2,069 research outputs found
Gravity and Nonequilibrium Thermodynamics of Classical Matter
Renewed interest in deriving gravity (more precisely, the Einstein equations)
from thermodynamics considerations [1, 2] is stirred up by a recent proposal
that 'gravity is an entropic force' [3] (see also [4]). Even though I find the
arguments justifying such a claim in this latest proposal rather ad hoc and
simplistic compared to the original one I would unreservedly support the call
to explore deeper the relation between gravity and thermodynamics, this having
the same spirit as my long-held view that general relativity is the
hydrodynamic limit [5, 6] of some underlying theories for the microscopic
structure of spacetime - all these proposals, together with that of [7, 8],
attest to the emergent nature of gravity [9]. In this first paper of two we set
the modest goal of studying the nonequilibrium thermodynamics of classical
matter only, bringing afore some interesting prior results, without invoking
any quantum considerations such as Bekenstein-Hawking entropy, holography or
Unruh effect. This is for the sake of understanding the nonequilibrium nature
of classical gravity which is at the root of many salient features of black
hole physics. One important property of gravitational systems, from
self-gravitating gas to black holes, is their negative heat capacity, which is
the source of many out-of-the ordinary dynamical and thermodynamic features
such as the non-existence in isolated systems of thermodynamically stable
configurations, which actually provides the condition for gravitational
stability. A related property is that, being systems with long range
interaction, they are nonextensive and relax extremely slowly towards
equilibrium. Here we explore how much of the known features of black hole
thermodynamics can be derived from this classical nonequilibrium perspective. A
sequel paper will address gravity and nonequilibrium thermodynamics of quantum
fields [10].Comment: 25 pages essay. Invited Talk at Mariofest, March 2010, Rosario,
Argentina. Festschrift to appear as an issue of IJMP
Long-term survival for a cohort of adults with cerebral palsy
The aim of this study was to investigate long-term survival and examine causes of death in adult patients with cerebral palsy (CP). A 1940–1950 birth cohort based on paediatric case referral allows for long-term survival follow-up. Survival is analyzed by birth characteristics and severity of disability from age 20 years (and age 2y for a subset of the data). Survival outcome compared with that expected in the general population based on English life tables. The main cohort consisted of 341 individuals, with 193 males and 148 females. Conditional on surviving to age 20 years, almost 85% of the cohort survived to age 50 years (a comparable estimate for the general population is 96%). Very few deaths were attributed to CP for those people dying over 20 years of age. Females survived better than males. However, females faced a greater increase in risk relative to the general population than did males. We conclude that survival outlook is good though lower than in the general population. The relative risk of death compared with the UK population decreases with age, although it shows some indication of rising again after age 50 years. Many more deaths were caused by diseases of the respiratory system among those dying in their 20s and 30s than would be expected in the general population. Many fewer deaths than expected in this age group are caused by injuries and accidents. For those people who die in their 40s and 50s, an increase in deaths due to diseases of the circulatory system and neoplasms is observed. More deaths than expected in this age group are due to diseases of the nervous system
Beyond the veil: Inner horizon instability and holography
We show that scalar perturbations of the eternal, rotating BTZ black hole
should lead to an instability of the inner (Cauchy) horizon, preserving strong
cosmic censorship. Because of backscattering from the geometry, plane wave
modes have a divergent stress tensor at the event horizon, but suitable
wavepackets avoid this difficulty, and are dominated at late times by
quasinormal behavior. The wavepackets have cuts in the complexified coordinate
plane that are controlled by requirements of continuity, single-valuedness and
positive energy. Due to a focusing effect, regular wavepackets nevertheless
have a divergent stress-energy at the inner horizon, signaling an instability.
