Electronic, magnetic, optical and thermoelectric properties of co-doped Sn1-2x Mn x A x O2 (A = Mo, Tc): a first principles insight.

The electronic, magnetic, optical and thermoelectric (TE) properties of Sn1-2x Mn x A x O2 (A = Mo/Tc) have been examined using density functional theory (DFT) based on the FP-LAPW approach. The results suggested that all the doped compounds show a half-metallic ferromagnet property with a 100% spin polarization at the Fermi level within GGA and mBJ. Moreover, doping SnO2 with double impurities reduces the bandgap. The reduced bandgaps are the result of impurity states which arise due to the Mn and Mo/Tc doping, leading to the shifts of the minima of the conduction band towards the Fermi energy caused by substantial hybridization between transition metals 3d-4d and O-2p states. Also, the (Mn, Mo) co-doped SnO2 system exhibits a ferromagnetic ground state which may be explained by the Zener double exchange mechanism. While the mechanism that controls the ferromagnetism in the (Mn, Tc) co-doped SnO2 system is p-d hybridization. Therefore, the role of this study is to illustrate the fact that half-metallic ferromagnet material is a good absorber of sunlight (visible range) and couples to give a combined effect of spintronics with optronics. Our analysis shows that Sn1-2x Mn x Mo x O2 and Sn1-2x Mn x Tc x O2 are more capable of absorbing sunlight in the visible range compared to pristine SnO2. In addition, we report a significant result for the thermoelectric efficiency ZT of ∼0.114 and ∼0.11 for Sn1-2x Mn x Mo x O2 and Sn1-2x Mn x Tc x O2, respectively. Thus, the coupling of these magnetic, optical, and thermoelectric properties in (Mn, A = Mo or Tc) co-doped SnO2 can predict that these materials are suitable for optoelectronic and thermoelectric systems.

Ferromagnetic alloy for high-efficiency photovoltaic conversion in solar cells: first-principles insights when doping SnO2 rutile with coupled Eu-Gd.

From results of first-principles all-electron full-potential augmented spherical-wave calculations within a generalized gradient approximation, a materials design for half-metallic ferromagnetic semiconductors based on (Eu,Gd)-doped SnO2 rutile is proposed. Moreover, their half-metallic ferromagnetic properties are homogenous and energetically stable for different crystallographic directions. Therefore, the interatomic exchange interaction between the spins of double impurity ions is a long-range ferromagnetic interaction that is sharply weakened when the distance between Eu-Gd increases. The double impurities most likely substitute adjacent Sn sites and result in strong ferromagnetic interactions by p-f hybridization between rare earth 4f and Op states. There is great interest in the configuration that has the lowest energy difference, where the double impurity substitutes the nearest neighbor Sn sites along the z-axis of SnO2 rutile. Generalized gradient approximation GGA and GGA+U calculations were performed. According to our revPBE-GGA calculations, the ferromagnetic compound is capable of absorbing 96% from the visible light. Furthermore, the transport properties at room temperature ensure excellent electrical conductivity, low thermal conductivity, and the most optimal figure of merit (ZT), which leads to high thermoelectric performance. As the latter are closely related to free flow charge carriers, we can subsequently predict that the ferromagnetic alloy will be able to be a great power source for highly effective photovoltaic conversion in solar cells. Further experimentation will be necessary to obtain confirmation of our ab initio predictions.

Rare-earth-doped TiO2 rutile as a promising ferromagnetic alloy for visible light absorption in solar cells: first principle insights.

The electronic structure and magneto-optic properties of TiO2 (rutile) doped with two concentrations of rare-earth (RE) elements are explored using a first-principle all-electron full-potential augmented spherical-wave method based on the PBEsol-GGA approximation, to examine their potential use as a spintronic and optoelectronic system. The results predict that all compounds exhibit half-metallic character, the only exception is by doping with Nd or that the material is magnetic but the cloud is still a half-metallic magnet. We also found that the localized level at the Fermi energy shifts to lower energy as the atomic number of the 4f-element increases. Consequently, the mechanism that controls the ferromagnetism in these systems has been proposed according to this positioning. The energy of the localized level due to Gd is sufficiently low to lie at the top of the valence band, while Eu produces a midgap state. However, the Fermi level was not noticed precisely at the middle of the energy gap. In contrast, the impurity states of the Nd-, Pm-, and Sm-dopants are close to the bottom of the conduction band of the host system. This allows electrons to be delocalized, and gives a higher scattering cross-section. Interestingly, the analysis of optical absorption and electrical conductivity emphasizes that this ferromagnetic DMS based on rare-earth elements has the power to be a promising spintronic device for visible light absorption in solar cells. Finally, the relationship between the mechanism that controls the ferromagnetism and the absorption efficiency of visible light is discussed.

