Fluorescence imaging has been shown to be a potential complement to visual inspection for demarcation of basal cell carcinoma (BCC), which is the most common type of skin cancer. Earlier studies have shown promising results when combining autofluorescence with protoporphyrin IX (Pp IX) fluorescence, induced by application of -5-aminolaevulinic acid (ALA). In this work, we have tried to further improve the ability of this technique to discriminate between areas of tumor and normal skin by implementing texture analysis and Fisher linear discrimination (FLD) on bispectral fluorescence data of BCCs located on the face. Classification maps of the lesions have been obtained from histopathologic mapping of the excised tumors. The contrast feature obtained from co-occurrence matrices was found to provide useful information, particularly for the ALA-induced Pp IX fluorescence data. Moreover, the neighborhood average features of both autofluorescence and Pp IX fluorescence were preferentially included in the analysis. The algorithm was trained by using a training set of images with good agreement with histopathology, which improved the discriminability of the validation set. In addition, cross validation of the training set showed good discriminability. Our results imply that FLD and texture analysis are preferential for correlation between bispectral fluorescence images and the histopathologic extension of the tumors.
The demand for fast and effective tools for diagnosis of skin
cancer is increasing due to the escalating incidence of skin
cancer in recent years. Fluorescence imaging has gained rising
interest for detection and delineation of basal cell carcinoma
(BCC), which is the most common type of skin cancer. By applying
delta-5-aminolaevulinic acid (ALA) protoporphyrin IX (Pp IX) is
accumulated in the tumour; hence, the Pp IX can be used as a
fluorescent marker for tumours. More information may be obtained
by combining the ALA induced fluorescence with fluorescence
without externally applied fluorophore, so called
autofluorescence. In this work we present a method for demarcation
of BCC, using a non-expensive multispectral imaging set up
assisted by image warping for image alignment. To calibrate the
method, histopathological mapping has been carried out by excising
the tumours with Mohs micrographic surgery. The Z-images,
combining information of autofluorescence and ALA induced
fluorescence, showed good agreement with the histopathological
mapping of BCCs located on the face in 5 out of 12 patients and
partial agreement in 7 patients. Since the face is an area where
demarcation of tumours usually is considered difficult, this
result shows a potential for the method as a pre-operative guiding
tool for this type of skin lesions.
We present in this article some studies of the chemical reactivity of free metal clusters (~8-50 atoms) investigated at single-collision-like conditions in a molecular beam experiment. A beam of clusters is generated with a pulsed laser vaporization source and after expansion into vacuum the cluster beam passes collision cells, in which the clusters can make one or a few collisions with reactive gas molecules. Pure clusters and reaction products are detected with laser ionization and mass spectrometry. A strong size dependence in the reaction probability of N2 with tungsten clusters is observed. When the temperature of the cluster source is lowered from room temperature to 80 K the reactivity increases strongly and N2 adsorbs in a weakly bound molecular state, whereas only a strongly bound dissociative state is stable at room temperature. The reactivity of platinum clusters with O2 is much less size dependent and the reaction probability is high on all investigated sizes. If the PtnOm products pass a second cell containing H2(D2) the number of adsorbed oxygen atoms decreases with increasing H2 pressure. This is explained by formation of water molecules in a catalytic reaction on the surface of the Pt clusters.
Fluorescence imaging has shown a potential for demarcation of basal cell carcinoma (BCC), which is the most common type of skin cancer. The technique is based on imaging the fluorescence from protoporphyrin IX (Pp IX), after application of α-5-aminolevulinic acid (ALA). One limitation with the technique is that it is sensitive for undesired local intensity variations. But it has been shown that by combining autofluorescence, i.e. fluorescence without any externally applied photosensitiser, and the Pp IX fluorescence, higher contrast between tumour and normal skin can be obtained. This has earlier been reported using a laser-based technique allowing for simultaneous recording of autofluorescence
and Pp IX fluorescence. In this work we present a method, using a simple set up for multispectral imaging assisted by computerised image warping. The set up was evaluated investigating 9 patients with histologically verified BCC located in the face. Z-images, defined as the ratio between the autofluorescence and the Pp IX fluorescence images, were obtained and compared to the clinically marked tumour borders. Agreement with the tumour border was found in 8 out
of the 9 patients. These results imply that multispectral fluorescence imaging is a potential diagnostic tool for
demarcation of BCC.
