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High-response UV detector based on TiO 2 /Pt-doped TiO 2 (PT) multilayer nanofilms with Au interdigitated electrodes was fabricated. PT film was used as the main light sensitive layer of the detector. By introducing a sufficiently thin TiO 2 film as an interfacial modified layer between Au electrodes and the PT film, the Schottky barrier height was effectively reduced, leading to the remarkable enhancement in the device photoresponse properties. At 5 V bias, a photocurrent of 191.77 μA and an ultrahigh responsivity of 3194 A/W were obtained under 260 nm UV illumination (15.8 μW/cm 2 ). The rise and the recovery time were 60.12 ms and 579.9 ms, respectively. The effects of Pt doping on TiO 2 film and device performance were also systematically investigated. These experimental results demonstrate the potential prospects of noble doping in fabricating high-response UV detectors.

The chemical and optical properties of 1D single-crystalline cadmium sulfide (CdS) nanowires (NWs) synthesized by a solvothermal method were discussed systematically. The CdS NW was characterized using different analytical techniques. In our work, CdS was employed as the active nanomaterial to detect ethanol gas for the first time and showed good gas sensing performance. Especially, the fast response (0.4 s) and recovery speed (0.2 s) to 100 ppm ethanol were much faster than the reported values. The visible-light detector based on CdS NWs demonstrated ultrafast decay speed (3.77 ms), which was the fastest in the reported photodetectors (PDs) based on randomly oriented CdS NW networks. This research indicates that the CdS NW is an excellent nanomaterial for high performance gas sensors and PDs.

TiO 2 nanowire arrays (TNAs) with different morphologies were synthesized on transparent conductive tin-doped indium oxide (ITO) and fluorine-doped tin oxide (FTO). Back-incident array TNA-based UV detectors were assembled. Effects of growth substrates on the morphologies of TNAs and the performance of UV detectors were investigated for the first time. The device based on the vertically aligned TNAs on FTO (TNFs) exhibited more excellent photoresponse properties than that based on the cluster-shaped TNAs on ITO (TNIs). This phenomenon can be ascribed to the easier and faster electron transport in the single crystallographic orientation TNFs. The outstanding performance also demonstrated the obvious superiority of TNFs in the application of UV detection.

Uniform NaTaO3 thin film was prepared on tantalum foils by a facile low temperature hydrothermal method. X-ray diffraction and field emission scanning electron microscopic characterizations revealed the film was well synthesized. The influence of synthesis temperature and time on the crystal structure and morphology of the film was investigated. Then Au film was deposited on NaTaO3 to fabricate interdigitated electrodes and photoelectric effects of the detector were systematically studied. At 5 V bias, the photocurrent was 0.56 μA under the irradiation of 260 nm ultraviolet light, which was 7 times larger than that under dark condition. The spectral responsivity of the device shows good sensitivity to ultraviolet light from 250 to 350 nm and the response peak appeared at 260 nm. These experimental results demonstrate the promising application of NaTaO3 in ultraviolet detection.

TiO2 has been widely used in ultraviolet (UV) photodetectors, but due to the large number of structural defects and strong band-to-band recombination of the exciton in TiO2, the devices usually have large dark current (I d) and low light current (I l), which seriously reduces the sensitivity and responsivity (R) of the TiO2 based devices. In this work, carbon (C) quantum dots (QDs) are introduced into TiO2 film to ameliorate these issues. Due to the difference of work function between TiO2 nanoparticles and C QDs, the built-in electric field (E bi) can be formed, which effectively facilitates the photogenerated exciton dissociation in the TiO2 film under UV illumination. Meanwhile, the constructed depletion region in dark reduces the majority carrier density, thus decreasing the I d of the photodetector. Moreover, the E bi and depletion region will also contribute to the faster charge collection under UV illumination and recombination of the electron in dark, which is beneficial for the improved response/recovery speed of the device.

