2,658 research outputs found
Subanesthetic ketamine treatment promotes abnormal interactions between neural subsystems and alters the properties of functional brain networks
Acute treatment with subanesthetic ketamine, a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, is widely utilized as a translational model for schizophrenia. However, how acute NMDA receptor blockade impacts on brain functioning at a systems level, to elicit translationally relevant symptomatology and behavioral deficits, has not yet been determined. Here, for the first time, we apply established and recently validated topological measures from network science to brain imaging data gained from ketamine-treated mice to elucidate how acute NMDA receptor blockade impacts on the properties of functional brain networks. We show that the effects of acute ketamine treatment on the global properties of these networks are divergent from those widely reported in schizophrenia. Where acute NMDA receptor blockade promotes hyperconnectivity in functional brain networks, pronounced dysconnectivity is found in schizophrenia. We also show that acute ketamine treatment increases the connectivity and importance of prefrontal and thalamic brain regions in brain networks, a finding also divergent to alterations seen in schizophrenia. In addition, we characterize how ketamine impacts on bipartite functional interactions between neural subsystems. A key feature includes the enhancement of prefrontal cortex (PFC)-neuromodulatory subsystem connectivity in ketamine-treated animals, a finding consistent with the known effects of ketamine on PFC neurotransmitter levels. Overall, our data suggest that, at a systems level, acute ketamine-induced alterations in brain network connectivity do not parallel those seen in chronic schizophrenia. Hence, the mechanisms through which acute ketamine treatment induces translationally relevant symptomatology may differ from those in chronic schizophrenia. Future effort should therefore be dedicated to resolve the conflicting observations between this putative translational model and schizophrenia
The combined effects of a long-term experimental drought and an extreme drought on the use of plant-water sources in a Mediterranean forest
Vegetation in water-limited ecosystems relies strongly on access to deep water reserves to withstand dry periods. Most of these ecosystems have shallow soils over deep groundwater reserves. Understanding the functioning and functional plasticity of species-specific root systems and the patterns of or differences in the use of water sources under more frequent or intense droughts is therefore necessary to properly predict the responses of seasonally dry ecosystems to future climate. We used stable isotopes to investigate the seasonal patterns of water uptake by a sclerophyll forest on sloped terrain with shallow soils. We assessed the effect of a long-term experimental drought (12 years) and the added impact of an extreme natural drought that produced widespread tree mortality and crown defoliation. The dominant species, Quercus ilex, Arbutus unedo and Phillyrea latifolia, all have dimorphic root systems enabling them to access different water sources in space and time. The plants extracted water mainly from the soil in the cold and wet seasons but increased their use of groundwater during the summer drought. Interestingly, the plants subjected to the long-term experimental drought shifted water uptake toward deeper (10-35 cm) soil layers during the wet season and reduced groundwater uptake in summer, indicating plasticity in the functional distribution of fine roots that dampened the effect of our experimental drought over the long term. An extreme drought in 2011, however, further reduced the contribution of deep soil layers and groundwater to transpiration, which resulted in greater crown defoliation in the drought-affected plants. The present study suggests that extreme droughts aggravate moderate but persistent drier conditions (simulated by our manipulation) and may lead to the depletion of water from groundwater reservoirs and weathered bedrock, threatening the preservation of these Mediterranean ecosystems in their current structures and composition
Complete off-shell effects in top quark pair hadroproduction with leptonic decay at next-to-leading order
Results for next-to-leading order QCD corrections to the pp(p\bar{p}) -> t
\bar{t} -> W^+W^- b\bar{b} -> e^{+} \nu_{e} \mu^{-} \bar{\nu}_{\mu} b \bar{b}
+X processes with complete off-shell effects are presented for the first time.
Double-, single- and non-resonant top contributions of the order
{\cal{O}}(\alpha_{s}^3 \alpha^4) are consistently taken into account, which
requires the introduction of a complex-mass scheme for unstable top quarks.
Moreover, the intermediate W bosons are treated off-shell. Comparison to the
narrow width approximation for top quarks, where non-factorizable corrections
are not accounted for is performed. Besides the total cross section and its
scale dependence, several differential distributions at the TeVatron run II and
the LHC are given. In case of the TeVatron the forward-backward asymmetry of
the top is recalculated afresh. With inclusive selection cuts, the
forward-backward asymmetry amounts to A^{t}_{FB} = 0.051 +/- 0.0013.
