Estimation of Ra-224 Content in Egyptian Black Sand by the Can- and Alpha-Autoradiography Techniques using LR-115 Plastic Detectors

Sealed can- and alpha-autoradiography techniques were used to estimate the effective and real contents of Ra-224 respectively in Egyptian black sand samples collected from Rosetta City in the Nile Delta at the North Coast of Egypt. The effective Ra-224 content was found to be 15 ± 3 Bq · kg^?1. From the average chemical composition of the black sand samples, the range-energy relation for the alpha-particles of the thorium series was calculated. Assuming radioactive equilibrium, the real Ra-224 content for samples collected from different regions were found to range from 90 to 900 Bq · kg^?1. As a result, the total emanation power was measured and then used to estimate grain diameter of the black sand. The average mass exhalation rate of the different locations in Rosetta City was also estimated.     

Ion–solid interactions: current status,new perspectives

In the past half century, we have witnessed an explosive growth of effort in that cross-discipline which is characterized by the deposition of localized high–energy densities in condensed matter by means of energetic ions—the field of ion–solid interactions. In this overview, the fundamental physical processes of ion–solid interaction are outlined. A brief discussion is given of the basic energy transfer mechanisms and the consequences of ion impact into solids such as scattering, sputtering and radiation damage. It is now understood that radiation damage is itself far from being restricted to deleterious and detrimental consequences. Our knowledge of the growing variety of changes in the physical, chemical and biological properties of target materials are growing exponentially. Many valuable beneficial technological applications, some of which we discuss, have their origin in physical processes taking place at the nanometric level.     

Coupled chemical reactions in dynamic nanometric confinement: Ag2O membrane formation during ion track etching

In this study, continuous swift heavy ion tracks in thin polymer foils were etched from both sides to create two conical nanopores opposing each other. Shortly before both cones merged, one of the nanopores was filled with a silver salt solution, whereas etching of the other cone continued. At the moment of track breakthrough, the etchant reacted with the silver salt solution by forming an impermeable and insulating membrane. Continued etching around the thus-created obstacle led to repetitive {etchant – silver salt solution} interactions. The coupling of the two chemical reactions, {etchant – polymer} and {etchant – silver salt solution}, within the confinement of etched tracks, with continuously changing shapes, showed a highly dynamic nature as recorded by measuring both the electrical current and the optical transmission across the foils. At low etching speeds, a central membrane that grew in radius and thickness with time until, at a critical thickness, the membrane became rather impermeable was formed. However, at high etching speeds, the emerging reaction products exhibited a sponge-like consistency, which allowed for their infinite growth. This precipitation was accompanied by a pronounced current spike formation. A simple theoretical model explains, at a minimum, the basic features.     

Critical approach distances and critical angles for channelling

The critical angles and critical approach distances, which determine the limits for the channelling of energetic ions, down open crystal directions are established by the methods of computer simulation and compared with simple analytical models. For non-vibrating rows or planes a good agreement between the two is obtained. The complicating effects of thermal vibrations can be accounted for by empirical formulae.     

A necessary condition for the appearance of damage-induced surface-topography during particle bombardment

A first approach to the establishment of an “order-of-magnitude” criterion for the initiation of damage-induced surface topography on clean and well-polished metal single crystals is proposed. It is based on a model proposing a mechanism of preferential erosion of parts from the sample surface due to a local increase of sputtering yield above “extensive defects”. These “extensive defects”, resulting of the migration of the point-defects, created during the collision-cascade started by the incoming ions, can indeed influence the sputtering yield if they are located close under the surface, i.e. when the surface has regressed, due to sputtering, to the level where these “extensive defects” have been formed.

The condition implies that the formation of “extensive defects” must have taken place before the surface reaches them. The condition is written in terms of the irradiation parameters and quantities characteristic for the migration of point-defects due to the presence of a potential gradient related to the “extensive defects” under formation.     

Rechnergestützte Auswertung experimenteller Inkohlungsuntersuchungen

Model investigations, carried out as laboratory coalification reactions with humous and sapropelitic sediments of different maturation degree, showed that conclusions can be drawn about the character of the parent rock of a natural gas using data of the chemical and isotopic composition of the organic substance in sediments and its coalification products.

Several examples demonstrate, that the following parameters have proved as suitable fades- and in part as maturity criteria: CH₄/Σ HKW; C₂H₆/CH₄, i-/n-C₄H₁₀, ¹³C-abundance of organic substance, ¹³C-abundance of methane.

For a complex interpretation all results obtained from coalification experiments over some years were stored in a data file. By means of cluster analysis all samples were classified in groups corresponding to their characteristics represented by the above mentioned five criteria. Four clusters resulted depending on maceral composition of the tested organic sediments. The differentiating criteria of these clusters are discussed.     