This study presents new stable isotope data for precipitation (δ18Op) and drip water (δ18Od) from eight cave sites in the monsoon regions of China (MRC), with monthly to bi-monthly sampling intervals from May-2011 to April-2014, to investigate the regional-scale climate forcing on δ18Op and how the isotopic signals are transmitted to various drip sites. The monthly δ18Op values show negative correlation with surface air temperature at all the cave sites except Shihua Cave, which is opposite to that expected from the temperature effect. In addition, although the monthly δ18Op values are negatively correlated with precipitation at all the cave sites, only three sites are significant at the 95% level. These indicate that, due to the various vapor sources, a large portion of variability in δ18Op in the MRC cannot be explained simply by either temperature or precipitation alone. All the thirty-four drip sites are classified into three types based on the δ18Od variability. About 82% of them are static drips with little discernable variation in δ18Od through the whole study period, but the drip rates of these drips are not necessary constant. Their discharge modes are site-specific and the oxygen isotopic composition of the stalagmites growing from them may record the average of multi-year climatic signals, which are modulated by the seasonality of recharge and potential effects of evaporation, and in some cases infiltration from large rainfall events. About 12% of the thirty-four drip sites are seasonal drips, although the amplitude of δ18Od is narrower than that of δ18Op, the monthly response of δ18Od to coeval precipitation is not completely damped, and some of them follow the seasonal trend of δ18Op very well. These drips may be mainly recharged by present-day precipitation, mixing with some stored water. Thus, the stalagmites growing under them may record portions of the seasonal climatic signals embedded in δ18Op. About 6% of the thirty-four drip sites are medium-variability drips, with constant and relatively low δ18Od values in the wet season, but with variable and relatively high δ18Od values in the dry season, reflecting flow switching in the karst or evaporation inside the cave.

The polypyrrole/ZnS core/shell coaxial nanowires are fabricated through a two-step process with the assistance of anodic aluminum oxide (AAO) templates. First, ZnS nanotube arrays are synthesized within AAO templates by using the metal organic chemical vapor deposition (MOCVD) method. Then, polypyrrole (PPy) is electrochemically deposited into as-prepared ZnS nanotubes, creating PPy/ZnS core/shell coaxial nanowires. The morphology and structure of PPy/ZnS coaxial nanowires are characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Fourier-transform infrared (FTIR) spectroscopy verifies that the in-plane deformation vibration of the pyrrole (Py) ring shows a blue shift from 1144 cm−1 in PPy nanowires to 1173 cm−1 in the PPy/ZnS coaxial nanowires. In X-ray photoelectron spectroscopy analysis (XPS), the changes of the N 1s peak and S 2p peak reveal an electron transfer from the ZnS shell to the PPy core in PPy/ZnS coaxial nanowires, which lowers the redu...

The density of a stalagmite (WX42A) from Wanxiang Cave, Wudu County, Gansu Province, China, in the western margin of the Asian summer monsoon region, presents regular fluctuations in different deposition periods during the last deglaciation. Over long timescales, high-precision 230Th dating and high-resolution stalagmite density data indicate that the density-time series between 17644 a BP and 12758 a BP is quite similar to the stalagmite δ 18O record which reflects Asian monsoon intensity. Strengthening/weakening (lighter/heavier stalagmite δ 18O values) of the Asian monsoon is accompanied by increase/decrease in stalagmite density. Over short timescales, decrease in stalagmite density correlates to monsoon-retreat events such as the Inter-Allerod Cold Period (IACP), Older Dryas (OD) and Inter-Bolling Cold Period (IBCP). Generally, this kind of decrease in stalagmite density reflects precipitation decrease with weakening of the Asian monsoon, which in turn slows cave dripwater rate and decreases crystal nuclei, leading to enlargement of calcite crystals, weakened biological activity and decreased soil pCO2 which increases the abundance of impure detrital materials in stalagmites. However, during the period of large amplitude reduction of precipitation and biological activity which resulted from extreme monsoon-retreat events, temperature variation would dominate fluctuation of stalagmite density. For example, stalagmite density increased suddenly when temperature dropped suddenly in the north Atlantic during Heinrich event 1 (H-1). This may be caused by low seepage water temperature, more dissolved calcium carbonate, compact regular crystals forming under higher supersaturation, leading to the stalagmite increased density. Stalagmite density fluctuation sensitively recorded stalagmite growth history and environment, demonstrating that stalagmite density can be used as a proxy for paleoclimatic research.

A visible-blind ultraviolet (UV) photodetector (PD) based on TiO2/polyvinyl carbazole doped with poly {[2,7-(9-(20-ethylhexyl)-9-hexyl-fluorene])-alt-[5,50-(40,70-di-2-thienyl-20,10,30-benzothid-iazole)]} (PFTBT) was successfully fabricated. The introduced PFTBT exhibits high absorbance in the UV region and high conductivity which increases the device absorbance and the efficiency of carrier mobility. Besides, PFTBT acts as traps which can increase the concentration of the majority carrier. Therefore, the doped device exhibits high responsivity and high specific detectivity with the value of 0.22 A W-1 and 1.78 × 1012 Jones which respectively has a 3.6 and 2.6 times greater enhancement than the device without doping. The response time is also improved from 27 ms to 22 ms. Owing to the different absorbances that the materials have, the PD has a narrow detection range from 320 nm to 340 nm which is helpful to the study of the specific wavelength. In other words, the research provides a potential way to fabricate practical high-performance UVPDs.

