EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

The reactions of group 13 metal trichlorides with aromatic azides were examined by CW EPR and pulsed ENDOR spectroscopies. Complex EPR spectra were obtained from reactions of aluminium, gallium and indium trichlorides with phenyl azides containing a variety of substituents. Analysis of the spectra showed that 4-methoxy-, 3-methoxy- and 2-methoxyphenyl azides all gave ‘dimer’ radical cations [ArNHC6H4NH2]+• and trimers [ArNHC6H4NHC6H4NH2]+• followed by polymers. 4-Azidobenzonitrile, with its electron-withdrawing substituent, did not react. In general the aromatic azides appeared to react most rapidly with AlCl3 but this reagent tended to generate much polymer. InCl3 was the least reactive group 13 halide. DFT computations of the radical cations provided corroborating evidence and suggested that the unpaired electrons were accommodated in extensive π-delocalised orbitals. A mechanism to account for the reductive conversion of aromatic azides to the corresponding anilines and thence to the dimers and trimers is proposedPublisher PDFPeer reviewe

Historical reconstruction climate variability and change in Mediterranean regions

In the frame of “US-Italy cooperation on Science and Technology of climatic change”, sponsored by INGV, we organized a meeting focusing on decadal climate variability in the Mediterranean regions in the context of long-term climate change. Our aim is to assess past climate variability using historical climate reconstructions and sources in the Mediterranean region both of western US and southern Europe. This report summarizes some key aspects of climate variability in the Mediterranean region in the past 200 years and identifies uncertainties and unresolved scientific questions still open for further research

Cosmic rays 10Be biennal data and their relationship to aurorae and sunspots

The galactic cosmic ray (C.R.) variations which should give information on three dimensional aspects of the heliospheric magnetic fields and on the solar wind, which modulate their influx into the Solar System were studied. In order to decode the information from the C.R. series it is necessary to know the mechanisms through which the modulation is produced. It it clear that a balance of effects with sources at different heliospheric latitudes results in the modulated C.R. intensity. It is found that the modulation of 10Be in polar ice may be due to at least two main contributions: (1) negative and in phase with the Solar flare activity modulating the cosmic ray flux in Forbush-type decreases, and (2) positive in phase with the appearance of large wind streams situated at both polar coronal holes. It is found that the high heliolatitude activity is related to a stable periodicity of 11.1y whereas the low heliolatitude activity contributes to the wondering of the solar cycles

Direct laser acceleration of electrons in free-space

Compact laser-driven accelerators are versatile and powerful tools of unarguable relevance on societal grounds for the diverse purposes of science, health, security, and technology because they bring enormous practicality to state-of-the-art achievements of conventional radio-frequency accelerators. Current benchmarking laser-based technologies rely on a medium to assist the light-matter interaction, which impose material limitations or strongly inhomogeneous fields. The advent of few cycle ultra-intense radially polarized lasers has materialized an extensively studied novel accelerator that adopts the simplest form of laser acceleration and is unique in requiring no medium to achieve strong longitudinal energy transfer directly from laser to particle. Here we present the first observation of direct longitudinal laser acceleration of non-relativistic electrons that undergo highly-directional multi-GeV/m accelerating gradients. This demonstration opens a new frontier for direct laser-driven particle acceleration capable of creating well collimated and relativistic attosecond electron bunches and x-ray pulses

Cosmic ray secular variations in terrestrial records and aurorae

The rediscovery that the Sun and the solar wind can undergo important changes on historical time scales has brought into question the stability of the cyclic behavior of past time series of solar and solar-terrestrial origin. It was found by Vector Fourier analysis that the solar 11 year cycle is present in the series of 10Be, delta 180, in ice cores and of thermoluminescence (TL) in sea sediments during the last Millennia with a frequency modulation, related to the Sun behavior, as tested by comparison with the Sunspot number R sub z series. It was shown that the cyclogram of the series of yearly Aurorae from 1721 to 1979 linear-regression-corrected-for-R sub z is straight for the periodicity zeta=11,1y, which indicates that such periodicity is constant in time corresponding to the only line present in the 11y band. The maxima of this component appear at the same time together with the high speed solar wind streams taking place in coronal holes situated in high heliolatitudes. It is evidenced that the 11 year cycle has undergone frequency oscillations on a time scale of two centuries, although it is very difficult to determine the periodicities with high accuracy

Geometrical size effect in high cycle fatigue strength of heavy-walled Ductile Cast Iron GJS400: Weakest link vs. defect-based approach

Fatigue strength is known to decrease with increasing dimension of the component. This is due to a technological size effect, related to the production process, and to a geometrical size effect, due to a higher probability of finding a large defect. To investigate the latter, an heavy-walled component made of Ductile Cast Iron (DCI) has been trepanned and a fatigue test plan has been carried out using 4 different specimen geometries. An attempt has been made to relate the resulting fatigue strength using a weakest-link approach based on the effective volumes and surfaces. This approach seems to work well only in cases of different specimen's lengths. Some of the fracture surfaces were analyzed by means of SEM and the initiating defects were identified and measured. An approach in which the defects population can be randomly distributed in the specimen has been tried. Virtual fatigue tests have been carried out by considering pure propagation of the worst defect. The resulting fatigue curves showed that this approach is promising but needs further description of the initiation phase

