Isomer triggering via nuclear excitation by electron capture

Triggering of long-lived nuclear isomeric states via coupling to the atomic shells in the process of nuclear excitation by electron capture (NEEC) is studied. NEEC occurring in highly-charged ions can excite the isomeric state to a triggering level that subsequently decays to the ground state. We present total cross sections for NEEC isomer triggering considering experimentally confirmed low-lying triggering levels and reaction rates based on realistic experimental parameters in ion storage rings. A comparison with other isomer triggering mechanisms shows that, among these, NEEC is the most efficient.Comment: minor changes - updated to the final version; 4 pages, 1 figur

Numerical Evaluation of the Effective Elastic Properties of 2D Overlapping Random Fibre Composites

We present a numerical investigation of the elastic coefficients of random fibre composites with high contrast of properties. Here we consider a numerical study based on the generation of representative volume elements (RVEs) with overlapping random fibre network. Such a concept requires an important Monte-Carlo draw of patterns as well as an accurate determination of RVE size. In this paper, this latter is done by estimating the evolution of the standard deviation according to the number of realizations for given values of RVE size. We consider the use of an appropriate model for an automatic, reliable and fast generation of RVEs : the model with an n-order approximate geometry that allows the construction of complex overlapping fibre network. It is well-established that the morphology of the microstructure greatly affects the mechanical response of such kind material. Some morphological features, namely orientation, aspect ratio and dispersion are investigated by considering them as random variables in the design of RVEs. The results are subsequently linked to the percolation phenomenon that occurs when fibres overlap and form some pathways inside the soft phase. This phenomenon influences effective properties of heterogeneous media, particularly in the case of a high contrast of properties

Identification and comparison of the yield and composition of essential oil constituents of four Eucalyptus species adapted to the climatic conditions of Khorramabad

Introduction: Eucalyptus has more than 400 species, while only a few species of this genus have been imported in Iran. In this study we aimed to investigate chemical compounds of the essential oils of Eucalyptus species adapted in Lorestan climate. Methods: In this study, the fresh young leaves of four different Eucalyptus species including E. suggrandis, E. globulus subsp. bicostata, E. nitens and E. globulus subsp. maidenii were collected in spring (the middle of May) in khorramabad, Iran. The powder of air-dried leaves of different species of Eucalyptus was subjected to hydro-distillation using a Clevenger-type apparatus. The chemical compositions of different essential oils were detected using gas chromatography (GC) and gas chromatography coupled with mass spectrometry (GC/MS) and determination of their retention time (RT), retention index (RI) and Mass Spectra. The obtained data were analyzed using SPSS software. Results: The results of this study indicated that there was significant difference (P&lt;0.01) among the yield and chemical compounds of the essential oils of studied species. The results showed that the yield of essential oil extracted from E. suggrandis, E. globulus bicostata, E. nitens and E. globulus maidenii were 1.12, 1.34, 2.57 and 5.38, respectively. Conclusion: The essential oil constituents of four Eucalyptus species plant were different in among of some compounds. E. globulus maidenii&nbsp; &nbsp;had most content of essential oil and 1.8-Cineole compound so it is necessary to identify quality and quantity characteristics of compounds available in this plant.</p

Influence of spark plasma sintering and baghdadite powder on mechanical properties of hydroxyapatite

AbstractSince hydroxyapatite-based materials have similar composition and crystallinity as natural calcified tissues, can be used for bone/tissue engineering. In the present study a novel nanocomposite based on bioceramics such as Natural Hydroxyapatite (NHA) and Baghdadite (BAG), was sintered by spark plasma sintering (SPS) technique. The prepared composite was characterized using scanning electron microscopy (SEM), X-ray diffractometer (XRD) and Brunauer–Emmett–Teller (BET) techniques. The porosity of the samples was measured by Archimedes method. The cold crushing strength (CCS) test was applied to evaluate their mechanical properties. Our results demonstrated that NHA-30wt. %BAG nanocomposite specimens have the lower CCS in comparison with other examined composites. Consequently, NHA/BAG samples exhibited acceptable mechanical properties and could be suitable candidates for bone tissue engineering applications especially orthopaedic fields

Estimation des coefficients d'élasticité de matériaux composites renforcés par des nanotubes de carbone multi-parois

Dans le cadre d'une approche multi-échelle, nous étudions le renforcement des matrices de matériaux composites par des nanotubes de carbone multi-parois. Nous bâtissons différents motifs de la matrice enrichie par des nanoparticules à l'aide des éléments finis puis déterminons les propriétés mécaniques du composite par homogénéisation stochastique. Dans le cadre d'une étude statistique, une base de données est construite visant à définir la pertinence de paramètres, tels le diamètre, la courbure, l'orientation, la fraction volumique, le phénomène d'agrégat et la dispersion des nanotubes

Coherent control of the cooperative branching ratio for nuclear x-ray pumping

Coherent control of nuclear pumping in a three level system driven by x-ray light is investigated. In single nuclei, the pumping performance is determined by the branching ratio of the excited state populated by the x-ray pulse. Our results are based on the observation that in ensembles of nuclei, cooperative excitation and decay leads to a greatly modified nuclear dynamics, which we characterize by a time-dependent cooperative branching ratio. We discuss prospects of steering the x-ray pumping by coherently controlling the cooperative decay. First, we study an ideal case with purely superradiant decay and perfect control of the cooperative emission. A numerical analysis of x-ray pumping in nuclear forward scattering with coherent control of the cooperative decay via externally applied magnetic fields is presented. Next, we provide an extended survey of nuclei suitable for our scheme, and propose proof-of-principle implementations already possible with typical M\"ossbauer nuclear systems such as $^{57}\mathrm{Fe}$. Finally, we discuss the application of such control techniques to the population or depletion of long-lived nuclear states.Comment: 11 pages, 8 figures; updated to the published versio

Variation in global treatment for subaxial cervical spine isolated unilateral facet fractures.

PURPOSE To determine the variation in the global treatment practices for subaxial unilateral cervical spine facet fractures based on surgeon experience, practice setting, and surgical subspecialty. METHODS A survey was sent to 272 members of the AO Spine Subaxial Injury Classification System Validation Group worldwide. Questions surveyed surgeon preferences with regard to diagnostic work-up and treatment of fracture types F1-F3, according to the AO Spine Subaxial Cervical Spine Injury Classification System, with various associated neurologic injuries. RESULTS A total of 161 responses were received. Academic surgeons use the facet portion of the AO Spine classification system less frequently (61.6%) compared to hospital-employed and private practice surgeons (81.1% and 81.8%, respectively) (p = 0.029). The overall consensus was in favor of operative treatment for any facet fracture with radicular symptoms (N2) and for any fractures categorized as F2N2 and above. For F3N0 fractures, significantly less surgeons from Africa/Asia/Middle East (49%) and Europe (59.2%) chose operative treatment than from North/Latin/South America (74.1%) (p = 0.025). For F3N1 fractures, significantly less surgeons from Africa/Asia/Middle East (52%) and Europe (63.3%) recommended operative treatment than from North/Latin/South America (84.5%) (p = 0.001). More than 95% of surgeons included CT in their work-up of facet fractures, regardless of the type. No statistically significant differences were seen in the need for MRI to decide treatment. CONCLUSION Considerable agreement exists between surgeon preferences with regard to unilateral facet fracture management with few exceptions. F2N2 fracture subtypes and subtypes with radiculopathy (N2) appear to be the threshold for operative treatment