| 1. |
- Feng, Bo, et al.
(författare)
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Mechanisms of N2O Formation from Char Combustion
- 1996
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 10:1, s. 203-208
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes an experimental study on N2O and NOx emission from char combustion. Experiments have been carried out in a fixed bed reactor in the temperature range of 973−1323 K. Oxygen concentrations for combustion, temperature, and char type have been found to have strong effects on both N2O and NOx emissions. With an increasing temperature, N2O reaches a peak at 1073 K and then decreases with temperature. At the same time NOx remains nearly the same. When oxygen concentration increases, the concentration of N2O increases and NOx first increases and then decreases. The char with higher nitrogen content emits more N2O, indicating that nitrogen oxides come from char-N. When NO is included in the inlet gases, much more N2O is produced from char combustion. This suggests that the reaction of NO + O2 + char is the main pathway for N2O formation. Another pathway, i.e., the homogeneous oxidation of HCN from the gasfication of char, seems to be important as well.
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| 2. |
- Feng, Bo, et al.
(författare)
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Nitrogen oxides emission from a circulating fluidized bed combustor
- 1998
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Ingår i: International Journal of Energy Research. - 1099-114X .- 0363-907X. ; 20:11, s. 1015-1025
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Tidskriftsartikel (refereegranskat)abstract
- Experiments were carried out in a pilot-scale circulating fluidized bed (CFB) coal combustor to investigate the mechanism of N,O formation, nitrogen oxides (including NO, and N,O) emission and the effect of temperature, excess air ratio, recirculation ratio, etc. The concentrations of nitrous oxide and nitric oxide were measured along the height of the CFB furnace. N,O concentration increased with height, and in the exit of the combustor N,O reached the highest level. NO,, however, decreased with height, showing the inverse trend compared with N,O. The N,O emission decreased sharply with the rise of temperature at the bottom of the combustor; at the same time, the NO, concentration increased.
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| 3. |
- Hellman, Per, et al.
(författare)
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Vitamin D and retinoids in parathyroid glands
- 1999
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Ingår i: International Journal of Molecular Medicine. - 1107-3756 .- 1791-244X. ; 3:4, s. 355-361
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Tidskriftsartikel (refereegranskat)abstract
- Vitamin D and retinoids are important regulators of differentiation and proliferation in a number of tissues, and have been implicated as chemopreventive agents in several different tumors. While vitamin D is known to be important for regulation of parathyroid function and proliferation, it has recently been established that parathyroid cells also are targets for retinoids. Hyperparathyroidism (HPT) is a common disorder, and evaluation of the disease has indicated high prevalence of subclinical disease, as well as clear benefits of offering treatment for the disease. This review summarizes the data so far gathered concerning parathyroid cells, vitamin D and retinoids, with clear implication on prospects of possible medical treatment of hyperparathyroidism.
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| 4. |
- Liu, Wei, et al.
(författare)
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Biosynthesis and function of all-trans- and 9-cis retinoic acid in parathyroid cells
- 1996
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 229:3, s. 922-929
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that cultured human and bovine parathyroid cells incubated with all-trans-[11,12-3H]-retinol convert this tracer into all-trans- and 9-cis-retinoic acid. By using RT-PCR, cellular retinol-binding protein type I (CRBP I), cellular retinoic acid binding protein I and II (CRABP I and II), retinoic acid receptors (RARs) alpha, beta and gamma, and 9-cis-retinoic acid receptor (RXR) alpha transcripts were detected in human parathyroid cDNA. CRBP I and CRABP I expression was confirmed by immunohistochemistry. Both 9-cis- and all-trans-RA were found to suppress parathyroid hormone (PTH) secretion from dispersed human adenomatous parathyroid cells, which was augmented by combined treatment with 1mM RA and 100 nM 1,25 (OH)2D3. The present data establish parathyroid gland as a target for retinoids and as a site of synthesis of the hormonal forms of vitamin A (retinol), all-trans- and 9-cis-retinoic acid.
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| 5. |
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| 6. |
- Löntz, Werner, et al.
