oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Carbon uptake and change in net primary productivity of oasis-desert ecosystem in arid western China with remote sensing technique

ZHANG Jie,PAN Xiaoling,GAO Zhiqiang,SHI Qingdong,LV Guanghui,

地理学报 , 2006,
Abstract: Arid and semi-arid ecosystems exhibit a spatially complex biogeophysical structure. According to arid western special climate-vegetation characters, the fractional cover of photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), bare soil and water are unmixed, using the remote sensing spectral mixture analysis. We try the method to unmix the canopy funation structure of arid land cover in order to avoid the differentiation of regional vegetation system and the disturbance of environmental background. We developed a modified production efficiency model NPP-PEM appropriate for the arid area at regional scale based on the concept of radiation use efficiency. This model refer to the GLO-PEM and CASA model was driven with remotely sensed observations, and calculates not just the conversion efficiency of absorbed photosynthetically active radiation but also the carbon fluxes that determine net primary productivity (NPP). We apply and validate the model in the Kaxger and Yarkant river basins in arid western China. The NPP of the study area in 1992 and 1998 was estimated based on the NPP-PEM model. The results show that the improved PEM model, considering the photosynthetical activation of heterogeneous functional vegetation, is in good agreement with field measurements and the existing literature. An accurate agreement (R2 = 0.85, P<0.001) between the estimates and the ground-based measurement was obtained. The spatial distribution of mountain-oasis-desert ecosystem shows an obvious heterogeneous carbon uptake. The results are applicable to arid ecosystem studies ranging from characterizing carbon cycle, carbon flux over arid areas to monitoring change in mountain-oasis-desert productivity, stress and management.
The kinetics of fluoride uptake by synthetic hydroxyapatite  [PDF]
Takudzwa Gomwe,Samantha E. Booth,John W. Nicholson
Ceramics-Silikáty , 2012,
Abstract: The kinetics of fluoride uptake by synthetic hydroxyapatite from aqueous solution has been studied. Experiments involved exposing 0.1 g of synthetic hydroxyapatite to 5 cm3 of sodium fluoride solution in the concentration range 100-1000 ppm fluoride and determining fluoride concentration at regular time intervals with a fluoride ion-selective electrode. In all cases, uptake was found to follow pseudo-second order kinetics with correlation coefficients of at least 0.998; all systems equilibrated by 24 hours with equilibrium uptake values that varied with the initial fluoride concentration. The kinetic results differ from those previously reported for much lower concentrations of fluoride, but in the present case, the concentrations were of clinical relevance, as they are those used in fluoride-containing dental products. Further work is necessary to determine how well these findings model uptake by natural hydroxyapatite and hence the extent to which they might apply in vivo.
Carbon uptake and change in net primary productivity of oasis-desert ecosystem in arid western China with remote sensing technique
干旱生态系统净初级生产力估算及变化探测

SHI Qingdong,LV Guanghui,ZHANG Jie,PAN Xiaoling,GAO Zhiqiang,SHI Qingdong,LV Guanghui,
张杰
,潘晓玲,高志强

地理学报(英文版) , 2006,
Abstract: Arid and semi-arid ecosystems exhibit a spatially complex biogeophysical structure. According to arid western special climate-vegetation characters, the fractional cover of photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), bare soil and water are unmixed, using the remote sensing spectral mixture analysis. We try the method to unmix the canopy funation structure of arid land cover in order to avoid the differentiation of regional vegetation system and the disturbance of environmental background. We developed a modified production efficiency model NPP-PEM appropriate for the arid area at regional scale based on the concept of radiation use efficiency. This model refer to the GLO-PEM and CASA model was driven with remotely sensed observations, and calculates not just the conversion efficiency of absorbed photosynthetically active radiation but also the carbon fluxes that determine net primary productivity (NPP). We apply and validate the model in the Kaxger and Yarkant river basins in arid western China. The NPP of the study area in 1992 and 1998 was estimated based on the NPP-PEM model. The results show that the improved PEM model, considering the photosynthetical activation of heterogeneous functional vegetation, is in good agreement with field measurements and the existing literature. An accurate agreement (R2 = 0.85, P<0.001) between the estimates and the ground-based measurement was obtained. The spatial distribution of mountain-oasis-desert ecosystem shows an obvious heterogeneous carbon uptake. The results are applicable to arid ecosystem studies ranging from characterizing carbon cycle, carbon flux over arid areas to monitoring change in mountain-oasis-desert productivity, stress and management.
