A Computational Treatment of 35 IPR Isomers of C88

Abstract

The complete sets of 35 isolated-pentagon-rule (IPR) isomers of C₈₈ is described by the SAM1 (Semi-Ab-initio Model 1) quantum-chemical method. The separation energetics is also computed at the HF/STO-3G, HF/3-21G, and HF/4-31G levels. The SAM1 and HF/4-31G data mostly agree within a few kJ/mol. As the SAM1 energetics does not reproduce the recent NMR observations, entropy contributions are included, too, being based on the harmonic-oscillator and rigid-rotator model. Considerable temperature effects on the relative stabilities in the system are found. The ground-state structure of C₈₈ is a C ₃ isomer, however, with an increase of temperature a C ₂ structure becomes important. At still higher temperatures a near C ₂ species is dominant. The results can be viewed as a good agreement with the available observations, and they further expand the family of the IPR sets where the thermodynamic equilibrium treatment allows for a satisfactory support of observations.     

Calculations of the water-dimer encapsulations into C84

The water-dimer formation and its encapsulation into D₂(22)-C₈₄ and D_2d(23)-C₈₄ fullerenes is evaluated. The water-dimer populations are computed using the potential-energy change from the G3 theory and anharmonic partition functions from the MP2/AUG-cc-pVQZ approach. The encapsulation energetics is treated at the M06-2X/6-31++G** level and it is found that the water-dimer storage in C₈₄ is attractive, yielding an energy gain of more than 10 kcal mol^?1. This substantial encapsulation energy together with the computed temperature increase of the water-dimer population in the saturated steam suggests that the (H₂O)₂@C₈₄ endohedrals could be produced in a high-temperature/high-pressure approach similarly to encapsulation of rare gases in fullerenes.     

Evaluation of the relative stabilities of two non-IPR isomers of Sm@C76

Density-functional theory calculations are presented for two low-energy Sm@C₇₆ isomers with the isolated-pentagon rule (IPR) violating cages. The relative isomeric populations at high temperatures are evaluated using the calculated molecular terms and relationships to observations are discussed. It is shown that the observed Sm@C_2v(19138)-C₇₆ species can be computed as the major isomer if the encapsulate motions are treated as relatively restricted. With the restriction conjecture, the major isomer is about two times more populated than the minor Sm@C₁(17459)-C₇₆ endohedral. The study points out the importance of symmetry considerations in stability evaluations for general nanocarbons.     

Solution‐Based Processing of Optoelectronically Active Indium Selenide

Layered indium selenide (InSe) presents unique properties for high‐performance electronic and optoelectronic device applications. However, efforts to process InSe using traditional liquid phase exfoliation methods based on surfactant‐assisted aqueous dispersions or organic solvents with high boiling points compromise electronic properties due to residual surface contamination and chemical degradation. Here, these limitations are overcome by utilizing a surfactant‐free, low boiling point, deoxygenated cosolvent system. The resulting InSe flakes and thin films possess minimal processing residues and are structurally and chemically pristine. When employed in photodetectors, individual InSe nanosheets exhibit a maximum photoresponsivity of ≈5 × 10⁷ A W^?1, which is the highest value of any solution‐processed monolithic semiconductor to date. Furthermore, the surfactant‐free cosolvent system not only stabilizes InSe dispersions but is also amenable to the assembly of electronically percolating InSe flake arrays without posttreatment, which enables the realization of ultrahigh performance thin‐film photodetectors. This surfactant‐free, deoxygenated cosolvent approach can be generalized to other layered materials, thereby presenting additional opportunities for solution‐processed thin‐film electronic and optoelectronic technologies.     

Near‐Stoichiometric Bulk Graphane from Halogenated Graphenes (X = Cl/Br/I) by the Birch Reduction for High Density Energy Storage

Hydrogen is a clean fuel with high specific energy and its handling and storage are important toward fuel cell research. Particularly, high‐density hydrogen storage is crucial for the viability of future hydrogen‐powered devices. This leads to the search for suitable methods; one such option is chemical storage in light materials with large surface areas, such as graphene. Here, the bulk production of graphane by Birch reduction of halogenated (Cl/Br/I) graphene precursors is reported as a potentially scalable procedure. Prior treatment with strong hydrohalic acids is used to remove oxygen‐groups and to substitute these with halogens, resulting in effective hydrogenation. An unprecedented level of hydrogen storage is obtained from the iodinated‐graphene starting material at 7.44 wt%, far above the U.S. Department of Energy's 2020 system target of 5.5 wt% and close to its ultimate 7.5 wt% goal. As the stored hydrogen is chemisorbed on the graphane scaffold it is stable at both room temperature and on atmospheric exposure, where neither temperature control nor pressure regulation is required. Hydrogen may then be desorbed at elevated temperatures above 400 °C.     

