2,686 research outputs found
Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars
The innermost stable cicular orbit (ISCO) of an accretion disc orbiting a
neutron star (NS) is often assumed a unique prediction of general relativity.
However, it has been argued that ISCO also appears around highly elliptic
bodies described by Newtonian theory. In this sense, the behaviour of an ISCO
around a rotating oblate neutron star is formed by the interplay between
relativistic and Newtonian effects. Here we briefly explore the consequences of
this interplay using a straightforward analytic approach as well as numerical
models that involve modern NS equations of state. We examine the ratio K
between the ISCO radius and the radius of the neutron star. We find that, with
growing NS spin, the ratio K first decreases, but then starts to increase. This
non-monotonic behaviour of K can give rise to a neutron star spin interval in
which ISCO appears for two very different ranges of NS mass. This may strongly
affect the distribution of neutron stars that have an ISCO (ISCO-NS). When
(all) neutron stars are distributed around a high mass M0, the ISCO-NS spin
distribution is roughly the same as the spin distribution corresponding to all
neutron stars. In contrast, if M0 is low, the ISCO-NS distribution can only
have a peak around a high value of spin. Finally, an intermediate value of M0
can imply an ISCO-NS distribution divided into two distinct groups of slow and
fast rotators. Our findings have immediate astrophysical applications. They can
be used for example to distinguish between different models of high-frequency
quasiperiodic oscillations observed in low-mass NS X-ray binaries.Comment: 4 pages, 2 figures, accepted by A&A Letter
Formation of convective cells in the scrape-off layer of the CASTOR tokamak
Understanding of the scrape-off layer (SOL) physics in tokamaks requires
diagnostics with sufficient temporal and spatial resolution. This contribution
describes results of experiments performed in the SOL of the CASTOR tokamak
(R=40 cm, a = 6 cm) by means of a ring of 124 Langmuir probes surrounding the
whole poloidal cross section. The individual probes measure either the ion
saturation current of the floating potential with the spatial resolution up to
3 mm. Experiments are performed in a particular magnetic configuration,
characterized by a long parallel connection length in the SOL, L_par ~q2piR. We
report on measurements in discharges, where the edge electric field is modified
by inserting a biased electrode into the edge plasma. In particular, a complex
picture is observed, if the biased electrode is located inside the SOL. The
poloidal distribution of the floating potential appears to be strongly
non-uniform at biasing. The peaks of potential are observed at particular
poloidal angles. This is interpreted as formation of a biased flux tube, which
emanates from the electrode along the magnetic field lines and snakes q times
around the torus. The resulting electric field in the SOL is 2-dimensional,
having the radial as well as the poloidal component. It is demonstrated that
the poloidal electric field E_pol convects the edge plasma radially due to the
E_pol x B_T drift either inward or outward depending on its sign. The
convective particle flux is by two orders of magnitude larger than the
fluctuation-induced one and consequently dominates.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Severe T2-high asthma in the biologics era: European experts' opinion
The European Respiratory Biologics Forum gathered participants from 21 countries in Madrid, Spain, to discuss the management and treatment of severe asthma in the era of biologics. The current insights on the pathophysiology of severe asthma were discussed, as well as the role of respiratory biologics in clinical practice and strategies for eliminating chronic use of oral corticosteroids. The participants also highlighted the key challenges in identifying patients with severe asthma based on phenotypes, biomarkers and treatable traits, and the existing problems in patient referral to specialist care. The monitoring of treatment was debated and the need for a change towards precision medicine and personalised care was emphasised throughout the meeting. This review provides a summary of the discussions and highlights important concerns identified by the participants regarding the current management of severe asthma
Multi-machine scaling of the main SOL parallel heat flux width in tokamak limiter plasmas
As in many of today’s tokamaks, plasma start-up in ITER will be performed in limiter
configuration on either the inner or outer midplane first wall (FW). The massive, beryllium
armored ITER FW panels are toroidally shaped to protect panel-to-panel misalignments,
increasing the deposited power flux density compared with a purely cylindrical surface.
The chosen shaping should thus be optimized for a given radial profile of parallel heat flux,
q in the scrape-off layer (SOL) to ensure optimal power spreading. For plasmas limited
on the outer wall in tokamaks, this profile is commonly observed to decay exponentially
as q q = − exp ( / r λ ) 0 q omp , or, for inner wall limiter plasmas with the double exponential
decay comprising a sharp near-SOL feature and a broader main SOL width, λq
omp. The initial choice of λq
omp
, which is critical in ensuring that current ramp-up or down will be
possible as planned in the ITER scenario design, was made on the basis of an extremely
restricted L-mode divertor dataset, using infra-red thermography measurements on the
outer divertor target to extrapolate to a heat flux width at the main plasma midplane. This
unsatisfactory situation has now been significantly improved by a dedicated multi-machine
ohmic and L-mode limiter plasma study, conducted under the auspices of the International
Tokamak Physics Activity, involving 11 tokamaks covering a wide parameter range with
R = = 0.4–2.8 m, 1 B I 0 p .2–7.5 T, = 9–2500 kA. Measurements of λq
omp
in the database
are made exclusively on all devices using a variety of fast reciprocating Langmuir probes
entering the plasma at a variety of poloidal locations, but with the majority being on the
low field side. Statistical analysis of the database reveals nine reasonable engineering
and dimensionless scalings. All yield, however, similar predicted values of λq
omp
mapped
to the outside midplane. The engineering scaling with the highest statistical significance,
λ = ( / ( )) ( / /κ) − −
q 10 P V W m a R omp tot 3 0.38 1.3
