19 research outputs found
N-body simulations of gravitational dynamics
We describe the astrophysical and numerical basis of N-body simulations, both
of collisional stellar systems (dense star clusters and galactic centres) and
collisionless stellar dynamics (galaxies and large-scale structure). We explain
and discuss the state-of-the-art algorithms used for these quite different
regimes, attempt to give a fair critique, and point out possible directions of
future improvement and development. We briefly touch upon the history of N-body
simulations and their most important results.Comment: invited review (28 pages), to appear in European Physics Journal Plu
The Concussion Recognition Tool 5th Edition (CRT5): Background and rationale
The Concussion Recognition Tool 5 (CRT5) is the most recent revision of the Pocket Sport Concussion Assessment Tool 2 that was initially introduced by the Concussion in Sport Group in 2005. The CRT5 is designed to assist non-medically trained individuals to recognise the signs and symptoms of possible sport-related concussion and provides guidance for removing an athlete from play/sport and to seek medical attention. This paper presents the development of the CRT5 and highlights the differences between the CRT5 and prior versions of the instrument
Using screen video capture software to aide and inform cognitive interviewing
Web-based surveys are a salient tool in the repertoire of social and behavioral scientists. The increase in web-based surveys is understandable considering the distinct advantages offered, including: (a) lower costs and reduced labor time, (b) ability to directly transfer data into statistical packages (reducing coding errors), (c) customization options enabling more attractive presentation, (d) ability to reduce respondent burden by embedding skip patterns, and (e) access to larger sample sizes in different geographic regions. It is important to note, however, that administering web-based surveys also introduces distinct sources of error (e.g., coverage, sampling and non-response). Regardless of format (e.g., paper-and-pencil or web-based), specific, prescribed steps must be followed when constructing an instrument in order to reduce survey error and lend credence to the data collected before subsequent analysis is performed. One of those crucial stages integral to the pretesting process is cognitive interviewing. Cognitive interviewing is a qualitative process, encompassing two main techniques: think aloud interviewing and verbal probing. Collectively, these two methods seek to (a) produce information on what the respondent is thinking while answering the questions, (b) the cognitive processes used to answer the questions, and (c) how the respondent answers the questions. The purpose of this article is to provide a practical guide outlining how Camtasia, a screen video capture software, can aide and inform the cognitive interview process
The structure of the climate debate
First-best climate policy is a uniform carbon tax which gradually rises over time. Civil servants have complicated climate policy to expand bureaucracies, politicians to create rents. Environmentalists have exaggerated climate change to gain influence, other activists have joined the climate bandwagon. Opponents to climate policy have attacked the weaknesses in climate research. The climate debate is convoluted and polarized as a result, and climate policy complex. Climate policy should become easier and more rational as the Paris Agreement has shifted climate policy back towards national governments. Changing political priorities, austerity, and a maturing bureaucracy should lead to a more constructive climate debate
A MODEST review
We present an account of the state of the art in the fields explored by the
research community invested in 'Modeling and Observing DEnse STellar systems'.
For this purpose, we take as a basis the activities of the MODEST-17
conference, which was held at Charles University, Prague, in September 2017.
Reviewed topics include recent advances in fundamental stellar dynamics,
numerical methods for the solution of the gravitational N-body problem,
formation and evolution of young and old star clusters and galactic nuclei,
their elusive stellar populations, planetary systems, and exotic compact
objects, with timely attention to black holes of different classes of mass and
their role as sources of gravitational waves.
Such a breadth of topics reflects the growing role played by collisional
stellar dynamics in numerous areas of modern astrophysics. Indeed, in the next
decade, many revolutionary instruments will enable the derivation of positions
and velocities of individual stars in the Milky Way and its satellites and will
detect signals from a range of astrophysical sources in different portions of
the electromagnetic and gravitational spectrum, with an unprecedented
sensitivity. On the one hand, this wealth of data will allow us to address a
number of long-standing open questions in star cluster studies; on the other
hand, many unexpected properties of these systems will come to light,
stimulating further progress of our understanding of their formation and
evolution.Comment: 42 pages; accepted for publication in 'Computational Astrophysics and
Cosmology'. We are much grateful to the organisers of the MODEST-17
conference (Charles University, Prague, September 2017). We acknowledge the
input provided by all MODEST-17 participants, and, more generally, by the
members of the MODEST communit
Evaluating a light-louver system for behavioural guidance of age-0 white sturgeon
Water diversions for hydropower and other applications are some of the most disruptive alterations affecting fish populations in lotic systems. Although many different strategies have been developed to reduce lethal encounters with such infrastructure, few studies have evaluated different forms of behavioural guidance concurrently. Here, we combine an LED-based light guidance device (LGD) equipped with adjustable wavelength and strobing output with a reverse-configured louver rack to assess the effectiveness of this two-part behavioural guidance system on downstream movement through a bypass by age-0 white sturgeon (Acipenser transmontanus). Several combinations of LGD and louver settings were tested under both simulated day and night (low light) conditions in a laboratory setting. In the absence of the LGD, louver slat spacings of 10 or 20 cm were most effective at achieving downstream bypasses with greater success rates (~ two-fold greater) under night conditions tha
Preferences of age-0 white sturgeon for different colours and strobe rates of LED lights may inform behavioural guidance strategies
Many populations of migratory fish species, including white sturgeon (Acipenser transmontanus Richardson), are threatened due to modification of riverine systems and may experience downstream displacement or mortality at water intake structures. Efforts to reduce the impacts of these structures are beginning to incorporate behavioural guidance, where the sensory capabilities of fishes are exploited to repel them from high-risk areas or attract them towards desirable pat
Ontogeny of light avoidance in juvenile lake sturgeon
Hatchery-reared age 1+Â and 4+Â lake sturgeon (Acipenser fulvescens) were assayed to determine the effectiveness of coloured, strobing LED light guidance device (LGD) at achieving behavioural guidance for attraction or avoidance responses. Base
Experimental evaluation of the effect of a light-emitting diode device on Chinook salmon smolt entrainment in a simulated river
The entrainment and impingement of fish into water diversion infrastructure is one of the several factors contributing to their decline. Here, controlled experiments assessed the potential for a behavioral guidance device [a light-emitting diode (LED) light array] strobing at various spectra to reduce the entrainment of juvenile Chinook salmon (Oncorhynchus tshawytscha) into a water diversion pipe. Fish were tested during the day and night, and under control conditions (light off) and red, blue, and white spectra strobing at 2 Hz. Fish entrainment into the diversion pipe was evaluated. Results indicated greater entrainment at night compared to day. All trials at night with the LED light strobing had higher entrainment than the control, with blue and white spectra corresponding to greater entrainment than red spectra. During the day, the white spectra treatment was different from the red treatment, with lower entrainment. LED lights employed to repel migratory juvenile salmon away from water intake structures may be ineffectual but there is potential for the light to be used as an attractant to guide fish towards desirable features such as âsafeâ areas (bypass channels or fishways)