9,802 research outputs found
Current-carrying string loops in black-hole spacetimes with a repulsive cosmological constant
Current-carrying string loop dynamics in Schwarzschild-de Sitter spacetimes
characterized by the cosmological parameter {\lambda}=1/3{\Lambda}M^2 is
investigated. With attention concentrated to the axisymmetric motion of string
loops it is shown that the resulting motion is governed by the presence of an
outer tension barrier and an inner angular momentum barrier that are influenced
by the black hole gravitational field given by the mass M and the cosmic
repulsion given by the cosmological constant {\Lambda}. The gravitational
attraction could cause capturing of the string having low energy by the black
hole or trapping in its vicinity; with high enough energy, the string can
escape (scatter) to infinity. The role of the cosmic repulsion becomes
important in vicinity of the so-called static radius where the gravitational
attraction is balanced by the cosmic repulsion-it is demonstrated both in terms
of the effective potential of the string motion and the basin boundary method
reflecting its chaotic character, that a potential barrier exists along the
static radius behind which no trapped oscillations may exist. The trapped
states of the string loops, governed by the interplay of the gravitating mass M
and the cosmic repulsion, are allowed only in Schwarzschild-de Sitter
spacetimes with the cosmological parameter {\lambda}<{\lambda}_trap 0.00497.
The trapped oscillations can extend close to the radius of photon circular
orbit, down to r_mt 3.3M.Comment: 21 pages, 22 figure
A comment on a paper by Carot et al
In a recent paper Carot et al. considered carefully the definition of
cylindrical symmetry as a specialisation of the case of axial symmetry. One of
their propositions states that if there is a second Killing vector, which
together with the one generating the axial symmetry, forms the basis of a
two-dimensional Lie algebra, then the two Killing vectors must commute, thus
generating an Abelian group. In this comment a similar result, valid under
considerably weaker assumptions, is recalled: any two-dimensional Lie
transformation group which contains a one-dimensional subgroup whose orbits are
circles, must be Abelian. The method used to prove this result is extended to
apply to three-dimensional Lie transformation groups. It is shown that the
existence of a one-dimensional subgroup with closed orbits restricts the
Bianchi type of the associated Lie algebra to be I (Abelian), II, III, VII_0,
VIII or IX. The relationship between the present approach and that of the
original paper is discussed.Comment: 6 pages, Te
Seeing Light from a Different Angle: The Effects of Diffuse Light Environments on the Function, Structure, and Growth of Tomato Plants
While considerable attention has been paid to how plants respond to changes in the spectral distribution, less attention has been paid to how plants respond to changes in the angular qualities of light. Evidence from both leaf- and ecosystem-scale measurements indicate that plants vary in their response to diffuse compared to direct light growing environments. Because of the significant implications for agricultural production, we quantified how changes in the angular quality of light affect the structure, function, and growth of Roma tomatoes in a greenhouse experiment with direct and diffuse light treatments. Diffuse light conditions (ca. 50-60% diffuse) were created with a glass coating that scattered incoming light. We measured leaf physiology and structure, as well as whole plant physiology, morphology, and growth. Light-saturated photosynthetic rates were set by the growing light environment and were unchanged by short-term exposure to the opposite light environment. After two months, plants in the diffuse light treatment demonstrated lower photosynthesis and had thinner leaves with higher chlorophyll concentration. However, relative growth rates did not differ between treatments and plants grown in diffuse light had significantly higher biomass at the conclusion of the experiment. While there was no difference in leaf or whole-plant water-use efficiency, plants in the diffuse light treatment demonstrated significantly lower leaf temperatures, highlighting the potential for diffuse light coatings and/or materials to reduce energy use for cooling. Our results highlight the need to advance our understanding of the effects of diffuse light conditions on agricultural crops growing on a changing planet
Cytokine-regulated expression of survivin in myeloid leukemia
: Survivin, a member of the inhibitors-of-apoptosis gene family, is expressed in a cell-cycle-dependent manner in all the most common cancers but not in normal differentiated adult tissues. Survivin expression and regulation were examined in acute myeloid leukemia (AML). Survivin was detected by Western blot analysis in all myeloid leukemia cell lines and in 16 of 18 primary AML samples tested. In contrast, normal CD34(+) cells and normal peripheral blood mononuclear cells expressed no or very low levels of survivin. Cytokine stimulation increased survivin expression in leukemic cell lines and in primary AML samples. In cultured primary samples, single-cytokine stimulation substantially increased survivin expression in comparison with control cells, and the combination of G-CSF, GM-CSF, and SCF increased survivin levels even further. Conversely, all-trans retinoic acid significantly decreased survivin protein levels in HL-60, OCI-AML3, and NB-4 cells within 96 hours, parallel to the induction of myelomonocytic differentiation. Using selective pharmacologic inhibitors, the differential involvement of mitogen-activated protein kinase kinase (MEK) and phosphatidylinositol-3 kinase (PI3K) pathways were demonstrated in the regulation of survivin expression. The MEK inhibitor PD98059 down-regulated survivin expression in both resting and GM-CSF-stimulated OCI-AML3 cells, whereas the PI3K inhibitor LY294002 inhibited survivin expression only on GM-CSF stimulation. In conclusion, these results demonstrate that survivin is highly expressed and cytokine-regulated in myeloid leukemias and suggest that hematopoietic cytokines exert their antiapoptotic and mitogenic effects, at least in part, by increasing survivin levels
The most general axially symmetric electrovac spacetime adimitting separable equations of motion
We obtain the most general solution of the Einstein electro - vacuum equation
for the stationary axially symmetric spacetime in which the Hamilton-Jacobi and
Klein - Gordon equations are separable. The most remarkable feature of the
solution is its invariance under the duality transformation involving mass and
