Spin coupling around a carbon atom vacancy in graphene

We investigate the details of the electronic structure in the neighborhoods of a carbon atom vacancy in graphene by employing magnetization-constrained density-functional theory on periodic slabs, and spin-exact, multi-reference, second-order perturbation theory on a finite cluster. The picture that emerges is that of two local magnetic moments (one \pi-like and one \sigma-like) decoupled from the \pi- band and coupled to each other. We find that the ground state is a triplet with a planar equilibrium geometry where an apical C atom opposes a pentagonal ring. This state lies ~0.2 eV lower in energy than the open-shell singlet with one spin flipped, which is a bistable system with two equivalent equilibrium lattice configurations (for the apical C atom above or below the lattice plane) and a barrier ~0.1 eV high separating them. Accordingly, a bare carbon-atom vacancy is predicted to be a spin-one paramagnetic species, but spin-half paramagnetism can be accommodated if binding to foreign species, ripples, coupling to a substrate, or doping are taken into account

Disorder in La1-xBa1+xGaO4-x/2 ionic conductor: resolving Pair Distribution Function through inside from first principles modeling

Ionic conduction in dry LaBaGaO4 occurs through the vacant oxygen sites formed by the substitution of Ba for La. The resulting La1 12xBa1+xGaO4 12x/2 solid solution shows significant disorder characteristics. The local structure of compositions x = 0, 0.20 and 0.30 was studied using the pair distribution function (PDF). Unfortunately, increasing peak overlap and the number of independent structural parameters make PDF modeling challenging when dealing with low-symmetry phases. To overcome this problem, density functional theory (DFT) was employed to create different structural models, each one with a different relative position for the substitutional Ba ion with respect to the oxygen vacancy. The atomic distributions generated by DFT were used as a starting point to refine experimental PDF data. All models result in the formation of Ga2O7 dimers, with their major axis oriented along the c axis. At the local scale, the most stable DFT model also provides the best fit of the PDF. This accounts for the dopant as first and second neighbors of the vacancy and of the O bridge in the dimer, suggesting that substitutional barium ions act as pinning centers for oxygen vacancies. Above 6 \uc5 the average orthorhombic structure fits the PDF better than the DFT models, thus indicating that Ga2O7 dimers are not correlated with each other to form extended ordered structures. The combination of DFT simulations and X-ray diffraction/PDF refinements was used successfully to model the local atomic structure in La1 12xBa1+xGaO4 12x/2, thus suggesting that this approach could be positively applied in general to disordered systems

EVALUATION OF TRAINING METHODS BY MEANS OF KINEMATIC MEASUREMENTS

INTRODUCTIONAim of this work is the evaluation of different training techniques developed for increasing the hip joint range of motion.The standard technique has been comparedwith a training program based on PNF(Proprioceptive Neuromuscolar Facilitation).The experimental data were acquired by using an electrogoniometer system for its easy application in sport exercices, for its reduced dimensions and weight and for its high sample rate (up to 1000 Hz).The quality of the results has been critically analysed and compared with experimental tests made by using both electrogoniometer and optoelectronic system. MATERIAL AND METHODS The flexion extension movement of hip joint of101 male volunteer students, aged between19 and 23 years, was evaluated before and after a training with PNF. The subjects, fastened to an experimental table in supine position, were asked top erform the maximum hip flexion. The tests consist also on passive movements. Preliminary 'results seem to confirm the adequacy of the training technique but the high dispersion of the results leads the authors to analyse the possible causes related to the phenomena. With this aim further tests have been acquired both with electrogoniometer and with an automated optoelectronic system. The experimental analysis included both planar motion of two hinged bar and athletes movement during the standard test. For these analysis reflective markers where rigidly fixed on the electrogonio meter bases. From the 3Dmarker coordinates the angle (a*) between the electrogoniometer bases has been evaluated and compared with that one obtained by the electrogoniometer output. RESULTS The results of the training program showed that the range of motion of the subjects increases after the PNF technique both for passive and active movements The angle between the bases is evaluated in[1.11in which RCHA and RCHB are the electrogoniometer output data representing the two active channels, a and 8 the angles represented in Fig. I.Fig.I In the evaluation of athlete movements the analysis of the result differences of the two systems adopted leads to these following considerations. For the analysed movement the effect of the goniometer cable torsion seems to be negligible while an incorrect calibration procedure seems to be the main source of errors. In fact in the evaluation of athlete movement the gauges have been zeroed at the initial movement position and not with the basis perfectly aligned. This error can be easily corrected if the relative position of the bases is known by using the [ I .2]where k~ and k~ are the output of the electrogoniometer previously correctly calibrated and then placed on the subjects. Another source of errors may be due to the skin where the bases and consequently the markers are fixed. This effect can be partially solved by using rigid cluster linked to the moving body segment. CONCLUSION This study leads to consider new aspects of the movement evaluation by using electrogoniometer and suggest some practical rules to correct the electrogoniometer acquired data

