Investigating of the conservation problems of oil paintings on paper supports

The initial results of a research project on the investigation of problems presented by a collection of oil paintings on paper supports are presented. The project focuses on the effect of the oil medium on the deterioration of cellulose, on the materials and techniques used by the artists and on comprehension of the resulting problems. Non destructive methodology was used to record the behaviour of the materials when examined in several regions of the electromagnetic spectrum which gives an indication of areas of damage. . Various analytical techniques were applied to investigate the painting materials and supports in original works of art. The increase in rate of the oxidation of cellulose in paper, when the paper is coated in oil, is investigated by analyzing volatile organic compounds emitted during ageing tests. The assessment of the results obtained will act as a pilot for a more extensive program of research, the ultimate aim of which is the formulation of a recommended methodology as a tool for the evaluation of the condition of these types of works, as well as the determination of conservation and care parameters

The removal of natural resin varnishes from hand-coloured oil printed media

Removing a varnish coating from an intaglio or planographic print is a potentially hazardous procedure. Difficulties are compounded if the ink contains additives and adulterants or the print has been hand-coloured with solvent sensitive media. In the case of seriously discoloured and damaged artefacts the risks involved in removing any varnish may be justified. Traditionally the paper conservator's choice of options has been rather limited which heightens the potential risks. Solvent poultices and gels may offer certain advantages over more traditional approaches and, although fears as to the long-term implications of residues have yet to be fully researched, current experiements look encouraging

Investigation into the use and effects of a Q-switched Nd:YAG laser for the removal of ink from paper

A Q-switched Nd:YAG laser is used to remove ballpoint pen ink from 'Roma', a 100% cotton rag art paper. The laser was operated at 1064 run, pulse duration 87 ns, and using a nominal fluence of 41 ± 12 Jcm-2. By shortening the pulse length (63 and 26 ns), using a Glan-Thompson prism the ink removal threshold was reduced to 24 ± 7 and 20 ± 6 Jcm-2 respectively. The physical damage to the paper is observed under SEM and found to be less disruptive to the surface fibres than contemporary mechanical methods of ink removal; scalpel and eraser. The tensile strength of laser treated paper is measured and found to remain unaffected below ink removal threshold fluences, although there is an increased tendency to tear at laser treatment sites. Repeat testing with artificially aged laser treated samples shows a marked decrease in tensile strength in comparison with an aged reference. Laser treated paper (nominal fluence of 41 ± 12 Jcm2, pulse length 87 ns) is tested for evidence of thermal degradation, via oxidation and depolymerisation. The tests include the Russell effect test for the presence of peroxides (oxidation), the methylene blue test for the presence of carboxyl groups (oxidation), FTIR spectroscopy to determine the presence of carboxyl, carbonyl, and conjugated groups (oxidation), and GC/MS to test for the presence of sugars (depolymerisation). The tests suggest that there is thermal degradation predominantly via depolymerisation. This is supported by repetition of the tests on laser treated samples prepared in an argon atmosphere. The laser treated paper is subjected to accelerated ageing in a humid oven to simulate natural is considered to be a reaction between the sizing agent (gelatin) and sugars formed during depolymerisation The tests are repeated on 'Roma' paper laser treated with shorter laser pulses (nominal fluence 24 ± 7 and 20 ± 6 Jcm-2, pulse durations of 63 and 26 ns), and this is found to have significantly less physical and chemical effect on the paper. Accelerated ageing of short pulse laser treated samples did not result in colour changes with respect to reference samples, indicating a more limited chemical interaction with the paper.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Demographic correlations for 100 most-cited authors in ophthalmic research; a bibliometric study

