Thermotropic liquid crystal behaviour of gemini imidazolium-based ionic amphiphiles

Thermotropic ionic liquid crystals (LCs) are useful for a number of applications such as anisotropic ion transport and as organised reaction media/solvents because of their ordered fluid properties and intrinsic charge units. A large number of different ionic LC architectures are known, but only a handful of examples of gemini (i.e. paired or dimeric) ionic LCs have been prepared and studied. In this work, a series of 20 new symmetric, imidazolium-based, gemini cationic LCs containing two bridged imidazolium cations and two pendant alkyl chains was synthesised, and the thermotropic LC behaviours were characterised. The imidazolium unit provides a highly tunable and modular platform for the design and synthesis of gemini cationic LCs which offers excellent structure control. As expected, the thermotropic LC properties of these new amphilphilic, gemini ionic LCs were found to be strongly influenced by the length of the spacer between the imidazolium units, the length of the pendant alkyl tails, and the nature of the anion. Smectic A (SmA) thermotropic LC phases were observed in more than half of the gemini imidazolium LC systems studied.     

Spatial updating, spatial transients, and regularities of a complex automaton with nonperiodic architecture

We study the dynamics of patterns exhibited by rule 52, a totalistic cellular automaton displaying intricate behaviors and wide regions of active/inactive synchronization patches. Systematic computer simulations involving 2(30) initial configurations reveal that all complexity in this automaton originates from random juxtaposition of a very small number of interfaces delimiting active/inactive patches. Such interfaces are studied with a sidewise spatial updating algorithm. This novel tool allows us to prove that the interfaces found empirically are the only interfaces possible for these periods, independently of the size of the automata. The spatial updating algorithm provides an alternative way to determine the dynamics of automata of arbitrary size, a way of taking into account the complexity of the connections in the lattice.     

Perturbation of Spin Crossover Behavior by Covalent Post‐Synthetic Modification of a Porous Metal–Organic Framework

Covalent post‐synthetic modification is a versatile method for gaining high‐level synthetic control over functionality within porous metal–organic frameworks and for generating new materials not accessible through one‐step framework syntheses. Here we apply this topotactic synthetic approach to a porous spin crossover framework and show through detailed comparison of the structures and properties of the as‐synthesised and covalently modified phases that the modification reaction proceeds quantitatively by a thermally activated single‐crystal‐to‐single‐crystal transformation to yield a material with lowered spin‐switching temperature, decreased lattice cooperativity, and altered color. Structure–function relationships to emerge from this comparison show that the approach provides a new route for tuning spin crossover through control over both outer‐sphere and steric interactions.     

Ultraviolet radiation as a limiting factor in leaf expansion and development

Reductions in leaf growth are a commonly observed response to ultraviolet radiation, but the underlying mechanisms remain poorly defined. This study examined the response of leaves exposed to a UV environment across a range of organizational scales, including leaf expansion rate, epidermal cell size and number, biomechanical properties, leaf–water relations and activity of cell-wall peroxidases. Two experimental approaches were used; Lettuce ( Lactuca sativa L.) plants were propagated under (a) supplementary UV-B (9 kJ m⁻² day⁻¹) in controlled environment (CE) conditions, and (b) field conditions, where plants were placed under three horticultural films with differing UV transmissions. In both experiments, UV-B caused the greatest reductions in leaf expansion and final leaf size, with some reductions attributable to UV-A wavelengths. In supplementary UV-B conditions, adaxial cell size was reduced, while in field plants, both cell size and cell number were lower in an increased UV environment, as was the case with abaxial cells in CE plants. Although leaf turgor and leaf extensibility were not affected by UV wavelengths, breaking strain of leaf tissue was decreased under supplementary UV-B. Cell-wall peroxidase activity was increased in both supplementary UV conditions and in the field, where only a zero UV environment showed no upregulation of cell-wall peroxidase.     

Fluctuations for the Ginzburg-Landau $${\nabla \phi}$$ Interface Model on a Bounded Domain

We study the massless field on \({D_n = D \cap \tfrac{1}{n} \mathbf{Z}^2}\), where \({D \subseteq \mathbf{R}^2}\) is a bounded domain with smooth boundary, with Hamiltonian \({\mathcal {H}(h) = \sum_{x \sim y} \mathcal {V}(h(x) - h(y))}\). The interaction \({\mathcal {V}}\) is assumed to be symmetric and uniformly convex. This is a general model for a (2 + 1)-dimensional effective interface where h represents the height. We take our boundary conditions to be a continuous perturbation of a macroscopic tilt: h(x) = n x · u + f(x) for \({x \in \partial D_n,\,u \in \mathbf{R}^2}\), and f : R ² → R continuous. We prove that the fluctuations of linear functionals of h(x) about the tilt converge in the limit to a Gaussian free field on D, the standard Gaussian with respect to the weighted Dirichlet inner product \({(f,g)_\nabla^\beta = \int_D \sum_i \beta_i \partial_i f_i \partial_i g_i}\) for some explicit β = β(u). In a subsequent article, we will employ the tools developed here to resolve a conjecture of Sheffield that the zero contour lines of h are asymptotically described by SLE(4), a conformally invariant random curve.     

