Proton spin dynamics in polymer melts: New perspectives for experimental investigations of polymer dynamics

The proton spin dynamics in polymer melts is determined by intramolecular and intermolecular magnetic dipole-dipole interactions among the proton spins. During many decades it was postulated that the main contribution is a result of intramolecular magnetic dipole-dipole interactions of protons belonging to the same polymer segment. This postulate is far from reality. The relative weights of intra- and intermolecular contributions are time (or frequency) dependent and sensitive to details of polymer chain dynamics. It is shown that for isotropic models of polymer dynamics, in which already at short times the segmental displacements are not correlated with the polymer chain's initial conformation, the influence of the intermolecular dipole-dipole interactions becomes stronger with increasing evolution time (i.e. decreasing frequency) than the corresponding influence of the intramolecular counterpart. On the other hand, an inverted situation is predicted by the tube-reptation model: here the influence of the intramolecular dipole-dipole interactions increases faster with time than the contribution from intermolecular interactions. This opens a new perspective for experimental investigations of polymer dynamics by proton NMR, and first results are reported. © 2014 Elsevier B.V

Proton spin dynamics in polymer melts: New perspectives for experimental investigations of polymer dynamics

© 2014 Elsevier B.V. All rights reserved. The proton spin dynamics in polymer melts is determined by intramolecular and intermolecular magnetic dipole-dipole interactions among the proton spins. During many decades it was postulated that the main contribution is a result of intramolecular magnetic dipole-dipole interactions of protons belonging to the same polymer segment. This postulate is far from reality. The relative weights of intra- and intermolecular contributions are time (or frequency) dependent and sensitive to details of polymer chain dynamics. It is shown that for isotropic models of polymer dynamics, in which already at short times the segmental displacements are not correlated with the polymer chain's initial conformation, the influence of the intermolecular dipole-dipole interactions becomes stronger with increasing evolution time (i.e. decreasing frequency) than the corresponding influence of the intramolecular counterpart. On the other hand, an inverted situation is predicted by the tube-reptation model: here the influence of the intramolecular dipole-dipole interactions increases faster with time than the contribution from intermolecular interactions. This opens a new perspective for experimental investigations of polymer dynamics by proton NMR, and first results are reported

Segmental dynamics of polyethylene-alt-propylene studied by NMR spin echo techniques

© 2017 Author(s). Segmental dynamics of a highly entangled melt of linear polyethylene-alt-propylene with a molecular weight of 200 kDa was studied with a novel proton nuclear magnetic resonance (NMR) approach based upon 1 H → 2 H isotope dilution as applied to a solid-echo build-up function I SE (t), which is constructed from the NMR spin echo signals arising from the Hahn echo (HE) and two variations of the solid-echo pulse sequence. The isotope dilution enables the separation of inter- and intramolecular contributions to this function and allows one to extract the segmental mean-squared displacements in the millisecond time range, which is hardly accessible by other experimental methods. The proposed technique in combination with time-temperature superposition yields information about segmental translation in polyethylene-alt-propylene over 6 decades in time from 10 -6 s up to 1 s. The time dependence of the mean-squared displacement obtained in this time range clearly shows three regimes of power law with exponents, which are in good agreement with the tube-reptation model predictions for the Rouse model, incoherent reptation and coherent reptation regimes. The results at short times coincide with the fast-field cycling relaxometry and neutron spin echo data, yet, significantly extending the probed time range. Furthermore, the obtained data are verified as well by the use of the dipolar-correlation effect on the Hahn echo, which was developed before by the co-authors. At the same time, the amplitude ratio of the intermolecular part of the proton dynamic dipole-dipole correlation function over the intramolecular part obtained from the experimental data is not in agreement with the predictions of the tube-reptation model for the regimes of incoherent and coherent reptation

