TEM and STEM investigations of SrO-doped Sr(Ti,Nb)O3-δ thermoelectrics

Sr(Ti1-xNbx)O3-δ solid solutions are promising materials for n-type high-temperature thermoelectrics1. In our study 10 mol% of SrO excess was added to stoichiometric composition with x=0.2 in order to introduce Ruddlesden-Popper (RP) type-planar faults2,3 into the material, thus minimizing thermal conductivity. TEM and STEM were used to study possible ordering and/or distribution of Nb on Ti sites in the perovskite structure. All results were obtained in a Jeol ARM-200F with a CFEG and Cs probe corrector. HAADF imaging was performed at angles from 70 to 175 mrad, while ABF imaging from 11 to 23 mrad. EDXS spectra were acquired using JEOL Centurio Dry SD100GV SDD Detector. RP planar faults, as viewed along [001] zone axis, are shown in HRTEM micrograph in figure 1. The commonly observed number of perovskite unit cells between the planar faults is >2, which corresponds to various homologous compounds with the formula Srn+1(Ti,Nb)nO3n+1. However, solid solution Sr(Ti,Nb)O3-type grains with no RP faults can also be observed (bottom inset in Fig. 1). A HR HAADF STEM image of ordered RP faults (Fig. 2) shows that while the measured intensities of individual Sr atomic columns along a single fault do not scatter significantly, the (Ti,Nb)O atom columns exhibit quite large differences in measured intensities, thus indicating significant variation in Nb and Ti content within a single atom column. Quantitative analysis of measured intensities is in progress. The comparison between simultaneously acquired HAADF and ABF images of a single RP fault is shown in figure 3. While pure oxygen atomic columns cannot be resolved in the HAADF image, they can be readily observed using ABF imaging. The positions of oxygen atom columns along the planar faults are in full agreement with the structural model of a RP planar fault. Additional information on Nb distribution within perovskite matrix/RP faults was obtained by EDXS. While low magnification EDXS mappings show enrichment of Sr at RP faults accompanied by a corresponding decrease in Ti and Nb content, atom-resolved EDXS mappings confirm that individual mixed (Ti,Nb)O atom columns contain different Nb content (annotated atom column). Additionally, the spot EDXS line analysis (net counts) again shows much larger scatter in accumulated net counts for Ti as compared with Sr. The results being presented clearly show that no Nb is incorporated into the SrO RP faults and that the Nb is inhomogeneously incorporated within (Ti,Nb)O atom columns

Role of nutrient-sensing taste 1 receptor (T1R) family members in gastrointestinal chemosensing

Luminal nutrient sensing by G-protein-coupled receptors (GPCR) expressed on the apical domain of enteroendocrine cells activates intracellular pathways leading to secretion of gut hormones that control vital physiological processes such as digestion, absorption, food intake and glucose homeostasis. The taste 1 receptor (T1R) family of GPCR consists of three members: T1R1; T1R2; T1R3. Expression of T1R1, T1R2 and T1R3 at mRNA and protein levels has been demonstrated in the intestinal tissue of various species. It has been shown that T1R2-T1R3, in association with G-protein gustducin, is expressed in intestinal K and L endocrine cells, where it acts as the intestinal glucose (sweet) sensor. A number of studies have demonstrated that activation of T1R2-T1R3 by natural sugars and artificial sweeteners leads to secretion of glucagon-like peptides 1&2 (GLP-1 and GLP-2) and glucose dependent insulinotropic peptide (GIP). GLP-1 and GIP enhance insulin secretion; GLP-2 increases intestinal growth and glucose absorption. T1R1-T1R3 combination co-expressed on the apical domain of cholecystokinin (CCK) expressing cells is a luminal sensor for a number of l-amino acids; with amino acid-activation of the receptor eliciting CCK secretion. This article focuses on the role of the gut-expressed T1R1, T1R2 and T1R3 in intestinal sweet and l-amino acid sensing. The impact of exploiting T1R2-T1R3 as a nutritional target for enhancing intestinal glucose absorption and gut structural maturity in young animals is also highlighte

