Effect of Si δ-Doping on the Linear and Nonlinear Optical Absorptions and Refractive Index Changes in InAlN/GaN Single Quantum Wells

In the framework of effective mass approximation, we theoretically investigate the electronic structure of the Si δ-doped InAIN/GaN single quantum well by solving numerically the coupled equations Schrodinger-Poisson self-consistently. The linear, nonlinear optical absorption coefficients and relative refractive index changes are calculated as functions of the doping concentration and its thickness. The obtained results show that the position and the amplitude of the linear and total optical absorption coefficients and the refractive index changes can be modified by varying the doping concentration and its thickness. In addition, it is found that the maximum of the optical absorption can be red-shifted or blue-shifted by varying the doping concentration. The obtained results are important for the design of various electronic components such as high-power FETs and infrared photonic devices.

Refractive Index Change and Color Center Formation in LiYF_4 Crystal Induced by a Femtosecond Laser

The refractive index change and color centers formation in LiYF4 crystal at room temperature are induced by a femtosecond laser irradiation. A mechanism for refractive index change and color centers formation is proposed.

Donor impurity-related optical absorption coefficients and refractive index changes in a rectangular GaAs quantum dot in the presence of electric field

Within the quasi-one-dimensional effective potential model and effective mass approximation,we obtain the wavefunctions and energy eigenvalues of the ground（j=1） and first 2 excited states（j=2 and 3） of a donor impurity in a rectangular GaAs quantum dot in the presence of electric field.The donor impurity-related linear and nonlinear optical absorption as well as refractive index changes for the transitions j=1-2 and j =2-3 are investigated.The results show that the impurity position,incident optical intensity and electric field play important roles in the optical absorption coefficients and refractive index changes.We find that the impurity effect induces the blueshift for j=1-2 and redshift for j=3-2 in the absence of the electric field,but it leads to redshift for j = 1-2 and blueshift for j = 3-2 in the existence of the field.Also,the optical coefficient for the higher energy transitions j =2-3 is insensitive to variation of impurity positions,while that for the low energy transition j =1-2 depends significantly on the positions of impurity.In addition,the saturation and splitting phenomenon of the optical absorption are observed as the incident optical intensity increases.

A novel coupled quantum well structure with large field-induced refractive index change and low absorption loss at 1.55 μm

A novel coupled quantum well structure - quasi-symmetric coupled quantum well （QSCQW） is proposed. In the case of low applied electric field （F = 25 kV/cm） and low absorption loss （a ≈ 100 cm^-1）, a large field-induced refractive index change （for TE mode, △n = 0.0106; for TM mode, △n = 0.0115） is obtained in QSCQW structure at operating wavelength λ = 1550 nm. The value is larger by over one to two order of magnitude compared to that in a rectangular quantum well （RQW） and about 50% larger than that of five-step asymmetric coupled quantum well （FACQW） structure under the above work conditions.

INDEX OF DIRECTION CHANGE OF ZONALLY AVERAGED WIND AND CHANGE OF SEASON

In this paper, a Wind Direction Change Index (WI), which can describe four-dimensional spatiotemporal changes of the atmospheric circulation objectively and quantitatively, is defined to study its evolution and seasonal variation. The first four modes can be obtained by EOF expansion of the zonally averaged WI. The first mode reveals the basic spatial distribution of the annually averaged WI. The second mode reflects the quasi-harmonic parts of the WI deviations. Tropical, subtropical and extratropical monsoon areas can be clearly reflected by this mode. The third mode reflects the non-harmonic parts of the WI deviations. It shows the so-called February reverse in stratospheric atmosphere as well as the asymmetric seasonal changes from spring to fall and from fall to spring due to both the land-sea distribution contrast between the Northern and Southern Hemispheres and the nonlinear effect of atmospheric and ocean fluids. The fourth mode reveals the northward advancing of the global reversed wind fields from spring to summer and their southward withdrawal from summer to autumn.

