166 research outputs found
Bistability of the climate around the habitable zone: a thermodynamic investigation
The goal of this paper is to explore the potential multistability of the
climate of a planet around the habitable zone. A thorough investigation of the
thermodynamics of the climate system is performed for very diverse conditions
of energy input and infrared atmosphere opacity. Using PlaSim, an Earth-like
general circulation model, the solar constant S* is modulated between 1160 and
1510 Wm-2 and the CO2 concentration, [CO2], from 90 to 2880 ppm. It is observed
that in such a parameter range the climate is bistable, i.e. there are two
coexisting attractors, one characterised by warm, moist climates (W) and one by
completely frozen sea surface (Snowball Earth, SB). Linear relationships are
found for the two transition lines (W\rightarrowSB and SB\rightarrowW) in
(S*,[CO2]) between S* and the logarithm of [CO2]. The dynamical and
thermodynamical properties - energy fluxes, Lorenz energy cycle, Carnot
efficiency, material entropy production - of the W and SB states are very
different: W states are dominated by the hydrological cycle and latent heat is
prominent in the material entropy production; the SB states are predominantly
dry climates where heat transport is realized through sensible heat fluxes and
entropy mostly generated by dissipation of kinetic energy. We also show that
the Carnot efficiency regularly increases towards each transition between W and
SB, with a large decrease in each transition. Finally, we propose well-defined
empirical functions allowing for expressing the global non-equilibrium
thermodynamical properties of the system in terms of either the mean surface
temperature or the mean planetary emission temperature. This paves the way for
the possibility of proposing efficient parametrisations of complex
non-equilibrium properties and of practically deducing fundamental properties
of a planetary system from a relatively simple observable
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Water pathways for the Hindu-Kush-Himalaya and analysis of three flood events
The climatology of major sources and pathways of moisture for three locales along the Hindu-Kush-Himalayan region are examined, by use of Lagrangian methods applied to the ERA-Interim dataset, over the period from 1980 to 2016 for both summer (JJA) and winter (NDJ) periods. We also investigate the major flooding events of 2010, 2013, and 2017 in Pakistan, Uttarakhand, and Kathmandu, respectively, and analyse a subset of the climatology associated with the 20 most significant rainfall events over each region of interest. A comparison is made between the climatology and extreme events, in the three regions of interest, during the summer monsoon period. For Northern Pakistan and Uttarakhand, the Indus basin plays the largest role in moisture uptake. Moisture is also gathered from Eastern Europe and Russia. Extreme events display an increased influence of sub-tropical weather systems, which manifest themselves through low-level moisture transport; predominantly from the Arabian sea and along the Gangetic plain. In the Kathmandu region, it is found that the major moisture sources come from the Gangetic plain, Arabian Sea, Red Sea, Bay of Bengal, and the Indus basin. In this case, extreme event pathways largely match those of the climatology, although an increased number of parcels originate from the western end of the Gangetic plain. These results provide insights into the rather significant influence of mid-latitudinal weather systems, even during the monsoon season, in defining the climatology of the Hindu-Kush-Himalaya region, as well as how extreme precipitation events in this region represent atypical moisture pathways. We propose a detailed investigation of how such water pathways are represented in climate models for the present climate conditions and in future climate scenarios, as this may be extremely relevant for understanding the impacts of climate change on the cryosphere and hydrosphere of the region
Heterocyclic ring cleavage upon collision-induced dissociation of deprotonated 3-hydroxy-1,2,5-oxadiazoles (3-hydroxyfurazans)
Cluster Monte Carlo Simulations of the Nematic--Isotropic Transition
We report the results of simulations of the Lebwohl-Lasher model of the
nematic-isotropic transition using a new cluster Monte Carlo algorithm. The
algorithm is a modification of the Wolff algorithm for spin systems, and
greatly reduces critical slowing down. We calculate the free energy in the
neighborhood of the transition for systems up to linear size 70. We find a
double well structure with a barrier that grows with increasing system size,
obeying finite size scaling for systems of size greater than 35. We thus obtain
an estimate of the value of the transition temperature in the thermodynamic
limit.Comment: 4 figure
New trends in active faulting studies for seismic hazard assessment
Vulnerability to earthquakes increases steadily as urbanization and development expand in areas that are prone to the effects of significant earthquakes. As virtually all of the largest earthquakes of the past decade demonstrated,
the development of large cities in high seismicity areas is often based on an insufficient knowledge or distorted perception of the local seismic hazard, a condition often worsened by the construction of seismically unsafe buildings and infrastructures
Classical wave-optics analogy of quantum information processing
An analogous model system for quantum information processing is discussed,
