| 1. |
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| 2. |
- Andersson, Mats, 1963, et al.
(author)
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Adsorption and reactions of O2 and D2 on small free palladium clusters in a cluster-molecule scattering experiment
- 2010
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In: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 22:33, s. 334223-
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Journal article (peer-reviewed)abstract
- The adsorption of oxygen and hydrogen (deuterium) on small neutral palladium clusters was investigated in a cluster beam experiment. The beam passes through two low-pressure reaction cells, and the clusters, with and without adsorbed molecules, are detected using laser ionization and mass spectrometry. Both H2 and O2 adsorb efficiently on the palladium clusters with only moderate variations with cluster size in the investigated range, i.e. between 8 and 28 atoms. The co-adsorption of H2 and O2 results in the formation of H2O, detected as a decrease in the number of adsorbed oxygen atoms with an increasing number of collisions with H2 molecules. A comparison is done with an earlier similar study of clusters of Pt. Furthermore a comparison is done with what is known for sticking and reactivity of surfaces.
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| 3. |
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| 4. |
- Bender, Johanna, 1975, et al.
(author)
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Lipid cubic phases for improved topical drug delivery in photodynamic therapy.
- 2005
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In: Journal of Controlled Release. - : Elsevier BV. - 0168-3659 .- 1873-4995. ; 106:3, s. 350-360
-
Journal article (peer-reviewed)abstract
- We have evaluated the efficacy of lipid cubic phases, highly ordered self-assembly systems on the nanometer level, as drug delivery vehicles for in vivo topical administration of delta-aminolevulinic acid (ALA) and its methyl ester (m-ALA) on nude mice skin. ALA, a precursor of heme, induces the production of the photosensitizer protoporphyrin IX (PpIX) in living tissue. Measuring the PpIX fluorescence at the skin surface, after topical administration, makes indirect quantification of the penetration of ALA into the tissue possible. Cubic phases were formed of lipid (monoolein or phytantriol), water and drug. In some cases, propylene glycol was included in the cubic phase as well. The drug concentration was 3% (w/w, based on the total sample weight) in all investigated vehicles. When the formulations were applied for 1 h, the monoolein cubic systems and the three-component phytantriol sample showed higher fluorescence compared to the standard ointment during the 10 h of measurement. Both ALA and m-ALA yielded similar results, although the differences between the investigated vehicles were more pronounced when using m-ALA. For the 24-h applications, the monoolein cubic systems with m-ALA showed faster PpIX formation than the standard ointment, implying higher PpIX levels at short application times (less than 4 h). The systemic PpIX fluorescence of ALA was elevated by using the lipid cubic formulations. Notably, a small systemic effect was also observed for the monoolein cubic sample with m-ALA. These results imply improved PpIX formation when using the lipid cubic systems, most probably due to enhanced drug penetration.
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| 5. |
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| 6. |
- Bolton, Kim, 1964, et al.
(author)
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Atomistic simulations of catalyzed carbon nanotube growth
- 2006
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In: JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY. - : American Scientific Publishers. - 1533-4880 .- 0000-0000. ; 6:5, s. 1211-1224
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Journal article (peer-reviewed)abstract
- We review the advances made in understanding the mechanism of catalyzed carbon nanotube growth, with the main focus on direct dynamics and molecular dynamics studies of single-walled carbon nanotube (SWNT) growth. These studies have deepened our understanding of the catalytic SWNT nucleation and growth mechanisms, but more accurate and efficient methods are required for a complete investigation at experimental growth conditions.
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| 7. |
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| 8. |
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| 9. |
- Claeson, Magdalena, 1976, et al.
(author)
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Incidence of cutaneous melanoma in Western Sweden, 1970-2007.
