Trajectories Of Fragments Research Articles

3D optical diagnostics for explosively driven deformation and fragmentation

High-speed, optical imaging diagnostics are presented for three-dimensional (3D) quantification of explosively driven metal fragmentation. At early times after detonation, Digital Image Correlation (DIC) provides non-contact measures of 3D case velocities, strains, and strain rates, while a proposed stereo imaging configuration quantifies in-flight fragment masses and velocities at later times. Experiments are performed using commercially obtained RP-80 detonators from Teledyne RISI, which are shown to create a reproducible fragment field at the benchtop scale. DIC measurements are compared with 3D simulations, which have been ‘leveled’ to match the spatial resolution of DIC. Results demonstrate improved ability to identify predicted quantities-of-interest that fall outside of measurement uncertainty and shot-to-shot variability. Similarly, video measures of fragment trajectories and masses allow rapid experimental repetition and provide correlated fragment size-velocity measurements. Measured and simulated fragment mass distributions are shown to agree within confidence bounds, while some statistically meaningful differences are observed between the measured and predicted conditionally averaged fragment velocities. Together these techniques demonstrate new opportunities to improve future model validation.

Determination of kinetic properties in unimolecular dissociation of complex systems from graph theory based analysis of an ensemble of reactive trajectories.

In this paper, we report how graph theory can be used to analyze an ensemble of independent molecular trajectories, which can react during the simulation time-length, and obtain structural and kinetic information. This method is totally general and here is applied to the prototypical case of gas phase fragmentation of protonated cyclo-di-glycine. This methodology allows us to analyze the whole set of trajectories in an automatic computer-based way without the need of visual inspection but by getting all the needed information. In particular, we not only determine the appearance of different products and intermediates but also characterize the corresponding kinetics. The use of colored graph and canonical labeling allows for the correct characterization of the chemical species involved. In the present case, the simulations consist of an ensemble of unimolecular fragmentation trajectories at constant energy such that from the rate constants at different energies, the threshold energy can also be obtained for both global and specific pathways. This approach allows for the characterization of ion-molecule complexes, likely through a roaming mechanism, by properly taking into account the elusive nature of such species. Finally, it is possible to directly obtain the theoretical mass spectrum of the fragmenting species if the reacting system is an ion as in the specific example.

Insights into the dynamic trajectories of protein filament division revealed by numerical investigation into the mathematical model of pure fragmentation.

The dynamics by which polymeric protein filaments divide in the presence of negligible growth, for example due to the depletion of free monomeric precursors, can be described by the universal mathematical equations of 'pure fragmentation'. The rates of fragmentation reactions reflect the stability of the protein filaments towards breakage, which is of importance in biology and biomedicine for instance in governing the creation of amyloid seeds and the propagation of prions. Here, we devised from mathematical theory inversion formulae to recover the division rates and division kernel information from time-dependent experimental measurements of filament size distribution. The numerical approach to systematically analyze the behaviour of pure fragmentation trajectories was also developed. We illustrate how these formulae can be used, provide some insights on their robustness, and show how they inform the design of experiments to measure fibril fragmentation dynamics. These advances are made possible by our central theoretical result on how the length distribution profile of the solution to the pure fragmentation equation aligns with a steady distribution profile for large times.

Nuclear Fragmentation Imaging for Carbon-Ion Radiation Therapy Monitoring: an In Silico Study.