based on classical wave optics. The model system is applied to three examples
that involve three qubits: ({\em i}) three-particle Greenberger-Horne-Zeilinger
entanglement, ({\em ii}) quantum teleportation, and ({\em iii}) a simple
quantum error correction network. It is found that the model system can
successfully simulate most features of entanglement, but fails to simulate
quantum nonlocality. Investigations of how far the classical simulation can be
pushed show that {\em quantum nonlocality} is the essential ingredient of a
quantum computer, even more so than entanglement. The well known problem of
exponential resources required for a classical simulation of a quantum
computer, is also linked to the nonlocal nature of entanglement, rather than to
the nonfactorizability of the state vector.Comment: 9 pages, 6 figure
Nonequilibrium thermodynamics of circulation regimes in optically-thin, dry atmospheres
An extensive analysis of an optically-thin, dry atmosphere at different
values of the thermal Rossby number Ro and of the Taylor number Ff is per-
formed with a general circulation model by varying the rotation rate {\Omega}
and the surface drag {\tau} in a wide parametric range. By using nonequilibrium
thermodynamics diagnostics such as material entropy production, efficiency,
meridional heat transport and kinetic energy dissipation we characterize in a
new way the different circulation regimes. Baroclinic circulations feature high
mechanical dissipation, meridional heat transport, material entropy pro-
duction and are fairly efficient in converting heat into mechanical work. The
thermal dissipation associated with the sensible heat flux is found to depend
mainly on the surface properties, almost independent from the rotation rate and
very low for quasi-barotropic circulations and regimes approaching equa- torial
super-rotation. Slowly rotating, axisymmetric circulations have the highest
meridional heat transport. At high rotation rates and intermediate- high drag,
atmospheric circulations are zonostrohic with very low mechanical dissipation,
meridional heat transport and efficiency. When {\tau} is interpreted as a
tunable parameter associated with the turbulent boundary layer trans- fer of
momentum and sensible heat, our results confirm the possibility of using the
Maximum Entropy Production Principle as a tuning guideline in the range of
values of {\Omega}. This study suggests the effectiveness of using fun-
damental nonequilibrium thermodynamics for investigating the properties of
planetary atmospheres and extends our knowledge of the thermodynamics of the
atmospheric circulation regimes
Diarrhea incidence in low- and middle-income countries in 1990 and 2010: a systematic review
<p>Abstract</p> <p>Background</p> <p>Diarrhea is recognized as a leading cause of morbidity and mortality among children under 5 years of age in low- and middle-income countries yet updated estimates of diarrhea incidence by age for these countries are greatly needed. We conducted a systematic literature review to identify cohort studies that sought to quantify diarrhea incidence among any age group of children 0-59 mo of age.</p> <p>Methods</p> <p>We used the Expectation-Maximization algorithm as a part of a two-stage regression model to handle diverse age data and overall incidence rate variation by study to generate country specific incidence rates for low- and middle-income countries for 1990 and 2010. We then calculated regional incidence rates and uncertainty ranges using the bootstrap method, and estimated the total number of episodes for children 0-59 mo of age in 1990 and 2010.</p> <p>Results</p> <p>We estimate that incidence has declined from 3.4 episodes/child year in 1990 to 2.9 episodes/child year in 2010. As was the case previously, incidence rates are highest among infants 6-11 mo of age; 4.5 episodes/child year in 2010. Among these 139 countries there were nearly 1.9 billion episodes of childhood diarrhea in 1990 and nearly 1.7 billion episodes in 2010.</p> <p>Conclusions</p> <p>Although our results indicate that diarrhea incidence rates may be declining slightly, the total burden on the health of each child due to multiple episodes per year is tremendous and additional funds are needed to improve both prevention and treatment practices in low- and middle-income countries.</p
Measurement and subtraction of Schumann resonances at gravitational-wave interferometers
Correlated magnetic noise from Schumann resonances threatens to contaminate the observation of a stochastic gravitational-wave background in interferometric detectors. In previous work, we reported on the first effort to eliminate global correlated noise from the Schumann resonances using Wiener filtering, demonstrating as much as a factor of two reduction in the coherence between magnetometers on different continents. In this work, we present results from dedicated magnetometer measurements at the Virgo and KAGRA sites, which are the first results for subtraction using data from gravitational-wave detector sites. We compare these measurements to a growing network of permanent magnetometer stations, including at the LIGO sites. We show the effect of mutual magnetometer attraction, arguing that magnetometers should be placed at least one meter from one another. In addition, for the first time, we show how dedicated measurements by magnetometers near to the interferometers can reduce coherence to a level consistent with uncorrelated noise, making a potential detection of a stochastic gravitational-wave background possible
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