- 2012
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In: Melanoma research. - 1473-5636. ; 22:5, s. 392-8
-
Journal article (peer-reviewed)abstract
- The aim of this study was to describe the increasing incidence of cutaneous malignant melanoma (CMM) in Western Sweden during the period 1970-2007. A secondary aim was to show a geographical variation in incidence between coastal and inland areas, considering the effects of the local average duration of sunshine, and the sun exposure-related behavior in the populations. The Swedish Cancer Registry provided data on invasive melanomas during 1970-2007. Meteorological maps showed the annual average duration of sunshine during 1961-1990. A survey from 2007 with 2871 participants, carried out by the National Board of Health and Welfare, provided data on self-reported sun exposure. During the period studied, the age-standardized incidence for men in Western Sweden more than quadrupled to 31.1/100 000 inhabitants, whereas it tripled for women to 27.1/100 000. Coastal areas, including Gothenburg city, had a high average duration of sunshine (1701-1900 h of sun/year), whereas inland areas had lower average duration of sunshine (≤1700 h). The incidence of CMM was higher in coastal areas and in Gothenburg city, compared with inland areas. This may be linked to ultraviolet radiation, a consequence of the higher average duration of sunshine. The sun exposure survey showed additional factors, which possibly led to the increased incidence, for example high sun exposure on holidays abroad. The alarming increase in the incidence of CMM in Western Sweden, during the period 1970-2007, shows the need for additional primary preventive measures, for example sun protection programs targeted at populations in this area.
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| 10. |
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| 11. |
- Claeson, Magdalena, 1976, et al.
(author)
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Modelling the Future: System Dynamics in the Cutaneous Malignant Melanoma Care Pathway
- 2016
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In: Acta dermato-venereologica. - : Medical Journals Sweden AB. - 1651-2057 .- 0001-5555. ; 96:2, s. 181-185
-
Journal article (peer-reviewed)abstract
- Incidence rates for cutaneous malignant melanoma are increasing worldwide. Estimates of the future number of melanoma cases are important for strategic planning of the care pathway. The aim of this study was to use system dynamics modelling to evaluate the long-term effects of changes in incidence, population growth and preventive interventions. Historical data on invasive melanoma cases in Western Sweden from 1990 to 2006 were obtained. Using computer simulation software, a model estimating the accumulated number of melanoma cases for 2014 to 2023 was developed. Five future scenarios were designed: stable incidence, business-as-usual, 25% reduced patient's delay, 50% reduced doctor's delay, and a combination of the last 2, called improved overall secondary prevention. After 10 years, improved overall secondary prevention would have resulted in a 42% decrease in melanomas >4 mm and a 10% increase in melanomas ≤1 mm, compared with business-as-usual. System dynamics is a valuable tool, which can help policymakers choose the preventive interventions with the greatest impact.
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| 12. |
- Claeson, Magdalena, 1976, et al.
(author)
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Multiple primary melanomas in Western Sweden; 1990-2013
- 2016
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In: 3rd International Conference on UV and Skin Cancer Prevention, Melbourne.
-
Conference paper (other academic/artistic)abstract
- IntroductionIn Sweden, the incidence of cutaneous malignant melanoma rises yearly with 5.5% for men and 5.2% for women and has now reached world standard rates of 17.6 for men and 18.8 for women per 100,000 population. Over the past decades, the incidence of melanoma has been higher in Western Sweden than the national average. Previous international studies have shown that melanoma patients have an elevated risk of developing a new separate primary melanoma. This study aimed at describing multiple primary melanomas (MPMs) in Western Sweden with focus on the number of tumours detected, tumour characteristics and the time to diagnosis of a subsequent melanoma.MethodsData was extracted retrospectively from the Swedish Melanoma Registry and provided information on all invasive and in situ melanoma cases in Western Sweden (1.6 million inhabitants) from 1990 to 2013. Results Within the studied period, 12,152 patients developed 13,291 melanomas. 11,254 of the patients developed only a single primary melanoma. In total, 898 patients (7.4% of all melanoma patients) developed 2,037 MPMs. Preliminary results show that the median Breslow thickness for all invasive melanomas was below 1 mm. The median Breslow thickness for the MPMs was slightly thinner for the second and third invasive melanoma as compared to the first invasive melanoma. Further, there was a higher percentage of in situ tumours among the subsequent melanomas. The median time to diagnosis of a subsequent melanoma was approximately 3 years. DiscussionSubsequent primary melanomas in Western Sweden are most commonly diagnosed with a somewhat thinner Breslow thickness than the first primary melanoma. The comparatively high percentage of melanoma survivors developing MPMs and the short median time to diagnosis of a subsequent melanoma stresses the importance of follow-up for melanoma patients, particularly during the first years.
