A new approach is described to computer simulate cation distribution in octahedral sheets of dioctahedral 2:1 layer silicates with vacant trans-octahedra. This approach makes use of the information on cation distribution at the one-dimensional level provided by integrated IR optical densities for the region of OH-stretching frequencies. By using this program it is possible to show that (1) the Mössbauer spectrum of glauconite B. Patom conforms to the structural model composed of celandonite-like and illite-like domains whose dimensions are limited by approximately 2 or 4 unit cells; (2) non-equivalency of “left” and “right” cis-positions (with fixed b-direction) with respect to R2+ and R3+ occupancy is a characteristic feature of a celadonite-like domain.

Alumina-pillared montmorillonite is prepared by intercalation of polyoxyhydroxy aluminum cations (Al137+) of a natural montmorillonite from Dimitrovgrad, Bulgaria. Transmission electron microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy, and surface area (BET) methods are used to study the untreated and pillared forms of the montmorillonite. A structural model involving deformed Al13 pillars is proposed. Four pillar types are derived and these pillars are uniformly distributed over the interlayer-cation positions of montmorillonite. Calculated electron diffraction patterns were simulated using the multi-slice method. The structural model explains the increased ordering along the c axis of the pillared form compared with the untreated montmorillonite. The model explains the structure of a pillared montmorillonite with different distributions of the pillars in the interlayer. The proposed model is consistent with the observed data.

We report a combined experimental and theoretical study of uranyl complexes that form on the interlayer siloxane surfaces of montmorillonite. We also consider the effect of isomorphic substitution on surface complexation since our montmorillonite sample contains charge sites in both the octahedral and tetrahedral sheets. Results are given for the two-layer hydrate with a layer spacing of 14.58 Å. Polarized-dependent X-ray absorption fine structure spectra are nearly invariant with the incident angle, indicating that the uranyl ions are oriented neither perpendicular nor parallel to the basal plane of montmorillonite. The equilibrated geometry from Monte Carlo simulations suggests that uranyl ions form outer-sphere surface complexes with the [O=U=O]2+ axis tilted at an angle of ~45° to the surface normal.

We performed Monte Carlo and molecular dynamics simulations to investigate the interlayer structure of a uranyl-substituted smectite clay. Our clay model is a dioctahedral montmorillonite with negative charge sites in the octahedral sheet only. We simulated a wide range of interlayer water content (0 mg H2O/g clay — 260 mg H2O/g clay), but we were particularly interested in the two-layer hydrate that has been the focus of recent X-ray absorption experiments. Our simulation results for the two-layer hydrate of uranyl-montmorillonite yield a water content of 160 mg H2O/g clay and a layer spacing of 14.66 Å. Except at extremely low water content, uranyl cations are oriented nearly parallel to the surface normal in an outer-sphere complex. The first coordination shell consists of five water molecules with an average U-O distance of 2.45 Å, in good agreement with experimental data. At low water content, the cations can assume a perpendicular orientation to include surface oxygen atoms in the first coordination shell. Our molecular dynamics results show that ${\text{UO}}_2{\left({\text{H}}_2\text{O}\right)}_5^{2+}$ complexes translate within the clay pore through a jump diffusion process, and that first-shell water molecules are exchangeable and interchangeable.

