Electronic structure of triangular, hexagonal and round graphene flakes near the Fermi level

The electronic shell structure of triangular, hexagonal and round graphene quantum dots (flakes) near the Fermi level has been studied using a tight-binding method. The results show that close to the Fermi level the shell structure of a triangular flake is that of free massless particles, and that triangles with an armchair edge show an additional sequence of levels ("ghost states"). These levels result from the graphene band structure and the plane wave solution of the wave equation, and they are absent for triangles with an zigzag edge. All zigzag triangles exhibit a prominent edge state at the Fermi level, and few low-energy conduction electron states occur both in triangular and hexagonal flakes due to symmetry reasons. Armchair triangles can be used as building blocks for other types of flakes that support the ghost states. Edge roughness has only a small effect on the level structure of the triangular flakes, but the effect is considerably enhanced in the other types of flakes. In round flakes, the states near the Fermi level depend strongly on the flake radius, and they are always localized on the zigzag parts of the edge

The coronal line regions of planetary nebulae NGC6302 and NGC6537: 3-13um grating and echelle spectroscopy

We report on advances in the study of the cores of NGC6302 and NGC6537 using infrared grating and echelle spectroscopy. In NGC6302, emission lines from species spanning a large range of ionization potential, and in particular [SiIX]3.934um, are interpreted using photoionization models (including CLOUDY), which allow us to reestimate the central star's temperature to be about 250000K. All of the detected lines are consistent with this value, except for [AlV] and [AlVI]. Aluminium is found to be depleted to one hundredth of the solar abundance, which provides further evidence for some dust being mixed with the highly ionized gas (with photons harder than 154eV). A similar depletion pattern is observed in NGC6537. Echelle spectroscopy of IR coronal ions in NGC6302 reveals a stratified structure in ionization potential, which confirms photoionization to be the dominant ionization mechanism. The lines are narrow (< 22km/s FWHM), with no evidence of the broad wings found in optical lines from species with similar ionization potentials, such as [NeV]3426A. We note the absence of a hot bubble, or a wind blown bipolar cavity filled with a hot plasma, at least on 1'' and 10km/s scales. We also provide accurate new wavelengths for several of the infrared coronal lines observed with the echelle.Comment: Accepted for publication in MNRA

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. III - Further observations of NGC 5548 at optical wavelengths

The results of the second year of an intensive ground-based spectroscopic and photometric study of variability in the bright Seyfert 1 galaxy NGC 5548 are reported in order to study the relationship between continuum and emission-line variability. Relative to the first year of the monitoring program, the nucleus of NGC 5548 was considerably fainter and the continuum variations slower during the second year, but the continuum H-beta cross-correlation results for the two years are nearly identical. The variations in the broad H-beta emission-line lag behind those in the continuum by somewhat less than 20 days, as concluded from the first year's dat

Prediction of function in daily life following multidisciplinary rehabilitation for individuals with chronic musculoskeletal pain; a prospective study

Background: The prevalence of chronic musculoskeletal pain is high, with widespread negative economic, psychological, and social consequences for the individual. It is therefore important to find ways to predict the outcome of rehabilitation programmes in terms of function in daily life. The aims of this study were to investigate the improvements over time from multidisciplinary rehabilitation in terms of pain and function, and analyse the relative impact of individual and psychosocial factors as predictors of function in daily life in individuals with chronic musculoskeletal pain. Methods: A prospective study was conducted among one hundred and forty three (N = 143) musculoskeletal pain patients. Measures of pain, function, and functional health status were obtained at baseline, after 5 weeks of intensive training, at the end of the 57-week rehabilitation programme, and at a 1 year follow-up, using validated self-administrated measures. Linear regression analysis was applied to investigate the relative impact of musculoskeletal pain, individual- , and psychosocial factors in function. Results: The participants studied showed a significant increase in function during the 57 weeks rehabilitation period. There was also a significant increase in function from the end of the rehabilitation period (57th week) to the one year follow-up measures. Pain intensity associated significantly with pain experience over all measurement periods. High levels of pain intensity (β = .42**) and pain experience (β = .37*), and poor psychological capacity (β = -.68*) at baseline, as well as poor physiological capacity (β = -.44**) and high levels of anxiety (β = .48**) and depression (β = .58***) at the end of the rehabilitation program were the most important prognostic factors of variance in functioning over the 4 measurement periods. Conclusion: The data suggest that physical capacity, emotional distress and coping skills should be priority areas in rehabilitation programmes to improve functioning in daily life

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. IV - Intensity variations of the optical emission lines of NGC 5548

Measurements of optical emission-line flux variations based on spectra of the Seyfert galaxy NGC 5548 obtained between December 1988 and October 1989 are reported. All of the measured optical emission lines, H-alpha, H-beta, H-gamma, He I 5876, and He II 4686, exhibit the same qualitative behavior as the UV and optical continua, but with short time delays, or lags, which are different for the various lines. Cross-correlation analysis is applied to measure the lags between the various lines and the continuum. Similar lags are found with respect to the UV continuum for H-alpha and H-beta, 17 and 19 d, respectively. The lag for H-gamma is shorter (13 d), only somewhat larger than the lag measured for Ly-alpha (about 10 d). The helium lines respond to continuum variations more rapidly than the hydrogen lines, with lags of about 7 d for He II 4686 and 11 d for He I 5876.Astronom