This instability, which is localized behind the event horizon, is detected
holographically as a breakdown in the semiclassical computation of dual CFT
expectation values in which the analytic behavior of wavepackets in the
complexified coordinate plane plays an integral role. In the dual field theory,
this is interpreted as an encoding of physics behind the horizon in the
entanglement between otherwise independent CFTs.Comment: 40 pages, LaTeX, 3 eps figures, v2: references adde
Excursions beyond the horizon: Black hole singularities in Yang-Mills theories (I)
We study black hole singularities in the AdS/CFT correspondence. These
singularities show up in CFT in the behavior of finite-temperature correlation
functions. We first establish a direct relation between space-like geodesics in
the bulk and momentum space Wightman functions of CFT operators of large
dimensions. This allows us to probe the regions inside the horizon and near the
singularity using the CFT. Information about the black hole singularity is
encoded in the exponential falloff of finite-temperature correlators at large
imaginary frequency. We construct new gauge invariant observables whose
divergences reflect the presence of the singularity. We also find a UV/UV
connection that governs physics inside the horizon. Additionally, we comment on
the possible resolution of the singularity.Comment: 34 page, 10 figures, uses harvmac, references adde
Hawking Radiation from AdS Black Holes
We investigate Hawking radiation from black holes in (d+1)-dimensional
anti-de Sitter space. We focus on s-waves, make use of the geometrical optics
approximation, and follow three approaches to analyze the radiation. First, we
compute a Bogoliubov transformation between Kruskal and asymptotic coordinates
and compare the different vacua. Second, following a method due to Kraus,
Parikh, and Wilczek, we view Hawking radiation as a tunneling process across
the horizon and compute the tunneling probablility. This approach uses an
anti-de Sitter version of a metric originally introduced by Painleve for
Schwarzschild black holes. From the tunneling probability one also finds a
leading correction to the semi-classical emission rate arising from the
backreaction to the background geometry. Finally, we consider a spherically
symmetric collapse geometry and the Bogoliubov transformation between the
initial vacuum state and the vacuum of an asymptotic observer.Comment: 13 pages, latex2e, v2: some clarifications and references adde
The Impact of a Simple Representation of Non-Structural Carbohydrates on the Simulated Response of Tropical Forests to Drought
This is the final version. Available on open access from European Geosciences Union via the DOI in this recordCode availability.
A model example of SUGAR for a single site and set-up to run at Caxiuanã using output from JULES is available at https://doi.org/10.5281/zenodo.3547613 (Jones, 2019). For further information or code please contact [email protected] representing the response of ecosystems to environmental change in land surface models (LSMs) is crucial to making accurate predictions of future climate. Many LSMs do not correctly capture plant respiration and growth fluxes, particularly in response to extreme climatic events. This is in part due to the unrealistic assumption that total plant carbon expenditure (PCE) is always equal to gross carbon accumulation by photosynthesis. We present and evaluate a simple model of labile carbon storage and utilisation (SUGAR) designed to be integrated into an LSM, which allows simulated plant respiration and growth to vary independent of photosynthesis. SUGAR buffers simulated PCE against seasonal variation in photosynthesis, producing more constant (less variable) predictions of plant growth and respiration relative to an LSM that does not represent labile carbon storage. This allows the model to more accurately capture observed carbon fluxes at a large-scale drought experiment in a tropical moist forest in the Amazon, relative to the Joint UK Land Environment Simulator LSM (JULES). SUGAR is designed to improve the representation of carbon storage in LSMs and provides a simple framework that allows new processes to be integrated as the empirical understanding of carbon storage in plants improves. The study highlights the need for future research into carbon storage and allocation in plants, particularly in response to extreme climate events such as drought.Natural Environment Research Council (NERC)Newton FundAustralian Research Council (ARC)Spanish Ministry of Economy and Competitiveness (MINECO)Engineering and Physical Sciences Research Council (EPSRC)JPL-Caltech President's and Director's Research & Development FundMet Office Hadley Centre Climate ProgrammeEuropean Union Horizon 202
Theoretical and practical development of the TOPSY self-management intervention for women who use a vaginal pessary for pelvic organ prolapse
