Multifunctional Cantilevers as Working Elements in Solid-State Cooling Devices

Despite the challenges of practical implementation, electrocaloric (EC) cooling remains a promising technology because of its good scalability and high efficiency. Here, we investigate the feasibility of an EC cooling device that couples the EC and electromechanical (EM) responses of a highly functionally, efficient, lead magnesium niobate ceramic material. We fabricated multifunctional cantilevers from this material and characterized their electrical, EM and EC properties. Two active cantilevers were stacked in a cascade structure, forming a proof-of-concept device, which was then analyzed in detail. The cooling effect was lower than the EC effect of the material itself, mainly due to the poor solid-to-solid heat transfer. However, we show that the use of ethylene glycol in the thermal contact area can significantly reduce the contact resistance, thereby improving the heat transfer. Although this solution is most likely impractical from the design point of view, the results clearly show that in this and similar cooling devices, a non-destructive, surface-modification method, with the same effectiveness as that of ethylene glycol, will have to be developed to reduce the thermal contact resistance. We hope this study will motivate the further development of multifunctional cooling devices.

Prenatal metal mixtures and child blood pressure in the Rhea mother-child cohort in Greece

Background Child blood pressure (BP) is predictive of future cardiovascular risk. Prenatal exposure to metals has been associated with higher BP in childhood, but most studies have evaluated elements individually and measured BP at a single time point. We investigated impacts of prenatal metal mixture exposures on longitudinal changes in BP during childhood and elevated BP at 11 years of age. Methods The current study included 176 mother-child pairs from the Rhea Study in Heraklion, Greece and focused on eight elements (antimony, arsenic, cadmium, cobalt, lead, magnesium, molybdenum, selenium) measured in maternal urine samples collected during pregnancy (median gestational age at collection: 12 weeks). BP was measured at approximately 4, 6, and 11 years of age. Covariate-adjusted Bayesian Varying Coefficient Kernel Machine Regression and Bayesian Kernel Machine Regression (BKMR) were used to evaluate metal mixture impacts on baseline and longitudinal changes in BP (from ages 4 to 11) and the development of elevated BP at age 11, respectively. BKMR results were compared using static versus percentile-based cutoffs to define elevated BP. Results Molybdenum and lead were the mixture components most consistently associated with BP. J-shaped relationships were observed between molybdenum and both systolic and diastolic BP at age 4. Similar associations were identified for both molybdenum and lead in relation to elevated BP at age 11. For molybdenum concentrations above the inflection points (~ 40–80 μg/L), positive associations with BP at age 4 were stronger at high levels of lead. Lead was positively associated with BP measures at age 4, but only at high levels of molybdenum. Potential interactions between molybdenum and lead were also identified for BP at age 11, but were sensitive to the cutoffs used to define elevated BP. Conclusions Prenatal exposure to high levels of molybdenum and lead, particularly in combination, may contribute to higher BP at age 4. These early effects appear to persist throughout childhood, contributing to elevated BP in adolescence. Future studies are needed to identify the major sources of molybdenum and lead in this population.

Accumulation of heavy metals in the organs of herbaceous plants

The purpose of the work is to establish the characteristics of the accumulation of heavy metals of aboveground and underground organs in plant samples of 8 varieties of Narcissus hybridus and Camassia cusickii in the urbanized environment of the city of Ufa. The study of the elemental composition of the samples was carried out according to the method of quantitative chemical analysis ‘Determination of As, Pb, Cd, Sn, Cr, Cu, Fe, Mn and Ni in laboratory samples of food products and food raw materials by the atomic absorption method with electrothermal atomization’. It was found that the content of nickel, copper, cadmium, lead, magnesium, iron, chromium in all the samples studied does not exceed the standards specified in the State Pharmacopoeia of the Russian Federation (SP RF). The arsenic content exceeds the standards specified in the SP RF by 3.4 times. Revealed a high intensity of biological absorption of copper. It has been established that the concentrations of As, Cu, Pl, Mn, Fe in the aboveground organs are higher than in the underground part of plants; the ratio of the content of Ni, Cr, Cd in aboveground and underground organs is the same.

SIMULATION OF IRON CORROSION IN LEAD-MAGNESIUM EUTECTIC (LME) USING OXYGEN INHIBITOR

SIMULATION OF IRON CORROSION IN LEAD-MAGNESIUM EUTECTIC (LME) USING OXYGEN INHIBITOR. Lead-magnesium (Pb-Mg) is a metal that considered to have potential as a coolant raw material in the heat transfer system of nuclear reactors. However, the coolant in the form of Pb-Mg eutectic is corrosive to structured materials (eg steel cladding) used in reactors. In this research, steel material is represented by pure iron to simplify the simulation and calculation. This research aims to determine the effect of temperature on iron corrosion and the effect of adding oxygen as an inhibitor to reduce the iron corrosion rate in LME. In this study, corrosion was observed by looking at (coefficient) the diffusion of iron atoms into LME. A large iron diffusion coefficient represents high iron corrosion. To see inhibition effectivity with oxygen, the most effective oxygen concentration that can reduce the iron diffusion coefficient is searched. Simulations of iron corrosion and inhibition are performed using molecular dynamics simulation. The result of this research showed that oxygen concentration mixed into LME for effective inhibition of iron corrosion was in the range of 0.125 wt% - 0.135 wt% (for temperatures of 973K). Thus, oxygen is believed that able to inhibit iron corrosion in Pb-Mg eutectic up to 98.44%

Investigation of Structural and Dielectric Properties of Polycrystalline PbMg1∕3 Ti1∕3W1∕3O3 Tungsten Perovskite

Lead magnesium tungsten titanate PbMg[Formula: see text] Ti[Formula: see text]W[Formula: see text]O3 was prepared by adopting a high-temperature solid-state reaction method. The sample has tetragonal crystal structure having average crystallite size 45.1325[Formula: see text]nm calculated using Scherer’s relation and the average grain size is about 40[Formula: see text]nm from Scanning Electron Microscope (SEM) measurement. Measurements of dielectric permittivity ([Formula: see text]) and loss ([Formula: see text]) have been investigated, both as a function of frequency (1[Formula: see text]kHz to 5[Formula: see text]MHz) and temperature (25–[Formula: see text]C) and the results showed the presence of interfacial polarization of the material. The dielectric spectra with frequency and temperature suggest that the prepared sample is semiconducting in nature following the NTCR behavior. The complex impedance results showed the contribution of grain and grain boundaries in the conduction mechanism. The activation energies were determined from the ac conductivity data in the temperature ranges of 200–[Formula: see text]C and 360–[Formula: see text]C. It has been observed that with the rise of frequency and temperature, the activation energy increases in the sample. The greater value of the activation energy always supports the conduction mechanism due to hopping of the charge carriers. The semicircular arcs of Cole–Cole plots confirm that the sample is semiconducting in nature which supports our dielectric results.