Diffusion bonding of Cu atoms with molecular dynamics simulations

Diffusion bonding of copper disks is an important step during the assembly of accelerating structures -the main components of power radio-frequency linear accelerators-. During the diffusion bonding copper disks are subjected to pressure at high temperatures. Finding the optimal combination of pressure and temperature will enable an accurate design of manufacturing workflow and machining tolerances. However, required optimization is not possible without good understanding of physical processes developed in copper under pressure and high temperature. In this work, the combined effect of temperature and pressure on closing time of inter-granular voids is examined by means of molecular dynamics simulations. In particular, a nano-void of 3.5–5.5 nm in diameter representing a peak and a valley of surface roughness facing each other was inserted between identical copper grains. The simulations performed at T = 1250 K, the temperature used in experimental condition, and the 300–800 MPa pressure range indicated the dislocation-mediated enhancement of atomic diffusion leading to full void closure.Peer reviewe

The GTC exoplanet transit spectroscopy survey. VII. An optical transmission spectrum of WASP-48b

We obtained long-slit optical spectroscopy of one transit of WASP-48b with the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) spectrograph at the 10.4 m Gran Telescopio Canarias (GTC). We integrated the spectrum of WASP-48 and one reference star in several channels with different wavelength ranges, creating numerous color light curves of the transit. We fit analytic transit curves to the data taking into account the systematic effects present in the time series in an effort to measure the change of the planet-to-star radius ratio ($R_p/R_s$) across wavelength. After removing the transit model and systematic trends to the curves we reached precisions between 261 ppm and 455-755 ppm for the white and spectroscopic light curves, respectively. We obtained $R_p/R_s$ uncertainty values between $0.8 \times 10^{-3}$ and $1.5\times 10^{-3}$ for all the curves analyzed in this work. The measured transit depth for the curves made by integrating the wavelength range between 530 nm and 905 nm is in agreement with previous studies. We report a relatively flat transmission spectrum for WASP-48b with no statistical significant detection of atmospheric species, although the theoretical models that fit the data more closely include of TiO and VO.Comment: 8 pages, 8 figures. Accepted for publication in Astronomy and Astrophysic

Transition metal triflate catalyzed conversion of alcohols, ethers and esters to olefins

Herein, we report an efficient transition metal triflate catalyzed approach to convert biomass-based compounds, such as monoterpene alcohols, sugar alcohols, octyl acetate and tea tree oil, to their corresponding olefins in high yields. The reaction proceeds through C-O bond cleavage under solvent-free conditions, where the catalytic activity is determined by the oxophilicity and the Lewis acidity of the metal catalyst. In addition, we demonstrate how the oxygen containing functionality affects the formation of the olefins. Furthermore, the robustness of the used metal triflate catalysts, Fe(OTf)(3) and Hf(OTf)(4), is highlighted by their ability to convert an over 2400-fold excess of 2-octanol to octenes in high isolated yields.Peer reviewe

Strict Forest Reserve Research in the Margin of the Carpathians, the Vár-hegy Case-Study

Sixteen forest reserves are situated in the northern part of Hungary which belongs to the Carpathian region according to EURAC delimitation (Ruffini et al. 2006). These Hungarian forest reserves expand the natural forest remnant/forest reserve net of the Carpathians towards the lower hilly region, representing the deciduous beech and oak forest belts near their lower (xeric) distribution limits. This paper outlines the Hungarian forest reserves belonging to the Carpathian region and the preliminary results of current projects in the Vár-hegy Forest Reserve (Bükk Mts., Hungary) as a case study. The alteration of tree species composition was investigated here based on the reconstruction of forest history in the previous 130 years (management period) and analyses of forest stand inventory. In another project CO2 sequestration changes of these forest stands were modeled since the clear-cutting in the 1880th and carbon stored in the forest ecosystem compartments was estimated. Our results show that the forest reserve stands are presently in a transition state from the managed forest towards a more natural mixed forest with several age-classes

Stellar activity and rotation of the planet host Kepler-17 from long-term space-borne photometry

