Determining the region of origin of blood spatter patterns considering fluid dynamics and statistical uncertainties

Trajectory reconstruction in bloodstain pattern analysis is currently performed by assuming that blood drop trajectories are straight along directions inferred from stain inspection. Recently, several attempts have been made at reconstructing ballistic trajectories backwards, considering the effects of gravity and drag forces. Here, we propose a method to reconstruct the region of origin of impact blood spatter patterns that considers fluid dynamics and statistical uncertainties. The fluid dynamics relies on defining for each stain a range of physically possible trajectories, based on known physics of how drops deform, both in flight and upon slanted impact. Statistical uncertainties are estimated and propagated along the calculations, and a probabilistic approach is used to determine the region of origin as a volume most compatible with the backward trajectories. A publicly available data set of impact spatter patterns on a vertical wall with various impactor velocities and distances to target is used to test the model and evaluate its robustness, precision, and accuracy. Results show that the proposed method allows reconstruction of bloodletting events with distances between the wall and blood source larger than ∼1 m. The uncertainty of the method is determined, and its dependency on the distance between the blood source and the wall is characterized. Causes of error and uncertainty are discussed. The proposed method allows the consideration of stains indicating impact velocities that point downwards, which are typically not used for determining the height of the origin. Based on the proposed method, two practical recommendations on crime scene documentation are drawn

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.Publisher PDFPeer reviewe

Fluid Mechanics of Blood Motion Resulting from Common Bloodletting Events

Blood motion resulting from a gunshot is a complex phenomenon which requires fluid mechanics to properly understand. The atomization of blood is a result of fluid instabilities due to the impact of a bullet and the resultant flight of blood droplets must include the effects of gravity, air drag, and the collective effect. This effect is the drag reduction present in groups of droplets where the leading droplets take the bulk of the drag force whereas the ones behind do not. As a result, those blood droplets travel faster, eventually becoming the leading droplets, and the group can travel further. Through particle image velocimetry, this effect is seen to occur in blood spatter due to a gunshot when analyzing high-speed videos for simulated crime scenes. Standard spatter angles, drop sizes, and velocity histories were also analyzed from the videos. The atomization of backward spattered blood is attributed to the Rayleigh-Taylor instability which arises when a dense fluid is accelerated towards a lighter one. This atomization model is produced for an idealized sharp and blunt bullet, and the trajectories of blood are issued into quiescent air. The atomization of forward spattered blood is shown to require a more complex analysis as a cascade of instabilities is present. Therefore, the chaotic disintegration of blood is considered in the framework of percolation theory and is generalized for a bullet of arbitrary shape. Both atomization models were compared with experiments and agreement was good. The interaction of muzzle gases arising from the muzzle of a gun due to the chemical propulsion of the bullet on backward spattered blood droplets is considered. It is shown that the important components are the propellant gases which forms a turbulent vortex ring, the self-similar motion of which is solved and the interaction and effect on backward spattered blood droplets is shown. The gunpowder particle concentration swept by the turbulent vortex ring is also solved aiding in the understanding of the distribution of gunshot residue. Finally, the motion of intact jets of blood is considered and the rheological properties of blood are discussed in the context of forensic science

Determining the region of origin of blood spatter patterns considering fluid dynamics and statistical uncertainties

Trajectory reconstruction in bloodstain pattern analysis is currently performed by assuming that blood drop trajectories are straight along directions inferred from stain inspection. Recently, several attempts have been made at reconstructing ballistic trajectories backwards, considering the effects of gravity and drag forces. Here, we propose a method to reconstruct the region of origin of impact blood spatter patterns that considers fluid dynamics and statistical uncertainties. The fluid dynamics relies on defining for each stain a range of physically possible trajectories, based on known physics of how drops deform, both in flight and upon slanted impact. Statistical uncertainties are estimated and propagated along the calculations, and a probabilistic approach is used to determine the region of origin as a volume most compatible with the backward trajectories. A publicly available data set of impact spatter patterns on a vertical wall with various impactor velocities and distances to target is used to test the model and evaluate its robustness, precision, and accuracy. Results show that the proposed method allows reconstruction of bloodletting events with distances between the wall and blood source larger than ∼1 m. The uncertainty of the method is determined, and its dependency on the distance between the blood source and the wall is characterized. Causes of error and uncertainty are discussed. The proposed method allows the consideration of stains indicating impact velocities that point downwards, which are typically not used for determining the height of the origin. Based on the proposed method, two practical recommendations on crime scene documentation are drawn.This is a manuscript of an article published as Attinger, Daniel, Patrick M. Comiskey, Alexander L. Yarin, and Kris De Brabanter. "Determining the region of origin of blood spatter patterns considering fluid dynamics and statistical uncertainties." Forensic science international 298 (2019): 323-331. Posted with permission of CSAFE.</p

