Study of synthesis parameters and active layer morphology of interfacially polymerized polyamide-polysulfone membranes

Thin film composite (TFC) polyamide membranes were prepared on a polysulfone support membrane and the effect of various synthesis conditions on the active layer morphology, the physicochemical properties and the membrane performance was investigated. The support membrane porosity factor had a significant effect on the TFC membrane performance. A polyamide top layer was formed within 15 s of reaction. Prolonging the reaction time, although resulting in a thicker active layer, only had a minor influence on the membrane performance. This highlights the importance of the incipient layer of the polyamide structure on its performance. The addition of both a surfactant and a base to the amine solution resulted in a change of the active layer morphology and an improved performance. The effect of additives was attributed to changes in the polymerization mechanism. In addition, it was demonstrated that curing at 50°C resulted in an improved membrane performance, due to more cross-linking of the active layer. Curing at higher temperatures deteriorated the structure of the support membrane. This research shows that the TFC membrane performance is well correlated with the changes in the active layer morphology, measured using SEM, AFM and TEM; whereas only minor changes in the physicochemical characteristics of the membranes were detected by zeta potential and ATR-FTIR spectroscopy when the same synthesis parameters were varied.status: publishe

Thermal Depinning of Abrikosov Vortices in a Nb Polycrystalline Bulk Absorber for Gamma-Ray Superconducting Detector

Abstract The threshold temperature at which the thermal depinning of Abrikosov vortices starts to be pronounced, defines the upper temperature limit for secure operation of a gamma-ray superconducting detector based on Abrikosov vortices. Indeed, because of the flux creep phenomenon, unwanted spontaneous vortex jumps can take place concurrently with those resulting from the gamma-ray photon absorption, resulting in the appearance of dark counts. Low temperature magnetic force microscopy (MFM) was applied for the evaluation of the threshold temperature for a 0.3 mm thick Nb polycrystalline bulk absorber with dimensions of 5×5 mm2, which was chosen for the fabrication of Josephson tunnel junctions serving as vortex sensor element of the gamma-ray detector. Vortices were generated by cooling the sample to 4.3 K in a small magnetic field. A field of 0.1 mT was chosen in order to produce more than two vortices within the 7×7 μm2 scan area, but with sufficiently large inter-vortex spacing such that vortex-vortex interactions would be negligible. The threshold temperature associated with the thermal depinning of a single vortex was found to be 6.3 ± 0.2 K, whereas the threshold temperature associated with the thermal depinning of half of vortices was found to be 7.2 ± 0.2 K

Energy-efficient communication system based on nonlinear scattering of standard OFDM signals

Development of miniaturized communication systems for exchanging data over short distances with little power consumption is an actual problem. This problem is solved by such standards as Bluetooth, ZigBee etc. Nowadays for extra size devices with power supply from external electromagnetic field are considered. In the paper we propose using nonlinear scattering effect for reusing energy radiated with standard wireless devices such as mobile phones, access points etc. For proposed solution link budget estimation is given. Performance of different types of receivers in communications system is investigated with both theoretical analysis and simulation

Noncomputability Arising In Dynamical Triangulation Model Of Four-Dimensional Quantum Gravity

Computations in Dynamical Triangulation Models of Four-Dimensional Quantum Gravity involve weighted averaging over sets of all distinct triangulations of compact four-dimensional manifolds. In order to be able to perform such computations one needs an algorithm which for any given $N$ and a given compact four-dimensional manifold $M$ constructs all possible triangulations of $M$ with $\leq N$ simplices. Our first result is that such algorithm does not exist. Then we discuss recursion-theoretic limitations of any algorithm designed to perform approximate calculations of sums over all possible triangulations of a compact four-dimensional manifold.Comment: 8 Pages, LaTex, PUPT-132

