Search results for "solution"

Préface Special Issue 'The Future of Agricultural Landscapes' part 1

2020

Préface de Advances in Ecological Research, Volume 63, the latest release in this ongoing series includes specific chapters on Tropical Ecosystems in the 21st Century. Chapters in this volume cover topics such as Landscape-scale expansion of agroecology to enhance natural pest control: a systematic review and Ecosystem services and the resilience of agricultural landscapes

Ba/Ca ratios in shells of Arctica islandica —Potential environmental proxy and crossdating tool

2017

Abstract Ba/Ca shell time-series of marine bivalves typically show flat background levels which are interrupted by erratic sharp peaks. Evidence from the literature indicates that background Ba/Ca shell ratios broadly reflect salinity conditions. However, the causes for the Ba/Ca shell peaks are still controversial and widely debated although many researchers link these changes to primary productivity, freshwater input or spawning events. The most striking feature is that the Ba/Ca shell peaks are highly synchronous in contemporaneous specimens from the same population. For the first time, we studied Ba/Ca shell in mature and ontogenetically old (up to 251 year-old) specimens of the long-li…

Porosity of anodic alumina membranes from electrochemical measurements

2005

A procedure based on the high-field mechanism of the growth of anodic oxides was developed in order to evaluate the morphological features of porous layers. Since the thickness of the barrier film, separating the porous layer from the metal, does not change during the steady-state growth of an anodic porous layer, the rate of displacement of the metal-oxide interface to the metal direction must be equal to the rate of displacement of the pore base to the oxide direction. As a consequence, porosity can be expressed in terms of the ratio i diss/i ion, where i diss is the dissolution current density at the pore base, and i ion is the ionic current density at the metal-oxide interface. Pore dia…

Quantitation of Metal Ions in Archaeological Glass by Abrasive Stripping Square-Wave Voltammetry Using Graphite/Polyester Composite Electrodes

2003

A method for identifying Co, Cu, Sb, Sn, Fe, Zn, and Zr pigments in glasses using square-wave voltammetry as the detection mode is described. It is based on the abrasive attachment of glass microsamples to graphite/polyester composite electrodes. Sample amounts less than 1 μg are used allowing for the study of archaeological samples. In all cases well-defined anodic stripping peaks corresponding to the oxidation of metal deposits generated at potentials ranging from −0.6 to −1.6 V (vs. SCE) are obtained. This response is in agreement with that displayed by the corresponding metal oxides. Quantitative estimates of the relative population of metal ions in glasses are obtained from peak area m…

A Side-by-Side Single Sex Age-Structured Human Population Dynamic Model: Exact Solution and Model Validation

2008

A side-by-side single sex age-structured population dynamic model is presented in this paper. The model consists of two coupled von Foerster-McKendrick-type quasi-linear partial differential equations, two initial conditions, and two boundary conditions. The state variables of the model are male and female population densities. The solutions of these partial differential equations provide explicit time and age dependence of the variables. The initial conditions define the male and female population densities at the initial time, while the boundary conditions compute the male and female births at zero-age by using fertility rates. The assumptions of the nontime-dependence of the death and fe…

Bargaining for the Spoils of War: Somalia’s Failing Path from War to Peace

2014

ABSTRACTFor more than 20 years, Somalia has experienced state failure. Today, radical political Islam and groups such as al-Shabab with links to al-Qaida are gaining ground. The current federal government is failing to provide public goods, such as security, education, and health, to the population it claims to represent. To date, more than a dozen peace negotiations to end this conflict have failed. The objective of this article is to shed light on why past peace processes have failed. The study of the Mbagathi peace process that preceded the United Nations–led Djibouti peace process can help to better understand the current political stalemate and conflict in Somalia. Moreover, some of th…

Generalized curved beam on elastic foundation solved by Transfer Matrix Method

2011

A solution of space curved bars with generalized Winkler soil found by means of Transfer Matrix Method is presented. Distributed, concentrated loads and imposed strains are applied to the beam as well as rigid or elastic boundaries are considered at the ends. The proposed approach gives the analytical and numerical exact solution for circular beams and rings, loaded in the plane or perpendicular to it. A well-approximated solution can be found for general space curved bars with complex geometry. Elastic foundation is characterized by six parameters of stiffness in different directions: three for rectilinear springs and three for rotational springs. The beam has axial, shear, bending and tor…

On the critical velocities and free vibrations of axially moving elastic webs

2014

Real-time observation of the charge transfer to solvent dynamics

2013

Intermolecular electron-transfer reactions have a crucial role in biology, solution chemistry and electrochemistry. The first step of such reactions is the expulsion of the electron to the solvent, whose mechanism is determined by the structure and dynamical response of the latter. Here we visualize the electron transfer to water using ultrafast fluorescence spectroscopy with polychromatic detection from the ultraviolet to the visible region, upon photo-excitation of the so-called charge transfer to solvent states of aqueous iodide. The initial emission is short lived (similar to 60 fs) and it relaxes to a broad distribution of lower-energy charge transfer to solvent states upon rearrangeme…

Universal method to determine acidic licit and illicit drugs and personal care products in water by liquid chromatography quadrupole time-of-flight

2016

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