844 research outputs found
Slingshot Dynamics for Self Replicating Probes and the Effect on Exploration Timescales
Interstellar probes can carry out slingshot manoeuvres around the stars they
visit, gaining a boost in velocity by extracting energy from the star's motion
around the Galactic Centre. These maneouvres carry little to no extra energy
cost, and in previous work it has been shown that a single Voyager-like probe
exploring the galaxy does so 100 times faster when carrying out these
slingshots than when navigating purely by powered flight (Forgan et al. 2012).
We expand on these results by repeating the experiment with self-replicating
probes. The probes explore a box of stars representative of the local Solar
neighbourhood, to investigate how self-replication affects exploration
timescales when compared with a single non-replicating probe.
We explore three different scenarios of probe behaviour: i) standard powered
flight to the nearest unvisited star (no slingshot techniques used), ii) flight
to the nearest unvisited star using slingshot techniques, and iii) flight to
the next unvisited star that will give the maximum velocity boost under a
slingshot trajectory.
In all three scenarios we find that as expected, using self-replicating
probes greatly reduces the exploration time, by up to three orders of magnitude
for scenario i) and iii) and two orders of magnitude for ii). The second case
(i.e. nearest-star slingshots) remains the most time effective way to explore a
population of stars. As the decision-making algorithms for the fleet are
simple, unanticipated "race conditions" amongst probes are set up, causing the
exploration time of the final stars to become much longer than necessary. From
the scaling of the probes' performance with star number, we conclude that a
fleet of self-replicating probes can indeed explore the Galaxy in a
sufficiently short time to warrant the existence of the Fermi Paradox.Comment: Accepted for publication in the International Journal of
Astrobiology, 13 pages, 7 figure
Baseline study of employability related activities in Scottish colleges
In October 2004, the Scottish Funding Council (SFC)'s predecessor bodies, theSFEFC and the SHEFC, publishedLearning to Work(SFC 2004), a discussion paperabout how Scotland's colleges and universities can help to enhance learners'employability. In subsequent dialogue with stakeholders, there was agreement thatemployability should be a specific focus for quality enhancement in the college sectorfrom 2006-07. As a basis for further development, the SFC commissioned this studyto provide information on the range of current activities and practices in Scotland'scolleges which contribute to enhancing employability
Achieving Good Angular Resolution in 3D Arc Diagrams
We study a three-dimensional analogue to the well-known graph visualization
approach known as arc diagrams. We provide several algorithms that achieve good
angular resolution for 3D arc diagrams, even for cases when the arcs must
project to a given 2D straight-line drawing of the input graph. Our methods
make use of various graph coloring algorithms, including an algorithm for a new
coloring problem, which we call localized edge coloring.Comment: 12 pages, 5 figures; to appear at the 21st International Symposium on
Graph Drawing (GD 2013
One-pot multistep mechanochemical synthesis of fluorinated pyrazolones
Solventless mechanochemical synthesis represents a technique with improved sustainability metrics compared to solvent-based processes. Herein, we describe a methodical process to run one solventless reaction directly into another through multistep mechanochemistry, effectively amplifying the solvent savings. The approach has to consider the solid form of the materials and compatibility of any auxiliary used. This has culminated in the development of a two-step, one-jar protocol for heterocycle formation and subsequent fluorination that has been successfully applied across a range of substrates, resulting in 12 difluorinated pyrazolones in moderate to excellent yields
Macroeconomics and Drug Use: A Review of the Literature and Hypotheses for Future Research
Despite more than a century of drug prohibition, problems of addiction and drug abuse continue to be major global public health and criminal justice concerns (United Nations Office on Drugs and Crime, 2015). It has long been obvious that many of these problems are entwined with other economic and social issues. The editors of The Economist, in reporting evidence of a decline in drug use in the UK, speculated on the impact of the concurrent economic slowdown and commented that, "few academics have studied the link between drug use and macroeconomic performance, and what work exists is inconclusive" (Drug use and abuse: The fire next time, 2011). The goal of this paper will be to examine the work that exists on this topic and to propose a set of hypotheses to be tested in future studies
Robust Buchwald-Hartwig amination enabled by ball-milling
An operationally simple mechanochemical method for the Pd catalysed BuchwaldâHartwig amination of arylhalides with secondary amines has been developed using a Pd PEPPSI catalyst system. The system is demonstrated on 30 substrates and applied in the context of a target synthesis. Furthermore, the performance of the reaction under aerobic conditions has been probed under traditional solution and mechanochemical conditions, the observations are discussed herein
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Twenty-one years of heave monitoring in London Clay at Horseferry Road Basement
An 11 m-deep basement structure in London SW1 was left vacant from 1968 to 1989. The basement heaved significantly during this period due to the lack of a superstructure, providing a unique opportunity to study the development of long-term heave in London Clay. May (1975) presented the monitoring results from 1968-73 and excerpts of site data collected after 1973 have also been circulating informally in the industry since the 1990s. However, the full set of monitoring data remains hitherto unpublished.
