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As an advanced metal additive manufacturing technology, laser-directed energy deposition (DED-LB) has attracted a lot of attention in recent years, and is increasingly used in aerospace, automotive, marine, and biomedical applications. However, as industry application standards continue to improve, the challenges of part quality, process stability, and molding efficiency faced by DED-LB are becoming more and more prominent. On-line monitoring and real-time quality regulation can effectively avoid quality defects in processing, which is an effective measure to solve the problem. This paper summarizes the current research status of on-line monitoring means and closed-loop quality regulation technology for DED-LB. The on-line monitoring signals and related sensing devices mainly based on image signals, temperature signals, spectral signals, acoustic emission signals, and X-ray imaging, as well as the closed-loop control strategies and intelligent optimization methods in the process are discussed. Finally, a view on the future direction of on-line monitoring-control system for DED-LB is presented. [ABSTRACT FROM AUTHOR]

Coal seam microbes, as endogenous drivers of secondary biogenic gas production in coal seams, might be related to methane production in coal seams. In this study, we carried out anaerobic indoor culture experiments of microorganisms from three different depths of bituminous coal seams in Huainan mining area, and revealed the secondary biogas generation mechanism of bituminous coal seams by using the combined analysis of macro-genome and metabolism multi-omics. The results showed that the cumulative mass molar concentrations (Molality) of biomethane production increased with the increase of the coal seam depth in two consecutive cycles. At the genus level, there were significant differences in the bacterial and archaeal community structures corresponding to the three coal seams 1#, 6#, and 9#(p < 0.05). The volatile matter of air-dry basis (Vad) of coal was significantly correlated with differences in genus-level composition of bacteria and archaea, with correlations of R bacterial = 0.368 and R archaeal = 0.463, respectively. Functional gene analysis showed that the relative abundance of methanogenesis increased by 42% before and after anaerobic fermentation cultivation. Meanwhile, a total of 11 classes of carbon metabolism homologues closely related to methanogenesis were detected in the liquid metabolites of coal bed microbes after 60 days of incubation. Finally, the fatty acid, amino acid and carbohydrate synergistic methanogenic metabolic pathway was reconstructed based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The expression level of mcrA gene within the metabolic pathway of the 1# deep coal sample was significantly higher than that of the other two groups (p < 0.05 for significance), and the efficient expression of mcrA gene at the end of the methanogenic pathway promoted the conversion of bituminous coal organic matter to methane. Therefore, coal matrix compositions may be the key factors causing diversity in microbial community and metabolic function, which might be related to the different methane content in different coal seams. [ABSTRACT FROM AUTHOR]

A novel phytic acid-modified corn stalk-composite superabsorbent (PACS-g-p(AA-AM-VP)) with water absorbency of 391 g/g, water retention around 30% at 200 min under 90 °C, adsorption capacities of 284 mg/g and 448 mg/g for Ni(II) and Cu (II), respectively, was synthesized by graft copolymerization of acrylamide(AM), vinyl pyrrolidone(VP) and itaconic acid(IA) with phytic acid-modified corn stalk (PACS) in aqueous solution, using N,N-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) and sodium bisulfite (SBS) as redox initiator. Factors influencing water absorbency and water retention of PACS-g-p (AA-AM-VP), such as PACS amount, initiator amount, crosslinker amount, neutralization degree of IA, IA/VP mass ratio and IA/AM mass ratio, were investigated. Morphologies and structure of PACS-g-p (AA-AM-VP) were characterized by FTIR and SEM. FTIR spectra indicate the structure of phytic acid-modified corn stalk graft-copolymer. SEM data shows that fiber structure of corn stalk is partially destroyed after phytic acid modification under ultrasonic wave. PACS-g-p (AA-AM-VP) has a coarse, fluffy and porous structure, facilitating the permeation of water and heavy metal ions into the polymeric network. Given these properties, PACS-g-p (AA-AM-VP) can be extensively applied in agriculture and horticulture as a water-retaining and soil remediation material which increases agricultural irrigation efficiency and remediates heavy metal-contaminated soil due to its low cost, environmental friendliness, high water retention and good adsorption for heavy metal ions. [ABSTRACT FROM AUTHOR]

