2,107 research outputs found
The Spin Distribution of Fast Spinning Neutron Stars in Low Mass X-Ray Binaries: Evidence for Two Sub-Populations
We study the current sample of rapidly rotating neutron stars in both
accreting and non-accreting binaries in order to determine whether the spin
distribution of accreting neutron stars in low-mass X-ray binaries can be
reconciled with current accretion torque models. We perform a statistical
analysis of the spin distributions and show that there is evidence for two
sub-populations among low-mass X-ray binaries, one at relatively low spin
frequency, with an average of ~300 Hz and a broad spread, and a peaked
population at higher frequency with average spin frequency of ~575 Hz. We show
that the two sub-populations are separated by a cut-point at a frequency of
~540 Hz. We also show that the spin frequency of radio millisecond pulsars does
not follow a log-normal distribution and shows no evidence for the existence of
distinct sub-populations. We discuss the uncertainties of different accretion
models and speculate that either the accreting neutron star cut-point marks the
onset of gravitational waves as an efficient mechanism to remove angular
momentum or some of the neutron stars in the fast sub-population do not evolve
into radio millisecond pulsars.Comment: Submitted to Ap
The dynamics of neutron star crusts: Lagrangian perturbation theory for a relativistic superfluid-elastic system
The inner crust of a mature neutron star is composed of an elastic lattice of
neutron-rich nuclei penetrated by free neutrons. These neutrons can flow
relative to the crust once the star cools below the superfluid transition
temperature. In order to model the dynamics of this system, which is relevant
for a range of problems from pulsar glitches to magnetar seismology and
continuous gravitational-wave emission from rotating deformed neutron stars, we
need to understand general relativistic Lagrangian perturbation theory for
elastic matter coupled to a superfluid component. This paper develops the
relevant formalism to the level required for astrophysical applications.Comment: 31 pages, double spacing, minor typos fixe
Robert N. Haskell Letter Concerning the Cross Rock Project, 1963
A letter written by Robert N. Haskell, President of the Bangor Hydro-Electric Company, warning the state legislature of Maine against the Cross Rock Project. Relates to 101st Maine Legislature bills LD 115 & 874 and the Maine Power Authority.https://digicom.bpl.lib.me.us/bangorhydro_news/1062/thumbnail.jp
Bangor Hydro Electric Company Letter Addressed to Company C.E.O in the Year 2076
Robert N. Haskell, Chairman of the Board and long-time employee of the Bangor Hydro Electric Company, wrote this letter which is included in a time capsule buried in Bangor to be opened in 2076. The letter covers the history of the Bangor Hydro Electric Company from 1887 to 1976. Mr. Haskell served a famously short five-day term as Governor in Maine in early 1959.
Letter found in the collected papers of the Bangor Hydro Electric Company housed here at Bangor Public Library. We feel the benefits outweigh the drawbacks of releasing this letter 58 years before its author\u27s suspected it to be read.https://digicom.bpl.lib.me.us/bangorhydro_news/1055/thumbnail.jp
Gravitational waves from rapidly rotating neutron stars
Rapidly rotating neutron stars in Low Mass X-ray Binaries have been proposed
as an interesting source of gravitational waves. In this chapter we present
estimates of the gravitational wave emission for various scenarios, given the
(electromagnetically) observed characteristics of these systems. First of all
we focus on the r-mode instability and show that a 'minimal' neutron star model
(which does not incorporate exotica in the core, dynamically important magnetic
fields or superfluid degrees of freedom), is not consistent with observations.