Based on 5 high-precision 230Th dates and 103 stable oxygen isotope ratios (δ18O) obtained from the top 16 mm of a stalagmite collected from Wanxiang Cave, Wudu, Gansu, variation of monsoonal precipitation in the modern Asian Monsoon (AM) marginal zone over the past 100 years was reconstructed. Comparison of the speleothem δ18O record with instrumental precipitation data at Wudu in the past 50 years indicates a high parallelism between the two curves, suggesting that the speleothem δ18O is a good proxy for the AM strength and associated precipitation, controlled by “amount effect” of the precipitation. Variation of the monsoonal precipitation during the past 100 years can be divided into three stages, increasing from AD 1875 to 1900, then decreasing from AD 1901 to 1946, and increasing again thereafter. This variation is quite similar to that of the Drought/Flooding index archived from Chinese historical documents. This speleothem-derived AM record shows a close association with the Pacific Decadal Oscillation (PDO) between AD 1875 and 1977, with higher monsoonal precipitation corresponding to cold PDO phase and vice versa at decadal timescale. The monsoonal precipitation variation is out of phase with the PDO after AD 1977, probably resulting from the decadal climate jump in the north Pacific occurring at around AD 1976/77. These results demonstrate a strong linkage between the AM and associated precipitation and the Pacific Ocean via ocean/atmosphere interaction. This relationship will aid to forecast future hydrological cycle for the AM monsoon region, and to improve forecasting potential of climatic model with observation data from cave.

Deproteinization is a technical bottleneck in the purification of viscous water-soluble polysaccharides. The aim of this work is to provide an appropriate approach to deproteinize crude gellan gum. Several methods of deproteinization were investigated, including Sevag method, alkaline protease, papain and neutral protease. The results revealed that Sevag method had high deproteinization efficiency (87.9%), but it showed dissatisfactory recovery efficiency of gellan gum (28.6%), which made it less advisable in industrial applications. The deproteinization by alkaline protease was demonstrated in this work for the first time, indicating alkaline protease was preferred in the deproteinization of crude gellan gum with high polysaccharide recovery (89.3%) and high deproteinization efficiency (86.4%).

A novel dark self-depleting ultraviolet (UV) photodetector based on a TiO2/NiO pn heterojunction was demonstrated and exhibited lower dark current (I dark) and noise. Both the NiO layer and Ni/Au composite electrode were fabricated by a smart, one-step oxidation method which was first employed in the fabrication of the UV photodetector. In dark, the depleted pn heterojunction structure effectively reduced the majority carrier density in TiO2/NiO films, demonstrating a high resistance state and contributing to a lower I dark of 0.033 nA, two orders of magnitude lower than that of the single-material devices. Under UV illumination, the interface self-depleting effect arising from the dissociation and accumulation of photogenerated carriers was eliminated, ensuring loss-free responsivity (R) and a remarkable specific detectivity (D*) of 1.56 × 1014 cm Hz1/2 W-1 for the optimal device. The device with the structure of ITO/TiO2/NiO/Au was measured to prove the mechanisms of interface self-depleting in dark and elimination of the depletion layer under UV illumination. Meanwhile, shortened decay time was achieved in the pn heterojunction UV photodetector. This suggests that the self-depleting devices possess the potential to further enhance photodetection performance.

In recent years, the China National Petroleum Corporation (CNPC) has adopted many state‐of‐the‐art technologies in order to explore additional regions and improve field productivity.

[1] Central Asia is currently a semiarid-arid region, dominated by the Westerlies. It is important to understand mechanisms of climate and precipitation changes here, as water availability in the region is crucial today and in the future. High-resolution, absolutely-dated oxygen isotope (δ18O) records of stalagmites from Kesang Cave characterize a dynamic precipitation history over most of the past 500,000 years. This record demonstrates, for the first time, that climate change in the region exhibits a processional rhythm with abrupt inceptions of low δ18O speleothem growth at times of high Northern Hemisphere summer insolation followed by gradual δ18O increases that track decreases of insolation. These observations and interpretations contrast with the interpretation of nearby, but higher elevation ice core records. The absolutely-dated caveδ18O shifts can be used to correlate the regional climate variability by providing chronological marks. Combined with other paleoclimate records, the Kesang observations suggest that possible incursions of Asian summer monsoon rainfall or related moisture into the Kesang site and/or adjacent areas during the high insolation times may play an important role in changing orbital-scale hydrology of the region. Based on our record, arid climate will prevail in this region for the next several millennia, providing that anthropogenic effects do not supersede natural processes.