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| 13. |
- Claeson, Magdalena, 1976, et al.
(author)
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MultiplePrimary Melanomas: A Common Occurrencein Western Sweden.
- 2017
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In: Acta dermato-venereologica. - : Medical Journals Sweden AB. - 1651-2057 .- 0001-5555. ; 97:6, s. 715-719
-
Journal article (peer-reviewed)abstract
- Patients diagnosed with a single primary cutaneous melanoma are at increased risk of developing multiple primary melanomas. The aim of this study is to describe the epidemiology of multiple primary melanomas (invasive and in situ) in Western Sweden. Data from the Swedish Melanoma Registry from 1990 to 2013 revealed that 898 patients (7.4%) developed 2,037 multiple primary lesions and 11,254 patients developed single lesions. The proportion of subsequent lesions that were melanoma in situ was 47%, compared with 26% of first melanomas (p<0.0001). The median time to diagnosis of a subsequent melanoma was 38 months (95% confidence interval (CI), 53-62 months). In total, 49% of subsequent melanomas were detected within 3 years. Patients and physicians should be aware of the high proportion of multiple primary melanomas in Western Sweden, especially during the first years of follow-up.
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| 14. |
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| 15. |
- Ding, Feng, 1970, et al.
(author)
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Graphitic encapsulation of catalyst particles in carbon nanotube production
- 2006
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 110:15, s. 7666-7670
-
Journal article (peer-reviewed)abstract
- A new model is proposed for the encapsulation of catalyst metal particles by graphite layers that are obtained, for example, in low-temperature chemical vapor deposition production of carbon nanotubes (CNTs). In this model graphite layers are primarily formed from the dissolved carbon atoms in the metal-carbide particle when the particle cools. This mechanism is in good agreement with molecular dynamics simulations (which show that precipitated carbon atoms preferentially form graphite sheets instead of CNTs at low temperatures) and experimental results (e.g., encapsulated metal particles are found in low-temperature zones and CNTs in high-temperature regions of production apparatus, very small catalyst particles are generally not encapsulated, and the ratio of the number of graphitic layers to the diameter of the catalyst particle is typically 0.25 nm(-1)).
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| 16. |
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| 17. |
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| 18. |
- Ding, Feng, 1970, et al.
(author)
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Modeling the melting of supported clusters
- 2006
-
In: APPLIED PHYSICS LETTERS. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88:13
-
Journal article (peer-reviewed)abstract
- 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 10 000 atoms. 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.
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| 19. |
- Ding, Feng, 1970, et al.
(author)
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Molecular dynamics study of bamboo-like carbon nanotube nucleation
- 2006
-
In: JOURNAL OF ELECTRONIC MATERIALS. - 0361-5235. ; 35:2, s. 207-210
-
Journal article (peer-reviewed)abstract
- Molecular dynamics (MD) simulations based on an empirical potential energy surface were used to study the nucleation of bamboo-like carbon nanotubes (BCNTs). The simulations reveal that inner walls of the bamboo structure start to nucleate at the junction between the outer nanotube wall and the catalyst particle. In agreement with experimental results, the simulations show that BCNTs nucleate at higher dissolved carbon concentrations (i.e., feedstock pressures) than those where nonbamboo-like carbon nanotubes are nucleated.
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| 20. |
- Ding, Feng, 1970, et al.