Changes of biochemical indexes in patients with acute cerebral infarction after treatment with simvastatin

BACKGROUND: At present, it is believed that the important causes of cerebral infarction are the disorders of lipid metabolism and endothelial function, and the outcomes of clinical treatment can be improved by regulating serum lipids and antiinflammation, etc. OBJECTIVE: To observe the effect of simvastatin, inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, on the levels of serum lipids, serum enzymic indexes and inflammatory metabolic indexes in patients with cerebral infarction. DESIGN: A comparative observation. SETTING: Department of Geriatrics, Longquanshan Hospital of Liuzhou City. PARTICIPANTS: Forty-eight patients with acute cerebral infarction were selected from the Department of Geriatrics of Longquanshan Hospital of Liuzhou from March 2004 to February 2006, including 24 males and 24 females, the mean age was (54±12) years, average disease course was (10.0±4.5) days. They were all accorded with the diagnostic standard for cerebral infarction set by the Fourth National Academic Meeting for Cerebrovascular Disease in 1999, and cerebral hemorrhage was excluded by cranial CT scanning. The 48 patients were randomly divided into control group (n =24) and treatment group (n =24). Informed consents were obtained from all the participants. METHODS: ① All the patients were treated according to the symptoms, besides those in the treatment group were given simvastatin (Harbin Pharm. Group Sanjing Pharmaceutical Shareholding, Co.,Ltd., No. H20010454; Batch number: 20040218; 5 mg/tablet). The initial dosage was 10 mg per day for 4 weeks, and then increased to 30 mg per day for another 4 weeks. ② Before treatment and within 1 week after treatment, the total cholesterol, triglyceride, high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), aspartate aminotransferase (AST), creatine kinase and C reactive protein in serum were determined with Beckman-cx7 automatic biochemical analytical apparatus in both groups. ③ The differences of intergroup and intragroup data were compared with the independent-samples t test and paired samples t test. MAIN OUTCOME MEASURES: Changes of total cholesterol, triglyceride, HDL-C, LDL-C, AST, creatine kinase and C reactive protein before and treatment in both groups. RESULTS: All the 48 patients with cerebral infarction were involved in the analysis of results. ① Changes of serum lipids: The levels of serum lipids were close between the two groups before treatment (P > 0.05). After treatment, the HDL-C level in the treatment group was obviously higher than that in the control group and that before treatment [(1.34±0.12), (0.92±0.33), (0.93±0.21) mmol/L, t =7.922, 11.699, P < 0.01], and the levels of total cholesterol, triglyceride and LDL-C were obviously lower than those in the control group and those before treatment (t =2.780-7.591, P < 0.01). ② Changes of serum enzymic indexes and C reactive protein in serum: The levels of enzymes and C reactive protein in serum had no obvious differences between the two groups before treatment (P > 0.05). The levels of AST, creatine kinase and C reactive protein in serum after treatment were obviously lower than those before treatment in both groups (t =7.259-17.996, P < 0.01). The levels of levels of creatine kinase and C reactive protein in serum after treatment in the treatment group were obviously lower than those in the control group [(3.061±0.522) μkat/L, (4.6±3.1) mg/L; (4.348±0.580) μkat/L, (12.3±4.8) mg/L, t =7.910, 6.463, P < 0.01]. CONCLUSION: Compared with common treatment according to symptoms, the additional administration of simvastatin is better for improving the serum lipids, serum enzymic indexes of patients with cerebral infarction at acute period, and benefit for repairing their inflammatory damages.

