142 research outputs found
Budget of Primary Production and Dinitrogen Fixation in a Highly Seasonal Red Sea Coral Reef
Biological dinitrogen (N2) fixation (diazotrophy, BNF) relieves marine primary producers of nitrogen (N) limitation in a large part of the world oceans. N concentrations are particularly low in tropical regions where coral reefs are located, and N is therefore a key limiting nutrient for these productive ecosystems. In this context, the importance of diazotrophy for reef productivity is still not resolved, with studies up to now lacking organismal and seasonal resolution. Here, we present a budget of gross primary production (GPP) and BNF for a highly seasonal Red Sea fringing reef, based on ecophysiological and benthic cover measurements combined with geospatial analyses. Benthic GPP varied from 215 to 262 mmol C m−2 reef d−1, with hard corals making the largest contribution (41–76%). Diazotrophy was omnipresent in space and time, and benthic BNF varied from 0.16 to 0.92 mmol N m−2 reef d−1. Planktonic GPP and BNF rates were respectively approximately 60- and 20-fold lower than those of the benthos, emphasizing the importance of the benthic compartment in reef biogeochemical cycling. BNF showed higher sensitivity to seasonality than GPP, implying greater climatic control on reef BNF. Up to about 20% of net reef primary production could be supported by BNF during summer, suggesting a strong biogeochemical coupling between diazotrophy and the reef carbon cycle
Tree rings of Scots pine (Pinus sylvestris L.) as a source of information about past climate in northern Poland
Scots pine (Pinus sylvestris) is a very common tree in Polish forests, and therefore was widely used as timber. A relatively large amount of available wood allowed a long-term chronology to be built up and used as a source of information about past climate. The analysis of reconstructed indexed values of mean temperature in 51-year moving intervals allowed the recognition of the coldest periods in the years 1207–1346, 1383–1425, 1455–1482, 1533–1574, 1627–1646, and 1694–1785. The analysis of extreme wide and narrow rings forms a complementary method of examining climatic data within tree rings. The tree ring widths, early wood and late wood widths of 16 samples were assessed during the period 1581–1676. The most apparent effect is noted in the dry summer of 1616. According to previous research and our findings, temperature from February to March seems to be one of the most stable climatic factors which influenced pine growth in Poland. Correlation coefficients in the calibration and validation procedure gave promising results for temperature reconstruction from the pine chronology
Second primary cancers after radiation for prostate cancer: a review of data from planning studies
A review of planning studies was undertaken to evaluate estimated risks of radiation induced second primary cancers (RISPC) associated with different prostate radiotherapy techniques for localised prostate cancer. A total of 83 publications were identified which employed a variety of methods to estimate RISPC risk. Of these, the 16 planning studies which specifically addressed absolute or relative second cancer risk using dose–response models were selected for inclusion within this review. There are uncertainties and limitations related to all the different methods for estimating RISPC risk. Whether or not dose models include the effects of the primary radiation beam, as well as out-of-field regions, influences estimated risks. Regarding the impact of IMRT compared to 3D-CRT, at equivalent energies, several studies suggest an increase in risk related to increased leakage contributing to out-of-field RISPC risk, although in absolute terms this increase in risk may be very small. IMRT also results in increased low dose normal tissue irradiation, but the extent to which this has been estimated to contribute to RISPC risk is variable, and may also be very small. IMRT is often delivered using 6MV photons while conventional radiotherapy often requires higher energies to achieve adequate tissue penetration, and so comparisons between IMRT and older techniques should not be restricted to equivalent energies. Proton and brachytherapy planning studies suggest very low RISPC risks associated with these techniques. Until there is sufficient clinical evidence regarding RISPC risks associated with modern irradiation techniques, the data produced from planning studies is relevant when considering which patients to irradiate, and which technique to employ
Self-trapping of excitons, violation of condon approximation, and efficient fluorescence in conjugated cycloparaphenylenes