The study of young Sun-like stars is of fundamental importance to understand the magnetic activity and rotational evolution of the Sun. Space-borne photometry by the Kepler telescope provides unprecedented datasets to investigate these phenomena in Sun-like stars. We present a new analysis of the entire Kepler photometric time series of the moderately young Sun-like star Kepler-17 that is accompanied by a transiting hot Jupiter. We applied a maximum-entropy spot model to the long-cadence out-of-transit photometry of the target to derive maps of the starspot filling factor versus the longitude and the time. These maps are compared to the spots occulted during transits to validate our reconstruction and derive information on the latitudes of the starspots. We find two main active longitudes on the photosphere of Kepler-17, one of which has a lifetime of at least $\sim 1400$ days, although with a varying level of activity. The latitudinal differential rotation is of solar type, that is, with the equator rotating faster than the poles. We estimate a minimum relative amplitude $\Delta \Omega/ \Omega$ between $\sim 0.08 \pm 0.05$ and $0.14 \pm 0.05$, our determination being affected by the finite lifetime of individual starspots and depending on the adopted spot model parameters. We find marginal evidence of a short-term intermittent activity cycle of $\sim 48$ days and an indication of a longer cycle of $400-600$ days characterized by an equatorward migration of the mean latitude of the spots as in the Sun. The rotation of Kepler-17 is likely to be significantly affected by the tides raised by its massive close-by planet. We confirm the reliability of maximum-entropy spot models to map starspots in young active stars and characterize the activity and differential rotation of this young Sun-like planetary host.Comment: Accepted by Astronomy and Astrophysics - 22 pages, 29 figure, 1 table, 2 appendixe

Corticomuscular Coherence Is Tuned to the Spontaneous Rhythmicity of Speech at 2-3 Hz

Human speech features rhythmicity that frames distinctive, fine-grained speech patterns. Speech can thus be counted among rhythmic motor behaviors that generally manifest characteristic spontaneous rates. However, the critical neural evidence for tuning of articulatory control to a spontaneous rate of speech has not been uncovered. The present study examined the spontaneous rhythmicity in speech production and its relationship to cortex–muscle neurocommunication, which is essential for speech control. Our MEG results show that, during articulation, coherent oscillatory coupling between the mouth sensorimotor cortex and the mouth muscles is strongest at the frequency of spontaneous rhythmicity of speech at 2–3 Hz, which is also the typical rate of word production. Corticomuscular coherence, a measure of efficient cortex–muscle neurocommunication, thus reveals behaviorally relevant oscillatory tuning for spoken language.Peer reviewe

Exhaust emissions of non-road mobile machine : Real-world and laboratory studies with diesel and HVO fuels

Exhaust emissions emitted by a non-road mobile machine were studied chasing a tractor in real-world conditions and repeating the same transient tests with a similar engine on an engine dynamometer where additionally, non-road steady state tests were carried out. The engines were equipped with an oxidation catalyst (DOC) and a selective catalytic reduction (SCR)system, and they were fuelled by fossil diesel fuel with ultra-low sulphur content and hydrotreated vegetable oil (HVO). By substituting diesel fuel with HVO the on-road emissions of nitrogen oxides (NOx) reduced 20% and particle number 44%, the emission factors being EFNOx =1.62 +/- 0.04 g/kWh and EFN = (28.2 +/- 7.8) x 10(13) #/kWh. Similar trend was observed for NOx at laboratory although the emissions were somewhat smaller than on-road. In contrast to real-world, in the laboratory experiment the EFN was only 2% smaller with HVO than with diesel, and these emission factors were almost one order of magnitude smaller than observed on-road. The number size distribution and volatility measurements showed that in real-world experiments small nucleation mode particles were formed during uphill and during downhill in engine braking conditions. These were not observed at laboratory. However, nucleation mode particles were observed in the laboratory experiments at high load steady driving conditions. At steady state tests the emissions strongly depended on engine load and engine speed with both fuels. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe