166 research outputs found
Gravitational Radiation Instability in Hot Young Neutron Stars
We show that gravitational radiation drives an instability in hot young
rapidly rotating neutron stars. This instability occurs primarily in the l=2
r-mode and will carry away most of the angular momentum of a rapidly rotating
star by gravitational radiation. On the timescale needed to cool a young
neutron star to about T=10^9 K (about one year) this instability can reduce the
rotation rate of a rapidly rotating star to about 0.076\Omega_K, where \Omega_K
is the Keplerian angular velocity where mass shedding occurs. In older colder
neutron stars this instability is suppressed by viscous effects, allowing older
stars to be spun up by accretion to larger angular velocities.Comment: 4 Pages, 2 Figure
The Effect of Neutron Star Binding Energy on Gravitational-Radiation-Driven Mass-Transfer Binaries
In a relativistic model of a neutron star, the star's mass is less than the
mass of the individual component baryons. This is due to the fact that the
star's negative binding energy makes a contribution to the star's total energy
and its mass. A consequence of this relativistic mass deficit is that a neutron
star that is accreting matter increases its mass at a rate which is slower than
the mass of a baryon times the rate that baryons are accreted. This difference
in the rate of change of the masses has a simple relation with the star's
gravitational redshift. We show that this effect has the potential to be
observed in binaries where the mass transfer is driven by angular momentum
losses from the gravitational radiation emitted by the binary motion.Comment: 9 pages, 3 figures, accepted by Ap
Overview of BIM integration into the Construction Sector in European Member States and European Union Acquis
The amount of information involved in any construction project and the necessity of control of time, cost and waste, has established Building Information Modelling (BIM) as an integral part of construction sector towards achieving adequate communication of information among various parties involved in construction projects. Moreover, it can be considered as a valuable tool for the optimum selection of materials, systems and design decisions, regarding not only the improve of a structure’s performance, but also in terms of reducing its carbon footprint during its life cycle. The study attempts to present the integration of BIM into the national legislation of European Member States, with a special focus on the energy related aspects of BIM analysis. This study performs an overview of the introduction of BIM into different aspects and requirements of the EU Member States building practices, through a comprehensive literature and legislation review of relative legislative documents of the construction sector. According to the findings of this overview study, the concept of BIM has already been incorporated in many aspects of the Acquis of EU Member States, which is recognized as a valuable tool to be exploited by the construction sector, however there is still room for development in this area. The study has revealed that especially in the energy assessment of the built environment, BIM applications are still lacking from the European Legislation. Examples and good practices of employing BIM for the implementation of the European Energy targets in the building sector are also presented and discussed. The findings of this study aim to shed light on the needs and requirements in the field of BIM development for the construction sector, as well as to indicate gaps and weaknesses of the European Member States Acquis towards harmonizing with BIM practices
Measuring the neutron star equation of state using X-ray timing
One of the primary science goals of the next generation of hard X-ray timing
instruments is to determine the equation of state of the matter at supranuclear
densities inside neutron stars, by measuring the radius of neutron stars with
different masses to accuracies of a few percent. Three main techniques can be
used to achieve this goal. The first involves waveform modelling. The flux we
observe from a hotspot on the neutron star surface offset from the rotational
pole will be modulated by the star's rotation, giving rise to a pulsation.
Information about mass and radius is encoded into the pulse profile via
relativistic effects, and tight constraints on mass and radius can be obtained.
The second technique involves characterising the spin distribution of accreting
neutron stars. The most rapidly rotating stars provide a very clean constraint,
since the mass-shedding limit is a function of mass and radius. However the
overall spin distribution also provides a guide to the torque mechanisms in
operation and the moment of inertia, both of which can depend sensitively on
dense matter physics. The third technique is to search for quasi-periodic
oscillations in X-ray flux associated with global seismic vibrations of
magnetars (the most highly magnetized neutron stars), triggered by magnetic
explosions. The vibrational frequencies depend on stellar parameters including
the dense matter equation of state. We illustrate how these complementary X-ray
timing techniques can be used to constrain the dense matter equation of state,
and discuss the results that might be expected from a 10m instrument. We
also discuss how the results from such a facility would compare to other
astronomical investigations of neutron star properties. [Modified for arXiv]Comment: To appear in Reviews of Modern Physics as a Colloquium, 23 pages, 9
figure
Exact Black Hole and Cosmological Solutions in a Two-Dimensional Dilaton-Spectator Theory of Gravity
Exact black hole and cosmological solutions are obtained for a special
two-dimensional dilaton-spectator () theory of gravity. We show how
in this context any desired spacetime behaviour can be determined by an
appropriate choice of a dilaton potential function and a ``coupling
function'' in the action. We illustrate several black hole solutions
as examples. In particular, asymptotically flat double- and multiple- horizon
black hole solutions are obtained. One solution bears an interesting
resemblance to the string-theoretic black hole and contains the same
thermodynamic properties; another resembles the Reissner-Nordstrom
solution. We find two characteristic features of all the black hole solutions.
