Energetic potential of pyrolyzed biomass from different sources: a comparative study

Journal of Thermal Analysis and Calorimetry - The use of biomass has been a recent trend as a potential feedstock for char generation with improved energetic value. In this work, agricultural...     

Hyperfine Parameters for Muonium in Copper (I), Silver (I) and Cadmium Oxides

Muonium centres in Cu₂O, Ag₂O and CdO show hyperfine parameters spanning four orders of magnitude. They exemplify the three different categories of hydrogen defect centre in semiconducting and dielectric solids, with very different electronic structure and electrical activity, namely quasi-atomic (possibly deep acceptor), deep donor and shallow donor.     

Development of Analyses of Biological Steroids Using Chromatography——Special Reference to Vitamin D Compounds and Neurosteroids

Steroids comprise a large group of natural substances that must frequently be monitored in various biological materials. Due to the metabolic versatility of steroid molecules, extremely complex mixtures are often encountered, necessitating the use of a chromatographic procedure prior to measurement. In this article we present our work, that is, the development of analyses of biological steroids (especially vitamin D compounds and neurosteroids) using gas chromatography/mass spectrometry, high-performance liquid chromatography (including inclusion chromatography using cyclodextrin) and liquid chromatography/mass spectrometry.     

Design and Analysis of Compact Directionally Coupled Bistable Laser Diodes

A compact optical flip-flop with a directional coupler has been designed and analyzed. Using a narrow gap directional coupler, we have predicted the device length could be reduced down to 500 μm from 1300 μm.     

Investigations and explorations in the mathematics classroom

In Portugal, since the beginning of the 1990s, problem solving became increasingly identified with mathematical explorations and investigations. A number of research studies have been conducted, focusing on students’ learning, teachers’ classroom practices and teacher education. Currently, this line of work involves studies from primary school to university mathematics. This perspective impacted the mathematics curriculum documents that explicitly recommend teachers to propose mathematics investigations in their classrooms. On national meetings, many teachers report experiences involving students’ doing investigations and indicate to use regularly such tasks in their practice. However, this still appears to be a marginal activity in most mathematics classes, especially when there is pressure for preparation for external examinations (at grades 9 and 12). International assessments such as PISA and national assessments (at grades 4 and 6) emphasize tasks with realistic contexts. They reinforce the view that mathematics tasks must be varied beyond simple computational exercises or intricate abstract problems but they do not support the notion of extended explorations. Future developments will show what paths will emerge from these contradictions between promising research and classroom reports, curriculum orientations, professional experience, and assessment frameworks and instruments.     

La2-xSrxCu1-yZnyO4: Tc and ns/m* correlations seen with muon spin rotation

We report the muon spin rotation experiments on Zn substituted La_1-x Sr_x CuO₄, for four zinc concentrations y=0.0,0.0025,0.005,0.01, at strontium concentrations x=0.15,0.20. We find that T_ c in the optimally doped (x=0.15) and overdoped (x=0.20) 2:1:4 decreases linearly with increasing zinc concentration. Plotted against the planar zinc concentration, the T_c’s of both series seem to fall on the same line. The superconducting carrier density/effective mass ratio, n_ s/m^*, at first decreases linearly, rising above this line for higher zinc concentrations. This behavior may result from the localization of carriers in an area \xi_ab around each zinc atom. This revised version was published online in August 2006 with corrections to the Cover Date.     

Same-sign dileptons as a signature for heavy Majorana neutrinos in hadron-hadron collisions

We discuss the possibility of same-sign dileptons as a signature for Majorana neutrinos. The production mechanism is given by a single heavy neutrino production and decay pp → l^±NX → l^±l^±X′. Cross section and distributions are presented for the LHC energies.     

A model for domain and domain wall NMR signals in magnetic materials

Spin echo NMR signals in magnetic materials (simple metals, alloys or intermetallic compounds) generally result from mixed contributions of distinct magnetic regions of the sample, the magnetic domains and the domain walls. The amplitude of the signal is proportional to the so-called enhancement factor which in most of the cases greatly differs in these two regions, depending upon the wall mobility, the magnetic anisotropy, etc. The experimental access to domain and domain walls is possible, in principle, by a careful control of the RF power applied to the sample. In this paper a simple superposition model is proposed which includes both contributions to the NMR signal. We calculate the amplitude of the spin echo in magnetic powder samples and compare it with experimental situations where it has been possible to separate different contributions to the signal. This has been done in some RCo₂ magnetic rare-earth intermetallic compounds by analyzing the spectral line widths and the curve of the spin echo amplitude versus the applied RF field. Despite its simplicity, the present model allows the understanding of the main features of the NMR spectra and the dependence of the echo amplitude with the RF power in these compounds.