510 resultados para Weapons.
Resumo:
It is generally difficult to establish a timeline for the appearance of different technologies and tools during human cultural evolution. Here I use stochastic character mapping of discrete traits using human mtDNA phylogenies rooted to the Reconstructed Sapiens Reference Sequence (RSRS) as a model to address this question. The analysis reveals that the ancestral state of Homo sapiens was hunting, using material innovations that included bows and arrows, stone axes and spears. However, around 80,000 y before present, a transition occurred, from this ancestral hunting tradition, toward the invention of protective weapons such as shields, the appearance of ritual fighting as a socially accepted behavior and the construction of war canoes for the fast transport of large numbers of warriors. This model suggests a major cultural change, during the Palaeolithic, from hunters to warriors. Moreover, in the light of the recent Out of Africa Theory, it suggests that the “Out of Africa Tribe” was a tribe of warriors that had developed protective weapons such as shields and used big war canoes to travel the sea coast and big rivers in raiding expeditions.
Resumo:
The defense of plants against herbivores and pathogens involves the participation of an enormous range of different metabolites, some of which act directly as defensive weapons against enemies (toxins or deterrents) and some of which act as components of the complex internal signaling network that insures that defense is timed to enemy attack. Recent work reveals a surprising trend: The same compounds may act as both weapons and signals of defense. For example, two groups of well-studied defensive weapons, glucosinolates and benzoxazinoids, trigger the accumulation of the protective polysaccharide callose as a barrier against aphids and pathogens. In the other direction, several hormones acting in defense signaling (and their precursors and products) exhibit activity as weapons against pathogens. Knowing which compounds are defensive weapons, which are defensive signals and which are both is vital for understanding the functioning of plant defense systems.
Resumo:
Aviation security strongly depends on screeners' performance in the detection of threat objects in x-ray images of passenger bags. We examined for the first time the effects of stress and stress-induced cortisol increases on detection performance of hidden weapons in an x-ray baggage screening task. We randomly assigned 48 participants either to a stress or a nonstress group. The stress group was exposed to a standardized psychosocial stress test (TSST). Before and after stress/nonstress, participants had to detect threat objects in a computer-based object recognition test (X-ray ORT). We repeatedly measured salivary cortisol and X-ray ORT performance before and after stress/nonstress. Cortisol increases in reaction to psychosocial stress induction but not to nonstress independently impaired x-ray detection performance. Our results suggest that stress-induced cortisol increases at peak reactivity impair x-ray screening performance.