Optical and structural properties of the GaAs heterostructures grown using AlGaAs superlattice buffer layer on compliant Si(100) substrates with the preformed porous-Si (por-Si) layer

360 nm and 700 nm thick GaAs layers were grown by MO MOCVD growth technique directly on compliant Si (100) substrate and on supper-lattice (SL) AlGaAs buffer layer. The XRD study revealed better structural quality for the sample grown on SL / por-Si buffer. AFM study revealed a smoother sample surface with blocks of more regular rectangular shape and larger size as well. Photoluminescence spectra of the samples revealed an energy shift of PL maximum intensity for both samples. Sample grown on SL buffer also showed higher PL intensity corresponding to better crystalline perfection

HRXRD study of the effect of a nanoporous silicon layer on the epitaxial growth quality of GaN layer on the templates of SiC/por-Si/c-Si

Using High Resolution X-ray Diffraction (HRXRD) diagnostic techniques the influence of the transition layer of nanoporous silicon on the practical implementation and certain features of the epitaxial growth of GaN layers with the use of molecular beam epitaxy were investigated by means of plasma activation of nitrogen (MBE PA) on the templates of SiC/por-Si/c-Si. For the first time it was shown that introducing of the transition layer of nanoporous silicon in the template of SiC/por-Si/c-Si where the layer of 3C-SiC was obtained by substitution of the atoms had a number of indisputable advantages as compared with conventional silicon substrates. Particularly, such an approach, in fact, enabled a 90% reduction in the level of stresses in the crystalline lattice of the epitaxial GaN layer which was synthesized on SiC surface of SiC/por-Si/c-Si template by means of MBE PA technique as well as to decrease some of vertical dislocations within GaN layer. © 2020 The AuthorsRussian Science Foundation, RSFThe work was executed under support of the grant of Russian Science Foundation 19-72-10007 . Access to KNMF equipment was obtained under the grant of the President of the Russian Federation MD-42.2019.2

Measuring spatial pressure distribution from explosives buried in dry Leighton Buzzard sand

Direct measurement of the intense loading produced by the detonation of a buried explosive is an extremely difficult task. Historically, high-fidelity measurement techniques have not been sufficiently robust to capture the extremely high pressures associated with such events, and researchers have relied on ‘global’ measurements such as the average loading acting over a particular area of interest. Recently, a large-scale experimental approach to the direct measurement of the spatial and temporal variation in loading resulting from an explosive event has been developed, which utilises Hopkinson pressure bars (HPBs) inserted through holes in a large target plate such that their faces lie flush with the loaded face. This article presents results from ten experiments conducted at 1/4 scale, using 17 HPBs to measure the spatial pressure distribution from explosives buried in dry Leighton Buzzard sand, a commonly available sand used in many geotechnical applications. Localised pressure measurements are used in conjunction with high speed video to provide a detailed examination of the physical processes occurring at the loaded face, as well allowing quantification of these effects. Example pressure–time and impulse–time traces are provided in full to allow researchers to use this data for validation of numerical modelling approaches

Constraining the S factor of 15N(p,g)16O at Astrophysical Energies

The 15N(p,g)16O reaction represents a break out reaction linking the first and second cycle of the CNO cycles redistributing the carbon and nitrogen abundances into the oxygen range. The reaction is dominated by two broad resonances at Ep = 338 keV and 1028 keV and a Direct Capture contribution to the ground state of 16O. Interference effects between these contributions in both the low energy region (Ep < 338 keV) and in between the two resonances (338 <Ep < 1028 keV) can dramatically effect the extrapolation to energies of astrophysical interest. To facilitate a reliable extrapolation the 15N(p,g)16O reaction has been remeasured covering the energy range from Ep=1800 keV down to 130 keV. The results have been analyzed in the framework of a multi-level R-matrix theory and a S(0) value of 39.6 keV b has been found.Comment: 15 pages, 9 figure

Study of Spin and Decay-Plane Correlations of W Bosons in the e+e- -> W+W- Process at LEP

Data collected at LEP at centre-of-mass energies \sqrt(s) = 189 - 209 GeV are used to study correlations of the spin of W bosons using e+e- -> W+W- -> lnqq~ events. Spin correlations are favoured by data, and found to agree with the Standard Model predictions. In addition, correlations between the W-boson decay planes are studied in e+e- -> W+W- -> lnqq~ and e+e- -> W+W- -> qq~qq~ events. Decay-plane correlations, consistent with zero and with the Standard Model predictions, are measured

Search for Branons at LEP

We search, in the context of extra-dimension scenarios, for the possible existence of brane fluctuations, called branons. Events with a single photon or a single Z-boson and missing energy and momentum collected with the L3 detector in e^+ e^- collisions at centre-of-mass energies sqrt{s}=189-209$ GeV are analysed. No excess over the Standard Model expectations is found and a lower limit at 95% confidence level of 103 GeV is derived for the mass of branons, for a scenario with small brane tensions. Alternatively, under the assumption of a light branon, brane tensions below 180 GeV are excluded