In the direct laser deposition (DLD) process, it is common to employ constant processing parameters. The utilization of the constant parameters may lead to fluctuations in the dynamic evolution of the molten pool, primarily due to the intricate thermal effects involved, which will significantly impact the processing quality. To address this issue, this study proposed a closed-loop control approach that effectively modifies processing parameters in real time by targeting on the molten pool transient area. The type of the laser used in this study is a flat-top beam. Laser power, powder feeder rate, and scanning speed are the input variables of the study to control molten pool, considering the manufacturing system. The most suitable processing parameter to control the molten pool area was found to be the laser power by a set of orthogonal experiments, with a correlation coefficient of 0.706, and significance level of 0.002. Then, the dynamic response relationship between laser power and the molten pool area was mathematically characterized by a third-order transfer function model to simplify the complex physical model of the DLD process. Subsequently, a PID controller with a filtering coefficient and anti-windup compensation was chosen compared with the other controller. In the validation experiments, it was observed that the closed-loop processing group demonstrated improved stability in maintaining the molten pool transient area, with a notable decrease of 33.7% in variability compared to the open-loop processing group. As a result, the deposited layer of the closed-loop processing group exhibited a much more satisfying surface quality and heat affect zone than the open-loop group. This study established a third-order mathematical model of the dynamic molten pool and realized the optimization of deposition quality by controlling the molten pool transient area with an enhanced PID controller, providing a fundamental basis for improving the consistency of the direct laser deposition processing quality through the implementation of real-time feedback control of molten pool physics. [ABSTRACT FROM AUTHOR]

This paper mainly deals with the current status and development trends of research on the microstructure and properties of additive manufacturing formed parts. According to the laser processes and powder processing, the microstructure of the parts including morphologies, phase composition, and grain orientation is analyzed; the forming quality of the parts including hardness, wear resistance, corrosion resistance, strength, fracture toughness, residual stresses, and fatigue properties is analyzed in many ways. At the same time, we expect to find the research directions that conform to the future development trends for LAM. [ABSTRACT FROM AUTHOR]

The increasing global climate change has resulted in more frequent drought disasters, and using the drought index to assess spatial and temporal changes accurately is of practical importance. In this study, the Spatio-temporal evolution characteristics of different drought indicators at annual and seasonal scales were analyzed by combining spatial interpolation, correlation analysis, trend tests, and the empirical orthogonal function based on the meteorological drought composite index (MCI) of Penman–Monteith. The study focused on drought research in the Pearl River basin from 1961 to 2020. The results indicated that (1) on the annual scale, drought exhibited a high spatial distribution in the west and low in the east, as well as high in the south and low in the north. The frequency, intensity, and extent displayed a non-significant decreasing trend, with the drought degree being mild in the past ten years. (2) On the seasonal scale, drought exhibited seasonal variability, particularly in spring and autumn, which were inversely distributed. Summer drought was the least severe, with the drought range mostly below 10%, while winter drought was the severest, exceeding 50%, indicating an areawide drought. (3) The consistent change of drought intensity across the basin is the primary mode, and the reverse distribution of east–west and north–south is the secondary mode. The overall higher year of drought intensity is close to 24 years, and the overall lower year is close to 28 years. The study based on the MCI can provide a reference for drought research and management in different regions. [ABSTRACT FROM AUTHOR]