Media Access Control (MAC) plays an important role in coordinating channel access among the nodes. This is especially important for Mobile Ad-hoc Networks (MANETs), where all mobile nodes use the same frequency spectrum for transmission. In this paper, a hybrid MAC protocol ADAPT-CND (ADAPT Considering Node Degree) is proposed, which is based on ADAPT. In ADAPT, back-off mechanism similar to Binary Exponential Back-off (BEB) is adopted to regulate the contention probability, while in ADAPT-CND, a modified BEB is proposed. In the modified back-off mechanism, each node regulates its contention window with varied step length, the step length is set according to each node's degree. By doing this, the modified back-off mechanism enables each node to regulate its contention probability adaptively with the aggravating competition, thereby obtain satisfied throughput even under the existing of large quantities of competition nodes. In this way, ADAPT-CND enables each node to self-adjust its behavior based on both traffic loads and its own node degree. From simulation results, we see evident improvement of throughput performance with respect to packet arrival rate and node density relative to ADAPT.

Clustering is an effective approach to hierarchically organizing network topology and to prolong the lifetime of a wireless sensor network. Current clustering protocols usually utilize two techniques: selecting cluster heads with more residual energy and rotating cluster heads periodically to distribute the energy consumption among nodes in each cluster. Most of the researches in this field has focused on energy-efficient solutions, but caring less about the communication between Cluster Head (CH) nodes and Base Station (BS). When the sensor field is far away from the base station, the cluster heads are burdened with heavier relay traffic and tend to die much faster. To mitigate the problem, we propose an Energy-Efficient Hierarchical Routing Protocol (EEHRP) for long range transmission in the wireless sensor networks. It uses a number of gateway nodes, which do not engage in clustering, to connect the CHs and base station. They are responsible for transmitting packets received from the CHs to the base station, thus the CHs can preserve some energy in data forwarding and the gateway nodes can ease their burden by not participating in clustering. Simulation results show that EEHRP obviously increases the network lifetime and well balances the energy consumption among the sensor nodes.

Ouring the past decade, wireless Ad-hoc network have been more and more popular in both military and civil areas, which due to its distinguishing characteristics as following: strongly network constructing, highly mobility, rapidly transmission. A SoC design for broad band wireless ad-hoc network node is proposed in this paper. In details, the system architecture design is given as well as the hardware design for customized IP core and the specific device driver. At the same time, a kind of data exchange technology which makes use of Network Bridge is designed to support the connection between Ethernet and ad-hoc network. The results of the hardware simulation and experiment show that the SoC system operates normally and has a good performance index.

A record from Wanxiang Cave, China, characterizes Asian Monsoon (AM) history over the past 1810 years. The summer monsoon correlates with solar variability, Northern Hemisphere and Chinese temperature, Alpine glacial retreat, and Chinese cultural changes. It was generally strong during Europe's Medieval Warm Period and weak during Europe's Little Ice Age, as well as during the final decades of the Tang, Yuan, and Ming Dynasties, all times that were characterized by popular unrest. It was strong during the first several decades of the Northern Song Dynasty, a period of increased rice cultivation and dramatic population increase. The sign of the correlation between the AM and temperature switches around 1960, suggesting that anthropogenic forcing superseded natural forcing as the major driver of AM changes in the late 20th century.

Gellan gum production was carried out by Sphingomonas paucimobilis ATCC 31461 in a simplified medium with a short incubation time, and a kinetic model for understanding, controlling, and optimizing the fermentation process was proposed. The results revealed that glucose was the best carbon source and that the optimal concentration was 30 g liter −1 . As for the fermenting parameters, considerably large amounts of gellan gum were yielded by an 8-h-old culture and a 4% inoculum at 200 rpm on a rotary shaker. Under the optimized conditions, the maximum level of gellan gum (14.75 g liter −1 ) and the highest conversion efficiency (49.17%) were obtained in a 30-liter fermentor in batch fermentation. Logistic and Luedeking-Piret models were confirmed to provide a good description of gellan gum fermentation, which gave some support for the study of gellan gum fermentation kinetics. Additionally, this study is the first demonstration that gellan gum production is largely growth associated by analysis of kinetics in its batch fermentation process. Based on model prediction, higher gellan gum production (17.71 g liter −1 ) and higher conversion efficiency (57.12%) were obtained in fed-batch fermentation at the same total glucose concentration (30 g liter −1 ).