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Palm phytoliths of mid-elevation Andean forests
Palms are one of the most common tropical plant groups. They are widespread across lowland tropical forests, but many are found in higher altitudes have more constrained environmental ranges. The limited range of these species makes them particularly useful in paleoecological and paleoclimate reconstructions. Palms produce phytoliths, or silica structures, which are found in their vegetative parts (e.g., wood, leaves, etc.). Recent research has shown that several palms in the lowland tropical forests produce phytoliths that are diagnostic to the sub-family or genus-level. Here we characterize Andean palm phytoliths, and determine whether many of these species can also be identified by their silica structures. All of our sampled Andean palm species produced phytoliths, and we were able to characterize several previously unclassified morphotypes. Some species contained unique phytoliths that did not occur in other species, particularly Ceroxylon alpinium, which is indicative of specific climatic conditions. The differences in the morphologies of the Andean species indicate that palm phytolith analysis is particularly useful in paleoecological reconstructions. Future phytolith analyses will allow researchers to track how these palm species with limited environmental ranges have migrated up and down the Andean slopes as a result of past climatic change. The phytolith analyses can track local-scale vegetation dynamics, whereas pollen, which is commonly used in paleoecological reconstructions, reflects regional-scale vegetation change
Analytic Perturbation Theory: A New Approach to the Analytic Continuation of the Strong Coupling Constant into the Timelike Region
The renormalization group applied to perturbation theory is ordinarily used
to define the running coupling constant in the spacelike region. However, to
describe processes with timelike momenta transfers, it is important to have a
self-consistent determination of the running coupling constant in the timelike
region. The technique called analytic perturbation theory (APT) allows a
consistent determination of this running coupling constant. The results are
found to disagree significantly with those obtained in the standard
perturbative approach. Comparison between the standard approach and APT is
carried out to two loops, and threshold matching in APT is applied in the
timelike region.Comment: 16 pages, REVTeX, 7 postscript figure
Experimental Constraints on the Neutrino Oscillations and a Simple Model of Three Flavour Mixing
A simple model of the neutrino mixing is considered, which contains only one
right-handed neutrino field, coupled via the mass term to the three usual
left-handed fields. This is a simplest model that allows for three-flavour
neutrino oscillations. The existing experimental limits on the neutrino
oscillations are used to obtain constraints on the two free mixing parameters
of the model. A specific sum rule relating the oscillation probabilities of
different flavours is derived.Comment: 10 pages, 3 figures in post script, Latex, IFT 2/9
Study of shock waves generation, hot electron production and role of parametric instabilities in an intensity regime relevant for the shock ignition
We present experimental results at intensities relevant to Shock Ignition
obtained at the sub-ns Prague Asterix Laser System in 2012 . We studied shock waves
produced by laser-matter interaction in presence of a pre-plasma. We used a first beam at
1ω (1315 nm) at 7 × 10 13 W/cm 2 to create a pre-plasma on the front side of the target and
a second at 3ω (438 nm) at ∼ 10 16 W/cm 2 to create the shock wave. Multilayer targets
composed of 25 (or 40 μm) of plastic (doped with Cl), 5 μm of Cu (for Kα diagnostics)
and 20 μm of Al for shock measurement were used. We used X-ray spectroscopy of Cl
to evaluate the plasma temperature, Kα imaging and spectroscopy to evaluate spatial and
spectral properties of the fast electrons and a streak camera for shock breakout measurements.
Parametric instabilities (Stimulated Raman Scattering, Stimulated Brillouin Scattering and
Two Plasmon Decay) were studied by collecting the back scattered light and analysing its
spectrum. Back scattered energy was measured with calorimeters. To evaluate the maximum
pressure reached in our experiment we performed hydro simulations with CHIC and DUED
codes. The maximum shock pressure generated in our experiment at the front side of the
target during laser-interaction is 90 Mbar. The conversion efficiency into hot electrons was
estimated to be of the order of ∼ 0.1% and their mean energy in the order ∼50 keV.