Precipitation whiplash, including abrupt shifts between wet and dry extremes, can cause large adverse impacts on human and natural systems. Here we quantify observed and projected changes in characteristics of sub-seasonal precipitation whiplash and investigate the role of individual anthropogenic influences on these changes. Results show that the occurrence frequency of global precipitation whiplash is projected to be 2.56 ± 0.16 times higher than in 1979–2019 by the end of the 21st Century, with increasingly rapid and intense transitions between two extremes. The most dramatic increases of whiplash show in the polar and monsoon regions. Changes in precipitation whiplash show a much higher percentage change than precipitation totals. In historical simulations, anthropogenic greenhouse gas (GHG) and aerosol emissions have increased and decreased precipitation whiplash occurrences, respectively. By 2079, anthropogenic GHGs are projected to increase 55 ± 4% of the occurrences risk of precipitation whiplash, which is driven by shifts in circulation patterns conducive to precipitation extremes. This study shows that the occurrence frequency of global precipitation whiplash is projected to be ~2.6 times higher by the end of the 21st century compared to 1979–2019, with increasingly rapid and intense transitions between the two extremes. [ABSTRACT FROM AUTHOR]

Drought is one of the most frequent and devastating natural disasters. Based on future climate scenarios and land use/land cover (LULC) patterns, the copula framework was employed to calculate the probabilities of meteorological and hydrological drought risks for the next 30 years (2021–2050) in the Wanquan River Basin, meanwhile, the relationship between hydrological and meteorological droughts was revealed by correlation analysis and cross-wavelet transform (XWT). The results are as follows: (1) In the next 30 years, the risk of intra-seasonal meteorological drought (short-term drought) in the WRB is high at a probability of 40–70%, while the risk of inter-seasonal meteorological drought is relatively small at a probability of close to 30%; (2) compared with meteorological drought, the risk of intra-seasonal hydrological drought is small, but the probability of inter-seasonal hydrological drought (medium- or long-term drought) is 30–50%, and the risk of hydrological drought in the upstream is greater than that in the downstream; (3) the future meteorological and hydrological droughts in the WRB are significantly and positively correlated, and that hydrological drought lags behind meteorological drought. [ABSTRACT FROM AUTHOR]

Spatiotemporal changes in characteristics of rainfall events with different duration occurring in the rainy season in Guangzhou, a typical city in South China with high urbanization, were detected using the observed hourly precipitation data. Rainfall changes were further related to urbanization showing in high-resolution land use/land cover data. Results showed that Guangzhou had experienced accelerated urbanization with the fraction of urban land cover increasing from 2.9% in the 1980s to 14.9% in the 2000s. In the context of rapid urbanization, the precipitation amount over the urban center and downwind area were also higher than that over the upwind area during 1984–2016. Rainfall events with a short duration (≤ 6 h) over the urban center and downwind area were more intensive than those over the upwind area. The intensive rainstorms with a short duration tended to occurred more frequently in the afternoon than the early morning. The unimodal rainfall events with a frontal peak were more likely to occur more over the urban center than the upwind area, while the bimodal rainfall events with two peaks in the early and the middle occurred more frequently over the downwind than the urban center and the upwind area. [ABSTRACT FROM AUTHOR]

The electrolyte, one of the key components for the energy storage in the vanadium redox flow battery (VRFB), hinders the further commercial applications of the VRFB due to the poor thermal stability of the positive electrolyte at the elevated temperature and the inferior activity on the interface of electrode. To enhance the performance of the positive electrolyte, a zwitterion-type molecule pyridinium propyl sulphobetaine (PPS) with negatively charged sulfonic group and positively charged pyridine group is adopted as the additive for the positive electrolyte. In this study, we have proved that PPS can be adsorbed on the electrode through sulfonic group and pyridine group under both positive potential and negative potential, which can effectively modify the interface of electrode. Compared to other additives containing –NH2/–SO3H groups, PPS containing pyridine group may effectively eliminate the side effects of protonation (–NH3+) and intermolecular hydrogen bonding (-SO3−---+H3N-) in acidic electrolyte. Moreover, the PPS-containing V(V) electrolyte presents a better stability at 50 °C compared to the blank V(V) electrolyte. As a consequence, with the addition of 1% PPS in positive electrolyte, the VRFB exhibits higher efficiencies (80.78% VE and 78.17% EE compared to 78.95% VE and 76.87% EE of the blank VRFB at 100 mA cm−2) and 76.28% capacity retention after 100 cycles which is 5.22% higher than that of the pristine VRFB. Herein, the study of zwitterion molecules provides a meaningful reference for the further research on organic additives for VRFB. [ABSTRACT FROM AUTHOR]