, dependent on input power density, aspect ratio and elongation, yields λq omp = [7, 4, 5] cm for Ip = [2.5, 5.0, 7.5] MA, the three reference limiter plasma currents specified in the ITER heat and nuclear load specifications. Mapped to the inboard midplane, the worst case (7.5 MA) corresponds to λq ~ 57 1 ± 4 imp mm, thus consolidating the 50mm width used to optimize the FW panel toroidal shape.EURATOM 633053Czech Science Foundation GA CR P205/12/2327, GA15-10723S, MSMT LM2011021US Department of Energy DE-FG02- 07ER54917, DE-AC02-09CH11466, DE-FC02-04ER5469
‘Hunger would kill us instead of COVID-19’: Elders' response to the pandemic in Debre Markos Town, Ethiopia
The COVID-19 pandemic has posed unpredictable challenges globally. Older adults are among the population groups most vulnerable to COVID-19. Poor urban elders in Ethiopia struggle to meet their basic needs due to waning traditional familial norms of providing care for elders as a result of urbanisation, poverty and migration. The aim of this study was to give voice to vulnerable elders during the COVID-19 lockdown in Ethiopia and to reveal their sources of support. Using a qualitative case study design, data were collected from 27 elders aged 60 and above in Debre Markos Town, Ethiopia via in-depth interviews conducted from March–May 2020. To determine the nature of support provided for destitute elders, data were also gathered from two local officials. Narrative data were analysed using thematic analysis. Four prominent themes were identified: ‘Hunger would kill us instead of COVID-19,’ ‘Feeling hopeless and begging to die,’ ‘We prefer social support rather than food donations’ and ‘Gratitude.’ Elders considered the practice of social distancing to fight COVID-19 as an unwelcome luxury for people whose livelihood depends on begging and petty trade. The physical distancing programme put elders in isolation, diminishing their capacity to maintain their livelihood. Due to the increasing disrespectful attitudes towards aged people, elders felt even less valued than usual. Interactions were described as undermining, embarrassing and abusive. A special emergency fund and organised social supports are needed to minimise the effect of the pandemic on vulnerable groups like destitute elders in Ethiopia. Moreover, an institutional welfare response is needed to ensure elders can live a dignified life
Decay of flux vacua to nothing
We construct instanton solutions describing the decay of flux
compactifications of a gauge theory by generalizing the Kaluza-Klein
bubble of nothing. The surface of the bubble is described by a smooth
magnetically charged solitonic brane whose asymptotic flux is precisely that
responsible for stabilizing the 4d compactification. We describe several
instances of bubble geometries for the various vacua occurring in a
Einstein-Maxwell theory namely, AdS_4 x S^2, R^{1,3} x S^2, and dS_4 x S^2.
Unlike conventional solutions, the bubbles of nothing introduced here occur
where a {\em two}-sphere compactification manifold homogeneously degenerates.Comment: 31 pages, 15 figure
Persistence, extinction and spatio-temporal synchronization of SIRS cellular automata models
Spatially explicit models have been widely used in today's mathematical
ecology and epidemiology to study persistence and extinction of populations as
well as their spatial patterns. Here we extend the earlier work--static
dispersal between neighbouring individuals to mobility of individuals as well
as multi-patches environment. As is commonly found, the basic reproductive
ratio is maximized for the evolutionary stable strategy (ESS) on diseases'
persistence in mean-field theory. This has important implications, as it
implies that for a wide range of parameters that infection rate will tend
maximum. This is opposite with present results obtained in spatial explicit
models that infection rate is limited by upper bound. We observe the emergence
of trade-offs of extinction and persistence on the parameters of the infection
period and infection rate and show the extinction time having a linear
relationship with respect to system size. We further find that the higher
mobility can pronouncedly promote the persistence of spread of epidemics, i.e.,
the phase transition occurs from extinction domain to persistence domain, and
the spirals' wavelength increases as the mobility increasing and ultimately, it
will saturate at a certain value. Furthermore, for multi-patches case, we find
that the lower coupling strength leads to anti-phase oscillation of infected
fraction, while higher coupling strength corresponds to in-phase oscillation.Comment: 12page
K-Space at TRECVID 2008
In this paper we describe K-Space’s participation in
TRECVid 2008 in the interactive search task. For 2008
the K-Space group performed one of the largest interactive
video information retrieval experiments conducted
in a laboratory setting. We had three institutions participating
in a multi-site multi-system experiment. In
total 36 users participated, 12 each from Dublin City
University (DCU, Ireland), University of Glasgow (GU,
Scotland) and Centrum Wiskunde and Informatica (CWI,
the Netherlands). Three user interfaces were developed,
two from DCU which were also used in 2007 as well as
an interface from GU. All interfaces leveraged the same
search service. Using a latin squares arrangement, each
user conducted 12 topics, leading in total to 6 runs per
site, 18 in total. We officially submitted for evaluation 3
of these runs to NIST with an additional expert run using
a 4th system. Our submitted runs performed around
the median. In this paper we will present an overview of
the search system utilized, the experimental setup and a
preliminary analysis of our results
Tunneling and propagation of vacuum bubbles on dynamical backgrounds
In the context of bubble universes produced by a first-order phase transition
with large nucleation rates compared to the inverse dynamical time scale of the
parent bubble, we extend the usual analysis to non-vacuum backgrounds. In
particular, we provide semi-analytic and numerical results for the modified
nucleation rate in FLRW backgrounds, as well as a parameter study of bubble
walls propagating into inhomogeneous (LTB) or FLRW spacetimes, both in the
thin-wall approximation. We show that in our model, matter in the background
often prevents bubbles from successful expansion and forces them to collapse.
For cases where they do expand, we give arguments why the effects on the
interior spacetime are small for a wide range of reasonable parameters and
discuss the limitations of the employed approximations.Comment: 29 pages, 8 figures, typos corrected, matches published versio
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