Physiological control of the urinary concentrating mechanism by peptide hormones

Since Wirz's study [1] the mechanisms by which the kidney produces concentrated or dilute urine have been the object of much theoretical and experimental work. In the sixties, proof of the presence of a counter current concentrating process was progressively established. They led to a coherent idea of the functioning of the system under steady state conditions: the loops of Henle, especially the thick ascending limbs, carry out the necessary osmotic work of maintaining the longitudinal osmotic pressure gradient and, in the presence of ADH (antidiuretic hormone), the final concentration process is ensured along the collecting ducts by osmotic equilibration with the surrounding medium. Several aspects of the urinary concentrating mechanism, however, are not well understood. For instance, the exact way in which the longitudinal osmotic pressure gradient, which adjusts the urine osmolality, is established or suppressed, is unknown. Knowledge of the functional properties of the various nephron segments, although considerably advanced by in vitro physiological and biochemical studies of isolated tubules, which throw light on the potentialities of each segment, is still inadequate to explain the integrated functioning of all the mechanisms concerned. However, research in this field has recently derived a renewed stimulus from in vivo studies of the endocrine factors affecting tubular transport

Managing tensions and paradoxes between stakeholders in a complex project context: Case study and model proposal

Stakeholder (SH) management has recently undertaken a turn from the traditional management "of" to managing "for" and "with" SH. Relating to this relational trend, identification and management tensions between SH is an important area of study. Indeed, from how to live with and/or resolve or not those tensions depend on the possibility of building the most beneficial cooperation possible between SH for the continuation of the project, to obtain win-win results, and to promote the shared value and common good. For this purpose, a theoretical model is suggested, based on the approaches of paradoxes and conventionalist economy of worth, supporting the identification of tensions between SH and their justifications, and the clarification it helps to bring as to win-win or shared value outcomes, or the absence of such, in the context of a complex project. The suggested model is then used in an exploratory case study. The goal is to assess its relevance, usefulness, and quality. Two theoretical contributions emerge from the data analyzed: 1) several tensions over various categories (allegiance, dimensional, temporal, learning, performance and spatial) can draw on the same justifications (rationale that opposes industrial and domestic conventions); 2) prioritization of tension categories can make it easier to resolve them. © 2016 Editora Mundos Sociais. All rights reserved

Phonons of graphene and graphitic materials derived from the empirical potential LCBOPII

We present the interatomic force constants and phonon dispersions of graphite and graphene from the LCBOPII empirical bond order potential. We find a good agreement with experimental results, particularly in comparison to other bond order potentials. From the flexural mode we determine the bending rigidity of graphene to be 0.69 eV at zero temperature. We discuss the large increase of this constant with temperature and argue that derivation of force constants from experimental values should take this feature into account. We examine also other graphitic systems, including multilayer graphene for which we show that the splitting of the flexural mode can provide a tool for characterization

Vibrations of a chain of Xe atoms in a groove of carbon nanotube bundle

We present a lattice dynamics study of the vibrations of a linear chain of Xe adsorbates in groove positions of a bundle of carbon nanotubes. The characteristic phonon frequencies are calculated and the adsorbate polarization vectors discussed. Comparison of the present results with the ones previously published shows that the adsorbate vibrations cannot be treated as completely decoupled from the vibrations of carbon nanotubes and that a significant hybridization between the adsorbate and the tube modes occurs for phonons of large wavelengths.Comment: 3 PS figure

Renal magnesium handling: New insights in understanding old problems

Many sharp-eyed readers have pointed out to us that in the photo next to the article about yams in Ghana (Spore 87, June 2000, page 8), the woman had put all her cassava in one basket, and not the yams she planned to use. Point taken. Whatever you want to point out, point to or point at, your letters, faxes and emails are always welcome at the Spore address in the box on the right. Write now.MailboxMany sharp-eyed readers have pointed out to us that in the photo next to the article about yams in Ghana (Spore 87, June 2000, page 8), the woman had put all her cassava in one basket, and not the yams she planned to use. Point taken...

Middle and Late Pleistocene environmental history of the Marsworth area, south-central England

To elucidate the Middle and Late Pleistocene environmental history of south-central England, we report the stratigraphy, sedimentology, palaeoecology and geochronology of some deposits near the foot of the Chiltern Hills scarp at Marsworth, Buckinghamshire. The Marsworth site is important because its sedimentary sequences contain a rich record of warm stages and cold stages, and it lies close to the Anglian glacial limit. Critical to its history are the origin and age of a brown pebbly silty clay (diamicton) previously interpreted as weathered till. The deposits described infill a river channel incised into chalk bedrock. They comprise clayey, silty and gravelly sediments, many containing locally derived chalk and some with molluscan, ostracod and vertebrate remains. Most of the deposits are readily attributed to periglacial and fluvial processes, and some are dated by optically stimulated luminescence to Marine Isotope Stage (MIS) 6. Although our sedimentological data do not discriminate between a glacial or periglacial interpretation of the diamicton, amino-acid dating of three molluscan taxa from beneath it indicates that it is younger than MIS 9 and older than MIS 5e. This makes a glacial interpretation unlikely, and we interpret the diamicton as a periglacial slope deposit. The Pleistocene history reconstructed for Marsworth identifies four key elements: (1) Anglian glaciation during MIS 12 closely approached Marsworth, introducing far-travelled pebbles such as Rhaxella chert and possibly some fine sand minerals into the area. (2) Interglacial environments inferred from fluvial sediments during MIS 7 varied from fully interglacial conditions during sub-stages 7e and 7c, cool temperate conditions during sub-stage 7b or 7a, temperate conditions similar to those today in central England towards the end of the interglacial, and cool temperate conditions during sub-stage 7a. (3) Periglacial activity during MIS 6 involved thermal contraction cracking, permafrost development, fracturing of chalk bedrock, fluvial activity, slopewash, mass movement and deposition of loess and coversand. (4) Fully interglacial conditions during sub-stage 5e led to renewed fluvial activity, soil formation and acidic weathering

Heteroepitaxy of La2O3La_2O_3 and La2−xYxO3La_{2-x}Y_xO_3 on GaAs (111)A by Atomic Layer Deposition: Achieving Low Interface Trap Density

GaAs metal–oxide–semiconductor devices historically suffer from Fermi-level pinning, which is mainly due to the high trap density of states at the oxide/GaAs interface. In this work, we present a new way of passivating the interface trap states by growing an epitaxial layer of high-k dielectric oxide, $La_{2–x}Y_xO_3$, on GaAs(111)A. High-quality epitaxial $La_{2–x}Y_xO_3$ thin films are achieved by an ex situ atomic layer deposition (ALD) process, and GaAs MOS capacitors made from this epitaxial structure show very good interface quality with small frequency dispersion and low interface trap densities $(D_{it})$. In particular, the $La_2O_3$/GaAs interface, which has a lattice mismatch of only 0.04%, shows very low $D_{it}$ in the GaAs bandgap, below $3 × 10^{11} cm^{–2} eV^{–1}$ near the conduction band edge. The $La_2O_3$/GaAs capacitors also show the lowest frequency dispersion of any dielectric on GaAs. This is the first achievement of such low trap densities for oxides on GaAs.Chemistry and Chemical Biolog