Temperature and current density distributions at spark plasma sintering of inhomogeneous samples

We analyze the effect of inhomogeneity in the properties of a material on the conditions of obtaining thermoelectrics by spark plasma sintering. Inclusions localized and distributed over the volume of materials with different values of electric and thermal conductivities are considered. It is found that the presence of macroscopic inhomogeneities changes the current density distribution in the cross section of the sample being sintered. It is shown that inhomogeneity in the properties of materials during sintering do not substantially affect the temperature field in the sample at the macroscopic level, but change the current density distribution profile. The ranges of variation of the current density in the regions with inhomogeneous electric and thermal conductivities are determined for various types of macroscopically inhomogeneous inclusions and their distribution. The applicability of various models for describing spark plasma sintering is considered.     

Solid phase synthesis of selectively deuterated arenes

A novel access to deuterated and D(3)CO-substituted arenes has been developed using immobilized triazenes as precursors. The linker system and the deuterating cleavage methodology could be shown to be compatible with various functional groups and are therefore suitable for the synthesis of derivatives only hardly available via comparable protocols.     

Lateral diffusion in equimolar mixtures of natural sphingomyelins with dioleoylphosphatidylcholine

Cellular membranes of mammals are composed of a complex assembly of diverse phospholipids. Sphingomyelin (SM) and phosphatidylcholine (PC) are important lipids of eukaryotic cellular membranes and neuronal tissues, and presumably participate in the formation of membrane domains, known as "rafts," through intermolecular interaction and lateral microphase decomposition. In these two-dimensional membrane systems, lateral diffusion of lipids is an essential dynamic factor, which might even be indicative of lipid phase separation process. Here, we used pulsed field gradient nuclear magnetic resonance to study lateral diffusion of lipid components in macroscopically oriented bilayers composed of equimolar mixtures of natural SMs of egg yolk, bovine brain, bovine milk and dipalmitoylphosphatidylcholine (DPPC) with dioleoylphosphatidylcholine (DOPC). In addition, differential scanning calorimetry was used as a complementary technique to characterize the phase state of the lipid bilayers. In fully liquid bilayers, the lateral diffusion coefficients in both DOPC/DPPC and DOPC/SM systems exhibit mean values of the pure bilayers. For DOPC/SM bilayer system, this behavior can be explained by a model where most SM molecules form short-lived lateral domains with preferential SM-SM interactions occurring within them. However, for bilayers in the presence of their low-temperature gel phase, lateral diffusion becomes complicated and cannot simply be understood solely by a simple change in the liquid phase decomposition.     

Synthesis of novel 1,2,3-triazolyl nucleoside analogues bearing uracil, 6-methyluracil, 3,6-dimethyluracil,thymine, and quinazoline-2,4-dione moieties

A series of novel 1,2,3-triazolyl nucleoside analogues was synthesized via the CuAAC reaction of N1-alkynyl uracil, 6-methyluracil, 3,6-dimethyl uracil, thymine and quinazolin-2,4-dione with protected azido β-d-ribofuranose. The obtained compounds differ in both the nature of the pyrimidine-2,4-dione fragment and the length of the polymethylene linker connecting it with the β-d-ribofuranosyl-1,2,3-triazol-4-yl moiety. The 1,2,3-triazolyl nucleoside analogues were evaluated for their cytotoxicity in vitro.     

Content and Isotope Ratios of Noble Gases in Congelation Ice of Lake Vostok

Isotope ratios of noble gases (He, Ne, Ar) were studied in samples collected by degassing of cores of water frozen over a glacier of Lake Vostok. The gases were collected into glass retorts during three days of degassing of cores, which have just been extracted from the borehole. Within the error, the isotope ³He/⁴He ratios of 0.28 ± 0.08 R_A (R_A = 1.38 × 10^–6 is the ratio for air) correspond to those from [1]. The ⁴He/²⁰Ne and ⁴⁰Ar/³⁶Ar ratios (12.4 ± 4.6 R_A and 1.0074 ± 0.0023 R_A, respectively) exceed their contents in air (⁴He/²⁰Ne_A = 0.29; ⁴⁰Ar/³⁶Ar_A = 298.6) and may indicate some contribution of terrigenous gas to the gaseous balance of the lake, as well as the high content of ancient ground waters in the lake. The ³He/⁴He ratio of 0.28 R_A means low mantle ³He flux typical of continental platforms far from active rift zones.     

Three-dimensional diffraction of a shock wave

The diffraction of a shock wave (M₀=4.7) at an angle close to 180 has been experimentally investigated for the three-dimensional case. Interferograms of the flow and the pressure distribution on the back wall in the course of its interaction with the diffracted wave were obtained. Rotation of the flow structure behind the shock wave relative to the axis of symmetry was observed as the flow pattern develops in time and space.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 200–201 March–April, 1993.     

Influence of grain size distribution on the lattice thermal conductivity of Bi2Te3-Sb2Te3-based nanostructured materials

The change of the lattice thermal conductivity of bulk nanostructured materials based on Bi₂Te₃-Sb₂Te₃ solid solutions with grain size distribution has been studied. These materials have a polycrystalline structure with grain sizes ranging from a few tens of a nanometer to a few micrometers. Large grains may contain inclusions or consist of several smaller parts which can be identified with coherent scattering regions seen in X-ray diffraction. The change of the lattice thermal conductivity mediated by additional scattering by inclusions and grain boundaries has been calculated. This calculation allows for the effect of nanoparticle size distribution. The calculated estimates are compared with the available experimental data.     

II. Greetings by the Board of the Mechanics Division of the National Academy of Sciences of Ukraine

International Applied Mechanics -     

Imaging Glycosylation In Vivo by Metabolic Labeling and Magnetic Resonance Imaging

Glycosylation is a ubiquitous post‐translational modification, present in over 50 % of the proteins in the human genome, 1 with important roles in cell–cell communication and migration. Interest in glycome profiling has increased with the realization that glycans can be used as biomarkers of many diseases, 2 including cancer. 3 We report here the first tomographic imaging of glycosylated tissues in live mice by using metabolic labeling and a gadolinium‐based bioorthogonal MRI probe. Significant N‐azidoacetylgalactosamine dependent T₁ contrast was observed in vivo two hours after probe administration. Tumor, kidney, and liver showed significant contrast, and several other tissues, including the pancreas, spleen, heart, and intestines, showed a very high contrast (>10‐fold). This approach has the potential to enable the rapid and non‐invasive magnetic resonance imaging of glycosylated tissues in vivo in preclinical models of disease.