 3-4 (2.11.2020): 187–201. http://dx.doi.org/10.1007/s41887-020-00054-z.
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Abstract Research question How accurately can all locations of 44 fatal collisions in 1 year be forecasted across 1403 micro-areas in Toronto, based upon locations of all 1482 non-fatal collisions in the preceding 4 years? Data All 1482 non-fatal traffic collisions from 2008 through 2011 and all 44 fatal traffic collisions in 2012 in the City of Toronto, Ontario, were geocoded from public records to 1403 micro-areas called ‘hexagonal tessellations’. Methods The total number of non-fatal traffic collisions in Period 1 (2008 through 2011) was summed within each micro-area. The areas were then classified into seven categories of frequency of non-fatal collisions: 0, 1, 2, 3, 4, 5, and 6 or more. We then divided the number of micro-areas in each category in Period 1 into the total number of fatal traffic collisions in each category in Period 2 (2012). The sensitivity and specificity of forecasting fatal collision risk based on prior non-fatal collisions were then calculated for five different targeting strategies. Findings The micro-locations of 70.5% of fatal collisions in Period 2 had experienced at least 1 non-fatal collision in Period 1. In micro-areas that had zero non-fatal collisions during Period 1, only 1.7% had a fatal collision in Period 2. Across all areas, the probability of a fatal collision in the area during Period 2 increased with the number of non-fatal collisions in Period 1, with 6 or more non-fatal collisions in Period 1 yielding a risk of fatal collision in Period 2 that was 8.7 times higher than in areas with no non-fatal collisions. This pattern is evidence that targeting 25% of micro-areas effectively could cut total traffic fatalities in a given year by up to 50%. Conclusion Highly elevated risks of traffic fatalities can be forecasted based on prior non-fatal collisions, targeting a smaller portion of the city for more concentrated investment in saving lives.
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Pokorny, Petr, i Alena Høye. "Descriptive analysis of reports on autonomous vehicle collisions in California: January 2021–June 2022". Traffic Safety Research 2 (28.09.2022): 000011. http://dx.doi.org/10.55329/xydm4000.
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The characteristics of autonomous vehicles’ collisions from 2021 and the first half of 2022 in California confirm trends reported in previous years. Driving in autonomous mode was associated with fewer instances in which the AV was deemed to be at fault in a collision. Most collisions in autonomous mode were rear-end collisions at intersections. Single vehicle collisions occurred mostly in manual mode. Collisions with vulnerable road users occurred mostly while the autonomous vehicle was in manual mode, often right after disengagement from autonomous mode. In collisions with other vehicles that occurred after disengagement, the other vehicles were frequently deemed to be at fault. Compared to 2021, the collision reports from the first half of 2022 indicate higher shares of collisions in autonomous mode, rear-end collisions, and collisions with vulnerable road users.
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Abedin, Abedin Y., J. J. Kavelaars, Jean-Marc Petit, Brett Gladman, Michele Bannister, Mike Alexandersen, Ying-Tung Chen, Stephen Gwyn i Kathryn Volk. "OSSOS. XXVI. On the Lack of Catastrophic Collisions in the Present Kuiper Belt". Astronomical Journal 164, nr 6 (30.11.2022): 261. http://dx.doi.org/10.3847/1538-3881/ac9cdb.
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Abstract We investigate different conditions, including the orbital and size–frequency distribution (SFD) of the early Kuiper Belt, that can trigger catastrophic planetesimal destruction. The goal of this study is to test if there is evidence for collisional grinding in the Kuiper Belt that has occurred since its formation. This analysis has important implications for whether the present-day SFD of the cold classical trans-Neptunian objects (TNOs) is a result of collisional equilibrium or if it reflects the primordial stage of planetesimal accretion. As an input to our modeling, we use the most up-to-date debiased OSSOS++ ensemble sample of the TNO population and orbital model based on the present-day architecture of the Kuiper Belt. We calculate the specific impact energies between impactor–target pairs from different TNO groups and compare our computed energies to catastrophic disruption results from smoothed particle hydrodynamics simulations. We explore different scenarios by considering different total primordial Kuiper Belt masses and power slopes of the SFD and allowing collisions to take place over different timescales. The collisional evolution of the Kuiper Belt is a strong function of the unknown initial mass in the trans-Neptunian region, where collisional grinding of planetesimals requires a total primordial Kuiper Belt mass of M > 5 M ⊕, collision speeds as high as 3 km s−1, and collisions over at least 0.5 Gyr. We conclude that presently, most of the collisions in the trans-Neptunian region are in the cratering rather than disruption regime. Given the low collision rates among the cold classical Kuiper Belt objects, their SFD most likely represents the primordial planetesimal accretion.
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Hendy, Shaun C., i Aruna Awasthi. "Dependence of Adhesion and Reflection on Orientation in Nanocluster Deposition". Advances in Science and Technology 51 (październik 2006): 127–33. http://dx.doi.org/10.4028/www.scientific.net/ast.51.127.
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We consider the deposition of icosahedral clusters on a weakly adhesive substrate using molecular dynamics. We identify three characteristic orientations that lead to distinct collision behavior: vertexfirst, edgefirst and facetfirst. At low velocities, the collision depends strongly on cluster orientation with vertexfirst collisions leading to reflections and edgefirst collisions leading to adhesion. At high velocities, the collisions depend only weakly on orientation with the majority of collisions leading to reflection.
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Psaralexi, Maria, Maria Lazarina, Yorgos Mertzanis, Danai-Eleni Michaelidou i Stefanos Sgardelis. "Exploring 15 years of brown bear (Ursus arctos)-vehicle collisions in northwestern Greece". Nature Conservation 47 (25.03.2022): 105–19. http://dx.doi.org/10.3897/natureconservation.47.71348.