Background: Pelvic organ prolapse (POP) is a common condition in women, where the downward descent of pelvic organs into the vagina causes symptoms which impacts quality of life. Vaginal pessaries offer an effective alternative to surgery for the management of POP. However, the need for regular follow-up can be burdensome for women and requires significant healthcare resources. The TOPSY study is a randomised controlled trial which aims to determine the clinical and cost-effectiveness of self-management of vaginal pessaries. This paper describes the theoretical and practical development of the self-management intervention. Methods: The intervention was developed using the MRC complex intervention framework, normalisation process theory (NPT) and self-management theory. The intervention aims to boost perceived self-efficacy in accordance with Bandura’s social cognitive theory and is guided by the tasks and skills Lorig and Hollman describe as necessary to self-manage a health condition. Results: The TOPSY intervention was designed to support women to undertake the medical management, role management and emotional management of their pessary. The six self-management skills described by Lorig and Hollman: problem-solving, decision-making, resource utilisation, formation of a patient-provider partnership role, action planning and self-tailoring, are discussed in detail, including how women were supported to achieve each task within the context of pessary self-management. The TOPSY intervention includes a self-management support session with a pessary practitioner trained in intervention delivery, a follow-up phone call 2 weeks later and ongoing telephone or face-to-face support as required by the woman initiated by contacting a member of the research team. Conclusions: The TOPSY study intervention was developed utilising the findings from a prior service development project, intervention development and self-efficacy theory, relevant literature, clinician experience and feedback from pessary using women and members of the public. In 2022, the findings of the TOPSY study will provide further evidence to inform this important aspect of pessary management. Trial registration: ISRCTN Registry ISRCTN62510577. Registered on June 10, 2017
Alpha-Vacua, Black Holes, and AdS/CFT
The Schwarzschild, Schwarzschild-AdS, and Schwarzschild-de Sitter solutions
all admit freely acting discrete involutions which commute with the continuous
symmetries of the spacetimes. Intuitively, these involutions correspond to the
antipodal map of the corresponding spacetimes. In analogy with the ordinary de
Sitter example, this allows us to construct new vacua by performing a
Mottola-Allen transform on the modes associated with the Hartle-Hawking, or
Euclidean, vacuum. These vacua are the `alpha'-vacua for these black holes. The
causal structure of a typical black hole may ameliorate certain difficulties
which are encountered in the case of de Sitter alpha-vacua. For
Schwarzschild-AdS black holes, a Bogoliubov transformation which mixes
operators of the two boundary CFT's provides a construction of the dual CFT
alpha-states. Finally, we analyze the thermal properties of these vacua.Comment: 40 pages REVTeX and AMSLaTeX, 17 black&white eps figures. v3:
references added. v4: details of the pinch singularity avoidance for the
string quantization of the Rindler space toy model have been added in both
the body of the paper and in a new 7 page appendix. Other clarifications and
references added. This is the version accepted for publication in Class.
Quant. Gra
Radiocarbon dating of methane and carbon dioxide evaded from a temperate peatland stream
Streams draining peatlands export large quantities of carbon in different chemical forms and
are an important part of the carbon cycle. Radiocarbon (14C) analysis/dating provides unique
information on the source and rate that carbon is cycled through ecosystems, as has recently
been demonstrated at the air-water interface through analysis of carbon dioxide (CO2) lost
from peatland streams by evasion (degassing). Peatland streams also have the potential to
release large amounts of methane (CH4) and, though 14C analysis of CH4 emitted by ebullition
(bubbling) has been previously reported, diffusive emissions have not. We describe methods
that enable the 14C analysis of CH4 evaded from peatland streams. Using these methods, we
investigated the 14C age and stable carbon isotope composition of both CH4 and CO2 evaded
from a small peatland stream draining a temperate raised mire. Methane was aged between
1617-1987 years BP, and was much older than CO2 which had an age range of 303-521 years
BP. Isotope mass balance modelling of the results indicated that the CO2 and CH4 evaded
from the stream were derived from different source areas, with most evaded CO2 originating
from younger layers located nearer the peat surface compared to CH4. The study demonstrates
the insight that can be gained into peatland carbon cycling from a methodological
development which enables dual isotope (14C and 13C) analysis of both CH4 and CO2 collected
at the same time and in the same way
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