186 research outputs found
Are physical objects necessarily burnt up by the blue sheet inside a black hole?
The electromagnetic radiation that falls into a Reissner-Nordstrom black hole
develops a ``blue sheet'' of infinite energy density at the Cauchy horizon. We
consider classical electromagnetic fields (that were produced during the
collapse and then backscattered into the black hole), and investigate the
blue-sheet effects of these fields on infalling objects within a simplified
model. These effects are found to be finite and even negligible for typical
parameters.Comment: 13 pages, ordinary LaTex. Accepted for Physical Review Letters
Fuel-cell performance of multiply-crosslinked polymer electrolyte membranes prepared by two-step radiation technique
A multiply-crosslinked polymer electrolyte membrane was
prepared by the radiation-induced co-grafting of styrene and a
bis(vinyl phenyl)ethane (BVPE) crosslinker into a
radiation-crosslinked polytetrafluoroethylene (cPTFE) film. We
then investigated its H2/O2 fuel-cell performance at 60 and 80ºC in
terms of the effect of radiation and chemical crosslinking. At 60ºC,
all the membranes initially exhibited similar performance, but only
the cPTFE-based membranes were durable at 80ºC, indicating the
necessity of radiation crosslinking in the PTFE main chains.
Importantly, cell performance of the multiply-crosslinked
membrane was found high enough to reach that of a Nafion112
membrane. This is probably because the BVPE crosslinks in the
graft component improved the membrane-electrode interface in
addition to membrane durability. After severe OCV hold tests at 80
and 95ºC, the performance deteriorated, while no significant
change was observed in ohmic resistivity. Accordingly, our
membranes seemed so chemically stable that an influence on
overall performance loss could be negligible
Group Scheduling in a Cellular Manufacturing Shop to Minimise Total Tardiness and nT: a Comparative Genetic Algorithm and Mathematical Modelling Approach
In this paper, family and job scheduling in a cellular manufacturing shop is addressed where jobs have individual due dates. The objectives are to minimise total tardiness and the number of tardy jobs. Family splitting among cells is allowed but job splitting is not. Two optimisation methods are employed in order to solve this problem, namely mathematical modelling (MM) and genetic algorithm (GA). The results showed that GA found the optimal solution for most of the problems with high frequency. Furthermore, the proposed GA is efficient compared to the MM especially for larger problems in terms of execution times. Other critical aspects of the problem such as family preemption only, impact of family splitting on common due date scenarios and dual objective scenarios are also solved. In short, the proposed comparative approach provides critical insights for the group scheduling problem in a cellular manufacturing shop with distinctive cases
On the gravitational field of static and stationary axial symmetric bodies with multi-polar structure
We give a physical interpretation to the multi-polar Erez-Rozen-Quevedo
solution of the Einstein Equations in terms of bars. We find that each
multi-pole correspond to the Newtonian potential of a bar with linear density
proportional to a Legendre Polynomial. We use this fact to find an integral
representation of the function. These integral representations are
used in the context of the inverse scattering method to find solutions
associated to one or more rotating bodies each one with their own multi-polar
structure.Comment: To be published in Classical and Quantum Gravit
Sustainability Organic Agriculture and Livestock Production with Respect to European Union in Eastern Anatolia and East Black Sea Regions
The majority of farm households in Turkey and especially the Eastern Anatolia are still based on low-input semi subsistence agriculture and livestock production. Despite a slow decline in recent years, agriculture and livestock production remains a major employer in Turkey and it is a significant contributor to the country’s gross domestic product, GDP. Whist Turkey is one of the EU candidate countries, is self sufficient in food production and Turkish agriculture is poorly structured inefficient, with farming in the Eastern Anatolia being mainly subsistence farming. Yet, these traditional rural structures combined with poor access to low level of education and low level of off-farm unemployment problem makes the situation more complicated and unsustainable. The best way to promote sustainability, better and higher production of Eastern Anatolian and rural Turkey is to invest in the local people, villages through improved, continuing and effective agricultural and livestock programs in particular. Investment in human capital especially in the rural areas leads to more employment opportunities through entrepreneurship and innovation in organic agriculture and livestock production. A holistic approach to developing and improving supply chains could unlock the potential for sophisticated, state-of-the-art organic agriculture and livestock producers and businesses in the region to become EU and global players. Eastern Anatolian livestock producers and the farmers have the ambitions to take part in future progress because the region is naturally organic not by design but default. It is for sure that present potential of the region has not been fully determined and utilized. EU has greatly benefited from previous enlargements economically, politically and socially. When European Union (EU) and Turkish Government relations considered and accession of Turkey to EU would be the logical consequence of the previous accessions. The screening on chapter 11 (Agriculture and rural development) is one of the important criteria and Turkey is working on to meet these benchmarks
Toward an optimal search strategy of optical and gravitational wave emissions from binary neutron star coalescence
Observations of an optical source coincident with gravitational wave emission
detected from a binary neutron star coalescence will improve the confidence of
detection, provide host galaxy localisation, and test models for the
progenitors of short gamma ray bursts. We employ optical observations of three
short gamma ray bursts, 050724, 050709, 051221, to estimate the detection rate
of a coordinated optical and gravitational wave search of neutron star mergers.
