Arne Rosén

Optical spectrum of the icosahedral C60- “follene-60”

Abstract The electronic structure and spectra of the icosahedral C 60 , “follene-60”, are examined by use of the CNDO/S method. The calculated ionization energy and electron affinity are in accord with experimental results. The first allowed optical transition is at higher energy than calculated previously.

Pain caused by photodynamic therapy of skin cancer

Summary Pain resulting from photodynamic therapy (PDT) of skin cancer was investigated. The study included 69 lesions (60 patients) with different types of skin tumours or precursors. Protoporphyrin IX, which is produced by the topical application of δ‐aminolevulinic acid, was used as a photosensitizing agent. Twenty‐three of the lesions (19 patients) were examined with a fluorescence imaging system which demarcates the tumour area from the healthy skin and visualizes the contrast between the fluorescence from healthy skin and that from the tumour. EMLA® is used on all patients as part of our routine PDT protocol but despite this the major side‐effect of PDT is pain during treatment. There is a large variation in pain intensity experienced by the patients, as measured by a visual analogue scale (VAS). Patients with actinic keratoses experienced more pain than those with Bowens disease or basal cell carcinoma. The mean VAS score was higher when treating lesions located on the head than when treating lesions on the torso or the extremities. Also, treatment of large skin areas resulted in more pain than treatment of small areas, and men experienced more pain than women. The pain experienced by the patients did not correlate with treatment dose, Fitzpatrick skin type, age or fluorescence intensity.

Photodynamic therapy of actinic keratosis at varying fluence rates: assessment of photobleaching, pain and primary clinical outcome

Background  Although photodynamic therapy (PDT) is becoming an important treatment method for skin lesions such as actinic keratosis (AK) and superficial basal cell carcinoma, there are still discussions about which fluence rate and light dose are preferable. Recent studies in rodents have shown that a low fluence rate is preferable due to depletion of oxygen at high fluence rates. However, these results have not yet been verified in humans.

Molecular dynamics study of the catalyst particle size dependence on carbon nanotube growth

The molecular dynamics method, based on an empirical potential energy surface, was used to study the effect of catalyst particle size on the growth mechanism and structure of single-walled carbon nanotubes (SWNTs). The temperature for nanotube nucleation (800-1100 K), which occurs on the surface of the cluster, is similar to that used in catalyst chemical vapor deposition experiments, and the growth mechanism, which is described within the vapor-liquid-solid model, is the same for all cluster sizes studied here (iron clusters containing between 10 and 200 atoms were simulated). Large catalyst particles, which contain at least 20 iron atoms, nucleate SWNTs that have a far better tubular structure than SWNTs nucleated from smaller clusters. In addition, the SWNTs that grow from the larger clusters have diameters that are similar to the cluster diameter, whereas the smaller clusters, which have diameters less than 0.5 nm, nucleate nanotubes that are approximately 0.6-0.7 nm in diameter. This is in agreement with the experimental observations that SWNT diameters are similar to the catalyst particle diameter, and that the narrowest free-standing SWNT is 0.6-0.7 nm.

An experimental study of the kinetics of OH and H2O formation on Pt in the H2 + O2 reaction

We have investigated the kinetics of OH desorption and H2O production on polycrystalline Pt during the H2 + 12O2 → H2O reaction in the pressure range 2–200 mTorr, and temperature interval 900–1300 K. The OH desorption was recorded using laser induced fluorescence. The absolute rate of water production was measured via the dissipated chemical power. Mass spectrometry was used to control the reactant mixtures. The OH production maximum at constant total pressure occurs at a small relative H2 concentration (around 3%–8%) while the H2O production has its maximum in the range of 15%–22% H2, depending on the reaction conditions. With D2 the maximum moves to higher concentrations in proportion to the square root of the mass ratio. Most of these results can be described by a recently developed kinetic model [Hellsing et al., Surface Sci. 189/190 (1987) 851] assuming a Langmuir-Hinshelwood type of reaction, proceeding by sequential addition of atomic hydrogen to atomic oxygen (to form OH), and to hydroxyl (to form H2O), respectively. Approximate values of the high temperature sticking coefficients, SH2(0) = 0.04 and SO2(0) = 0.02 at 1200 K, on the bare surface are derived from the position of the H2O maximum and the absolute water production rate.

Iron-carbide cluster thermal dynamics for catalyzed carbon nanotube growth

Molecular dynamics simulations have been used to study the thermal behavior of FeN−mCm clusters where N, the total number of atoms, extends up to 2400. Comparison of the computed results with experimental data shows that the simulations yield the correct trends for the liquid–solid region of the iron-carbide phase diagram as well as the correct dependence of cluster melting point as a function of cluster size. The calculation indicates that, when carbon nanotubes (CNTs) are grown on large (>3–4 nm) catalyst particles at low temperatures (<1200 K), the catalyst particles are not completely molten. It is argued that the mechanism of CNT growth under these conditions may be governed by the surface melting of the cluster.

Modeling the melting of supported clusters

Molecular dynamics simulations have been used to study the structural and dynamic changes during melting of free and supported iron clusters ranging from 150 to 10000atoms. The results reveal a method for determining effective diameters of supported metal clusters, so that the melting point dependence on cluster size can be predicted in a physically meaningful way by the same analytic model used for free clusters.

Bispectral fluorescence imaging of aggressive basal cell carcinoma combined with histopathological mapping: a preliminary study indicating a possible adjunct to Mohs micrographic surgery

Background  Fluorescence imaging is an attractive diagnostic technique for skin tumour demarcation with potential to move to clinical use. Bispectral fluorescence imaging combines skin autofluorescence with δ‐aminolaevulinic acid‐induced fluorescence. To evaluate the technique, fluorescence data must be compared with the histopathological extent of the tumour, which is the purpose of the current study.

Calculations of the ionization thresholds and electron affinities of the neutral, positively and negatively charged C60—‘‘follene‐60’’

Ionization thresholds and electron affinities are calculated within the local density approximation for the neutral, positively and negatively charged clusters of C60. The evaluated energies are found to be in good agreement with available experimental data.

Geometric and electronic properties of small vanadium clusters: A density functional study

The geometric and electronic properties of vanadium clusters in the range from V2 to V8 have been investigated using the density functional theory, and an LCAO approach for the expansion of the electronic wavefunctions. The optimized low energy isomers are found to be three dimensional for clusters larger than the tetramer, and the evaluated bond dissociation energies, ionization potentials and electron affinities are in good agreement with experimental results. All cluster sizes are found to possess low magnetic moments as ground states, which is in contrast with previous suggestions. In the case of V3− and V4−, a comparison with photo-electron spectra is done by computing the self consistent excitation spectra.