Experimental investigation of anomalous molecular probe diffusion in entangled polymer melts

Investigations on the diffusion of small molecules or particles in polymeric materials are important to numerous technologies and can also be used to gain insight on polymer chain dynamics. Systems where the probe size is comparable to (or smaller than) a characteristic length of the polymer chain, the tube diameter for example, are of particular interest because the diffusion coefficient of the probe can be orders of magnitude larger than the value predicted by the Stokes-Einstein relation. In the present study, we employ the optical technique known as forced Rayleigh scattering to study the diffusion of a molecular probe (dye) in several entangled polymer melts over a wide range of length and time scales. The probe size is much smaller than the tube diameter for the systems studied. We find the diffusion coefficient is larger by four to five orders of magnitude than the Stokes-Einstein prediction. More interestingly, we observe anomalous, non-Fickian, diffusion where the value of the measured diffusion coefficient can abruptly change by as much as 50%. We suggest that this unexpected behavior occurs when the time scale for diffusion is larger than the relaxation time associated with the constraint release mechanism for polymer chain dynamics

Nanoparticle-Assisted Water-Flooding in Berea Sandstones

The use of nanoparticles to improve reservoir characterization or to enhance oil recovery (EOR) has recently received intensive interest; however, there are still many unresolved questions. This work reports a systematic study of the effect of rutile TiO2 nanoparticle-assisted brine flooding. Rutile ellipsoid TiO2 nanoparticles were synthesized and stabilized by trisodium citrate dihydrate for brine flooding of water-wet Berea sandstone cores. Careful characterization of the rock samples and nanomaterials before and after the flooding was conducted, and the relative contributions to the modified flooding results from the stabilizer and the nanoparticles of different concentrations were examined. The oil recovery performance was evaluated both at the breakthrough (BT) point and at the end of flooding (∼3.2 pore volumes). Nanoparticle migration behavior was also investigated in order to understand the potential mechanisms for oil recovery. The results showed that both nanoparticle transport rate and EOR effect were strongly dependent on the particle concentration. The oil recovery efficiency at the BT point was found to increase at low nanoparticle concentrations but decrease at higher values. A maximum 33% increase of the recovery factor was observed at the BT point for a TiO2 concentration of 20 ppm, but higher nanoparticle concentrations usually had higher ultimate recovery factors. The presence of an oil phase was found to accelerate the particle migration though the core. The discussion of various mechanisms suggested that the improvement in the mobility ratio, possible wettability change, and log-jamming effect were responsible for the observed phenomena

Direct Ophthalmic Healthcare Resource Use among Geographic Atrophy Patients in a Large Cohort from the United Kingdom

Objective To estimate the direct ophthalmic health care resource use in patients with geographic atrophy (GA) secondary to age-related macular degeneration (AMD). Design Retrospective analysis of anonymized data derived from electronic medical records acquired at 10 clinical sites in the United Kingdom. Participants Patients aged ≥50 years with ≥1 eye with a clinical record of GA or, for comparison, bilateral early/intermediate AMD. Four subgroups were identified: GA in both eyes (GA : GA); GA in 1 eye, choroidal neovascularization (CNV) in the fellow eye (GA : CNV); GA in 1 eye with early or intermediate AMD in the fellow eye (GA : E); and early/intermediate AMD in both eyes (E : E). Methods Electronic medical records were analyzed to derive the median number of visits over the first 2 years following diagnosis of GA or early/intermediate AMD. Clinical tests recorded at visits were used to calculate estimated costs (payer perspective) of monitoring. Analyses were restricted to patients with an initial diagnosis on or after January 1, 2011 to represent present day monitoring and costs associated with AMD. Main Outcome Measures Median number of visits and estimated monitoring costs per patient (in £) over the first 2 years among patients with ≥2 years of follow-up and in the individual subgroups. Intravitreal treatment costs in the GA : CNV group were excluded. Results For all 3 GA subgroups (n = 1080), the median number of visits over the first 2 years was 5 and monitoring costs were £460.80 per patient. The GA : CNV subgroup (n = 355) had the highest number of visits (median, 15), with a cost of £1581, compared with the GA : E subgroup (n = 283; median 4 visits; cost ∼£369) and the GA : GA subgroup (n = 442; median 3 visits; cost ∼£277). Ophthalmic tests were conducted most frequently in the GA : CNV subgroup. Visits and costs in the E : E subgroup (n = 6079) were lower. Conclusions Resource use in patients with GA varies considerably and is strongly influenced by the concomitant presence of CNV and lack of monitoring strategies for GA

Experimental and theoretical studies of nanofluid thermal conductivity enhancement: a review

Nanofluids, i.e., well-dispersed (metallic) nanoparticles at low- volume fractions in liquids, may enhance the mixture's thermal conductivity, knf, over the base-fluid values. Thus, they are potentially useful for advanced cooling of micro-systems. Focusing mainly on dilute suspensions of well-dispersed spherical nanoparticles in water or ethylene glycol, recent experimental observations, associated measurement techniques, and new theories as well as useful correlations have been reviewed

First Assessment of the Impacts of the COVID-19 Pandemic on Global Marine Recreational Fisheries

This work is the result of an international research effort to determine the main impacts of the COVID-19 pandemic on marine recreational fishing. Changes were assessed on (1) access to fishing, derived from lockdowns and other mobility restrictions; (2) ecosystems, because of alterations in fishing intensity and human presence; (3) the blue economy, derived from alterations in the investments and expenses of the fishers; and (4) society, in relation to variations in fishers’ health and well-being. For this, a consultation with experts from 16 countries was carried out, as well as an international online survey aimed at recreational fishers, that included specific questions designed to capture fishers’ heterogeneity in relation to behavior, skills and know-how, and vital involvement. Fishers’ participation in the online survey (5,998 recreational fishers in 15 countries) was promoted through a marketing campaign. The sensitivity of the fishers’ clustering procedure, based on the captured heterogeneity, was evaluated by SIMPER analysis and by generalized linear models. Results from the expert consultation highlighted a worldwide reduction in marine recreational fishing activity. Lower human-driven pressures are expected to generate some benefits for marine ecosystems. However, experts also identified high negative impacts on the blue economy, as well as on fisher health and well-being because of the loss of recreational fishing opportunities. Most (98%) of the fishers who participated in the online survey were identified as advanced, showing a much higher degree of commitment to recreational fishing than basic fishers (2%). Advanced fishers were, in general, more pessimistic about the impacts of COVID-19, reporting higher reductions in physical activity and fish consumption, as well as poorer quality of night rest, foul mood, and raised more concerns about their health status. Controlled and safe access to marine recreational fisheries during pandemics would provide benefits to the health and well-being of people and reduce negative socioeconomic impacts, especially for vulnerable social groups.Versión del edito