Induced current in the presence of magnetic flux tube of small radius

The induced current density, corresponding to the massless Dirac equation in (2+1) dimensions in a magnetic flux tube of small radius is considered. This problem is important for graphene. In the case, when an electron can not penetrate the region of nonzero magnetic field, this current is the odd periodical function of the magnetic flux. If the region inside the magnetic tube is not forbidden for penetration of electron, the induced current is not a periodical function of the magnetic flux. However in the limit $R\to 0$, where $R$ is the radius of magnetic flux tube, this function has the universal form which is independent of the magnetic field distribution inside the magnetic tube at fixed value of the magnetic flux.Comment: 5 pages, 1 figur

The Induced Charge Generated By The Potential Well In Graphene

The induced charge density, $\rho_{ind}(\bm r)$, generated in graphene by the potential well of the finite radius $R$ is considered. The result for $\rho_{ind}(\bm r)$ is derived for large distances $r\gg R$. We also obtained the induced charges outside of the radius $r\gg R$ and inside of this radius for subcritical and supercritical regimes. The consideration is based on the convenient representation of the induced charge density via the Green's function of electron in the field.Comment: 12 pages, 2 figures, version published in Phys.Rev.

Screening of Coulomb Impurities in Graphene

We calculate exactly the vacuum polarization charge density in the field of a subcritical Coulomb impurity, $Z|e|/r$, in graphene. Our analysis is based on the exact electron Green's function, obtained by using the operator method, and leads to results that are exact in the parameter $Z\alpha$, where $\alpha$ is the "fine structure constant" of graphene. Taking into account also electron-electron interactions in the Hartree approximation, we solve the problem self-consistently in the subcritical regime, where the impurity has an effective charge $Z_{eff}$, determined by the localized induced charge. We find that an impurity with bare charge Z=1 remains subcritical, $Z_{eff} \alpha < 1/2$, for any $\alpha$, while impurities with $Z=2,3$ and higher can become supercritical at certain values of $\alpha$.Comment: 4 pages, 2 figure

Epoxy Compositions with Reduced Flammability Based on DER-354 Resin and a Curing Agent Containing Aminophosphazenes Synthesized in Bulk Isophoronediamine

A method for the synthesis of an amine-containing epoxy resin curing agent by dissolving hexakis-[(4-formyl)phenoxy]cyclotriphosphazene in an excess of isophoronediamine was developed. The curing agent was characterized via NMR and IR spectroscopy and MALDI-TOF mass spectrometry, and its rheological characteristics were studied. Compositions based on DER-354 epoxy resin and the synthesized curing agent with different amounts of phosphazene content were obtained. The rheological characteristics of these compositions were studied, followed by their curing. An improvement in several thermal (DSC), mechanical (compression, tension, and adhesion), and physicochemical (water absorption and water solubility) characteristics, as well as the fire resistance of the obtained materials modified with phosphazene, was observed, compared with unmodified samples. In particular, there was an improvement in adhesive characteristics and fire resistance. Thus, compositions based on a curing agent containing a 30% modifier were shown to fulfill the V-1 fire resistance category. The developed compositions can be processed by contact molding, winding, and resin transfer molding (RTM), and the resulting material is suitable for use in aircraft, automotive products, design applications, and home repairs

Bremsstrahlung in α decay reexamined

A high-statistics measurement of bremsstrahlung emitted in the α decay of 210Po has been performed, which allows us to follow the photon spectra up to energies of ~500keV. The measured differential emission probability is in good agreement with our theoretical results obtained within the quasiclassical approximation as well as with the exact quantum mechanical calculation. It is shown that, due to the small effective electric dipole charge of the radiating system, a significant interference between the electric dipole and quadrupole contributions occurs, which is altering substantially the angular correlation between the α particle and the emitted photon

Mechanical safety of reinforced concrete structures at all stages of the life cycle

Ensuring the mechanical safety of operated buildings at all stages of the life cycle is an urgent task. This is especially important when planning major repairs and reconstruction in buildings, as well as determining the period of safe operation from the moment of the survey, i.e. clarification of the remaining service life. The total service life at the design stage is set by the customer and the general designer in accordance with the recommendations of GOST 27751-2014 «Reliability for constructions and foundations. General principles». Mechanical safety and durability are ensured when calculating structures using the limit state method, assigning protection measures depending on the operating conditions, as well as complying with the requirements of SP 255.1325800.2016 «Buildings and structures. Operating rules. General Provisions». A method for preliminary assessment of the mechanical safety of buildings and their structures is proposed for consideration, which eliminates some of the shortcomings of existing methods for calculating the residual life by physical wear (damage) of building structures based on the results of a visual inspection, the basis of which is the dependence of the allowable safe operation period on the percentage of reduced bearing capacity. It is proposed to use the results of a visual inspection performed in accordance with GOST 31937-2011 «Buildings and constructions. Rules of inspection and monitoring of the technical condition»

QM/MM Description of Newly Selected Catalytic Bioscavengers Against Organophosphorus Compounds Revealed Reactivation Stimulus Mediated by Histidine Residue in the Acyl-Binding Loop

Butyrylcholinesterase (BChE) is considered as an efficient stoichiometric antidote against organophosphorus (OP) poisons. Recently we utilized combination of calculations and ultrahigh-throughput screening (uHTS) to select BChE variants capable of catalytic destruction of OP pesticide paraoxon. The purpose of this study was to elucidate the molecular mechanism underlying enzymatic hydrolysis of paraoxon by BChE variants using hybrid quantum mechanical/molecular mechanical (QM/MM) calculations. Detailed analysis of accomplished QM/MM runs revealed that histidine residues introduced into the acyl-binding loop are always located in close proximity with aspartate residue at position 70. Histidine residue acts as general base thus leading to attacking water molecule activation and subsequent SN2 inline hydrolysis resulting in BChE reactivation. This combination resembles canonical catalytic triad found in active centers of various proteases. Carboxyl group activates histidine residue by altering its pKa, which in turn promotes the activation of water molecule in terms of its nucleophilicity. Observed re-protonation of catalytic serine residue at position 198 from histidine residue at position 438 recovers initial configuration of the enzyme’s active center, facilitating next catalytic cycle. We therefore suggest that utilization of uHTS platform in combination with deciphering of molecular mechanisms by QM/MM calculations may significantly improve our knowledge of enzyme function, propose new strategies for enzyme design and open new horizons in generation of catalytic bioscavengers against OP poisons

Clustering of airport cities and cluster dynamic for the air passenger demand forecasting model based on a socio-economic scenario

This study presents methods of grouping cities into clusters by their socio-economic indicators and tracing changes in the content of cluster within a socio-economic scenario. For cities’ grouping, three main clustering approaches have been analyzed: hierarchical, exclusive and probabilistic clustering. Analyzing advantages and disadvantages of these approaches, probabilistic clustering of normal mixture has been chosen to separate cities from the air passenger demand (APD) forecasting model. Three parameters, a city’s GDP, population and GDP per capita, have been used for clustering. Utilizing these parameters and based on special metrics, separation of cities into 9 clusters has been chosen. Furthermore, this study introduces the “cluster dynamic”. The cluster dynamic defines how cities are allocated to the various clusters at a given point in time within a socio-economic scenario