(author)
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Molecular dynamics study of SWNT growth on catalyst particles without temperature gradients
- 2006
-
In: COMPUTATIONAL MATERIALS SCIENCE. - : Elsevier BV. - 0927-0256. ; 35:3, s. 243-246
-
Journal article (peer-reviewed)abstract
- A temperature gradient (TG) is often included in the Vapor-Liquid-Solid model to describe catalyzed nucleation and growth of carbon nanotubes (CNTs). Although the TG may be important to describe the growth of large CNTs, it has been suggested that a carbon concentration gradient (CG) is more important for the growth of single-walled carbon nanotubes (SWNTs) on small catalyst particles. The molecular dynamics study performed here shows that the CG is more important than the TG for the growth of SWNTs on small metal particles and that SWNTs growth can, in fact, even occur in the presence of an opposing TG (i.e., the SWNTs grow from the hot region of the catalyst particle). This shows that a TG is not required for SWNT growth on small catalyst particles.
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| 21. |
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| 22. |
- Ding, Feng, 1970, et al.
(author)
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Molecular dynamics study of the surface melting of iron clusters
- 2005
-
In: European Physical Journal D : Atomic, Molecular and Optical Physics. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 34:1-3, s. 275-277
-
Journal article (peer-reviewed)abstract
- Molecular dynamics simulations have been used to study the surface melting of iron clusters. It is found that, even when the temperature is several hundreds of Kelvin below the cluster melting point, the crystalline center of the cluster is surrounded by surface atoms that exhibit large amplitude diffusion from their original positions. This results in surface melting of the cluster.
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| 23. |
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| 24. |
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| 25. |
- Ding, Feng, 1970, et al.
(author)
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Structure and thermal properties of supported catalyst clusters for single-walled carbon nanotube growth
- 2006
-
In: APPLIED SURFACE SCIENCE. - : Elsevier BV. - 0169-4332. ; 252:15, s. 5254-5258
-
Journal article (peer-reviewed)abstract
- Structure and thermal properties of supported iron clusters were studied using molecular dynamics simulations. When supported clusters are in the liquid state, their surfaces have spherical curvature, whereas solid clusters form a layered crystalline structure. The cluster freezing (melting) point increases dramatically with increasing cluster-substrate interaction strength, and rapid diffusion of cluster surface atoms is observed below the freezing point.
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| 26. |
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| 27. |
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| 28. |
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| 29. |
- Duan, Haiming, et al.
(author)
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Initial growth of single-walled carbon nanotubes on supported iron clusters: a molecular dynamics study
- 2007
-
In: EUROPEAN PHYSICAL JOURNAL D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 43:1-3, s. 185-188
-
Journal article (peer-reviewed)abstract
- Molecular dynamics simulations were used to study the initial growth of single-walled carbon nanotubes (SWNTs) on a supported iron cluster (Fe-50). Statistical analysis shows that the growth direction of SWNTs becomes more perpendicular to the substrate over time due to the weak interaction between carbon nanotube and the substrate. The diameter of the nanotube also increases with the simulation time and approaches the size of the supported iron cluster.
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| 30. |
- Duan, Haiming, et al.
(author)
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Size dependent melting mechanisms of iron nanoclusters
- 2007
-
In: CHEMICAL PHYSICS. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 333:1, s. 57-62
-
Journal article (peer-reviewed)abstract
- Molecular dynamics simulations were used to study the change in the mechanism of iron cluster melting with increasing cluster size. Melting of smaller clusters (e.g., Fe-55 and Fe-100) occurs over a large temperature interval where the phase of the cluster repeatedly oscillates between liquid and solid. In contrast, larger clusters (e.g., Fe-300) have sharper melting points with surface melting preceding bulk melting. The importance of the simulation time, the force field and the definition of cluster melting is also discussed.
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| 31. |
- Ericson, Marica B, 1974, et al.
(author)
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Bispectral fluorescence imaging combined with texture analysis and linear discrimination for correlation with histopathologic extent of basal cell carcinoma
- 2005
-
In: Journal of Biomedical Optics. - : SPIE-Intl Soc Optical Eng. - 1083-3668 .- 1560-2281. ; 10:3
-
Journal article (peer-reviewed)abstract
- 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 delta-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.
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| 32. |
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| 33. |
- Ericson, Marica, 1974, et al.
