The Einstein-Friedrich-nonlinear scalar field system and the stability of scalar field Cosmologies

A frame representation is used to derive a first order quasi-linear symmetric hyperbolic system for a scalar field minimally coupled to gravity. This procedure is inspired by similar evolution equations introduced by Friedrich to study the Einstein-Euler system. The resulting evolution system is used to show that small nonlinear perturbations of expanding Friedman-Lema\^itre-Robertson-Walker backgrounds, with scalar field potentials satisfying certain future asymptotic conditions, decay exponentially to zero, in synchronous time.Comment: Version 4: Matches final published versio

Dynamics of Robertson-Walker spacetimes with diffusion

We study the dynamics of spatially homogeneous and isotropic spacetimes containing a fluid undergoing microscopic velocity diffusion in a cosmological scalar field. After deriving a few exact solutions of the equations, we continue by analyzing the qualitative behavior of general solutions. To this purpose we recast the equations in the form of a two dimensional dynamical system and perform a global analysis of the flow. Among the admissible behaviors, we find solutions that are asymptotically de-Sitter both in the past and future time directions and which undergo accelerated expansion at all times.Fundação para a Ciência e a Tecnologia (FCT

Pyrolysis final temperature effects on biochar stability.

Pyrolysis technology can be used for producing biochar and bio-oil simultaneously, as an effective and sustainable mean to produce renewable bioenergy and a carbon rich soil amendment that can be used for carbon sequestration and agronomic benefits. However, pyrolysis products yields and biochar stability are strongly affected by the feedstock and pyrolysis variables, especially the final temperature. This study was carried out to evaluate the effect of pyrolysis final temperature on biochar stability after thermochemical oxidation. For this experiment, two species of hardwood and two species of softwood with particle size between 0.5 and 2.0 mm were pyrolized at five different final temperatures (350, 400, 450, 500 and 550°C) for 60 min at an muffle furnace with limited supply of O2. Thermochemical oxidation was performed for the solid products (biochar). As pyrolysis final temperature increased, biochar stability increased as well, indicating that these materials would be more resistant to degradation when applied into soil

Biochar stable fraction quantification by thermochemical oxidation and assessement by 13C-NMR spectrocopy.

Although biochar is often regarded lized into carbon dioxide. However, it is unclear how much of this material is rapidly oxidized, that is, how much remain in the soil for NQPIGTRGTKQFU'ƑQTVUJCXGDGGPWPFGTVCMGP to develop methodologies to quantify the stable fraction present in biochar, quickly, easily reproducible, and that somehow represents TGCN?GNFEQPFKVKQPU6JGTGHQTGVJGCKOQHVJKU UVWF[YCUVQGXCNWCVGVJGGƑGEVQHFKƑGTGPV R[TQN[UKU?PCNVGORGTCVWTGUQPVJGUVCDKNKV[QH biochar produced from Eucalyptus dunnii wood by analyzing biochar samples before and after a thermo-chemical oxidation using 13 C NMR spec- troscopy. Stable-C fraction increased as higher R[TQN[UKU?PCNVGORGTCVWTGYCU6JGTOQEJGOical oxidation was responsible for removing labile structures still present as well as aromatic structures less resistant to degradation. Thermo-chemical oxidation was also responsible for the functionalization of biochars, being this ef- HGEVOKNFGTCUJKIJGTR[TQN[UKU?PCNVGORGTCVWTG was. The balance between C storage (Stable-C HTCEVKQPCPFCITQPQOKEDGPG?VU HWPEVKQPCNK\Ction) of biochar should be carefully evaluated, as its characteristics can vary depending on the conditions by which it was produced

Quantum critical lines in holographic phases with (un)broken symmetry

All possible scaling IR asymptotics in homogeneous, translation invariant holographic phases preserving or breaking a U(1) symmetry in the IR are classified. Scale invariant geometries where the scalar extremizes its effective potential are distinguished from hyperscaling violating geometries where the scalar runs logarithmically. It is shown that the general critical saddle-point solutions are characterized by three critical exponents ($\theta, z, \zeta$). Both exact solutions as well as leading behaviors are exhibited. Using them, neutral or charged geometries realizing both fractionalized or cohesive phases are found. The generic global IR picture emerging is that of quantum critical lines, separated by quantum critical points which correspond to the scale invariant solutions with a constant scalar.Comment: v3: 32+29 pages, 2 figures. Matches version published in JHEP. Important addition of an exponent characterizing the IR scaling of the electric potentia

Perbandingan Pendekatan Tradisional dan Semantic Web untuk Akses Informasi Sebagai Penunjang Pengambilan Keputusan

Pengambilan keputusan pada dunia industry akan membutuhkan data teks, grafik dan juga bentuk data traditional lainnya. Dengan perkembangan teknologi informasi saat ini makasifat dari sumber informasi berkembang sehingga berjumlah sangat besar, keragaman jenis sumber informasi (sintaktik, struktur, semantic) dan data volume data semakin besar serta komplek

Monitoring international migration flows in Europe. Towards a statistical data base combining data from different sources

The paper reviews techniques developed in demography, geography and statistics that are useful for bridging the gap between available data on international migration flows and the information required for policy making and research. The basic idea of the paper is as follows: to establish a coherent and consistent data base that contains sufficiently detailed, up-to-date and accurate information, data from several sources should be combined. That raises issues of definition and measurement, and of how to combine data from different origins properly. The issues may be tackled more easily if the statistics that are being compiled are viewed as different outcomes or manifestations of underlying stochastic processes governing migration. The link between the processes and their outcomes is described by models, the parameters of which must be estimated from the available data. That may be done within the context of socio-demographic accounting. The paper discusses the experience of the U.S. Bureau of the Census in combining migration data from several sources. It also summarizes the many efforts in Europe to establish a coherent and consistent data base on international migration. The paper was written at IIASA. It is part of the Migration Estimation Study, which is a collaborative IIASA-University of Groningen project, funded by the Netherlands Organization for Scientific Research (NWO). The project aims at developing techniques to obtain improved estimates of international migration flows by country of origin and country of destination