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributio
Tall tales from de Sitter space II: Field theory dualities
We consider the evolution of massive scalar fields in (asymptotically) de
Sitter spacetimes of arbitrary dimension. Through the proposed dS/CFT
correspondence, our analysis points to the existence of new nonlocal dualities
for the Euclidean conformal field theory. A massless conformally coupled scalar
field provides an example where the analysis is easily explicitly extended to
'tall' background spacetimes.Comment: 31 pages, 2 figure
Asymptotic Improvement of Resummation and Perturbative Predictions in Quantum Field Theory
The improvement of resummation algorithms for divergent perturbative
expansions in quantum field theory by asymptotic information about perturbative
coefficients is investigated. Various asymptotically optimized resummation
prescriptions are considered. The improvement of perturbative predictions
beyond the reexpansion of rational approximants is discussed.Comment: 21 pages, LaTeX, 3 tables; title shortened; typographical errors
corrected; minor changes of style; 2 references adde
The Determination of alpha_s from Tau Decays Revisited
We revisit the determination of alpha_s(m_tau) using a fit to inclusive tau
hadronic spectral moments in light of (1) the recent calculation of the
fourth-order perturbative coefficient K_4 in the expansion of the Adler
function, (2) new precision measurements from BABAR of e+e- annihilation cross
sections, which decrease the uncertainty in the separation of vector and
axial-vector spectral functions, and (3) improved results from BABAR and Belle
on tau branching fractions involving kaons. We estimate that the fourth-order
perturbative prediction reduces the theoretical uncertainty, introduced by the
truncation of the series, by 20% with respect to earlier determinations. We
discuss to some detail the perturbative prediction and show that the effect of
the incomplete knowledge of the series is reduced by using the so-called
contour-improved calculation, as opposed to fixed-order perturbation theory
which manifests convergence problems. The corresponding theoretical
uncertainties are studied at the tau and Z mass scales. Nonperturbative
contributions extracted from the most inclusive fit are small, in agreement
with earlier determinations. Systematic effects from quark-hadron duality
violation are estimated with simple models and found to be within the quoted
systematic errors. The fit gives alpha_s(m_tau) = 0.344 +- 0.005 +- 0.007,
where the first error is experimental and the second theoretical. After
evolution to M_Z we obtain alpha_s(M_Z) = 0.1212 +- 0.0005 +- 0.0008 +- 0.0005,
where the errors are respectively experimental, theoretical and due to the
evolution. The result is in agreement with the corresponding NNNLO value
derived from essentially the Z width in the global electroweak fit. The
alpha_s(M_Z) determination from tau decays is the most precise one to date.Comment: 22 pages, 7 figure
Terrestrial Biosphere Model Performance for Inter-Annual Variability of Land-Atmosphere CO2 Exchange
Interannual variability in biosphere-atmosphere exchange of CO2 is driven by a diverse range of biotic and abiotic factors. Replicating this variability thus represents the ‘acid test’ for terrestrial biosphere models. Although such models are commonly used to project responses to both normal and anomalous variability in climate, they are rarely tested explicitly against inter-annual variability in observations. Herein, using standardized data from the North American Carbon Program, we assess the performance of 16 terrestrial biosphere models and 3 remote sensing products against long-term measurements of biosphere-atmosphere CO2 exchange made with eddy-covariance flux towers at 11 forested sites in North America. Instead of focusing on model-data agreement we take a systematic, variability-oriented approach and show that although the models tend to reproduce the mean magnitude of the observed annual flux variability, they fail to reproduce the timing. Large biases in modeled annual means are evident for all models. Observed interannual variability is found to commonly be on the order of magnitude of the mean fluxes. None of the models consistently reproduce observed interannual variability within measurement uncertainty. Underrepresentation of variability in spring phenology, soil thaw and snowpack melting, and difficulties in reproducing the lagged response to extreme climatic events are identified as systematic errors, common to all models included in this study.Organismic and Evolutionary Biolog
Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements
Droughts in the western United States are expected to intensify with climate
change. Thus, an adequate representation of ecosystem response to water
stress in land models is critical for predicting carbon dynamics. The goal of
this study was to evaluate the performance of the Community Land Model (CLM)
version 4.5 against observations at an old-growth coniferous forest site in
the Pacific Northwest region of the United States (Wind River AmeriFlux
site), characterized by a Mediterranean climate that subjects trees to water
stress each summer. CLM was driven by site-observed meteorology and
calibrated primarily using parameter values observed at the site or at
similar stands in the region. Key model adjustments included parameters
controlling specific leaf area and stomatal conductance. Default values of
these parameters led to significant underestimation of gross primary
production, overestimation of evapotranspiration, and consequently
overestimation of photosynthetic 13C discrimination, reflected in
reduced 13C : 12C ratios of carbon fluxes and pools. Adjustments
in soil hydraulic parameters within CLM were also critical, preventing
significant underestimation of soil water content and unrealistic soil
moisture stress during summer. After calibration, CLM was able to simulate
energy and carbon fluxes, leaf area index, biomass stocks, and carbon isotope
ratios of carbon fluxes and pools in reasonable agreement with site
observations. Overall, the calibrated CLM was able to simulate the observed
response of canopy conductance to atmospheric vapor pressure deficit (VPD)
and soil water content, reasonably capturing the impact of water stress on
ecosystem functioning. Both simulations and observations indicate that
stomatal response from water stress at Wind River was primarily driven by VPD
and not soil moisture. The calibration of the Ball–Berry stomatal
conductance slope (mbb) at Wind River aligned with findings from recent CLM experiments at sites characterized by the same plant functional
type (needleleaf evergreen temperate forest), despite significant differences
in stand composition and age and climatology, suggesting that CLM could
benefit from a revised mbb value of 6, rather than the default
value of 9, for this plant functional type. Conversely, Wind River required a
unique calibration of the hydrology submodel to simulate soil moisture,
suggesting that the default hydrology has a more limited applicability. This
study demonstrates that carbon isotope data can be used to constrain stomatal
conductance and intrinsic water use efficiency in CLM, as an alternative to
eddy covariance flux measurements. It also demonstrates that carbon isotopes
can expose structural weaknesses in the model and provide a key constraint
that may guide future model development
Brazilian montane rainforest expansion induced by Heinrich Stadial 1 event
The origin of modern disjunct plant distributions in the Brazilian Highlands with strong floristic affinities
to distant montane rainforests of isolated mountaintops in the northeast and northern Amazonia and
the Guyana Shield remains unknown. We tested the hypothesis that these unexplained biogeographical
patterns reflect former ecosystem rearrangements sustained by widespread plant migrations possibly
due to climatic patterns that are very dissimilar from present-day conditions. To address this issue, we
mapped the presence of the montane arboreal taxa Araucaria, Podocarpus, Drimys, Hedyosmum, Ilex,
Myrsine, Symplocos, and Weinmannia, and cool-adapted plants in the families Myrtaceae, Ericaceae, and
Arecaceae (palms) in 29 palynological records during Heinrich Stadial 1 Event, encompassing a latitudinal
range of 30°S to 0°S. In addition, Principal Component Analysis and Species Distribution Modelling were
used to represent past and modern habitat suitability for Podocarpus and Araucaria. The data reveals
two long-distance patterns of plant migration connecting south/southeast to northeastern Brazil and
Amazonia with a third short route extending from one of them. Their paleofloristic compositions suggest
a climatic scenario of abundant rainfall and relative lower continental surface temperatures, possibly
intensified by the effects of polar air incursions forming cold fronts into the Brazilian Highlands. Although
these taxa are sensitive to changes in temperature, the combined pollen and speleothems proxy data
indicate that this montane rainforest expansion during Heinrich Stadial 1 Event was triggered mainly by
a less seasonal rainfall regime from the subtropics to the equatorial region.This work was funded by FAPESP research grant 2015/50683-2 to P.E. De Oliveira, VULPES Project, Belmount
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