Furthermore, the corrections with respect to leading order are positive and of
the order 2.3% for the TeVatron and 47% for the LHC. A study of the scale
dependence of our NLO predictions indicates that the residual theoretical
uncertainty due to higher order corrections is 8% for the TeVatron and 9% for
the LHC.Comment: 35 pages, 39 figures, 3 tables. References and note added, version to
appear in JHE
Transit Timing and Duration Variations for the Discovery and Characterization of Exoplanets
Transiting exoplanets in multi-planet systems have non-Keplerian orbits which
can cause the times and durations of transits to vary. The theory and
observations of transit timing variations (TTV) and transit duration variations
(TDV) are reviewed. Since the last review, the Kepler spacecraft has detected
several hundred perturbed planets. In a few cases, these data have been used to
discover additional planets, similar to the historical discovery of Neptune in
our own Solar System. However, the more impactful aspect of TTV and TDV studies
has been characterization of planetary systems in which multiple planets
transit. After addressing the equations of motion and parameter scalings, the
main dynamical mechanisms for TTV and TDV are described, with citations to the
observational literature for real examples. We describe parameter constraints,
particularly the origin of the mass/eccentricity degeneracy and how it is
overcome by the high-frequency component of the signal. On the observational
side, derivation of timing precision and introduction to the timing diagram are
given. Science results are reviewed, with an emphasis on mass measurements of
transiting sub-Neptunes and super-Earths, from which bulk compositions may be
inferred.Comment: Revised version. Invited review submitted to 'Handbook of
Exoplanets,' Exoplanet Discovery Methods section, Springer Reference Works,
Juan Antonio Belmonte and Hans Deeg, Eds. TeX and figures may be found at
https://github.com/ericagol/TTV_revie
'The Drug Survey App': a protocol for developing and validating an interactive population survey tool for drug use among Aboriginal and Torres Strait Islander Australians.
BACKGROUND: Disadvantage and transgenerational trauma contribute to Aboriginal and Torres Strait Islander (Indigenous) Australians being more likely to experience adverse health consequences from alcohol and other drug use than non-Indigenous peoples. Addressing these health inequities requires local monitoring of alcohol and other drug use. While culturally appropriate methods for measuring drinking patterns among Indigenous Australians have been established, no similar methods are available for measuring other drug use patterns (amount and frequency of consumption). This paper describes a protocol for creating and validating a tablet-based survey for alcohol and other drugs ("The Drug Survey App"). METHODS: The Drug Survey App will be co-designed with stakeholders including Indigenous Australian health professionals, addiction specialists, community leaders, and researchers. The App will allow participants to describe their drug use flexibly with an interactive, visual interface. The validity of estimated consumption patterns, and risk assessments will be tested against those made in clinical interviews conducted by Indigenous Australian health professionals. We will then trial the App as a population survey tool by using the App to determine the prevalence of substance use in two Indigenous communities. DISCUSSION: The App could empower Indigenous Australian communities to conduct independent research that informs local prevention and treatment efforts
NLO QCD bottom corrections to Higgs boson production in the MSSM
We present a calculation of the two-loop bottom-sbottom-gluino contributions
to Higgs boson production via gluon fusion in the MSSM. The calculation is
based on an asymptotic expansion in the masses of the supersymmetric particles,
which are assumed to be much heavier than the bottom quark and the Higgs
bosons. We obtain explicit analytic results that allow for a straightforward
identification of the dominant contributions in the NLO bottom corrections. We
emphasize the interplay between the calculations of the masses and the
production cross sections of the Higgs bosons, discussing sensible choices of
renormalization scheme for the parameters in the bottom/sbottom sector.Comment: 25 pages, 4 figures. v2: references and two figures added, version
published in JHE
A simple combinatorial treatment of constructions and threshold gaps of ramp schemes
We give easy proofs of some recent results concerning threshold gaps in ramp schemes. We then generalise a construction method for ramp schemes employing error-correcting codes so that it can be applied using nonlinear (as well as linear) codes. Finally, as an immediate consequence of these results, we provide a new explicit bound on the minimum length of a code having a specified distance and dual distance
Formation of Super-Earths
Super-Earths are the most abundant planets known to date and are
characterized by having sizes between that of Earth and Neptune, typical
orbital periods of less than 100 days and gaseous envelopes that are often
massive enough to significantly contribute to the planet's overall radius.
Furthermore, super-Earths regularly appear in tightly-packed multiple-planet
systems, but resonant configurations in such systems are rare. This chapters
summarizes current super-Earth formation theories. It starts from the formation
of rocky cores and subsequent accretion of gaseous envelopes. We follow the
thermal evolution of newly formed super-Earths and discuss their atmospheric
mass loss due to disk dispersal, photoevaporation, core-cooling and collisions.
We conclude with a comparison of observations and theoretical predictions,
highlighting that even super-Earths that appear as barren rocky cores today
likely formed with primordial hydrogen and helium envelopes and discuss some
paths forward for the future.Comment: Invited review accepted for publication in the 'Handbook of
Exoplanets,' Planet Formation section, Springer Reference Works, Juan Antonio
Belmonte and Hans Deeg, Ed
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