An analysis of the non-preemptive mixed-criticality match-up scheduling problem

Many applications have a mixed-criticality nature. They contain tasks with a different criticality, meaning that a task with a lower criticality can be skipped if a task with a higher criticality needs more time to be executed. This paper deals with a mixed-criticality scheduling problem where each task has a criticality given by a positive integer number. The exact processing time of the task is not known. Instead, we use different upper bounds of the processing time for different criticality levels of the schedule. A schedule with different criticality levels is generated off-line, but its on-line execution switches among the criticality levels depending on the actual values of the processing times. The advantage is that after the transient prolongation of a higher criticality task, the system is able to match up with the schedule on a lower criticality level. While using this model, we achieve significant schedule efficiency (assuming that the prolongation of the higher criticality task rarely occurs), and at the same time, we are able to grant a sufficient amount of time to higher criticality tasks (in such cases, some of the lower criticality tasks may be skipped). This paper shows a motivation for the non-preemptive mixed-criticality match-up scheduling problem arising from the area of the communication protocols. Using a polynomial reduction from the 3-partition problem, we prove the problem to be \(\mathcal {NP}\)-hard in the strong sense even when the release dates and deadlines are dropped and only two criticality levels are considered.     

Use of partial least squares within the control relevant identification for buildings

Climate changes, diminishing world supplies of non-renewable fuels, as well as economic aspects are probably the most significant driving factors of the current effort to save energy. As buildings account for about 40 % of global final energy use, efficient building climate control can significantly contribute to the saving effort. Predictive building automation can be used to operate buildings in an energy and cost effective manner with minimum retrofitting requirements. In such a predictive control approach, dynamic building models are of crucial importance for a good control performance. An algorithm which has not been used in building modeling yet, namely a combination of minimization of multi-step ahead prediction errors and partial least squares will be investigated. Subsequently, two case studies are presented: the first is an artificial model of a building constructed in Trnsys environment, while the second is a real-life case study. The proposed identification algorithm is then validated and tested.     

A scalable FETI-DP algorithm for a semi-coercive variational inequality

We develop an optimal algorithm for the numerical solution of semi-coercive variational inequalities by combining dual-primal FETI algorithms with recent results for bound and equality constrained quadratic programming problems. The discretized version of the model problem, obtained by using the FETI-DP methodology, is reduced by the duality theory of convex optimization to a quadratic programming problem with bound and equality constraints, which is solved by a new algorithm with a known rate of convergence given in terms of the spectral condition number of the quadratic problem. We present convergence bounds that guarantee the scalability of the algorithm. These results are confirmed by numerical experiments.     

Wavelet-based de-noising techniques in MRI

The paper deals with techniques for the enhancement of magnetic resonance (MR) images using the wavelet analysis, which is assessed from the viewpoint of choosing the mother wavelet and the thresholding technique. Three parameters are used as objective criteria of the quality of image enhancement: the signal-to-noise ratio (SNR), image contrast, and linear approximation of edge steepness. Unlike most of the standard methods, which work exclusively with image magnitude, we also examined the influence of image phase, i.e. the image is processed as a complex signal. In addition to the interpretation of results, a short summary is given that deals with the choice of the optimal mother wavelet and thresholding technique for different types of MR images.     

Practical prediction of creep and shrinkage of high strength concrete

Model for practical prediction of creep and shrinkage of normal strength concrete, developed previously, is extended to high strength concrete. It is found that only a minor adjustment for the concrete strength effect is needed in the formulas for drying creep. The formulas for basic creep and shrinkage need no adjustment. The prediction model is compared with test data for creep and shrinkage obtained recently by Ngab, Nilson and Slate, and by Collepardi, Corradi and Valente, and a satisfactory agreement is demonstrated. The coefficient of variation of the deviations from test data is not larger than that for the normal cient of variation of the deviations from test data is not larger than that for the normal strength range. However, the existing data are rather limited and further testing is desirable.