NUT parameter, and the radial and angle coordinates. It is the general solution
for a rotating (gravitational dyon) particle which is endowed with both
gravoelectric and gravomagnetic charges, and there exists a duality
transformation from one to the other. It also happens to be a transform of the
Kerr - NUT solution. Like the Kerr family, it is also possible to make this
solution radiating which asymptotically conforms to the Vaidya null radiation.Comment: 9 pages, RevTex, Accepted by Class. Quantum Grav. Title, Abstract and
some expressions have been modified, typos corrected. The solution and main
result remain unaltere
Seeing Light from a Different Angle: The Effects of Diffuse Light Environments on the Function, Structure, and Growth of Tomato Plants
While considerable attention has been paid to how plants respond to changes in the spectral distribution, less attention has been paid to how plants respond to changes in the angular qualities of light. Evidence from both leaf- and ecosystem-scale measurements indicate that plants vary in their response to diffuse compared to direct light growing environments. Because of the significant implications for agricultural production, we quantified how changes in the angular quality of light affect the structure, function, and growth of Roma tomatoes in a greenhouse experiment with direct and diffuse light treatments. Diffuse light conditions (ca. 50-60% diffuse) were created with a glass coating that scattered incoming light. We measured leaf physiology and structure, as well as whole plant physiology, morphology, and growth. Light-saturated photosynthetic rates were set by the growing light environment and were unchanged by short-term exposure to the opposite light environment. After two months, plants in the diffuse light treatment demonstrated lower photosynthesis and had thinner leaves with higher chlorophyll concentration. However, relative growth rates did not differ between treatments and plants grown in diffuse light had significantly higher biomass at the conclusion of the experiment. While there was no difference in leaf or whole-plant water-use efficiency, plants in the diffuse light treatment demonstrated significantly lower leaf temperatures, highlighting the potential for diffuse light coatings and/or materials to reduce energy use for cooling. Our results highlight the need to advance our understanding of the effects of diffuse light conditions on agricultural crops growing on a changing planet
Electromagnetic Properties of Kerr-Anti-de Sitter Black Holes
We examine the electromagnetic properties of Kerr-anti-de Sitter (Kerr-AdS)
black holes in four and higher spacetime dimensions. Assuming that the black
holes may carry a test electric charge we show that the Killing one-form which
represents the difference between the timelike generators in the spacetime and
in the reference background can be used as a potential one-form for the
associated electromagnetic field. In four dimensions the potential one-form and
the Kerr-AdS metric with properly re-scaled mass parameter solve the
Einstein-Maxwell equations, thereby resulting in the familiar Kerr-Newman-AdS
solution. We solve the quartic equation governing the location of the event
horizons of the Kerr-Newman-AdS black holes and present closed analytic
expressions for the radii of the horizons. We also compute the gyromagnetic
ratio for these black holes and show that it corresponds to g=2 just as for
ordinary black holes in asymptotically flat spacetime. Next, we compute the
gyromagnetic ratio for the Kerr-AdS black holes with a single angular momentum
and with a test electric charge in all higher dimensions. The gyromagnetic
ratio crucially depends on the dimensionless ratio of the rotation parameter to
the curvature radius of the AdS background. At the critical limit, when the
boundary Einstein universe is rotating at the speed of light, it tends to g=2
irrespective of the spacetime dimension. Finally, we consider the case of a
five dimensional Kerr-AdS black hole with two angular momenta and show that it
possesses two distinct gyromagnetic ratios in accordance with its two
orthogonal 2-planes of rotation. In the special case of two equal angular
momenta, the two gyromagnetic ratios merge into one leading to g=4 at the
maximum angular velocities of rotation.Comment: Typos corrected; 31 pages, REVTe
Aberrational Effects for Shadows of Black Holes
In this paper, we discuss how the shadow of a Kerr black hole depends on the
motion of the observer. In particular, we derive an analytical formula for the
boundary curve of the shadow for an observer moving with given four-velocity at
given Boyer--Lindquist coordinates. We visualize the shadow for various values
of parameters.Comment: 12 pages, 3 figures; Proceedings of the 524. WE-Heraeus-Seminar held
at the Physikzentrum, Bad Honnef, Germany, 17.--23.2.201
A local characterisation for static charged black holes
We obtain a purely local characterisation that singles out the
Majumdar-Papapetrou class, the near-horizon Bertotti-Robinson geometry and the
Reissner-Nordstr\"om exterior solution, together with its plane and hyperbolic
counterparts, among the static electrovacuum spacetimes. These five classes are
found to form the whole set of static Einstein-Maxwell fields without sources
and conformally flat space of orbits, this is, the conformastat electrovacuum
spacetimes. The main part of the proof consists in showing that a functional
relationship between the gravitational and electromagnetic potentials must
always exist. The classification procedure provides also an improved
characterisation of Majumdar-Papapetrou, by only requiring a conformally flat
space of orbits with a vanishing Ricci scalar of the usual conveniently
rescaled 3-metric. A simple global consideration allows us to state that the
asymptotically flat subset of the Majumdar-Papapetrou class and the
Reissner-Nordstr\"om exterior solution are the only asymptotically flat
conformastat electrovacuum spacetimes.Comment: LaTeX; 31 pages. Uses iopart style file
Local free-fall temperature of a RN-AdS black hole
We use the global embedding Minkowski space (GEMS) geometries of a
(3+1)-dimensional curved Reissner-Nordstr\"om(RN)-AdS black hole spacetime into
a (5+2)-dimensional flat spacetime to define a proper local temperature, which
remains finite at the event horizon, for freely falling observers outside a
static black hole. Our extended results include the known limiting cases of the
RN, Schwarzschild--AdS, and Schwarzschild black holes.Comment: 18 pages, 11 figures, version to appear in Int. J. Mod. Phys.
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