Absorption of laser-radiation energy by femtosecond laser spark in air

The fraction of focused femtosecond laser radiation energy absorbed by a laser-induced spark in air has been studied. It is established that the absorbed energy exhibits nonlinear growth with increasing energy of the laser pulse. The threshold power for laser-induced spark formation in air is 5.2 GW.     

Tissue distribution of liver regulating protein. Evidence for a cell recognition signal common to liver, pancreas, gonads, and hemopoietic tissues

Liver regulating protein (LRP) is an integral plasma membrane protein that plays a critical role in maintaining the differentiated phenotype of adult rat hepatocytes by mediating cell-cell interactions with rat liver epithelial cells. Using a specific monoclonal antibody (MAb L8) capable of inhibiting the interactions between these two cell types, the cellular distribution of LRP was analyzed in the liver. Various cell types, including hepatocytes and several sinusoidal cells, were found to be positive, whereas vascular endothelial cells and bile duct cells were consistently negative. This observation led us to question whether cells of nonhepatic origin would also express LRP. We show that MAb L8 immunoreactive material was detected in only three groups of tissues and corresponded to molecules similar to LRP but with different molecular weights. LRP-like molecules were demonstrated on acinar cells of the exocrine pancreas and on all hemopoietic cells regardless of their localization in the organism. LRP-like molecules were also expressed by germ cells and surrounding feeder cells in the testis and ovary in a stage-dependent manner. These results demonstrate the existence of a family of LRP proteins and strongly suggest a critical role for these molecules in regulating cell-cell communication in specific tissues.     

Conditions and features of matrix and bulk carbonization of the organic precursors

Comparative research of matrix and bulk carbonization of some organic precursors (sucrose, acetonitrile) in silica mesoporous materials SBA-15 and KIT-6 was conducted. X-ray diffraction, nitrogen adsorption analysis, Raman spectroscopy were used for determination of the structural-sorption characteristics of the obtained materials. It was shown that the carbon mesoporous materials CMK-8 obtained in the mesopores of KIT-6 had higher adsorption characteristics because of features of three-dimensional cubic structure, larger pore volume and framework’s wall thickness. It was established that partially graphitized spatially well-organized carbon materials were formed as a result of pyrolysis of acetonitrile in the silica matrices SBA-15 and KIT-6. It was conditioned by the absence of considerable spatial limitations for growth of graphite structures on the initial stage of the synthesis when the pores of the matrix were not filled up with the organic precursor. Product of bulk carbonization of sucrose is compact carbon microporous framework with low sorption characteristics (micropore volume is 0.09 cm³/g).     

Adhesive properties of liquid crystalline hydroxypropyl cellulose–propylene glycol blends

Adhesion (tack) of the liquid crystalline hydroxypropyl cellulose–propylene glycol (HPC/PG) systems has been studied under various loading modes as well as their rheology and phase state. The system with the optimum tack according to the Dahlquist criterion (HPC/PG?=?85/15 wt.%) was chosen based on its rheological properties (viscosity, storage and loss moduli at 20 and 50?°C). Tack measurements were carried out for this system. Rheological measurements revealed the presence of the critical stress detected by the abrupt drop of viscosity. The adhesive behavior of the system deviates significantly from one of the conventional pressure sensitive adhesives (PSAs): almost no tack is observed when using contact force and contact time typical for a PSA. To achieve good adhesion with this system one needs substantially higher pressure and contact time. At 20?°C, adhesive failure is observed in most cases and high contact forces (over 500–600?g) are required to overcome critical stress and obtain noticeable tack characteristics. At 50?°C, fibrillation and cohesive failure are usually observed with some residue of the system on the probe after debonding. Usage of high contact forces (600–1000?g) and contact times (up to 1000?s) allows us to reach significant values of the maximum debonding stress (up to 1.25?MPa) and energy (up to 420?J/m²). These values are on the same level or even higher than the corresponding values for standard PSAs.     

