255 research outputs found
The Subpulse Modulation Properties of Pulsars and its Frequency Dependence
A large sample of about two hundred pulsars have been observed to study their
subpulse modulation at an observing wavelength of (when achievable) both 21 and
92 cm using the Westerbork Synthesis Radio Telescope. For 57 pulsars drifting
subpulses are discovered for the first time and are confirmed for many others.
This leads to the conclusion that it could well be that the drifting subpulse
mechanism is an intrinsic property of the emission mechanism itself, although
for some pulsars it is difficult or impossible to detect. It appears that the
youngest pulsars have the most disordered subpulses and the subpulses become
more and more organized into drifting subpulses as the pulsar ages. Drifting
subpulses are in general found at both frequencies and the measured values of
P3 at the two frequencies are highly correlated, showing the broadband nature
of this phenomenon. Also the modulation indices measured at the two frequencies
are clearly correlated, although at 92 cm they are on average possibly higher.
The correlations with the modulation indices are argued to be consistent with
the picture in which the radio emission is composed out of a drifting subpulse
signal plus a quasi-steady signal which becomes, on average, stronger at high
observing frequencies. There is no obvious correlation found between P3 and the
pulsar age (or any other pulsar parameter) contrary to reports in the past.Comment: Proceedings of the 40 Years of Pulsars: Millisecond Pulsars,
Magnetars and More conference in Montrea
Older adults, falls and technologies for independent living: a life space approach
This paper draws attention to the need for further understanding of the fine details of routine and taken-for-granted daily activities and mobility. It argues that such understanding is critical if technologies designed to mitigate the negative impacts of falls and fear-of-falling are to provide unobtrusive support for independent living. The reported research was part of a large, multidisciplinary, multi-site research programme into responses to population ageing in Ireland, Technologies for Independent Living (TRIL). A small, exploratory, qualitative life-space diary study was conducted. Working with eight community-dwelling older adults with different experiences of falls or of fear-of-falls, data were collected through weekly life-space diaries, daily-activity logs, two-dimensional house plans and a pedometer. For some participants, self-recording of their daily activities and movements revealed routine, potentially risky behaviour about which they had been unaware, which may have implications for falls-prevention advice. The findings are presented and discussed around four key themes: ‘being pragmatic’, ‘not just a faller’, ‘heightened awareness and blind spots’ and ‘working with technology’. The findings suggest a need to think creatively about how technological and other solutions best fit with people's everyday challenges and needs and of critical importance, that their installation does not reduce an older adult to ‘just a faller’ or a person with a fear-of-falls
Arbor -- a morphologically-detailed neural network simulation library for contemporary high-performance computing architectures
We introduce Arbor, a performance portable library for simulation of large
networks of multi-compartment neurons on HPC systems. Arbor is open source
software, developed under the auspices of the HBP. The performance portability
is by virtue of back-end specific optimizations for x86 multicore, Intel KNL,
and NVIDIA GPUs. When coupled with low memory overheads, these optimizations
make Arbor an order of magnitude faster than the most widely-used comparable
simulation software. The single-node performance can be scaled out to run very
large models at extreme scale with efficient weak scaling.