Most knowledge on catalytic reaction mechanisms has up until now been gathered with UHV-based techniques. The extrapolation of such obtained reaction parameters to the pressure range of real application conditions is called the pressure gap. The nonlinear optical technique Second Harmonic Generation (SHG) allows studies covering the whole pressure range between UHV and application pressures. Of special importance for this purpose is the possibility to distinguish coverages of different adsorbates. In this work we show how the application of phase sensitive SHG can be used to determine coverages of different adsorbates in-situ allowing the determination of important reaction parameters. Our choice of reaction is the catalytic water formation on platinum which is already widely investigated in the literature.
The discovery of the fullerenes in 1985 by Kroto, Heath, O'Brien, Curl and Smalley and the development of a method for production of macroscopic amounts in 1990 by Kraetschmer, Lamb, Fostiropoulos and Huffman opened a new area of carbon research with possible production of new materials with unique properties. The field has developed further later on with discoveries of nanotubes, metal filled nanotubes, carbon onions and more recently metal covered fullerenes. All these new discoveries show how cluster science opens approaches to the area of meososcopic physics. The general trend is here in the direction from small to large contrary to the general trend of modern meososcopic physics or micro-electronics where the movement is from large to small. It is especially fascinating how the whole area of fullerene research was initiated by problems in astrophysics. Originally Kraetschmer and Huffman had the intention to explain an observed strong extinction form interstellar dust and produced in experiments special carbon soot with a characteristics optical absorption known as 'the camel hump smoke'. This paper gives a short overview of some of our more recent theoretical work of the electronic properties of C60, metal covered C60 and nanotubes. In addition some results are also presented of optical properties of metal covered C60 as a function of metal coverage.
For in-situ investigations of catalytic reactions with second harmonic generation (SHG) it is necessary to distinguish the adsorbate induced signal due to the presence of different species. A further requirement is the quantitative determination of coverages of the reactants and products. We present in this work, how one can distinguish different adsorbates by the use of phase sensitive signal detection and how their coverages can be determined. It turns out that the relative sensitivity for the adsorbates can be varied by changing the azimuthal angle of the sample. Systematic SHG studies of the effect of coadsorbing oxygen and hydrogen show that nonlocal effects are influencing the SHG signal strongly. In contrast these nonlocal effects are negligible during experiments using only one adsorbate. The coadsorption studies are carried out under controlled UHV conditions at a temperature of T equals 100 K. At such low temperatures no reaction between the adsorbates occurs. The experiments are necessary to calibrate the SHG signal to varying coverages of the reactants coadsorbed for the later use during the in-situ study of the catalytical reaction H2 PLU 1/2O2 yields H2O.
We have used the planar laser induced fluorescence, PLIF, technique to study the OH concentration distributions outside a catalytic surface at different pressures and gas compositions. In the experiments a flow of hydrogen and oxygen at a total pressure of 0.2 - 1 Torr is directed towards a platinum foil, which is resistively heated to 1300 K. OH radicals are formed on the catalyst surface as an intermediate in the 2H2 + O2 yields 2H2O reaction. A small fraction of the OH radicals desorb to the gas phase, instead of reacting with adsorbed H atoms to form H2O. These desorbed radicals are detected with the PLIF technique in a region 1 - 6 mm from the surface, i.e., spatial distribution patterns are obtained. The recorded fluorescence patterns are corrected for laser beam intensity variations. The corrected patterns are used to determine the relative OH concentration distributions outside the surface at different pressures and gas compositions. The recorded fluorescence patterns from different transitions are used to determine rotational temperature distributions. The measurements are compared with results from a computer model that simulates the laminar stagnation point flow of hydrogen and oxygen on the catalyst. The model includes both gas phase reactions and surface reactions. The relative amount of OH radicals as function of the distance from the platinum foil and gas temperatures with the simulated temperature profiles we found that the gas phase temperature can not be calculated assuming continuity in the temperature over the gas-surface boundary.
The size-dependent reactivity of several transition-metal clusters: Con, Nbn, Rhn, and Wn with CO has been investigated in a cluster beam experiment. The reactions occur at single-collision-like conditions and the results are evaluated in terms of the reaction probability (S) in a collision. For all the four metals, clusters with more than 10 - 15 atoms show a high reaction probability, S >= 0.4, rather independent of size. For smaller Nbn and Wn, the reaction probability is lower, and for Nbn, large variations in the CO reactivity are observed in the n equals 8 - 13 range with a distinct minimum at Nb10. Using an LCAO approach within the local spin density approximation (LSDA) the adsorption of molecular CO on Nbn has also been investigated theoretically. The geometries of the bare clusters were optimized and two different sites for CO were investigated. The discussion is based on a detailed analysis of Nb4. The calculations show that compact structures with high coordination numbers are the most stable ones for the bare Nb clusters and hollow sites, also maximizing the coordination, are preferred for CO adsorption. The calculations indicate that a high CO-Nbn bond strength is obtained for clusters with a high density of states close to the Fermi level and for which the HOMO level has a symmetry that allows for an efficient back-donation of electrons to the 2(pi) *-orbital of CO. A particularly low chemisorption energy was calculated for the Nb10 cluster.
After the development of a method for macroscopic production of fullerenes, in particular the C60 molecule, a lot of attention has been given to the optical and collective properties of C60 in gas phase, solid and film. The more recent development in fullerene related research is the synthesis of coaxial carbon sheets, usually referred to as carbon tubes or nano tubes. Also spherical concentric graphitic shells called carbon onions have made the field still more exciting and opened the doorway to a new area of materials science. In this work we present how a model based on classical electrodynamics can be used to describe the collective dynamics of electrons in these systems and give insight into the most important physics. We demonstrate the existence of a rich spectrum of collective resonances for both carbon onions and carbon tubes. Evaluated polarizability, oscillator strength distributions, and the EELS loss function are compared to available experimental data and other theoretical studies for especially C60.
Ground state local density calculations have been performed to evaluate the free response of the wavelength dependent microscopic nonlinear polarizabilities (gamma) (3)(-3(omega) ;(omega) ,(omega) ,(omega) ), for the C60 molecule and the macroscopic susceptibilities (chi) (3)(-3(omega) ;(omega) ,(omega) ,(omega) ) i.e. Third Harmonic Generation, for films using a sum-over-states approach. The influence of screening was determined by applying an external static electric field in separate self-consistent calculations to evaluate the induced dipole moment which was used to determine the static linear and nonlinear polarizabilities. The polarizabilities calculated in the static limit were used to determine effective screening parameters which were in turn used together with an RPA approach to calculate screened wave-dispersed, third-order nonlinear optical properties such as (gamma) (3)(-3(omega) ;(omega) ,(omega) ,(omega) ) and (chi) (3)(-3(omega) ;(omega) ,(omega) ,(omega) ). Inclusion of screening results in susceptibilities about two orders of magnitude below the experimental values.
The discovery in 1985 by Kroto, Heath, O'Brien, Curl and Smalley of the existence of a new form of carbon known as Buckminsterfullerene or C60 initiated a new field of carbon research. The development of the field was however rather limited and it was not until Kratschmer, Lamb, Fostiropoulos and Huffman developed a technique for production of macroscopic amounts that a number of new applications became possible. Originally Kratschmer and Huffman had the intention to explain an observed strong extinction from interstellar dust and produced a special carbon soot with a characteristic optical absorption known as `the camel hump smoke'. The observed absorption was in rather good agreement with excitation energies and oscillator strengths for C60 evaluated by Larsson, Volosov and Rosen (one of the authors) in 1987, using the semi-empirical CNDO/S-CI method. This good agreement seems to have encouraged Kratschmer and Huffman to continue with the development of the technique. This paper gives a historical overview and a presentation of recent calculations of optical spectra for C60 in the gas phase and the dielectric constants for films of C60 with a comparison with experimental data.
When applying the differential optical absorption spectroscopy (DOAS) technique for in-situ monitoring of flue-gas emissions, two main problems may occur in comparison to the atmospheric monitoring DOAS application. The first problem is due to the high and variable temperatures of flue gases, which significantly affects the magnitude of the differential absorption cross-sections. The second problem is caused by the limited choice of optical path- lengths, causing non-linearity effects due to large gas absorption. Measurements of the differential absorption cross-sections for NO, NO2, and SO2 have therefore been performed in a pyrex-glass cell contained in a heat-pipe, at temperatures between 20 and 400 degree(s)C, in the wavelength range of 205 to 440 nm. We also have performed measurements of the linear regions of the technique for measurements of SO2, NO2, and NO. The linear regions were shown to be 1 - 3200 mgm-2 for NO2, 0 - 2000 mgm-2 for SO2, and 0 - 120 mgm-2 for NO, in the spectral resolution range between 0.2 to 0.95 nm. The differential absorption cross-sections of NO2 and SO2 are strongly temperature dependent causing considerable errors in evaluated concentrations when using the DOAS technique. The relative errors due to temperature were of the order of 70% for SO2 and NO2 and of the order of 15% for NO at 400 degree(s)C.
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