Fabrication of microfiltration membranes from polyisobutylene/polymethylpentene blends

An approach for fabrication of microfiltration membranes by solvent extraction of one of the immiscible components from a polymer blend was developed. Poly(4‐methyl‐1‐pentene) (PMP) was the membrane material, and poly(isobutylene) (PIB) was the extractable component. The PIB content varied in the wide range 0–45 wt%, and all blends could be melted and processed at a temperature of 240 °C. A rheological study demonstrated a pronounced non‐Newtonian behavior of PMP/PIB blends and their very low viscosity due to interlayer slip. With a PMP content of 55 and 60 wt%, it was possible to fabricate microfiltration membranes with a water permeability of 31 and 3.7 m³ m^?2 h^–1 bar^–1, respectively. The microfiltration membranes based on both compositions demonstrated good rejection performance at the level of 93%–98% for submicron particles of phthalocyanine dye with a size of 240 nm. These results indicate that the PMP/PIB system can be utilized for fabrication of filtration membranes by means of 3D printing followed by solvent extraction. © 2019 Society of Chemical Industry     

Ion Doping of Silicon Carbide in the Technology of High-Power Electronic Devices (Review)

Semiconductors - Ion implantation is a key technology without alternative for doping silicon carbide SiC in the manufacturing processes of SiC devices. SiC technology has a number of distinctive...     

Analysis of the Gas Phase Epitaxy of Silicon Carbide as a Basic Process for the Technology of Power Electronics

Semiconductors - Currently, chemical gas deposition is the main method for producing high-quality and reproducible epitaxial layers for commercial silicon carbide (SiC) power devices. Based on the...     

Change of interstrand contact resistance and coupling loss in various prototype ITER NbTi conductors with transverse loading in the Twente Cryogenic Cable Press up to 40,000 cycles

The multistrand NbTi conductors for the Poloidal Field (PF) Coils of the International Thermonuclear Experimental Reactor (ITER) are subjected to heavy transverse loading due to the Lorentz forces in the coils. The current in the multistage Cable-In-Conduit Conductors (CICC) exceeds 50 kA and the magnetic field reaches up to more than 6 T for a few tens of thousands of pulses. The large transverse forces, accumulating from strand to strand over the cable cross-section, cause a severe deformation of the cable bundle inside the conduit and this goes along with electromagnetic, mechanical, and thermohydraulic effects. In order to study the electromagnetic and mechanical behaviour in more detail, a Cryogenic Cable Press is build to simulate the effect of the Lorentz forces on a conductor comparable to the present design for ITER in magnet operating conditions. The magnetisation of the conductor (and from this the coupling loss expressed in nτ) and the interstrand resistance (R_c) between various strands and strand bundles inside the cable can be measured along the loading history, starting at virgin condition and accordingly subjected to various loads. The results, all obtained on eight full-size ITER type NbTi conductor samples with a variety of cable strand layout and coatings, are reported here.A consistent correlation is found between the experimental AC loss and interstrand contact resistance (R_c) results. It is also observed that there is a strong impact of cyclic loading on the AC loss and R_c which may change up to orders of magnitude. The variation of the AC loss due to transverse cyclic loading of CICC conductors in ITER coils can be accomplished by reducing the void fraction. The results point out that cyclic loading with a significant number of cycles, sufficient to reach a saturation after having passed the peak transverse resistance, should be included in next tests on large NbTi CICC's and PF Model Coils as the AC loss and ability of current sharing among strands will vary along the loading history.     

Features of passivation, oxidation and combustion of tungsten nanopowders by air

The passivation, oxidation and combustion of tungsten nanopowders (NP) (a_s  100 nm), produced by an electrical explosion of wires (WEE) method, has been studied in air medium. The phase transformation for W nanopowders under air-oxidation was investigated. The oxidation process and an analysis of passivated powders were studied by FESEM, EDS, XPS, XRD, TEM, DTA-TGA and size distribution analysis was also observed by a video camera. After the comprehensive testing of passivated, oxidized and burned powders, a chemical process of oxidation of W nanoparticles was suggested.