Simulation of ionic current through the nanopore in a double-layered semiconductor membrane

We study the effects of different nanopore geometries (double-conical, single-conical, cylindrical) on the electrostatic potential distribution and ionic conductivity in a double-layered semiconductor nanopore device as functions of the applied membrane bias. Ionic current-voltage characteristics as well as their rectification ratios are calculated using a simple ion transport model. Based on our calculations, we find that the double-layered semiconductor membrane with a single-conical nanopore with a narrow opening in the n-Si layer exhibits the largest range of available potential variations in the pore and, thus, may be better suited for control of polymer translocation through the nanopore.     

Structural characterization of β-propiolactone inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) particles

The severe COVID-19 pandemic drives the research toward the SARS-CoV-2 virion structure and the possible therapies against it. Here, we characterized the β-propiolactone inactivated SARS-CoV-2 virions using transmission electron microscopy (TEM) and atomic force microscopy (AFM). We compared the SARS-CoV-2 samples purified by two consecutive chromatographic procedures (size exclusion chromatography [SEC], followed by ion-exchange chromatography [IEC]) with samples purified by ultracentrifugation. The samples prepared using SEC and IEC retained more spikes on the surface than the ones prepared using ultracentrifugation, as confirmed by TEM and AFM. TEM showed that the spike (S) proteins were in the pre-fusion conformation. Notably, the S proteins could be recognized by specific monoclonal antibodies. Analytical TEM showed that the inactivated virions retained nucleic acid. Altogether, we demonstrated that the inactivated SARS-CoV-2 virions retain the structural features of native viruses and provide a prospective vaccine candidate.     

Poisson–Nernst–Planck model for an ionic transistor based on a semiconductor membrane

In this paper we developed a Poisson–Nernst–Planck model of an ionic current flowing through a nanopore in a layered solid-state membrane made of a single highly-doped \(n\) -Si layer sandwiched between two thick oxide layers which we call the ionic transistor. We studied this layered membrane for a range of source-drain voltages while keeping the gate (the semiconductor membrane) voltage fixed at a certain value, which was later varied too. We find that for this ionic transistor to be effective in controling the ion fluxes through the nanopore, the gate voltage must be kept relatively large. Another solution could be to increase the surface negative charge on the membrane or to replace the outer oxide layers with the semiconductor material, such as the \(p\) -Si material. The developed model can be applied to study ionic filtering and separation properties of membranes of different composition and nanopore geometries.     

Compacted Modified Propellant Blocks as Traveling Charge in the Hybrid Shot Scheme

The burning of compacted modified propellant charges applied as a traveling charge in the hybrid shot scheme was studied. The block charges were manufactured by pressing fine propellant grains coated by a thin film of polyvinyl butyral. A stick from several pressed pellets was insulated over its lateral surface by a thin layer of silicon paste, glued to the back of the projectile and inserted into the barrel of the 23‐mm smooth‐bore laboratory gun. The loose‐packed accelerator charge was placed in the breech. Combustion was initiated by an igniter plug placed between the traveling and breech charges. A set of piezo‐quartz gauges placed in the breech and along the barrel, as well as a frame‐target device were used for recording characteristics of the firings. It is shown that blocks of this type, applied as the traveling charge, provide a stable burning process resulting in high ballistic performance. The block traveling charge preserves its integrity in the course of its motion along the barrel, and burning envelopes its total mass when pressure in the breach passes the maximum value. The descending portion of the pressure diagram demonstrates appreciable transformation, with convex or secondary hump sections. The shape of spatial pressure profiles behind the moving projectile is also transformed, and the pressure at the projectile butt end may be higher than the pressure in the breech. Compared to the conventional charges at the same maximum pressures the muzzle velocity increment attains 340 m s⁻¹ (or 23 %) for a light 35‐g projectile and 200 m s⁻¹ (or 19 %) for a heavy 104‐g projectile.     

Study of reasons of increased active force using coolant with uncut chip thickness

The use of coolant usually leads to a decrease in active force. However, it is well known that when cutting with small uncut chip thickness while using a coolant, the active force may be greater than when cutting without a coolant. For this reason, finish turning with very small uncut chip thickness and manual scraping is carried out without a coolant. The current explanation of this phenomenon is that the coolant increases the plowing force. The aim of this research is to study the impact of the coolant on the plowing force and to explain the reasons for the increase in active force at small uncut chip thickness. In the chipping process, a new reason was found that explains the increase in the active force when using coolant. It was established that the coolant prevents the buildup. Due to this phenomenon, cutting is performed with the radius of the cutting tool at a negative rake angle and with greater active force than when cutting without a coolant. When cutting without a coolant, a buildup is formed on the radius of the cutting tool; the geometry of the cutting part is improved. This is the real reason for decrease in active force when cutting without a coolant. When using the method of extrapolation on a zero uncut chip thickness under the same conditions without buildup, it was found that using a coolant does not increase, but decrease the plowing force.     

