1,431 research outputs found
Defining Renewable Groundwater Use and Its Relevance to Sustainable Groundwater Management
Groundwater systems are commonly defined as renewable or non‐renewable based on natural fluxes of recharge or on estimates of aquifer storage and groundwater residence time. However, we show here that the principle of capture (i.e., how recharge and discharge change due to pumping) challenges simple definitions so that a groundwater system cannot be renewable or non‐renewable in and of itself, but only with reference to how the groundwater is being used. We develop and propose more hydraulically informed definitions for flux‐renewable and storage‐renewable groundwater use, and a combined definition that encompasses both the flux‐based and storage‐based perspectives such that: renewable groundwater use allows for dynamically stable re‐equilibrium of groundwater levels and quality on human timescales. Further, we show how a matrix of combinations of (a) the ratio of pumping rate to the maximum rate of capture along with (b) the response or recovery timescales implicit in this definition, leads to a useful four‐quadrant framework for characterizing groundwater use, illustrated using case studies from aquifers around the world. Renewable groundwater use may inform pathways to groundwater sustainability, which encompasses a broader set of dimensions (e.g., socio‐political, economic, ecological and cultural) beyond the scope of groundwater science. We propose that separating physically robust definitions of renewable groundwater use from the inherently value‐based language of sustainability, can help bring much needed clarity to wider discussions about sustainable groundwater management strategies, and the role of groundwater science and scientists in such endeavors
The Large-scale and Small-scale Clustering of Lyman-Break Galaxies at 3.5 < z< 5.5 from the GOODS survey
We report on the angular correlation function of Lyman-break galaxies (LBGs)
at z~4 and 5 from deep samples obtained from the Great Observatories Deep
Origins Survey (GOODS). Similar to LBGs at z~3, the shape of w(theta) of the
GOODS LBGs is well approximated by a power-law with slope beta~0.6 at angular
separation theta > 10 arcsec. The clustering strength of z~4, 5 LBGs also
depends on the rest-frame UV luminosity, with brighter galaxies more strongly
clustered than fainter ones, implying a general correlation between halos' mass
and LBGs' star-formation rate. At smaller separations, w(theta) of deep samples
significantly exceeds the extrapolation of the large-scale power-law fit,
implying enhanced spatial clustering at scales r < 1 Mpc. We also find that
bright LBGs statistically have more faint companions on scales theta < 20
arcsec than fainter ones, showing that the enhanced small-scale clustering is
very likely due to sub-structure, namely the fact that massive halos can host
multiple galaxies. A simple model for the halo occupation distribution and the
CDM halo mass function reproduce well the observed w(theta). The scaling
relationship of the clustering strength with volume density and with redshift
is quantitatively consistent with that of CDM halos. A comparison of the
clustering strength of three samples of equal luminosity limit at z ~ 3, 4 and
5 shows that the LBGs at z~5 are hosted in halos about one order of magnitude
less massive than those in the lower redshift bins, suggesting that
star-formation was more efficient at higher-redshift.Comment: replaced with the version accepted for publication in ApJ. 46 pages,
10 figures; minor changes to text, one subsection adde
Transcription factor MYB26 is key to spatial specificity in anther secondary thickening formation
Successful fertilization relies on the production and effective release of viable pollen. Failure of anther opening (dehiscence), results in male sterility, although the pollen may be fully functional. MYB26 regulates the formation of secondary thickening in the anther endothecium, which is critical for anther dehiscence and fertility. Here, we show that although the MYB26 transcript shows expression in multiple floral organs, the MYB26 protein is localized specifically to the anther endothecium nuclei and that it directly regulates two NAC domain genes, NST1 and NST2, which are critical for the induction of secondary thickening biosynthesis genes. However, there is a complex relationship of regulation between these genes and MYB26. Using DEX-inducible MYB26 lines and overexpression in the various mutant backgrounds, we have shown that MYB26 up-regulates both NST1 and NST2 expression. Surprisingly normal thickening and fertility rescue does not occur in the absence of MYB26, even with constitutively induced NST1 and NST2, suggesting an additional essential role for MYB26 in this regulation. Combined overexpression of NST1 and NST2 in myb26 facilitates limited ectopic thickening in the anther epidermis, but not in the endothecium, and thus fails to rescue dehiscence. Therefore, by a series of regulatory controls through MYB26, NST1, NST2, secondary thickening is formed specifically within the endothecium; this specificity is essential for anther opening
Harassment Origin for Kinematic Substructures in Dwarf Elliptical Galaxies?