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Road networks provide several benefits to human societies; however, they are also one of the major drivers of fragmentation and habitat degradation. Their negative effects include wildlife-vehicle collisions which are associated with increased barrier effects, restricted gene flow, and increased local extinction risk. Large carnivores, such as the brown bear (Ursus arctos), are vulnerable to road mortality while they also put human safety at risk in every collision. We recorded approximately 100 bear-vehicle collisions during the last 15 years (2005–2020) in northwestern Greece and identified common aspects for collisions, i.e., spatial, or temporal segregation of collision events, road features, and age or sex of the involved animals. We recorded collisions in both the core distribution area of brown bears, as well as at the periphery, where few individuals, mostly males, disperse. According to our findings, there are four collision hotspots which include ca. 60% of total collisions. Bear-vehicle collisions occurred mostly in periods of increased animal mobility, under poor light conditions and low visibility. In most cases, we deem that a collision was unavoidable at the time of animal detection, because the driver could not have reacted in time to avoid it. Appropriate fencing, in combination with the retention of safe passages for the animals, can minimize collisions. Therefore, such mitigation measures, wildlife warning signs and other collision prevention systems, such as animal detection systems, should be adopted to decrease the number of bear-vehicle collisions and improve road safety.
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Ocampo-Peñuela, Natalia, R. Scott Winton, Charlene J. Wu, Erika Zambello, Thomas W. Wittig i Nicolette L. Cagle. "Patterns of bird-window collisions inform mitigation on a university campus". PeerJ 4 (1.02.2016): e1652. http://dx.doi.org/10.7717/peerj.1652.
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Bird-window collisions cause an estimated one billion bird deaths annually in the United States. Building characteristics and surrounding habitat affect collision frequency. Given the importance of collisions as an anthropogenic threat to birds, mitigation is essential. Patterned glass and UV-reflective films have been proven to prevent collisions. At Duke University’s West campus in Durham, North Carolina, we set out to identify the buildings and building characteristics associated with the highest frequencies of collisions in order to propose a mitigation strategy. We surveyed six buildings, stratified by size, and measured architectural characteristics and surrounding area variables. During 21 consecutive days in spring and fall 2014, and spring 2015, we conducted carcass surveys to document collisions. In addition, we also collected ad hoc collision data year-round and recorded the data using the app iNaturalist. Consistent with previous studies, we found a positive relationship between glass area and collisions. Fitzpatrick, the building with the most window area, caused the most collisions. Schwartz and the Perk, the two small buildings with small window areas, had the lowest collision frequencies. Penn, the only building with bird deterrent pattern, caused just two collisions, despite being almost completely made out of glass. Unlike many research projects, our data collection led to mitigation action. A resolution supported by the student government, including news stories in the local media, resulted in the application of a bird deterrent film to the building with the most collisions: Fitzpatrick. We present our collision data and mitigation result to inspire other researchers and organizations to prevent bird-window collisions.
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Chernoff, David F., i Xiaolan Huang. "Frequency of Stellar Collisions in Three-Body Heating". Symposium - International Astronomical Union 174 (1996): 263–72. http://dx.doi.org/10.1017/s0074180900001601.
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The probability for collisional interaction of three body binaries is calculated as a function of the physical radius and mass of the stellar objects and the depth of the cluster potential well. For typical cluster parameters, there is a significant chance of physical collision for objects as small as white dwarfs. One consequence of the collisions is to lower the amount of heat produced from hardening a binary, thereby diminishing the efficiency of the three-body heating mechanism.
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Regehr, Jonathan D., Jeannette Montufar i Garreth Rempel. "Safety performance of longer combination vehicles relative to other articulated trucks". Canadian Journal of Civil Engineering 36, nr 1 (styczeń 2009): 40–49. http://dx.doi.org/10.1139/l08-109.
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This article helps improve the understanding about the safety performance of longer combination vehicles (LCVs) relative to other articulated trucks operating on rural highways, using evidence from the Canadian portion of the CANAMEX trade corridor. The analysis reveals that from a collision rate perspective, LCVs as a group have better safety performance than other articulated trucks. Turnpike doubles have the lowest collision rate of all articulated truck types (16 collisions per 100 million vehicle-kilometres of travel or VKT), followed by Rocky Mountain doubles (32 collisions per 100 million VKT). The collision rate for triple trailer combinations (62 collisions per 100 million VKT) is higher than the collision rates for tractor semitrailers (42 collisions per 100 million VKT) and legal-length tractor double trailers (44 collisions per 100 million VKT). These results are an important input for civil engineering and transport policy decisions concerning longer combination vehicle operations.
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Samuels, Brendon, Brock Fenton, Esteban Fernández-Juricic i Scott A. MacDougall-Shackleton. "Opening the black box of bird-window collisions: passive video recordings in a residential backyard". PeerJ 10 (20.12.2022): e14604. http://dx.doi.org/10.7717/peerj.14604.
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Collisions with windows on buildings are a major source of bird mortality. The current understanding of daytime collisions is limited by a lack of empirical data on how collisions occur in the real world because most data are collected by recording evidence of mortality rather than pre-collision behaviour. Based on published literature suggesting a causal relationship between bird collision risk and the appearance of reflections on glass, the fact that reflections vary in appearance depending on viewing angle, and general principles of object collision kinematics, we hypothesized that the risk and lethality of window collisions may be related to the angle and velocity of birds’ flight. We deployed a home security camera system to passively record interactions between common North American bird species and residential windows in a backyard setting over spring, summer and fall seasons over 2 years. We captured 38 events including 29 collisions and nine near-misses in which birds approached the glass but avoided impact. Only two of the collisions resulted in immediate fatality, while 23 birds flew away immediately following impact. Birds approached the glass at variable flight speeds and from a wide range of angles, suggesting that the dynamic appearance of reflections on glass at different times of day may play a causal role in collision risk. Birds that approached the window at higher velocity were more likely to be immediately killed or stunned. Most collisions were not detected by the building occupants and, given that most birds flew away immediately, carcass surveys would only document a small fraction of window collisions. We discuss the implications of characterizing pre-collision behaviour for designing effective collision prevention methods.
