4,699 research outputs found
NHS research ethics committees : still need more common sense and less bureaucracy
National Health Service research ethics committees exist to ensure that research performed within the NHS complies with recognised ethical standards and to protect the rights, safety, and dignity of all actual or potential participants. In the past decade the operation of research ethics committees has come under, and continues to come under, close scrutiny. Researchers now consider the process of acquiring ethical approval to be so onerous that it is compromising clinical research. Medical educators also think that the process is too unwieldy to allow undergraduate students to acquire research experience, an essential learning outcome required by the General Medical Council
Hiding in the Shadows II: Collisional Dust as Exoplanet Markers
Observations of the youngest planets (1-10 Myr for a transitional disk)
will increase the accuracy of our planet formation models. Unfortunately,
observations of such planets are challenging and time-consuming to undertake
even in ideal circumstances. Therefore, we propose the determination of a set
of markers that can pre-select promising exoplanet-hosting candidate disks. To
this end, N-body simulations were conducted to investigate the effect of an
embedded Jupiter mass planet on the dynamics of the surrounding planetesimal
disk and the resulting creation of second generation collisional dust. We use a
new collision model that allows fragmentation and erosion of planetesimals, and
dust-sized fragments are simulated in a post process step including
non-gravitational forces due to stellar radiation and a gaseous protoplanetary
disk. Synthetic images from our numerical simulations show a bright double ring
at 850 m for a low eccentricity planet, whereas a high eccentricity planet
would produce a characteristic inner ring with asymmetries in the disk. In the
presence of first generation primordial dust these markers would be difficult
to detect far from the orbit of the embedded planet, but would be detectable
inside a gap of planetary origin in a transitional disk.Comment: Accepted for publication in Ap
Separability of Black Holes in String Theory
We analyze the origin of separability for rotating black holes in string
theory, considering both massless and massive geodesic equations as well as the
corresponding wave equations. We construct a conformal Killing-Stackel tensor
for a general class of black holes with four independent charges, then identify
two-charge configurations where enhancement to an exact Killing-Stackel tensor
is possible. We show that further enhancement to a conserved Killing-Yano
tensor is possible only for the special case of Kerr-Newman black holes. We
construct natural null congruences for all these black holes and use the
results to show that only the Kerr-Newman black holes are algebraically special
in the sense of Petrov. Modifying the asymptotic behavior by the subtraction
procedure that induces an exact SL(2)^2 also preserves only the conformal
Killing-Stackel tensor. Similarly, we find that a rotating Kaluza-Klein black
hole possesses a conformal Killing-Stackel tensor but has no further
enhancements.Comment: 27 page
THE UNIQUENESS THEOREM FOR ROTATING BLACK HOLE SOLUTIONS OF SELF-GRAVITATING HARMONIC MAPPINGS
We consider rotating black hole configurations of self-gravitating maps from
spacetime into arbitrary Riemannian manifolds. We first establish the
integrability conditions for the Killing fields generating the stationary and
the axisymmetric isometry (circularity theorem). Restricting ourselves to
mappings with harmonic action, we subsequently prove that the only stationary
and axisymmetric, asymptotically flat black hole solution with regular event
horizon is the Kerr metric. Together with the uniqueness result for
non-rotating configurations and the strong rigidity theorem, this establishes
the uniqueness of the Kerr family amongst all stationary black hole solutions
of self-gravitating harmonic mappings.Comment: 18 pages, latex, no figure
The sensory features of a food cue influence its ability to act as an incentive stimulus and evoke dopamine release in the nucleus accumbens core
The sensory properties of a reward-paired cue (a Conditioned Stimulus; CS) may impact the motivational value attributed to the cue, and in turn influence the form of the conditioned response (CR) that develops. A cue with multiple sensory qualities, such as a moving lever-CS, may activate numerous neural pathways that process auditory and visual information, resulting in CRs that vary both within and between individuals. For example, CRs include approach to the lever-CS itself (rats that âsign-track;â ST), approach to the location of reward delivery (rats that âgoal-track;â GT), or an âintermediateâ combination of these behaviors. We found that the multimodal sensory features of the lever-CS were important to the development and expression of sign-tracking. When the lever-CS was covered, and thus could only be heard moving, STs continued to approach the lever location, but also started to approach the food cup during the CS period. While still predictive of reward, the auditory component of the lever-CS was a much weaker conditioned reinforcer than the visible lever-CS. This plasticity in behavioral responding observed in STs closely resembled behaviors normally seen in rats classified as âintermediates.â Furthermore, the ability of both the lever-CS and reward-delivery to evoke dopamine release in the nucleus accumbens was also altered by covering the lever â dopamine signaling in STs resembled neurotransmission observed in rats that normally only GT. These data suggest that while the visible lever-CS was attractive, wanted, and had incentive value for STs, when presented in isolation the auditory component of the cue was simply predictive of reward, lacking incentive salience. Therefore, the specific sensory features of cues may differentially contribute to responding and ensure behavioral flexibility
