Stochastic simulation of destruction processes in self-irradiated materials

Self-irradiation damages resulting from fission processes are common phenomena observed in nuclear fuel containing (NFC) materials. Numerous $\alpha$-decays lead to local structure transformations in NFC materials. The damages appearing due to the impacts of heavy nuclear recoils in the subsurface layer can cause detachments of material particles. Such a behaviour is similar to sputtering processes observed during a bombardment of the material surface by a flux of energetic particles. However, in the NFC material, the impacts are initiated from the bulk. In this work we propose a two-dimensional mesoscopic model to perform a stochastic simulation of the destruction processes occurring in a subsurface region of NFC material. We describe the erosion of the material surface, the evolution of its roughness and predict the detachment of the material particles. Size distributions of the emitted particles are obtained in this study. The simulation results of the model are in a qualitative agreement with the size histogram of particles produced from the material containing lava-like fuel formed during the Chernobyl nuclear power plant disaster.Comment: 11 pages, 8 figure

Entwicklung von Nanofaser-Hydrogel-Kompositen, als fixierbare und transparente Wundauflagen für die Anwendung in der Augenheilkunde

The human eye is a sophisticated sensory organ that enables our perception of the environ-ment through light stimuli. However, due to its exposed location, it is susceptible to injury. The current gold standard in surgical treatment of superficial wounds is the application of an amniotic membrane. Due to its human origin, however, it is subject to variations in its properties, such as high variation in thickness as well as large differences in mechanical stability and transparency. In addition, application of donor tissue, despite good serological tests, includes a risk for transmission of diseases to the patient. In this work, new materials have been developed as potential replacement for amniotic membranes in the ocular wound care based on the production of polymeric nanofibers by electrospinning. After extensive optimization of the manufacturing parameters, membranes were produced of fine fibers that were not only homogeneous but also free of defects. In cell experiments, these mem-branes showed high compatibility with two ocular cell lines. Subsequent treatment of the fibers to improve their wettability surface properties enabled the incorporation of hydrogels into the nanofiber structures. The resulting composite showed a very good homogeneity in its properties. This allowed the production of membranes with reproducible layer thickness-es and at the same time high transparencies. In addition, a quality control model has been developed to allow the assessment of membrane transparency in a quick and easy way. Based on the high point-load of the composites through sewing threads, during the sutur-ing of the membranes on the ocular surface, experiments were performed on their mechani-cal stability. Here, the membranes, depending on the composition, showed a mechanical robustness which is similar to the amniotic membrane. The attempt to suture such a compo-site on a donor cornea as proof of principle was also successful. These results highlighted the positive properties of the developed membranes and their potential for use in the wound care of the eye.Das menschliche Auge ist ein hochentwickeltes Sinnesorgan, das uns die Wahrnehmung unserer Umgebung mittels Lichtreizen ermöglicht. Aufgrund seiner exponierten Lage ist es jedoch anfällig für Verletzungen. Der aktuelle Gold-Standard bei der initialen chirurgi-schen Behandlung von oberflächlichen Wunden ist die Applikation einer Amnionmembran. Wegen ihres humanen Ursprungs kann es in der Amnionmembran zu Schwankungen ihrer Eigenschaften kommen. Dies äußert sich dadurch, dass beispielsweise eine hohe Variation in den Dicken sowie große Unterschiede in der mechanischen Stabilität und Transparenz auftreten. Zusätzlich besteht bei der Applikation von Spendergewebe, trotz guter serologi-scher Untersuchungen, eine Gefahr für Übertragungen von Krankheiten auf den Patienten. Deshalb war es das Ziel dieser Arbeit neue Materialien zu entwickeln, die sich als Ersatz für die Amnionmembran, bei der Wundversorgung des Auges eignen. Als Basis dienten dazu polymere Nanofasern, die mittels Elektrospinnen hergestellt wurden. Nach einer um-fassenden Optimierung der Herstellungsparameter, konnten Membranen aus feinen Fasern hergestellt werden, die nicht nur homogen, sondern auch frei von Defekten waren. In Zell-experimenten zeigten die Membranen eine hohe Kompatibilität mit zwei Zelllinien des menschlichen Auges. Eine anschließende Behandlung der Fasern, zur Verbesserung ihrer Oberflächeneigenschaften bezüglich Ihrer Benetzbarkeit, ermöglichte den Einbau von Hyd-rogelen in die Nanofaserstrukturen. Das daraus resultierende Komposit zeigte in Untersu-chungen eine sehr gute Homogenität in den Eigenschaften. So konnten Membranen mit reproduzierbaren Schichtdicken und zugleich hohen Transparenzen hergestellt werden. Zu-sätzlich wurde eine Methode für die Qualitätsprüfung entwickelt, mit der die Beurteilung der Membrantransparenz auf schnellem und unkompliziertem Weg durchgeführt werden kann. Basierend auf der hohen punktuellen Belastung der Komposite durch Fäden, wäh-rend des Vernähens der Membranen auf der Augenoberfläche, wurden Experimente zu deren mechanischer Stabilität durchgeführt. Hierbei zeigten die Membranen, abhängig von der Zusammensetzung, eine mechanische Robustheit die der Amnionmembran ähnelt. Der Versuch ein solches Komposit auf eine Spenderhornhaut aufzunähen, konnte ebenfalls er-folgreich durchgeführt werden. Diese Ergebnisse unterstrichen die positiven Eigenschaften der entwickelten Membranen und ihr Potential für den Einsatz in der Wundversorgung des Auges

