1,454 research outputs found
Investigating the productivity and sustainability of weathered basement aquifers in tropical Africa using numerical simulation and global sensitivity analysis
Groundwater stored in weathered basement aquifers (WBAs) is a strategic water resource. In this study, we investigate the productivity of WBAs and sustainability of groundwater abstractions using a novel processâbased stochastic modeling approach, which is applied to simulate abstractions in the Precambrian basement aquifer in Ghana. The statistical distribution of the generated synthetic yield data was found in very good agreement with observed yield data from the same Ghanaian aquifer. Further analysis provided robust insights regarding how different hydrogeological parameters of the WBA, and their interplay, control aquifer productivity and sustainability. Results indicate that 97% of the simulated abstractions could sustain the yield of a hand pump (6 L/min), approximately 30% could also sustain yields >60 L/min, while only 1% could sustain yields greater than 300 L/min. The model indicates that an aquifer transmissivity value of approximately 1.4 m2/day is required for a successful handâpumped borehole, while a higher yielding source (60 L/min) requires a transmissivity value of at least 9.5 m2/day. A global sensitivity analysis of 13 model input parameters shows that the thickness of the regolith and the maximum hydraulic conductivity developed at the base of the saprolite are the critical factors controlling success and sustainability for low yielding handâpumped boreholes. For higher yielding supplies, the net recharge, the depth to groundwater, and the aquifer extent become increasingly significant. Results from this work have important implications for the potential for increased development of groundwater from WBAs in tropical Africa
Universal Features of Holographic Anomalies
We study the mechanism by which gravitational actions reproduce the trace
anomalies of the holographically related conformal field theories. Two
universal features emerge: a) the ratios of type B trace anomalies in any even
dimension are independent of the gravitational action, being uniquely
determined by the underlying algebraic structure b) the normalization of the
type A and the overall normalization of the type B anomalies are given by
action dependent expressions with the dimension dependence completely fixed.Comment: 17 pages, harvma
Short distance properties of cascading gauge theories
We study the short distance (large momentum) properties of correlation
functions of cascading gauge theories by performing a tree-level computation in
their dual gravitational background. We prove that these theories are
holographically renormalizable; the correlators have only analytic ultraviolet
divergences, which may be removed by appropriate local counterterms. We find
that n-point correlation functions of properly normalized operators have the
expected scaling in the semi-classical gravity (large N) limit: they scale as
N_{eff}^{2-n} with N_{eff} proportional to ln(k/Lambda) where k is a typical
momentum. Our analysis thus confirms the interpretation of the cascading gauge
theories as renormalizable four-dimensional quantum field theories with an
effective number of degrees of freedom which logarithmically increases with the
energy.Comment: 47 pages, no figure
From Fake Supergravity to Superstars
The fake supergravity method is applied to 5-dimensional asymptotically AdS
spacetimes containing gravity coupled to a real scalar and an abelian gauge
field. The motivation is to obtain bulk solutions with R x S^3 symmetry in
order to explore the AdS/CFT correspondence when the boundary gauge theory is
on R x S^3. A fake supergravity action, invariant under local supersymmetry
through linear order in fermion fields, is obtained. The gauge field makes
things more restrictive than in previous applications of fake supergravity
which allowed quite general scalar potentials. Here the superpotential must
take the form W(\phi) ~ exp(-k\phi) + c exp(2\phi/(3k)), and the only freedom
is the choice of the constant k. The fermion transformation rules of fake
supergravity lead to fake Killing spinor equations. From their integrability
conditions, we obtain first order differential equations which we solve
analytically to find singular electrically charged solutions of the Lagrangian
field equations. A Schwarzschild mass term can be added to produce a horizon
which shields the singularity. The solutions, which include "superstars", turn
out to be known in the literature. We compute their holographic parameters.Comment: 42 pages, 3 figure
Stringy Instantons and Cascading Quivers
D-brane instantons can perturb the quantum field theories on space-time
filling D-branes by interesting operators. In some cases, these D-brane
instantons are novel "stringy" effects (not interpretable directly as instanton
effects in the low-energy quantum field theory), while in others the D-brane
instantons can be directly interpreted as field theory effects. In this note,
we describe a situation where both perspectives are available, by studying
stringy instantons in quivers which arise at simple Calabi-Yau singularities.