We have run high resolution N-body models simulating the encounter of a dwarf
galaxy with a bright elliptical galaxy. The dwarf absorbs orbital angular
momentum and shows counter-rotating features in the external regions of the
galaxy. To explain the core-envelope kinematic decoupling observed in some
dwarf galaxies in high-density environments requires nearly head-on collisions
and very little dark matter bound to the dwarf. These kinematic structures
appear under rather restrictive conditions. As a consequence, in a cluster like
Virgo ~1% of dwarf galaxies may present counter-rotation formed by harassment.Comment: 10 pages, 7 figures; Accepted for publication in Astronomy and
Astrophysic
The Stellar Mass Components of Galaxies: Comparing Semi-Analytical Models with Observation
We compare the stellar masses of central and satellite galaxies predicted by
three independent semianalytical models with observational results obtained
from a large galaxy group catalogue constructed from the Sloan Digital Sky
Survey. In particular, we compare the stellar mass functions of centrals and
satellites, the relation between total stellar mass and halo mass, and the
conditional stellar mass functions, which specify the average number of
galaxies of stellar mass M_* that reside in a halo of mass M_h. The
semi-analytical models only predict the correct stellar masses of central
galaxies within a limited mass range and all models fail to reproduce the sharp
decline of stellar mass with decreasing halo mass observed at the low mass end.
In addition, all models over-predict the number of satellite galaxies by
roughly a factor of two. The predicted stellar mass in satellite galaxies can
be made to match the data by assuming that a significant fraction of satellite
galaxies are tidally stripped and disrupted, giving rise to a population of
intra-cluster stars in their host halos. However, the amount of intra-cluster
stars thus predicted is too large compared to observation. This suggests that
current galaxy formation models still have serious problems in modeling star
formation in low-mass halos.Comment: 12 pages, 6 figures, accepted for publication in Ap
Industrial work placement in higher education: a study of civil engineering student engagement
For civil engineering undergraduates, the opportunity to spend a period of time in formal industrial work placement provides an invaluable learning experience. This paper reviews student engagement with short-term industrial placement and provides analysis of questionnaires (n=174) returned by undergraduates studying civil engineering at four Higher Education Institutes (HEI’s) in the West of Scotland. The data captures industrial placement statistics, employability skill-sets and presents brief testimonies from students. Whilst the journey to becoming a professional civil engineer is undoubtedly enhanced by short-term placement clear opportunities exist for HEI’s to affect and change existing pedagogical discourse. Commentary is likely to resonate beyond civil engineering and serve as a timely reminder of the need to re-invigorate academia / industry curriculum partnerships
From z>6 to z~2: Unearthing Galaxies at the Edge of the Dark Ages
Galaxies undergoing formation and evolution can now be observed over a time
baseline of some 12 Gyr. An inherent difficulty with high-redshift observations
is that the objects are very faint and the best resolution (HST) is only ~0.5
kpc. Such studies thereby combine in a highly synergistic way with the great
detail that can be obtained for nearby galaxies. 3 new developments are
highlighted. First is the derivation of stellar masses for galaxies from SEDs
using HST and now Spitzer data, and dynamical masses from both sub-mm
observations of CO lines and near-IR observations of optical lines like Halpha.
A major step has been taken with evidence that points to the z~2-3 LBGs having
masses that are a few x 10^10 Msolar. Second is the discovery of a population
of evolved red galaxies at z~2-3 which appear to be the progenitors of the more
massive early-type galaxies of today, with dynamical masses around a few x
10^11 Msolar. Third are the remarkable advances that have occurred in
characterizing dropout galaxies to z~6 and beyond, < 1 Gyr from recombination.
The HST ACS has played a key role here, with the dropout technique being
applied to i & z images in several deep ACS fields, yielding large samples of
these objects. This has allowed a detailed determination of their properties
and meaningful comparisons against lower-z samples. The use of cloning
techniques has overcome many of the strong selection biases affecting the study
of these objects. A clear trend of size with redshift has been identified, and
its impact on the luminosity density and SFR estimated. There is a significant
though modest decrease in the SFR from z~2.5 to z~6. The latest data also allow
for the first robust determination of the LF at z~6. Finally, the latest UDF
ACS and NICMOS data has resulted in the detection of some galaxies at z~7-8.Comment: 18 pages, 8 figures. To appear in Penetrating Bars through Masks of
Cosmic Dust: The Hubble Tuning Fork Strikes a New Note, eds. D. Block, K.