Parabens do not increase fluoride uptake by dental enamel  [PDF]
Vanessa Silva Tramontino,Daniela Labbate,Cínthia Pereira Machado TABCHOURY,Jaime Aparecido CURY
RGO : Revista Gaúcha de Odontologia , 2010,
Abstract: Objective: To evaluate whether methylparaben and propylparaben, which present a similar chemical structure, increase fluoride uptake by demineralized dental enamel when present in buffered solutions. Methods: The study comprised an in vitro experiment using blocks of bovine dental enamel with artificial carious lesions. Enamel blocks were exposed to the following treatment (n=12): fluoride solution (200 ppm fluoride) - control; solution containing fluoride and 13 mM methylparaben; solution containing fluoride and 13 mM propylparaben in 35% propylene glycol; solution containing fluoride in 35% propylene glycol. All solutions were buffered (0.01 M cacodilate) and the pH was adjusted to 6.27. The blocks were exposed to the treatment solutions in the proportion of 2 ml per mm2 of exposed enamel area and fluoride formed was estimated after removing an enamel layer by acid etching. Fluoride extracted was determined by ion specific electrode and the amount of enamel removed was estimated by phosphorus analysis. ANOVA followed by Tukey’s test were used for statistical analysis, with significance level at 5%. Results: The dental blocks of treatment groups containing both parabens and the control group presented similar fluoride concentration in enamel and no statistical difference was observed among them (p>0.05). The dental blocks of treatment group containing fluoride and propylene glycol showed the lowest value of fluoride present in enamel, which was significantly different from the control and fluoride and methylparaben groups (p<0.05). Conclusion: Methyl and propylparaben in a buffered solution do not enhance fluoride uptake by demineralized dental enamel.
Fluoride Distribution in Groundwater, Soil and Some Crops in Isfahan Region  [cached]
N. Mirghaffari,H. Shariatmadari
Journal of Science and Technology of Agriculture and Natural Resources , 2007,
Abstract: Concentration of soluble fluoride in groundwater, soil, and some crops in Isfahan region was determined by Ion Selective Electrode (ISE) method. The mean fluoride concentration of water samples in the study area was 0.3 and 0.05 mg L-1 in the spring and summer, respectively. These values are in an acceptable limit for irrigation, whereas for drinking water, they are in deficiency range. The average and maximum concentrations of soluble fluoride in soil samples were 1.0 and 3.2 mg kg-1, respectively. In general, the spatial distribution of fluoride in soils showed that fluoride content around major industrial centers such as Isfahan Steel Factory, Mobarakeh Steel Co., and Isfahan oil refinery was higher than other sites. The minimum and maximum fluoride contents of crops were observed in alfalfa as 0.2 and in corn as 4.2 mg kg-1, respectively. Tomato had the highest mean concentration of fluoride as 3.6 mg kg-1. The fluoride concentration in plants positively correlated with the fluoride concentration in irrigation water and soil (P < 0.01) and negatively correlated with cation exchange capacity of soil (P < 0.05).
Fluoride Uptake Level of the Enamel by a Fluoride Varnish and a Fluoride Gel (APF)
Navabi B.,Ansari G.,Khan Z.,Kheirieh P.
Journal of Dentistry , 2011,
Abstract: Statement of Problem: Various forms of fluoride-contained products are used to increase the resistance of the tooth against caries for preventive purposes. Furthermore, studies demonstrated higher fluoride uptake with varnish and gel among the wide range of products.Purpose: This study compared fluoride uptake of Duraflor varnish (Practicon Dent, USA) with fluoride gel (APF, Sultan ), used on the enamel surface of the intact teeth.Materials and Method: In this experimental in-vitro study, 20 intact pre-molar teeth extracted for orthodontic purposes were randomly assigned to two groups of 10 teeth. The teeth were sectioned into two mesial and distal halves as the control and experimental sides. Defined semi-circular areas on the enamel surface of the experimental halves were treated with gel or varnish for 1 hour. The sample halves were stored in artificial saliva for 24 hours at 37°c, etched for 30 seconds by 0.5 M perchloric acid, and washed by 0.2 m KOH after each etching process. Biopsies of the samples were obtained by Acid Etch Enamel Biopsy technique and the fluoride and calcium concentrations were calculated by potentiometer and spectrophotometer, respectively. Kolmogorov-smirnov, Paired t-test and Student t- test were used for statistical analyses.Results: The results demonstrated an increase in the enamel fluoride content after exposure of the teeth to both Duraflor varnish and APF gel (Sultan ). The results of the paired t-test revealed significant differences between the experimental and control halves in both groups (varnish: p =0.002, gel: p =0.039). The fluoride uptake value in varnish and gel groups was 2069.78 ppm and 1050.99 ppm, respectively. The student t-test showed a statistically significant difference ( p =0.01).Conclusion: Both APF gel and Duraflor varnish increased the fluoride content of the tooth enamel after application, although Duraflor varnish had a higher fluoride uptake level than APF gel.