Determining the region of origin of blood spatter patterns considering fluid dynamics, statistical uncertainties

Trajectory reconstruction in bloodstain pattern analysis is currently performed by assuming that blood drop trajectories are straight along directions provided by stain inspection. Recently, several attempts have been made at reconstructing ballistic trajectories backwards, considering the effects of gravity and drag forces. Here, we propose a method to reconstruct the region of origin of impact blood spatter patterns that considers fluid dynamics and statistical uncertainties. The fluid dynamics relies on defining for each stain a range of physically possible trajectories, based on known physics of how drops deform, both in flight and upon slanted impact. Statistical uncertainties are estimated and propagated along the calculations, and a probabilistic approach is used to determine the region of origin as a volume most compatible with the backward trajectories. A publicly available data set of impact spatter patterns on a vertical wall with various impactor velocities and distances to target is used to test the model and evaluate its robustness, precision, and accuracy. Results show that the proposed method allows reconstruction of bloodletting events with distances between the wall and blood source larger than ˜1 m. The uncertainty of the method is determined, and its dependency on the distance between the blood source and the wall is characterized. Causes of error and uncertainty are discussed. The proposed method allows the consideration of stains indicating impact velocities that point downwards, which have typically been excluded from trajectory reconstruction. Based on the proposed method, two practical recommendations on crime scene documentation are drawn.This article is published as Attinger, Daniel, Patrick M. Comiskey, Alexander L. Yarin, and Kris De Brabanter. "Determining the region of origin of blood spatter patterns considering fluid dynamics, statistical uncertainties." Forensic Science International (2019). DOI: 10.1016/j.forsciint.2019.02.003. Posted with permission.</p

A data set of bloodstain patterns for teaching and research in bloodstain pattern analysis: Gunshot backspatters

This is a data set of blood spatter patterns scanned at high resolution, generated in controlled experiments. The spatter patterns were generated with a rifle or a handgun with varying ammunition. The resulting atomized blood droplets travelled opposite to the bullet direction, generating a gunshot backspatter on a poster board target sheet. Fresh blood with anticoagulants was used; its hematocrit and temperature were measured. The main parameters of the study were the bullet shape, size and speed, and the distance between the blood source and target sheet. Several other parameters were explored in a less systematic way. This new and original data set is suitable for training or research purposes in the forensic discipline of bloodstain pattern analysis.This article is published as Attinger, Daniel, Yu Liu, Ricky Faflak, Yalin Rao, Bryce A. Struttman, Kris De Brabanter, Patrick M. Comiskey, and Alexander L. Yarin. "A data set of bloodstain patterns for teaching and research in bloodstain pattern analysis: Gunshot backspatters." Data in brief 22 (2019): 269-278.</p

A data set of bloodstain patterns for teaching and research in bloodstain pattern analysis: Gunshot backspatters

This is a data set of blood spatter patterns scanned at high resolution, generated in controlled experiments. The spatter patterns were generated with a rifle or a handgun with varying ammunition. The resulting atomized blood droplets travelled opposite to the bullet direction, generating a gunshot backspatter on a poster board target sheet. Fresh blood with anticoagulants was used; its hematocrit and temperature were measured. The main parameters of the study were the bullet shape, size and speed, and the distance between the blood source and target sheet. Several other parameters were explored in a less systematic way. This new and original data set is suitable for training or research purposes in the forensic discipline of bloodstain pattern analysis

A data set of bloodstain patterns for teaching and research in bloodstain pattern analysis: Gunshot backspatters

This is a data set of blood spatter patterns scanned at high resolution, generated in controlled experiments. The spatter patterns were generated with a rifle or a handgun, and different ammunitions. The resulting atomized blood droplets travelled opposite to the bullet direction, generating a gunshot backspatter on a poster board target sheet. Fresh blood with anticoagulants was used; its hematocrit and temperature were measured. Main parameters of the study were the bullet shape, size and speed, and the distance between the blood source and target sheet. Several other parameters were explored in a less systematic way. This new and original data set is suitable for training or research purposes in the forensic discipline of bloodstain pattern analysis.This is a manuscript of an article published as Attinger, Daniel, Yu Liu, Ricky Faflak, Yalin Rao, Bryce A. Struttman, Kris De Brabanter, Patrick M. Comiskey, and Alex L. Yarin. "A data set of bloodstain patterns for teaching and research in bloodstain pattern analysis: Gunshot backspatters." Data in Brief (2018). DOI: 10.1016/j.dib.2018.11.075. Posted with permission.</p