We show that a stringy instanton which wraps an unoccupied node of the quiver,
and gives rise to a non-perturbative mass in the space-time field theory, can
be reinterpreted as a conventional gauge theory effect by going up in an
appropriate renormalization group cascade. Interestingly, in the cascade, the
contribution of the stringy instanton does not come from gauge theory
instantons but from strong coupling dynamics.Comment: 17 pages, 6 figures, harvma
Transcriptional regulation of the urokinase receptor (u-PAR) - A central molecule of invasion and metastasis
The phenomenon of tumor-associated proteolysis has been acknowledged as a decisive step in the progression of cancer. This short review focuses on the urokinase receptor (u-PAR), a central molecule involved in tumor-associated invasion and metastasis, and summarizes the transcriptional regulation of u-PAR. The urokinase receptor (u-PAR) is a heavily glycosylated cell surface protein and binds the serine protease urokinase specifically and with high affinity. It consists of three similar cysteine-rich repeats and is anchored to the cell membrane via a GPI-anchor. The u-PAR gene comprises 7 exons and is located on chromosome 19q13. Transcriptional activation of the u-PAR promoter region can be induced by binding of transcription factors (Sp1, AP-1, AP-2, NF-kappaB). One current study gives an example for transcriptional downregulation of u-PAR through a PEA3/ets transcriptional silencing element. Knowledge of the molecular regulation of this molecule in tumor cells could be very important for diagnosis and therapy in the near future
Counterterms and dual holographic anomalies in CS gravity
The holographic Weyl anomaly associated to Chern-Simons gravity in 2n+1
dimensions is proportional to the Euler term in 2n dimensions, with no
contributions from the Weyl tensor. We compute the holographic energy-momentum
tensor associated to Chern-Simons gravity directly from the action, in an
arbitrary odd-dimensional spacetime. We show, in particular, that the
counterterms rendering the action finite contain only terms of the Lovelock
type.Comment: 10 pages, no figure
Exact beta function from the holographic loop equation of large-N QCD_4
We construct and study a previously defined quantum holographic effective
action whose critical equation implies the holographic loop equation of large-N
QCD_4 for planar self-avoiding loops in a certain regularization scheme. We
extract from the effective action the exact beta function in the given scheme.
For the Wilsonean coupling constant the beta function is exacly one loop and
the first coefficient agrees with its value in perturbation theory. For the
canonical coupling constant the exact beta function has a NSVZ form and the
first two coefficients agree with their value in perturbation theory.Comment: 42 pages, latex. The exponent of the Vandermonde determinant in the
quantum effective action has been changed, because it has been employed a
holomorphic rather than a hermitean resolution of identity in the functional
integral. Beta function unchanged. New explanations and references added,
typos correcte
Instantons of Type IIB Supergravity in Ten Dimensions
A family of SO(10) symmetric instanton solutions in Type IIB supergravity is
developed. The instanton of least action is a candidate for the low-energy,
semiclassical approximation to the {D=--1} brane. Unlike a previously published
solution,[GGP] this admits an interpretation as a tunneling amplitude between
perturbatively degenerate asymptotic states, but with action twice that found
previously. A number of associated issues are discussed such as the relation
between the magnetic and electric pictures, an inversion symmetry of the
dilaton and the metric, the topology of the background, and some
properties of the solution in an "instanton frame" corresponding to a
Lagrangian in which the dilaton's kinetic energy vanishes.Comment: 15 pages, no figures; Version 2 has revised sections IV and V.
Earlier equations are essentially unchanged, but interpretation changed, on
advice of counse
Assessing regional variation in yield from weathered basement aquifers in West Africa and modelling their future groundwater development and sustainability
A data-driven modelling approach was applied to quantify the potential groundwater yield from weathered crystalline basement aquifers in West Africa, which are a strategic resource for achieving water and food security. To account for possible geological control on aquifer productivity, seven major geological domains were identified based on lithological, stratigraphic, and structural characteristics of the crystalline basement. Extensive data mining was conducted for the hydrogeological parameterisation that led to the identification of representative distributions of input parameters for numerical simulations of groundwater abstractions. These were calibrated to match distributions of measured yields for each domain. Calibrated models were then applied to investigate aquifer and borehole scenarios to assess groundwater productivity. Considering the entire region, modelling results indicate that approximately 50% of well-sited standard 60-m-deep boreholes could sustain yields exceeding 0.5 L/s, and 25% could sustain the yield required for small irrigation systems (> 1.0 L/s). Results also highlighted some regional differences in the ranges of productivities for the different domains, and the significance of the depth of the static water table and the lateral extent of aquifers across all geological domains. This approach can be applied to derive groundwater maps for the region and provide the quantitative information required to evaluate the potential of different designs of groundwater supply networks
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