Advanced Materials Research Vol. 684

Abstract: To solve the problems in the construction of ecological environment, this paper studies the application, effect and investment of sprinkling irrigation and drip irrigation in the ecological environment construction by the field trials. The results show that the optimal irrigation technique for the restoration and reconstruction of ecological environment in desert area is the drip irrigation technique, followed by the point watering technology with portable hoses.

Abstract: By using linear regression, moving average, Mann-Kendall test and Morlet wavelet analysis method, the annual, flood seasonal and dry seasonal precipitation series during 1954~2008 in Weihe River basin are analyzed. The results indicate that: ①Annual precipitation and precipitation in flood season and dry season present decreasing trends during the past 55 years, and the variation trends are not significant. ②There is an irregular spatial distribution of mean annual precipitation, which shows a decreasing trend from southeast to northwest. ③Annual precipitation exists principal periods of about 2, 10, 17 and 50 years, and the phase changes of 2 and 50 years period are most obvious. Time scales of phase change of precipitation series in flood season and dry season are roughly consistent with those in annual. The research results will provide reference for climate analysis and future weather forecasting in Weihe River basin.

Abstract: The purpose of this study is to validate the use of piezoelectric transducers into the road asphalt pavement in terms of effectiveness and production of energy. FEM and laboratory test were conducted for transducers within an asphalt pavement, in order to study traffic load effects, the better suitable position, the pavement materials and environmental factors influence. The energy produced by the piezoelectric transducer within the pavement is very low if referred to a single sample as the one in the experiment and when compared to the amount which can be produced by the transducer not embedded in the pavement layers. It is necessary to highlight that higher energy production can be obtained using PZT of different size and with a network connection.

Abstract: The high power light emitting diode (LED) array integrated with the microchannel heat sink is designed. Detailed theoretical analysis of the thermal resistance for the microchannel heat sink is obtained. The thermal resistance minimum is achieved by the heat sink structure optimization, the result of theoretical analysis is simulated by MATLAB software. The result shows that: the system acquired the best heat dissipation effect, when the total size of the radiator is fixed, the width of the cooling channel is 0.1mm, and the cooling water flow rate is 1 m/s, the minimum of thermal resistance is 0.019w/°C.

Abstract: Gain properties of dc and ac photocurrent generated between two Schottky barriers coplanarly placed on silicon metal-semiconductor-metal photodetector have been investigated experimentally. The test structure has two square Mo/n-Si Schottky barrier junctions on an n-type silicon substrate with a resistivity of 9-12 Ω-cm and the junction internal separation is 20 m. The current-voltage (I-V) characteristics under illumination in visible range showed a rapid increase in the photocurrent at higher bias region. From the I-V characteristics and noise measurements, increase in photocurrent was ascribed to avalanche multiplication of carriers photogenerated in the reverse-biased Schottky junction. From observation of optical signal demodulation at low frequencies (10 kHz and 50 kHz), it was found that multiplication factor larger than 100 at 10 kHz and 30 at 50 kHz was achieved respectively.

Abstract: This paper analyzed a kind of two-diode model and reasonably simplified the mathematical calculation process under different irradiance, proposing a method which can use maximum power point to calculate simultaneously series and parallel resistance. Two kinds of PV modules should be tested in order to validating the accuracy of the proposed method. It is calculated that the relative error of single diode model is 1.72% and the two-diode model is 0.45%. The result shows that more accuracy can be performed for two-diode model in reflecting the output characteristics of photovoltaic cells.

Abstract: A Eu³⁺ activated YInGe²O⁷phosphor was synthesized by solid-state reaction and lithium carbonate was added to change the morphology and photoluminescence properties. Scanning electron microscopy showed large particle size and necking shape were obtained as the concentrations of Li⁺ ions increase. In the PL studies, the excitation spectrum of YInGe²O⁷:Eu³⁺ phosphors exhibited a broad band in the UV region centered at about 272 nm attributed to charge transfer state (CTS) band, which has a little shift after Li⁺ ion was added. As the Li⁺ ion concentration increased, the photoluminescence intensity of the red emission at 620 nm of Eu³⁺ ions was enhanced, and the optimized concentration of of added Li⁺ ion is 0.05. The results showed that addition of Li⁺ ion allows YInGe²O⁷:Eu³⁺ phosphors emitting relatively pure red light.

Abstract: In this paper, the Indium Tin Oxide (ITO) thin films were prepared by a sol-gel dip coating method and then annealed at 600°C under different atmosphere (vacuum, N₂ and 96.25%N₂+3.75%H₂). Their microstructure, optical and electrical properties were investigated and discussed. Suitable atmosphere can improve the crystalline of the ITO films, therefore the optical and electrical properties of the ITO films are improved. The uv-vis results showed the maximum of transmittance in the visible range (380-780 nm) of 85.6% and the lowest resistivity of 4.4×10^-2 Ω-cm when the ITO films were annealed under 96.25% N2 with 3.75% H2 atmosphere.

Abstract: Two different approaches are pursued to realize densely packed gallium (arsenic) antimonide (Ga(As)Sb) quantum dots (QDs) for efficient QD lasers. In the first method nano¬structures are realized by self-organization using mask-less dry-etching. GaSb cone structures are achieved with a maximum density of 1.2 ∙ 1011 cm-2. During etching a 5 nm thick amor¬phous Ga layer is formed, also the surface oxidizes immediately under atmosphere, and as a consequence the dots are optoelectronically inactive, thus no photoluminescence (PL) can be achieved. Several attempts are made to revoke these effects, but the nanostructures stay inactive. In the second approach self-assembled optoelectronically active GaAsSb QDs are grown on GaAs in Stranski-Krastanov mode. With these QDs efficient lasers are grown, exemplarily with an emission wavelength around 900 nm. In pulsed mode a minimum thres¬hold current density of jth = 121.7 A/cm2 and a maximum in differential quantum effi¬ciency of ηd = 0.66 are measured at T = 130 K. The internal quantum efficiency is ηi = 0.76 with internal losses of αi = 4.86 cm-1.

Abstract: In this paper, we report the experimental measurements of the group index of a photonic crystal waveguide based on silicon-on-insulator slab. The time-delay of the pulse is also measured, and it is in good agreement with the theoretical result calculated according to the group index with the phase-delay method, which is about 4.7ps.