RESUMO

Heterogenization of homogenous catalysts on electrode surfaces provides a valuable approach for characterization of catalytic processes in operando conditions using surface selective spectroelectrochemistry methods. Ligand design plays a central role in the attachment mode and the resulting functionality of the heterogenized catalyst as determined by the orientation of the catalyst relative to the surface and the nature of specific interactions that modulate the redox properties under the heterogeneous electrode conditions. Here, we introduce new [Re(L)(CO)3Cl] catalysts for CO2 reduction with sulfur-based anchoring groups on a bipyridyl ligand, where L = 3,3'-disulfide-2,2'-bipyridine (SSbpy) and 3,3'-thio-2,2'-bipyridine (Sbpy). Spectroscopic and electrochemical analysis complemented by computational modeling at the density functional theory level identify the complex [Re(SSbpy)(CO)3Cl] as a multi-electron acceptor that combines the redox properties of both the rhenium tricarbonyl core and the disulfide functional group on the bipyridyl ligand. The first reduction at -0.85 V (vs. SCE) involves a two-electron process that breaks the disulfide bond, activating it for surface attachment. The heterogenized complex exhibits robust anchoring on gold surfaces, as probed by vibrational sum-frequency generation (SFG) spectroscopy. The binding configuration is normal to the surface, exposing the active site to the CO2 substrate in solution. The attachment mode is thus particularly suitable for electrocatalytic CO2 reduction.

RESUMO

There is an increasing awareness of microplastics within the global problem of marine plastic pollution. In 2018, small plastic pellets or "nurdles" were observed on the beaches of Corpus Christi, Texas. A citizen science project, "Nurdle Patrol," was established by the Mission-Aransas National Estuarine Research Reserve to monitor the presence of nurdles, with volunteer interest enabling this project to expand across the Gulf of Mexico region. This case study describes the sampling methodology, the policy framework, and initial quantitative data from the citizen science project on nurdle distribution along the Gulf coast. A total of 2042 Nurdle Patrol surveys have been conducted by 744 citizen scientists covering shorelines from Mahahual, Mexico to Fort Jefferson, Florida. All 20 of the highest standardized nurdle counts were recorded at sites in Texas. Results can inform decision-maker response across regulatory scales and further research on nurdle pollution.

Assuntos

RESUMO

AIM: To determine the recent demographic data, risk factors and results of retinopathy of prematurity (ROP) screening and treatment in Costa Rica. METHODS: The medical records of all preterm infants meeting ROP screening criteria (≤34 weeks' gestational age (GA) or birth weight (BW) ≤1750g, and those determined at risk by neonatologists) in the national healthcare system, Costa Rica, January 2010-December 2014, were retrospectively reviewed. The numbers and percentages of infants with ROP, risk factors, percentage of patients treated and treatment outcomes were determined. Comparison is made with screening criteria and literature reports of ROP incidence in other countries. RESULTS: The study population included 3018 preterm infants. Overall, 585 patients (585/3018, 19.4%) were found to have ROP. Of these, 15.4% (90 patients) required laser treatment, and 53% of those requiring treatment had BW <1000g. Five babies requiring treatment were ≥32 weeks' GA but with BW ≤1750g. Aggressive posterior disease was found in nine patients, and two infants of those screened (2/3018, 0.07%) suffered severe visual impairment during the 5-year study period. CONCLUSION: We provide comprehensive data of ROP care in Costa Rica allowing assessment and comparison of screening criteria and protocol.

Assuntos

RESUMO

Sweeping double probe measurements in an atmospheric pressure direct current vortex-stabilized plasma jet are reported (plasma conditions: 100 A discharge current, N2 gas flow rate of 25 Nl/min, thoriated tungsten rod-type cathode, copper anode with 5 mm inner diameter). The interpretation of the double probe characteristic was based on a generalization of the standard double floating probe formulae for non-uniform plasmas coupled to a non-equilibrium plasma composition model. Perturbations caused by the current to the probe together with collisional and thermal processes inside the probe perturbed region were taken into account. Radial values of the average electron and heavy particle temperatures as well as the electron density were obtained. The calculation of the temperature values did not require any specific assumption about a temperature relationship between different particle species. An electron temperature of 10,900 ± 900 K, a heavy particle temperature of 9300 ± 900 K, and an electron density of about 3.5 × 10(22) m(-3) were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found toward the outer border of the plasma jet. These results showed good agreement with those previously reported by the authors by using a single probe technique. The calculations have shown that this method is particularly useful for studying spraying-type plasma torches operated at power levels of about 15 kW.

RESUMO

This work describes the application of Langmuir probe diagnostics to the measurement of the electron temperature in a time-fluctuating-highly ionized, non-equilibrium cutting arc. The electron retarding part of the time-averaged current-voltage characteristic of the probe was analysed, assuming that the standard exponential expression describing the electron current to the probe in collision-free plasmas can be applied under the investigated conditions. A procedure is described which allows the determination of the errors introduced in time-averaged probe data due to small-amplitude plasma fluctuations. It was found that the experimental points can be gathered into two well defined groups allowing defining two quite different averaged electron temperature values. In the low-current region the averaged characteristic was not significantly disturbed by the fluctuations and can reliably be used to obtain the actual value of the averaged electron temperature. In particular, an averaged electron temperature of 0.98 ± 0.07 eV (= 11400 ± 800 K) was found for the central core of the arc (30 A) at 3.5 mm downstream from the nozzle exit. This average included not only a time-average over the time fluctuations but also a spatial-average along the probe collecting length. The fitting of the high-current region of the characteristic using such electron temperature value together with the corrections given by the fluctuation analysis showed a relevant departure of local thermal equilibrium in the arc core.

Assuntos

RESUMO

OBJECTIVES: We sought to determine whether mild-moderate persistent asthma sufficient to produce a decrease in baseline lung function is associated with an adverse effect on growth and bone mineral density (BMD) in children. METHODS: This was a cross-sectional study of 1041 children, 5 to 12 years old (32% ethnic/racial minorities and 40% female), enrolled into the Childhood Asthma Management Program (CAMP). Measures of asthma severity included: Spirometry; bronchial hyperresponsiveness; duration of asthma symptoms; and symptom-based assessment of severity. Multiple regression analyses were used to relate the asthma severity on the primary outcome variables: Height by stadiometry and BMD by dual energy radiographic absorptiometry. RESULTS: The mean +/- SD height percentile was 56.0 +/- 28.5 percentile for the population. The only significant relationship between asthma severity and height percentile was with methacholine bronchoprovocation in girls (beta 2.98, P =.019, covariate multiple regression). The mean +/- SD BMD was 0.65 +/- 0.10 g/cm(2) for the population. The past use of corticosteroids did not adversely affect either growth or BMD. CONCLUSIONS: We found that mild-moderate asthma of as long as 4 to 7 years duration in children does not produce an adverse effect on linear growth or BMD.

Assuntos

Assuntos

Assuntos

Assuntos