Expression of Na+/glucose co-transporter 1 (SGLT1) in the intestine of piglets weaned to different concentrations of dietary carbohydrate

Na+/glucose co-transporter 1 (SGLT1) transports dietary sugars from the lumen of the intestine into enterocytes. Regulation of this protein is essential for the provision of glucose to the body and, thus, is important for maintenance of glucose homeostasis. We have assessed expression of SGLT1 at mRNA, protein and functional levels in the intestinal tissue of 28d old piglets weaned onto isoenergetic diets with differing concentrations of digestible carbohydrate (CHO). We show that expression of SGLT1 remains constant when piglets are fed up to 40% CHO-containing diets. However, there is a significant increase in SGLT1 expression when the CHO content of the diet is>50%. Morphometric analyses indicate that the increased expression is not due to a trophic effect. It has been proposed that in rat intestine, in response to a high-CHO diet, GLUT2 (the classical basolateral membrane monosaccharide transporter) is translocated to the luminal membrane of enterocytes to absorb excess dietary glucose. We show, using immunohistochemistry and Western blotting with antibodies raised to amino acids in different epitopes of GLUT2, that under all dietary conditions, low to high CHO, GLUT2 is expressed on the basolateral membrane of pig enterocytes. Furthermore, functional studies indicate that there is no uptake of 2-deoxy-d-glucopyranoside, a specific substrate of Na+-independent glucose transporters into brush-border membrane vesicles isolated from the intestines of piglets either maintained on low- or high-CHO diets. Thus, SGLT1 is the major route for absorption of dietary sugars across the luminal membrane of swine enterocyte

Expression of Na+/glucose co-transporter 1 (SGLT1) is enhanced by supplementation of the diet of weaning piglets with artificial sweeteners

In an intensive livestock production, a shorter suckling period allows more piglets to be born. However, this practice leads to a number of disorders including nutrient malabsorption, resulting in diarrhoea, malnutrition and dehydration. A number of strategies have been proposed to overcome weaning problems. Artificial sweeteners, routinely included in piglets' diet, were thought to enhance feed palatability. However, it is shown in rodent models that when included in the diet, they enhance the expression of Na+/glucose co-transporter (SGLT1) and the capacity of the gut to absorb glucose. Here, we show that supplementation of piglets' feed with a combination of artificial sweeteners saccharin and neohesperidin dihydrochalcone enhances the expression of SGLT1 and intestinal glucose transport function. Artificial sweeteners are known to act on the intestinal sweet taste receptor T1R2/T1R3 and its partner G-protein, gustducin, to activate pathways leading to SGLT1 up-regulation. Here, we demonstrate that T1R2, T1R3 and gustducin are expressed together in the enteroendocrine cells of piglet intestine. Furthermore, gut hormones secreted by the endocrine cells in response to dietary carbohydrates, glucagon-like peptides (GLP)-1, GLP-2 and glucose-dependent insulinotrophic peptide (GIP), are co-expressed with type 1 G-protein-coupled receptors (T1R) and gustducin, indicating that L- and K-enteroendocrine cells express these taste elements. In a fewer endocrine cells, T1R are also co-expressed with serotonin. Lactisole, an inhibitor of human T1R3, had no inhibitory effect on sweetener-induced SGLT1 up-regulation in piglet intestine. A better understanding of the mechanism(s) involved in sweetener up-regulation of SGLT1 will allow the identification of nutritional targets with implications for the prevention of weaning-related malabsorptio

TEM and STEM investigations of Sr(Ti,Nb)O3-δ thermoelectric with the addition of CaO and SrO