PurposeThis article presents an in vivo imaging technique based on nuclear fragmentation of carbon ions in irradiated tissues for potential real-time monitoring of carbon-ion radiation therapy (CIRT) treatment delivery and quality assurance purposes in clinical settings.Materials and MethodsA proof-of-concept imaging and monitoring system (IMS) was devised to implement the technique. Monte Carlo simulations were performed for a prospective pencil-beam scanning CIRT nozzle. The development IMS benchmark considered a 5×5-cm2 pixelated charged-particle detector stack positioned downstream from a target phantom and list-mode data acquisition. The abundance and production origins, that is, vertices, of the detected fragments were studied. Fragment trajectories were approximated by straight lines and a beam back-projection algorithm was built to reconstruct the vertices. The spatial distribution of the vertices was then used to determine plan relevant markers.ResultsThe IMS technique was applied for a simulated CIRT case, a primary brain tumor. Four treatment plan monitoring markers were conclusively recovered: a depth dose distribution correlated profile, ion beam range, treatment target boundaries, and the beam spot position. Promising millimeter-scale (3-mm, ≤10% uncertainty) beam range and submillimeter (≤0.6-mm precision for shifts <3 cm) beam spot position verification accuracies were obtained for typical therapeutic energies between 150 and 290 MeV/u.ConclusionsThis work demonstrated a viable online monitoring technique for CIRT treatment delivery. The method's strong advantage is that it requires few signal inputs (position and timing), which can be simultaneously acquired with readily available technology. Future investigations will probe the technique's applicability to motion-sensitive organ sites and patient tissue heterogeneities. In-beam measurements with candidate detector-acquisition systems are ultimately essential to validate the IMS benchmark performance and subsequent deployment in the clinic.

Effects of settlement designs on deforestation and fragmentation in the Brazilian Amazon

Tropical forests are providers of relevant ecosystem services at different spatial scales, but they have been under intense human pressure in recent decades, primarily because of their conversion into agricultural or pasture lands. Colonization projects have been a significant driver of deforestation in the Brazilian Amazon since the 1970s. Such projects are mostly agricultural settlements that were established following specific spatial designs that affected land distribution, social connections, access to natural resource and infrastructure, and the mitigation of environmental disturbances. We analyzed spatiotemporal deforestation datasets from settlement projects planned and implemented using three spatial designs (fishbone, dendritic, and spontaneous) to assess the effects on deforestation and landscape fragmentation in the state of Rondônia, in the Brazilian Amazon. We applied landscape metrics to estimate the different impacts on landscape between 1985 and 2015. Our results indicate that approximately 50% of the primary forests, mostly tropical forests, were converted to other types of land uses during the study period. We observed that while the fishbone design allowed the connection of forest patches along an East-West axis, it showed an opposite effect on the North-South one. In contrast, the dendritic design proved to be more efficient in protecting primary forests by causing lesser landscape fragmentation and conserving larger forest patches. However, the landscape impacts by different settlement spatial designs showed similar fragmentation trajectories and deforestation rates overtime. Based on our results, we have concluded that the combination of settlement designs, presence of protected areas, and local community participation have helped prevent forest fragmentation and deforestation in the study region. Our analysis suggests that settlement designs alone are not sufficient to curb deforestation and forest fragmentation in the Brazilian Amazon. As a result, we indicate that controlling both processes will require the enforcement of public and environmental policies integrated with land occupation planning and strategies to support sustainable agricultural systems.

Casualty Risks Induced by Primary Fragmentation Hazards from High-explosive munitions

Fatalities and injuries are mainly attributed to primary fragmentation if accidental or malevolent detonation of high-explosive munitions occurs in an open space. This study aims to develop a simulation-based approach to assess individual casualty risks from primary fragments naturally generated by detonation of high-explosive munitions, which enables a stochastic characterization of fragment generation, trajectories, modelling uncertainties, and human vulnerability. The proposed method is demonstrated by a numerical example estimating the fatality and injury risks for an individual in a standing position exposed to the detonation of a single 105 mm projectile. The results suggest that, as expected, the individual fatality and injury risks decrease with an increasing stand-off distance. At a stand-off distance greater than 40 m, an individual is more likely to suffer injuries rather than fatality. The safety distance obtained from the present study is 97 m which is close to but less conservative than a safety distance of 104 m in existing literature and standards.

