Definite oeculiarities of toxic and potentially toxic elements distribution in coal seams of Pavlograd-Petropavlovka region

Викладені методики та результати визначення складу геохімічних тапарагенетичних асоціацій токсичних елементів в основних робочих пластах Павлоград Петропавлівського району Західного Донбасу, факторного та кластерного аналізу їх вмістів.Изложены методики и результаты определения состава геохимических и парагенетических ассоциаций токсичных элементов в основных рабочих угольных пластах Павлоград-Петропавловского района Западного Донбасса, факторного и кластерного анализа их содержаний.Procedures and results to determine composition of toxic element geochemical and paragenetic assemblages within mother working coal seams of Pavlograd-Petropavlovka district in Western Donbass as well as their factor and cluster analysis are represented

Problems of prevention of rabies virus

Every year 70000 people in the world die of rabies in spite of the fact, that effective rabies vaccines and the ways of the prevention of this disease for humans and animals exist. Taking into account the positive situation in the countries of Western Europe it is especially alarming that rabies still exists in Russia and is shown generally in the central, the Volga and southern federal districts. What is the reason? I’ll try to find it out in this paper

Theoretical and experimental study of polymer melt dynamics: role of intermolecular dipolar interactions

In dieser Arbeit wird die Dynamik verschränkter Polymerschmelzen mittels eines neuartigen vielseitigen NMR-Formalismus umfassend untersucht. Der theoretische Hintergrund für seine Anwendung wird vorgestellt und ausführlich diskutiert. Es wird gezeigt, dass das Regime der langsamen anomalen segmentalen Diffusion, die den verschränkten Polymerschmelzen in einem breiten Zeitraum innewohnt, durch Analyse der Beiträge der intermolekularen dipolaren Wechselwirkungen zu speziellen Varianten von Aufbaufunktionen untersucht werden kann. Einer von ihnen kombiniert die Signale von drei Doppelpuls-Spin-Echo-NMR-Impulsfolgen und wird als Solid-echo Build-up Funktion bezeichnet. Der andere korreliert die Hahn-Echosignale, die zu verschiedenen Zeitpunkten erhalten werden, und wird als Dipolar-correlation Build-up Funktion eingeführt. Beide spiegeln im Wesentlichen die Eigenschaften dipolarer Wechselwirkungen zwischen Spins in einem System wider. Diese Wechselwirkung ist wiederum empfindlich gegenüber der lokalen segmentalen Translation und Reorientierung, was eine Möglichkeit bietet, diese Bewegungen zu untersuchen. Die beiden vorgestellten Methoden werden sowohl auf den konventionellen Niederfeld-NMR-Spektrometern als auch auf der im Rahmen dieser Arbeit aufgebauten Hochtemperatureinheit eingesetzt. Unter Verwendung dieser Ausrüstung wird der vorgeschlagene Ansatz auf die Untersuchung von Polybutadien, Poly(ethylen-alt-propylen) und Polyethylenoxidschmelzen angewendet. Die gefundene Zeitabhängigkeit der Segmentverschiebungen stimmt mit den Resultaten konventioneller Techniken bei kurzen Zeiten gut überein. Darüberhinaus sind die neuen Methoden geeignet, den untersuchten Dynamikbereich sowohl in der Zeit- als auch in der Verschiebungsdomäne signifikant zu erweitern und damit Informationen zu liefern, die für andere experimentelle Methoden kaum zugänglich sind. Daher wird der vorgestellte Ansatz als ein neues leistungsfähiges Werkzeug auf dem Gebiet der Polymerphysik angesehen. Die breite Palette von Informationen, die durch den Dipolar-correlation und den Solid-echo Formalismus geliefert werden, erlaubt einen umfassenden experimentellen Test der Gültigkeit des Tube-Reptation-Modells, das die am häufigsten verwendete und wohletablierte theoretische Beschreibung der verschränkten Polymerschmelzen ist. Die Zeitabhängigkeit der Segmentverschiebung, die in Poly(ethylen-alt-propylen) erhalten wurde, stimmt gut mit den entsprechenden Vorhersagen des Modells überein. Es werden drei verschiedene Potenzgesetze beobachtet, die im Rahmen des Tube-Reptationsmodells dem Rouse-, den inkohärenten und den kohärenten Reptationsregimen zugeschrieben werden. Wichtig ist, dass der Übergang von der inkohärenten zur kohärenten Reptation bei dieser Polymerspezies mit einem so hohen Molekulargewicht zum ersten Mal experimentell beschrieben wird. Auf der anderen Seite zeigen Segmentverschiebungen, die in den Polyethylenoxidschmelzen mit unterschiedlichen Molekulargewichten erhalten werden, keine Merkmale der extrem langsamen t^0.25 Dynamik, die für die inkohärente