3D cellular automata simulations of intra and intergranular corrosion

tA simple model for the effect of intergranular corrosion on overall corrosion processes is investigatedusing a cellular automata approach. The corroding polycrystalline material consists of domains and theirboundaries. The domains represent the monocrystalline cores while their boundaries represent the inter-granular defects. Either, a periodic pattern or randomly generated domains of Voronoï tessellation areused to represent the polycrystalline structure. The parameters of the model, taking into account thepolycrystalline aspect of corrosion, are the domain density and the corrosion probabilities of metal graincore and grain boundary sites. The corrosion probability for grain boundary is set to a value higher thanit is for the grain core. A complex surface structure appears with a high geometrical roughness whendefects are not too dense. A strong correlation is established between the roughness evolution, the metalcrystalline properties and the corrosion mechanism of metal dissolution. This work concerns simulationsin 3D and extends the previous work limited to 2D simulations

Crossover of interface growth dynamics during corrosion and passivation

We study a model of corrosion and passivation of a metalic surface in contact with a solution using scaling arguments and simulation. The passive layer is porous so that the metal surface is in contact with the solution. The volume excess of the products may suppress the access of the solution to the metal surface, but it is then restored by a diffusion mechanism. A metalic site in contact with the solution or with the porous layer can be passivated with rate p and volume excess diffuses with rate D. At small times, the corrosion front linearly grows in time, but the growth velocity shows a t^{-1/2} decrease after a crossover time of order t_c ~ D/p^2, where the average front height is of order h_c ~ D/p. A universal scaling relation between h/h_c and t/t_c is proposed and confirmed by simulation for 0.00005 <= p <= 0.5 in square lattices. The roughness of the corrosion front shows a crossover from Kardar-Parisi-Zhang scaling to Laplacian growth (diffusion-limited erosion - DLE) at t_c. The amplitudes of roughness scaling are obtained by the same kind of arguments as previously applied to other competitive growth models. The simulation results confirm their validity. Since the proposed model captures the essential ingredients of different corrosion processes, we also expect these universal features to appear in real systems.Comment: 17 pages, including 7 figures; submitted articl

Endothelial Cell Markers in Patients with Pseudoexfoliation Syndrome

The aim of the study was the assessment of the von Willebrand antigen (vWF Ag), E-selectin, and P-selectin concentration in blood plasma of patients with pseudoexfoliation syndrome (PEX). The group studied comprised 30 patients with PEX, aged from 50 to 86 years (mean 73, SD ± 8 years). Patients with cardiovascular and cerebrovascular diseases, diabetes mellitus, infectious disease, cancer, renal or liver insufficiency, connective tissue disease, current smoking, and hormone, antiplatelet, hypolipidemic, antioxidant, or antihypertensive drug therapy were excluded from the study. Each subject underwent a complete ophthalmological examination. Venous blood samples from the cubital vein were taken into sodium citrate solution. VWF Ag, sP-selectin, and sE-selectin concentration were determined by a commercially available enzyme-linked immunosorbent assay (MedSystems, Diagnostica Stago/Roche, R&D). Concentrations of vWF Ag, soluble E-selectin, and soluble P-selectin in blood plasma in the study group were compared with the levels in blood plasma in the control group. No significant differences were found between the groups. Our results indicate that there might be no correlation between PEX and such endothelial cell markers as vWF Ag, sP-selectin, and sE-selectin concentrations. Since the study size is limited, further investigations to confirm that there is no association between endothelial dysfunction in PEX and risk of future cardiovascular disease are necessary

