Concentration Dependence of the Flory Chi Parameter within Two-State Models

The Flory chi parameter is typically assumed to depend only on the temperature, T. Experimental results often require the replacement of this chi(T) by chieff, that depends also on the monomer volume fraction, phi, chieff(phi,T). Such chieff(phi,T) can arise from two state-models, proposed for polyetheleneoxide (PEO) and other neutral water-soluble polymers. The predicted phi dependence of chibar=chieff-(1-phi)\partial \chieff/\partial phi, obtainable from colligative properties, differs qualitatively between the various models: (i) The model of Karlstrom (J. Phys. Chem. 1985, 89, 4962) yields \partial chibar/\partial phi > 0 while the model of Matsuyama and Tanaka (Phys. Rev. Lett. 1990, 65, 341) and of Bekiranov et al (Phys. Rev. E 1997, 55, 577) allows for \partial chibar/\partial phi <0 (ii) chibar(phi) as calculated from the Karlstrom model, utilizing the parameters used to fit the phase diagram of PEO, agrees semiquantitatively with the experimental values. On the other hand, chibar(phi) similarly calculated from the model of Bekiranov et al. differs qualitatively from the measured results. Altogether, chibar(phi) provides useful measure for the performance of a model.Comment: 8 pages, 5 figures, Macromolecules, in pres

Signatures of a Concentration Dependent Flory chi Parameter: Swelling and Collapse of Coils and Brushes

The quality of solvents of polymers is often described in terms of the Flory chi parameter typically assumed to depend only on the temperature, T. In certain polymer-solvent systems fitting the experimental data enforces the replacement of chi(T) by a concentration dependent chieff. In turn, this modifies the swelling and collapse behavior. These effects are studied, in the framework of a mean-field theory, for isolated coils and for planar brushes. The phi dependence of chieff gives rise to three main consequences: (i) Shift in the cross-over between Gaussian and self-avoidance regimes; (ii) A possibility of first-order collapse transition for isolated flexible coils; (iii) The possibility of a first-order phase transition leading to a vertical phase separation within the brush. The discussion relates these effects directly to thermodynamic measurements and does not involve a specific microscopic model. The implementation for the case of Poly(N-isopropylacrylamide) (PNIPAM) is discussed.Comment: 12 pages, 9 figure

The social behavior formation of master students in the process of their university studies

The article contains results of the factors analysis that form a social behavior of master students in the learning process and during training period at a higher educational institution. In the research was distinguished: the degree of information of students about the purpose of magistracy, their motivation for studying in the magistracy, the tendency to implement research activities, and the financial situation of students. The object of research is the bachelor’s degrees’ students of a third and fourth years of study and master students of a first and second year of study from eight regional state universities of Russia. The article also provides comparative data with the results of studies implemented earlier, in 2011, 2014, and 2016 years, by the authors from eight Russian universities. The results of the study enable us to identify problems concerning certain aspects of the functioning of the institute of magistracy in the system of Russian higher education institutions

Thermoformation of composite sheets on the basis of abs – plastics with high surface luster

The possibility of application of composite sheet materials on the basis of acrylonitrile-butadienstyrene plastics (ABS-plastics) for production of details of the exterior and interior parts of roadbuilding equipment by a method of a positive thermoformation has been investigated in the article. It was of a great interest to estimate physicomechanical properties of composite ABSplastic formable products, to study the influence of technological parameters of a termoformation on operational properties of details. Objects of research are the multilayered sheet products received by a method of positive thermoformation. The resistance of ABS-plastics in the conditions of practical use has also been investigated.The authors have made recommendations on the use of thermoformed ABS-plastic details for manufacturing of road-building technics

Double-spiral magnetic structure of the Fe/Cr multilayer revealed by nuclear resonance scattering

We have studied the magnetization depth profiles in a [57Fe(dFe)/Cr(dCr)]x30 multilayer with ultrathin Fe layers and nominal thickness of the chromium spacers dCr 2.0 nm using nuclear resonance scattering of synchrotron radiation. The presence of a broad pure-magnetic half-order (1/2) Bragg reflection has been detected at zero external field. The joint fit of the reflectivity curves and Mossbauer spectra of reflectivity measured near the critical angle and at the "magnetic" peak reveals that the magnetic structure of the multilayer is formed by two spirals, one in the odd and another one in the even iron layers, with the opposite signs of rotation. The double-spiral structure starts from the surface with the almost antiferromagnetic alignment of the adjacent Fe layers. The rotation of the two spirals leads to nearly ferromagnetic alignment of the two magnetic subsystems at some depth, where the sudden turn of the magnetic vectors by ~180 deg (spin-flop) appears, and both spirals start to rotate in opposite directions. The observation of this unusual double-spiral magnetic structure suggests that the unique properties of giant magneto-resistance devices can be further tailored using ultrathin magnetic layers.Comment: 9 pages, 3 figure

