V. I. Nikolaev

Whole-Genome Shotgun Sequencing of Mitochondria from Ancient Hair Shafts

Although the application of sequencing-by-synthesis techniques to DNA extracted from bones has revolutionized the study of ancient DNA, it has been plagued by large fractions of contaminating environmental DNA. The genetic analyses of hair shafts could be a solution: We present 10 previously unexamined Siberian mammoth (Mammuthus primigenius) mitochondrial genomes, sequenced with up to 48-fold coverage. The observed levels of damage-derived sequencing errors were lower than those observed in previously published frozen bone samples, even though one of the specimens was >50,000 14C years old and another had been stored for 200 years at room temperature. The method therefore sets the stage for molecular-genetic analysis of museum collections.

Intraspecific phylogenetic analysis of Siberian woolly mammoths using complete mitochondrial genomes

We report five new complete mitochondrial DNA (mtDNA) genomes of Siberian woolly mammoth (Mammuthus primigenius), sequenced with up to 73-fold coverage from DNA extracted from hair shaft material. Three of the sequences present the first complete mtDNA genomes of mammoth clade II. Analysis of these and 13 recently published mtDNA genomes demonstrates the existence of two apparently sympatric mtDNA clades that exhibit high interclade divergence. The analytical power afforded by the analysis of the complete mtDNA genomes reveals a surprisingly ancient coalescence age of the two clades, ≈1–2 million years, depending on the calibration technique. Furthermore, statistical analysis of the temporal distribution of the 14C ages of these and previously identified members of the two mammoth clades suggests that clade II went extinct before clade I. Modeling of protein structures failed to indicate any important functional difference between genomes belonging to the two clades, suggesting that the loss of clade II more likely is due to genetic drift than a selective sweep.

Oxygen isotope measurements of mammoth and reindeer skeletal remains: an archive of Late Pleistocene environmental conditions in Eurasian Arctic

58 samples of fossil mammoth and reindeer teeth and bones of various ages and coming from different locations were studied for the oxygen isotopic composition of their phosphate. Samples from Siberia have interstadial (Marine Isotope Stage 3), stadial (MIS 2), late-glacial and post-glacial ages. Russian and Ukrainian samples refer to the late-glacial and transitional (between the interstadial and glacial stages) time. The δ18O of palaeoenvironmental waters were calculated from the δ18Op obtained from fossil samples by means of the isotope equations calibrated on modern specimens of elephants and deer respectively. The δ18Ow obtained are generally lighter than those measured nowadays in the same areas and not far from those measured on ice cores of Holocene age, the isotopic differences being not greater than a few δ units. The calculated values are also in fairly good agreement with some isotopic values obtained from Siberian permafrost samples. According to the results obtained it seems that the elephant and deer equations can be reasonably used respectively in the case of fossil mammoth and deer skeletons to evaluate environmental palaeowaters.

Modern reindeer and mice: revised phosphate–water isotope equations

Abstract The oxygen isotope composition of bone and tooth phosphate of 34 mice specimens (Pitymus sp., Microtus arvalis and Arvicola terrestris) coming from seven different locations in Italy, Germany and Switzerland was measured by means of well-established techniques. These measurements were carried out with the purpose of establishing quantitative relationships between the δ18Op from different mice genera and the mean δ18Ow values and to compare these data to previous measurements carried out on various specimens belonging to the genus Apodemus. The three genera studied showed a similar behaviour when compared to the mean δ18Ow values. The slope of the equation calculated for these three genera is significantly different from the slope obtained from Apodemus specimens. Reconsidering the δ18Ow values suggested in the case of Apodemus due to the small number of data available at that time, it seems that these values are too negative by 0.5 to about 1.5‰. If so, the Apodemus equation becomes almost identical to the equation calculated for the new mice values and, consequently, one could conclude that several micromammal genera and species might behave in the same way and obey the same relationship with the mean δ18Ow values. A set of 25 samples of modern reindeer skeletal material from Spitzbergen, Russia and Siberia was also studied with the aim of improving the reindeer isotope equation obtained from a previous study. In fact, the slope of that equation was somehow uncertain due to a rather large range of isotope values obtained from each group of reindeers coming from the same location. The new results confirm such ‘anomalous’ behaviour already shown by other mammals and probably related to dietary behaviours, water fluxes with the environment and isotopic composition of ingested food and water rather than to imperfect equilibrium conditions with environmental water. However, the equation calculated from both the old and new, statistically more significant, isotope results is not far from the previous one.