Effects of octreotide treatment on early TNF-alpha production and localization in experimental chronic colitis.

BACKGROUND: Colitis induced by trinitrobenzene sulphonic acid (TNB) is a model of Th1 disease, mainly explored from the third day of induction. It has recently been shown that octreotide and other somatostatin analogues can modify inflammatory/immune processes by acting on cytokines. AIM: To examine TNFalpha production and the effect of preventive treatment with octreotide, during the early phase of TNB-colitis. METHODS: Thirty milligrams TNB with 50% ethanol was instilled into the colon of male Wistar rats. Treated groups received octreotide (2x10 microg x day/rat) or dexamethasone (1x2 mg x day/kg), subcutaneously, with the first injection before TNB. Eight and 80 h later, the colon was excised and processed for histology, TNFalpha immunohistochemistry, quantification of cytokine release ex vivo and tissue-inducible NO synthase (iNOS) activity. RESULTS: Maximal TNFalpha production was observed at the 8th hour, associated with intense immunostaining of the external muscle layer. Octreotide treatment decreased TNFalpha expression (staining and activity) and iNOS activity. At the 80th hour, submucosal macrophages were positive for TNFalpha and colonic production of IL1beta and interferon gamma was increased; all these effects were reduced by octreotide treatment. CONCLUSIONS: TNFalpha was expressed early by resident muscle cells, before staining of infiltrated immune cells and increased production of interferon gamma. TNFalpha regulation by octreotide suggests that this drug might exert anti-inflammatory properties via smooth muscle cells.

Role of tumour necrosis factor-alpha and inducible nitric oxide synthase in the prevention of nitro-flurbiprofen small intestine toxicity.

The present study compares the intestinal toxicity of nitro-flurbiprofen and flurbiprofen in order to determine their differential properties on tumour necrosis factor-alpha production and inducible nitric oxide synthase induction. Rats received one s.c. injection of flurbiprofen, nitro-flurbiprofen at equimolar dose of solvent. Twenty-four hours later, the rats were sacrificed and small intestine tissue was taken up for macroscopical quantification of ulceration, ex vivo production of tumour necrosis factor-alpha and nitrites, and determination of tissue inducible nitric oxide synthase and myeloperoxidase activities. Anti-inflammatory activity was examined in the carrageenan-induced paw edema model. We demonstrated that flurbiprofen induced dose-dependently small intestine production of tumour necrosis factor-alpha, nitrites, myeloperoxidase and inducible nitric oxide synthase activities. On the other hand, nitro-flurbiprofen did neither induce tumour necrosis factor-alpha nor nitrite production. Concurrently, no small intestine ulceration was observed with nitro-flurbiprofen whereas flurbiprofen induced dose-dependent ulceration. Nitro-flurbiprofen is devoid of intestinal toxicity despite inhibiting cyclooxygenase activity. This is associated with the absence of tumour necrosis factor-alpha and inducible nitric oxide synthase induction in normal rats. Nitro-flurbiprofen is an anti-inflammatory drug with a much more favorable gastro-intestinal toxicity profile than flurbiprofen.

Effects of lanreotide, a somatostatin analogue, on postprandial gastric functions and biliopancreatic secretions in humans.

AIMS: Lanreotide is a novel synthetic somatostatin analogue. A long-acting formulation of lanreotide has been shown to be effective for the treatment of gastroentero-pancreatic hormone-producing tumours but effects on postprandial digestive and absorptive functions remain obscure. The aim of the present study was to evaluate the effects of intravenous lanreotide on gastric and biliopancreatic secretions in man as well as the absorption of nutrients and the duodeno-caecal transit time after ingestion of an homogenized meal (500 kcal, 55% carbohydrates, 15% proteins, 30% lipids). METHODS: Eight healthy male volunteers were studied on two occasions within a 2 weeks interval, using a perfusion method. They received in single-blind and random order continuous i.v. infusion of either placebo or lanreotide (100 micrograms h-t after a bolus of 100 micrograms 15 min before the beginning of the study). RESULTS: Lanreotide significantly decreased gastric acid secretion (90%) for the initial 3 h period. Gastric emptying was not significantly modified by lanreotide infusion. Compared with placebo, lanreotide almost completely abolished both bile salts and lipase responses to the meal. It largely increased the duodeno-caecal transit time and decreased significantly the duodenal absorption of carbohydrates and triglycerides. CONCLUSIONS: Since lanreotide has powerful effects on gastrointestinal functions, it could be useful in the prevention or in the treatment of pancreatic and bowel fistulas as well as short bowel syndrome.