Predicting the fragmentation survival probability of brittle spheres upon impact from statistical distribution of material properties

Fragmentation of rocks upon impact during rockfall is a phenomenon that is poorly understood, scarcely researched and difficult to predict. However, to adequately predict the outcomes of rockfall events, it is essential to know whether a given block is likely to fragment given the impact conditions and what will be the outcome of the fragmentation process; that is, the number, size and trajectory of fragments. To date, there is no model or data that can be used to fully answer these questions. This paper presents the first theoretical model that can predict the fragmentation survival probability of brittle spherical blocks upon dynamic impact (i.e. drop tests) from the statistical distribution of material properties, determined from a range of standard quasi-static tests. Considering that survival probabilities tend to follow a Weibull distribution, the model focuses on predicting the two Weibull parameters, commonly known as the shape parameter (m) and the scale parameter (here, the critical kinetic energy). The model is based on theoretically-derived conversion factors used to turn the critical work required to fail disc samples in quasi-static indirect tension into the critical kinetic energy to cause failure of spheres at impact in drop tests. The mechanistic conversion factors specifically account for the shape and size of the specimens tested and the increase of strength under dynamic loading (strain rate effect). Three series of drop tests were conducted (on spheres of three different diameters) and complemented by extensive material characterisation testing in order to validate the novel predictive model. The variability of material properties was characterised, and it was found that the material strength found by the characterisation tests generally follows a Weibull form, but the survival probability distribution of the drop tests seems to be linear. The predicted conversion factors were first compared against their experimental counterparts before validating the prediction of survival probability of the spheres upon dynamic impact (in drop tests). It was found that it is possible to predict the survival probability of artificial rock of three different diameters (50 mm, 75 mm, 100 mm) and two different strengths upon impact solely from the statistical information coming from Brazilian tests and with an average relative error of less than 9%.

Trajectory estimation model for a solid body with an irregular shape undergoing extremely high aerodynamic forces

A generalized (6DOF) model for evaluating fragment trajectory elements is defined, which incorporates a novel model for estimating the projected surface of the body and novel model for estimating aerodynamic force and moment. This 6DOF model is developed on the basis of differential equations of the center of mass motion and movement around the center of mass (currently no known model incorporates movement of the body around its center of mass), and can model the parameters that play an essential role in movement of the bodies with irregular shape through the atmosphere. In our model the basic parameters (i.e. body dimensions) can be arbitrarily changed in the initial part of the analysis, and based on their values and values of initial kinematic parameters (initial velocity, position, orientation), trajectories can be determined (as well as other parameters: velocities, orientation) in a relatively short amount of time. The calculation of the complete trajectory of the fragments can be used in a number of applications: the analysis of the effects of the fragments (i.e. the safety analysis of the location of the ammunition depots, due to the potential explosion of the projectile) or in the estimation of a danger zones when demining larger quantities of the munition. Also, from the point of view of the parameters of the lethal zone of HE projectiles, it is generally important to estimate the trajectory of the fragments in the range up to 50m, so this model can be used to model such a scenario also. This model could also be potentially used wherever there is a need to calculate flight mechanics parameters of irregularly shaped bodies. Generalized (6DOF) model for estimation of an irregularly shaped body trajectory is implemented in a computer program, written in MatLab. Based on the model, the trajectory calculations were performed for the complete trajectory and for shorter distances to the center of the explosion, with varied geometric-inertial parameters and initial kinematic conditions for the given fragment.

Trajectory estimation model for a solid body with an irregular shape undergoing extremely high aerodynamic forces

A generalized (6DOF) model for evaluating fragment trajectory elements is defined, which incorporates a novel model for estimating the projected surface of the body and novel model for estimating aerodynamic force and moment. This 6DOF model is developed on the basis of differential equations of the center of mass motion and movement around the center of mass (currently no known model incorporates movement of the body around its center of mass), and can model the parameters that play an essential role in movement of the bodies with irregular shape through the atmosphere. In our model the basic parameters (i.e. body dimensions) can be arbitrarily changed in the initial part of the analysis, and based on their values and values of initial kinematic parameters (initial velocity, position, orientation), trajectories can be determined (as well as other parameters: velocities, orientation) in a relatively short amount of time. The calculation of the complete trajectory of the fragments can be used in a number of applications: the analysis of the effects of the fragments (i.e. the safety analysis of the location of the ammunition depots, due to the potential explosion of the projectile) or in the estimation of a danger zones when demining larger quantities of the munition. Also, from the point of view of the parameters of the lethal zone of HE projectiles, it is generally important to estimate the trajectory of the fragments in the range up to 50m, so this model can be used to model such a scenario also. This model could also be potentially used wherever there is a need to calculate flight mechanics parameters of irregularly shaped bodies. Generalized (6DOF) model for estimation of an irregularly shaped body trajectory is implemented in a computer program, written in MatLab. Based on the model, the trajectory calculations were performed for the complete trajectory and for shorter distances to the center of the explosion, with varied geometric-inertial parameters and initial kinematic conditions for the given fragment.

