Spectra profile expansion of Bragg wavelength on nano-particle embedded fiber-Bragg-grating

 This article presents the results of a detailed study on the effects of spectra profile expansion of Bragg wavelength on the performance of the nano-particle embedded fiber-Bragg-grating (nano-EFBG) for sensing applications. The fiber-Bragg- grating (FBG) was coated by CdSe-nano-particle layers with various thicknesses (600-2000 nm) and bonded on substrates of epoxy or epoxy/Teflon with a large thermal expansion coefficient. With this embedding method, a variation of the line-width expansion of Bragg wavelength with cooling down FBG has been controlled. The nano-EFBG morphology was investigated by FE-SEM and the nano-EFBG sensors are studied in ambient from 77 K (liquid nitrogen) to 393 K. The expansion of spectral profile, which caused by transverse loading from nano-particle/epoxy layers, can be changed in the range of 0.1-1.3 nm between before and after cooling down. This result is for the strain-temperature sensors, but has the potential application in the FBG dispersion compensation devices and many other measurands.

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Coastal livelihood transitions: Socio-economic consequences of changing mangrove forest management and land allocation in a commune of Central Vietnam

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Adaptation of turbo coding and equalization in turbo equalization for time-varying and frequency-selective channels

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A number of authors have sought to combine equalization and decoding in an iterative system in order to reduce the effects of frequency and temporal dispersiveness of time-varying frequency-selective channels. In the recent literature, several architectures based on these iterative systems have been proposed. One can note architectures which combine a maximum a posteriori (MAP) equalizer and decoder, architectures formed by an interference canceller and MAP decoder, architectures implementing a decision feedback equalizer and a MAP decoder, etc. Most of these architectures require accurate channel estimation to adapt the equalizer filters or to execute the MAP equalizers. This article presents a turbo equalizer architecture for time-varying frequency-selective channels without channel estimators. The proposed turbo equalizer consists of an interference canceller in direct-adaptation mode and a turbo decoder. In order to reduce noise correlation, the addition of a transverse filter to the interference-canceller architecture is proposed. The reliability factor for variable time-varying frequency-selective channels is also redefined in order to improve the performance of the turbo decoder. The architecture of the proposed turbo equalizer reduces considerably the effects of frequency and temporal dispersiveness of time-varying frequency-selective channels depending on the normalized Doppler frequency range.

Giáo trình lý thuyết tài chính - tiền tệ

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Hydrological and sedimentary controls leading to arsenic contamination of groundwater in the Hanoi area, Vietnam: The impact of iron-arsenic ratios, peat, river bank deposits, and excessive groundwater abstraction

 Groundwater contamination by arsenic in Vietnam poses a serious health threat to millions of people. In the larger Hanoi area, elevated arsenic levels are present in both, the Holocene and Pleistocene aquifers. Family-based tubewells predominantly tap the Holocene aquifer, while the Hanoi water works extract more than 600,000 m(3)/day of groundwater from the Pleistocene aquifer. Detailed groundwater and sediment investigations were conducted at three locations exhibiting distinct geochemical conditions, i.e., i) high levels of dissolved arsenic (av. 121 mu g/L) at the river bank, ii) low levels of dissolved arsenic (av. 21 mu g/L) at the river bank and, iii) medium levels of dissolved arsenic (60 mu g/L) in an area of buried peat and excessive groundwater abstraction. Seasonal fluctuations in water chemistry were studied over a time span of 14 months. Sediment-bound arsenic (1.3-22 mu g/g) is in a natural range. Arsenic correlates with iron (r(2) > 0.8) with variation related to grain size. Sediment leaching experiments showed that arsenic can readily be mobilized at each of the three locations. Low levels of arsenic in groundwater (<10 mu g/L) generally exhibit manganese reducing conditions, whereas elevated levels are caused by reductive dissolution under iron- and sulphate reducing conditions. Average arsenic concentrations in groundwater are twofold higher at the river bank than in the peat area. The lower levels of arsenic contamination in the peat area are likely controlled by the high abundance of iron present in both the aqueous and sediment phases. With median molar Fe/As ratios of 350 in water and 8700 in the sediments of the peat area, reduced iron possibly forms new mineral phases that resorb (or sequester) previously released arsenic to the sediment. Despite similar redox conditions, resorption is much less significant at the river bank (Fe/As(aq)=68, Fe/As(s)=4700), and hence, arsenic concentrations in groundwater reach considerably higher levels. Drawdown of Holocene water to the Pleistocene aquifer in the peat area, caused by the pumping for the Hanoi water works, clearly prornotes reducing conditions in Pleistocene groundwater. This demonstrates that excessive abstraction of water from deep wells, i.e.. wells tapping water below the arsenic burdened depth, can cause a downward shift of iron-reducing conditions and concurrently mobilize arsenic along the way. Vertical migration of reduced groundwater may also impact aquifers under natural hydrological conditions. Seepage of DOC-enriched groundwater derived from degradation of organic matter in the clayey sediments at the river bank was observed to enhance (and maintain) iron-reducing conditions in the aquifer where organic matter is scarce. Once the aquifer becomes reduced, arsenic is released from the aquifer solid-hosts but additionally derives from the arsenic-enriched groundwater seeping from the clay into the aquifer. This behaviour is an important mechanism for arsenic contamination in aquifers that might not necessarily contain enough organic matter in their sediments to induce reducing conditions independently.

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Divalent manganese in A-position of perovskite cell: X-ray absorption finite structure study of La(0.6)Sr(0.4-x)MnTi(x)O(3) manganites

Local structure and magnetic properties of Ti doped A-site deficient La(0.6)Sr(0.4-x)MnTi(x)O(3+delta) manganites (0.15 >= x >= 0) have been studied. The compositions belong to rhombohedral R (3) over barc phase. Segregation of (La(0.6)Sr(0.4-x)Mn(y))(Mn(1-y-z)Ti(x))O(3+delta) phase and fallout of (z/3)Mn(3)O(4) oxide was observed with x increase. Some amount (y) of Mn, being in divalent valence state, occupies the A (=La,Sr)-position of perovskite cell. Samples with x=0 and 0.05 are ferromagnetic with Curie temperature T(C)=350 and 172 K, respectively. Samples with x=0.1 and 0.15 are in spin(cluster)-glass states at low temperatures. (c) 2008 American Institute of Physics.
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Ownership, organization, and income inequality: Market transition in rural Vietnam

 In transitional economies, the scale of economic enterprise and the allocation of property rights shape social structures and influence income distribution. In agrarian economies, where labor-intensive family enterprises dominate, political officials' income advantages decline rapidly relative to those of private entrepreneurs. Larger enterprises, however provide greater income opportunities for officials, especially when a government retains an ownership stake in the initial phases of reform. This article replicates the findings from an earlier study of rural China using comparable survey data from Vietnam. We find that during the first two decades of rural market reform in Vietnam and China, the scale and ownership of firms differed radically. Small family enterprises dominated rural development in Vietnam, whereas China development was dominated by larger firms, initially established by rural governments. Consequently, while cadre income advantages have kept pace with those of private entrepreneurs in China, they have declined rapidly in Vietnam.

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