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Yang, Han. "The Effect of colliding galaxies on star formation rates based on IllustrisTNG". Highlights in Science, Engineering and Technology 38 (16.03.2023): 30–36. http://dx.doi.org/10.54097/hset.v38i.5692.
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Galaxy collisions are a complex and common cosmic phenomenon that attracts attention of plenty of scholars. In this paper, the effect of colliding galaxies on the star formation rates will be investigated based on IllustrisTNG, considering three properties of colliding galaxies: distance, velocity and mass. According to the analysis, the deeper the galaxies collide, the larger the SFR values they have. Besides, the effect of collisional and tidal forces on the SFR is continuous. In collisions, galaxies with high relative velocity have higher SFR values compared to galaxies with low velocity; the lighter galaxies have higher SFR values and are more pronounced as the mass ratio of the two galaxies becomes larger. When the colliding galaxies are close in mass, the collision does not have a significant effect on the SFR of both sides. In connection with these results, the possible reasons are discussed for the changing of the SFR by galaxy collisions, i.e., galaxy collisions lead to structural instability of gas clouds in galaxies, causing star formation. These results shed light on guiding further exploration of star formation.
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Nicolas, Timothée. "Impact of azimuthal forcing on the Brillouin limit in a collisional two-species Ohkawa filter". Physics of Plasmas 29, nr 4 (kwiecień 2022): 042105. http://dx.doi.org/10.1063/5.0073198.
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This paper investigates the physics of plasma separation in a two species rotating collisional Ohkawa filter, when the source of rotation is an orbital angular momentum carrying wave. The electric field is treated self-consistently with ion and electron radial motion. The injection of angular momentum causes radial currents leading to charge penetration and electric field build up. The electric field varies until an equilibrium with the friction forces is reached. Both collisions with neutrals and Coulomb collisions are considered. In the case where the electric field is driven by the resonant wave, there is no collisional breakdown of the Brillouin limit [Rax et al., Phys. Plasmas 22, 092101 (2015)]; on the contrary, the maximum achievable electric field decreases when the collision frequency is increased. When two species are present, one that undergoes the wave forcing while the second does not interact with the wave, we find the following: the first species is confined, while the second species can be expelled or confined depending on the charge to mass ratio and the collisionalities. Assuming equal charge numbers, if the second species is the heavy one, it is always expelled, which is a standard result. When the second species is the light one, it can also be expelled in the common case where neutral collisions dominate over Coulomb collisions, which constitutes a new result.
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Van Staal, Cees, i Alexandre Zagorevski. "Accretion, Soft and Hard Collision: Similarities, Differences and an Application from the Newfoundland Appalachian Orogen". Geoscience Canada 47, nr 3 (28.09.2020): 103–18. http://dx.doi.org/10.12789/geocanj.2020.47.161.
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We argue there is no distinction between accretion and collision as a process, except when accretion is used in the sense of incorporating small bodies of sedimentary and/or volcanic rocks into an accretionary wedge by off-scraping or underplating. There is also a distinction when these terms are used in classifying mountain belts into accretionary and collisional orogens, although such classifications are commonly based on a qualitative assessment of the scale and nature of the accreted terranes and continents involved in formation of mountain belts. Soft collisions occur when contractional deformation and associated metamorphism are principally concentrated in rocks of the leading edge of the partially pulled-down buoyant plate and the upper plate forearc terrane. Several young arc-continent collisions show evidence for partial or wholesale subduction of the forearc such that the arc is structurally juxtaposed directly against lower plate rocks. This process may explain the poor preservation of forearcs in the geological record. Soft collisions generally change into hard collisions over time, except if the collision is rapidly followed by formation of a new subduction zone due to step-back or polarity reversal. Thickening and metamorphism of the arc's suprastructure and retro-arc part of upper plate due to contractional deformation and burial are the characteristics of a hard collision or an advancing Andean-type margin. Strong rheological coupling of the converging plates and lower and upper crust in the down-going continental margin promotes a hard collision. Application of the soft–hard terminology supports a structural juxtaposition of the Taconic soft collision recorded in the Humber margin of western Newfoundland with a hard collision recorded in the adjacent Dashwoods block. It is postulated that Dashwoods was translated dextrally along the Cabot-Baie Verte fault system from a position to the north of Newfoundland where the Notre Dame arc collided ca. 10 m.y. earlier with a wide promontory in a hyperextended segment of the Laurentian margin.
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Rose, Sanaea C., i Morgan MacLeod. "Collisional Shaping of Nuclear Star Cluster Density Profiles". Astrophysical Journal Letters 963, nr 1 (22.02.2024): L17. http://dx.doi.org/10.3847/2041-8213/ad251f.
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Abstract A supermassive black hole surrounded by a dense, nuclear star cluster resides at the center of many galaxies. In this dense environment, high-velocity collisions frequently occur between stars. About 10% of the stars within the Milky Way’s nuclear star cluster collide with other stars before evolving off the main sequence. Collisions preferentially affect tightly bound stars, which orbit most quickly and pass through regions of the highest stellar density. Over time, collisions therefore shape the bulk properties of the nuclear star cluster. We examine the effect of collisions on the cluster’s stellar density profile. We show that collisions produce a turning point in the density profile, which can be determined analytically. Varying the initial density profile and collision model, we characterize the evolution of the stellar density profile over 10 Gyr. We find that old, initially cuspy populations exhibit a break around 0.1 pc in their density profile, while shallow density profiles retain their initial shape outside of 0.01 pc. The initial density profile is always preserved outside of a few tenths of a parsec irrespective of initial conditions. We generalize this model to an arbitrary galactic nucleus and show that the location of the collisional break can be simply estimated from the nuclear properties. Lastly, we comment on the implications of collisions for the luminosity and color of stars in the collisionally shaped inner cluster.