Model R-band optical afterglow light curves of these bursts that include a
jet-break are extrapolated for these sources at the sensitivity horizon of an
Advanced LIGO/Virgo network. Using optical sensitivity limits of three
telescopes, namely TAROT (m=18), Zadko (m=21) and an (8-10) meter class
telescope (m=26), we approximate detection rates and cadence times for imaging.
We find a median coincident detection rate of 4 yr^{-1} for the three bursts.
GRB 050724 like bursts, with wide opening jet angles, offer the most optimistic
rate of 13 coincident detections yr^{-1}, and would be detectable by Zadko up
to five days after the trigger. Late time imaging to m=26 could detect off-axis
afterglows for GRB 051221 like bursts several months after the trigger. For a
broad distribution of beaming angles, the optimal strategy for identifying the
optical emissions triggered by gravitational wave detectors is rapid response
searches with robotic telescopes followed by deeper imaging at later times if
an afterglow is not detected within several days of the trigger.Comment: 6 pages, 1 figure, Accepted for publication in MNRAS Letters (2011
April 22
QED blue-sheet effects inside black holes
The interaction of the unboundedly blue-shifted photons of the cosmic
microwave background radiation with a physical object falling towards the inner
horizon of a Reissner-Nordstrom black hole is analyzed. To evaluate this
interaction we consider the QED effects up to the second order in the
perturbation expansion. We then extrapolate the QED effects up to a cutoff,
which we introduce at the Planckian level. (Our results are not sensitive to
the cutoff energy.) We find that the energy absorbed by an infalling observer
is finite, and for typical parameters would not lead to a catastrophic heating.
However, this interaction would almost certainly be fatal for a human being, or
other living organism of similar size. On the other hand, we find that smaller
objects may survive the interaction. Our results do not provide support to the
idea that the Cauchy horizon is to be regarded as the boundary of spacetime.Comment: 6 pages, LaTeX. To appear in Phys. Rev.
Astrophysics from data analysis of spherical gravitational wave detectors
The direct detection of gravitational waves will provide valuable
astrophysical information about many celestial objects. Also, it will be an
important test to general relativity and other theories of gravitation. The
gravitational wave detector SCHENBERG has recently undergone its first test
run. It is expected to have its first scientific run soon. In this work the
data analysis system of this spherical, resonant mass detector is tested
through the simulation of the detection of gravitational waves generated during
the inspiralling phase of a binary system. It is shown from the simulated data
that it is not necessary to have all six transducers operational in order to
determine the source's direction and the wave's amplitudes.Comment: 8 pages and 3 figure
Time-Translation Invariance of Scattering Maps and Blue-Shift Instabilities on Kerr Black Hole Spacetimes
In this paper, we provide an elementary, unified treatment of two distinct
blue-shift instabilities for the scalar wave equation on a fixed Kerr black
hole background: the celebrated blue-shift at the Cauchy horizon (familiar from
the strong cosmic censorship conjecture) and the time-reversed red-shift at the
event horizon (relevant in classical scattering theory).
Our first theorem concerns the latter and constructs solutions to the wave
equation on Kerr spacetimes such that the radiation field along the future
event horizon vanishes and the radiation field along future null infinity
decays at an arbitrarily fast polynomial rate, yet, the local energy of the
solution is infinite near any point on the future event horizon. Our second
theorem constructs solutions to the wave equation on rotating Kerr spacetimes
such that the radiation field along the past event horizon (extended into the
black hole) vanishes and the radiation field along past null infinity decays at
an arbitrarily fast polynomial rate, yet, the local energy of the solution is
infinite near any point on the Cauchy horizon.
The results make essential use of the scattering theory developed in [M.
Dafermos, I. Rodnianski and Y. Shlapentokh-Rothman, A scattering theory for the
wave equation on Kerr black hole exteriors, preprint (2014) available at
\url{http://arxiv.org/abs/1412.8379}] and exploit directly the time-translation
invariance of the scattering map and the non-triviality of the transmission
map.Comment: 26 pages, 12 figure
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