Determination of elastic moduli of GaN epitaxial layers by microindentation technique

It is demonstrated that Young’s modulus of epitaxial gallium nitride layers can be determined by the microindentation of their growth surface. The technique is based on the solution of the Hertz problem for the elastic indentation of a steel sphere into the studied surface. It is established that the isotropic approximation applied in this case is justified and leads to the satisfactory results. The microhardness measurements of epitaxial layers are carried out.

Pleistocene ice at the bottom of the Vavilov ice cap, Severnaya Zemlya, Russian Arctic

The Vavilov ice cap was perforated in 1988 by a drilling which reached the underlying frozen sediments. In contrast to the overlying glacier ice, the basal ice is composed of different ice layers with a variable debris load. The stable-isotope composition of these layers shows δ values much lower than everywhere else in the core or in the Vavilov ice cap. This is most probably the signature of a remnant of Pleistocene ice which, for the first time, is shown to occur in the Russian Arctic.

Pseudoelastic deformation and generation of reactive stresses in a Cu-Al-Ni shape-memory alloy in the temperature range 4.2–293 K

Pseudoelastic deformation and the magnitude of reactive stresses in Cu-14.2% Al-4.5% Ni shape-memory alloy single crystals were studied experimentally in the temperature range 4.2–293 K. It is established that pseudoelasticity and the shape-memory effect are observed in this alloy over the entire temperature range indicated above. It is found that, as the constrained samples are heated at a constant rate from liquid-helium temperature, the reactive stresses increase continuously at temperatures of up to 100 K and then remain constant. When the temperature of preliminary deformation is 77 K, the generation of reactive stresses with an increase in temperature occurs by two stages, which agrees with the multistage behavior of the pseudoelastic-deformation curves of this alloy above the liquid-nitrogen boiling temperature. Using the theory of diffuse martensitic transitions, a quantitative calculation is performed of pseudoelastic-deformation curves and reactive-stress curves over the temperature range 4.2–293 K under conditions of two-stage behavior of the martensitic transformation.

Influence of partial shape memory deformation on the burst character of its recovery in heated Ni–Fe–Ga–Co alloy crystals

Room-temperature stress–strain curves of Ni49Fe18Ga27Co6 alloy single crystals possessing shape memory (SM) have been studied. Specific features of these diagrams are revealed upon compressive loading of these single crystals in the [110]A direction. The influence of preliminary SM deformation on the process of its recovery during the reverse martensite transformation has been studied. It is established that SM deformation above 4.2% leads to a sharp increase in the shape recovery on heating and the process exhibits a burst character, involving motion of the entire crystal. The experimental data are analyzed and stress–strain curves are simulated in the framework of the theory of diffuse martensitic transitions.

Burst character of thermoelastic shape memory deformation in ferromagnetic Ni-Fe-Ga-Co alloy

The shape memory deformation in single crystals of Ni49Fe27Ga18Co6 alloy under uniaxial compression conditions has been studied. It was found that samples in the martensite state deformed in the [110] and [100] directions exhibit strongly anisotropic properties. Despite virtually equal residual strain and the work of deformation in the two cases, the subsequent behavior of samples during shape recovery on heating at a constant rate is principally different. In the former case, the shape memory deformation exhibits a burst character and takes place at a temperature that is significantly higher than the martensite transformation temperature in the initial (undeformed) crystal. In contrast, the shape recovery in the latter case proceeds smoothly at a temperature that is only slightly higher than the martensite transformation temperature in the initial crystal. Due to the burst character of shape memory deformation, the crystal standing on a solid base acquires a velocity above 20 m/s. The results are quantitatively analyzed in terms of the theory of diffuse phase transitions.

Influence of the deformation type and medium on the mechanodynamic penetration of nitrogen molecules into surface layers of armco iron

The extraction of nitrogen molecules from deformed samples of armco iron with different initial structures (annealed and subjected to equal-channel angular pressing) and different deformation prehistories (deformation in liquid nitrogen at 77 K, rolling in air at room temperature, and their combination) has been studied. It has been shown that the preliminary deformation in liquid nitrogen increases its concentration in the surface layer of the material and shifts the principal peak of its release toward low temperatures during heating. The results are associated with the existence of different types of nitrogen traps in annealed and nanostructured armco iron and with their changes during subsequent deformation.