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

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

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

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

Targeted LC–MS derivatization for aldehydes and carboxylic acids with a new derivatization agent 4-APEBA

Based on the template of a recently introduced derivatization reagent for aldehydes, 4-(2-(trimethylammonio)ethoxy)benzeneaminium dibromide (4-APC), a new derivatization agent was designed with additional features for the analysis and screening of biomarkers of lipid peroxidation. The new derivatization reagent, 4-(2-((4-bromophenethyl)dimethylammonio)ethoxy)benzenaminium dibromide (4-APEBA) contains a bromophenethyl group to incorporate an isotopic signature to the derivatives and to add additional fragmentation identifiers, collectively enhancing the abilities for detection and screening of unknown aldehydes. Derivatization can be achieved under mild conditions (pH 5.7, 10 °C). By changing the secondary reagent (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide instead of sodium cyanoborohydride), 4-APEBA is also applicable to the selective derivatization of carboxylic acids. Synthesis of the new label, exploration of the derivatization conditions, characterization of the fragmentation of the aldehyde and carboxylic acid derivatives in MS/MS, and preliminary applications of the labeling strategy for the analysis of aldehydes in urine and plasma are described

Tractography passes the test: Results from the diffusion-simulated connectivity (disco) challenge.

Estimating structural connectivity from diffusion-weighted magnetic resonance imaging is a challenging task, partly due to the presence of false-positive connections and the misestimation of connection weights. Building on previous efforts, the MICCAI-CDMRI Diffusion-Simulated Connectivity (DiSCo) challenge was carried out to evaluate state-of-the-art connectivity methods using novel large-scale numerical phantoms. The diffusion signal for the phantoms was obtained from Monte Carlo simulations. The results of the challenge suggest that methods selected by the 14 teams participating in the challenge can provide high correlations between estimated and ground-truth connectivity weights, in complex numerical environments. Additionally, the methods used by the participating teams were able to accurately identify the binary connectivity of the numerical dataset. However, specific false positive and false negative connections were consistently estimated across all methods. Although the challenge dataset doesn't capture the complexity of a real brain, it provided unique data with known macrostructure and microstructure ground-truth properties to facilitate the development of connectivity estimation methods