(författare)
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Increased mRNA expression of manganese superoxide dismutase in psoriasis skin lesions and in cultured human keratinocytes exposed to IL-1 beta and TNF-alpha
- 1995
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Ingår i: Free Radical Biology & Medicine. - 0891-5849 .- 1873-4596. ; 18:2, s. 349-355
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Tidskriftsartikel (refereegranskat)abstract
- Because reactive oxygen species have been implicated in the pathogenesis of various hyperproliferative and inflammatory diseases, the mRNA expression of the antioxidant enzyme superoxide dismutase was studied in psoriatic skin tissue. By using reverse transcription-PCR we found similar expression of copper, zinc superoxide dismutase (CuZnSOD) in the involved vs. uninvolved psoriatic skin. In contrast, the level of the manganese superoxide dismutase (MnSOD) mRNA message was consistently higher in lesional psoriatic skin as compared to adjacent uninvolved skin and healthy control skin. Parallel investigation of those cytokines that are thought to be direct or indirect inducers of the MnSOD activity revealed an increased mRNA expression of IL-1 beta, TNF-alpha, and GM-CSF in lesional psoriatic skin. To study if these cytokines exert a direct effect on dismutase expression in epidermal cells, human keratinocytes in culture were challenged with IL-1 beta, TNF-alpha, and GM-CSF. It was found that IL-1 beta and TNF-alpha, but not GM-CSF, induced the mRNA expression of MnSOD, and an additive effect was demonstrated for the two former cytokines. Further, the expression of both CuZnSOD and MnSOD transcripts was similar in cultured keratinocytes maintained at low differentiation (low Ca2+ medium) and cells forced to terminal differentiation (by high Ca2+ medium). Our results indicate that the abnormal expression of MnSOD mRNA in lesional psoriatic skin is not directly linked to the pathologic state of keratinocyte differentiation in the skin. It seems more likely that the cutaneous overexpression of MnSOD in psoriatic epidermis represents a protective cellular response evoked by cytokines released from inflammatory cells invading the diseased skin.
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| 7. |
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| 8. |
- Wei, Liu
(författare)
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Retinoids and vitamin D in skin and parathyroid glands
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vitamin D3 (VitD3) and retinoids are important factors involved in differentiation and proliferation in many cell systems. Their effects in skin, where retinoids and vitamin D are known to be crucially involved in keratinocyte differentiation and function,, and in the parathyroid, the overall regulatory organ in calcium homeostasis were studied. It is discovered that transcripts for retinal-binding protein (RBP), cellular retinol binding protein (CRBP) I and cellular retinoic acid binding protein (CRABP) I and II are found in normal skin and keratinocytes. Decreased CRABP I and increased CRABP II mRNA expressions were found in lesional psoriatic skin compared with uninvolved skin. Transcripts for CRBP I, CRABP I and II, retinoic acid receptor (RAR) type α, β and γ and retinoic X receptor (RXR) α were also detected in human parathyroid adenomas. Cultured human and bovine parathyroid cells were able to produce all-trans retinoic acid (atRA) and 9-cis retinoic acid (9cRA) from all-trans-[11,12-3H]-retinol. VitD3, atRA and 9cRA were found to suppress parathyroid hormone (PTH) mRNA level and PTH secretion from human adenomatous and bovine parathyroid cells. Further, atRA, 9cRA and vitD3 inhibited proliferation of human parathyroid cells in vitro.Calcium receptors are crucially involved in sensing of extracellular calcium concentrations in the parathyroid. Two receptors are discovered; CAS (megalin, gp330; 550 kDa) and CaR (120 kDa); but their respective role in calcium homeostasis is not yet clarified. A recently established rat kidney proximal tubule cell line (IRPTC) express CAS, but not CaR, but nevertheless responds to changes in external calcium similar to parathyroid cells and placental cytotrophoblasts. CAS expression in IRPTC's increased after addition of atRA, 9cRA or VitD3, alone or in combinations, similar to what was seen in the human choriocarcinoma cell line JEG-3 and differentiated F9 cells (murine teratocarcinoma incubated with atRA and cAMP). In primary cultured bovine parathyroid cells, CaR, CAS and PTH mRNA levels gradually decreased during culture up to 5 days, and vitD3 atRA or 9cRA inhibited PTH mRNA but failed to influence CAS or CaR mRNA levels during this culture period.In conclusion, the results in this thesis confirm that parathyroid gland as well as skin are target organs of vitamins A and D, which are influencing cell proliferation, differentiation, and hormone production. These factors exert tissue specific effects on CAS mRNA expression.
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| 10. |
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