(author)
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Photodynamic therapy of actinic keratosis at varying fluence rates : Assessment of photobleaching, pain and primary clinical outcome
- 2004
-
In: British Journal of Dermatology. - : Oxford University Press (OUP). - 0007-0963 .- 1365-2133. ; 151, s. 1204-1212
-
Journal article (peer-reviewed)abstract
- 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. Objectives: The objective was to investigate the impact of fluence rate and spectral range on primary treatment outcome and bleaching rate in AK using aminolaevulinic acid PDT. In addition, the pain experienced by the patients has been monitored during treatment. Patients/methods Thirty-seven patients (mean age 71 years) with AK located on the head, neck and upper chest were treated with PDT, randomly allocated to four groups: two groups with narrow filter (580-650 nm) and fluence rates of 30 or 45 mW cm-2, and two groups with broad filter (580-690 nm) and fluence rates of 50 or 75 mW cm-2. The total cumulative light dose was 100 J cm-2 in all treatments. Photobleaching was monitored by fluorescence imaging, and pain experienced by the patients was registered by using a visual analogue scale graded from 0 (no pain) to 10 (unbearable pain). The primary treatment outcome was evaluated at a follow-up visit after 7 weeks. Results: Our data showed a significant correlation between fluence rate and initial treatment outcome, where lower fluence rate resulted in favourable treatment response. Moreover, the photo-bleaching dose (1/e) was found to be related to fluence rate, ranging from 4.5 ± 1.0 J cm -2 at 30 mW cm-2, to 7.3 ± 0.7 J cm-2 at 75 mW cm-2, indicating higher oxygen levels in tissue at lower fluence rates. After a cumulative light dose of 40 J cm-2 no further photobleaching took place, implying that higher doses are excessive. No significant difference in pain experienced by the patients during PDT was observed in varying the fluence rate from 30 to 75 mW cm-2. However, the pain was found to be most intense up to a cumulative light dose of 20 J cm-2. Conclusions: Our results imply that the photobleaching rate and primary treatment outcome are dependent on fluence rate, and that a low fluence rate (30 mW cm-2) seems preferable when performing PDT of AK using noncoherent light sources.
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| 34. |
- Gonzalez, Helena, 1971, et al.
(author)
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Photostability of commercial sunscreens upon sun exposure and irradiation by ultraviolet lamps
- 2007
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In: BMC Dermatol. - 1471-5945. ; 7
-
Journal article (peer-reviewed)abstract
- BACKGROUND: Sunscreens are being widely used to reduce exposure to harmful ultraviolet (UV) radiation. The fact that some sunscreens are photounstable has been known for many years. Since the UV-absorbing ingredients of sunscreens may be photounstable, especially in the long wavelength region, it is of great interest to determine their degradation during exposure to UV radiation. Our aim was to investigate the photostability of seven commercial sunscreen products after natural UV exposure (UVnat) and artificial UV exposure (UVart). METHODS: Seven commercial sunscreens were studied with absorption spectroscopy. Sunscreen product, 0.5 mg/cm2, was placed between plates of silica. The area under the curve (AUC) in the spectrum was calculated for UVA (320-400 nm), UVA1 (340-400 nm), UVA2 (320-340 nm) and UVB (290-320 nm) before (AUCbefore) and after (AUCafter) UVart (980 kJ/m2 UVA and 12 kJ/m2 of UVB) and before and after UVnat. If theAUC Index (AUCI), defined as AUCI = AUCafter/AUCbefore, was > 0.80, the sunscreen was considered photostable. RESULTS: Three sunscreens were unstable after 90 min of UVnat; in the UVA range the AUCI was between 0.41 and 0.76. In the UVB range one of these sunscreens was unstable with an AUCI of 0.75 after 90 min. Three sunscreens were photostable after 120 min of UVnat; in the UVA range the AUCI was between 0.85 and 0.99 and in the UVB range between 0.92 and 1.0. One sunscreen showed in the UVA range an AUCI of 0.87 after UVnat but an AUCI of 0.72 after UVart. Five of the sunscreens were stable in the UVB region. CONCLUSION: The present study shows that several sunscreens are photounstable in the UVA range after UVnat and UVart. There is a need for a standardized method to measure photostability, and the photostability should be marked on the sunscreen product.