Regional Variability of Climate Change Hot-Spots in East Asia

The regional climate change index （RCCI） is employed to investigate hot-spots under 21st century global warming over East Asia. The RCCI is calculated on a 1-degree resolution grid from the ensemble of CMIP3 simulations for the B1, AIB, and A2 IPCC emission scenarios. The RCCI over East Asia exhibits marked sub-regional variability. Five sub-regional hot-spots are identified over the area of investigation： three in the northern regions （Northeast China, Mongolia, and Northwest China）, one in eastern China, and one over the Tibetan Plateau. Contributions from different factors to the RCCI are discussed for the sub-regions. Analysis of the temporal evolution of the hot-spots throughout the 21st century shows different speeds of response time to global warming for the different sub-regions. Hot-spots firstly emerge in Northwest China and Mongolia. The Northeast China hot-spot becomes evident by the mid of the 21st century and it is the most prominent by the end of the century. While hot-spots are generally evident in all the 5 sub-regions for the A1B and A2 scenarios, only the Tibetan Plateau and Northwest China hot-spots emerge in the B1 scenario, which has the lowest greenhouse gas （GHG） concentrations. Our analysis indicates that subregional hot-spots show a rather complex spatial and temporal dependency on the GHG concentration and on the different factors contributing to the RCCI.

Spatial-temporal Changes of Vegetation Cover in Guizhou Province, Southern China

Guizhou Province is an important karst area in the world and a fragile ecological area in China. Ecological risk assessment is very necessary to be conducted in this region. This study investigates different characteristics of the spatial-temporal changes of vegetation cover in Guizhou Province of Southern China using the data set of SPOT VEGETATION(1999–2015) at spatial resolution of 1-km and temporal resolution of 10-day. The coefficient of variation, the Theil-Sen median trend analysis, and the Mann-Kendall test are used to investigate the spatial-temporal change of vegetation cover and its future trend. Results show that: 1) the spatial distribution pattern of vegetation cover in Guizhou Plateau is high in the east whereas low in the west. The average annual normalized difference vegetation index(NDVI) from west to east is higher than that from south to north. 2) Average annual NDVI improved obviously in the past 17 years. The growth rate of average annual NDVI is 0.028/10 yr, which is slower than that of vegetation in the country(0.048/10 yr) from 1998 to 2007. Average annual NDVI in karst area is lower than that in non-karst area. However, the growing rate of average annual NDVI in karst area(0.030/10 yr) is faster than that in non-karst area(0.023/10 yr), indicating that vegetation coverage increases more rapidly in karst area. 3) Vegetation coverage in the study area is stable overall, but fluctuates in the local scales. 4) Vegetation coverage presents a continuous increasing trend. The Hurst exponent of NDVI in different vegetation types has an obvious threshold in various elevations. 5) The proportion of vegetation cover with sustainable increase is higher than that of vegetation cover with sustainable decrease. The improvement in vegetation cover may expand to most parts of the study area.

Estimating Field Source Parameters of Gravity Change in North China Based on the Euler Deconvolution Method

Based on the absolute and relative gravity observations in North China from 2009 to 2014,spatial dynamic variations of the regional gravity field are obtained. We employed the Euler deconvolution method and the theoretical model to get the best estimates of parameters. Gravity field change caused by the depth and distribution in North China is calculated by back analysis. The results show the structural index that equals 1 is suitable for inversion of the gravity variation data. The inversion results indicate that the depths of anomaly field sources are spread over the Hetao fault. The research method of this paper can be used in the quantitative study on the field source and may shed new light on the interpretations of gravity change, and also provide quantitative basis for earthquake prediction index criterions based on the gravity change.

Changes in Temporal Concentration Property of Summer Precipitation in China during 1961–2010 Based on a New Index

Based on the property of entropy,a new index Q was defined to measure the temporal concentration property of summertime daily rainfall in China,based on daily precipitation data collected at 553 observation stations in China during 1961–2010.Furthermore,changes in the temporal concentration property of summer precipitation in China were investigated.The results indicate that the regions with larger Q values were located in most parts of Northwest China and the north of the Yellow River,where daily precipitation tended to become temporally concentrated during the study period.On the contrary,smaller Q values were found in eastern Tibetan Plateau,southeastern Northwest China,and most parts of Southwest and South China.The most obvious increasing trend of Q index was found in South China and most parts of Southwest China,where precipitation showed a temporal concentration trend.However,a decreasing trend of Q index was found in Northwest China,the Tibetan Plateau,and the north of the Huaihe River.Variations of the Q index and the summer rainfall total during 1961–2010 in China both exhibited an increasing trend,implying larger temporal variability in rainfall attributes.It is illustrated that the summer precipitation in general became more temporally concentrated with more intense rainfall events and wetter days.