Child droplets from micro-explosion of emulsion and immiscible two-component droplets

Here we present the experimental findings of the research into the integral characteristics of secondary droplets produced from the micro-explosive fragmentation of two types of initial droplets. Both types are based on water and tetradecane: an emulsion droplet and a two-component immiscible droplet with water as the core and tetradecane as the envelope. We study the threshold (critical) conditions for the micro-explosion of droplets on a substrate heated up to 550 °C. In the course of experiments, we recorded the number, sizes, velocities, temperatures, and component composition of child droplets. It is shown that the parameters of child droplets differ significantly in the case of two-component droplets and emulsion droplets. The decisive impact comes from the heating temperature. Using a combination of Schlieren Photography, Particle Tracking Velocimetry, and 2-Color Laser Induced Fluorescence, we have determined the proportions of the concentration and size of secondary water droplets and combustible component droplets in the emerging aerosol cloud. We have also calculated the kinetic energies of child droplets. When generalizing the experimental findings, we established the conditions for the generation of a high-temperature fine mist aerosol through the micro-explosive breakup of two-component droplets and recorded the typical trajectories of secondary fragments. We show that such conditions are possible for both emulsion droplets and immiscible two-component droplets with a pronounced interface. It is established that much more secondary fragments of water are produced in the second case. This result shows that water separates from the combustible component more intensely in the second case, and the micro-explosion systems relying on water and combustible liquid droplets mixing in the combustion chamber bear more promise.

Field test and probabilistic analysis of irregular steel debris casualty risks from a person-borne improvised explosive device

Person-borne improvised explosive devices (PBIEDs) are often used in terrorist attacks in Western countries. This study aims to predict the trajectories of PBIED fragments and the subsequent safety risks for people exposed to this hazard. An explosive field test with a typical PBIED composed of a plastic explosive charge and steel nut enhancements was performed to record initial fragment behaviour, including positions, velocity, and trajectory angles. These data were used to predict the full trajectory of PBIED fragments using a probabilistic analysis. In the probabilistic analyses a probability of fatality or serious injury was computed. Based on the results presented, many practical conclusions can be drawn, for instance, regarding safe evacuation distances if a person were exposed to a suspected PBIED.

Fragmentation dynamics of single agglomerate-to-wall impaction

The de-agglomeration characteristics of single agglomerate-wall impaction are examined using high-resolution shadowgraph imaging. Experiments are performed to investigate the effects of constituent particle size (D50 from 3 to 7 μm) and air velocity on the individual size and velocity of de-agglomerated fragments at conditions relevant to dry powder inhalation systems. De-agglomerated fragment area and trajectories were used to differentiate between pseudo-elastic and inelastic collisions during de-agglomeration. Advanced image processing techniques have enabled provision of joint population distributions of fragment area and aspect ratio, which identify a bimodal dispersion of fragments during de-agglomeration. The bimodality is destroyed with increasing air velocity and also generally diminishes with time after impact. The experiment presented forms a platform for the detailed quantitative characterisation of de-agglomeration behaviour and can be useful towards the development and validation of related computational models for pharmaceutical dry powder inhalers.