Three kaolinite reference samples identified as KGa-1, KGa-1b, and KGa-2 from the Source Clays Repository of The Clay Mineral Society (CMS) are used widely in diverse fields, but the defect structures have still not been determined with certainty. To solve this problem, powder diffraction patterns of the KGa-1, KGa-1b, and KGa-2 samples were modeled. In a kaolinite layer among three symmetrically independent octahedral sites named as A, B, and C and separated from each other by b/3 along the b parameter, the A and B sites are occupied by Al cations, whereas, the C sites located along the long diagonal of the oblique kaolinite unit cell are vacant. The layer displacement vectors t1 and t2 are related by a pseudo-mirror plane from defect-free 1Tc kaolinite enantiomorphs, whereas, the random interstratification within individual kaolinite crystallites creates right-hand and left-hand layer sub-sequences producing structural disorder. A third layer displacement vector, t0, located along the long diagonal of the oblique layer unit cell that contains the vacant octahedral site and coincides with the layer pseudo-mirror plane may exist. Thus, a structural model should be defined by the probability of t1, t2, and t0 layer displacement translations Wt1, Wt2, and Wt0, respectively, determined by simulated experimental X-ray diffraction (XRD) patterns. X-ray diffraction patterns were calculated for structures with a given content of randomly interstratified displacement vectors, and other XRD patterns were calculated for a physical mixture of crystallites having contrasting structural order with only C-vacant layers. The samples differ from each other by the content of high- and low-ordered phases referred to as HOK and LOK. The HOK phase has an almost defect-free structure in which 97% of the layer pairs are related by just the layer displacement vector t1 and only 3% of the layer pairs form the enantiomorphic fragments. In contrast, the LOK phases in the KGa-1, KGa-1b, and KGa-2 samples differ from HOK phases by the occurrence probabilities for the t1, t2, and t0 layer displacements. In addition, the LOK phases contain stacking faults that displace adjacent layers in arbitrary lengths and directions. Low XRD profile factors (Rp = 8-11%) support the defect structure models. Additional structural defects and previously published models are discussed.

The article is devoted to computer modeling, visualization, and synthesis of a digital antenna array used for transmitting and receiving signals in industrial applications. The paper proposes an iterative method for the amplitude-phase synthesis of an antenna array according to the requirements for the envelope of the side lobes. The proposed method allows to determine the complex amplitudes of the elements of a digital antenna array for any given weight function, based on the theorems of matrix theory. The difference of the method lies in the iterative procedure for choosing the weight function, taking into account the excess level of the side lobes of the digital antenna array. In this regard, in the course of solving the synthesis problem, a weight function was found that leads to the fulfilment of the requirements for radiation patterns and does not lead to a decrease in the directivity coefficient. The signal-to-noise ratio was used as a criterion. For the first time, an analytical expression is given for the formation of a weight function in the course of an iterative process that takes into account the requirements for the envelope of the side lobes. The operability and convergence of the proposed method was confirmed in the course of numerical studies on the example of a digital antenna array. The performed numerical analysis confirmed the effectiveness of the proposed synthesis method.

The biotic scenario of the selection of biological homochirality is one of the most interesting applications of computer modelling to astrobiology. These scenarios have been studied for more than 70 years, yet there are plenty of studies to better assess them, in particular in the development of models of the selective extinction process. In this paper, we review former studies performed by biology-grounded models of this process and present a new class of computer programs: they further demonstrate the complexity of the selective extinction dynamics and the role played into it by non-trivial chemical-physical concepts. Indeed, the results display large and persistent differences between the populations of the two different chiral types, made possible by the freedom of individual populations to fluctuate wildly while the total population is stabilized by the limited availability of chemical energy. Such strong differences ultimately lead to the selective extinction of one of the two types. This way, computer simulations provide increasing evidence in favour of the biotic scenario.

The electroretinogram (ERG) has been employed for years to collect information about retinal function and pathology. The usefulness of this noninvasive test depends on our understanding of the cell sources that generate the ERG. Important contributors to the ERG are glial Müller cells (MCs), which are capable of generating substantial transretinal potentials in response to light-induced changes in extracellular K+ concentration ([K+]o). For instance, the MCs generate the slow PIII (sPIII) component of the ERG as a reaction to a photoreceptor-induced [K+]o decrease in the subretinal space. Similarly, an increase of [K+]o related to activity of postreceptor retinal neurons also produces transretinal glial currents, which can potentially influence the amplitude and shape of the b-wave, one of the most frequently analyzed ERG components. Although it is well documented that the majority of the b-wave originates from On-bipolar cells, some contribution from MCs was suggested many years ago and has never been experimentally rejected. In this work, detailed information about light-evoked [K+]o changes in the isolated mouse retina was collected and then analyzed with a relatively simple linear electrical model of MCs. The results demonstrate that the cornea-positive potential generated by MCs is too small to contribute noticeably to the b-wave. The analysis also explains why MCs produce the large cornea-negative sPIII subcomponent of the ERG, but no substantial cornea-positive potential.