A field theoretical approach to the Debye-Huckel electrolyte differential capacitance in a slab

The effective Hamiltonian of our field theoretical model yields the linearized Debye-H¨uckel theory in the bulk. Here we consider it for a confined geometry of a slab. The differential capacitance is computed using two ways. The first relates it to the charge-charge correlation function by calculating the response to charging of the slab walls. The other relates it to the fluctuation of charge in one half of the slab. Since the model is exactly soluble in terms of the diagonal representation we can verify the fact that the two ways are consistent with each other and with the Gouy-Chapman differential capacitance in the limit of a thick slab. The interest of this derivation is to relate a measurable quantity to the structural information contained in the charge-charge correlation function.Ефективний гамільтоніан нашої теоретико-польової моделі дає лінеаризовану теорію Дебая-Гюкеля для об’ємних властивостей. Тут ми розглядаємо його для обмеженої геометрії пластини. Диференціальна ємність обчислюється двома способами. Перший пов’язує її з прямою кореляційною функцією заряд-заряд на основі обчислення відгуку до заряджання стінок пластини. Інші методи пов’язують її з флуктуацією заряду в одній половині пластини. Оскільки модель є точно розв’язувана в термінах діагонального представлення, ми можемо перевірити той факт, що два способи узгоджуються між собою і з виразом для диференційної ємності Гуї-Чепмена в границі тонкої пластини. Цінність цього висновку мусить пов’язувати вимірювальну величину зі структурною інформацією, яка міститься в кореляційній функції заряд-заряд

Mapping between two models of etching process

We consider two models for the etching processes using numerical simulations based on cellular-automata discrete-lattice approach. In one model we use a uniform etching probability for each surface site. In another model the etching probability at a given site depends on the local environment of this site. In contrast to the first model we have now a non-local description of the surface evolution. It is natural to consider the following question: is this non-locality sufficient to induce new physics? To answer this question is the main goal of the paper. We show that there exists an equivalence between the two models. This means that the non-local model gives results similar to the local one provided we use an effective value of the etching probability.Використовуючи комп’ютерне моделювання на основi комiркового автомату, дослiджено двi гратковi моделi, якi описують процеси витравлювання. В однiй моделi використано однакову iмовiрнiсть витравлювання для всiх поверхневих вузлiв. В iншiй моделi iмовiрнiсть витравлювання вузла залежить вiд оточення даного вузла. Таким чином, на противагу першiй моделi, в другiй моделi присутнiй нелокальний опис розвитку поверхнi. Тому природно розглянути наступне питання: чи ця нелокальнiсть є достатньою, щоб спричинити якiсно новi результати? Вiдповiдь на дане запитання є основною метою цiєї роботи. Показано, що iснує еквiвалентнiсть мiж двома розглянутими моделями. Це значить, що нелокальна модель приводить до якiсно подiбних результатiв, що i локальна модель, яка описується певною ефективною iмовiрнiстю витравлювання

A formally exact field theory for classical systems at equilibrium

We propose a formally exact statistical field theory for describing classical fluids with ingredients similar to those introduced in quantum field theory. We consider the following essential and related problems : i) how to find the correct field functional (Hamiltonian) which determines the partition function, ii) how to introduce in a field theory the equivalent of the indiscernibility of particles, iii) how to test the validity of this approach. We can use a simple Hamiltonian in which a local functional transposes, in terms of fields, the equivalent of the indiscernibility of particles. The diagrammatic expansion and the renormalization of this term is presented. This corresponds to a non standard problem in Feynman expansion and requires a careful investigation. Then a non-local term associated with an interaction pair potential is introduced in the Hamiltonian. It has been shown that there exists a mapping between this approach and the standard statistical mechanics given in terms of Mayer function expansion. We show on three properties (the chemical potential, the so-called contact theorem and the interfacial properties) that in the field theory the correlations are shifted on non usual quantities. Some perspectives of the theory are given.Comment: 20 pages, 8 figure