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| 35. |
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| 36. |
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| 37. |
- Hallberg, Stefan, 1955, et al.
(author)
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Developing a simulation model for the patient pathway of cutaneous malignant melanoma
- 2015
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In: Operations Research for Health Care. - : Elsevier BV. - 2211-6923. ; 6, s. 23-30
-
Journal article (peer-reviewed)abstract
- In this study, a system dynamic simulation model for a part of the patient pathway of cutaneous malignant melanoma was developed. A model was built that produced quantified out-put of diagnosed patients staged by severity, using System dynamic simulation. Data from the Swedish Melanoma Registry were combined with current scientific results and used in this analytical tool. Solutions to how these results are adapted into a simulation are described. The simulation model has the ability to generate alternative quantitative output of patient health in a population corresponding to realistic interventions in health care programmes as well as population and incidence development.
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| 38. |
- Hanstorp, Karl, et al.
(author)
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Numerical Simulation and Experimental Scheme for Monitoring Hoof Wall Structure and Health in Sport Horses
- 2016
-
In: Proceedings of the 4th International Congress on Sport Sciences Research and Technology Support. - : SCITEPRESS - Science and Technology Publications. - 9789897582059 ; , s. 171-175
-
Conference paper (peer-reviewed)abstract
- This study provides a computational model developed to demonstrate the possibility of monitoring hoof structure and health in equestrian sport. This is achieved by employing finite element simulation of threedimensional heat flow from a surface heat source into a hoof structure while simultaneously sensing the surface temperature. The time evolution of the recorded surface temperature, transient curve, is used to investigate hoof structure and predict its intactness by comparing these curves for three different models. We have observed differences between the transient curves obtained from a normal hoof structure, a hoof structure containing a foreign material and hoof capsule subjected to wall separation. An experimental method for probing hoof profile was briefly discussed. It uses temperature sensor/heat source. The method can determine the thermal conductivity of the hoof along the hoof structure from the recorded transient curve. Thus, it displays the hoof structure by utilizing the thermal conductivity variation between the hoof parts.
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| 39. |
- Harutyunyan, Avetik, et al.
(author)
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Hidden features of the catalyst nanoparticles favorable for single-walled carbon nanotube growth
- 2007
-
In: APPLIED PHYSICS LETTERS. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:16
-
Journal article (peer-reviewed)abstract
- Combining in situ studies of the catalyst activity during single-walled carbon nanotube (SWCNT) growth by mass spectrometry with differential scanning calorimetry and Raman spectroscopy results, the authors expose the favorable features of small catalyst for SWCNT growth and their relationship with synthesis parameters. The sequential introduction of C-12 and C-13 labeled hydrocarbon reveals the influence of catalyst composition on its lifetime and the growth termination path. Ab initio and molecular dynamics simulations corroborate "V"-shape liquidus line of metal-carbon nanoparticle binary phase diagram, which explains observed carbon-induced solid-liquid-solid phase transitions during nanotube growth.
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| 40. |
- Hedman, Daniel, et al.
(author)
-
On the Stability and Abundance of Single Walled Carbon Nanotubes
- 2015
-
In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
-
Journal article (peer-reviewed)abstract
- Many nanotechnological applications, using single-walled carbon nanotubes (SWNTs), are only possible with a uniform product. Thus, direct control over the product during chemical vapor deposition (CVD) growth of SWNT is desirable, and much effort has been made towards the ultimate goal of chirality-controlled growth of SWNTs. We have used density functional theory (DFT) to compute the stability of SWNT fragments of all chiralities in the series representing the targeted products for such applications, which we compare to the chiralities of the actual CVD products from all properly analyzed experiments. From this comparison we find that in 84% of the cases the experimental product represents chiralities among the most stable SWNT fragments (within 0.2 eV) from the computations. Our analysis shows that the diameter of the SWNT product is governed by the well-known relation to size of the catalytic nanoparticles, and the specific chirality is normally determined by the product's relative stability, suggesting thermodynamic control at the early stage of product formation. Based on our findings, we discuss the effect of other experimental parameters on the chirality of the product. Furthermore, we highlight the possibility to produce any tube chirality in the context of recent published work on seeded-controlled growth.
