57,611 research outputs found
A Hybrid Gyrokinetic Ion and Isothermal Electron Fluid Code for Astrophysical Plasma
This paper describes a new code for simulating astrophysical plasmas that
solves a hybrid model composed of gyrokinetic ions (GKI) and an isothermal
electron fluid (ITEF) [A. Schekochihin et al., Astrophys. J. Suppl.
\textbf{182}, 310 (2009)]. This model captures ion kinetic effects that are
important near the ion gyro-radius scale while electron kinetic effects are
ordered out by an electron-ion mass ratio expansion. The code is developed by
incorporating the ITEF approximation into {\tt AstroGK}, an Eulerian
gyrokinetics code specialized to a slab geometry [R. Numata et al., J. Compute.
Pays. \textbf{229}, 9347 (2010)]. The new code treats the linear terms in the
ITEF equations implicitly while the nonlinear terms are treated explicitly. We
show linear and nonlinear benchmark tests to prove the validity and
applicability of the simulation code. Since the fast electron timescale is
eliminated by the mass ratio expansion, the Courant--Friedrichs--Lewy condition
is much less restrictive than in full gyrokinetic codes; the present hybrid
code runs times faster than
{\tt AstroGK}\ with a single ion species and kinetic electrons where
is the ion-electron mass ratio. The improvement of
the computational time makes it feasible to execute ion scale gyrokinetic
simulations with a high velocity space resolution and to run multiple
simulations to determine the dependence of turbulent dynamics on parameters
such as electron--ion temperature ratio and plasma beta
Police powers and human rights in the context of terrorism
Purpose – The object of the paper is to analyse the justifications for the modification of police
powers in response to terrorist threats, placing this issue in a European context.
Design/methodology/approach – The paper consists of a critical examination of provisions
relating to terrorism emanating from the European Union and the Council of Europe (European
Convention on Human Rights (ECHR)), and the relevant English law on police powers of stop and
search, arrest, and detention.
Findings – Nothing in European law requires the amendments to police powers contained in English
law; European law requires respect for human rights, even in dealing with terrorism; a shoot-to-kill
policy is prohibited by the ECHR; and balance is an unsatisfactory method of resolving conflicts in
this area.
Research limitations/implications – The research was limited in its scope to certain areas of
police powers, and to certain fundamental European documents. Future research should consider the
issue in relation to wider areas.
Originality/value – It challenges the idea of balance between liberty and security, proposing a test
based on necessity instead
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Pictures of life in older age: a quantitative analysis of the lived experience of ageing using the Understanding Society survey
Volitional control of anticipatory ocular smooth pursuit after viewing, but not pursuing, a moving target: evidence for a re-afferent velocity store
Although human subjects cannot normally initiate smooth eye movements in the absence of a moving target, previous experiments have established that such movements can be evoked if the subject is required to pursue a regularly repeated, transient target motion stimulus. We sought to determine whether active pursuit was necessary to evoke such an anticipatory response or whether it could be induced after merely viewing the target motion. Subjects were presented with a succession of ramp target motion stimuli of identical velocity and alternating direction in the horizontal axis. In initial experiments, the target was exposed for only 120 ms as it passed through centre, with a constant interval between presentations. Ramp velocity was varied from +/- 9 to 45 degrees/s in one set of trials; the interval between ramp presentations was varied from 640 to 1920 ms in another. Subjects were instructed either to pursue the moving target from the first presentation or to hold fixation on another, stationary target during the first one, two or three presentations of the moving display. Without fixation, the first smooth movement was initiated with a mean latency of 95 ms after target onset, but with repeated presentations anticipatory smooth movements started to build up before target onset. In contrast, when the subjects fixated the stationary target for three presentations of the moving target, the first movement they made was already anticipatory and had a peak velocity that was significantly greater than that of the first response without prior fixation. The conditions of experiment 1 were repeated in experiment 3 with a longer duration of target exposure (480 ms), to allow higher eye velocities to build up. Again, after three prior fixations, the anticipatory velocity measured at 100 ms after target onset (when visual feedback would be expected to start) was not significantly different to that evoked after the subjects had made three active pursuit responses to the same target motion, reaching a mean of 20 degrees/s for a 50 degrees/s target movement. In a further experiment, we determined whether subjects could use stored information from prior active pursuit to generate anticipatory pursuit in darkness if there was a high expectancy that the target would reappear with identical velocity. Subjects made one predictive response immediately after target disappearance, but very little response thereafter until the time at which they expected the target to reappear, when they were again able to re-vitalize the anticipatory response before target appearance. The findings of these experiments provide evidence that information related to target velocity can be stored and used to generate future anticipatory responses even in the absence of eye movement. This suggests that information for storage is probably derived from a common pre-motor drive signal that is inhibited during fixation, rather than an efference copy of eye movement itself. Furthermore, a high level of expectancy of target appearance can facilitate the release of this stored information in darkness
Exploring racial bias in a European country with a recent history of immigration of black Africans
Self-calibrating threshold detector
A self calibrating threshold detector comprises a single demodulating channel which includes a mixer having one input receiving the incoming signal and another input receiving a local replica code. During a short time interval, an incorrect local code is applied to the mixer to incorrectly demodulate the incoming signal and to provide a reference level that calibrates the noise propagating through the channel. A sample and hold circuit is coupled to the channel for storing a sample of the reference level. During a relatively long time interval, the correct replica code provides an output level which ranges between the reference level and a maximum level that represents incoming signal presence and synchronism with the replica code. A summer substracts the stored sample reference from the output level to provide a resultant difference signal indicative of the acquisition of the expected signal
Current status of plague and plague control in the United States
During the first quarter of the 20th century, massive rat-borne plague epidemics occurred in port cities of the United States in conjunction with the last world-wide pandemic which originated in China in 1893. By 1950, plague was found to be firmly established in wild rodent populations in states west of the 100th meridian. Presumably because of improved sanitation coupled with retreat of the world-wide pandemic, there have been no human cases in this country associated with urban rats since 1924. However, sporadic cases, fewer than 10 per year, are reported as due to contact with wild rodents, lagomorphs, rural rats, and/or their fleas. Recent observations suggest that: a) in the current decade there has been an increase in human plague cases; b) there continues to be a serious potential of a single undiagnosed and untreated case, which possibility is intensified by the very paucity of human cases decreasing the likelihood of a correct diagnosis and by changing patterns of life exhibited by members of our society (e.g., hippie communes and a generally increased mobility); and c) the apparent distribution of plague only in the area west of the 100th meridian might be found to represent an unrealistic generalization if adequate surveillance were carried out. At the present time human plague cases from wild animal sources tend to be isolated events both spatially and temporally and often cannot be attributed to confined and definable epizootic sources amenable to effective control programs. Improved means for epizootic control and long-term management of enzootic plague sources must be sought aggressively. These measures should include development of: a) a surveillance network to detect plague activity in rodent and lagomorph populations throughout the western United States; b) effective, yet ecologically sound, means of ectoparasite control, including suitable materials and methods of application; c) methods for management of plague-susceptible wild animal populations, particularly where they exist in contact with high use recreation and residential areas; and d) more extensive knowledge of enzootic plague and the factors that bring about epizootic plague and potential human contact
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