1,051 research outputs found
Discussion of: A statistical analysis of multiple temperature proxies: Are reconstructions of surface temperatures over the last 1000 years reliable?
Discussion of "A statistical analysis of multiple temperature proxies: Are
reconstructions of surface temperatures over the last 1000 years reliable?" by
B.B. McShane and A.J. Wyner [arXiv:1104.4002]Comment: Published in at http://dx.doi.org/10.1214/10-AOAS398M the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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Erroneous Model Field Representations in Multiple Pseudoproxy Studies: Corrections and Implications
Pseudoproxy experiments evaluate statistical methods used to reconstruct climate fields from paleoclimatic proxies during the Common Era. These experiments typically employ output from millennial simulations by general circulation models (GCMs). It is demonstrated that multiple published pseudoproxy studies have used erroneously processed GCM surface temperature fields: the NCAR Community Climate System Model (CCSM), version 1.4, field was incorrectly oriented geographically and the GKSS ECHO-g FOR1 field was corrupted by a hemispheric-scale smoothing in the Western Hemisphere. These problems are not associated with the original model simulations; they instead arose because of incorrect processing of the model data for the pseudoproxy experiments. The consequences of these problems are evaluated for the studies in which the incorrect fields were used. Some quantitative results are invalidated by the findings: these include all experiments that used the corrupted ECHO-g field and those aspects of previous CCSM experiments that focused on Niño-3 reconstructions. Other results derived from the CCSM field can be reinterpreted based on the information provided herein and their qualitative characteristics remain similar
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A Pseudoproxy Evaluation of the CCA and RegEM Methods for Reconstructing Climate Fields of the Last Millennium
Canonical correlation analysis (CCA) is evaluated for paleoclimate field reconstructions in the context of pseudoproxy experiments assembled from the millennial integration (850–1999 c.e.) of the National Center for Atmospheric Research Community Climate System Model, version 1.4. A parsimonious method for selecting the order of the CCA model is presented. Results suggest that the method is capable of resolving multiple (3–13) climatic patterns given the estimated proxy observational network and the amount of observational uncertainty. CCA reconstructions are compared to those derived from the regularized expectation maximization method using ridge regression regularization (RegEM-Ridge). CCA and RegEM-Ridge yield similar skill patterns that are characterized by high correlation regions collocated with dense pseudoproxy sampling areas in North America and Europe. Both methods also produce reconstructions characterized by spatially variable warm biases and variance losses, particularly at high pseudoproxy noise levels. RegEM-Ridge in particular is subject to significantly larger variance losses than CCA, even though the spatial correlation patterns of the two methods are comparable. Results collectively indicate the importance of evaluating the field performance of methods that target spatial climate patterns during the last several millennia and indicate that the results of currently available climate field reconstructions should be interpreted carefully
Reply to “Comments on ‘Erroneous Model Field Representations in Multiple Pseudoproxy Studies: Corrections and Implications’”
The commenters confirm the errors identified and discussed in Smerdon et al., which either invalidated or required the reinterpretation of quantitative results from pseudoproxy experiments presented or used in several earlier papers. These errors have a strong influence on the spatial skill assessments of climate field reconstructions (CFRs), despite their small impacts on skill statistics averaged over the Northern Hemisphere. On the basis of spatial performance and contrary to the claim by the commenters, the Regularized Expectation Maximization method using truncated total least squares (RegEM-TTLS) cannot be considered a preferred CFR technique. Moreover, distinctions between CFR methods in the context of the discussion in the original paper are immaterial. Continued investigations using accurately described and faithfully executed pseudoproxy experiments are critical for further evaluation and improvement of CFR methods
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Predictability of El Niño over the past 148 years
