Thermal state of permafrost in Russia Romanovsky, V. E.; Drozdov, D. S.; Oberman, N. G. ...
Permafrost and periglacial processes,
April/June 2010, Letnik:
21, Številka:
2
Journal Article
Crystalline silicon (Si) nanoparticles present an extremely promising object for bioimaging based on photoluminescence (PL) in the visible and near-infrared spectral regions, but their efficient PL ...emission in aqueous suspension is typically observed after wet chemistry procedures leading to residual toxicity issues. Here, we introduce ultrapure laser-synthesized Si-based quantum dots (QDs), which are water-dispersible and exhibit bright exciton PL in the window of relative tissue transparency near 800 nm. Based on the laser ablation of crystalline Si targets in gaseous helium, followed by ultrasound-assisted dispersion of the deposited films in physiological saline, the proposed method avoids any toxic by-products during the synthesis. We demonstrate efficient contrast of the Si QDs in living cells by following the exciton PL. We also show that the prepared QDs do not provoke any cytoxicity effects while penetrating into the cells and efficiently accumulating near the cell membrane and in the cytoplasm. Combined with the possibility of enabling parallel therapeutic channels, ultrapure laser-synthesized Si nanostructures present unique object for cancer theranostic applications.
Surface properties of superprotonic (K1-х(NH4)x)3H(SO4)2 (x ≥ 0.57) single crystals and their evolution under humidity were studied by optical polarization microscopy, scanning electron microscopy ...(SEM), and energy-dispersive X-ray spectroscopy (EDXS). Traditional method of atomic force microscopy (AFM) and sophisticated methods such as Kelvin probe force microscopy (KPFM) and scanning capacitance force microscopy (SCFM) were also used. Fresh and aged cleavage surfaces perpendicular and parallel to the c axis of the trigonal superprotonic phase were examined. The effect of air humidity on the surface morphology, surface conductivity, surface potential and surface capacitance was studied. The influence of material composition and surface orientation was considered. During ageing for 430 h, the (001) sample surfaces, initially stepped, were smoothened, surface electric potential changed from negative greater than a hundred of millivolts in absolute value to positive of about 80 mV, and a modified layer containing new crystal phases was formed.
•Superprotonic phases (K1-x(NH4)x)3H(SO4)2 (x ≥ 0.57) are stabilized at room temperature and demonstrate high proton conductivity.•Their surface properties were studied by AFM. C-AFM, KPFM, SCFM, optical and electron microscopy, and structural analysis.•Local CVCs have shown that conductivity is anisotropic and is due to the composition and structure of superprotonic phases.•Based on morphological data, the stability of the surface of samples of different composition to humidity was assessed.•The formation of a modified layer with new phases on the crystal surface during prolonged exposure under humidity is shown.
The core@shell nanostructures were obtained in the process of transformation of ferrocene Fe(C5H5)2 at high pressure (HP) of 8 GPa and high temperature (HT) of 900 °C with an isothermal exposure time ...t varying from 10 to 10000 s. At t > 300 s, the iron carbide o-Fe7C3 nanoparticles with an orthorhombic crystal structure (sp.gr. Pnma) can be created, which are dispersed in highly defective carbon matrix. After opening the high-pressure cell, a series of redox reactions occurs, leading to a formation of iron oxides on the surface of the iron carbide core. When the size of Fe7C3 nanoparticle is less than critical one the nanoparticle is fully oxidized, while in the larger particle an amorphous iron oxide shell is formed. A sequential increase in t initiates crystallization processes both in the iron carbide subsystem and in the carbon subsystem, resulting in the formation of core@shell Fe7C3/FexOy/C structures. Iron oxides with a cubic spinel-type structure (Fe3O4/γ-Fe2O3) appear in the shell. However, under oxygen reduction, part of magnetite can be transformed into wüstite FeO. The magnetic properties of magnetite and wüstite are radically different, and by varying the thickness of these layers, structures with the desired functional properties can be obtained.
Display omitted
The article outlines main stages in the development of a low emission combustor (LEC) for a GTE-110M gas turbine and the results obtained in the single-burner compartment on a test bench of full ...parameters. A list of necessary works for preparing tests of flame tubes on a test bench as part of a gas turbine is presented. Potential risks include the following: overheating in individual sections of the metal walls of the flame tubes, excess pressure losses on the fuel lines, deviation from the given diagram of the temperature field at the turbine inlet, lack of ignition of individual flame tubes, occurrence of pressure fluctuations with high amplitudes, etc. The ways to eliminate the risks are suggested. Crucial imported components that require replacement with domestic counterparts are considered.