Integration of gis technology, remote sensing and multivariate analysis in the delimitation of physiographic units for pedological mapping

Este trabalho foi conduzido com o propósito de estabelecer-se um levantamento pedológico semidetalhado no Município de Ivatuba-PR, usando a associação entre técnicas e equipamentos que pudessem levar a delimitação de unidades físiográfícas cujos limites e subdivisões não se restringissem apenas ao critério do foto intérprete. Para tanto, foi avaliada uma matriz de dados obtida através do cruzamento, por meio de um Sistema de Informações Geográficas (SIG), entre uma grade regular com células de 300 x 300 metros e um mapa base de drenagem da área de estudos, bandas 3, 4, 5 e 7 do TM-LANDSAT e um mapa de declividades da área gerado em SIG. As variáveis coletadas dentro de cada célula da grade regular foram: canais longo, médio e curto das ordens 1ª à 7ª, declividade ponderada e o nível de cinza das bandas, resultando na produção de uma matriz com 1167 indivíduos com vinte e sete variáveis, cujos dados foram expostos à analise de agrupamentos. A análise propiciou a produção de dendrogramas que foram analisados, permitindo a representação pelas células da grade regular, com a finalidade de criação de pictogramas em que a separação de grupos de indivíduos servissem de "guias" que, sobrepostos às imagens orbitais HRV-SPOT devidamente tratadas e manipuladas, pudessem orientar a discriminação de unidades fisiográfícas através da interpretação destas sobre o monitor colorido do sistema SITIM. Foram delimitados 62 polígonos que configuraram a presença de nove unidades fisiográficas que geraram um mapa de solos semidetalhado do município. Em relação à possibilidade de mapeamento das unidades fisiográficas sobre o monitor colorido, os resultados apresentados demonstraram que, através da utilização dos guias, tais unidades podem ser delimitadas com grande redução da subjetividade do foto intérprete. Os polígonos semelhantes, delimitados pela metodologia utilizada, apresentaram solos homogêneos dentro de sua classe taxonómica. Já os polígonos diferentes apresentaram solos com características diferenciadoras entre si.This study was based on an association of techniques and equipment that could lead to the delimitation of physiographic units not merely restricted to the photointerpreter's criteria. A data matrix was evaluated which was obtained from the crossing, by means of Geographic Information System (GIS), of a regular grid with cells 300 x 300 meters and a drainage base map of the study area and bands 3, 4, 5 and 7 from TM-LANDSAT and a slope map generated in a GIS. The variables collected in each cell of the regular grid were: long, medium and short channels from the first to the seventh order, weighted slope and the grey levels (DNs) in bands, resulting in a matrix with 1167 individuals with 27 variables, whose data were subjected to cluster analysis. This analysis provided dendrograms which enabled the separation of groups of individuals represented by cells from the regular grid, aiming at creating pictograms to serve as "guides". These guides overlaid upon properly treated and handled orbital HRV-SPOT images oriented the discrimination of physiographic units on the color monitor of the image processing system. Among the variables used, those referring to drainage network were best for cluster analysis of regular grid cells. The variables relief and grey levels of TM-LANDSAT image also presented satisfactory results with the methodology applied

Application of Frustrated Total Internal Reflection of Millimeter Waves for Detection and Evaluation of Disbonds in Dielectric Joints

Millimeter waves penetrate inside of low loss dielectric materials and they are sensitive to the presence of internal interfaces and nonuniformities. This allows millimeter wave nondestructive inspection techniques to be utilized for inspecting dielectric composite structures. A disbond (a thin and extended airgap) in structures possessing adhesively bonded joints with complex geometries is commonly difficult to inspect. In this letter, we demonstrate the operational principle and the useful features of a millimeter wave technique, employing a frustrated total internal reflection of signals transmitted and received by dielectric waveguide probes for detecting and evaluating disbonds in such joints

Terahertz-driven linear electron acceleration

The cost, size and availability of electron accelerators is dominated by the achievable accelerating gradient. Conventional high-brightness radio-frequency (RF) accelerating structures operate with 30-50 MeV/m gradients. Electron accelerators driven with optical or infrared sources have demonstrated accelerating gradients orders of magnitude above that achievable with conventional RF structures. However, laser-driven wakefield accelerators require intense femtosecond sources and direct laser-driven accelerators and suffer from low bunch charge, sub-micron tolerances and sub-femtosecond timing requirements due to the short wavelength of operation. Here, we demonstrate the first linear acceleration of electrons with keV energy gain using optically-generated terahertz (THz) pulses. THz-driven accelerating structures enable high-gradient electron or proton accelerators with simple accelerating structures, high repetition rates and significant charge per bunch. Increasing the operational frequency of accelerators into the THz band allows for greatly increased accelerating gradients due to reduced complications with respect to breakdown and pulsed heating. Electric fields in the GV/m range have been achieved in the THz frequency band using all optical methods. With recent advances in the generation of THz pulses via optical rectification of slightly sub-picosecond pulses, in particular improvements in conversion efficiency and multi-cycle pulses, increasing accelerating gradients by two orders of magnitude over conventional linear accelerators (LINACs) has become a possibility. These ultra-compact THz accelerators with extremely short electron bunches hold great potential to have a transformative impact for free electron lasers, future linear particle colliders, ultra-fast electron diffraction, x-ray science, and medical therapy with x-rays and electron beams