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| 41. |
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| 42. |
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| 43. |
- Johansson, Åsa, 1975, et al.
(author)
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Determination of OH number densities outside of a platinum catalyst using cavity ringdown spectroscopy
- 2007
-
In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 111:29, s. 6798-6805
-
Journal article (peer-reviewed)abstract
- It is demonstrated that cavity ringdown spectroscopy (CRDS) can be used to probe reaction intermediates desorbing from the surface during a heterogeneous catalytic reaction and provide information valuable in understanding the reaction kinetics. During water formation from H-2 and O-2, desorbed OH molecules outside of a polycrystalline platinum catalyst were quantified as a function of the relative hydrogen concentration, alpha(H2) using CRDS. The temperature of the catalyst was 1500 K, the total pressure was 26 Pa, and the flow was set to 100 sccm. At a distance of 6.5 mm from the Pt catalyst, the maximum OH concentration was found to be 1.5 +/- 0.2 x 10(12) cm(-3) at an alpha(H2) value of 10%, and the rotational temperature was determined to be 775 +/- 24 K. The desorbed OH molecules were also probed using laser-induced fluorescence (LIF), and the alpha(H2)-dependent OH abundance was compared with the CRDS results. The relative concentration of OH probed with LIF appeared to be lower at alpha(H2) = 30-50% compared to what was determined by CRDS. The observed discrepancy is suggested to be due to electronic quenching, as was indicated by a shorter fluorescence lifetime at alpha(H2) = 30% compared to at alpha(H2) = 10%.
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| 44. |
- Larsson, Peter, 1979-, et al.
(author)
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Calculating carbon nanotube–catalyst adhesion strengths
- 2007
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 75:11
-
Journal article (peer-reviewed)abstract
- Density-functional theory is used to assess the validity of modeling metal clusters as single atoms or rings of atoms when determining adhesion strengths between clusters and single-walled carbon nanotubes (SWNTs). Representing a cluster by a single atom or ring gives the correct trends in SWNT-cluster adhesion strengths (Fe ≈ Co > Ni), but the single-atom model yields incorrect minimum-energy structures for all three metals. We have found that this is because of directional bonding between the SWNT end and the metal cluster, which is captured in the ring model but not by the single atom. Hence, pairwise potential models that do not describe directional bonding correctly, and which are commonly used to study these systems, are expected to give incorrect minimum-energy structures.
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| 45. |
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| 46. |
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| 47. |
- Mekonnen Mihiretie, Besira, 1983, et al.
(author)
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Finite element modeling of the Hot Disc method
- 2017
-
In: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 115, s. 216-223
-
Journal article (peer-reviewed)abstract
- The Hot Disc method, also known as the transient plane source (TPS) technique, is an experimental approach to determine the thermal transport properties of materials. The core of the method is the Hot Disc sensor, an electrically conducting metallic strip, shaped as a double spiral clad with a protective polymer film. The mean temperature increase in the sensor has been approximated from various analytical approaches such as: the concentric ring sources model, the thermal quadrupoles formalism, and concentric circular strips structure approach. However, full numerical simulation of the sensor has not been addressed so far. Here we develop a 3D model of Hot Disc sensors and compare simulated mean temperature increase to experimental recordings. Joule heating coupled with heat transfer of solids (of COMSOL Multiphysics software) is used to simulate the working principle of the sensor. The volume mean temperature increase in the sensor from the simulations proves to be in a good agreement with the corresponding experimental recordings. The temperature distributions of the metallic strip are also evaluated and discussed with respect to the previous experimental findings. Furthermore, the current distribution across the strip is obtained. Such simulation can potentially be used in further optimizing geometry and parameter estimation.