A climatological northern boundary index for the East Asian summer monsoon and its interannual variability

A long-term perspective on the spatial variation of the northern boundary of the East Asian summer monsoon(EASM) and the related physical mechanisms is important for understanding past climate change in Asia and for predicting future changes. However, most of the meteorological definitions of the EASM northern boundary do not correspond well to the actual geographical environment, which is problematic for paleoclimatic research. Here, we use monthly CMAP and GPCP precipitation data to define a new EASM northern boundary index by using the concept of the global monsoon, which is readily applicable to paleoclimatic research. The results show that the distribution of the 2 mm day^(-1) precipitation isoline(i.e., 300 mm precipitation)has a good relationship with the spatial distribution of modern land cover types, the transitional climate zone and the potential natural vegetation types, in China. The locations of the precipitation isolines also correspond well to the locations of major shifts in wind direction. These results suggest that the 2 mm day^(-1) isoline has a clear physical significance since the climatic, ecological,and geographical boundary can be used as the northern boundary index of the EASM(which we call the climatological northern boundary index). The index depicts the northeast-southwest orientation of the climatological(1981-2010) EASM northern boundary, along the eastern part of the Qilian Mountains-southern foothills of the Helan Mountains-Daqing Mountains-western margin of the Greater Khingan Range, from west to east across Northwest and Northeast China. The interannual change of the EASM northern boundary from 1980 to 2015 covers the central part of Gansu, the northern part of Ningxia, the eastern part of Inner Mongolia and the northeastern region in China. It can extend northward to the border between China and Mongolia and retreat southward to Shangdong-central Henan. There is a 200-700 km fluctuation range of the interannual EASM northern boundaries around the locations of the climatological northern boundary. In addition, the spatial variation of the interannual EASM northern boundaries gradually increases from west to east, whereas the trend of north-south fluctuations maintains a roughly consistent location in different regions.

The experience of land cover change detection by satellite data

Sigificant dependence from climate and anthropogenic influences characterize ecological systems of Kazakhstan. As result of the geographical location of the republic and ecological situation vegetative degradation sites exist throughout the territory of Kazakhstan. The major process of desertification takes place in the arid and semi-arid areas. To allocate spots of stable degradation of vegetation, the transition zone was first identified. Productivity of vegetation in transfer zone is slightly dependent on climate conditions. Multi-year digital maps of vegetation index were generated with NOAA satellite images. According to the result, the territory of the republic was zoned by means of vegetation productivity criterion. All the arable lands in Kazakhstan are in the risky agriculture zone. Estimation of the productivity of agricultural lands is highly important in the context of risky agriculture, where natural factors, such as wind and water erosion, can significantly change land quality in a relatively short time period. We used an integrated vegetation index to indicate land degradation measures to assess the inter-annual features in the response of vegetation to variations in climate conditions from low- resolution satellite data for all of Kazakhstan. This analysis allowed a better understanding of the spatial and temporal variations of land degradation in the country.