Developing an Efficient Technology for Key Intermediates Production Used in Enzymatic Synthesis of Cladribine and Nelarabine

The pilot-scale process for preparing 2-amino-6-chloro-9-（2＇,3＇,5＇-tri-O-acetyl-Dq3-ribofuranosyl）-purine and 2-chloroadenosine has been developed with a total yield of the desired compounds 73% and 44.5%, respectively. These compounds are useful intermediates for enzymatic synthesis of active pharmaceutical ingredients Nelarabine and Cladribine. The starting material--commercially avaliable guanosine--was acetylated with acetic anhydride, yielding 2,3,5-tri-O-acetylguanosine, which was further deoxyhalogenated with phosphorous oxychloride in presence of tetraethylammonia chloride. Diazotization of the resulting intermediate with tert-butylnitrite leads to the corresponding ribofuranosyl-substituted 2,6-dichloropurine, which was converted to 6-chloroadenosine by reaction with methanolic ammonia.     

Advances in femtosecond laser direct writing of fiber Bragg gratings in multicore fibers: technology,sensor and laser applications

In this article, we review recent advances in the technology of writing fiber Bragg gratings (FBGs) in selected cores of multicore fibers (MCFs) by using femtos...     

Beyond the Limits: Palladium‐N‐Heterocyclic Carbene‐Based Catalytic System Enables Highly Efficient [4+2] Benzannulation Reactions

A highly efficient catalytic system for the palladium‐catalyzed [4+2] benzannulation reaction of enynes and enynophiles has been developed. The use of an N‐heterocyclic carbene‐based palladium precursor allowed us to achieve turnover numbers up to 1800. The new catalytic system has enabled an expansion of the scope of the [4+2] homo‐benzannulation reaction.     

Collapse of magnetic moment drives the Mott transition in MnO

The metal-insulator transition in correlated electron systems, where electron states transform from itinerant to localized, has been one of the central themes of condensed-matter physics for more than half a century. The persistence of this question has been a consequence both of the intricacy of the fundamental issues and the growing recognition of the complexities that arise in real materials, when strong repulsive interactions play the primary role. The initial concept of Mott was based on the relative importance of kinetic hopping (measured by the bandwidth) and onsite repulsion of electrons. Real materials, however, have many further degrees of freedom that, as is recently attracting note, give rise to a rich variety of scenarios for a 'Mott transition'. Here, we report results for the classic correlated insulator MnO that reproduce a simultaneous moment collapse, volume collapse and metallization transition near the observed pressure, and identify the mechanism as collapse of the magnetic moment due to an increase of crystal-field splitting, rather than to variation in the bandwidth.     

Characterization of a yeast D-amino acid oxidase microbiosensor for D-serine detection in the central nervous system

d-Serine is an endogenous ligand for N-methyl-d-aspartate (NMDA) receptors, and alterations in its concentration have been related to several brain disorders, especially schizophrenia. It is therefore an important target neuromodulator for the pharmaceutical industry. To monitor d-serine levels in vivo, we have developed a microbiosensor based on cylindrical platinum microelectrodes, covered with a membrane of poly-m-phenylenediamine (PPD) and a layer of immobilized d-amino acid oxidase from the yeast Rhodotorula gracilis (RgDAAO). By detecting the hydrogen peroxide produced by enzymatic degradation of d-serine, this microbiosensor shows a detection limit of 16 nM and a mean response time of 2 s. Interferences by ascorbic acid, uric acid, l-cysteine, and by biogenic amines and their metabolites are rejected at more than 97% by the PPD layer. Although several d-amino acids are potential substrates for RgDAAO, d-serine was the only endogenous substrate present in sufficient concentration to be detected by our microbiosensor in the central nervous system. When implanted in the cortex of anesthetized rats, this microbiosensor detected the increase in concentration of d-serine resulting from its diffusion across the blood-brain barrier after an intraperitoneal injection. This new device will make it possible to investigate in vivo the variations in d-serine concentrations occurring under normal and pathological conditions and to assess the pharmacological potency of new drugs designed to impact d-serine metabolism.