1,721,099 research outputs found
Combined use of radiotherapy and photodynamic therapy (pdt) for subfoveal choroidal neovascular membranes reduces the need for repeat treatments with Pdt: Results from a pilot study
No full textPurpose: To determine whether teletherapy followed by one or more doses of PDT using verteporfin has any vision threatening effects on the macular and to determine whether the PDT retreatment rate in the first year is less than expected.
Methods: Nine eyes of eight patients underwent teletherapy (20Gy) for subfoveal choroidal neovascular membranes followed by PDT for sub-foveal recurrences. A control group of 20 patients received PDT only. All patients were followed-up at 3 month intervals and patients with recurrences received PDT if they were predominantly classic in nature. At each visit the Log Mar and EDTRS vision was recorded and a fluorescein angiogram was performed.
Results: The time between radiotherapy and the first session of PDT was a mean of 14 months (range 4-24 months). Nine eyes of eight patients were followed up for 1 year after PDT. In the combined radiotherapy with PDT group, the mean visual acuity (VA) prior to PDT was 0.83 (0.36-1.36), at 3 months post treatment VA was 0.80 (0.34-1.36), at 6 months post treatment it was 1.0 (0.24-2.0), at 9 months post treatment it was 0.86 (0.28-1.3) and at 12 months, VA was 0.99 (0.4-2.0). There was no statistically significant difference in VA at base line compared with any of the other time point. No eye suffered a significant drop in VA immediately after PDT. In the control group the mean visual acuity was 0.61 (0.18 -1.66) prior to treatment, at 3 months 0.83 (0.32 - 1.66) at 6 months 0.82 (0.34 - 1.66), at 9 months 0.71 (0.34 - 1.66) and at 12 months 0.76 (0.36 - 1.8). At the 9 months time point, there had been an average 2.3 PDT treatment sessions per eye in the combined teletherapy and PDT group, whereas there had been an average of 3.3 treatment session per eye in PDT only group. This difference in the mean number of treatment sessions was found to be statistically significant (p <0.01, t-test).
Conclusion: PDT appears to be a safe treatment when utilised after teletherapy for recurrences of predominantly classic choroidal neovascular membranes. The results from this series strongly suggest that combined radiotherapy and PDT leads to a reduction in the number of treatment sessions for PDT and indicates that clinicians should investigate further the benefits of combined radiotherapy and PDT for patients with subfoveal choroidal neovascular membranes
Methylation of ethene by surface methoxides: A periodic PBE+D study across zeolites
No full textThe role of zeolite topology in the stepwise methylation of ethene by surface methoxides was investigated. Density functional theory was employed in the determination of reaction mechanisms and energy barriers. Elementary steps were studied across multiple frameworks (i.e., BEA, CHA, FER, MFI, and MOR) constituting a wide variety of confinement environments. Surface methoxides were found to react with ethene through a transition state containing planar CH3 species, which was best stabilized at the intersection of the 10-membered ring channels of MFI. A cyclopropane reaction intermediate was found in all cases; its decomposition necessitated a transition state containing a primary carbocation, which was best stabilized within the 8-membered ring side pockets of MOR. The activation energies corresponding to each transition state geometry depend upon different aspects of the local pore topology, implying that confinement effects can not be simply correlated to pore size
β-scission of olefins on acidic zeolites: A periodic PBE-D study in H-ZSM-5
No full textEight beta-scission modes involving C-6 and C-8 olefin isomers are investigated using dispersion-corrected density functional theory (i.e., PBE-D) calculations. Potential energy surfaces are evaluated within an acidic H-ZSM-5 supercell containing a single, isolated active site. Minimum energy pathways are localized using the nudged elastic band method. The relative enthalpic barriers of beta-scission steps can be described by the substitution order of the carbocationic carbon atom present in the reactant and transition states. Specifically, the total charge on the hydrocarbon fragment containing the beta C atom increases going from the physi- or chemisorbed reactant state to the beta-scission transition state; the magnitude of this change (+0.37e-0.97e) is found to correlate nearly monotonically with the activation energy (89-233 kJ mol(-1)). A comparison of 1 degrees to 3 degrees (E-1) and 3 degrees to 1 degrees (E-2) beta-scission modes as well as 2 degrees to 3 degrees (B-1) and 3 degrees to 2 degrees (B-2) beta-scission modes reveals that the barrier heights depend on the substitution order of the beta C, indicating that a subcategorization of beta-scission modes is required based on the substitution order of the beta C atom. Isomerization reactions, which are fast with respect to beta-scission, enable reactant hydrocarbons to explore and find low-barrier beta-scission pathways. Selectivities predicted on the basis of the relative barrier heights of beta-scission modes accessible to C-6 and C-8 species indicate agreement with experimental observations
Sarcomatoid carcinoma; an ultrastructural study, with light microscopis and immonohistochemical correlation, of ten cases from various anatomical sites
No full text20 Gy external beam radiotherapy can stablise vision in patients with subfoveal choroidal neovascular membranes in the first 12 months
No full textAbstract: : Purpose: To determine the effect of a higher dose of external beam radiotherapy on patients with subfoveal choroidal neovascular membranes (SCNV).
