193 research outputs found
Sensitivity of Hawking radiation to superluminal dispersion relations
We analyze the Hawking radiation process due to collapsing configurations in
the presence of superluminal modifications of the dispersion relation. With
such superluminal dispersion relations, the horizon effectively becomes a
frequency-dependent concept. In particular, at every moment of the collapse,
there is a critical frequency above which no horizon is experienced. We show
that, as a consequence, the late-time radiation suffers strong modifications,
both quantitative and qualitative, compared to the standard Hawking picture.
Concretely, we show that the radiation spectrum becomes dependent on the
measuring time, on the surface gravities associated with different frequencies,
and on the critical frequency. Even if the critical frequency is well above the
Planck scale, important modifications still show up.Comment: 14 pages, 7 figures. Extensive paragraph added in conclusions to
clarify obtained result
DNA extraction from old herbarium material of Veronica subgen. Pseudolysimachium (Plantaginaceae)
Herbarium specimens have become a major source of information in molecular biodiversity research, framing the term "herbarium genomics". However, obtaining good DNA from old herbarium specimens is still a challenge. Currently, DNA extraction methods from old herbarium material often yield highly degraded and fragmented DNA. A number of studies have discussed such methods, especially how to avoid further DNA fragmentation. This study aims to compare different DNA extraction methods applied to old herbarium material from Veronica subg. Pseudolysimachium. One such method is a CTABbased DNA extraction followed by a clean-up with paramagnetic beads that is used in the Jodrell Laboratory, Royal Botanic Gardens Kew, UK. This method was compared to a modified NucleoSpin Plant II protocol, based on silica columns, as used at the Technical University Munich-Freising, which was already successfully used for extracting DNA from a Linnean type specimen. Further tests were conducted on the influence of incubation time on the CTAB DNA extraction protocol with a subsample of specimens. Our preliminary results suggest that CTAB DNA extraction might have some advantages in specific cases but also that silica column-based methods have fewer problems with contamination by polysaccharides and polyphenolic compounds. Regarding the incubation time, we did not observe a clear pattern, but we developed several ideas on how to proceed with tests to find an optimal DNA extraction protocol to deal with highly fragmented DNA. Taking practical considerations into account, the column-based method proves to be preferable, especially when trying to reduce the amount of leaf tissue used, but further modifications of both methods should be explored
Some comments on "The Mathematical Universe"
I discuss some problems related to extreme mathematical realism, focusing on
a recently proposed "shut-up-and-calculate" approach to physics
(arXiv:0704.0646, arXiv:0709.4024). I offer arguments for a moderate
alternative, the essence of which lies in the acceptance that mathematics is
(at least in part) a human construction, and discuss concrete consequences of
this--at first sight purely philosophical--difference in point of view.Comment: 11 page
The Basics of Water Waves Theory for Analogue Gravity
This chapter gives an introduction to the connection between the physics of
water waves and analogue gravity. Only a basic knowledge of fluid mechanics is
assumed as a prerequisite.Comment: 36 pages. Lecture Notes for the IX SIGRAV School on "Analogue
Gravity", Como (Italy), May 201
Transformational acoustic metamaterials based on pressure gradients
We apply a homogenization process to the acoustic velocity potential wave equation. The study of various
examples shows that the resulting effective properties are different from those of the homogenized pressure
wave equation for the same underlying acoustic parameters. A careful analysis reveals that a given set of
inhomogeneous parameters represents an entirely different physical system depending on the considered equation.
Our findings unveil a different way of tailoring acoustic properties through gradients of the static pressure. In
contrast to standard metafluids based on isobaric composites, this alternative kind of metafluid is suitable for the
implementation of transformational devices designed via the velocity potential equation. This includes acoustic
systems in a moving background or arising from general space-time transformations. As an example, we design
a device able to cloak the acoustic velocity potential.This work was developed under the framework of the ARIADNA Contract No. 4000104572/12/NL/KML of the European Space Agency. C.G.-M., J.S.-D., and A.M. also acknowledge support from Consolider project CSD2008-00066, A.M. from project TEC2011-28664-C02-02, and C.B. and G.J. from the project FIS2011-30145-C03-01. J.S.-D. acknowledges support from the USA Office of Naval Research. All authors contributed equally to this work.García Meca, C.; Carloni, S.; Barceló, C.; Jannes, GGP.; Sánchez-Dehesa Moreno-Cid, J.; Martínez Abietar, AJ. (2014). Transformational acoustic metamaterials based on pressure gradients. Physical Review B. 90(2):24310-1-24310-9. https://doi.org/10.1103/PhysRevB.90.024310S24310-124310-990
Massive gravity from bimetric gravity
We discuss the subtle relationship between massive gravity and bimetric
gravity, focusing particularly on the manner in which massive gravity may be
viewed as a suitable limit of bimetric gravity. The limiting procedure is more
delicate than currently appreciated. Specifically, this limiting procedure
should not unnecessarily constrain the background metric, which must be
externally specified by the theory of massive gravity itself. The fact that in
bimetric theories one always has two sets of metric equations of motion
continues to have an effect even in the massive gravity limit, leading to
additional constraints besides the one set of equations of motion naively
expected. Thus, since solutions of bimetric gravity in the limit of vanishing
kinetic term are also solutions of massive gravity, but the contrary statement
is not necessarily true, there is not complete continuity in the parameter
space of the theory. In particular, we study the massive cosmological solutions
which are continuous in the parameter space, showing that many interesting
cosmologies belong to this class.Comment: v1: 25 pages; v2: 6 references added, discussion streamlined; v3: 24
pages, 20 references added, section 2 summarized, new comments added to
section 3, conclusions improved but unchanged. This version accepted for
publication in Classical and Quantum Gravit
The cosmological constant: A lesson from the effective gravity of topological Weyl media
Topological matter with Weyl points, such as superfluid 3He-A, provide an
explicit example where there is a direct connection between the properly
determined vacuum energy and the cosmological constant of the effective gravity
emerging in condensed matter. This is in contrast to the acoustic gravity
emerging in Bose-Einstein condensates, where the "value of this constant cannot
be easily predicted by just looking at the ground state energy of the
microscopic system from which spacetime and its dynamics should emerge" (S.
