Structural mechanisms of formation of adiabatic shear bands

The paper focuses on the experimental and theoretical study of plastic deformation instability and localization in materials subjected to dynamic loading and high-velocity perforation. We investigate the behavior of samples dynamically loaded during Hopkinson-Kolsky pressure bar tests in a regime close to simple shear conditions. Experiments were carried out using samples of a special shape and appropriate test rigging, which allowed us to realize a plane strain state. Also, the shear-compression specimens proposed in were investigated. The lateral surface of the samples was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. Use of a transmission electron microscope for studying the surface of samples showed that in the regions of strain localization there are parts taking the shape of bands and honeycomb structure in the deformed layer. The process of target perforation involving plug formation and ejection was investigated using a high-speed infra-red camera. A specially designed ballistic set-up for studying perforation was used to test samples in different impulse loading regimes followed by plastic flow instability and plug ejection. Changes in the velocity of the rear surface at different time of plug ejection were analyzed by Doppler interferometry techniques. The microstructure of tested samples was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The subsequent processing of 3D deformation relief data enabled estimation of the distribution of plastic strain gradients at different time of plug formation and ejection. It has been found that in strain localization areas the subgrains are elongated taking the shape of bands and undergo fragmentation leading to the formation of super-microcrystalline structure, in which the size of grains is ~300nm. Rotational deformation modes give rise to the high angular disorientations of grains. The development of plastic shear instability regions has been simulated numerically. For this purpose, we use a recently developed theory, in which the influence of microshears on the deformation properties of materials has been studied by the methods of statistical physics and thermodynamics of irreversible processes. The results of theoretical and experimental studies suggest that one of the mechanisms of the plastic shear instability and localization of plastic strain at high-velocity perforation is related to structural and kinetic transitions in microshear ensembles.&nbsp

Nucleoside Analogs with Fleximer Nucleobase

[Figure not available: see fulltext.] This review article is devoted to the so-called fleximer nucleoside analogs, containing two or more planar moieties in the heterocyclic base, connected by a bond that permits rotation. Such analogs have been proposed as molecular probes for detecting enzyme–substrate interactions and studying the transcription and translation of nucleic acids, but subsequently have attracted the interest of researchers by their antiviral and antitumor activity. The methods used in the synthesis of such compounds, along with their structural features and also biological activity are considered in this review

Metastability, adiabatic shear bands initiation and plastic strain localization in the AMg6 alloy under dynamic loading

New conception of adiabatic shear bands (ASB) and adiabatic shear failure mechanisms are proposed as special type of critical phenomen, structural-scaling transition, in the ensembles of microshears, governed by the characteristic non-linearity (metastability) of stored (free) energy of solid with mesodefects.  Corresponding free energy release kinetics provides experimentally observed ASB induced staging of plastic strain localization and transition to adiabatic shear failure. ASB staging follows to collective properties of microshears ensemble given by the self-similar solutions of evolution equation providing spatial-temporal microshears localization, momentum transfer and damage localization. The criticality of ASB induced plastic strain localization and failure allows us to avoid the discrepancy in the interpretation of ASB effects as thermo-plastic instability in the balance of the stored energy and structural DRX transformation. The microshear ensemble is considered as the second phase and initiation of collective modes provide different staging according to the metastability decomposition and ASB scaling properties following to the self-similar solutions. Self-similar nature of microshears collective modes providing the ASB dynamics is analyzed as the mechanism of steady plastic wave front unversality in shocked materials. The dynamic split Hopkinson pressure bar tests were conducted with AlMg6 alloy combined with “in-situ” imaging of temperature kinetics by CEDIP Silver 450M high-speed infrared camera with conclusion of the secondary role of thermoplastic instability at the ASB staging. The microstructural study performed by an electron microscopy revealed the correlated behavior of the ensemble of defects, which can be classified as a structural transition and precursor of ASB induced strain localization and failure. The modeling reflecting the links of self-similar solutions in microshear ensembles with relaxation properies and damage localization was applied for the comparative analysis of ASB staging and temperature dynamics given be the infrared imaging.