Cycloparaphenylenes, the simplest structural unit of armchair carbon nanotubes, have unique optoelectronic properties counterintuitive in the class of conjugated organic materials. Our time-dependent density functional theory study and excited state dynamics simulations of cycloparaphenylene chromophores provide a simple and conceptually appealing physical picture explaining experimentally observed trends in optical properties in this family of molecules. Fully delocalized degenerate second and third excitonic states define linear absorption spectra. Self-trapping of the lowest excitonic state due to electron-phonon coupling leads to the formation of spatially localized excitation in large cycloparaphenylenes within 100 fs. This invalidates the commonly used Condon approximation and breaks optical selection rules, making these materials superior fluorophores. This process does not occur in the small molecules, which remain inefficient emitters. A complex interplay of symmetry, π-conjugation, conformational distortion and bending strain controls all photophysics of cycloparaphenylenes.Fil: Adamska, Lyudmyla. Los Alamos National Laboratory. Los Alamos; Estados UnidosFil: Nayyar, Iffat. Los Alamos National Laboratory. Los Alamos; Estados UnidosFil: Chen, Hang. Boston University; Estados UnidosFil: Swan, Anna K.. Boston University; Estados UnidosFil: Oldani, Andres Nicolas. Universidad Nacional de Quilmes; ArgentinaFil: Fernández Alberti, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Golder, Matthew R.. University of Oregon; Estados UnidosFil: Jasti, Ramesh. University of Oregon; Estados UnidosFil: Doorn, Stephen K.. Los Alamos National Laboratory. Los Alamos; Estados UnidosFil: Tretiak, Sergei. Los Alamos National Laboratory. Los Alamos; Estados Unido
Update of complications and functional outcome of the ileo-pouch anal anastomosis: overview of evidence and meta-analysis of 96 observational studies
Item does not contain fulltextOBJECTIVE: The objective of this study is to provide a comprehensive update of the outcome of the ileo-pouch anal anastomosis (IPAA). DATA SOURCES: An extensive search in PubMed, EMBASE, and The Cochrane Library was conducted. STUDY SELECTION AND DATA EXTRACTION: All studies published after 2000 reporting on complications or functional outcome after a primary open IPAA procedure for UC or FAP were selected. Study characteristics, functional outcome, and complications were extracted. DATA SYNTHESIS: A review with similar methodology conducted 10 years earlier was used to evaluate developments in outcome over time. Pooled estimates were compared using a random-effects logistic meta-analyzing technique. Analyses focusing on the effect of time of study conductance, centralization, and variation in surgical techniques were performed. RESULTS: Fifty-three studies including 14,966 patients were included. Pooled rates of pouch failure and pelvic sepsis were 4.3% (95% CI, 3.5-6.3) and 7.5% (95% CI 6.1-9.1), respectively. Compared to studies published before 2000, a reduction of 2.5% was observed in the pouch failure rate (p = 0.0038). Analysis on the effect of the time of study conductance confirmed a decline in pouch failure. Functional outcome remained stable over time, with a 24-h defecation frequency of 5.9 (95% CI, 5.0-6.9). Technical surgery aspects did not have an important effect on outcome. CONCLUSION: This review provides up to date outcome estimates of the IPAA procedure that can be useful as reference values for practice and research. It is also shows a reduction in pouch failure over time.1 juli 201
Topical Issues for Particle Acceleration Mechanisms in Astrophysical Shocks
Particle acceleration at plasma shocks appears to be ubiquitous in the
universe, spanning systems in the heliosphere, supernova remnants, and
relativistic jets in distant active galaxies and gamma-ray bursts. This review
addresses some of the key issues for shock acceleration theory that require
resolution in order to propel our understanding of particle energization in
astrophysical environments. These include magnetic field amplification in shock
ramps, the non-linear hydrodynamic interplay between thermal ions and their
extremely energetic counterparts possessing ultrarelativistic energies, and the
ability to inject and accelerate electrons in both non-relativistic and
relativistic shocks. Recent observational developments that impact these issues
are summarized. While these topics are currently being probed by
astrophysicists using numerical simulations, they are also ripe for
investigation in laboratory experiments, which potentially can provide valuable
insights into the physics of cosmic shocks.Comment: 13 pages, no figures. Invited review, accepted for publication in
Astrophysics and Space Science, as part of the HEDLA 2006 conference
proceeding
Ready for O4 II: GRANDMA Observations of Swift GRBs during eight-weeks of Spring 2022
We present a campaign designed to train the GRANDMA network and its
infrastructure to follow up on transient alerts and detect their early
afterglows. In preparation for O4 II campaign, we focused on GRB alerts as they
are expected to be an electromagnetic counterpart of gravitational-wave events.