Fluoride Release and Uptake by Glass Ionomer Cements, Compomers and Giomers
S. Mostafa Mousavinasab,Ian Meyers
Research Journal of Biological Sciences , 2012,
Abstract: Daily fluoride release/uptake by glass ionomer cements, compomers and Giomers. To measure the amounts of fluoride released from fluoride-containing materials before and after fluoride applications 4 glass ionomer cements (Fuji IX, Fuji VII, Fuji IX Extra, Fuji II LC), a Compomer (Dyract Extra) and a Giomer (Beautifil) were used in this study. Cylindrical specimens prepared and the amount of released fluoride was measured during the 1st week and on the days 14 and 21 by using specific fluoride electrode and an ion-analyzer. After 21 days, the specimens divided into 1 groups each of 10. The specimens of 1 group exposed to 220 ppm Mouth wash solution and the other group specimens exposed to 1000 ppm F NaF toothpaste. Fluoride release after recharge was measured and recorded daily for a total of 7 days. The results were statistically analyzed using 2 ways ANOV A and Tukey Kramer multiple comparison tests. Significant differences were seen in fluoride release before and after recharge for different days and materials. FVII released the maximum amount of fluoride followed by FIX EX, FII LC, FIX, DE and BT. On the 21st the maximum fluoride release was related to FVII, followed by FII LC, FIX EX, FIX, DE and BT. The maximum and minimum fluoride in samples treated by mouthwash or toothpaste released by FVII and BT, respectively. The maximum amount of fluoride released by F VII and the minimum by BT before and after recharge, respectively. It seems that the extent of the glass ionomer matrix plays an important part in determining the fluoride recharging ability of GICs materials.
A Comparison of Fluoride Uptake by Sound Enamel Following Application of Sodium Fluoride Mouthrinses and APF Gels Produced in Iran with Standardized Foreign Samples
J Mahmoodian,A Kowsari,B Esmaeili
Journal of Dental Medicine , 2002,
Abstract: The goal of this investigation is to compare the extent of fluoride uptake by sound enamel following application of two commercial mouthrinses containing sodium fluoride (0.2%) and a topical gel containing APF (1.23%) produced in Iran with those of foreign standardized ones. Sixty extracted premolars were used. Each tooth was divided into two lingual and buccal halves, one half as control, the other one as experimental. Enamel biopsy technique (two- step acid etching) was used to determine the concentration of fluoride and calcium in each sample. For data comparison and fluoride uptake estimation, the depths of layers with the use of linear regression analysis were standardized to 25 and 50um. The analysis showed that in Iranian mouthrinse no. 1, there is linear correlation between fluoride concentration and enamel depth, in both control and experimental group at the first and second layers, while, in other groups, this correlation was observed just at the first layer (superficial enamel layer). The greatest fluoride uptake was seen at Iranian mouthrinse no.2 and the least was seen at foreign mouthrinse no. 3. From among two APF gels, the greatest uptake was observed at gel no. 1 (Iranian). The results showed that all three Iranian products increase fluoride content of enamel, moreover the level of fluoride uptake, while applying Iranian products, in comparison with foreign ones, shows considerable increase.
Effect of 0.02% NaF solution on enamel demineralization and fluoride uptake by deciduous teeth in vitro
Chedid, Silvia José;Cury, Jaime Aparecido;
Brazilian Oral Research , 2004, DOI: 10.1590/S1806-83242004000100004
Abstract: the application of 0.02% naf solution on teeth with a cotton swab instead of brushing with fluoride dentifrice has been suggested for young children to reduce the risk of dental fluorosis, but its anticariogenic effect has not been evaluated. thus, we studied the in vitro effect of 0.02% naf solution on enamel demineralization and fluoride uptake in deciduous teeth; non-fluoride dentifrice and fluoride dentifrice (1,100 mg f/g) were used, respectively, as negative and positive controls. the treatment with fluoride dentifrice was more effective in reducing enamel demineralization (p < 0.05) and on fluoride uptake by the enamel (p < 0.05) than the non-fluoride dentifrice and the 0.02% naf solution. data suggest that the alternative use of 0.02% naf solution instead of fluoride dentifrice should be reevaluated especially if dental caries are to be controlled.
The Analysis of Productivity Growth of Tuber Crops in Nigeria (1995-2006)  [cached]
Ogunniyi, L. T.,Ajao, A. O.
Asian Journal of Agriculture and Rural Development , 2012,
Abstract: This study analyzed the productivity of Tuber crops in Nigeria from twenty states between the periods of 1995 -2006 using Data Envelopment Analysis (DEA) to estimate the total factor productivity (TFP) which was further decomposed to reveal the source of productivity growth over the reference period. Negative TFP growth was observed for all the tuber crops considered in the study on the average but an evidence of convergence in productivity level was observed when considering the starting TFP, majority of the states had low TFP (<0.6) but grew over the years by about 0.2 with Kaduna and Adamawa having the highest TFP for cocoyam and cassava respectively
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.