Energy backtransfer and infrared photoresponse in erbium-doped silicon p-n diodes

Temperature-dependent measurements of the photoluminescence (PL) intensity, PL lifetime, and infrared photocurrent, were performed on an erbium-implanted silicon p - n junction in order to investigate the energy transfer processes between the silicon electronic system and the Er 4 f energy levels. The device features excellent light trapping properties due to a textured front surface and a highly reflective rear surface. The PL intensity and PL lifetime measurements show weak temperature quenching of the erbium intra-4 f transition at 1.535 mm for temperatures up to 150 K, attributed to Auger energy transfer to free carriers. For higher temperatures, much stronger quenching is observed, which is attributed to an energy backtransfer process, in which Er deexcites by generation of a bound exciton at an Er-related trap. Dissociation of this exciton leads to the generation of electron-hole pairs that can be collected as a photocurrent. In addition, nonradiative recombination takes place at the trap. It is shown for the first time that all temperature-dependent data for PL intensity, PL lifetime, and photocurrent can be described using a single model. By fitting all temperature-dependent data simultaneously, we are able to extract the numerical values of the parameters that determine the ~temperature-dependent! energy transfer rates in erbium-doped silicon. While the external quantum efficiency of the photocurrent generation process is small (1.831026) due to the small erbium absorption cross section and the low erbium concentration, the conversion of Er excitations into free e - h pairs occurs with an efficiency of 70% at room temperature

Smoking status in relation to serum folate and dietary vitamin intake

Objective Cigarette smoke itself is an abundant source of free radicals and a major cause of oxidative stress, to which plasma antioxidants function as a vital protective and counterbalancing mechanism. The objective of this study was to investigate into the relationship between smoking status and serum and dietary micronutrient concentrations. Design Cross-sectional study Subjects ' Setting 502 farmers from the Valley of Messara in Crete were randomly selected and examined. Complete three-day and 24-hr recall questionnaires were collected along with anthropometrical, physical activity and clinical data from all participating subjects. Results After adjusting for age, gender and number of fasting days adhered to per year, current smokers were found to have a lower dietary intake of vitamin C (112.1 mg vs. 136.4 mg, p = 0.03), fibre (16.6 g vs. 19.1 g, p = 0.006) and fruits and vegetables (339 g vs. 412 g, p = 0.014), while dietary vitamin B1 intake was found to be higher (1.7 mg vs. 1.4 mg, p = 0.02) in comparison to non/ex smokers. Dietary intake of meat, folate and vitami A, E, B2, B6 and B12 did not differ between the groups. Controlling age, gender, fasting days and dietary micronutrient intake, serum folate levels were found to be lower among smokers (geometric mean 15.3 nmol/L vs. 17.7 nmol/L, p = 0.023), while serum iron and vitamin B12 levels were not affected by smoking status. Conclusion Current smoking status affects dietary nutrient intake as well as plasma folate levels. The above coherence between antioxidant depletion and reduced antioxidant intake may predispose smokers to the premature development of tobacco related mortality and morbidity

Embryonal subregion-derived stromal cell lines from novel temperature-sensitive SV40 T antigen transgenic mice support hematopoiesis

Throughout life, the hematopoietic system requires a supportive microenvironment that allows for the maintenance and differentiation of hematopoietic stem cells (HSC). To understand the cellular interactions and molecules that provide these functions, investigators have previously established stromal cell lines from the late gestational stage and adult murine hematopoietic microenvironments. However, the stromal cell microenvironment that supports the emergence, expansion and maintenance of HSCs during mid-gestational stages has been largely unexplored. Since several tissues within the mouse embryo are known to harbor HSCs (i.e. aortagonads-mesonephros, yolk sac, liver), we generated numerous stromal cell clones from these mid-gestational sites. Owing to the limited cell numbers, isolations were performed with tissues from transgenic embryos containing the ts SV40 Tag gene (tsA58) under the transcriptional control of constitutive and ubiquitously expressing promoters. We report here that the growth and cloning efficiency of embryonic cells (with the exception of the aorta) is increased in the presence of the tsA58 transgene. Furthermore, our results show that the large panel of stromal clones isolated from the different embryonal subregions exhibit heterogeneity in their ability to promote murine and human hematopoietic differentiation. Despite our findings of heterogeneity in hematopoietic growth factor gene expression profiles, high-level expression of some factors may influence hematopoietic differentiation. Interestingly, a few of these stromal clones express a recently described chordin-like protein, which is an inhibitor of bone morphogenic proteins and is preferentially expressed in cells of the mesenchymal lineage