Breakaway of a motor vehicle from skidding with the use of friction material on public and toting roads

The goal of the paper is to provide breakaway of a motor vehicle from skidding with the use of friction material on public and toting roads.The development of an anti-skid device is reasonable because road services are not always able to maintain the proper road conditions due to overall highway mileage which leads to road icing and snow knurling, which in turn lowers the friction coefficient of tires with the road. Model analysis and practical experiments are carried out to model breakaway modes while using friction material. This process can be automated for the use in off-road vehicles with a dedicated device that will deliver large grained friction material. The mentioned device had been developed by the authors of the paper. A technical effect of increased adhesion coefficient is achieved within the research. This effect allows the increase in transportation reliability under difficult meteorological and road conditions on public and toting roads. Practical experiments showed that addition of large grain friction material when skidding modifies the surface in front of the tire into a segmented area (angled surface) that helps the vehicle to breakaway and move further without skidding

Exploration of Spirocyclic Derivatives of Ciprofloxacin as Antibacterial Agents

The previously reported as well as newly synthesized derivatives of the 1-oxa-9-azaspiro[5.5]undecane were employed in the synthesis of thirty-six derivatives of ciprofloxacin using commercially available 7-chloro-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid and the literature protocol involving the preparation of boron chelate complex to facilitate nucleophilic aromatic substitution. All new fluoroquinolone derivatives were tested against two gram-positive as well as three gram-negative strains of bacteria. With the activity spectrum of the new derivatives being substantially narrower than that of ciprofloxacin, compounds were distinctly active against two of the five strains: gram-negative Acinetobacter baumannii 987® and gram-positive Bacillus cereus 138®. Towards these two strains, a large group of compounds displayed equal or higher potency than ciprofloxacin

A comparative analysis of right-wing radical and Islamist communities’ strategies for survival in social networks (evidence from the Russian social network VKontakte)

This article presents a comparative analysis of online communities of right-wing radicals and Islamists, who are considered to be numerous and dangerous extremist groups in Russian society. The online communities were selected based on the content posted on the largest Russian social networking site VKontakte. The goal of this article is to determine the strategy and tactics employed by extremist online communities for survival on social networking sites. The authors discovered that both right-wing radical and Islamist groups employ similar behavioural techniques, with the mimicry of ideologically neutral content as the most common. In addition, every extremist community also applies some unique methods. For example, if there is a risk of being blocked, right-wing radicals tend to shift their activity and communication to the other internet-based platforms that are not under state control; however, Islamists prefer to suddenly change the content of their communities (i.e. by using secondary mimicry)

Islamist communities on Vkontakte: Identification mechanisms and network structure

This article examines the presence of extremist online communities on the Russian social network VKontakte following the tightening by Russian federal аuthorities of internet counter-extremism policies and censorship. Extremist communities were detected using linguistic markers for extremist attitudes and radical violence. The study of socio-demographic data and network metrics of Islamist extremist communities reveals some general tendencies in the Russian context: a majority of female participants, a highly decentralised community network structure, radical Salafism as the mainstream ideology and covert proselytisation through the discussion of Islamic theology and lifestyle issues that are not in themselves extremist

5-Nitrofuran-Tagged Oxazolyl Pyrazolopiperidines: Synthesis and Activity against ESKAPE Pathogens

A series of eight 5-nitrofuran-tagged oxazolyl tetrahydropyrazolopyridines (THPPs) has been prepared in six stages with excellent regioselectivity. The testing of these compounds against pathogens of the ESKAPE panel showed a good activity of lead compound 1-(2-methoxyethyl)-5-(5-nitro-2-furoyl)-3-(1,3-oxazol-5-yl)-4,5,6,7-tetrahydro-1H-pyrazolo[4,3-c] pyridine (13g), which is superior to nitrofurantoin. These results confirmed the benefit of combining a THPP scaffold with a nitrofuran warhead. Certain structure–activity relationships were established in the course of this study which were rationalized by the induced-fit docking experiments in silico

Molecular Periphery Design Allows Control of the New Nitrofurans Antimicrobial Selectivity

A series of 13 new 3-substituted 5-(5-nitro-2-furyl)-1,2,4-oxadiazoles was synthesized from different aminonitriles. All compounds were screened in the disc diffusion test at a 100 μg/mL concentration to determine the bacterial growth inhibition zone presence and diameter, and then the minimum inhibitory concentrations (MICs) were determined for the most active compounds by serial dilution. The compounds showed antibacterial activity against ESKAPE bacteria, predominantly suppressing the growth of 5 species out of the panel. Some compounds had similar or lower MICs against ESKAPE pathogens compared to ciprofloxacin, nitrofurantoin, and furazidin. In particular, 3-azetidin-3-yl-5-(5-nitro-2-furyl)-1,2,4-oxadiazole (2h) inhibited S. aureus at a concentration lower than all comparators. Compound 2e (5-(5-nitro-2-furyl)-3-[4-(pyrrolidin-3-yloxy)phenyl]-1,2,4-oxadiazole) was active against Gram-positive ESKAPE pathogens as well as M. tuberculosis. Differences in the molecular periphery led to high selectivity for the compounds. The induced-fit docking (IFD) modeling technique was applied to in silico research. Molecular docking results indicated the targeting of compounds against various nitrofuran-associated biological targets