Methods: 21 patients with SCNV as a result of Age Related Macular Degeneration (ARMD) were recruited and underwent teletherapy using 10 fractions of 2 Gy (total of 20Gy). All patients were followed-up at 3-month intervals for a period of 12 months and then at 6 monthly intervals thereafter. At each visit the Log Mar vision was recorded and fluorescein angiography was performed at 6 months intervals. A group of 24 patients with SCNV due to ARMD received no therapy and acted as controls. Results: The mean follow-up of patients was 17.2 months. The mean LogMAR visual acuity at diagnosis was 1.21 for the control group and 0.73 for the radiotherapy group. The mean logMAR visual acuity in the control group at 3 months, 6 months, 9 months and 12 months were 1.48, 1.47, 1.64 and 1.8 Log MAR units respectively. In the radiotherapy group, the mean LogMAR visual acuites were 0.76, 0.83, 0.86 and 0.9 LogMAR units. No adverse effects were noted in the radiotherapy treated group. The mean visual acuity loss at 12 months from the time at diagnosis was 0.1 logMAR units for the radiotherapy group and in the untreated control group it was 0.5 log MAR units. This difference in the visual acuity loss at 12 months from the start of treatment was found to be found to be statistically significant between the two groups (p <0.01, t-test). Conclusion: The data from this trial indicate that 20 Gy of external beam radiotherapy delivered in 10 fractions can stabilise visual loss for 12 months in patients with subretinal choroidal neovascular membranes, the finding supports work from others who use higher dose radiotherapy to treat SCNV
Comparing the reaction profiles of single iron catalytic sites in enzymes and in reticular frameworks for methane-to-methanol oxidation
Get PDFThe design of synthetic inorganic catalysts mimicking the first coordination spheres of enzymatic cofactors often results in lower yields and selectivity than their biological counterparts. In this study, we exploit Kohn-Sham density functional methods to compare the reaction profiles of four single iron-based catalysts for the direct oxidation of methane to methanol: two biomimetic models based on two enzymes (cytochrome P450 and taurine dioxygenase [TauD]) and two synthetic reticular frameworks (iron-BEA zeolite and tri-iron oxo-center-based metal-organic framework). Both the biomimetic and inorganic catalysts show almost zero selectivity toward methanol for methane conversions >1% at ambient temperature. This study highlights that iron's first coordination shell can influence selectivity toward methanol but to a limited extent. In the absence of methanol protection strategies, high selectivity can be reached only by mimicking the reaction microenvironment of enzymes beyond the first coordination shell of iron
Alkane metathesis by tantalum metal hydride on ferrierite: A computational study
No full textThe full catalytic cycle for the self-metathesis of ethane was studied by density functional theory (DFT). The active site was a Ta-dihydride grafted on a Bronsted acid site [( AlO)(2)Ta(H-2)] of the internal pore surface of the FER zeolite. The transition state geometries and activation energies were determined through the nudged elastic band (NEB) method for each elementary step, and the complete cycle was found to be thermodynamically consistent. Investigated elementary steps include ethane C-H sigma-bond activation, ethylene desorption through alpha and beta hydrogen elimination mechanisms, Ta-ethylcarbene formation, olefin metathesis, and hydrogenation of olefin metathesis products. For the activation of ethane, as compared to catalytic systems involving zeolite-supported Ga and Zn, a low barrier (similar to 64 kJ mol(-1)) was observed. In the olefin metathesis step, where Ta-ethylcarbene reacts with ethylene, it was found that the Ta-metallacyclobutane has a relatively high stability (similar to 143 kJ mol(-1)) as compared to similar metallacyclobutane species and that the forward decomposition of the Ta-metallacyclobutane is the most energetically demanding step
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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