Иммунопрофилактика инфекционных болезней у недоношенных детей

Premature infants are especially in need of timely and effective specific immunoprophylaxis due to their vulnerability to infectious diseases. The article describes the basic principles for vaccination of premature infants used in healthcare by the leading countries of the world. Based on the results of clinical trials, the peculiarities of the vaccination schedule for certain infections have been determined, the specific features of the course of the post-vaccinal period have been described. The operating procedures for active immunoprophylaxis of various types of infections have been explained in detail depending on the pathology and the therapy being performed. The article uses the key points of the recommended practices for prevention of the main controlled types of infections developed by the professional association of pediatricians ‘Union of Pediatricians of Russia’ and approved by the Ministry of Healthcare of the Russian Federation.Недоношенные младенцы вследствие уязвимости к инфекционным заболеваниям особо нуждаются в своевременной и эффективной специфической иммунопрофилактике. В статье приведены основополагающие принципы проведения вакцинации детей, рожденных раньше срока, применяемые в практике здравоохранения ведущих стран мира. На основании результатов клинических исследований определены особенности схемы вакцинации против отдельных инфекций, описаны характерные признаки течения поствакцинального периода. Подробно разъяснен алгоритм действий при проведении активной иммунопрофилактики различного вида инфекций в зависимости от имеющей место патологии и проводимой терапии. В публикации использованы ключевые позиции методических рекомендаций по вакцинопрофилактике основных управляемых видов инфекций, разработанных профессиональной ассоциацией детских врачей «Союз педиатров России» и утвержденных Министерством здравоохранения РФ

Various Approaches to Studying the Phase Transition in an Octamethylcyclotetrasiloxane Crystal: From X-ray Structural Analysis to Metadynamics

The structure, thermodynamic parameters, and the character of thermal motion in octamethylcyclotetrasiloxane (D4) were investigated using the combination of experimental (single-crystal X-ray diffraction, thermochemistry) and theoretical (density functional theory calculations, ab initio molecular dynamics and metadynamics) methods. Single crystals of D4 were grown in a glass capillary in situ and the structures of high- (238–270 K) and low-temperature (100–230 K) phases were studied in detail. In the temperature interval 230–238 K, a phase transition with rather low enthalpy (−1.04(7) kcal/mol) was detected. It was found that phase transition is accompanied by change of conformation of cyclosiloxane moiety from boat-saddle (cradle) to chair. According to PBE0/6-311G(d,p) calculation of isolated D4, such conformation changes are characterized by a low barrier (0.07 kcal/mol). The character of molecular thermal motion and the path of phase transition were established with combination of periodic DFT calculations, including molecular dynamics and metadynamics. The effect of crystal field led to an increase in the calculated phase transition barrier (4.27 kcal/mol from low- to high-temperature phase and 3.20 kcal/mol in opposite direction)

Molecular Structures Polymorphism the Role of F…F Interactions in Crystal Packing of Fluorinated Tosylates

The peculiarities of interatomic interactions formed by fluorine atoms were studied in four tosylate derivatives p-CH3C6H4OSO2CH2CF2CF3 and p-CH3C6H4OSO2CH2(CF2)nCHF2 (n = 1, 5, 7) using X-ray diffraction and quantum chemical calculations. Compounds p-CH3C6H4OSO2CH2(CF2)nCHF2 (n = 1, 5) were crystallized in several polymorph modifications. Analysis of intermolecular bonding was carried out using QTAIM approach and energy partitioning. All compounds are characterized by crystal packing of similar type and the contribution of intermolecular interactions formed by fluorine atoms to lattice energy is raised along with the increase of their amount. The energy of intra- and intermolecular F…F interactions is varied in range 0.5−13.0 kJ/mol. Total contribution of F…F interactions to lattice energy does not exceed 40%. Crystal structures of studied compounds are stabilized mainly by C-H…O and C-H…F weak hydrogen bonds. The analysis of intermolecular interactions and lattice energies in polymorphs of p-CH3C6H4OSO2CH2(CF2)nCHF2 (n = 1, 5) has shown that most stabilized are characterized by the least contribution of F…F interactions

110th Anniversary: Cellulose Nanocrystals as Organic Nanofillers for Cellulose Triacetate Membranes Used for Desalination by Pervaporation

status: publishe

Blending PPO-based molecules with Pebax MH 1657 in membranes for gas separation

© 2018 Wiley Periodicals, Inc. This work explores the possibilities to blend block copolymers, i.e., Pebax MH 1657, with a variety of cheap poly(propylene oxide)-rich molecules which could potentially play a double role in the resulting membranes as dispersing/stabilizing agents in multi-component casting solutions and as a gas transport medium in the final membrane. These membranes were prepared by solution casting and were characterized by differential scanning calorimetry, scanning electron microscopy, atomic force microscopy, X-ray diffraction, density measurements, and Fourier transform infrared-attenuated total reflection, while additive incorporation was also studied with theoretical calculations. Gas permeation measurements showed that this approach resulted in increased permeabilities at the expense of mixed-gas selectivity. An interpretation of the blend structure was finally made using gas transport models. The compatibility of these additives with the synthesis of selective gas separation membranes may enable a potential double role in membrane synthesis, i.e., as stabilizing agents in membrane synthesis and as a gas transport medium in the final membrane. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46433.status: publishe