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| 48. |
- Mekonnen Mihiretie, Besira, 1983, et al.
(author)
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SIMULATION OF THE HOT DISK SENSOR: TEMPERATURE AND ELECTRIC CURRENT DISTRIBUTION
- 2017
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In: Proceedings of the Asian Conference on Thermal Sciences 2017.
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Conference paper (peer-reviewed)abstract
- The Hot Disk method, also known as the transient plane source (TPS) technique, is an experimental approach for determining the thermal transport properties of materials. The core of the method is the Hot Disk sensor, an electrically conducting metallic foil (typically nickel), shaped as a double spiral, clad with a protective polymer film or mica. The double spiral serves simultaneously as heat source and temperature probe. The mean temperature increase of the TPS- sensor has been formulated from various analytical approaches such as: the concentric ring sources model, the thermal quadrupoles formalism, and concentric circular strips structure approach. However, full numerical simulation of the sensor has not been addressed so far. Here we develop 3D model of a Hot Disk sensor. The simulation provides information such as temperature and current distribution along each spiral which is not accessible from the experiment. Modeling feature, Joule heating coupled with heat transfer in solids of COMSOL Multiphysics software is used to simulate the sensor. The temperature and current distributions along the nickel wire is obtained. This can potentially be used in further optimizing geometry and estimating better parameters.
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| 49. |
- Mekonnen Mihiretie, Besira, 1983, et al.
(author)
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Thermal depth profiling of materials for defect detection using hot disk technique
- 2016
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In: AIP Advances. - : AIP Publishing. - 2158-3226. ; 6:8
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Journal article (peer-reviewed)abstract
- A novel application of the hot disk transient plane source technique is described. The new application yields the thermal conductivity of materials as a function of the thermal penetration depth which opens up opportunities in nondestructive testing of inhomogeneous materials. The system uses the hot disk sensor placed on the material surface to create a time varying temperature field. The thermal conductivity is then deduced from temperature evolution of the sensor, whereas the probing depth (the distance the heat front advanced away from the source) is related to the product of measurement time and thermal diffusivity. The presence of inhomogeneity in the structure is manifested in thermal conductivity versus probing depth plot. Such a plot for homogeneous materials provides fairly constant value. The deviation from the homogeneous curve caused by defects in the structure is used for inhomogeneity detection. The size and location of the defect in the structure determines the sensitivity and possibility of detection. In addition, a complementary finite element numerical simulation through COMSOL Multiphysics is employed to solve the heat transfer equation. Temperature field profile of a model material is obtained from these simulations. The average rise in temperature of the heat source is calculated and used to demonstrate the effect of the presence of inhomogeneity in the system.
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| 50. |
- Mellqvist, Johan, 1965, et al.
(author)
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DOAS for flue gas monitoring—I. Temperature effects in the UV/visible absorption spectra of NO, NO2, SO2 and NH3
- 1996
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In: Journal of Quantitative Spectroscopy and Radiative Transfer. - 0022-4073. ; 56:2, s. 187-208
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Journal article (peer-reviewed)abstract
- The temperature dependence of the absolute and the differential absorption cross-sections for NO, SO2, NO2 and NH3 were studied by recordings of spectra in a heat-pipe cell and by simulations of theoretical spectra for NO. A review and comparison of the present results with other relevant works were also made. The experimental results showed that the differential absorption features for some of the studied species change dramatically with temperature. For SO2 and NO2 the quantitative change in differential structure was very large with a relative change in magnitude of 70% between 300 and 700 K. For the two other species studied, NO and NH3, the change in magnitude of the differential structure was only 15–20%, over the same temperature range. Simulations for NO showed that the temperature effect was strongly dependent on the spectral resolution of the instrument and that it became smaller at lower resolution. The qualitative change in the spectral features was a continuous lowering of absorbance peaks and an increase in valleys which made the band integral of the absorbance quite insensitive to the temperature. Hot bands also appeared for SO2 and NH3 around 220 nm. The temperature affected the spectral features more in a quantitative than in a qualitative manner.
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