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

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»

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»

Deep Functional Profiling Facilitates the Evaluation of the Antibacterial Potential of the Antibiotic Amicoumacin

The global spread of antibiotic resistance is forcing the scientific community to find new molecular strategies to counteract it. Deep functional profiling of microbiomes provides an alternative source for the discovery of novel antibiotic producers and probiotics. Recently, we implemented this ultrahigh-throughput screening approach for the isolation of Bacillus pumilus strains efficiently producing the ribosome-targeting antibiotic amicoumacin A (Ami). Proteomics and metabolomics revealed essential insight into the activation of Ami biosynthesis. Here, we applied omics to boost Ami biosynthesis, providing the optimized cultivation conditions for high-scale production of Ami. Ami displayed a pronounced activity against Lactobacillales and Staphylococcaceae, including methicillin-resistant Staphylococcus aureus (MRSA) strains, which was determined using both classical and massive single-cell microfluidic assays. However, the practical application of Ami is limited by its high cytotoxicity and particularly low stability. The former is associated with its self-lactonization, serving as an improvised intermediate state of Ami hydrolysis. This intramolecular reaction decreases Ami half-life at physiological conditions to less than 2 h, which is unprecedented for a terminal amide. While we speculate that the instability of Ami is essential for Bacillus ecology, we believe that its stable analogs represent attractive lead compounds both for antibiotic discovery and for anticancer drug development

First Multy-Proxy Studies Of High-Mountain Lakes In Armenia: Preliminary Results

Within the framework of the Russian-Armenian project “The Paleolimnological Aspect of Studying the Evolution of Ecosystems of High-Mountain Lakes of Russia and Armenia” in July-August 2018, we investigated four high-mountain lakes of Armenia. The research focuses on the lakes Kari, Umroi, Akna and Sev. All investigated lakes are located at the altitudes about 3000 m above sea level. We first time these lakes were investigated using a multi-proxy method that includes paleolimnological, geomorphological, hydrological, geochemical and biogeographic studies. The research offers the first statistical characteristics of lake depth distribution, water volume and other morphometrics. Lake sediments sequences and radiocarbon dates were received and analyzed for Armenian small lakes for the first time. We determined that all the studied lakes were formed during the Holocene. Sediments of Lake Kari were deposited in the last 4000 years, sediments of Lake Umroi – within the last 8000 years, while maximum thickness of sediments is around 1 m in both lakes. Hence, we assume low deposition rate in Armenian high-mountain lakes, however, it varied significantly in different periods of lake history