597 research outputs found
The complete set of solutions of the geodesic equations in the space-time of a Schwarzschild black hole pierced by a cosmic string
We study the geodesic equations in the space-time of a Schwarzschild black
hole pierced by an infinitely thin cosmic string and give the complete set of
analytical solutions of these equations for massive and massless particles,
respectively. The solutions of the geodesic equations can be classified
according to the particle's energy and angular momentum, the ratio between the
component of the angular momentum aligned with the axis of the string and the
total angular momentum, the deficit angle of the space-time and as well the
horizon radius (or mass) of the black hole. For bound orbits of massive test
particles we calculate the perihelion shift, we discuss light deflection and
comment on the Newtonian limit.Comment: 21 pages; section 3 shortened, references added; accepted for
publication in Phys. Rev.
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Functional morphology and efficiency of the antenna cleaner in Camponotus rufifemur ants
Contamination of body surfaces can negatively affect many physiological functions. Insects have evolved different adaptations for removing contamination, including surfaces that allow passive self-cleaning and structures for active cleaning. Here, we study the function of the antenna cleaner in Camponotus rufifemur ants, a clamp-like structure consisting of a notch on the basitarsus facing a spur on the tibia, both bearing cuticular ’combs’ and ’brushes’. The ants clamp one antenna tightly between notch and
spur, pull it through, and subsequently clean the antenna cleaner itself with the mouthparts. We simulated cleaning strokes by moving notch or spur over antennae contaminated with fluorescent particles. The notch removed particles more efficiently than the spur, but both components eliminated >60% of the particles with the first stroke. Ablation of bristles, brush and comb strongly reduced the efficiency, indicating that they are essential for cleaning. To study how comb and brush remove particles of different sizes, we contaminated antennae of living ants, and anaesthetized them immediately after they had performed the first cleaning stroke. Different sized beads were trapped in distinct zones of the notch, consistent with the gap widths between cuticular outgrowths. This suggests that the antenna cleaner operates like a series of sieves that remove the largest objects first, followed by smaller ones, down to the smallest particles that get caught by adhesion.To AH: Research grant from the Konrad-Adenauer-Foundation
To DL: Research grant from the Cusanuswerk
To WF: UK Biotechnology and Biological Sciences Research Council (BB/I008667/1)This is the final version of the article. It first appeared from RSC via http://dx.doi.org/10.1098/rsos.15012
Analytic treatment of complete and incomplete geodesics in Taub-NUT space-times
We present the complete set of analytical solutions of the geodesic equation
in Taub-NUT space-times in terms of the Weierstrass elliptic function. We
systematically study the underlying polynomials and characterize the motion of
test particles by its zeros. Since the presence of the "Misner string" in the
Taub-NUT metric has led to different interpretations, we consider these in
terms of the geodesics of the space-time. In particular, we address the
geodesic incompleteness at the horizons discussed by Misner and Taub, and the
analytic extension of Miller, Kruskal and Godfrey, and compare with the
Reissner-Nordstr\"om space-time.Comment: 22 pages, 14 figures, accepted for publication in PR
Particle motion in the field of a five-dimensional charged black hole
In this paper, we have investigated the geodesics of neutral particles near a
five-dimensional charged black hole using a comparative approach. The effective
potential method is used to determine the location of the horizons and to study
radial and circular trajectories. This also helps us to analyze the stability
of radial and circular orbits. The radius of the innermost stable circular
orbits have also been determined. Contrary to the case of massive particles for
which, the circular orbits may have up to eight possible values of specific
radius, we find that the photons will only have two distinct values for the
specific radii of circular trajectories. Finally we have used the dynamical
systems analysis to determine the critical points and the nature of the
trajectories for the timelike and null geodesics.Comment: 15 pages, accepted for publication in Astrophysics and Space Scienc
Geodesic motion in the space-time of a cosmic string
We study the geodesic equation in the space-time of an Abelian-Higgs string
and discuss the motion of massless and massive test particles. The geodesics
can be classified according to the particles energy, angular momentum and
linear momentum along the string axis. We observe that bound orbits of massive
particles are only possible if the Higgs boson mass is smaller than the gauge
boson mass, while massless particles always move on escape orbits. Moreover,
neither massive nor massless particles can ever reach the string axis for
non-vanishing angular momentum. We also discuss the dependence of light
deflection by a cosmic string as well as the perihelion shift of bound orbits
of massive particles on the ratio between Higgs and gauge boson mass and the
ratio between symmetry breaking scale and Planck mass, respectively.Comment: 20 pages including 14 figures; v2: references added, discussion on
null geodesics extended, numerical results adde
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