Background: To analyze the academic characteristics, career trajectory, scholarly publications, and demographic background of the 100 most-cited authors in ophthalmic literature. Methods: In this observational cross-sectional study, a database containing every ophthalmology journal article from 1967 to 2018 was built using Scopus journal article information. The 100 authors with the most citations were identified, along with a control group of authors with at least five publications. Information about each author, such as gender, institution, and educational degrees were found from online web searches. Intra- and inter-group analyses were performed to identify correlations that may lead to having a high level of impact in ophthalmology literature. Results: Of the 100 most-cited ophthalmologists, 56 practice in the United States (US) and only 12 are female. In an odds ratio (OR) analysis, highly-cited researchers more often lived in the US (OR, 2.97; P < 0.001), were male (OR, 2.4; P = 0.02), and graduated from an elite medical school (OR, 3.89; P = 0.02) and/or residency (OR, 3.67; P = 0.02), but were not from an undergraduate institution (P = 0.75). There was no difference in citation numbers between different ophthalmology subspecialties (P = 0.22) or advanced degrees (PhD, MPH in addition to MD). Women among the top-100-cited authors were more likely to author high impact journal articles (P < 0.05). Conclusions: Among highly-cited ophthalmologists, practicing in the US and attending a top medical school or residency program may provide training for a successful research career in ophthalmology. Additionally, top female ophthalmologists participate in more influential research

Different frequencies of RIP among early vs. late ascospores of Neurospora crassa

We have noticed that the frequency of RIP can be quite variable, even in crosses of the same strains. One possible source of variability is the time at which ascospores are harvested. We reasoned that the earliest ascospores shot from a perithecium might contain DNA that went through relatively few mitotic divisions in pre-meiosis. RIP occurs between fertilization and premeiotic DNA synthesis (Selker et al. 1987 Cell 51:741-752). Thus, early spores might have less exposure to RIP than late spores. Since all ascospores from a perithecium are thought to arise from a single fertilization event, a minimum of 7- 10 divisions are required to account for the number of ascospores normally produced (Perkins and Barry, 1977 Adv. Genet. 211:541-544). It is likely, however, that some ascospore lineages contain fewer divisions than others

Correlation of ignimbrites using characteristic remanent magnetization and anisotropy of magnetic susceptibility, Central Andes, Bolivia

Large ignimbrite flare-ups provide records of profound crustal modification during batholith formation at depth. The locations of source calderas and volumes and ages of the eruptions must be determined to develop models for the tectonomagmatic processes that occur during these events. Although high-precision isotopic ages of the ignimbrites are critical, less expensive and more rapid techniques, such as paleomagnetism, can extend the temporal information from dated outcrops. Paleomagnetic and rock magnetic data, including characteristic remanent magnetization (ChRM) and anisotropy of magnetic susceptibility (AMS), from the Altiplano-Puna Volcanic Complex of the Central Andes reliably identify calderas and eight associated Mio-Pliocene ignimbrites. ChRM results indicate a larger between-site error for most ignimbrites, in comparison to within-site scatter. Part of this dispersion may be due to tumescence/detumescence associated with the caldera-forming eruptions, but most of the effect is probably due to the recording of paleosecular variation during cooling and vapor-phase crystallization of the thick ignimbrites. AMS data identify the source calderas for four ignimbrites and provide limits on possible post-emplacement rotations of the deposits. AMS data indicate significant topographic control on inferred flow directions, implying that the flows were dense and/or of low mobility

Astronomical and Tectonic Influences on Climate and Deposition Revealed Through Radioisotopic Geochronology and Bayesian Age-Depth Modeling of the Early Eocene Green River Formation, Wyoming, USA

The Wilkins Peak Member (WPM) of the Green River Formation in Wyoming, USA, comprises alternating lacustrine and alluvial strata that preserve a record of terrestrial climate during the early Eocene climatic optimum. We use a Bayesian framework to develop age-depth models for three sites, based on new 40Ar/39Ar sanidine and 206Pb/238U zircon ages from seven tuffs. The new models provide two- to ten-fold increases in temporal resolution compared to previous radioisotopic age models, confirming eccentricity-scale pacing of WPM facies, and permitting their direct comparison to astronomical solutions. Starting at ca. 51 Ma, the median ages for basin-wide flooding surfaces atop six successive alluvial marker beds coincide with short eccentricity maxima in the astronomical solutions. These eccentricity maxima have been associated with hyperthermal events recorded in marine strata during the early Eocene. WPM strata older than ca. 51 Ma do not exhibit a clear relationship to the eccentricity solutions, but accumulated 31%–35% more rapidly, suggesting that the influence of astronomical forcing on sedimentation was modulated by basin tectonics. Additional high-precision radioisotopic ages are needed to reduce the uncertainty of the Bayesian model, but this approach shows promise for unambiguous evaluation of the phase relationship between alluvial marker beds and theoretical eccentricity solutions