Degradation versus self-assembly of block copolymer micelles

The stability of micelles self-assembled from block copolymers can be altered by the degradation of the blocks. Slow degradation shifts the equilibrium size distribution of block copolymer micelles and change their properties. Quasi-equilibrium scaling theory shows that the degradation of hydrophobic blocks in the core of micelles destabilize the micelles reducing their size, while the degradation of hydrophilic blocks forming coronas of micelles favors larger micelles and may, at certain conditions, induce the formation of micelles from individual chains.Comment: Published in Langmuir http://pubs.acs.org/doi/pdf/10.1021/la204625

Pyrazole derivatives as polyethylene oxidative destruction stabilizers

The possibility of newly synthesized pyrazole derivatives using as heat stabilizers of high-pressure polyethylene (LDPE): 1-acetyl-4-methyl-3(5)-(2-(3-nitrophenyl)vinyl)-1H-pyrazole (additive 1) and 4benzoyl-3-(2-(4-nitrophenyl)vinyl-5-phenyl-1-tosyl-1H-pyrazole (additive 2)) has been studied. It is established that the introduction of additive 1 or 2 in the amount of 0,05-0,10 wt % to the high-pressure polyethylene leads to the increasing of such physical-mechanical properties of the samples as tensile strength by 1,2–1,5 times and elongation by 2,3–3,0 times in comparison with the unstabilized sample. Synthesized substances are more effective than Tioalkofen MBP used in industry

The formability of sheet blanks in the product under conditions of intense heat

When forming products from thermoplastic polymers and compositions on their basis, including sheet blanks, are passing heat and mechanical processes, which require special study: heating and cool-ing, viscous-plastic flow, sealing and shrinkage, the deformation of viscous stretching, consolidation. For sheet workpieces made of recycled polypropylene it was determined the kinetics of cooling in two modes: convective heat transfer in air and contact heat exchange in the chilled form. The work-pieces sheets for the study were obtained at the extrusion head of the manifold type. When molding product the experiment took place in conditions that are very close to real. Temperature measurement was carried out on the surface and in the center of the workpiece. To obtain the temperature profile across the thickness of the blank numerical analysis on the basis of the solution of the heat equation for one-dimensional flow was carried out. It is shown that the results of analytical calculation and experiment correlate well. The derived dependences used to determine the magnitude of the visco-fluid layer by thickness of the workpiece, which ensures the formab ility of the material in the fina l product, as well as to identify the optimal temperature and time parameters, while ensuring the adhesion bonds between the two heat-ed molds in the process of forming a composite product

Biomolecule surface patterning may enhance membrane association

Under dehydration conditions, amphipathic Late Embryogenesis Abundant (LEA) proteins fold spontaneously from a random conformation into alpha-helical structures and this transition is promoted by the presence of membranes. To gain insight into the thermodynamics of membrane association we model the resulting alpha-helical structures as infinite rigid cylinders patterned with hydrophobic and hydrophilic stripes oriented parallel to their axis. Statistical thermodynamic calculations using Single Chain Mean Field (SCMF) theory show that the relative thickness of the stripes controls the free energy of interaction of the alpha-helices with a phospholipid bilayer, as does the bilayer structure and the depth of the equilibrium penetration of the cylinders into the bilayer. The results may suggest the optimal thickness of the stripes to mimic the association of such protein with membranes.Comment: Published in ACS Nano http://pubs.acs.org/doi/pdf/10.1021/nn204736

Application of a diagnostic algorithm for differential diagnosis in a patient with recurrent abdominal pain

