8,775 research outputs found
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Modelling the inorganic nitrogen behaviour in a small Mediterranean forested catchment, Fuirosos (Catalonia)
The aim of this work was to couple a nitrogen (N) sub-model to already existent hydrological lumped (LU4-N) and semi-distributed (LU4-R-N and SD4-R-N) conceptual models, to improve our understanding of the factors and processes controlling nitrogen cycling and losses in Mediterranean catchments. The N model adopted provides a simplified conceptualization of the soil nitrogen cycle considering mineralization, nitrification, immobilization, denitrification, plant uptake, and ammonium adsorption/desorption. It also includes nitrification and denitrification in the shallow perched aquifer. We included a soil moisture threshold for all the considered soil biological processes. The results suggested that all the nitrogen processes were highly influenced by the rain episodes and that soil microbial processes occurred in pulses stimulated by soil moisture increasing after rain. Our simulation highlighted the riparian zone as a possible source of nitrate, especially after the summer drought period, but it can also act as an important sink of nitrate due to denitrification, in particular during the wettest period of the year. The riparian zone was a key element to simulate the catchment nitrate behaviour. The lumped LU4-N model (which does not include the riparian zone) could not be validated, while both the semi-distributed LU4-R-N and SD4-R-N model (which include the riparian zone) gave satisfactory results for the calibration process and acceptable results for the temporal validation process
Influencing the central heating technologies installed in homes: The role of social capital in supply chain networks
The likely installation of, and potential energy savings from, low carbon technologies in domestic buildings is not only dependent on those who fit them, but also the broader supply chains of which they are part. Despite this, the role of supply chain actors has been largely overlooked in strategies seeking to encourage the installation of more sustainable domestic heating technologies. With reference to central heating, this paper responds through an ethnographic analysis of how plumbers' merchants and sales representatives can influence the work of heating installers in the United Kingdom. It applies two dimensions of the concept of 'social capital': relational and structural. Relational social capital focuses on the trust, loyalty and reciprocity at play in relations, whilst structural social capital considers how the strength of tie can influence those to whom people turn for advice and support. Together, these ideas demonstrate how relationships amongst these groups can serve to influence product choice and facilitate information exchange. The paper concludes by discussing how these supply chains might be engaged with as a means of encouraging the installation of low carbon domestic technologies
Discovery of starspots on Vega - First spectroscopic detection of surface structures on a normal A-type star
The theoretically studied impact of rapid rotation on stellar evolution needs
to be confronted with the results of high resolution spectroscopy-velocimetry
observations. A weak surface magnetic field had recently been detected in the
A0 prototype star Vega, potentially leading to a (yet undetected) structured
surface. The goal of this article is to present a thorough analysis of the line
profile variations and associated estimators in the early-type standard star
Vega (A0) in order reveal potential activity tracers, exoplanet companions and
stellar oscillations. Vega was monitored in high-resolution spectroscopy with
the velocimeter Sophie/OHP. A total of 2588 high S/N spectra was obtained
during 5 nights (August 2012) at R = 75000 and covering the visible domain. For
each reduced spectrum, Least Square Deconvolved (LSD) equivalent photospheric
profiles were calculated with a Teff = 9500 and logg = 4.0 spectral line mask.
Several methods were applied to study the dynamic behavior of the profile
variations (evolution of radial velocity, bisectors, vspan, 2D profiles,
amongst others). We present the discovery of a starspotted stellar surface in
an A-type standard star with faint spot amplitudes Delta F/Fc ~5 10^{-4}. A
rotational modulation of spectral lines with a period of rotation P = 0.68 d
has clearly been exhibited, confirming the results of previous
spectropolarimetric studies. Either a very thin convective layer can be
responsible for magnetic field generation at small amplitudes, or a new
mechanism has to be invoked in order to explain the existence of activity
tracing starspots. This first strong evidence that standard A-type stars can
show surface structures opens a new field of research and asks the question
about a potential link with the recently discovered weak magnetic field
discoveries in this category of stars.Comment: accepted for publication by Astronomy & Astrophysics (23rd of March
2015
Ultraviolet Spectra of CV Accretion Disks with Non-Steady T(r) Laws
An extensive grid of synthetic mid- and far-ultraviolet spectra for accretion
disks in cataclysmic variables has been presented by Wade and Hubeny (1998). In
those models, the disk was assumed to be in steady-state, that is T_eff(r) is
specified completely by the mass M_WD and radius R_WD of the accreting white
dwarf star and the mass transfer rate M_dot which is constant throughout the
disk. In these models, T_eff(r) is proportional to r^{-3/4} except as modified
by a cutoff term near the white dwarf.