We then present estimates of both thermally induced and magnetically sustained
mountains in the crust. In general magnetic mountains are likely to be
detectable only if the buried magnetic field of the star is of the order of
G. In the thermal mountain case we find that gravitational
wave emission from persistent systems may be detected by ground based
interferometers. Finally we re-asses the idea that gravitational wave emission
may be balancing the accretion torque in these systems, and show that in most
cases the disc/magnetosphere interaction can account for the observed spin
periods.Comment: To appear in 'Gravitational Waves Astrophysics: 3rd Session of the
Sant Cugat Forum on Astrophysics, 2014', Editor: Carlos F. Sopuert
Future care: rethinking technology enhanced aged care environments
© 2018, Emerald Publishing Limited. Purpose: Cutting-edge hospital and residential care architecture and interior design aim to address the emotional and practical needs of patients, staff and visitors. Yet, whilst improving on past practice, current approaches to design still rarely recognise or respond to individuals. The purpose of this paper is to provide a review of design-led research into digital technology across disciplines for the personalisation of healthcare environments and is informed by the authors’ ongoing hospital-based research. Design/methodology/approach: This review is based on a design anthropology framework providing insight into designing for changing the experience for older patients in current healthcare contexts and future focused strategies, integrating digital technologies and human-centred design across scale and disciplines. It is informed by ongoing hospital studies based on design-led research methodology, drawing on design anthropology and ethnographical methods. Findings: Technology enhanced, human-centred, assistive devices and environments implemented into healthcare across scale are developing but integration is needed for meaningful experiences. Research limitations/implications: This review is a positioning paper for design-led research into digital technology across scale and medium. Practical implications: This paper provides the basis for practical research including the ongoing hospital-based research of the authors. Social implications: This approach potentially enhances emotional experiences of connected healthcare. Originality/value: Future care scenarios are proposed, with technology and human experience as key drivers. Individualised and personalised solutions better cater for diversity. Within this context, it is strategic to question and test new ways of crafting the older persons care experience. This paper brings new direction to this discussion
The enigmatic spin evolution of PSR J0537-6910: r-modes, gravitational waves and the case for continued timing
We discuss the unique spin evolution of the young X-ray pulsar PSR
J0537-6910, a system in which the regular spin down is interrupted by glitches
every few months. Drawing on the complete timing data from the Rossi X-ray
Timing Explorer (RXTE, from 1999-2011), we argue that a trend in the
inter-glitch behaviour points to an effective braking index close to ,
much larger than expected. This value is interesting because it would accord
with the neutron star spinning down due to gravitational waves from an unstable
r-mode. We discuss to what extent this, admittedly speculative, scenario may be
consistent and if the associated gravitational-wave signal would be within
reach of ground based detectors. Our estimates suggest that one may, indeed, be
able to use future observations to test the idea. Further precision timing
would help enhance the achievable sensitivity and we advocate a joint observing
campaign between the Neutron Star Interior Composition ExploreR (NICER) and the
LIGO-Virgo network.Comment: 10 pages, 4 figures, emulate ApJ forma
The dynamics of dissipative multi-fluid neutron star cores
We present a Newtonian multi-fluid formalism for superfluid neutron star
cores, focussing on the additional dissipative terms that arise when one takes
into account the individual dynamical degrees of freedom associated with the
coupled "fluids". The problem is of direct astrophysical interest as the nature
of the dissipative terms can have significant impact on the damping of the
various oscillation modes of the star and the associated gravitational-wave
signatures. A particularly interesting application concerns the
gravitational-wave driven instability of f- and r-modes. We apply the developed
formalism to two specific three-fluid systems: (i) a hyperon core in which both
Lambda and Sigma^- hyperons are present, and (ii) a core of deconfined quarks
in the colour-flavour-locked phase in which a population of neutral K^0 kaons
is present. The formalism is, however, general and can be applied to other
problems in neutron-star dynamics (such as the effect of thermal excitations
close to the superfluid transition temperature) as well as laboratory
multi-fluid systems.Comment: RevTex, no figure
A new misfit function for multimodal inversion of surface waves
Higher-mode contribution is important in surface-wave inversion because it allows more information to be exploited, increases investigation depth, and improves model resolution. A new misfit function for multimodal inversion of surface waves, based on the Haskell-Thomson matrix method, allows higher modes to be taken into account without the need to associate experimental data points to a specific mode, thus avoiding mode-misidentification errors in the retrieved velocity profiles. Computing cost is reduced by avoiding the need for calculating synthetic apparent or modal dispersion curves. Based on several synthetic and real examples with inversion results from the classical and the proposed methods, we find that correct velocity models can be retrieved through the multimodal inversion when higher modes are superimposed in the apparent dispersion-curve or when it is not trivial to determine a priori to which mode each data point of the experimental dispersion curve belongs. The main drawback of the method is related to the presence of several local minima in the misfit function. This feature makes the choice of a consistent initial model very importan
Examination of traditional botnet detection on Iot-based bots
A botnet is a collection of Internet-connected computers that have been suborned and are controlled externally for malicious purposes. Concomitant with the growth of the Internet of Things (IoT), botnets have been expanding to use IoT devices as their attack vectors. IoT devices utilise specific protocols and network topologies distinct from conventional computers that may render detection techniques ineffective on compromised IoT devices. This paper describes experiments involving the acquisition of several traditional botnet detection techniques, BotMiner, BotProbe, and BotHunter, to evaluate their capabilities when applied to IoT-based botnets. Multiple simulation environments, using internally developed network traffic generation software, were created to test these techniques on traditional and IoT-based networks, with multiple scenarios differentiated by the total number of hosts, the total number of infected hosts, the botnet command and control (CnC) type, and the presence of aberrant activity. Externally acquired datasets were also used to further test and validate the capabilities of each botnet detection technique. The results indicated, contrary to expectations, that BotMiner and BotProbe were able to detect IoT-based botnets—though they exhibited certain limitations specific to their operation. The results show that traditional botnet detection techniques are capable of detecting IoT-based botnets and that the different techniques may offer capabilities that complement one another
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