Our goal was to improve our response to the alerts and start prompt
observations as soon as possible to better prepare the GRANDMA network for the
fourth observational run of LIGO-Virgo-Kagra (which started at the end of May
2023), and future missions such as SM. To receive, manage and send out
observational plans to our partner telescopes we set up dedicated
infrastructure and a rota of follow-up adcates were organized to guarantee
round-the-clock assistance to our telescope teams. To ensure a great number of
observations, we focused on Swift GRBs whose localization errors were generally
smaller than the GRANDMA telescopes' field of view. This allowed us to bypass
the transient identification process and focus on the reaction time and
efficiency of the network. During 'Ready for O4 II', 11 Swift/INTEGRAL GRB
triggers were selected, nine fields had been observed, and three afterglows
were detected (GRB 220403B, GRB 220427A, GRB 220514A), with 17 GRANDMA
telescopes and 17 amateur astronomers from the citizen science project
Kilonova-Catcher. Here we highlight the GRB 220427A analysis where our
long-term follow-up of the host galaxy allowed us to obtain a photometric
redshift of , its lightcurve elution, fit the decay slope of the
afterglows, and study the properties of the host galaxy
Estimates of ozone return dates from Chemistry-Climate Model Initiative simulations
We analyse simulations performed for the
Chemistry-Climate Model Initiative (CCMI) to estimate the
return dates of the stratospheric ozone layer from depletion
caused by anthropogenic stratospheric chlorine and bromine.
We consider a total of 155 simulations from 20 models, including
a range of sensitivity studies which examine the impact
of climate change on ozone recovery. For the control
simulations (unconstrained by nudging towards analysed meteorology)
there is a large spread (±20 DU in the global average)
in the predictions of the absolute ozone column. Therefore,
the model results need to be adjusted for biases against
historical data. Also, the interannual variability in the model
results need to be smoothed in order to provide a reasonably
narrow estimate of the range of ozone return dates. Consistent
with previous studies, but here for a Representative
Concentration Pathway (RCP) of 6.0, these new CCMI simulations
project that global total column ozone will return to
1980 values in 2049 (with a 1σ uncertainty of 2043–2055).
At Southern Hemisphere mid-latitudes column ozone is projected
to return to 1980 values in 2045 (2039–2050), and at
Northern Hemisphere mid-latitudes in 2032 (2020–2044). In
the polar regions, the return dates are 2060 (2055–2066) in
the Antarctic in October and 2034 (2025–2043) in the Arctic
in March. The earlier return dates in the Northern Hemisphere
reflect the larger sensitivity to dynamical changes.
Our estimates of return dates are later than those presented
in the 2014 Ozone Assessment by approximately 5–17 years,
depending on the region, with the previous best estimates
often falling outside of our uncertainty range. In the tropics
only around half the models predict a return of ozone to
1980 values, around 2040, while the other half do not reach
the 1980 value. All models show a negative trend in tropical
total column ozone towards the end of the 21st century. The
CCMI models generally agree in their simulation of the time
evolution of stratospheric chlorine and bromine, which are
the main drivers of ozone loss and recovery. However, there
are a few outliers which show that the multi-model mean results
for ozone recovery are not as tightly constrained as possible.
Throughout the stratosphere the spread of ozone return
dates to 1980 values between models tends to correlate with
the spread of the return of inorganic chlorine to 1980 values.
In the upper stratosphere, greenhouse gas-induced cooling
speeds up the return by about 10–20 years. In the lower
stratosphere, and for the column, there is a more direct link
in the timing of the return dates of ozone and chlorine, especially
for the large Antarctic depletion. Comparisons of total
column ozone between the models is affected by different
predictions of the evolution of tropospheric ozone within
the same scenario, presumably due to differing treatment
of tropospheric chemistry. Therefore, for many scenarios,
clear conclusions can only be drawn for stratospheric ozone
columns rather than the total column. As noted by previous
studies, the timing of ozone recovery is affected by the evolution
of N2O and CH4. However, quantifying the effect in the
simulations analysed here is limited by the few realisations
available for these experiments compared to internal model
variability. The large increase in N2O given in RCP 6.0 extends
the ozone return globally by ∼ 15 years relative to N2O
fixed at 1960 abundances, mainly because it allows tropical
column ozone to be depleted. The effect in extratropical latitudes
is much smaller. The large increase in CH4 given in the
RCP 8.5 scenario compared to RCP 6.0 also lengthens ozone
return by ∼ 15 years, again mainly through its impact in the
tropics. Overall, our estimates of ozone return dates are uncertain
due to both uncertainties in future scenarios, in particular
those of greenhouse gases, and uncertainties in models.
The scenario uncertainty is small in the short term but increases
with time, and becomes large by the end of the century.
There are still some model–model differences related
to well-known processes which affect ozone recovery. Efforts
need to continue to ensure that models used for assessment
purposes accurately represent stratospheric chemistry
and the prescribed scenarios of ozone-depleting substances,
and only those models are used to calculate return dates. For
future assessments of single forcing or combined effects of
CO2, CH4, and N2O on the stratospheric column ozone return
dates, this work suggests that it is more important to
have multi-member (at least three) ensembles for each scenario
from every established participating model, rather than
a large number of individual models
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