Freeman, R. Groess, I. Puerari, & E.K. Block (Dordrecht: Kluwer), in pres
The origin of the mu_e - M_B and Kormendy relations in dwarf elliptical galaxies
The present work is aimed at studying the distribution of galaxies of
different types and luminosities along different structural scaling relations
to see whether massive and dwarf ellipticals have been shaped by the same
formation process. This exercise is here done by comparing the distribution of
Virgo cluster massive and dwarf ellipticals and star forming galaxies along the
B band effective surface brightness and effective radius vs. absolute magnitude
relations and the Kormendy relation to the predictions of models tracing the
effects of ram-pressure stripping on disc galaxies entering the cluster
environment and galaxy harassment. Dwarf ellipticals might have been formed
from low luminosity, late-type spirals that recently entered into the cluster
and lost their gas because of a ram-pressure stripping event, stopping their
activity of star formation. The perturbations induced by the abrupt decrease of
the star formation activity are sufficient to modify the structural properties
of disc galaxies into those of dwarf ellipticals. Galaxy harassment induce a
truncation of the disc and generally an increase of the effective surface
brightness of the perturbed galaxies. The lack of dynamical simulations of
perturbed galaxies spanning a wide range in luminosity prevents us to drive any
firm conclusion on a possible harassment-induced origin of the low surface
brightness dwarf elliptical galaxy population inhabiting the Virgo cluster.
Although the observed scaling relations are consistent with the idea that the
distribution of elliptical galaxies along the mentioned scaling relation is
just due to a gradual variation with luminosity of the Sersic index n, the
comparison with models indicates that dwarf ellipticals might have been formed
by a totally different process than giant ellipticalsComment: Accepted for publication on A&
The origin of the light distribution in spiral galaxies
We analyse a high-resolution, fully cosmological, hydrodynamical disc galaxy simulation, to study the source of the double-exponential light profiles seen in many stellar discs, and the effects of stellar radial migration upon the spatiotemporal evolution of both the disc age and metallicity distributions. We find a ‘break’ in the pure exponential stellar surface brightness profile, and trace its origin to a sharp decrease in the star formation per unit surface area, itself produced by a decrease in the gas volume density due to a warping of the gas disc. Star formation in the disc continues well beyond the break. We find that the break is more pronounced in bluer wavebands. By contrast, we find little or no break in the mass density profile. This is, in part, due to the net radial migration of stars towards the external parts of the disc. Beyond the break radius, we find that ∼60 per cent of the resident stars migrated from the inner disc, while ∼25 per cent formed in situ. Our simulated galaxy also has a minimum in the age profile at the break radius but, in disagreement with some previous studies, migration is not the main mechanism producing this shape. In our simulation, the disc metallicity gradient flattens with time, consistent with an ‘inside-out’ formation scenario. We do not find any difference in the intensity or the position of the break with inclination, suggesting that perhaps the differences found in empirical studies are driven by dust extinction
Role of Complement Regulatory Proteins in the Survival of Murine Allo-transplanted Sertoli Cells
Sertoli cells (SC) are known to contain immunoprotective properties, which allow them to survive as allografts without the use of immunosuppressive drugs. Experiments were designed to determine which factors are related to prolonged survival of allogeneic SC. Balb/c derived Sertoli (TM4) and colon cancer (CT-26) cell lines were implanted beneath the kidney capsule of non-immunosuppressed C57BL/6 mice and compared their survival as allografts. Compared to TM4 graft, which survived more than 7 days after transplantation, CT-26 showed massive infiltration of polymorphonuclear cells, necrosis and enlargement of draining lymph nodes. Cultured cell lines showed no differences in their expression patterns of FasL, TGF β1, clusterin and two complement regulatory proteins (CRP, i.e., membrane cofactor protein, MCP; decay accelerating factor, DAF), but protectin (CD59), another member of CRP was expressed only on TM4. These results suggest that CD59 and unknown factors may contribute to the prolonged survival of SC in non-immunoprivileged sites
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