Surface structural evolution during the thermal decomposition of a PdO(101) thin film

We used scanning tunneling microscopy (STM) to characterize PdO(101) thin films grown on Pd(111), and the structural changes that occur during isothermal decomposition. We find that the PdO(101) thin films have high-quality surface structures that are characterized by large, crystalline terraces with low concentrations of point defects. Small domains of single-layer oxide are also present on the top layer of relatively thick PdO(101) films grown at 500 K. The thinner PdO(101) films exhibit negligible quantities of such domains, apparently because new domains agglomerate rapidly as the film thickness decreases. We find that the isothermal decomposition rate of a PdO(101) film at 720 K exhibits an autocatalytic regime in which the rate of oxygen desorption increases as the oxide decomposes. Our STM results demonstrate that reduced sites created during oxide decomposition catalyze further PdO decomposition, and reveal strong kinetic anisotropies in the decomposition. The kinetic anisotropies produce one-dimensional reaction fronts that propagate preferentially along the atomic rows of the PdO(101) surface, resulting in the formation of long chains of reduced sites. We also find that reduced sites promote oxygen recombination in neighboring rows of the Pd(101) structure, causing loops and larger aggregates of reduced sites to form. The promotion of decomposition across the atomic rows can qualitatively explain the autocatalytic desorption kinetics. Finally, the STM images provide evidence that underlying PdO(101) layers transfer oxygen to reduced surface domains, thus producing large domains of PdO(101) islands that coexist with reduced domains as well as the larger PdO(101) terraces of the initial surface. Re-oxidation of the surface acts to sustain the autocatalytic decomposition kinetics, and provides a mechanism for oxygen atoms to ultimately evolve from the subsurface of the PdO(101) film.     

Stop coannihilation in the CMSSM and SubGUT models

Stop coannihilation may bring the relic density of heavy supersymmetric dark matter particles into the range allowed by cosmology. The efficiency of this process is enhanced by stop-antistop annihilations into the longitudinal (Goldstone) modes of the W and Z bosons, as well as by Sommerfeld enhancement of stop annihilations and the effects of bound states. Since the couplings of the stops to the Goldstone modes are proportional to the trilinear soft supersymmetry-breaking A-terms, these annihilations are enhanced when the A-terms are large. However, the Higgs mass may be reduced below the measured value if the A-terms are too large. Unfortunately, the interpretation of this constraint on the stop coannihilation strip is clouded by differences between the available Higgs mass calculators. For our study, we use as our default calculator FeynHiggs 2.13.0, the most recent publicly available version of this code. Exploring the CMSSM parameter space, we find that along the stop coannihilation strip the masses of the stops are severely split by the large A-terms. This suppresses the Higgs mass drastically for \(\mu \) and \(A_0 > 0\), whilst the extent of the stop coannihilation strip is limited for \(A_0 < 0\) and either sign of \(\mu \). However, in sub-GUT models, reduced renormalization-group running mitigates the effect of the large A-terms, allowing larger LSP masses to be consistent with the Higgs mass calculation. We give examples where the dark matter particle mass may reach \(\gtrsim 8\) TeV.     

On the imaginary parts of chromatic roots

While much attention has been directed to the maximum modulus and maximum real part of chromatic roots of graphs of order $n$ (ie, with $n$ vertices), relatively little is known about the maximum imaginary part of such graphs. We prove that the maximum imaginary part can grow linearly in the order of the graph. We also show that for any fixed $\text{◂+▸}p\in \left(0,1\right)$, almost every random graph $G$ in the Erdös-Rényi model has a nonreal root.     

A novel single particle study of steam gasification kinetics of a coal-derived char at high temperatures and pressures

A novel single particle experiment was developed to allow for detailed char gasification measurements in pure steam at temperatures from 1000 °C to 1400  °C and pressures from 1  bar to 15  bar. A coal-derived activated carbon was thoroughly characterized with respect to its composition, physical structure, and reactivity revealing properties consistent with chars reported in the literature. The single particle approach allowed for the boundary and initial conditions to be well known and for the mass of the particle to be accurately measured before and after testing to provide high-quality conversion data. The resulting conversion data were analyzed using the random pore model and the shrinking core model, of which the random pore model provided the best fit. Apparent activation energies were calculated using the random pore model which provided values ranging from 57.1 kJ/mol to 129 kJ/mol which are nominally half of the magnitude of the values reported in the literature under kinetically controlled conditions, thus demonstrating that regime II conditions were present. Additionally, the activation energies decreased with increasing temperature further demonstrating the presence of regime II conditions. The calculated reaction order ranged from 0 to 0.5 and decreased with increasing pressure agreeing well with literature values and trends.