Diagnostic work-up of arrhythmogenic right ventricular cardiomyopathy by cardiovascular magnetic resonance

Cardiovascular magnetic resonance (CMR) has become a widespread diagnostic tool. Since its introduction, CMR has been used to image patients with a known or suspected arrhythmogenic right ventricular cardiomyopathy (ARVC). Several abnormalities have been found and described by CMR and at present this diagnostic tool is considered very important for the diagnosis. However, the diagnosis of ARVC relies upon the fulfillment of both clinical and functional criteria and CMR can provide several but not all the information useful for the diagnosis. Furthermore, some findings such as evidence of right ventricular epicardial fat, once considered a peculiar marker of ARVC, have been shown to possess a low specificity. This document was prepared by representatives of the three Italian official Organizations involved in CMR. Its main scope is to highlight the problems encountered when studying patients with suspected ARVC at CMR, to indicate the basic technical equipment needed, to recommend a proper imaging protocol and to offer a consensus on the main features relevant for the diagnosis

On the character degree graph of finite groups

Given a finite group G, let cd (G) denote the set of degrees of the irreducible complex characters of G. The character degree graph of G is defined as the simple undirected graph whose vertices are the prime divisors of the numbers in cd (G) , two distinct vertices p and q being adjacent if and only if pq divides some number in cd (G). In this paper, we consider the complement of the character degree graph, and we characterize the finite groups for which this complement graph is not bipartite. This extends the analysis of Akhlaghi et al. (Proc Am Math Soc 146:1505\u20131513, 2018), where the solvable case was treated

Few simple rules governing hydrogenation of graphene dots

We investigated binding of hydrogen atoms to small Polycyclic Aromatic Hydrocarbons (PAHs) - i.e. graphene dots with hydrogen-terminated edges - using density functional theory and correlated wavefunction techniques. We considered a number of PAHs with 3 to 7 hexagonal rings and computed binding energies for most of the symmetry unique sites, along with the minimum energy paths for significant cases. The chosen PAHs are small enough to not present radical character at their edges, yet show a clear preference for adsorption at the edge sites which can be attributed to electronic effects. We show how the results, as obtained at different level of theory, can be rationalized in detail with the help of few simple concepts derivable from a tight-binding model of the $\pi$ electrons

Hydrogen Recombination and Dimer Formation on Graphite from Ab Initio Molecular Dynamics Simulations

We studied Eley-Rideal molecular hydrogen formation on graphite using ab initio molecular dynamics, in the energy range relevant for the chemistry of the interstellar medium and for terrestrial experiments employing cold plasma (0.02-1 eV). We found substantial projectile steering effects that prevent dimer formation at low energies, thereby ruling out any catalytic synthetic pathways that form hydrogen molecules. Ortho and para dimers do form efficiently thanks to preferential sticking, but only at energies that are too high to be relevant for the chemistry of the interstellar medium. Computed reaction cross sections and ro-vibrational product populations are in good agreement with available experimental data and capable of generating adsorbate configurations similar to those observed with scanning tunneling microscopy techniques

Density functional investigations of defect induced mid-gap states in graphane

We have carried out ab initio electronic structure calculations on graphane (hydrogenated graphene) with single and double vacancy defects. Our analysis of the density of states reveal that such vacancies induce the mid gap states and modify the band gap. The induced states are due to the unpaired electrons on carbon atoms. Interestingly the placement and the number of such states is found to be sensitive to the distance between the vacancies. Furthermore we also found that in most of the cases the vacancies induce a local magnetic moment.Comment: 15 page