Introduction Among the diseases of urgent pathology the leading place belongs to acute pancreatitis, which is second only to acute appendicitis and acute cholecystitis. Moreover, a significant share is occupied by mild forms, which account for 85%. In the Clinical Recommendations for Acute pancreatitis in the section “Prevention and dispensary monitoring”, the authors recommend regular dispensary monitoring by a gastroenterologist and a surgeon. However, this nosology according to the Order of the Ministry of Health of the Russian Federation from 03.15.2022 No 168N is not included in the dispensary observation. In this regard, patients remain without proper attention of doctors when they are discharged from hospitals, or when they refuse hospitalization after examination in the emergency room. The aim of the work – is to present the result of applying the diagnostic algorithm of differential diagnosis of diseases and detection of gastrointestinal tract pathology on the clinical example of a patient with recurrent abdominal pain syndrome. Materials and methods The analysis of medical records of a 59-year-old patient who repeatedly applied to the network of polyclinics and hospitals providing emergency specialized medical care for recurrent abdominal syndrome was carried out. Results and discussion In this clinical observation of recurrent abdominal syndrome in a patient, the biliary mask of acute pancreatitis was revealed. In outpatient conditions using the developed diagnostic algorithm, choledocholithiasis, juxtapapillary diverticulum of the duodenum and hernia of the esophageal aperture of the diaphragm were detected. The diagnosis made it possible to perform the treatment competently and lead to the patient's recovery. Thanks to the dispensary observation and additional methods of investigation according to the developed algorithm, the following were detected: juxtapapillary diverticulum of the duodenum, which may not be visualized at video esophagogastroduodenoscopy with direct optics, as well as ductal stones, which are not always visualized at transabdominal ultrasound and are detected at endoscopic retrograde cholangiopancreatography or endoscopic ultrasonography. Difficulties may arise in the diagnosis of gastrointestinal diseases due to the variability of the clinical course and polymorphism of symptoms in this category of patients. Such a course of diseases causes difficulties at the stage of patients' admission to the emergency room of clinics, can lead to diagnostic errors that lead to incorrect treatment tactics. Conclusion The application of an algorithm based on the assessment of clinical criteria in conjunction with instrumental imaging methods and laboratory tests allowed to optimize the diagnostic process and facilitated the choice of optimal therapy and surgical tactics for the treatment of the patient with recurrent abdominal pain syndrome.Введение. Среди заболеваний ургентной патологии ведущее место принадлежит острому панкреатиту, который уступает лишь острому аппендициту и острому холециститу. Причем значительную долю занимают легкие формы, которые составляют 85 %. В Клинических рекомендациях по острому панкреатиту в разделе «Профилактика и диспансерное наблюдение» рекомендовано регулярное диспансерное наблюдение у врача-гастроэнтеролога и врача-хирурга. Однако данная нозология согласно Приказу Минздрава РФ от 15.03.2022 № 168Н в диспансерное наблюдение не включена. В связи с этим пациенты остаются без должного внимания врачей при выписке из стационаров либо при отказе от госпитализации после обследования в условиях приемного отделения. Цель работы – на клиническом примере пациентки с рецидивирующим абдоминальным болевым синдромом представить результат применения диагностического алгоритма дифференциальной диагностики заболеваний и выявления патологии желудочно-кишечного тракта. Материалы и методы. Проведен анализ медицинской документации пациентки 59 лет, неоднократно обращавшейся в сеть поликлиник и стационаров, оказывающих экстренную специализированную медицинскую помощь при рецидивирующем абдоминальном синдроме. Результаты и обсуждение. В данном клиническом наблюдении рецидивирующего абдоминального синдрома у пациентки была выявлена билиарная маска острого панкреатита. В амбулаторных условиях с помощью разработанного диагностического алгоритма выявлены: холедохолитиаз, юкстапапиллярный дивертикул двенадцатиперстной кишки (ДПК) и грыжа пищеводного отверстия диафрагмы. Поставленный диагноз позволил грамотно выполнить лечение и привести к выздоровлению пациентки. Благодаря диспансерному наблюдению и дополнительным методам исследования согласно разработанному алгоритму выявлены: юкстапапиллярный дивертикул ДПК, который может не визуализироваться при видеоэзофагогастродуоденоскопии с прямой оптикой, а также протоковые камни, которые не всегда визуализируются при трансабдоминальном ультразвуковом исследовании и выявляются при эндоскопической ретроградной холангиопанкреатографии либо эндоскопической ультрасонографии. В диагностике желудочно-кишечных заболеваний могут возникать трудности, связанные с вариабельностью клинического течения и полиморфизмом симптоматики у пациентов. Такое течение заболеваний обуславливает сложности на этапе поступления пациентов в приемное отделение клиник, может вызывать диагностические ошибки, которые приводят к неправильной тактике лечения. Заключение. Применение алгоритма, основанного на оценке клинических критериев, в совокупности с инструментальными методами визуализации и лабораторными тестами позволило оптимизировать процесс диагностики и способствовало выбору оптимальной терапии и хирургической тактики лечения больной с рецидивирующим абдоминальным болевым синдромом