Anomalous relaxation and self-organization in non-equilibrium processes

We study thermal relaxation in ordered arrays of coupled nonlinear elements with external driving. We find, that our model exhibits dynamic self-organization manifested in a universal stretched-exponential form of relaxation. We identify two types of self-organization, cooperative and anti-cooperative, which lead to fast and slow relaxation, respectively. We give a qualitative explanation for the behavior of the stretched exponent in different parameter ranges. We emphasize that this is a system exhibiting stretched-exponential relaxation without explicit disorder or frustration.Comment: submitted to PR

Phase transitions, hysteresis, and hyperbolicity for self-organized alignment dynamics

International audienceWe provide a complete and rigorous description of phase transitions for kinetic models of self-propelled particles interacting through alignment. These models exhibit a competition between alignment and noise. Both the alignment frequency and noise intensity depend on a measure of the local alignment. We show that, in the spatially homogeneous case, the phase transition features (number and nature of equilibria, stability, convergence rate, phase diagram, hysteresis) are totally encoded in how the ratio between the alignment and noise intensities depend on the local alignment. In the spatially inhomogeneous case, we derive the macroscopic models associated to the stable equilibria and classify their hyperbolicity according to the same function

Oral squamous cell carcinoma in "young" patients

Aim of the study — to provide for medical oncologists and surgeon, who specialize in treatment of head and neck oncology patients, the most recent information about incidence and feature of oral squamous cell carcinoma (OSCC) in young patientsЦель исследования — предоставить онкологам и хирургам, специализирующимся на лечении пациентов, страдающих раком головы и шеи, наиболее полную информацию о распространенности и особенностях плоскоклеточного рака полости рта у «молодых» пациентов на основе последних литературных данны

Клинический случай метастаза рака носоглотки в щитовидную железу

Background. Nasopharyngeal cancer is a rare head and neck cancer with a relatively high risk of locoregional recurrence and distant metastases. The most common sites of metastases are bones (70–80 %) followed by liver (30 %), lung (18 %), and lymph node (axillary, mediastinal, pelvic, and inguinal). Thyroid gland is an uncommon site of metastasis with an incidence ranging from 0.5% to 24 %. Thyroid metastasis from nasopharyngeal cancer has been reported in only 9 cases in the world literature and no one in Russia. Case report. We report a case of thyroid metastasis from nasopharyngeal cancer found incidentally in a 53-year-old female patient. Conclusion. Metastases to the thyroid gland are rare, and patients with metastatic thyroid disease rarely present with organ-specifc symptoms, thus raising diagnostic diffculties for both clinicians and the pathologists. This clinical report demonstrates the diffculties of differential diagnosis,as well as the importance of a thorough collection of complaints, anamnesis, and clinical examination.Актуальность. Рак носоглотки относится к редким заболеваниям в структуре опухолей головы и шеи. Данное новообразование имеет относительно высокий риск метастазов в регионарные лимфоузлы и отдаленные органы-мишени. Наиболее часто отдаленное метастазирование происходит в кости (70–80 %), печень (30 %), легкие (18 %), а также лимфоузлы (подмышечные, средостения, малого таза, паховые). Метастазы в щитовидную железу являются редким событием и встречаются в 0,5–24 % случаев. В мировой литературе описано 9 случаев метастазов рака носоглотки в щитовидную железу, подобных сообщений в отечественной литературе не найдено. Описание клинического случая. Представлено клиническое наблюдение 53-летней пациентки, у которой первично выявлен метастаз рака носоглотки в щитовидную железу как случайная находка. Заключение. Щитовидная железа редко является органом-мишенью для метастазов, при этом ее метастатическое поражение обычно не сопровождается функциональными нарушениями. По этой причине его диагностика является затруднительной как для клинициста, так и для патолога. Данный клинический случай демонстрирует трудности дифференциальной диагностики, а также показывает важность тщательного сбора жалоб, анамнеза, клинического осмотра.

Liquid crystals and their defects

These lecture notes discuss classical models of liquid crystals, and the different ways in which defects are described according to the different models.Comment: CIME lecture course, Cetraro, 201