35 research outputs found
Supernova 1987A: Rotation and a Binary Companion
In this paper we provide a possible link between the structure of the bipolar
nebula surrounding SN1987A and the properties of its progenitor star. A Wind
Blwon Bubble (WBB) scenario is emplyed, in which a fast, tenuous wind from a
Blue Supergiant expands into a slow, dense wind, expelled during an earlier Red
Supergiant phase. The bipolar shapre develops due to a pole-to-equator density
contrast in the slow wind (ie, the slow wind forms a slow torus). We use the
Wind Compressed Disk (WCD) model of Bjorkman & Cassinelli (1992) to determine
the shape of the slow torus. In the WCD scenario, the shape of the torus is
determined by the rotation of the progenitor star. We then use a self-similar
semi-analytical method for wind blown bubble evolution to determine the shape
of the resulting bipolar nebula.
We find that the union of the wind-compressed-disk and bipolar-wind-blown-
bubble models allows us to recover the salient properties of SN1987A's
circumstellar nebula. In particular, the size, speed and density of SN1987A's
inner ring are easily reproduced in our calculations. An exploration of
parameter space shows the the red supergiant progenitor must be been rotating
at > 0.3 of its breakup speed. We conclude that the progenitor was most likely
spun up by a merger with a binary companion. Using a simple model for the
binary merger we find that the companion is likely to have had a mass > 0.5
M_sun.Comment: 30 pages, 4 figure
Neuroelectric Evidence for Cognitive Association Formation: An Event-Related Potential Investigation
Although many types of learning require associations to be formed, little is known about the brain mechanisms engaged in association formation. In the present study, we measured event-related potentials (ERPs) while participants studied pairs of semantically related words, with each word of a pair presented sequentially. To narrow in on the associative component of the signal, the ERP difference between the first and second words of a pair (Word2-Word1) was derived separately for subsequently recalled and subsequently not-recalled pairs. When the resulting difference waveforms were contrasted, a parietal positivity was observed for subsequently recalled pairs around 460 ms after the word presentation onset, followed by a positive slow wave that lasted until around 845 ms. Together these results suggest that associations formed between semantically related words are correlated with a specific neural signature that is reflected in scalp recordings over the parietal region
How Might Crime-Scripts Be Used to Support the Understanding and Policing of Cloud Crime?
Crime scripts are becoming an increasingly popular method for understanding crime by turning a crime from a static event into a process, whereby every phase of the crime is scripted. It is based on the work relating to cognitive scripts and rational-choice theory. With the exponential growth of cyber-crime, and more specifically cloud-crime, policing/law enforcement agencies are struggling with the amount of reported cyber-crime. This paper argues that crime scripts are the most effective way forward in terms of helping understand the behaviour of the criminal during the crime itself. They act as a common language between different stakeholders, focusing attention and resources on the key phases of a crime. More importantly, they shine a light on the psychological element of a crime over the more technical cyber-related elements. The paper concludes with an example of what a cloud-crime script might look like, asking future research to better understand: (i) cloud criminal fantasy development; (ii) the online cultures around cloud crime; (iii) how the idea of digital-drift affects crime scripts, and; (iv) to improve on the work by Ekblom and Gill in improving crime scripts
How to Implement a CAD Database Interface
A CAD database interface means that elements from two different types of computer databases are being connected for a single purpose. Graphic elements in the CAD database are being linked with alphanumeric elements in a DBMS. The article describes how to create the interfac