Ab initio absorption spectrum of NiO combining molecular dynamics with the embedded cluster approach in a discrete reaction field

We developed a procedure that combines three complementary computational methodologies to improve the theoretical description of the electronic structure of nickel oxide. The starting point is a Car-Parrinello molecular dynamics simulation to incorporate vibrorotational degrees of freedom into the material model. By means ofcomplete active space self-consistent field second-order perturbation theory (CASPT2) calculations on embedded clusters extracted from the resulting trajectory, we describe localized spectroscopic phenomena on NiO with an efficient treatment of electron correlation. The inclusion of thermal motion into the theoretical description allowsus to study electronic transitions that, otherwise, would be dipole forbidden in the ideal structure and results in a natural reproduction of the band broadening. Moreover, we improved the embedded cluster model by incorporating self-consistently at the complete active space self-consistent field (CASSCF) level a discrete (or direct) reaction field (DRF) in the cluster surroundings. The DRF approach offers an efficient treatment ofelectric response effects of the crystalline embedding to the electronic transitions localized in the cluster. We offer accurate theoretical estimates of the absorption spectrum and the density of states around the Fermi level of NiO, and a comprehensive explanation of the source of the broadening and the relaxation of the charge transferstates due to the adaptation of the environment

Implementació d'un Laboratori Virtual d'Equips Electrònics per múltiples aplicacions específiqies com a reforç docent en l'àrea de l'electrònica VERiLAB (Virtual ElectRonic LABoratory)

S’ha dissenyat un Laboratori Virtual d’Equips Electrònics per múltiples aplicacions específiques com a reforç docent en l’àrea de l’electrònica VERiLAB (Virtual ElectRonic LABoratory) i, a més, s’han dissenyat un conjunt de 9 pràctiques guiades per treure el màxim rendiment al laboratori virtual. El laboratori Virtual és una potent eina de treball per aplicacions docents com a programari d’iniciació a la utilització d’equips electrònics bàsics que podem trobar a qualsevol laboratori d’electrònica. Aquesta eina permet augmentar el nombre d’hores de treball pràctic fora del laboratori. La primera versió d’aquest programari es va dissenyar a l’any 2004 a la Universitat de Barcelona amb el software LabVIEW_7, el qual permet obtenir un fitxer executable amb el qual els alumnes poden treballar fora del laboratori. D’aquesta forma els alumnes únicament necessiten un ordinador per a poder fer les pràctiques. La primera versió del laboratori disposava d’un generador de funcions, un oscil·loscopi i un analitzador d’espectres com a equips electrònics, i a més a més incorporava un mòdul de filtres i un motor DC per treballar amb els equips. La versió 2 del Laboratori Virtual es va desenvolupar amb aquest projecte MQD i es va introduir una font d’alimentació, un multímetre de sobre taula i un portàtil com a equips electrònics. Es van crear també diferents mòduls de sistemes electrònics: filtres analògics, configuracions bàsiques basades en l’amplificador operacional, l’amplificador operacional no ideal i un circuit de rectificació d’ona completa. Aquests mòduls han premés ampliar el camp d’aplicació del Laboratori Virtual a diferents assignatures de l’àrea de l’electrònica.

The effect of atmospheric absorption of sunlight on the runaway greenhouse point

The longwave emission of planetary atmospheres that contain a condensable absorbing gas in the infrared (i.e., longwave), which is in equilibrium with its liquid phase at the surface, may exhibit an upper bound. Here we analyze the effect of the atmospheric absorption of sunlight on this radiation limit. We assume that the atmospheric absorption of infrared radiation is independent of wavelength except within the spectral width of the atmospheric window, where it is zero. The temperature profile in radiative equilibrium is obtained analytically as a function of the longwave optical thickness. For illustrative purposes, numerical values for the infrared atmospheric absorption (i.e., greenhouse effect) and the liquid vapor equilibrium curve of the condensable absorbing gas refer to water. Values for the atmospheric absorption of sunlight (i.e., antigreenhouse effect) take a wide range since our aim is to provide a qualitative view of their effects. We find that atmospheres with a transparent region in the infrared spectrum do not present an absolute upper bound on the infrared emission. This result may be also found in atmospheres opaque at all infrared wavelengths if the fraction of absorbed sunlight in the atmosphere increases with the longwave opacity