Dynamic Changes of the Bush Encroachment in Low Altitude Area of Ethiopia

Bush encroachment is widely distributed in arid and semi-arid regions, and it has a serious impact on livestock production, especially in Africa where livestock is a primary source for the livelihoods of many people. In this study, methods of supervised classification and decision tree classification, and indexes of a land use change significance index（Ci） and a single land use dynamic degree, were applied to remote sensing imagery of Ethiopia for 1986–2016. The results show the dynamic characteristics of grassland bush encroachment in low altitude areas（pastures 1500 m above sea level） of Ethiopia in the 30 year period studied. The results revealed several interesting features of this phenomenon.（1） The area of bush encroachment showed an increasing trend, with a maximum of 3.74×10^3 km^2 in 2003, which represented 68.97% of the total area, and declined slightly from 2003~2016.（2） Among classification types, the area of severe shrub grassland was the largest, accounting for 28.36–49.10% of the total area, while the area of moderate bush encroachment accounted for 9.77–16.68%, and slight bush encroachment accounted for 5.52–7.57%.（3） The expansion rate of shrubby grassland was 0.74% for the 30 year period, while the average annual expansion rate was 2.16% for the 8 years from 1995–2003.（4） Forest land and grassland were the two main land use types of shrub grassland transformation in low altitude areas and bush encroachment changed large amounts of forest land into grassland due to shrub grassland management. The results of this study provide basic data for revealing the impacts of development processes on subsequent bush encroachment and can inform better management for the sustainable development of grasslands in low altitude systems.

Optical absorption via intersubband transition of electrons in GaAs/Al_xGa_(1-x)As multi-quantum wells in an electric field

Based on the effective mass approximation, the Schrodinger equation and Poisson equation in GaAs/AlGaAs multi-quantum wells(MQWs) are self-consistently solved to obtain the wave functions and energy levels of electrons in the conduction band for the ground first excited state by considering a lateral electric field(LEF). Then, the effects of size, ternary mixed crystal, doping concentration, and temperature on linear and nonlinear intersubband optical absorption coefficients(IOACs), and refractive index changes(RICs) due to the transition between ground states and the first excited states of electrons are discussed based on Fermi’s golden rule. The results show that, under a fixed LEF, with increase of A1 composition and doping concentration, the IOACs produce a red shift. With increases of both widths of the wells and barriers IOACs appear as blue shifts and their amplitudes increase, but the barrier width change is much more important to affect nonlinear IOACs, whereas increasing the temperature results in a blue shift first and then a red shift of IOACs. When the other parameters are fixed but there is an increase in the LEF, IOACs occur with a blue shift, and the RICs have similar properties.

The evolution and determinants of Chinese property insurance companies’profitability:A DEA-based perspective

The property insurance industry grows fast in China and it is necessary to further investigate the profitability of the Chinese property insurance industry.This study investigates the evolution and determinants of the profitability of 53 Chinese property insurers during the year 2013-2017.Profitability is measured by profit ratio efficiency by data envelopment analysis(DEA)methodology and a profit ratio change index is applied to compare the performance of these insurers over different periods.Tobit regression models are used to investigate several influencing factors of profitability.The empirical results show the importance of proper arrangement of costs and revenues for an insurer and help to better understand the effect of firm size,age,and product specification on profitability.Some policy implications and suggestions are also proposed.

Quantization Based Watermarking Methods Against Valumetric Distortions

Most of the quantization based watermarking algorithms are very sensitive to valumetric distortions, while these distortions are regarded as common processing in audio/video analysis. In recent years, watermarking methods which can resist this kind of distortions have attracted a lot of interests. But still many proposed methods can only deal with one certain kind of valumetric distortion such as amplitude scaling attack, and fail in other kinds of valumetric distortions like constant change attack, gamma correction or contrast stretching. In this paper, we propose a simple but effective method to tackle all the three kinds of valumetric distortions. This algorithm constructs an invariant domain first by spread transform which satisfies certain constraints. Then an amplitude scale invariant watermarking scheme is applied on the constructed domain. The validity of the approach has been confirmed by applying the watermarking scheme to Gaussian host data and real images. Experimental results confirm its intrinsic invariance against amplitude scaling, constant change attack and robustness improvement against nonlinear valumetric distortions.