Reptation vorhergesagt wurde. Dieses Ergebnis ist konsistent und wird durch andere NMR-Techniken bei kürzeren und längeren Zeiten bestätigt. Dieser Befund stellt die universelle Anwendbarkeit des Konzepts der Röhre für alle weiteren Polymerspezies in Frage. Darüber hinaus zeigt die Abschätzung der relativen Beiträge der intra- und intermolekularen dipolaren Wechselwirkungen zur transversalen Relaxation ein ähnliches Verhalten für alle untersuchten Polymerschmelzen. Interessanterweise steht dieses Verhalten im Widerspruch zur Vorhersage des Tube-Repation-Modells und zeigt keine Merkmale, die für die hoch anisotrope Bewegung innerhalb der fiktiven Röhre erwartet werden. Die Übereinstimmung dieses Ergebnisses in allen Proben lässt eine noch allgemeinere Frage nach der Gültigkeit des gesamten Konzeptes des Tube-Reptationsmodells aufkommen.In this work dynamics of entangled polymer melts is extensively investigated by means of the novel versatile NMR formalism. Theoretical background for its application is presented and thoroughly discussed. It is thereby demonstrated that regime of the slow anomalous segmental diffusion inherent to the entangled polymer melts in a broad time scale can be probed by analyzing the contributions of the intermolecular dipolar interactions to the build-up functions of a special type. One of them combines the signals from three double-pulse spin-echo NMR pulse sequences and is called the solid-echo build-up function. The other one correlates the Hahn echo signals obtained at different time moments and is introduced as the dipolar-correlation build-up function. Both of them essentially reflect the features of the dipolar interactions between spins in a system. These interaction are, in turn, sensitive to the local segmental translation and reorientation, thus providing a way to investigate these motions. The two introduced methods are implemented on the conventional low-field NMR spectrometers as well as on the high-temperature machine assembled in the course of this work. Using this equipment the proposed approach is applied to the study of entangled polybutadiene, poly(ethylene-alt-propylene) and polyethylene oxide melts. Obtained time dependencies of the segmental displacements are found to be in good agreement with the conventional techniques at short times. Moreover, the novel methods are capable of significantly extending the probed range of dynamics both in the time and in the displacement domain, thus providing information on the scale that is hardly accessible to the experimental methods established for the studies of entangled polymer melts. Therefore the introduced approach is considered to be a new powerful tool in the field of polymer physics. Wide range of information provided by the dipolar-correlation and the solid-echo formalism allows a comprehensive experimental test of the validity of the tube-reptation model that is the most commonly used and well-established theoretical description of the entangled polymer melts. Time dependence of the mean squared segmental displacement obtained in poly(ethylene-alt-propylene) is found to be in good agreement with the corresponding predictions of the model. Three distinct power-laws are observed that are attributed to the Rouse, the incoherent and the coherent reptation regimes in the framework of the tube-reptation model. Importantly, the transition from the incoherent to the coherent reptation is reached for the first time in this polymer species of such a high molecular weight. On the other hand, segmental displacements obtained in the set of polyethylene oxide melts of different molecular weights displays no features of the extremely slow t^0.25 dynamics predicted for the incoherent reptation. This result is consistent and is corroborated by other NMR techniques at shorter and longer times. This finding calls the universal applicability of the tube concept for all the polymer species in question. Moreover, estimation of the relative contributions of the intra- and the intermolecular dipolar interactions to the transverse relaxation demonstrates similar behavior for all the studied polymer melts. Interestingly, this behavior is in contradiction with the prediction of the tube-reptation model and demonstrates no features expected for the highly anisotropic motion within the fictitious tube. The consistency of this result in all the samples investigated in this work allows one to raise an even more general question about the validity of the whole concept of the tube-reptation model