HPC, GPU, neuroscience, neuron, softwareComment: PDP 2019 27th Euromicro International Conference on Parallel,
Distributed and Network-based Processin
Photochemically Mediated Ring Expansion of Indoles and Pyrroles with Chlorodiazirines: Synthetic Methodology and Thermal Hazard Assessment
We demonstrate that arylchlorodiazirines serve as photo-activated halocarbene precursors for the selective one-carbon ring expansion of N-substituted pyrroles and indoles to the corresponding pyridinium and quinolinium salts. Preliminary investigations indicate that the same strategy also enables the conversion of N-substituted pyrazoles to pyrimidinium salts. The N-substituent of the substrate plays an essential role in: (1) increasing substrate scope by preventing product degradation, (2) enhancing yields by suppressing co-product inhibition, and (3) activating the azinium products towards subsequent synthetic manipulations. This latter point is illustrated by subjecting the quinolinium salts to four complementary partial reductions, which provide concise access to ring-expanded products with different degrees of increased C(sp3) character. Thermal analysis of the diazirines by differential scanning calorimetry (DSC) provides detailed insight into their energetic properties, and highlights the safety benefits of photolyzing—rather than thermolyzing—these reagents
The Roles of Tidal Evolution and Evaporative Mass Loss in the Origin of CoRoT-7 b
CoRoT-7 b is the first confirmed rocky exoplanet, but, with an orbital
semi-major axis of 0.0172 AU, its origins may be unlike any rocky planet in our
solar system. In this study, we consider the roles of tidal evolution and
evaporative mass loss in CoRoT-7 b's history, which together have modified the
planet's mass and orbit. If CoRoT-7 b has always been a rocky body, evaporation
may have driven off almost half its original mass, but the mass loss may depend
sensitively on the extent of tidal decay of its orbit. As tides caused CoRoT-7
b's orbit to decay, they brought the planet closer to its host star, thereby
enhancing the mass loss rate. Such a large mass loss also suggests the
possibility that CoRoT-7 b began as a gas giant planet and had its original
atmosphere completely evaporated. In this case, we find that CoRoT-7 b's
original mass probably didn't exceed 200 Earth masses (about 2/3 of a Jupiter
mass). Tides raised on the host star by the planet may have significantly
reduced the orbital semi-major axis, perhaps causing the planet to migrate
through mean-motion resonances with the other planet in the system, CoRoT-7 c.
The coupling between tidal evolution and mass loss may be important not only
for CoRoT-7 b but also for other close-in exoplanets, and future studies of
mass loss and orbital evolution may provide insight into the origin and fate of
close-in planets, both rocky and gaseous.Comment: Accepted for publication by MNRAS on 2010 May
The role of spatial boundaries in shaping long-term event representations
When remembering the past, we typically recall ‘events’ that are bounded in time and space. However, as we navigate our environment our senses receive a continuous stream of information. How do we create discrete long-term episodic memories from continuous input? Although previous research has provided evidence for a role of spatial boundaries in the online segmentation of our sensory experience within working memory, it is not known how this segmentation contributes to subsequent long-term episodic memory. Here we show that the presence of a spatial boundary at encoding (a doorway between two rooms) impairs participants’ later ability to remember the order that objects were presented in. A sequence of two objects presented in the same room in a virtual reality environment is more accurately remembered than a sequence of two objects presented in adjoining rooms. The results are captured by a simple model in which items are associated to a context representation that changes gradually over time, and changes more rapidly when crossing a spatial boundary. We therefore provide the first evidence that the structure of long-term episodic memory is shaped by the presence of a spatial boundary and provide constraints on the nature of the interaction between working memory and long-term memory
Intrinsic monitoring of learning success facilitates memory encoding via the activation of the SN/VTA-Hippocampal loop
Humans constantly learn in the absence of explicit rewards. However, the neurobiological mechanisms supporting this type of internally-guided learning (without explicit feedback) are still unclear. Here, participants who completed a task in which no external reward/feedback was provided, exhibited enhanced fMRI-signals within the dopaminergic midbrain, hippocampus, and ventral striatum (the SN/VTA-Hippocampal loop) when successfully grasping the meaning of new-words. Importantly, new-words that were better remembered showed increased activation and enhanced functional connectivity between the midbrain, hippocampus, and ventral striatum. Moreover, enhanced emotion-related physiological measures and subjective pleasantness ratings during encoding were associated with remembered new-words after 24 hr. Furthermore, increased subjective pleasantness ratings were also related to new-words remembered after seven days. These results suggest that intrinsic-potentially reward-related-signals, triggered by self-monitoring of correct performance, can promote the storage of new information into long-term memory through the activation of the SN/VTA-Hippocampal loop, possibly via dopaminergic modulation of the midbrain
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