Observation of bands among the four lowest pseudorotational states of 1,3-dioxolane

The rotational transitions belonging to the pseudorotational bands n=0→1, n=2→3, and n=0→3 have been experimentally observed for 1,3-dioxolane in the spectral region of 153-364 GHz in a supersonic jet environment using the FASSST absorption spectrometer. Based on these observations, the symmetry ordering and the energy spacings of the four lowest states, n=0,1,2,3, have been established. The totality of the available data on this molecule, including those available from previously reported microwave studies has been analyzed, and a set of molecular constants has been obtained. Using the newly determined frequencies of the pseudorotational bands, along with the frequencies of the previously reported pseudorotational bands in the IR spectrum region, an empirical potential surface of 1,3-dioxolane has been obtained. The results of this analysis are compared to the potential surface and rotational constants obtained from quantum chemistry calculations.     

Body-centered tetragonal B2N2: a novel sp3 bonding boron nitride polymorph

A novel polymorph of boron nitride (BN) with a body-centered tetragonal structure (bct-BN) has been predicted using first-principles calculations. The structural, vibrational, and mechanical calculations indicated that bct-BN is mechanically stable at zero pressure. When pressure is above 6 GPa, bct-BN becomes energetically more stable than h-BN. The bct-BN appears to be an intermediate phase between h-BN and w-BN due to a low energy barrier from h-BN to w-BN via bct-BN. Our results also indicated that the structure of unknown E-BN phase might be bct-BN.     

Multi-step surface functionalization of polyimide based evanescent wave photonic biosensors and application for DNA hybridization by Mach-Zehnder interferometer

The process of surface functionalization involving silanization, biotinylation and streptavidin bonding as platform for biospecific ligand immobilization was optimized for thin film polyimide spin-coated silicon wafers, of which the polyimide film serves as a wave guiding layer in evanescent wave photonic biosensors. This type of optical sensors make great demands on the materials involved as well as on the layer properties, such as the optical quality, the layer thickness and the surface roughness. In this work we realized the binding of a 3-mercaptopropyl trimethoxysilane on an oxygen plasma activated polyimide surface followed by subsequent derivatization of the reactive thiol groups with maleimide-PEG₂-biotin and immobilization of streptavidin. The progress of the functionalization was monitored by using different fluorescence labels for optimization of the chemical derivatization steps. Further, X-ray photoelectron spectroscopy and atomic force microscopy were utilized for the characterization of the modified surface. These established analytical methods allowed to derive information like chemical composition of the surface, surface coverage with immobilized streptavidin, as well as parameters of the surface roughness. The proposed functionalization protocol furnished a surface density of 144 fmol mm⁻² streptavidin with good reproducibility (13.9% RSD, n = 10) and without inflicted damage to the surface. This surface modification was applied to polyimide based Mach-Zehnder interferometer sensors to realize a real-time measurement of streptavidin binding validating the functionality of the MZI biosensor. Subsequently, this streptavidin surface was employed to immobilize biotinylated single-stranded DNA and utilized for monitoring of selective DNA hybridization. These proved the usability of polyimide based evanescent photonic devices for biosensing application.     

Dynamic multi-axial behavior of shape memory alloy nanowires with coupled thermo-mechanical phase-field models

The objective of this paper is to provide new insight into the dynamic thermo-mechanical properties of shape memory alloy (SMA) nanowires subjected to multi-axial loadings. The phase-field model with Ginzburg–Landau energy, having appropriate strain based order parameter and strain gradient energy contributions, is used to study the martensitic transformations in the representative 2D square-to-rectangular phase transformations for FePd SMA nanowires. The microstructure and mechanical behavior of martensitic transformations in SMA nanostructures have been studied extensively in the literature for uniaxial loading, usually under isothermal assumptions. The developed model describes the martensitic transformations in SMAs based on the equations for momentum and energy with bi-directional coupling via strain, strain rate and temperature. These governing equations of the thermo-mechanical model are numerically solved simultaneously for different external loadings starting with the evolved twinned and austenitic phases. We observed a strong influence of multi-axial loading on dynamic thermo-mechanical properties of SMA nanowires. Notably, the multi-axial loadings are quite distinct as compared to the uniaxial loading case, and the particular axial stress level is reached at a lower strain. The SMA behaviors predicted by the model are in qualitative agreements with experimental and numerical results published in the literature. The new results reported here on the nanowire response to multi-axial loadings provide new physical insight into underlying phenomena and are important, for example, in developing better SMA-based MEMS and NEMS devices     

Laser-assisted generation of gold nanoparticles and nanostructures in liquid and their plasmonic luminescence