It is known that thermoelectric properties, i.e. figure of merit ZT of oxide-based polycrystalline thermoelectric materials can be improved by introducing planar faults into the microstructure of these materials. It is assumed that in-grown planar faults will reduce thermal conductivity without reducing electrical properties which would consequently increase the ZT value. In order to successfully tailor thermoelectric properties of chosen thermoelectric materials, it is prerequisite to know the structure and chemical composition of introduced planar faults. This is why we used HR TEM and HAADF STEM imaging with EDXS in order to study structure and chemical composition of the Ruddlesden-Popper-type (RP) planar faults1,2 in Sr(Ti,Nb)O3-d (STNO) thermoelectric material with the addition of SrO and/or CaO. All results were obtained in a Jeol ARM-200F with a CFEG and Cs probe corrector. HAADF imaging was performed at angles from 70 to 175 mrad (ADF from 42 to 168 mrad). EDX spectra were acquired using JEOL Centurio Dry SD100GV SDD Detector. TEM bright-field images of pure STNO showed that the STNO solid solution grains contained no planar faults of any kind. Furthermore, the interfaces between the grains were clean with no observable interface phase. However, when SrO and/or CaO were added to the STNO, various nanostructured features were observed. In SrO-doped STNO, one can observe three distinctly different regions, i.e. the STNO solid solution, the regions with ordered SrO faults and the region with a network of random SrO planar faults (Figure 1). In the ordered regions one SrO layer is always followed by two perovskite STNO blocks, which corresponds to the Sr3(Ti1-xNbx)2O7 RP-type phase in which Nb and Ti occupy the same crystallographic site. While the measured HAADF intensities across Sr atomic columns at the RP fault do not scatter significantly, the mixed (Ti1-xNbx)O6 atom columns on the other hand exhibit significant differences in measured intensities thus indicating variation in Nb and Ti content within a single mixed atom column (Figure 2). Semi-quantitative HAADF STEM of the perovskite matrix, i.e. the comparison of measured integrated intensities of the atom columns with the calculated intensities showed that that the Nb content on the Ti sites within the perovskite structure varied from app. X=0.05 to X=0.35 (from Sr(Ti0.95Nb0.05)O3-d to Sr(Ti0.65Nb0.35)O3-d). When RP-type planar faults are isolated they run parallel to the {001} low-index zone axes of the perovskite structure. A similar structural phenomenon was observed in STNO with excess of CaO. Again, ordered and/or random 3D networks of RP-type planar faults were observed in the STNO grains (Figure 3). In very thin regions of CaO-doped STNO specimen many orthogonal loops of RP faults were observed that were not detected in SrO doped STNO (Figure 4). The EDX analysis from a single fault and from the matrix showed higher concentration of Ca at the fault. This is in agreement with previously reported investigations3 since smaller Ca ions are easier incorporated at the RP fault than in the perovskite matrix. The TEM and STEM investigations thus confirmed that the addition of SrO and/or CaO to the STNO perovskite solid solution is structurally compensated via the formation of RP-type planar faults within the STNO grains. Finally, thermoelectric measurements confirmed that the existence of RP-type faults in the perovskite STNO matrix reduced the thermal conductivity of this oxide thermoelectric material

The changing times of Europe's largest remaining commercially harvested population of eel Anguilla anguilla L

Publication history: Accepted - 1 June 2021; Published online - 4 June 2021.This study quantifies the processes involved in regulating the European eel population of Lough Neagh, a lake in Northern Ireland. The relationship between glass eel input and silver eel output for the 1923–1997 cohorts was best described by a Beverton–Holt stock recruitment model. Glass eel input time series was not complete and was thus derived from the relationship between catches elsewhere in Europe and Lough Neagh, together with the addition of stocked glass eel. Silver eel output was the sum of silver eel escapement, catch and yellow eel catch converted to silver eel equivalents. Natural mortality increased with glass eel density, ranging from 0.017 to 0.142 year−1. The mean carrying capacity increased from ≈3.25 M silver eels (≈26 kg ha−1) for the 1923–1943 cohorts to ≈5.0 M (≈40 kg ha−1) for the 1948–1971 cohorts before regressing back to ≈3.25 M. The total silver eel output was highest during the late 1970s/early 1980s at 35–45 kg ha−1 year−1 and lowest during the early years of the 20th century and is currently at 10–15 kg ha−1 year−1. The findings are discussed in relation to (a) the ecological changes that have occurred within the lough, associated with eutrophication and the introduction of roach (Rutilus rutilus L.), and (b) the decline of the wider European eel stock across its distribution range. The findings from this study have relevance for the wider management of the European eel stock.Department of Agriculture Environment and Rural Affairs (Northern Ireland) and the Department for Environment, Food and Rural Affairs (UK) for funding this study