First the coupling constants in must be set equal to constants of
integration (typically the mass). Second, the spectator field and its
derivative both diverge at any event horizon. A test particle with
``spectator charge" ({\it i.e.} one coupled either to or ),
will therefore encounter an infinite tidal force at the horizon or an
``infinite potential barrier'' located outside the horizon respectively. We
also compute the Hawking temperature and entropy for our solutions. In
cosmology, two non-singular solutions which resemble two exact solutions
in string-motivated cosmology are obtained. In addition, we construct a
singular model which describes the standard non-inflationary big bang
cosmology (). Motivated by the
similaritiesbetween and gravitational field equations in
cosmology, we briefly discuss a special dilaton-spectator action
constructed from the bosonic part of the low energy heterotic string action andComment: 34 pgs. Plain Tex, revised version contains some clarifying comments
concerning the relationship between the constants of integration and the
coupling constants
Cosmological Models in Two Spacetime Dimensions
Various physical properties of cosmological models in (1+1) dimensions are
investigated. We demonstrate how a hot big bang and a hot big crunch can arise
in some models. In particular, we examine why particle horizons do not occur in
matter and radiation models. We also discuss under what circumstances
exponential inflation and matter/radiation decoupling can happen. Finally,
without assuming any particular equation of state, we show that physical
singularities can occur in both untilted and tilted universe models if certain
assumptions are satisfied, similar to the (3+1)-dimensional cases.Comment: 22 pgs., 2 figs. (available on request) (revised version contains
`paper.tex' macro file which was omitted in earlier version
CombiFlow:combinatorial AML-specific plasma membrane expression profiles allow longitudinal tracking of clones
Acute myeloid leukemia (AML) often presents as an oligoclonal disease whereby multiple genetically distinct subclones can coexist within patients. Differences in signaling and drug sensitivity of such subclones complicate treatment and warrant tools to identify them and track disease progression. We previously identified >50 AML-specific plasma membrane (PM) proteins, and 7 of these (CD82, CD97, FLT3, IL1RAP, TIM3, CD25, and CD123) were implemented in routine diagnostics in patients with AML (n = 256) and myelodysplastic syndrome (n = 33). We developed a pipeline termed CombiFlow in which expression data of multiple PM markers is merged, allowing a principal component–based analysis to identify distinctive marker expression profiles and to generate single-cell t-distributed stochastic neighbor embedding landscapes to longitudinally track clonal evolution. Positivity for one or more of the markers after 2 courses of intensive chemotherapy predicted a shorter relapse-free survival, supporting a role for these markers in measurable residual disease (MRD) detection. CombiFlow also allowed the tracking of clonal evolution in paired diagnosis and relapse samples. Extending the panel to 36 AML-specific markers further refined the CombiFlow pipeline. In conclusion, CombiFlow provides a valuable tool in the diagnosis, MRD detection, clonal tracking, and understanding of clonal heterogeneity in AML
Fermions Tunnelling from Black Holes
We investigate the tunnelling of spin 1/2 particles through event horizons.
We first apply the tunnelling method to Rindler spacetime and obtain the Unruh
temperature. We then apply fermion tunnelling to a general non-rotating black
hole metric and show that the Hawking temperature is recovered.Comment: 22 pages, v2: added references, v3: fixed minor typos, v4: added a
new section applying fermion tunnelling method to Kruskal-Szekers
coordinates, fixed minor typo, and added references, v5: modified
introduction and conclusion, fixed typo
- …