This paper introduces a dual-user training system whose design is based on an energetic approach. This kind of system is useful for supervised hands-on training where a trainer interacts with a trainee through two haptic devices, in order to practice on a manual task performed on a virtual or teleoperated robot (e.g., for an Minimally Invasive Surgery (MIS) task in a surgical context). This paper details the proof of stability of an Energy Shared Control (ESC) architecture we previously introduced for one degree of freedom (d.o.f.) devices. An extension to multiple degrees of freedom is proposed, along with an enhanced version of the Adaptive Authority Adjustment function. Experiments are carried out with 3 d.o.f. haptic devices in free motion as well as in contact contexts in order to show the relevance of this architecture.

We review some of the most recent developments in classical and quantum mechanical molecular dynamics simulations, in particular as applied to Earth-forming phases at conditions prevalent in the Earth's deep interior. We pay special attention to the modelling of high pressures and temperatures, elucidating the problems associated with both the classical and quantum approaches in view of the empirical potentials required for the former, and the limitations of finite temperature calculations for the latter. We show the current status of such calculations for major phases such as MgSiO3 perovskite.

The [4]Al/Si and [6]Al/Mg order-disorder behaviour of minerals in the tremolite-tschermakite solid solution (namely, end-member tschermakite and the 50:50 composition, magnesiohornblende) has been investigated by Monte Carlo simulation, using a model Hamiltonian in which atomic interaction parameters Ji were derived from empirical lattice energy calculations, and chemical potential terms μj (to express the preferences of cations for particular crystallographic sites) were derived from ab initio methods. The simulations performed were increasingly complex. Firstly, ordering in one tetrahedral double chain with Al:Si = 1:3 (tschermakite) was simulated. Although the low-temperature cation distribution in this system was ordered, there was no phase transition (due to the quasi-one-dimensional nature of the system). Next, interactions between tetrahedral Al:Si = 1:3 double chains were included, and a phase transition was observed, with the cation distribution in one double chain lining up with respect to that in the next. Finally, interactions between tetrahedral and octahedral sites were incorporated, to model the whole unit cell, and compositions corresponding to tschermakite and magnesiohornblende were investigated. The whole-cell simulation results compare favourably with experimental conclusions for magnesiohornblende, in that Al at T1 is preferred over Al at T2, and Al at M2 is favoured over that at M1 and M3, but the significant amount of Al at M1 is at odds with experimental observation.

How individuals tend to evaluate the combination of their own and other’s payoffs—social value orientations—is likely to be a potential target of future moral enhancers. However, the stability of cooperation in human societies has been buttressed by evolved mildly prosocial orientations. If they could be changed, would this destabilize the cooperative structure of society? We simulate a model of moral enhancement in which agents play games with each other and can enhance their orientations based on maximizing personal satisfaction. We find that given the assumption that very low payoffs lead agents to be removed from the population, there is a broadly stable prosocial attractor state. However, the balance between prosociality and individual payoff-maximization is affected by different factors. Agents maximizing their own satisfaction can produce emergent shifts in society that reduce everybody’s satisfaction. Moral enhancement considerations should take the issues of social emergence into account.

The practice of climate simulation takes place in a polarized social and political context. In this paper some methodological aspects of the practice of climate simulation are addressed and the potential value-ladenness of modelling assumptions is discussed. I claim that there is clearly a plurality of values guiding climate simulation efforts with climate scientists themselves also commonly holding different political views on the climate-change problem. There exist climate models of varying levels of concreteness and with different basic assumptions, and the modelling approaches behind these models are valued differently by different groups of climate scientists. The social and political context in which the climate modelling is done plays a role in these value judgements. In order to prevent one particular group of models from dominating the field for social and/or political reasons, the climate-modelling community should acknowledge the vital and necessary role of plurality in the practice of climate science and should stimulate reflection within this practice. Finally, while the IPCC partly addresses the issue by presenting model ensembles, the uncertainties in climate simulation should be better communicated to policy makers and politicians.