Динамическая модель трансмиссий машин с учетом распределенной массы валов

Виконано дослідження крутних коливань у лінії приводу прокатного стана, як системи з розподіленими параметрами. Визначено залежності кутів повертань поперечних перерізів валу і крутного моменту у часi захвату металу валками та уздовж шпинделя, що характеризує вимушені та власні коливання головної лінії.It has been carried out a research of torsional oscillations of the rolling mill drive train as a system with the distributed parameters. It was determined a function of the cross sections deformation angles and torsional torques in time and along the spindle length, which characterizes the forced and natural oscillations of the drive train

Measurement of calcium isotopes (δ44Ca) using a multicollector TIMS technique

We propose a new“multicollector technique” for the thermal ionization mass spectrometer (TIMS) measurement of calcium (Ca) isotope ratios improving average internal statistical uncertainty of the 44Ca/40Ca measurements by a factor of 2–4 and average sample throughput relative to the commonly used “peak jumping method” by a factor of 3. Isobaric interferences with potassium (40K+) and titanium (48Ti+) or positively charged molecules like 24Mg19F+, 25Mg19F+, 24Mg16O+ and 27Al16O+ can either be corrected or are negligible. Similar, peak shape defects introduced by the large dispersion of the whole Ca isotope mass range from 40–48 atomic mass units (amu) do not influence Ca-isotope ratios. We use a 43Ca/48Ca double spike with an iterative double spike correction algorithm for precise isotope measurement

Correlation between porosity and processing parameters in TiAl6V4 produced by selective laser melting

This study presents the correlation between process parameters and porosity formation in a TiAl6V4 alloy produced by selective laser melting. The porosity is investigated by 2D and 3D methods aiming to identify the mechanisms of void formation, their morphology as well as volume fraction as a function of the energy density. An evident minimumvolume fraction is observed between process parameters with significant overheating and insufficient fusion. It is shown that these two marginal regions define two mechanisms of void formation. Two dominant types of voids morphology are identified and examined regarding pore orientation versus their elongation, which together with the curvature distribution analysis allow revealing critical defects

Calcium isotopes in deep time: Potential and limitations

Calcium is an essential element in the biogeochemical cycles that regulate the long-term climate state of Earth. The removal of CO2 from the ocean-atmosphere system is controlled by the burial of carbonate sediments (CaCO3), ultimately linking the global calcium and carbon cycles. This fundamental link has driven the development of the stable calcium isotope proxy with applica-tion to both ancient skeletal and non-skeletal bulk carbonate sediments. Calcium isotope ratios (44/40Ca) have been used to track long-term changes in seawater chemistry (e.g., aragonite vs. calcite seas) and to elucidate short-term climatic perturbations associated with mass extinction events. However, developments in the calcium isotope proxy have shown that 44/40Ca values in carbonate minerals also are sensitive to changes in precipitation rates, mineralogy and diagene-sis, thereby complicating the application of the proxy to the reconstruction of global cycles. First, inorganic carbonate precipitation experiments have demonstrated that carbonate 44/40Ca values are sensitive to precipitation rates with higher rates generally leading to larger fractiona-tion. Second, 44/40Ca values are sensitive to carbonate mineralogy with inorganic aragonite and calcite being on average ~1.5‰ and ~0.9‰ depleted relative to contemporaneous seawater, re-spectively. The effects of both changes in carbonate mineralogy and precipitation rates affect primary and secondary minerals, but are particularly pronounced during carbonate diagenesis where relatively slow rates of recrystallization and neomorphism can lead to significant changes in bulk sediment 44/40Ca values. Third, changes in faunal composition expressed in skeletal fossil archives can lead to large changes in carbonate 44/40Ca values that are decoupled from changes in global cycles. Nevertheless, when these factors are appropriately considered the ap-plication of calcium isotopes in ancient carbonate sediments becomes a powerful tool for under-standing biogeochemical processes that operate over many scales; from diagenetic changes with-in the sediment pore-space, to regional changes across ancient carbonate platforms, and to global changes in seawater chemistry through time. Importantly, the processes that contribute to varia-bility in carbonate 44/40Ca values are likely to impact other carbonate-bound proxies, highlight-ing the potential for calcium isotopes as a hint to better understand the variability of other iso-tope systems

Proposal for International Agreement on Ca Notation resulting from discussion at workshops on stable isotope measurement held in Davos (Goldschmidt 2002) and Nice (EGS-AGU-EUG 2003)

A proposal is made to standardise the reporting of Ca isotope data to the δ44Ca/40Ca notation (or δ44Ca/42Ca) and to adopt NIST SRM 915a as the reference standard