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FISCH, LIOR, ASSAF TAL i GERSHON KURIZKI. "TRANSLATIONAL ENTANGLEMENT BY COLLISIONS AND HALF-COLLISIONS". International Journal of Modern Physics B 20, nr 11n13 (20.05.2006): 1648–60. http://dx.doi.org/10.1142/s0217979206034182.
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Here we aim at setting the principles of and quantifying translational entanglement by collisions and half-collisions. In collisions, the resonance width s and the initial phase-space distributions are shown to determine the degree of post-collisional momentum entanglement. Half-collisions (dissociation) are shown to yield different types of approximate EPR states. We analyse a feasible realization of translational EPR entanglement and teleportation via cold-molecule Raman dissociation and subsequent collisions, resolving both practical and conceptual difficulties it has faced so far.
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Tao, Junqi, Weihao Wu, Meng Wang, Hua Zheng, Wenchao Zhang, Lilin Zhu i Aldo Bonasera. "The Novel Scaling of Tsallis Parameters from the Transverse Momentum Spectra of Charged Particles in Heavy-Ion Collisions". Particles 5, nr 2 (9.05.2022): 146–56. http://dx.doi.org/10.3390/particles5020013.
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The transverse momentum (pT) spectra of charged particles measured in Au + Au collisions from the beam energy scan (BES) program, Cu + Cu collisions at sNN=62.4, 200 GeV at the RHIC and Pb + Pb, Xe + Xe collisions at the LHC are investigated in the framework of Tsallis thermodynamics. The theory can describe the experimental data well for all the collision systems, energies and centralities investigated. The collision energy and centrality dependence of the Tsallis distribution parameters, i.e., the temperature T and the nonextensive parameter q, for the A + A collisions are also studied and discussed. A novel scaling between the temperature divided by the natural logarithm of collision energy (T/lns) and the nonextensive parameter q is presented.
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Jungmann, Felix, i Gerhard Wurm. "Observation of bottom-up formation for charged grain aggregates related to pre-planetary evolution beyond the bouncing barrier". Astronomy & Astrophysics 650 (czerwiec 2021): A77. http://dx.doi.org/10.1051/0004-6361/202039430.
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Context. Particles in protoplanetary disks go through a number of phases that are dominated by collisions. In each of these events, grains exchange electrical charge via triboelectric effects. This enhances the stability of particle aggregates. Aims. Dielectric grains are easily charged by collisions. Here, we investigate whether a charge is capable of inducing an aggregation of particles and we consider how collision properties, such as sticking velocities and collisional cross-sections, are altered. Methods. We explored aggregation in microgravity experiments based on the observation of the motion of submillimeter (submm) grains following many collisions. In the process, grains attract each other, collide, stick, and ultimately form small aggregates. Results. We observed a bottom-up formation of irregular aggregates from submm grains. While some of the observed trajectories during the approach of grains reflect the presence of a pure Coulomb potential, the motion is not always in agreement with pure Kepler motion. Higher-order potentials of multipole charge distributions stand as a plausible explanation for this behavior. An immediate consequence of charging is that the particles continue to stick to each other at velocities of ~10 cm s−1, while surface forces of neutral grains are only expected to allow sticking below ~1 mm s−1. No bouncing collision was observed among hundreds of collisions in the given parameter range. Applied to early phases of planet formation, the forming aggregates are therefore the first steps in a new growth phase beyond the traditional bouncing barrier in planet formation.
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Stwalley, William C. "Collisions and reactions of ultracold molecules". Canadian Journal of Chemistry 82, nr 6 (1.06.2004): 709–12. http://dx.doi.org/10.1139/v04-035.
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It is argued that collision dynamics of atoms and molecules at ultracold temperatures (below 1 mK) are not readily predictable from knowledge of collision dynamics above 100 K. In the case of elastic collisions, it is well known that the collision cross section is constant as T → 0 K but mass and symmetry effects are dramatic. The cases of inelastic and reactive collisions are less studied, but a T1/2 dependence of the cross section as T → 0 K is expected. It seems that extrapolations of high-temperature inelastic and reactive behavior normally greatly underestimate ultracold-temperature rates. The prospects for experimental observation of ultracold collision dynamics are rapidly improving.Key words: ultracold molecules, collisions, reactions, hydrogen, scattering length.
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Yang, Bo, Yao Wu, Weihua Zhang i Jie Bao. "Modeling Collision Probability on Freeway: Accounting for Different Types and Severities in Various LOS". Sustainability 12, nr 18 (9.09.2020): 7386. http://dx.doi.org/10.3390/su12187386.
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In this study, collision-related data were collected on the I-880 freeway of California in the United States from 2006 to 2011. Our objective was to study the collision probability of different collision types and severities in different traffic states. The traffic states were divided by the traditional level of service (LOS) method. Various Bayesian conditional logit models have been established to analyze the relationship between the collision probability of different collision patterns and LOSs. The results showed that LOS A had the best safety performance associated with all of the collision types and severities, LOS C had the worst safety performance associated with hit object collisions, LOS D had the worst safety performance associated with sideswipe collisions and rear end collisions, and LOS F had the worst safety performance associated with injury collisions. The five-stage Bayesian random parameter sequential logit model was established to quantify the effects of different variables on the collision probability of various collision types and severities. In addition to LOS, the visibility, road surface, weather, ramp, and number of lanes had significant effects on different collision types and severities.
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Bayne, Erin M., Corey A. Scobie i Michael Rawson-Clark. "Factors influencing the annual risk of bird–window collisions at residential structures in Alberta, Canada". Wildlife Research 39, nr 7 (2012): 583. http://dx.doi.org/10.1071/wr11179.
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Context Increasingly, ornithologists are being asked to identify major sources of avian mortality so as to identify conservation priorities. Aims Considerable evidence suggests that windows of office towers are a lethal hazard for migrating birds. The factors influencing the risk of bird–window collisions in residential settings are not understood as well. Methods Citizen scientists were requested to participate in an online survey that asked about characteristics concerning their homes and yards, general demographic information about participants, and whether they had observed evidence of bird–window collisions at their home. Key results We found that 39.0% of 1458 participants observed a bird–window collision in the previous year. The mean number of reported collisions was 1.7 ± 4.6 per residence per year, with 38% of collisions resulting in a mortality. Conclusions Collisions were not random, with the highest collision and mortality rates at rural residences, with bird feeders > rural residences without feeders > urban residences with feeders > urban residences without feeders > apartments. At urban houses, the age of neighbourhood was a significant predictor of collision rates, with newer neighbourhoods reporting fewer collisions than older neighbourhoods. Most people remembered collisions occurring in the summer months. Implications Our results are consistent with past research, suggesting that window collisions with residential homes are an important source of mortality for birds. However, we found large variation in the frequency of collisions at different types of residences. Proper stratification of residence type is crucial to getting accurate estimates of bird–window collisions when scaling local data into larger-scale mortality estimates.
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Naik, Bharati. "Measurement of azimuthal correlations of D mesons with charged particles in pp collisions at √s=13$\sqrt s = 13$ TeV with ALICE at the LHC". EPJ Web of Conferences 199 (2019): 04002. http://dx.doi.org/10.1051/epjconf/201919904002.
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The ALICE (A Large Ion Collider Experiment) detector at the LHC (Large Hadron Collider) is dedicated to the study of the properties of the hot and dense QCD matter (Quark–Gluon Plasma) produced in the nucleus-nucleus collisions at high energy. Heavy quarks (charm and beauty), having large masses, are produced in the hard-parton scattering in the early stages of the collision. Therefore, they experience the whole evolution of the hot and dense medium, representing an important tool for its characterization. The study of angular correlations between D mesons and charged particles in Pb–Pb collisions gives insight about the energy loss of charm quarks and the medium-induced modification of its fragmentation into jets. Moreover, pp collisions help to understand the production mechanisms, fragmentation and hadronization of charm quarks and acts as a reference for p–Pb and Pb–Pb measurements. In this article, the measurement of azimuthal correlations between D0 meson and charged particles in pp collisions at $\sqrt s = 13$ TeV is presented. The collisional energy dependence of the correlations is extracted from the comparison with the results at $\sqrt s = 7$ TeV. The data are also compared with simulations performed with different event generators.
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Ashgriz, N., i J. Y. Poo. "Coalescence and separation in binary collisions of liquid drops". Journal of Fluid Mechanics 221 (grudzień 1990): 183–204. http://dx.doi.org/10.1017/s0022112090003536.
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An extensive experimental investigation of the binary collision dynamics of water drops for size ratios of 1. 0.75, and 0.5, for the Weber-number range of 1 to 100, and for all impact parameters is reported. Two different types of separating collisions, namely reflexive and stretching separations, are identified. Reflexive separation is found to occur for near head-on collisions, while stretching separation occurs for large-impact-parameter collisions. The boundaries between both of the separating collisions and coalescence collision are found experimentally. Theoretical models for predictions of the reflexive and stretching separation are also given.
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Danilatos, G. D. "Electron Beam Profile in the ESEM". Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988): 192–93. http://dx.doi.org/10.1017/s0424820100103048.
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The examination of specimens in the presence of gas in the environmental scanning electron microscope (ESEM) requires the electron beam to pass through a minimum (optimum) 1ayer of gas before it strikes the specimen. The electron scattering by the gas molecules results in a modification of the original beam profile. Some conclusions from a study on these profiles are presented here but more details can be found elsewhere.When an electron beam travels a distance L through a gas with n particles per unit volume, the average number of collisions per electron m= σ⊤nL, where σ⊤ is the characteristic total collision cross section for the gas. The electron beam collision process is described by the Poisson distribution P (x) =mx e-m/X!, where P(x) is the probability that an electron undergoes x number of collisions (X=0, 1 ,2. . . ) . Thus, when m=1 , about 37% of electrons undergo no collisions, 37% undergo a single collision, 18% two collisions, 6%. three collisions etc.
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Guo, Yanyong, i Tarek Sayed. "Before–After Evaluation of Left-Turn Lane Extension Considering Injury Severity and Collision Type". Transportation Research Record: Journal of the Transportation Research Board 2674, nr 8 (31.05.2020): 67–77. http://dx.doi.org/10.1177/0361198120920270.
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Left-turn lanes are commonly used to provide space to accommodate vehicle deceleration and provide adequate storage of turning vehicles. The objective of this study is to evaluate the safety effectiveness of extending the length of left-turn lanes at signalized intersection approaches. Five years of collision data including injury severity and collision type from three treatment sites and 31 comparison sites in the City of Surrey, Canada were used in the study. The analysis focused on target crashes including left-turn-related rear-end and left-turn-related sideswipe collisions. A full Bayesian (FB) before–after analysis was conducted for all collisions, severity levels, and collision types. Multivariate Poisson–lognormal linear intervention models were used for the analysis. The treatment effectiveness index was calculated to quantitatively measure the effectiveness of the safety treatment. The FB before–after results showed that the treatment-related collisions were reduced by 57.4% following the implementation of extended left-turn lane. The reduction in injuries and fatalities collisions (63.8%) was greater than that in property damage only collisions (55.7%). The decrease in rear-end collisions (62.8%) was greater than that in sideswipe collisions (58.1%). The findings indicate a remarkable improvement in safety after the length extension of the left-turn lane.