Sleep Fragmentation and Cognitive Trajectories After Critical Illness

ICU survivors can experience both cognitive dysfunction and persistent sleep disturbances after hospitalization. Sleep disturbances have been linked with cognitive impairment in various patient populations, and the apolipoprotein E (APOE) genotype has been linked to sleep-related impairments in cognition. Is there an association between sleep, long-term cognition, and APOE status in ICU survivors? We enrolled 150 patients from five centers who had been mechanically ventilated for at least 3days; 102 patients survived to ICU discharge. Actigraphy and cognitive testing were undertaken at 7days, 6months, and 12months after ICU discharge, and sleep duration, quality, and timing were estimated by actigraphy. APOE single nucleotide polymorphisms were assessed for each patient. Actigraphy-estimated sleep fragmentation, but not total sleep time or interdaily stability (estimate of circadian rhythmicity), was associated with worse cognitive impairment at 7days of ICU discharge. No actigraphy-estimated variable of sleep estimation at 7days post-ICU discharge predicted cognitive impairment or persistent sleep abnormalities at 6 and 12months of follow-up in subsequently assessed survivors. Possessing the APOE ε4 allele was not significantly associated with sleep disturbances and its presence did not modify the risk of sleep-related cognitive impairment at follow-up. Sleep fragmentation estimated by actigraphy was associated with worse cognitive performance in hospital, but not at later time intervals. Further research is needed to better delineate the relationship between persistent sleep disturbances and cognition in larger numbers of ICU survivors. ClinicalTrials.gov; No.: NCT02086877; URL: www.clinicaltrials.gov.

CFD 및 강체 동역학을 이용한 항공기의 결빙 궤적 예측

Ice shedding refers to the phenomenon that ice forms on the surface of an aircraft operating in icing conditions and then moves with the flow after break-up from the surface by aerodynamic forces. Collisions of shed ice fragments with aircraft components such as engine intake or control surface can cause serious threat to the safety of aircraft. The separated ice fragments show unpredictable and complex characteristics in their shape, size, orientation, formation position, and rotational speed. This study deals with the prediction of the trajectories of ice fragments using computational simulation methods. The trajectories of ice fragments of a fixed wing aircraft were calculated by the CFD code based on the overset grid method and the formulation of six degree of freedom. The method was first validated for the flat plate motion using the wind tunnel test results. Finally, the aerodynamic characteristics and trajectories of separated ices were investigated for various ice shapes and conditions.

A novel method for determination of lethal radius for high-explosive artillery projectiles

A new model has been defined that enables the estimation of the lethal radius (radius of efficiency) of HE (High Explosive) artillery projectiles against human targets. The model is made of several modules: CAD (Computer Aided Design) modeling, fragment mass distribution estimation, fragment initial velocity prediction, fragment trajectory calculation, effective fragment density estimation, and high explosive projectile lethal radius estimation. The results were compared with the experimental results obtained based on tests in the arena used in our country, and the agreement of the results was good. This model can be used in any terminal-ballistics scenario for high explosive projectiles since it is general, parametric, fast and relatively easy to implement.

Fission-track evolution in Macusanite volcanic glass

Macusanite is a natural volcanic glass, which is produced by the rapid cooling of magma during a volcanic eruption. Since it typically contains concentrations of uranium, it can be used for fission-track dating. Understanding the fission-track formation process and its morphology in natural volcanic glass is of major importance in this dating method. Therefore, in this work the latent fission-track structure was investigated using the geometry evolution of etched tracks. This evolution was characterized as a function of the chemical etching time via optical microscopy and atomic force microscopy. In this way, measurements of track diameters and theoretical estimation of track depths of normal incident fission fragments were made in order to determine the bulk and track etch rates. As a result, both rates yield constant values, and therefore the defect density along the fission fragment trajectory can be considered constant.