Nanoparticles (NPs) and surface nanostructures (NS) are produced via laser ablation of a bulk gold target in liquid using second harmonics of 10 ps Nd:YAG laser (532 nm) with repetition rate of 50 kHz. The morphology and plasmon photoluminescence (PL) properties of obtained nanoscale objects are described. Transmission electron microscopy and field emission scanning electron microscopy are used for morphology characterization of NPs and NS, respectively. Plasmon PL of both gold NPs and NS is experimentally studied using the third harmonics of the Nd:YAG picosecond laser (355 nm) as a pump. The wavelength of intensity maximum of PL of Au NPs colloidal solution virtually coincides with the position of Au NPs plasmon absorption peak. Real-time excitation of both plasmon PL and Raman scattering of surrounding liquid by picosecond laser pulses in aqueous colloidal solution is also investigated. The efficient cross section of plasmon PL of Au NPs colloid is evaluated using Raman scattering of water as a comparative parameter. The results are in good agreement with values obtained in previous works. Plasmon PL from self-organized NS on the Au surface produced via laser ablation is observed for the first time. Its spectrum is compared to PL spectra of both aqueous colloidal solutions of NPs and of NPs deposited on a Si wafer. The obtained experimental data are discussed with reference to the band structure of bulk Au.     

Synthesis of carbon films by magnetron sputtering of a graphite target using hydrogen as plasma-forming gas

During magnetron sputtering of graphite using hydrogen as plasma-forming gas, a material sputtered from the target deposited only on heated substrates. When using currentheated Ni-Fe foils as substrates, carbon deposits of different crystal structures were obtained. The conditions for growing single-crystal graphite layers and single- and multilayer graphenes are found by analyzing deposits by Raman scattering.     

Neutron Collimator for the Diagnostic System of Neutral Particle Analyzers of the ITER Tokamak

Physics of Atomic Nuclei - A neutron collimator is developed to attenuate the neutron flux and reduce the residual induced activity in the interportal space of the diagnostic system of neutral...     

Numerical simulation of formation of a concentrated brine lens subject to magma chamber degassing

The mathematical model of flow of a binary salt-water mixture through a porous medium in a wide range of pressure and temperature is developed taking different multiphase thermodynamic equilibria of the mixture into account. Formation of concentrated brine lenses above a degassing magma chamber is investigated within the framework of the model. The lenses are assumed to be coupled with generation of ore deposits. It is shown that the lens formation is caused by phase transitions of two different types undergoing at different depths in the magmatic fluid rising towards the surface. In the shallow zones salt precipitation on the skeleton of the porous medium in the form of a solid phase leads to clogging of pore space and reduction of the permeability. As a result, the magmatic fluid flow towards the surface is blocked and this facilitates the concentrated brine accumulation in a local zone.     

Design Features of the Neutral Particle Diagnostic System for the ITER Tokamak

The control of the deuterium–tritium (DT) fuel isotopic ratio has to ensure the best performance of the ITER thermonuclear fusion reactor. The diagnostic system described in this paper allows the measurement of this ratio analyzing the hydrogen isotope fluxes (performing neutral particle analysis (NPA)). The development and supply of the NPA diagnostics for ITER was delegated to the Russian Federation. The diagnostics is being developed at the Ioffe Institute. The system consists of two analyzers, viz., LENPA (Low Energy Neutral Particle Analyzer) with 10–200 keV energy range and HENPA (High Energy Neutral Particle Analyzer) with 0.1–4.0MeV energy range. Simultaneous operation of both analyzers in different energy ranges enables researchers to measure the DT fuel ratio both in the central burning plasma (thermonuclear burn zone) and at the edge as well. When developing the diagnostic complex, it was necessary to account for the impact of several factors: high levels of neutron and gamma radiation, the direct vacuum connection to the ITER vessel, implying high tritium containment, strict requirements on reliability of all units and mechanisms, and the limited space available for accommodation of the diagnostic hardware at the ITER tokamak. The paper describes the design of the diagnostic complex and the engineering solutions that make it possible to conduct measurements under tokamak reactor conditions. The proposed engineering solutions provide a safe—with respect to thermal and mechanical loads—common vacuum channel for hydrogen isotope atoms to pass to the analyzers; ensure efficient shielding of the analyzers from the ITER stray magnetic field (up to 1 kG); provide the remote control of the NPA diagnostic complex, in particular, connection/disconnection of the NPA vacuum beamline from the ITER vessel; meet the ITER radiation safety requirements; and ensure measurements of the fuel isotopic ratio under high levels of neutron and gamma radiation.     

Vibration of piezoelectric elements surrounded by fluid media

In this paper we analyse vibrational characteristics of piezoceramic shells surrounded by acoustic media. Main results are presented for radially polarized piezoceramic PZT5 elements of hollow cylindrical shapes. The coupling in the radial direction between the solid and the acoustic media is accounted for indirectly, via impedance boundary conditions. The model based on such impedance boundary condition approximations offers a robust simplified alternative to a full scale fluid-solid interaction modelling. By using this model, we analyse numerically the influence of the boundary conditions imposed in the axial direction for long, medium, and short (disk-like) piezoceramic elements.