A promising method of scanning transmission electron microscopy is the use of integrated differential phase contrast. Its advantages include high sensitivity to light elements, almost linear relation ...between the generated image contrast and atomic numbers of
Z
atoms contained in a sample, noise suppression, and much more. Using the modeling and mathematical processing, prospects of this technique for studying the crystal structure of materials consisting of light atoms have been analyzed by the example of boron carbide polytypes. It is shown that the sensitivity of the technique makes it possible to distinguish columns of boron atoms from columns consisting of carbon. Recommendations on using this technique for analyzing the structures consisting of light elements are formulated.
The morphology and crystal structure of Au nanoparticles obtained by irradiating a solution of hydrochloroauric acid HAuCl
4
with laser pulses have been investigated by transmission electron ...microscopy, electron diffraction, and electron tomography. Along with round and shapeless particles, characterized by a cubic structure with twins, there are flat particles with trigonal morphology. They have a layered microstructure, with alternation of face-centered cubic and close-packed hexagonal crystal structures of layers oriented parallel to the base prism planes.
We construct the phase diagram of a monotropic type for carbon under the Berman-Simon line. It describes metastable phase transformations occurring in diamond when the graphitization is delayed. ...However, thus far, monotropic phase transition of metastable diamond could not be experimentally observed. To produced delay conditions, we introduced at diamond surface a droplet of graphite melt with a temperature of about 4800K. We demonstrate that thermal shock provided mechanical stress and competition between phase transformations occurring at two high temperature and high pressure branches. At the so called “fast graphitization line” (reported by F.P. Bundy et al., Carbon 34 (1996) 141) the transformations take place tending to the spontaneous diamond graphitization, whereas at the line of monotropic phase diagram, they tend toward the melting of diamond. The transition can start as the graphitization, whereas change-over to the second branch can occur as a result of rapid unloading of mechanical stresses. The melting wins this is competition due to its faster kinetics. We have also found out the characteristic features underlying the initiation of processes near the “fast graphitization line” as are dealing with the spontaneous formation in diamond of a network of compressed graphite, and with the melting of such graphite in the course of its expansion taking place owing to the loss of mechanical stability of diamond caused by the network. This mechanism, apparently reveals a liquid-like nature of the transformations at the “fast graphitization line”.
Display omitted
High-pressure glass has attracted interest in terms of both its fundamental state under extreme conditions and its possible applications as an advanced material. In this context, natural impact ...glasses are of considerable interest because they are formed under ultrahigh-pressure and high-temperature (UHPHT) conditions in larger volumes than laboratory fabrication can produce. Studying the UHPHT glasses of the unique giant Kara astrobleme (Russia), we found that the specific geological position of the UHPHT melt glass veins points to an origin from a secondary ultrahigh-pressure (UHP) melt according to the characteristics of the host suevites, which suggest later bottom flow. Here, we propose a fundamentally novel model involving an upward-injected UHP melt complex with complicated multi-level and multi-process differentiation based on observations of the UHP silica glass, single-crystal coesite and related UHP smectite that crystallized from an impact-generated hydrous melt. This model proposes a secondary UHP crisis during the modification stage of the Kara crater formation. The results are very important for addressing fundamental problems in fields as diverse as condensed matter states under extreme pressure and temperature (PT) conditions, material and geological reconstructions of impact structures, water conditions in mineral substances under UHP conditions in the deep Earth, and the duration and magnitude of the catastrophic effects of large asteroid impacts.
Electrorheological fluids based on polydimethylsiloxane filled with halloysite nanotubes were studied. The filler structure was characterized by TEM, SEM, and X-ray diffraction. When an electric ...field is applied to suspensions, their rheological behavior changes - the contribution of the elastic component becomes significant and samples behave like a solid body. The effect of the electric field and filler concentration on the electrorheological behavior was investigated. The influence of water content on the filler structure, as well as on electrorheological and electrophysical properties of suspensions, was considered. Electrorheological fluids filled by halloysite with small water content exhibit slightly higher rheological characteristics under an electric field than dried ones. This study shows the prospects of using halloysite nanotubes as a dispersed phase for electrorheological fluids.
PDF
