1,248 research outputs found
Caracterización de pizarras comerciales del NO de España a partir de DRX, microscopía electrónica (EMPA, SEM, TEM) y FRX
Mathematical programming models for scheduling locks in sequence
We investigate the scheduling of series of consecutive locks. This setting occurs naturally along canals and waterways. We describe a problem that generalizes different models that have been studied in literature. Our contribution is to (i) provide two distinct mathematical programming formulations, and compare them empirically, (ii) show how these models allow for minimizing emission by having the speed of a ship as a decision variable, (iii) to compare, on realistic instances, the optimum solution found by solving the models with the outcome of a decentralized heuristic
Conformal Symmetries of the Self-Dual Yang-Mills Equations
We describe an infinite-dimensional Kac-Moody-Virasoro algebra of new hidden
symmetries for the self-dual Yang-Mills equations related to conformal
transformations of the 4-dimensional base space.Comment: 12 pages, Late
Seasonal forecasting of groundwater levels in principal aquifers of the United Kingdom
To date, the majority of hydrological forecasting studies have focussed on using medium-range (3–15 days) weather forecasts to drive hydrological models and make predictions of future river flows. With recent developments in seasonal (1–3 months) weather forecast skill, such as those from the latest version of the UK Met Office global seasonal forecast system (GloSea5), there is now an opportunity to use similar methodologies to forecast groundwater levels in more slowly responding aquifers on seasonal timescales. This study uses seasonal rainfall forecasts and a lumped groundwater model to simulate groundwater levels at 21 locations in the United Kingdom up to three months into the future. The results indicate that the forecasts have skill; outperforming a persistence forecast and demonstrating reliability, resolution and discrimination. However, there is currently little to gain from using seasonal rainfall forecasts over using site climatology for this type of application. Furthermore, the forecasts are not able to capture extreme groundwater levels, primarily because of inadequacies in the driving rainfall forecasts. The findings also show that the origin of forecast skill, be it from the meteorological input, groundwater model or initial condition, is site specific and related to the groundwater response characteristics to rainfall and antecedent hydro-meteorological conditions
Anti-self-dual conformal structures with null Killing vectors from projective structures
Using twistor methods, we explicitly construct all local forms of
four--dimensional real analytic neutral signature anti--self--dual conformal
structures with a null conformal Killing vector. We show that is
foliated by anti-self-dual null surfaces, and the two-dimensional leaf space
inherits a natural projective structure. The twistor space of this projective
structure is the quotient of the twistor space of by the group action
induced by the conformal Killing vector.
We obtain a local classification which branches according to whether or not
the conformal Killing vector is hyper-surface orthogonal in . We give
examples of conformal classes which contain Ricci--flat metrics on compact
complex surfaces and discuss other conformal classes with no Ricci--flat
metrics.Comment: 43 pages, 4 figures. Theorem 2 has been improved: ASD metrics are
given in terms of general projective structures without needing to choose
special representatives of the projective connection. More examples (primary
Kodaira surface, neutral Fefferman structure) have been included. Algebraic
type of the Weyl tensor has been clarified. Final version, to appear in
Commun Math Phy
XRD, electron microscopy (EMPA, SEM, TEM) and XRF characterization of roofing slates from NW Spain
[EN] The aim of this paper is to characterize thoroughly the mineralogy and petrography of a set of
ten different types of commercial roofing slates from the NW of Spain. Representative samples of
each type have been studied by transmitted and reflected-light optical microscopy, scanning and
transmission electron microscopy, electron microprobe, X-ray fluorescence and X-ray diffraction
techniques. Quantitative analyses of the main mineral percentages in each slate sample were
made from XRD data using the Siroquant™ interpretation software system, based on Rietveld
principles. The microscopic textures of the slates vary depending on the samples, and lepidoblastic
to porphyroblastic textures have been described. Some slates with bands of sand layers display
grano-lepidoblastic textures. White mica, quartz, chlorite and feldspar (albite) are the main minerals.
The white micas and the chlorites have similar compositions in all the analyzed samples. Electron
microprobe analyses indicate that the micas are K-rich dioctahedral varieties, having a composition close to muscovite with a phengitic component. They show the following average formula: (Na0.16
K1.39 Ca0.01) (Al3.83 Ti0.03 Fe0.15 Mg0.14) (Si6.22 Al1.78) O20 (OH)4. The chlorites are magnesian chamosites
with an average formula of (Na0.02 K0.04 Ca0.01Al3.24 Ti0.01 Fe5.13 Mn0.03 Mg3.28) (Si5.23 Al2.77) O20 (OH)16.