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Rice, Thomas M., Lara Troszak i Bryon G. Gustafson. "Epidemiology of law enforcement vehicle collisions in the US and California". Policing: An International Journal of Police Strategies & Management 38, nr 3 (17.08.2015): 425–35. http://dx.doi.org/10.1108/pijpsm-03-2015-0026.
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Purpose – Concerns about the risk of traffic collision injury to both police officers and bystanders are increasing as the use of in-vehicle technologies becoming widespread among agencies. This study used national and California data to characterize traffic collisions in which a police vehicle was involved. The paper aims to discuss these issues. Design/methodology/approach – The authors used a California traffic collision database to retrospectively identify collisions that involved police vehicles for years 2007-2010. The authors summarized collision characteristics with descriptive methods and used log-binomial regression to estimate associations between personal and collision characteristics with officer culpability. Findings – The authors identified 5,233 traffic collisions in California. In total, 10 percent of law enforcement vehicles were motorcycles. In all, 9 percent of cruisers struck a pedestrian or bicyclist, compared with only 2 percent of motorcycles. Compared with officers aged 50 or older, officers in younger age categories were progressively much more likely to have been culpable. Motorcycle officers were 33 percent less likely to be culpable for their collision involvements. Approximately 100 fatal collisions involving a law enforcement vehicle occur each year in the USA. Originality/value – The findings from this study indicate that approximately 1,300 injury-producing traffic collisions occur each year in California that involve a law enforcement vehicle. The authors found that younger age, female sex, cruiser operation, traveling unbelted, and single-vehicle collision involvement were positively associated with officer culpability. Officer race and community population were not significantly associated with culpability. The occurrence of fatal collisions in the USA was stable over a 12-year period.
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Cabrera-Arnau, Carmen, i Steven R. Bishop. "Urban population size and road traffic collisions in Europe". PLOS ONE 16, nr 8 (27.08.2021): e0256485. http://dx.doi.org/10.1371/journal.pone.0256485.
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Millions of road traffic collisions take place every year, leading to significant knock-on effects. Many of these traffic collisions take place in urban areas, where traffic levels can be elevated. Yet, little is known about the extent to which urban population size impacts road traffic collision rates. Here, we use urban scaling models to analyse geographic and road traffic collision data from over 300 European urban areas in order to study this issue. Our results show that there is no significant change in the number of road traffic collisions per person for urban areas of different sizes. However, we find individual urban locations with traffic collision rates which are remarkably high. These findings have the potential to inform policies for the allocation of resources to prevent road traffic collisions across the different cities.
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Edenstrasser, J. W., i M. M. M. Kassab. "Transport equations on different time scales for intermediately and strongly collisional regimes". Journal of Plasma Physics 56, nr 1 (sierpień 1996): 45–65. http://dx.doi.org/10.1017/s0022377800019085.
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The plasma transport equations for a weakly collisional plasma have previously been derived for four different time scales. This paper is devoted to the derivation of the plasma transport equations for the two other complementary regimes: the intermediately collisional regime (ICR) (i.e. for the case where the transit time w1 is of the same order as the collision time is of the same order as the collision time ), and the strongly collisional regime (SCR) (i.e. for the case of ) for different time scales. It is shown that the lowest-order gyromotion is unperturbed by collisions. On the Alfvén time scale, one merely obtains for both the intermediately collisional case and the strongly collisional case the single-fluid ideal MHD equations, if certain additional requirements are satisfied. On the MHD-collision time scale, one arrives at the full set of transport equations, where in both cases, contrary to the weakly collisional case, no turbulent terms are found. On the resistive diffusion timescale, one ends up with the known transport equations, with the addition of turbulent contributions.
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Ofek, Eran O., David Polishook, Doron Kushnir, Guy Nir, Sagi Ben-Ami, Yossi Shvartzvald, Nora L. Strotjohann i in. "Asteroid Collisions: Expected Visibility and Rate". Astronomical Journal 167, nr 5 (3.04.2024): 190. http://dx.doi.org/10.3847/1538-3881/ad2c03.
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Abstract Asteroid collisions are one of the main processes responsible for the evolution of bodies in the main belt. Using observations of the Dimorphos impact by the DART spacecraft, we estimate how asteroid collisions in the main belt may look in the first hours after the impact. If the DART event is representative of asteroid collisions with a ∼1 m sized impactor, then the light curves of these collisions will rise on timescales of about ≳100 s and will remain bright for about 1 hr. Next, the light curve will decay on a few hours' timescale to an intermediate luminosity level in which it will remain for several weeks, before slowly returning to its baseline magnitude. This estimate suffers from several uncertainties due to, e.g., the diversity of asteroid composition, their material strength, and spread in collision velocities. We estimate that the rate of collisions in the main belt with energy similar to or larger than the DART impact is of the order of 7000 yr−1 (±1 dex). The large range is due to the uncertainty in the abundance of ∼1 m sized asteroids. We estimate the magnitude distribution of such events in the main belt, and we show that ∼6% of these events may peak at magnitudes brighter than 21. The detection of these events requires a survey with ≲1 hr cadence and may contribute to our understanding of the asteroids’ size distribution, collisional physics, and dust production. With an adequate survey strategy, new survey telescopes may regularly detect asteroid collisions.
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Pinsky, M., A. Khain i H. Krugliak. "Collisions of Cloud Droplets in a Turbulent Flow. Part V: Application of Detailed Tables of Turbulent Collision Rate Enhancement to Simulation of Droplet Spectra Evolution". Journal of the Atmospheric Sciences 65, nr 2 (1.02.2008): 357–74. http://dx.doi.org/10.1175/2007jas2358.1.