Ground-state self-consistent calculation of quantum dots under magnetic fields: Addition spectrum

A density-functional self-consistent calculation of the ground-state electronic density of quantum dots under an arbitrary magnetic field is performed. We consider a parabolic lateral confining potential. The addition energy, E(N+1)-E(N), where N is the number of electrons, is compared with experimental data and the different contributions to the energy are analyzed. The Hamiltonian is modeled by a density functional, which includes the exchange and correlation interactions and the local formation of Landau levels for different equilibrium spin populations. We obtain an analytical expression for the critical density under which spontaneous polarization, induced by the exchange interaction, takes place.

Electronic structure of few-electron concentric double quantum rings

The ground state structure of few-electron concentric double quantum rings is investigated within the local spin density approximation. Signatures of inter-ring coupling in the addition energy spectrum are identified and discussed. We show that the electronic configurations in these structures can be greatly modulated by the inter-ring distance: At short and long distances the low-lying electron states localize in the inner and outer rings, respectively, and the energy structure is essentially that of an isolated single quantum ring. However, at intermediate distances the electron states localized in the inner and the outer ring become quasidegenerate and a rather entangled, strongly-correlated system is formed.

On the multiwavelength spectrum of the microquasar 1E1740.7-2942

The microquasar 1E 1740.7-2942 is a source located in the direction of the Galactic Center. It has been detected at X-rays, soft gamma-rays, and in the radio band, showing an extended radio component in the form of a double-sided jet. Although no optical counterpart has been found so far for 1E 1740.7-2942, its X-ray activity strongly points to a galactic nature. Aims.We aim to improve our understanding of the hard X-ray and gamma-ray production in the system, exploring whether the jet can emit significantly at high energies under the light of the present knowledge. Methods.We have modeled the source emission, from radio to gamma-rays, with a cold-matter dominated jet model. INTEGRAL data combined with radio and RXTE data, as well as EGRET and HESS upper-limits, are used to compare the computed and the observed spectra. Results.From our modeling, we find out that jet emission cannot explain the high fluxes observed at hard X-rays without violating at the same time the constraints from the radio data, favoring the corona origin of the hard X-rays. Also, 1E 1740.7-2942 might be detected by GLAST or AGILE at GeV energies, and by HESS and HESS-II beyond 100 GeV, with the spectral shape likely affected by photon-photon absorption in the disk and corona photon fields.

Use and users of electronic journals at Catalan universities: the results of a survey

Es presenten els resultats d’una enquesta sobre l’ús de revistes electròniques realitzada al professorat de les universitats que formen el Consorci de Biblioteques Universitàries de Catalunya (CBUC). Els resultats mostren un elevat grau de coneixement de la col·lecció de revistes electròniques entre el personal docent i investigador i una creixent preferència pel format electrònic en detriment de l’imprès. L’alt grau de coneixement i d’ús dels títols electrònics, i la preferència per aquest suport, comporten una elevada valoració de la col·lecció de revistes electròniques. Al mateix temps, la major part dels usuaris preveu un increment de l’ús dels títols electrònics durant els propers anys. Els resultats també confirmen la importància de la disciplina i de l’edat com a factors explicatius de l’ús de les revistes electròniques.

Preserving Electronic Theses through the MetaArchive network

In the recent years most libraries have focused on mass digitization programs and keeping electronic born documents, showing and organizing them in a repository. While those repositories have evolved to a much more manageable systems focusing on the user expectations and introducing web 2.0 tools, digital preservation is still in the to-do list of most of them. There is quite a lot of studies focused on preservation and some complex models exist, unfortunately, very few practical systems are running and its quite difficult for a library to get involved in a solution already tested by others. The CBUC (Consortium of University Catalan Libraries) runs TDX, an ETD repository now keeping more than 10.000 full text thesis from any of the 12 university members. After 10 years running TDX a solid preservation system was needed to ensure every thesis would be kept as it was regardless what happens to the repository. The perfect solution was found in the MetaArchive cooperative, this is the effort of many insitutions to keep a copy of each other content through a newtwork using the LOCKSS software as a mechanism to keep track of any change. The presentation will shortly introduce what TDX and MetaArchive is but will, in a practical way, show how the LOCKSS network for presrervation works. Finally a summary of the benefits of the overall experience will be shown.