Accessory minerals are ilmenite, rutile, sulphides, carbonates, graphite, monazite, apatite, zircon
and tourmaline. Two different associations of sulphide minerals are distinguished: 1) Type I with
pyrite, pyrrhotite, pentlandite, cobaltite, chalcopyrite, sphalerite, galena, ullmannite and gersdorffite
occurring as pre-kinematic porphydic aggregates; b) Type II mainly with post-kinematic pyrite and
sporadic chalcopyrite and galena. The main carbonate mineral is ankerite ((Mg0.26, Ca0.49, Mn0.05,
Fe0.19) CO3) with minor calcite and siderite also present.S
Hidden Symmetries and Integrable Hierarchy of the N=4 Supersymmetric Yang-Mills Equations
We describe an infinite-dimensional algebra of hidden symmetries of N=4
supersymmetric Yang-Mills (SYM) theory. Our derivation is based on a
generalization of the supertwistor correspondence. Using the latter, we
construct an infinite sequence of flows on the solution space of the N=4 SYM
equations. The dependence of the SYM fields on the parameters along the flows
can be recovered by solving the equations of the hierarchy. We embed the N=4
SYM equations in the infinite system of the hierarchy equations and show that
this SYM hierarchy is associated with an infinite set of graded symmetries
recursively generated from supertranslations. Presumably, the existence of such
nonlocal symmetries underlies the observed integrable structures in quantum N=4
SYM theory.Comment: 24 page
Optical microscope and SEM evaluation of roofing slate fissility and durability
Texto en español e inglés.[ES] Para evaluar la fisibilidad y la durabilidad de pizarras de
techar comerciales, muestras representativas de diez yacimientos
del NO de España han sido estudiadas mediante
microscopía óptica de luz transmitida y reflejada, microscopía
electrónica de barrido y ensayos tecnológicos.
Los sulfuros dominantes en las diferentes pizarras estudiadas
son pirita o pirrotina, por lo que la alterabilidad de
estas es muy variable. La especie carbonatada dominante
es ankerita, lo que explica la baja reactividad de estas
pizarras en medios ácidos. El espesor comercial mínimo
varía en función de la microtextura de la roca, oscilando
entre 3,5 y 5 mm.
Se propone el uso de la metodología desarrollada en este
trabajo, con objeto de eliminar la subjetividad de los
inputs de entrada utilizados en las metodologías actuales
de evaluación y modelización de yacimientos, lo que incidiría
en la mejora de los rendimientos de las explotaciones
y en la minimización de la producción de estériles.[EN] The fissility and durability of representative samples of
commercial roofing slates from ten deposits in the NW of
Spain have been evaluated using transmitted and reflectedlight
optical microscopy, scanning electron microscopy,
chemical testing and geomechanical procedures.
The dominant sulphides in the different slate samples
are pyrite and pyrrhotite, the weathering potential of
which can be highly variable. The dominant carbonate
mineral is ankerite, which explains the low reactivity of
these slates in acidic media. The minimum commercial
plate thickness varies between 3.5 and 5 mm, depending
on the microtexture of the rock.
The methodology used in this paper is proposed in order
to eliminate the subjectivity of input data that are used
in current methods of evaluation and modelling of slate
deposits, thus producing an improvement in the
profitability of mining operations and a reduction in
waste materials.S
Generation and phenotypic characterization of Pde1a mutant mice
Contains fulltext :
177029.pdf (publisher's version ) (Open Access)It has been proposed that a reduction in intracellular calcium causes an increase in intracellular cAMP and PKA activity through stimulation of calcium inhibitable adenylyl cyclase 6 and inhibition of phosphodiesterase 1 (PDE1), the main enzymes generating and degrading cAMP in the distal nephron and collecting duct, thus contributing to the development and progression of autosomal dominant polycystic kidney disease (ADPKD). In zebrafish pde1a depletion aggravates and overexpression ameliorates the cystic phenotype. To study the role of PDE1A in a mammalian system, we used a TALEN pair to Pde1a exon 7, targeting the histidine-aspartic acid dipeptide involved in ligating the active site Zn++ ion to generate two Pde1a null mouse lines. Pde1a mutants had a mild renal cystic disease and a urine concentrating defect (associated with upregulation of PDE4 activity and decreased protein kinase A dependent phosphorylation of aquaporin-2) on a wild-type genetic background and aggravated renal cystic disease on a Pkd2WS25/- background. Pde1a mutants additionally had lower aortic blood pressure and increased left ventricular (LV) ejection fraction, without a change in LV mass index, consistent with the high aortic and low cardiac expression of Pde1a in wild-type mice. These results support an important role of PDE1A in the renal pathogenesis of ADPKD and in the regulation of blood pressure
Managing groundwater supplies subject to drought: perspectives on current status and future priorities from England (UK)
Effective management of groundwater resources during drought is essential. How is groundwater currently managed during droughts, and in the face of environmental change, what should be the future priorities? Four themes are explored, from the perspective of groundwater management in England (UK): (1) integration of drought definitions; (2) enhanced fundamental monitoring; (3) integrated modelling of groundwater in the water cycle; and (4) better information sharing. Whilst these themes are considered in the context of England, globally, they are relevant wherever groundwater is affected by drought
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