Intramyocellular lipid content is increased after exercise in nonexercising human skeletal muscle

Intramyocellular lipid (IMCL) content has been reported to decrease after prolonged submaximal exercise in active muscle and, therefore, seems to form an important local substrate source. Because exercise leads to a substantial increase in plasma free fatty acid (FFA) availability with a concomitant increase in FFA uptake by muscle tissue, we aimed to investigate potential differences in the net changes in IMCL content between contracting and noncontracting skeletal muscle after prolonged endurance exercise. IMCL content was quantified by magnetic resonance spectroscopy in eight trained cyclists before and after a 3-h cycling protocol (55% maximal energy output) in the exercising vastus lateralis and the nonexercising biceps brachii muscle. Blood samples were taken before and after exercise to determine plasma FFA, glycerol, and triglyceride concentrations, and substrate oxidation was measured with indirect calorimetry. Prolonged endurance exercise resulted in a 20.4 ± 2.8% (P <0.001) decrease in IMCL content in the vastus lateralis muscle. In contrast, we observed a substantial (37.9 ± 9.7%; P <0.01) increase in IMCL content in the less active biceps brachii muscle. Plasma FFA and glycerol concentrations were substantially increased after exercise (from 85 ± 6 to 1,450 ± 55 and 57 ± 11 to 474 ± 54 µM, respectively; P <0.001), whereas plasma triglyceride concentrations were decreased (from 1,498 ± 39 to 703 ± 7 µM; P <0.001). IMCL is an important substrate source during prolonged moderate-intensity exercise and is substantially decreased in the active vastus lateralis muscle. However, prolonged endurance exercise with its concomitant increase in plasma FFA concentration results in a net increase in IMCL content in less active muscle

Mitochondrial transport from mesenchymal stromal cells to chondrocytes increases DNA content and proteoglycan deposition In vitro in 3D cultures

Objective: Allogeneic mesenchymal stromal cells (MSCs) are used in the 1-stage treatment of articular cartilage defects. The aim of this study is to investigate whether transport of mitochondria exists between chondrocytes and MSCs and to investigate whether the transfer of mitochondria to chondrocytes contributes to the mechanism of action of MSCs. Design: Chondrocytes and MSCs were stained with MitoTracker, and CellTrace was used to distinguish between cell types. The uptake of fluorescent mitochondria was measured in cocultures using flow cytometry. Transport was visualized using fluorescence microscopy. Microvesicles were isolated and the presence of mitochondria was assessed. Mitochondria were isolated from MSCs and transferred to chondrocytes using MitoCeption. Pellets of chondrocytes, chondrocytes with transferred MSC mitochondria, and cocultures were cultured for 28 days. DNA content and proteoglycan content were measured. Mitochondrial DNA of cultured pellets and of repair cartilage tissue was quantified. Results: Mitochondrial transfer occurred bidirectionally within the first 4 hours until 16 hours of coculture. Transport took place via tunneling nanotubes, direct cell-cell contact, and extracellular vesicles. After 28 days of pellet culture, DNA content and proteoglycan deposition were higher in chondrocyte pellets to which MSC mitochondria were transferred than the control groups. No donor mitochondrial DNA was traceable in the biopsies, whereas an increase in MSC mitochondrial DNA was seen in the pellets. Conclusions: These results suggest that mitochondrial transport plays a role in the chondroinductive effect of MSCs on chondrocytes in vitro. However, in vivo no transferred mitochondria could be traced back after 1 year.Molecular Technology and Informatics for Personalised Medicine and Healt