Forecasts of El Niño climate events are routinely provided and distributed, but the limits of El Niño predictability are still the subject of debate. Some recent studies suggest that the predictability is largely limited by the effects of high-frequency atmospheric ‘noise’1,2,3,4,5,6,7, whereas others emphasize limitations arising from the growth of initial errors in model simulations8,9,10. Here we present retrospective forecasts of the interannual climate fluctuations in the tropical Pacific Ocean for the period 1857 to 2003, using a coupled ocean–atmosphere model. The model successfully predicts all prominent El Niño events within this period at lead times of up to two years. Our analysis suggests that the evolution of El Niño is controlled to a larger degree by self-sustaining internal dynamics than by stochastic forcing. Model-based prediction of El Niño therefore depends more on the initial conditions than on unpredictable atmospheric noise. We conclude that throughout the past century, El Niño has been more predictable than previously envisaged
Brane World Susy Breaking from String/M Theory
String and M-theory realizations of brane world supersymmetry breaking
scenarios are considered in which visible sector Standard Model fields are
confined on a brane, with hidden sector supersymmetry breaking isolated on a
distant brane. In calculable examples with an internal manifold of any volume
the Kahler potential generically contains brane--brane non-derivative contact
interactions coupling the visible and hidden sectors and is not of the no-scale
sequestered form. This leads to non-universal scalar masses and without
additional assumptions about flavor symmetries may in general induce dangerous
sflavor violation even though the Standard Model and supersymmetry branes are
physically separated. Deviations from the sequestered form are dictated by bulk
supersymmetry and can in most cases be understood as arising from exchange of
bulk supergravity fields between branes or warping of the internal geometry.
Unacceptable visible sector tree-level tachyons arise in many models but may be
avoided in certain classes of compactifications. Anomaly mediated and gaugino
mediated contributions to scalar masses are sub-dominant except in special
circumstances such as a flat or AdS pure five--dimensional bulk geometry
without bulk vector multiplets.Comment: Latex, 83 pages, references adde
X(3872): Hadronic Molecules in Effective Field Theory
We consider the implications from the possibility that the recently observed
state X(3872) is a meson-antimeson molecule. We write an effective Lagrangian
consistent with the heavy-quark and chiral symmetries needed to describe
X(3872). We claim that if X(3872) is a molecular bound state of D^*0 and
anti-D^0 mesons, the heavy-quark symmetry requires the existence of the
molecular bound state X_b of B^*0 and anti-B^0 with the mass of 10604 MeV.Comment: 12 pages, 1 figure, 1 table, RevTe
Using of Magnetron Sputtering for Biocompatible Composites Creating
Biocompatible composites obtained using the magnetron sputtering for the production of minimally invasive implantation medical devices (stents) were investigated. Nano- and microdimensional surface layers of Ta, Ti, Ag, and Cu on flat and wire NiTi, Cu, Ti, and SiO2 substrates were created. The phase composition, surface morphology, and the layer-by-layer composition were investigated on an X-ray diffractometer, SEM, and Auger spectrometer. It was shown that the thickness and the structure of surface layers were affected by the sputtering distance, time, power, and the bias voltage at the substrate. The presence of the transition layer that contains both substrate and target elements and provides high adhesion of the surface layer to the substrate has been demonstrated. The material was tested for corrosion resistance under static conditions by dipping into solutions with various acidities (pH from 1.68 to 9.18) for 2 years, static mechanical properties, and biocompatibility in vitro and in vivo. A slight corrosive dissolution was observed only in a medium with a pH of 1.56. Dissolution in the other media is absent. An increase in strength and plasticity in comparison with substrate was attained depending on the nature of the sputtered substance and substrate. Toxicity of samples has not been revealed
Giant Faraday rotation in single- and multilayer graphene
Optical Faraday rotation is one of the most direct and practically important
manifestations of magnetically broken time-reversal symmetry. The rotation
angle is proportional to the distance traveled by the light, and up to now
sizeable effects were observed only in macroscopically thick samples and in
two-dimensional electron gases with effective thicknesses of several
nanometers. Here we demonstrate that a single atomic layer of carbon - graphene
- turns the polarization by several degrees in modest magnetic fields. The
rotation is found to be strongly enhanced by resonances originating from the
cyclotron effect in the classical regime and the inter-Landau-level transitions
in the quantum regime. Combined with the possibility of ambipolar doping, this
opens pathways to use graphene in fast tunable ultrathin infrared
magneto-optical devices
- …