Actual disks may vary from the steady-state prescription for T_eff(r),
however, e.g. owing to outburst cycles in dwarf novae M_dot not constant with
radius) or irradiation (in which case T_eff in the outer disk is raised above
T_steady). To show how the spectra of such disks might differ from the steady
case, we present a study of the ultraviolet (UV) spectra of models in which
power-law temperature profiles T_eff(r) is proportional to r^{-gamma} with
gamma < 3/4 are specified. Otherwise, the construction of the models is the
same as in the Wade & Hubeny grid, to allow comparison. We discuss both the UV
spectral energy distributions and the appearance of the UV line spectra. We
also briefly discuss the eclipse light curves of the non-standard models.
Comparison of these models with UV observations of novalike variables suggests
that better agreement may be possible with such modified T_eff(r) profiles.Comment: 13 pages, 6 figures (one reduced quality), ApJ in pres
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Intrinsic Frontolimbic Connectivity and Mood Symptoms in Young Adult Cannabis Users.
Objective: The endocannbinoid system and cannabis exposure has been implicated in emotional processing. The current study examined whether regular cannabis users demonstrated abnormal intrinsic (a.k.a. resting state) frontolimbic connectivity compared to non-users. A secondary aim examined the relationship between cannabis group connectivity differences and self-reported mood and affect symptoms. Method: Participants included 79 cannabis-using and 80 non-using control emerging adults (ages of 18-30), balanced for gender, reading ability, and age. Standard multiple regressions were used to predict if cannabis group status was associated with frontolimbic connectivity after controlling for site, past month alcohol and nicotine use, and days of abstinence from cannabis. Results: After controlling for research site, past month alcohol and nicotine use, and days of abstinence from cannabis, cannabis users demonstrated significantly greater connectivity between left rACC and the following: right rACC (p = 0.001; corrected p = 0.05; f 2 = 0.55), left amygdala (p = 0.03; corrected p = 0.47; f 2 = 0.17), and left insula (p = 0.03; corrected p = 0.47; f 2 = 0.16). Among cannabis users, greater bilateral rACC connectivity was significantly associated with greater subthreshold depressive symptoms (p = 0.02). Conclusions: Cannabis using young adults demonstrated greater connectivity within frontolimbic regions compared to controls. In cannabis users, greater bilateral rACC intrinsic connectivity was associated with greater levels of subthreshold depression symptoms. Current findings suggest that regular cannabis use during adolescence is associated with abnormal frontolimbic connectivity, especially in cognitive control and emotion regulation regions
Long-term magnetic field stability of Vega
We present new spectropolarimetric observations of the normal A-type star
Vega, obtained during the summer of 2010 with NARVAL at T\'elescope Bernard
Lyot (Pic du Midi Observatory). This new time-series is constituted of 615
spectra collected over 6 different nights. We use the
Least-Square-Deconvolution technique to compute, from each spectrum, a mean
line profile with a signal-to-noise ratio close to 20,000. After averaging all
615 polarized observations, we detect a circularly polarized Zeeman signature
consistent in shape and amplitude with the signatures previously reported from
our observations of 2008 and 2009. The surface magnetic geometry of the star,
reconstructed using the technique of Zeeman-Doppler Imaging, agrees with the
maps obtained in 2008 and 2009, showing that most recognizable features of the
photospheric field of Vega are only weakly distorted by large-scale surface
flows (differential rotation or meridional circulation).Comment: Proceedings of the conference "Stellar polarimetry: from birth to
death", 2011 Jun 27-30, Madiso
Anisotropic Magneto-Thermopower: the Contribution of Interband Relaxation
Spin injection in metallic normal/ferromagnetic junctions is investigated
taking into account the anisotropic magnetoresistance (AMR) occurring in the
ferromagnetic layer. It is shown, on the basis of a generalized two channel
model, that there is an interface resistance contribution due to anisotropic
scattering, beyond spin accumulation and giant magnetoresistance (GMR). The
corresponding expression of the thermopower is derived and compared with the
expression for the thermopower produced by the GMR. First measurements of
anisotropic magnetothermopower are presented in electrodeposited Ni nanowires
contacted with Ni, Au and Cu. The results of this study show that while the
giant magnetoresistance and corresponding thermopower demonstrates the role of
spin-flip scattering, the observed anisotropic magnetothermopower indicates
interband s-d relaxation mechanisms.Comment: 20 pages, 4 figure
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