877 research outputs found
The challenge of simulating the warmth of the mid-Miocene climatic optimum in CESM1
The mid-Miocene climatic optimum (MMCO) is an intriguing climatic period due
to its above-modern temperatures in mid-to-high latitudes in the presence of
close-to-modern CO<sub>2</sub> concentrations. We use the recently released Community
Earth System Model (CESM1.0) with a slab ocean to simulate this warm period,
incorporating recent Miocene CO<sub>2</sub> reconstructions of 400 ppm (parts per million). We simulate a
global mean annual temperature (MAT) of 18 °C, ~4 °C
above the preindustrial value, but 4 °C colder than the global
Miocene MAT we calculate from climate proxies. Sensitivity tests reveal that
the inclusion of a reduced Antarctic ice sheet, an equatorial Pacific temperature gradient
characteristic of a permanent El Niño, increased CO<sub>2</sub> to 560 ppm, and variations in
obliquity only marginally improve model–data agreement. All MMCO simulations
have an Equator to pole temperature gradient that is at least
~10 °C larger than that reconstructed from proxies. The MMCO
simulation most comparable to the proxy records requires a CO<sub>2</sub>
concentration of 800 ppm. Our results illustrate that MMCO warmth is not
reproducible using the CESM1.0 forced with CO<sub>2</sub> concentrations
reconstructed for the Miocene or including various proposed Earth system
feedbacks; the remaining discrepancy in the MAT is comparable to that
introduced by a CO<sub>2</sub> doubling. The model's tendency to underestimate proxy
derived global MAT and overestimate the Equator to pole temperature gradient
suggests a major climate problem in the MMCO akin to those in the Eocene. Our
results imply that this latest model, as with previous generations of climate
models, is either not sensitive enough or additional forcings remain missing
that explain half of the anomalous warmth and pronounced polar amplification
of the MMCO
High precision Monte Carlo study of the 3D XY-universality class
We present a Monte Carlo study of the two-component model on the
simple cubic lattice in three dimensions. By suitable tuning of the coupling
constant we eliminate leading order corrections to scaling. High
statistics simulations using finite size scaling techniques yield
and , where the statistical and
systematical errors are given in the first and second bracket, respectively.
These results are more precise than any previous theoretical estimate of the
critical exponents for the 3D XY universality class.Comment: 13 page
Inappropriate Implantable Cardioverter-Defibrillator Shocks Attributed to Alternating-Current Leak in a Swimming Pool
Implantable cardioverter-defibrillators (ICDs) are the standard of care for preventing sudden cardiac death in patients who are predisposed to malignant ventricular arrhythmias. Causes of inappropriate ICD shock include equipment malfunction, improper arrhythmia evaluation, misinterpretation of myopotentials, and electromagnetic interference. As the number of implanted ICDs has increased, other contributors to inappropriate therapy have become known, such as minimal electrical current leaks that mimic ventricular fibrillation. We present the case of a 63-year-old man with a biventricular ICD who received 2 inappropriate shocks, probably attributable to alternating-current leaks in a swimming pool. In addition, we discuss ICD sensitivity and offer recommendations to avoid similar occurrences
All-solid-state electrochromic reflectance device for emittance modulation in the far-infrared spectral region
All-solid-state electrochromic reflectance devices for thermal emittance modulation were designed for operation in the spectral region from mid- to far-infrared wavelengths (2–40 μm). All device constituent layers were grown by magnetron sputtering. The electrochromic (polycrystalline WO3), ion conductor (Ta2O5), and Li+ ion-storage layer (amorphous WO3), optimized for their infrared (IR) optical thicknesses, are sandwiched between a highly IR reflecting Al mirror, and a 90% IR transmissive Al grid top electrode, thereby meeting the requirements for a reversible Li+ ion insertion electrochromic device to operate within the 300 K blackbody emission range. Multicycle optical switching and emittance modulation is demonstrated. The measured change in emissivity of the device is to 20%
Influence of different PEEP levels and tidal volumes on the regional nonaerated tissue: experimental study
Relationship between superimposed pressure and pleural pressure gradient in an experimental model of ARDS
Scaling of the specific heat in superfluid films
We study the specific heat of the model on lattices with (i.e. on lattices representing a film geometry) using the
Cluster Monte--Carlo method. In the --direction we apply Dirichlet boundary
conditions so that the order parameter in the top and bottom layers is zero. We
find that our results for the specific heat of various thickness size
collapse on the same universal scaling function. The extracted scaling function
of the specific heat is in good agreement with the experimentally determined
universal scaling function using no free parameters.Comment: 4 pages, uuencoded compressed PostScrip
Scaling of the superfluid density in superfluid films
We study scaling of the superfluid density with respect to the film thickness
by simulating the model on films of size ()
using the cluster Monte Carlo. While periodic boundary conditions where used in
the planar () directions, Dirichlet boundary conditions where used along the
film thickness. We find that our results can be scaled on a universal curve by
introducing an effective thickness. In the limit of large our scaling
relations reduce to the conventional scaling forms. Using the same idea we find
scaling in the experimental results using the same value of .Comment: 4 pages, one postscript file replaced by one Latex file and 5
postscript figure
A Suite of Early Eocene (~55 Ma) Climate Model Boundary Conditions
We describe a set of early Eocene (~ 55 Ma) climate model boundary conditions constructed in a self-consistent reference frame and incorporating recent data and methodologies. Given the growing need for uniform experimental design within the Eocene climate modelling community and the challenges faced in simulating the prominent features of Eocene climate, we make publicly available our data sets of Eocene topography, bathymetry, tidal dissipation, vegetation, aerosol distributions and river runoff. Major improvements in our boundary conditions over previous efforts include the implementation of the ANTscape palaeotopography of Antarctica, more accurate representations of the Drake Passage and Tasman Gateway, as well as an approximation of sub grid cell topographic variability. Our boundary conditions also include for the first time modelled estimates of Eocene aerosol distributions and tidal dissipation, both consistent with our palaeotopography and palaeobathymetry. The resolution of our data sets is unprecedented and will facilitate high resolution climate simulations. In light of the inherent uncertainties involved in reconstructing global boundary conditions for past time periods these data sets should be considered as one interpretation of the available data and users are encouraged to modify them according to their needs and interpretations. This paper marks the beginning of a process for reconstructing a set of accurate, open-access Eocene boundary conditions for use in climate models
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