On the non-standard routes: vocational training measures in the school-to-work transitions of lower-qualified youth in Germany

ABSTRACT This study explores school-to-work transitions in Germany, aiming to achieve a richer understanding of the complexity of labour market entry trajectories while focusing on transition measures. The term transition measures refers to additional training courses that complement the regular vocational education and training system of firm-based or school-based qualification routes. The contribution of supplementary training measures to the school-to-work transitions of young adults is a controversial issue. While programmes aim to ease the transitions of low-skilled youth in the training and labour market, critics point to the risks of long-term subsidised careers or fragmented employment trajectories in subsequent years. By applying sequence analysis to administrative data of the Federal Employment Agency, individual trajectories of a cohort of school leavers with an at-most intermediate school-leaving certificate are analysed for the period 2008 to 2014. The results show a complex picture of ten distinct school-to-work transition patterns. Youth passing through transition measures tend to experience a less continuous but still purposeful transition pathway. We also identify a small number of youth experiencing at-risk trajectories characterised by a highly discontinuous transition process, which points to sustained detachment from the training and labour markets.

Contributions of Rock Mass Structure to the Emplacement of Fragmenting Rockfalls and Rockslides: Insights From Laboratory Experiments

AbstractRockfalls and rockslides often occur in mountainous areas, and they may develop into rock avalanches because of fragmentation. A series of laboratory experiments were conducted to study the contributions of rock mass structure to the emplacement of fragmenting rockfalls and rockslides. In these experiments, we considered the process of breakable analog blocks with different structures sliding along an inclined plane, impacting at the kink point with a horizontal plane where deposition occurs. The results show that the initial geometrical subdivision (i.e., the rock mass structure) of the source rock can greatly influence the impact of the fragmentation process and total runout, while the degree of fragmentation controls the travel distance of the center of mass. The occurrence of transversal discontinuities enhances the momentum transfer efficiency from the rear to the front part of the rock mass. A negative correlation between the apparent friction coefficient (linked to the total runout) and equivalent friction coefficient (linked to the center of mass runout) was found, which appears to be induced by fragmentation. We proposed a new fragmentation‐spreading model to describe this negative correlation. This simple physical model supports the importance of fragmentation in rock fragment trajectories and the runout of rockfalls and rockslides. Fragmentation is an energy‐sinking process that will shorten the runout of the center of mass. Thus, we suggest that impact fragmentation does not fully account for the long runout of large rockfalls and rockslides.

Characteristics of the Flying of Forest Combustible Materials Upstream of a Fire Barrage Under the Action of an Air Flow

Results of experiments on determination of the temperature, velocity, and mechanical trajectory of fragments of forest combustible materials subjected to pyrolysis, flying away under the action of high-velocity air flow, are presented. The effect of flying of such fragments over a fire barrage was mainly investigated. The experiments were performed with conifer needles and leaves, representing typical combustible materials in ground forest fires. On the basis of the experimentally determined effect of inclination of a flame over a fire barrage formed of moistened forest materials, physical and mathematical models of flying of fragments of forest combustible materials subjected to pyrolysis upstream of such a fire barrage have been developed. With the use of these models, the characteristic length of the zone of flame combustion of a forest material, the height of the flame in this zone, and the geometric dimensions of the fire barrage necessary and sufficient for reliable localization of the flame combustion and thermal decomposition of forest combustible material were determined.

Fragments of the Moon Formation: Geophysical Consequences of the Giant Impact

The most likely scenario for the Moon formation is given by calculations of the Giant Impact (GI) of the ProtoEarth with a protoplanet with a mass close to Mars. During the GI, gases and silicate fragments with a total mass of about 55 to 70% of the mass of the Moon go to infinity, but infinity for the runaway particles is infinity in the terrestrial reference frame. In the Solar System, these fragments go into finite orbits with periods both less and more than a year. The most important feature of their orbits is that they all pass through the region of the Earth’s orbit where the GI occurred. A concentrated gas–dust flow was formed there with a fading intensity; it existed for about a million years. Numerically solving the three-body problem yields numerous fragment trajectories. The probabilities of fragments colliding with the Earth and the Moon are estimated as a function of time after the GI. The scenario of fragments falling into the L4 and L5 triangular Lagrange points and the trajectories of their evolution is considered. The most important geophysical consequence of these collisions was the formation of the terrestrial atmosphere and ocean from the concentrated gas–dust flow.