This paper was initially drafted in the early 1990s when three of the authors (Nicholson, Chapman, and Solera) were working together with Arup. The paper somehow never got published as people and circumstances changed. More recently, the first author (Chan) started postgraduate research on heave and pressure beneath slabs in excavations in over-consolidated clays, using the heave monitoring data from the draft paper to complement centrifuge test results. For this reason, it was decided that the draft paper should be revised and published for the benefit of the wider industry.
This paper provides a comprehensive case history of the site, publishing further heave data to June 1989, giving a total of 21 years of heave monitoring. Further site investigation data and calculations are included for comparison. The data show that the presence of a basement did not significantly reduce the shear strength of the clay beneath it. The coefficient of consolidation of the clay was 38 â 52 mÂČ/year and long-term heave was still ongoing 21 years after the end of excavation.EPSRC grant reference number EP/L016095/
Generational Shift and Drug Abuse in Older Americans
Since the problem of substance abuse by older adults began to receive serious professional attention, the focus has been almost exclusively on alcohol abuse. This reality is changing as the âbaby boomersâ age. We examined data from the National Household Survey on Drug Abuse (1985) and the National Survey on Drug Use and Health (2006) comparing nationwide prevalence of both legal and illicit drugs. Use of drugs by category varied over the study period; some showed little change (e.g., alcohol) while others showed marked increase (e.g., marijuana, cocaine). We found that the population of older Americans in 2006 contained greater proportions of persons who had used or continued to use illicit drugs than did older Americans in 1985. Gerontologists and geriatric services will increasingly encounter older Americans who use or abuse illicit drugs
Integrity Testing of Pile Cover Using Distributed Fibre Optic Sensing.
The integrity of cast-in-place foundation piles is a major concern in geotechnical engineering. In this study, distributed fibre optic sensing (DFOS) cables, embedded in a pile during concreting, are used to measure the changes in concrete curing temperature profile to infer concrete cover thickness through modelling of heat transfer processes within the concrete and adjacent ground. A field trial was conducted at a high-rise building construction site in London during the construction of a 51 m long test pile. DFOS cables were attached to the reinforcement cage of the pile at four different axial directions to obtain distributed temperature change data along the pile. The monitoring data shows a clear development of concrete hydration temperature with time and the pattern of the change varies due to small changes in concrete cover. A one-dimensional axisymmetric heat transfer finite element (FE) model is used to estimate the pile geometry with depth by back analysing the DFOS data. The results show that the estimated pile diameter varies with depth in the range between 1.40 and 1.56 m for this instrumented pile. This average pile diameter profile compares well to that obtained with the standard Thermal Integrity Profiling (TIP) method. A parametric study is conducted to examine the sensitivity of concrete and soil thermal properties on estimating the pile geometry
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