High Temperature Fast Field Cycling Study of Crude Oil

A set of crude oil samples with different composition and characteristics is studied by means of Fast Field Cycling (FFC) 1H relaxometry, which probes the distribution of longitudinal relaxation times T1 as a function of the Larmor frequency. Investigation of T1 profiles at different temperatures is able to provide an insight into the dynamics and structural changes of oil components, with our particular interest being the high temperature behaviour of asphaltene. It is well-known that asphaltenes tend to form porous clusters in crude oils, which can cause severe problems for the process of oil extraction. Therefore, FFC experiments are conducted on Stelar Spinmaster FFC2000 in the temperature range 203K < T <443K, where the upper limit of 443K is aimed at approximating the typical maximal in-situ well temperatures. FFC relaxometry data of crude oils at such a high temperature are obtained for the first time with the use of a specially modified NMR probe. Inverse Laplace transformation is applied to the longitudinal agnetization decays, yielding T1 distributions at different frequencies. A comparative analysis of these distributions for different Larmor frequencies and temperatures showed that there is a systematic variation of the frequency dependence of T1 correlating with the asphaltene content in the samples, at temperatures similar to the well conditions

Segmental Dynamics of Entangled Poly(ethylene oxide) Melts: Deviations from the Tube-Reptation Model

© 2018 American Chemical Society. The dynamics of entangled polymer melts not only is of fundamental theoretical interest but also has wide-reaching consequences for developing a theoretical foundation for investigating biological macromolecules and complex systems relevant to material sciences. Despite several decades of intensive experimental and theoretical research in this field, open questions remain regarding segmental dynamics over the wide range of time scales from local to global motion. This work employs a novel approach based on nuclear magnetic relaxation to scrutinize the character of dipolar interactions in entangled polymer melts, thereby accessing unique information about segmental diffusion and rotation. The main focus is set on the separate consideration of intra- and intermolecular contributions to the proton dipolar interactions, which have been previously shown to possess a different, nontrivial time dependence. A combination of well-established field-cycling T1 relaxometry and recently developed methods based on spin echo is utilized to investigate dipolar couplings in entangled poly(ethylene oxide) melts of various molecular weights. Isolation of the intermolecular contributions to the corresponding experimental quantities provides a means to observe segmental translations taking place during more than 6 orders of magnitude in time. Time dependences of the mean-square displacement obtained in this way revealed apparent exponents of the power laws significantly deviating from predictions of the widely used tube-reptation model of polymer dynamics in the regime of entangled motion. In addition to that, the relative ratio of intermolecular dipolar interactions over the intramolecular counterpart is probed through their corresponding contributions to the transverse relaxation rate. A strong deviation from the tube-reptation model predictions for the evolution of this quantity is observed in the whole range probed experimentally. The obtained data do not reflect the restricted character of segmental motion anticipated in the corresponding time regime. It is emphasized that similar results, both in amplitude and in qualitative behavior, have been previously demonstrated in polybutadiene and polyethylene-alt-propylene, thereby allowing to discuss the universality of the observed deviation

Detection and modeling of hole capture by single point defects under variable electric fields

Understanding carrier trapping in solids has proven key to semiconductor technologies but observations thus far have relied on ensembles of point defects, where the impact of neighboring traps or carrier screening is often important. Here, we investigate the capture of photo-generated holes by an individual negatively-charged nitrogen-vacancy (NV) center in diamond at room temperature. Using an externally gated potential to minimize space-charge effects, we find the capture probability under electric fields of variable sign and amplitude shows an asymmetric-bell-shaped response with maximum at zero voltage. To interpret these observations, we run semi-classical Monte Carlo simulations modeling carrier trapping through a cascade process of phonon emission, and obtain electric-field-dependent capture probabilities in good agreement with experiment. Since the mechanisms at play are insensitive to the trap characteristics, the capture cross sections we observe - largely exceeding those derived from ensemble measurements - should also be present in materials platforms other than diamond