| 1. |
- 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
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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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| 2. |
- 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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| 3. |
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| 4. |
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| 5. |
- 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
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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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| 6. |
- Ding, Feng, 1970, et al.
(author)
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Modeling the melting of supported clusters
- 2006
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In: APPLIED PHYSICS LETTERS. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88:13
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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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| 7. |
- Ding, Feng, 1970, et al.
(author)
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Molecular dynamics study of bamboo-like carbon nanotube nucleation
- 2006
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In: JOURNAL OF ELECTRONIC MATERIALS. - 0361-5235. ; 35:2, s. 207-210
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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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| 8. |
- Ding, Feng, 1970, et al.
(author)
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Molecular dynamics study of SWNT growth on catalyst particles without temperature gradients
- 2006
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In: COMPUTATIONAL MATERIALS SCIENCE. - : Elsevier BV. - 0927-0256. ; 35:3, s. 243-246
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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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| 9. |
- Ding, Feng, 1970, et al.
(author)
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Molecular dynamics study of the surface melting of iron clusters
- 2005
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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
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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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| 10. |
- 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
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In: APPLIED SURFACE SCIENCE. - : Elsevier BV. - 0169-4332. ; 252:15, s. 5254-5258
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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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| 11. |
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| 12. |
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| 13. |
- 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
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In: EUROPEAN PHYSICAL JOURNAL D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 43:1-3, s. 185-188
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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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| 14. |
- Duan, Haiming, et al.
(author)
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Size dependent melting mechanisms of iron nanoclusters
- 2007
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In: CHEMICAL PHYSICS. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 333:1, s. 57-62
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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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| 15. |
- 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
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In: Journal of Biomedical Optics. - : SPIE-Intl Soc Optical Eng. - 1083-3668 .- 1560-2281. ; 10:3
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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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| 16. |
- 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
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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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| 17. |
- Harutyunyan, Avetik, et al.
(author)
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Hidden features of the catalyst nanoparticles favorable for single-walled carbon nanotube growth
- 2007
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In: APPLIED PHYSICS LETTERS. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:16
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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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| 18. |
- 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
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 111:29, s. 6798-6805
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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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| 19. |
- 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
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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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| 20. |
- Romero, H E, et al.
(author)
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Atom collision-induced resistivity of carbon nanotubes
- 2005
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In: SCIENCE. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 307:5706, s. 89-93
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Journal article (peer-reviewed)abstract
- We report the observation of unusually strong and systematic changes in the electron transport in metallic single-walled carbon nanotubes that are undergoing collisions with inert gas atoms or small molecules. At fixed gas temperature and pressure, changes in the resistance and thermopower of thin films are observed that scale as roughly M-1/3, where M is the mass of the colliding gas species (He, Ar, Ne, Kr, Xe, CH4, and N-2). Results of molecular dynamics simulations are also presented that show that the maximum deformation of the tube wall upon collision and the total energy transfer between the colliding atom and the nanotube also exhibit a roughly M-1/3 dependence. it appears that the transient deformation (or dent) in the tube wait may provide a previously unknown scattering mechanism needed to explain the atom collision-induced changes in the electrical transport.
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| 21. |
- Stenquist, Bo, 1937, et al.
(author)
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Bispectral fluorescence imaging of aggressive basal cell carcinoma combined with histopathological mapping: a preliminary study indicating a possible adjunct to Mohs micrographic surgery
- 2006
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In: Br J Dermatol. - : Oxford University Press (OUP). - 0007-0963. ; 154:2, s. 305-9
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Journal article (peer-reviewed)abstract
- 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 delta-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. OBJECTIVES: To investigate the agreement between bispectral fluorescence images and the histopathological tumour boundary of ill-defined basal cell carcinomas (BCCs). After fluorescence imaging the tumours were removed using Mohs micrographic surgery (MMS) to obtain histopathological maps of the tumour boundaries. METHODS: Twelve patients with aggressive BCC of mean diameter 16 mm (range 5-32) in the face were included in the study. The patients were subjected to bispectral fluorescence imaging within the 2 months prior to MMS. The fluorescence images and histopathological maps were aligned using image warping. RESULTS: Five patients (42%) showed good agreement with the histopathological mapping and the remaining seven patients (58%) showed partial agreement. Bispectral investigation combining autofluorescence with protoporphyrin IX (PpIX) fluorescence generally yielded better agreement with the histopathological boundaries of the tumours compared with using only the PpIX fluorescence. CONCLUSIONS: In this preliminary study the fluorescence has been compared with the histopathological tumour boundaries. The result implies that the technique can be applied as a useful tool for indicating tumour boundary of aggressive BCCs. Further refinement is needed to be able to indicate the exact tumour border.
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| 22. |
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