Dissolution of Dynamic Electronic Institutions, a first approach: Relevant factors and causes

In the context of the digital business ecosystems, small organizations cooperate between them in order to achieve common goals or offer new services for expanding their markets. There are different approaches for these cooperation models such as virtual enterprises, virtual organizations or dynamic electronic institutions which in their lifecycle have in common a dissolution phase. However this phase has not been studied deeply in the current literature and it lacks formalization. In this paper a first approach for achieving and managing the dissolution phase is proposed, as well as a CBR process in order to support it in a multi-agent system

Spectrum of some trianguled categories

In this paper, we compute the triangular spectrum (as de fined by P. Balmer) of two classes of tensor triangulated categories which are quite common in algebraic geometry. One of them is the derived category of G-equivariant sheaves on a smooth scheme X, for a fi nite group G. The other class is the derived category of split superschemes.

Electronic voting system for computer supported collaborative learning

The EVS4CSCL project starts in the context of a Computer Supported Collaborative Learning environment (CSCL). Previous UOC projects created a CSCL generic platform (CLPL) to facilitate the development of CSCL applications. A discussion forum (DF) was the first application developed over the framework. This discussion forum was different from other products on the marketplace because of its focus on the learning process. The DF carried out the specification and elaboration phases from the discussion learning process but there was a lack in the consensus phase. The consensus phase in a learning environment is not something to be achieved but tested. Common tests are done by Electronic Voting System (EVS) tools, but consensus test is not an assessment test. We are not evaluating our students by their answers but by their discussion activity. Our educational EVS would be used as a discussion catalyst proposing a discussion about the results after an initial query or it would be used after a discussion period in order to manifest how the discussion changed the students mind (consensus). It should be also used by the teacher as a quick way to know where the student needs some reinforcement. That is important in a distance-learning environment where there is no direct contact between the teacher and the student and it is difficult to detect the learning lacks. In an educational environment, assessment it is a must and the EVS will provide direct assessment by peer usefulness evaluation, teacher marks on every query created and indirect assessment from statistics regarding the user activity.

An electronic voting platform with elliptic curve cryptography

The future of elections seems to be electronic voting systems du to its advantatges over the traditional voting. Nowadays, there are some different paradigms to ensure the security and reliability of e-voting. This document is part of a wider project which presents an e-Voting platform based on elliptic curve cryptography. It uses an hybrid combination of two of the main e-Voting paradigms to guarantee privacy and security in the counting phase, these are precisely, the mixnets and the homomorphic protocols. This document is focused in the description of the system and the maths and programming needed to solve the homomorphic part of it. In later chapters, there is a comparison between a simple mixing system and our system proposal.

Runaway Greenhouse Effect in a Semigray Radiative-Convective Model

The effects of the nongray absorption (i.e., atmospheric opacity varying with wavelength) on the possible upper bound of the outgoing longwave radiation (OLR) emitted by a planetary atmosphere have been examined. This analysis is based on the semigray approach, which appears to be a reasonable compromise between the complexity of nongray models and the simplicity of the gray assumption (i.e., atmospheric absorption independent of wavelength). Atmospheric gases in semigray atmospheres make use of constant absorption coefficients in finite-width spectral bands. Here, such a semigray absorption is introduced in a one-dimensional (1D) radiative– convective model with a stratosphere in radiative equilibrium and a troposphere fully saturated with water vapor, which is the semigray gas. A single atmospheric window in the infrared spectrum has been assumed. In contrast to the single absolute limit of OLR found in gray atmospheres, semigray ones may also show a relative limit. This means that both finite and infinite runaway effects may arise in some semigray cases. Of particular importance is the finding of an entirely new branch of stable steady states that does not appear in gray atmospheres. This new multiple equilibrium is a consequence of the nongray absorption only. It is suspected that this new set of stable solutions has not been previously revealed in analyses of radiative–convective models since it does not appear for an atmosphere with nongray parameters similar to those for the earth’s current state