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Abstract The present study is a continuation of the series of studies dedicated to the investigation of cloud droplet collisions in turbulent flow with characteristics that are typical of real clouds. Detailed tables of collision kernels and collision efficiencies calculated in the presence of hydrodynamic interaction of droplets are presented. These tables were calculated for a wide range of turbulent parameters. To illustrate the sensitivity of droplet size distribution (DSD) evolution to the turbulence-induced increase in the collision rate, simulations of DSD evolution are preformed by solving the stochastic kinetic equation for collisions. The results can be applied to cloud modeling. The tables of collision efficiencies and collision kernels are available upon request. Some unsolved problems related to collisions of droplets and ice hydrometeors in turbulent clouds are discussed in the conclusion.
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Agina, Samaa, Faeze Momeni Rad i Karim El-Basyouny. "Linking Deployment Outcomes to Program Impacts for Mobile Photo Enforcement". Safety 9, nr 4 (7.12.2023): 88. http://dx.doi.org/10.3390/safety9040088.
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Previous research has delved into the effectiveness of Mobile Photo Enforcement (MPE) in curbing speed violations and enhancing road safety. This present study extends this investigation to explore the potential influence of MPE deployment efforts on subsequent collision occurrences. Specifically, the research team applied survival analysis techniques to examine the connection between MPE deployment variables and the duration between collisions. K-M survival estimates were employed to assess the survivability of classified groups, categorized based on deployment hours, visits, the ratio of hours to visits, and traffic count. The findings illuminated that the ratio of hours to visits emerged as the most impactful variable in prolonging the time interval between collisions and diminishing the likelihood of collisions. Notably, the anticipated reduction in collision hazards, signifying the occurrence of collisions, exhibited variations ranging from 22% to 52%. The most substantial decreases were observed when deployment occurred in high-traffic locations. These outcomes reinforce the positive impact of deployed MPE hours and visits in extending the duration between consecutive collisions, thus reducing the risk of collision occurrences.
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Burger, C., Á. Bazsó i C. M. Schäfer. "Realistic collisional water transport during terrestrial planet formation". Astronomy & Astrophysics 634 (luty 2020): A76. http://dx.doi.org/10.1051/0004-6361/201936366.
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Context. According to the latest theoretical and isotopic evidence, Earth’s water content originates mainly from today’s asteroid belt region, or at least from the same precursor material. This suggests that water was transported inwards to Earth, and to similar planets in their habitable zone, via (giant) collisions of planetary embryos and planetesimals during the chaotic final phase of planet formation. Aims. In current dynamical simulations water delivery to terrestrial planets is still studied almost exclusively by assuming oversimplified perfect merging, even though water and other volatiles are particularly prone to collisional transfer and loss. To close this gap we have developed a computational framework to model collisional water transport by direct combination of long-term N-body computations with dedicated 3D smooth particle hydrodynamics (SPH) collision simulations of differentiated, self-gravitating bodies for each event. Methods. Post-collision water inventories are traced self-consistently in the further dynamical evolution, in accretionary or erosive as well as hit-and-run encounters with two large surviving bodies, where besides collisional losses, water transfer between the encountering bodies has to be considered. This hybrid approach enables us for the first time to trace the full dynamical and collisional evolution of a system of approximately 200 bodies throughout the whole late-stage accretion phase (several hundred Myr). As a first application we choose a Solar System-like architecture with already formed giant planets on either circular or eccentric orbits and a debris disk spanning the whole terrestrial planet region (0.5–4 au). Results. Including realistic collision treatment leads to considerably different results than simple perfect merging, with lower mass planets and water inventories reduced regularly by a factor of two or more. Due to a combination of collisional losses and a considerably lengthened accretion phase, final water content, especially with giant planets on circular orbits, is strongly reduced to more Earth-like values, and closer to results with eccentric giant planets. Water delivery to potentially habitable planets is dominated by very few decisive collisions, mostly with embryo-sized or larger objects and only rarely with smaller bodies, at least if embryos have formed throughout the whole disk initially. The high frequency of hit-and-run collisions and the differences to predominantly accretionary encounters, such as generally low water (and mass) transfer efficiencies, are a crucial part of water delivery, and of system-wide evolution in general.
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Saroka, Mary D., i Nasser Ashgriz. "Separation Criteria for Off-Axis Binary Drop Collisions". Journal of Fluids 2015 (25.05.2015): 1–15. http://dx.doi.org/10.1155/2015/405696.
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Off-axis collisions of two equal size droplets are investigated numerically. Various governing processes in such collisions are discussed. Several commonly used theoretical models that predict the onset of separation after collision are evaluated based on the processes observed numerically. A separation criterion based on droplet deformation is found. The numerical results are used to assess the validity of some commonly used phenomenological models for drop separation after collision. Also, a critical Weber number for the droplet separation after grazing collision is reported. The effect of Reynolds number is investigated and regions of permanent coalescence and separation are plotted in a Weber-Reynolds number plane for high impact parameter collisions.
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Tanvir, Tabassum S., i James E. Dale. "Collision between molecular clouds – III: the effects of cloud initial density profile on head-on collisions". Monthly Notices of the Royal Astronomical Society 506, nr 1 (7.07.2021): 824–38. http://dx.doi.org/10.1093/mnras/stab1389.