Discovering the Growth Histories of Exoplanets: The Saturn Analog HD 149026b
The transiting "hot Saturn" HD 149026b, which has the highest mean density of
any confirmed planet in the Neptune-Jupiter mass range, has challenged theories
of planet formation since its discovery in 2005. Previous investigations could
not explain the origin of the planet's 45-110 Earth-mass solid core without
invoking catastrophes such as gas giant collisions or heavy planetesimal
bombardment launched by neighboring planets. Here we show that HD 149026b's
large core can be successfully explained by the standard core accretion theory
of planet formation. The keys to our reconstruction of HD 149026b are (1)
applying a model of the solar nebula to describe the protoplanet nursery; (2)
placing the planet initially on a long-period orbit at Saturn's heliocentric
distance of 9.5 AU; and (3) adjusting the solid mass in the HD 149026 disk to
twice that of the solar nebula in accordance with the star's heavy element
enrichment. We show that the planet's migration into its current orbit at 0.042
AU is consistent with our formation model. Our study of HD 149026b demonstrates
that it is possible to discover the growth history of any planet with a
well-defined core mass that orbits a solar-type star.Comment: 20 pages, including 3 figures. Accepted for publication in ApJ
letters. Discussion updated to include new NICMOS transit photometry (Carter
et al. 2009
Rotation and the AdS/CFT correspondence
In asymptotically flat space a rotating black hole cannot be in thermodynamic
equilibrium because the thermal radiation would have to be co-rotating faster
than light far from the black hole. However in asymptotically anti-de Sitter
space such equilibrium is possible for certain ranges of the parameters. We
examine the relationship between conformal field theory in rotating Einstein
universes of dimensions two to four and Kerr anti-de Sitter black holes in
dimensions three to five. The five dimensional solution is new. We find similar
divergences in the partition function of the conformal field theory and the
action of the black hole at the critical angular velocity at which the Einstein
rotates at the speed of light. This should be an interesting limit in which to
study large Yang-Mills.Comment: 24 pages, RevTeX, 1 figure, references adde
Extrema of Mass, First Law of Black Hole Mechanics and Staticity Theorem in Einstein-Maxwell-axion-dilaton Gravity
Using the ADM formulation of the Einstein-Maxwell axion-dilaton gravity we
derived the formulas for the variation of mass and other asymptotic conserved
quantities in the theory under consideration. Generalizing this kind of
reasoning to the initial dota for the manifold with an interior boundary we got
the generalized first law of black hole mechanics. We consider an
asymptotically flat solution to the Einstein-Maxwell axion-dilaton gravity
describing a black hole with a Killing vector field timelike at infinity, the
horizon of which comprises a bifurcate Killing horizon with a bifurcate
surface. Supposing that the Killing vector field is asymptotically orthogonal
to the static hypersurface with boundary S and compact interior, we find that
the solution is static in the exterior world, when the timelike vector field is
normal to the horizon and has vanishing electric and axion- electric fields on
static slices.Comment: 17 pages, Revtex, a few comments (introduction) and references adde
A nonstationary generalization of the Kerr congruence
Making use of the Kerr theorem for shear-free null congruences and of
Newman's representation for a virtual charge ``moving'' in complex space-time,
we obtain an axisymmetric time-dependent generalization of the Kerr congruence,
with a singular ring uniformly contracting to a point and expanding then to
infinity. Electromagnetic and complex eikonal field distributions are naturally
associated with the obtained congruence, with electric charge being
necesssarily unit (``elementary''). We conjecture that the corresponding
solution to the Einstein-Maxwell equations could describe the process of
continious transition of the naked ringlike singularitiy into a rotating black
hole and vice versa, under a particular current radius of the singular ring.Comment: 6 pages, twocolum
Uniqueness and non-uniqueness of static vacuum black holes in higher dimensions
We prove the uniqueness theorem for asymptotically flat static vacuum black
hole solutions in higher dimensional space-times. We also construct infinitely
many non-asymptotically flat regular static black holes on the same spacetime
manifold with the same spherical topology.Comment: to appear in Progress of Theoretical Physics Supplement No. 14
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