Determination of sweetener specificity of horse gut-expressed sweet taste receptor T1R2-T1R3 and its significance for energy provision and hydration.

Studies carried out in several species have demonstrated that detection of low-calorie sweeteners in the lumen of the intestine, by the sweet receptor, T1R2-T1R3, initiates a signaling pathway leading to enhanced expression and activity of intestinal Na+/glucose cotransporter 1, SGLT1. This results in an increased gut capacity to absorb glucose, sodium chloride and water, the basis for oral rehydration therapy. Horses express T1R2, T1R3 and downstream signaling elements in the intestinal tissue. As such, the potential of sweetener-stimulation of T1R2-T1R3 leading to upregulation of SGLT1 allows the provision of more glucose (energy) and hydration for horses. This is especially important when the need for glucose increases during strenuous exercise, pregnancy, and lactation. There are significant differences among species in the ability to detect sweeteners. Amino acid substitutions and pseudogenization of taste receptor genes underlie these variations. Nothing is known about the sweetener specificity of horse T1R2-T1R3. Using heterologous expression methodology, we demonstrate that sweeteners sucralose, stevia and neohesperidin dihydrochalcone (NHDC) activate horse T1R2-T1R3, but cyclamate does not. Determination of sweetener specificity of equine sweet receptor is crucial for developing suitable dietary additives to optimize glucose absorption, hydration and avoiding the intestinal disease brought about by microbial fermentation of unabsorbed carbohydrate reaching the large intestine

Determination of structure and chemistry of long-persistence strontium aluminate phosphor compounds in aberration-corrected tem/stem

Representing a source of short-term stored energy, strontium aluminate phosphor compounds of nominal stoichiometry (SrO)•(Al2O3)2 co-doped with 1 mol% Eu2+ and 1 mol% Dy3+ (SA2ED) exhibit long persistence that is even further extended by the incorporation of boron1. To elucidate the effect of boron on afterglow persistence, we synthesized the phosphor powders using a sol-gel (i.e., modified Pechini) method2 and investigated the chemistry and structure by applying high-resolution STEM imaging, energy dispersive X-ray (EDX) spectroscopy, and electron energy-loss spectroscopy (EELS). Large single-crystal grains were analyzed from as-reduced powders suspended on carbon-coated lacey formvar on copper support grids. Individual crystalline particles were tilted onto a low-index [0001] zone axis and imaged in both high resolution TEM and STEM, using a JEOL JEM-ARM 200CF, equipped with a cold field-emission tip and a probe-side Cs aberration corrector. High-angle annular dark-field (HAADF) images were formed using an annular detector with an inner diameter of 70 mrad and an outer diameter of 175 mrad, while annular bright-field (ABF) images were obtained from an annular detector of 11-mrad inner diameter and 23-mrad outer diameter. EDX spectra were collected using a JEOL Centurio Dry SD100GV SDD detector. EELS analysis was enabled by a Gatan GIF Quantum ER spectrometer. Rietveld refinement of XRD spectra obtained from the powders revealed a mixture of (SrO)4•(Al2O3)7, (SrO)•(Al2O3)2 , and (SrO)•(Al2O3)6 phases. Single crystal particles of the (SrO)•(Al2O3)6 phase were the most stable and allowed for tilting onto the [0001] zone axis for qualitative identification of the atomic columns in HAADF and ABF micrographs. Quantitative image simulations of the measured intensities are in progress. Local variations were observed in the energy loss near-edge fine structure of the B-K, O-K, Al-L2,3 edges