Finazzi, S. Liberati and L. Sindoni, The cosmological constant: a lesson from
Bose-Einstein condensates, Phys. Rev. Lett. 108, 071101 (2012)). The advantage
of topological matter is that the relativistic fermions and gauge bosons
emerging near the Weyl point obey the same effective metric and thus the
effective gravity is more closely related to real gravity. We study this
connection in the bi-metric gravity emerging in 3He-A, and its relation to the
graviton masses, by comparison with a fully relativistic bi-metric theory of
gravity. This shows that the parameter \lambda, which in 3He-A is the bi-metric
generalization of the cosmological constant, coincides with the difference in
the proper energy of the vacuum in two states (the nonequilibrium state without
gravity and the equilibrium state in which gravity emerges) and is on the order
of the characteristic Planck energy scale of the system. Although the
cosmological constant \lambda\ is huge, the cosmological term itself is
naturally non-constant and vanishes in the equilibrium vacuum, as dictated by
thermodynamics. This suggests that the equilibrium state of any system
including the final state of the Universe is not gravitating.Comment: 7 pages, no figure
The DYD-RCT protocol: an on-line randomised controlled trial of an interactive computer-based intervention compared with a standard information website to reduce alcohol consumption among hazardous drinkers
Background: Excessive alcohol consumption is a significant public health problem throughout the world. Although there are a range of effective interventions to help heavy drinkers reduce their alcohol consumption, these have little proven population-level impact. Researchers internationally are looking at the potential of Internet interventions in this area.Methods/Design: In a two-arm randomised controlled trial, an on-line psychologically enhanced interactive computer-based intervention is compared with a flat, text-based information web-site. Recruitment, consent, randomisation and data collection are all on-line. The primary outcome is total past-week alcohol consumption; secondary outcomes include hazardous or harmful drinking, dependence, harm caused by alcohol, and mental health. A health economic analysis is included.Discussion: This trial will provide information on the effectiveness and cost-effectiveness of an on-line intervention to help heavy drinkers drink less.Trial registration: International Standard Randomised Controlled Trial Number Register ISRCTN31070347
The Global Research Neglect of Unassisted Smoking Cessation: Causes and Consequences
Simon Chapman and Ross MacKenzie review the evidence and argue that health promotion messages should emphasize that the most successful method used by most ex-smokers is unassisted cessation
Search for Quantum Gravity Using Astrophysical Neutrino Flavour with IceCube
Along their long propagation from production to detection, neutrino states
undergo quantum interference which converts their types, or flavours.
High-energy astrophysical neutrinos, first observed by the IceCube Neutrino
Observatory, are known to propagate unperturbed over a billion light years in
vacuum. These neutrinos act as the largest quantum interferometer and are
sensitive to the smallest effects in vacuum due to new physics. Quantum gravity
(QG) aims to describe gravity in a quantum mechanical framework, unifying
matter, forces and space-time. QG effects are expected to appear at the
ultra-high-energy scale known as the Planck energy, ~giga-electronvolts (GeV). Such a high-energy universe would have
existed only right after the Big Bang and it is inaccessible by human
technologies. On the other hand, it is speculated that the effects of QG may
exist in our low-energy vacuum, but are suppressed by the Planck energy as
(~GeV), (~GeV), or its higher powers. The coupling of particles to these
effects is too small to measure in kinematic observables, but the phase shift
of neutrino waves could cause observable flavour conversions. Here, we report
the first result of neutrino interferometry~\cite{Aartsen:2017ibm} using
astrophysical neutrino flavours to search for new space-time structure. We did
not find any evidence of anomalous flavour conversion in IceCube astrophysical
neutrino flavour data. We place the most stringent limits of any known
technologies, down to ~GeV, on the dimension-six operators
that parameterize the space-time defects for preferred astrophysical production
scenarios. For the first time, we unambiguously reach the signal region of
quantum-gravity-motivated physics.Comment: The main text is 7 pages with 3 figures and 1 table. The Appendix
includes 5 pages with 3 figure
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