Strontium isotope fractionation of planktic foraminifera and inorganic calcite

We have investigated the strontium isotope fractionation (Δ88/86Srcarb–aq) between inorganic calcite and aqueous Sr2+ ions by precipitation experiments at a constant temperature of 25 °C and precipitation rates (R) ranging from 102.3 to 104.2 μmol/m2/h. Strontium isotope ratios were measured using the 87Sr–84Sr double spike technique. It was found that strontium isotope fractionation in these calcites is strongly dependent on the precipitation rate: View the MathML source The measured δ88/86Sr values are significantly correlated with previously measured δ44/40Ca and Sr/Ca values of the same calcite samples: Δ88/86Srcarb–aq=+0.18∗Δ44/40Cacarb–aq-0.01 View the MathML source The slope of 88Sr/86Sr versus 44Ca/40Ca fractionation is 0.18 ± 0.04 and compatible with a kinetic fractionation during dehydration of the strontium and calcium ions, but not with isotope fractionation in a diffusive boundary layer. Using published equilibrium Δ44/40Cacarb–aq and View the MathML source values we estimate the equilibrium isotope fractionation of strontium to be very close to zero (Δ88/86Sreq(carb–aq) = −0.01 ± 0.06‰). This estimate is confirmed by strontium isotope values of natural inorganic calcites that precipitated very slowly in basalts of the ocean crust. The results from the inorganic calcites are used to explain strontium isotope fractionation of planktic foraminifera. Specimens of two warm water species (Globigerinoides ruber and Globigerinoides sacculifer) were picked from the Holocene section of a Caribbean sediment core. We found no significant difference in δ88/86Sr between the two species. In addition, G. ruber specimens from Marine Isotope Stage 2 in the same core show δ88/86Sr values identical to the Holocene specimens. The strontium isotopes of both foraminifera species are strongly fractionated (Δ88/86Srcarb–aq = −0.248 ± 0.005‰) when compared to published data of other major marine calcifiers. Applying the results from the inorganic precipitation experiments we find that the strong foraminiferal strontium isotope fractionation can be explained by calcification in a largely open system at high precipitation rates, comparable in magnitude to rates known from scleractinian reef corals. This interpretation is in good agreement with the kinetic calcification model for planktic foraminifera by Kisakürek et al. (2011), which was based on calcium isotopes and elemental Sr/Ca ratios

Two-stage 2D-to-3D reconstruction of realistic microstructures: Implementation and numerical validation by effective properties

Realistic microscale domains are an essential step towards making modern multiscale simulations more applicable to computational materials engineering. For this purpose, 3D computed tomography scans can be very expensive or technically impossible for certain materials, whereas 2D information can be easier obtained. Based on a single or three orthogonal 2D slices, the recently proposed differentiable microstructure characterization and reconstruction (DMCR) algorithm is able to reconstruct multiple plausible 3D realizations of the microstructure based on statistical descriptors, i.e., without the need for a training data set. Building upon DMCR, this work introduces a highly accurate two-stage reconstruction algorithm that refines the DMCR results under consideration of microstructure descriptors. Furthermore, the 2D-to-3D reconstruction is validated using a real computed tomography (CT) scan of a recently developed beta-Ti/TiFe alloy as well as anisotropic "bone-like" spinodoid structures. After a detailed discussion of systematic errors in the descriptor space, the reconstructed microstructures are compared to the reference in terms of the numerically obtained effective elastic and plastic properties. Together with the free accessibility of the presented algorithms in MCRpy, the excellent results in this study motivate interdisciplinary cooperation in applying numerical multiscale simulations for computational materials engineering

Constraining calcium isotope fractionation (δ44/40Ca) in modern and fossil scleractinian coral skeleton

The present study investigates the influence of environmental (temperature, salinity) and biological (growth rate, inter-generic variations) parameters on calcium isotope fractionation (δ44/40Ca) in scleractinian coral skeleton to better constrain this record. Previous studies focused on the δ44/40Ca record in different marine organisms to reconstruct seawater composition or temperature, but only few studies investigated corals. This study presents measurements performed on modern corals from natural environments (from the Maldives for modern and from Tahiti for fossil corals) as well as from laboratory cultures (Centre Scientifique de Monaco). Measurements on Porites sp., Acropora sp., Montipora verrucosa and Stylophora pistillata allow constraining inter-generic variability. Our results show that the fractionation of δ44/40Ca ranges from 0.6 to 0.1‰, independent of the genus or the environmental conditions. No significant relationship between the rate of calcification and δ44/40Ca was found. The weak temperature dependence reported in earlier studies is most probably not the only parameter that is responsible for the fractionation. Indeed, sub-seasonal temperature variations reconstructed by δ18O and Sr/Ca ratio using a multi-proxy approach, are not mirrored in the coral's δ44/40Ca variations. The intergeneric variability and intrageneric variability among the studied samples are weak except for S. pistillata, which shows calcium isotopic values increasing with salinity. The variability between samples cultured at a salinity of 40 is higher than those cultured at a salinity of 36 for this species. The present study reveals a strong biological control of the skeletal calcium isotope composition by the polyp and a weak influence of environmental factors, specifically temperature and salinity (except for S. pistillata). Vital effects have to be investigated in situ to better constrain their influence on the calcium isotopic signal. If vital effects could be extracted from the isotopic signal, the calcium isotopic composition of coral skeletons could provide reliable information on the calcium composition and budget in ocean. Highlights ► Corals cultured in aquaria or from natural environment show the same Ca isotopic composition. ► δ44/40Ca of coral skeleton is independent of depositional setting environment. ► Strong influence of vital effects on coral skeleton δ44/40Ca composition and calcification mechanism