829 research outputs found
Challenges in operationalizing the water–energy–food nexus
Concerns about the water–energy–food (WEF) nexus have motivated many discussions regarding new approaches for managing water, energy and food resources. Despite the progress in recent years, there remain many challenges in scientific research on the WEF nexus, while implementation as a management tool is just beginning. The scientific challenges are primarily related to data, information and knowledge gaps in our understanding of the WEF inter-linkages. Our ability to untangle the WEF nexus is also limited by the lack of systematic tools that could address all the trade-offs involved in the nexus. Future research needs to strengthen the pool of information. It is also important to develop integrated software platforms and tools for systematic analysis of the WEF nexus. The experience made in integrated water resources management in the hydrological community, especially in the framework of Panta Rhei, is particularly well suited to take a lead in these advances
Epistemological dimensions of the water–energy–food nexus approach: reply to discussions of “Challenges in operationalizing the water–energy–food nexus”
We thank the authors, Varis and Keskinen, and Nauditt, for their constructive contributions. We endorse their key comments, further referring to recent literature and events, including the UN 2018 High Level Political Forum on sustainable development. Here, we elaborate on the epistemological perspective of the water–energy–food nexus conceptualization, assessment, discourse and operationalization
A novel coil array for combined TMS/fMRI experiments at 3 T
PURPOSE: To overcome current limitations in combined transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) studies by employing a dedicated coil array design for 3 Tesla. METHODS: The state-of-the-art setup for concurrent TMS/fMRI is to use a large birdcage head coil, with the TMS between the subject's head and the MR coil. This setup has drawbacks in sensitivity, positioning, and available imaging techniques. In this study, an ultraslim 7-channel receive-only coil array for 3 T, which can be placed between the subject's head and the TMS, is presented. Interactions between the devices are investigated and the performance of the new setup is evaluated in comparison to the state-of-the-art setup. RESULTS: MR sensitivity obtained at the depth of the TMS stimulation is increased by a factor of five. Parallel imaging with an acceleration factor of two is feasible with low g-factors. Possible interactions between TMS and the novel hardware were investigated and were found negligible. CONCLUSION: The novel coil array is safe, strongly improves signal-to-noise ratio in concurrent TMS/fMRI experiments, enables parallel imaging, and allows for flexible positioning of the TMS on the head while ensuring efficient TMS stimulation due to its ultraslim design
Statistical modeling of ground motion relations for seismic hazard analysis
We introduce a new approach for ground motion relations (GMR) in the
probabilistic seismic hazard analysis (PSHA), being influenced by the extreme
value theory of mathematical statistics. Therein, we understand a GMR as a
random function. We derive mathematically the principle of area-equivalence;
wherein two alternative GMRs have an equivalent influence on the hazard if
these GMRs have equivalent area functions. This includes local biases. An
interpretation of the difference between these GMRs (an actual and a modeled
one) as a random component leads to a general overestimation of residual
variance and hazard. Beside this, we discuss important aspects of classical
approaches and discover discrepancies with the state of the art of stochastics
and statistics (model selection and significance, test of distribution
assumptions, extreme value statistics). We criticize especially the assumption
of logarithmic normally distributed residuals of maxima like the peak ground
acceleration (PGA). The natural distribution of its individual random component
(equivalent to exp(epsilon_0) of Joyner and Boore 1993) is the generalized
extreme value. We show by numerical researches that the actual distribution can
be hidden and a wrong distribution assumption can influence the PSHA negatively
as the negligence of area equivalence does. Finally, we suggest an estimation
concept for GMRs of PSHA with a regression-free variance estimation of the
individual random component. We demonstrate the advantages of event-specific
GMRs by analyzing data sets from the PEER strong motion database and estimate
event-specific GMRs. Therein, the majority of the best models base on an
anisotropic point source approach. The residual variance of logarithmized PGA
is significantly smaller than in previous models. We validate the estimations
for the event with the largest sample by empirical area functions. etc
Giant Molecular clouds: what are they made from, and how do they get there?
We analyse the results of four simulations of isolated galaxies: two with a
rigid spiral potential of fixed pattern speed, but with different degrees of
star-formation induced feedback, one with an axisymmetric galactic potential
and one with a `live' self-gravitating stellar component. Since we use a
Lagrangian method we are able to select gas that lies within giant molecular
clouds (GMCs) at a particular timeframe, and to then study the properties of
this gas at earlier and later times. We find that gas which forms GMCs is not
typical of the interstellar medium at least 50 Myr before the clouds form and
reaches mean densities within an order of magnitude of mean cloud densities by
around 10 Myr before. The gas in GMCs takes at least 50 Myr to return to
typical ISM gas after dispersal by stellar feedback, and in some cases the gas
is never fully recycled. We also present a study of the two-dimensional,
vertically-averaged velocity fields within the ISM. We show that the velocity
fields corresponding to the shortest timescales (that is, those timescales
closest to the immediate formation and dissipation of the clouds) can be
readily understood in terms of the various cloud formation and dissipation
mechanisms. Properties of the flow patterns can be used to distinguish the
processes which drive converging flows (e.g.\ spiral shocks, supernovae) and
thus molecular cloud formation, and we note that such properties may be
detectable with future observations of nearby galaxies.Comment: 13 pages, 8 figures, accepted for publication in MNRA
Searching for links between magnetic fields and stellar evolution. II. The evolution of magnetic fields as revealed by observations of Ap stars in open clusters and associations
The evolution of magnetic fields in Ap stars during the main sequence phase
is presently mostly unconstrained by observation because of the difficulty of
assigning accurate ages to known field Ap stars.
We are carrying out a large survey of magnetic fields in cluster Ap stars
with the goal of obtaining a sample of these stars with well-determined ages.
In this paper we analyse the information available from the survey as it
currently stands.
We select from the available observational sample the stars that are probably
(1) cluster or association members and (2) magnetic Ap stars. For the stars in
this subsample we determine the fundamental parameters T_eff, log(L/L_o), and
M/M_o. With these data and the cluster ages we assign both absolute age and
fractional age (the fraction of the main sequence lifetime completed). For this
purpose we have derived new bolometric corrections for Ap stars.
Magnetic fields are present at the surfaces of Ap stars from the ZAMS to the
TAMS. Statistically for the stars with M > 3 M_o the fields decline with
advancing age approximately as expected from flux conservation together with
increased stellar radius, or perhaps even faster than this rate, on a time
scale of about 3 10^7 yr. In contrast, lower mass stars show no compelling
evidence for field decrease even on a timescale of several times 10^8 yr.
Study of magnetic cluster stars is now a powerful tool for obtaining
constraints on evolution of Ap stars through the main sequence. Enlarging the
sample of known cluster magnetic stars, and obtaining more precise RMS fields,
will help to clarify the results obtained so far. Further field observations
are in progress.Comment: Accepted by Astronomy & Astrophysic
GMC formation by agglomeration and self gravity
We investigate the formation of GMCs in spiral galaxies through both
agglomeration of clouds in the spiral arms, and self gravity. The simulations
presented include two-fluid models, which contain both cold and warm gas,
although there is no heating or cooling between them. We find agglomeration is
predominant when both the warm and cold components of the ISM are effectively
stable to gravitational instabilities. In this case, the spacing (and
consequently mass) of clouds and spurs along the spiral arms is determined by
the orbits of the gas particles and correlates with their epicyclic radii (or
equivalently spiral shock strength). Notably GMCs formed primarily by
agglomeration tend to be unbound associations of many smaller clouds, which
disperse upon leaving the spiral arms. These GMCs are likely to be more massive
in galaxies with stronger spiral shocks or higher surface densities. GMCs
formed by agglomeration are also found to exhibit both prograde and retrograde
rotation, a consequence of the clumpiness of the gas. At higher surface
densities, self gravity becomes more important in arranging both the warm and
cold gas into clouds and spurs, and determining the properties of the most
massive GMCs. These massive GMCs can be distinguished by their higher angular
momentum, exhibit prograde rotation and are more bound. For a 20 M
pc disc, the spacing between the GMCs fits both the agglomeration and
self gravity scenarios, as the maximum unstable wavelength of gravitational
perturbations in the warm gas is similar to the spacing found when GMCs form
solely by agglomeration.Comment: 16 pages, 12 figures, accepted for publication in MNRAS. Version with
higher resolution figures available at
http://www.astro.ex.ac.uk/people/dobbs/Dobbsgr.pd
On the Spiral Structure of the Milky Way Galaxy
We consider the possible pattern of the overall spiral structure of the
Galaxy, using data on the distribution of neutral (atomic), molecular, and
ionized hydrogen, on the base of the hypothesis of the spiral structure being
symmetric, i.e. the assumption that spiral arms are translated into each other
for a rotation around the galactic center by 180{\deg} (a two-arm pattern) or
by 90{\deg} (a four-arm pattern). We demonstrate that, for the inner region,
the observations are best represented with a four-arm scheme of the spiral
pattern, associated with all-Galaxy spiral density waves. The basic position is
that of the Carina arm, reliably determined from distances to HII regions and
from HI and H2 radial velocities. This pattern is continued in the quadrants
III and IV with weak outer HI arms; from their morphology, the Galaxy should be
considered an asymmetric multi-arm spiral. The kneed shape of the outer arms
that consist of straight segments can indicate that these arms are transient
formations that appeared due to a gravitational instability in the gas disk.
The distances between HI superclouds in the two arms that are the brightest in
neutral hydrogen, the Carina arm and the Cygnus (Outer) arm, concentrate to two
values, permitting to assume the presence of a regular magnetic field in these
arms.Comment: 21 pages, 14 fugures; accepted for publication in Astronomichesky
Journal (Astron. Rep.
Monocytes regulate the mechanism of T-cell death by inducing Fas-mediated apoptosis during bacterial infection.
Monocytes and T-cells are critical to the host response to acute bacterial infection but monocytes are primarily viewed as amplifying the inflammatory signal. The mechanisms of cell death regulating T-cell numbers at sites of infection are incompletely characterized. T-cell death in cultures of peripheral blood mononuclear cells (PBMC) showed 'classic' features of apoptosis following exposure to pneumococci. Conversely, purified CD3(+) T-cells cultured with pneumococci demonstrated necrosis with membrane permeabilization. The death of purified CD3(+) T-cells was not inhibited by necrostatin, but required the bacterial toxin pneumolysin. Apoptosis of CD3(+) T-cells in PBMC cultures required 'classical' CD14(+) monocytes, which enhanced T-cell activation. CD3(+) T-cell death was enhanced in HIV-seropositive individuals. Monocyte-mediated CD3(+) T-cell apoptotic death was Fas-dependent both in vitro and in vivo. In the early stages of the T-cell dependent host response to pneumococci reduced Fas ligand mediated T-cell apoptosis was associated with decreased bacterial clearance in the lung and increased bacteremia. In summary monocytes converted pathogen-associated necrosis into Fas-dependent apoptosis and regulated levels of activated T-cells at sites of acute bacterial infection. These changes were associated with enhanced bacterial clearance in the lung and reduced levels of invasive pneumococcal disease
Capacity development and knowledge transfer on the climate, land, water and energy nexus
Applying the concept of the nexus of climate, land, energy and water systems (CLEWs) to sustainable development requires the integration of knowledge from different disciplines to solve complicated multi-systems challenges. Such knowledge and expertise are not solely situated in scientific research’s theoretical realm (i.e. branch of knowledge). For the approach to be successful, integration is also required in a variety of decision spaces. The development of nexus knowledge, which we define as information related to systems’ physical, natural and socioeconomic interactions, broadly emerged from project-oriented research and case
study applications, extending the system’s coverage to several resource systems, climate and governance
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