A simple model for latent track formation due to cluster ion stopping and fragmentation in solids

An estimate of the electronic stopping of a swift cluster ion during different stages of penetration in a given material is presented. We take a simplified approach to the stopping process by neglecting vicinage effects on the stopping cross section as well as spatial distortion due to Coulomb forces among ions. The different stages of penetration and energy loss are based on the hypothesis of formation of a transient plasma (the plasma stopping regime)—due to the release of energetic electrons from the target material—within and around the spatial region defined by the correlated positions of each cluster constituent ion (atom). The density of the transient plasma is treated as a function of the rate of energy deposition and depth up to a point where the rate of energy deposition yields a threshold value where the ejected target electrons immediately recombine so that stopping in a cold target begins (conventional stopping regime) and where the cluster constituent ions start being neutralized according to a charge equilibration scheme as depicted by the effective charge relation of Betz. The model is applied to the stopping of 40.2 Mev C₆₀³⁺ projectiles penetrating an Yttrium–Iron Garnet (YIG) target. Also, in this case, a possible explanation for the experimentally observed cluster-fragmentation events at a certain depth is presented.     

“Wheels vs. tracks” – A fundamental evaluation from the traction perspective

The issue of wheeled vehicles vs. tracked vehicles for off-road operations has been a subject of debate for a long period of time. Recent interest in the development of vehicles for the rapid deployment of armed forces has given a new impetus to this debate. While a number of experimental studies in comparing the performances of specific wheeled vehicles with those of tracked vehicles under selected operating environments have been performed, it appears that relatively little fundamental analysis on this subject has been published in the open literature, including the Journal of Terramechanics. This paper is aimed at evaluating the tractive performance of wheeled and tracked vehicles from the standpoint of the mechanics of vehicle–terrain interaction. The differences between a tire and a track in generating thrust are elucidated. The basic factors that affect the gross traction of wheeled and tracked vehicles are identified. A general comparison of the thrust developed by a multi-axle wheeled vehicle with that of a tracked vehicle is made, based on certain simplifying assumptions. As the interaction between an off-road vehicle and unprepared terrain is very complex, to compare the performance of a wheeled vehicle with that of a tracked vehicle realistically, comprehensive computer simulation models are required. Two computer simulation models, one for wheeled vehicles, known as NWVPM, and the other for tracked vehicles, known as NTVPM, are described. As an example of the applications of these two computer simulation models, the mobility of an 8 × 8 wheeled vehicle, similar to a light armoured vehicle (LAV), is compared with that of a tracked vehicle, similar to an armoured personnel carrier (APC). It is hoped that this study will illustrate the fundamental factors that limit the traction of wheeled vehicles in comparison with that of tracked vehicles, hence contributing to a better understanding of the issue of wheels vs. tracks.     

中国制氢技术的发展现状

氢能是一种高效清洁的二次能源,在实现“碳中和”目标中起重要作用。随着制氢规模不断扩大、制氢成本不断降低,氢能将有望与电能共同成为二次能源主体,通过氢电互补推动我国能源结构转型、降低碳排放、保障我国能源安全。目前,我国已成为世界第一大产氢国,主要有三类工业制氢路线:化石燃料重整制氢、工业副产氢和清洁能源电解水制氢。依托清洁能源发展起来的其他制氢新技术,如太阳能光解水制氢、生物质制氢、核能制氢等也受到广泛研究和关注。此外,制氢系统组成复杂,建模和优化难度高,人工智能在制氢系统的预测、评估和优化方面表现出独特的优势,受到国际学者的关注。本文结合最新研究进展,对上述制氢路线的发展情况进行了综述,并通过技术成熟度、经济性和环保性比较,结合国情对我国未来氢气供应结构做出展望。同时,本文综述了人工智能在制氢系统中的最新应用进展,以期为我国制氢工艺发展提供新思路。     

Polluting resource extraction and climate risk

Using a fossil fuel extraction model that treats the atmosphere as a depletable resource, we study the optimal price of carbon in the presence of endogenous uncertainty around a climatic regime shift. We find that the optimal carbon tax should account an uncertainty-adjusted cost term associated with the environment's scarcity. This term is shown to be sensitive to the natural sequestration rate of the atmosphere and to the probability surrounding a climate tail event. Our analysis also shows that in the presence of uncertainty, the shadow price of the environment should grow at a faster rate. Lastly, compared to the endogenous uncertainty case, we find that if the probability surrounding a regime shift is exogenously given, this shadow price should even grow at a higher rate.