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ABSTRACT In this third paper of our cloud collision series, we present the results from simulations of head-on collisions with a strongly centrally condensed initial density profile of ρ ∝ R−2. We investigate the impact of these density profiles on the overall evolution of the simulations: the structures formed, their dynamical evolution, and their star formation activity. We consider clouds that are globally bound and globally unbound, leading to three different scenarios – the collision of a bound cloud with a bound cloud, the collision of two unbound clouds, or the collision of one cloud of each type. In all the simulations, dense star clusters form before the collisions occur, and we find that star formation remains confined to these systems and is little affected by the collisions. If the clouds are both initially bound, the collision forms a filamentary structure, but otherwise this does not occur. We observe that rotating structures form around the clusters, but they also form in our non-colliding control simulations, so are not a consequence of the collisions. The dissipation of kinetic energy in these simulations is inefficient because of the substructure created in the clouds by turbulence before the collisions. As a result, although some gas is left bound in the COM frame, the star clusters formed in the simulations do not become bound to each other.
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Iqbal, Akhtar, Khusniddin K. Olimov, Kosim Olimov, Mushtaq Ahmad, Sh Z. Kanokova, Sagdulla L. Lutpullaev, Alisher K. Olimov, Kadyr G. Gulamov, Sh D. Tojimamatov i Bekhzod S. Yuldashev. "Collision centrality dependencies of charged pion production in 12C+ 181 Ta collisions at 4.2 A GeV/c". International Journal of Modern Physics E 27, nr 11 (listopad 2018): 1850092. http://dx.doi.org/10.1142/s0218301318500921.
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The collision centrality dependencies of the average kinematical characteristics of the negative and positive pions, produced in [Formula: see text] collisions at [Formula: see text], were investigated. The ratio [Formula: see text] proved to be [Formula: see text], [Formula: see text] and [Formula: see text] in the peripheral, semicentral, and central [Formula: see text] collision events, respectively, decreasing noticeably with increasing collision centrality. The suppression (decrease) of the ratio [Formula: see text] was observed in the semicentral and central [Formula: see text] collisions as compared to the ratio [Formula: see text], estimated using the simple model for [Formula: see text] collision system. The ratio [Formula: see text] estimated using the simple model agreed well with the corresponding ratio [Formula: see text], estimated for [Formula: see text] collisions at [Formula: see text] based on the Wounded Nucleon Model (WNM). Comparison of the emission angle as well as momentum distributions of the charged pions in the peripheral and central [Formula: see text] collisions revealed the significant decrease of the fraction of the relatively fast charged pions (with smaller emission angles) and increase of the fraction of the relatively slow charged pions (with larger emission angles) with an increase in collision centrality. The results of the present analysis can be useful for analysis of the centrality dependence of the charged pion production in heavy ion collisions at high energies.
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Rysaeva, Leysan Kh, Ivan P. Lobzenko, Julia A. Baimova, Sergey V. Dmitriev i Kun Zhou. "Modeling C540-C20 Fullerene Collisions". REVIEWS ON ADVANCED MATERIALS SCIENCE 57, nr 2 (1.07.2018): 143–50. http://dx.doi.org/10.1515/rams-2018-0058.
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Abstract Collisions of C20 and C540 fullerenes are studied in a wide range of velocities by means of classical molecular dynamics. The simulations show that the collision scenario strongly depends on the collision velocity of the fullerenes. At low collision energies, the fullerenes are repelled by the van der Waals forces, and after bouncing off a part of the kinetic energy of their translational motion is converted into the energy of cage vibrations. At higher collision energies, the fullerenes overcome the potential barrier of Pauli repulsion with the formation of the new chemical bonds, and a significant change in the geometry of the molecules is observed. At very high collision energies, structure of the molecules is destroyed with the formation of new carbon clusters. Analysis of collisions for fullerenes of significantly different size revealed some new features associated with their asymmetric energy exchange.
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Grzegorczyk, Pierre, Sudha Yadav, Florian Zanger, Alexander Theis, Subir K. Mitra, Stephan Borrmann i Miklós Szakáll. "Fragmentation of ice particles: laboratory experiments on graupel–graupel and graupel–snowflake collisions". Atmospheric Chemistry and Physics 23, nr 20 (25.10.2023): 13505–21. http://dx.doi.org/10.5194/acp-23-13505-2023.
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Abstract. Until now, the processes involved in secondary ice production which generate high concentrations of ice crystals in clouds have been poorly understood. However, collisions that involve rimed ice particles or crystal aggregates have the potential to effectively produce secondary ice from their fragmentation. Unfortunately, there have only been a few laboratory studies on ice–ice collision so far, resulting in an inaccurate representation of this process in microphysical schemes. To address this issue, experiments were conducted at the wind tunnel laboratory of the Johannes Gutenberg University, Mainz, on graupel–graupel and graupel–snowflake collisions under still-air conditions at −15 ∘C and water supersaturation. The particles were synthetically generated within a cold room through two distinct methods: by riming and vapor deposition for graupel with diameters of 2 and 4 mm and by manually sticking vapor-grown ice which was generated above a warm bath to form snowflakes with a diameter of 10 mm. All fragments resulting from graupel–graupel collisions were collected and investigated by means of a digital optical microscope, while fragments from graupel–snowflake collisions were observed and recorded instantly after collision using a holographic instrument. From these experiments, distributions were obtained for fragment sizes, cross-sectional areas, and aspect ratios. The results showed a higher number of fragments at lower kinetic energy compared to those presented in the literature. A total of 150 to 600 fragments were observed for graupel–graupel with dendrites collisions, as well as 70 to 500 fragments for graupel–snowflake collisions for collision kinetic energies between 10−7 and 10−5 J. Parameterizations for fragment size distributions are provided with a mode at 75 µm for graupel–graupel with dendrites collisions and at 400 µm for graupel–snowflake collisions. We also propose new coefficients fitted on our experiments to parameterize the number of fragments generated by collisions based on the theoretical formulation of Phillips et al. (2017). These results can be used to improve the representation of ice collision breakup in microphysical schemes.