Changes in precipitation seasonality or redistribution of precipitation could exert significant influences on regional water resources availability and the well-being of the ecosystem. However, due to the nonuniform distribution of precipitation stations and intermittency of precipitation, precise detection of changes in precipitation seasonality on the global scale is absent. This study identifies and inter-compares trends in precipitation seasonality within seven precipitation datasets during the past three decades, including two gauge-based datasets derived from the Climatic Research Unit (CRU) and the Global Precipitation Climatology Centre (GPCC), one remote sensing-retrieval obtained from Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR), three reanalysis datasets obtained from National Centers for Environmental Prediction reanalysis II (NCEP2), European Centre for Medium-Range Weather Forecasts Interim Reanalysis (ERA-Interim), and Modern Era Reanalysis for Research and Applications Version 2 (MERRA2), and one precipitation dataset merged from above three types, Multi-Source Weighted Ensemble Precipitation Version 1.2 (MSWEP_V1.2). Values of two indices representing the precipitation seasonality, the normal seasonality index (SI) and the dimensionless seasonality index (DSI), are estimated for each land grid in each precipitation dataset. The results show that DSI is more sensitive to changes in the temporal distribution of precipitation as it considers both annual amount and monthly fluctuations of precipitation, compared to SI that only considers monthly fluctuations of precipitation. There are large differences in precipitation seasonality at annual and climatologic scales between precipitation datasets for both SI and DSI. Within the seven precipitation datasets, PERSIANN-CDR SI and DSI show high precipitation seasonality while CRU SI, and ERA-Interim and MERRA2 DSI show the low precipitation seasonality in all continental regions. During 1988–2013, PERSIANN-CDR, NCEP2 and ERA-Interim show more widespread, statistically significant trends in precipitation seasonality than other four precipitation datasets. PERSIANN-CDR and NCEP2 show statistically significant decreases in SI over Middle East and Central Asia, while ERA-Interim, MERRA2 and MSWEP_V1.2 SI increase over Central and South Africa. Increases in SI over the most of South America are significant. Regions of Canada/Greenland/Iceland, East and South Africa show significant increases in precipitation seasonality, while South Europe/Mediterranean and Central Africa show significant decreases in precipitation seasonality in most datasets. Although time series of seasonality indices values fluctuate correlatively in recent three decades, there are no regions on which all precipitation datasets show a consistent, statistically significant, positive or negative trend in indices of precipitation seasonality. These inconsistent changes in precipitation seasonality within various precipitation datasets imply the importance of choosing dataset when studying changes in regional precipitation seasonality. [ABSTRACT FROM AUTHOR]

This study inter-compares the spatiotemporal features of precipitation extremes at global and regional scales within six daily precipitation datasets, i.e., gauge-based (Global Precipitation Climatology Center dataset, GPCC), satellite-retrieval (Precipitation Estimation From Remotely Sensed Information Using Artificial Neural Networks-Climate Data Record, PERSIANN-CDR), three reanalysis datasets (ERA-Interim, ERAI; the National Center for Atmospheric Research Reanalysis 2, NCEP2; and the WATCH-Forcing-Data-ERA-Interim, WFDEI), and products merged from the three type datasets (the Multi-Source Weighted-Ensemble Precipitation, MSWEP). All datasets reproduce similar spatial patterns of both annual and seasonal precipitation extremes over the period from 1979 to 2017. Compared to the reference dataset gauge-based GPCC, the reanalysis WFDEI outperforms among six products with spatial correlation coefficients of 0.89 and 0.80 for the annual extreme indices (i.e., annual total amount of 95th precipitation and maximum 1-day precipitation), respectively. The satellite-based product PERSIANN-CDR performs better than reanalyses and merged datasets in capturing the temporal variability of the intensity and amount of precipitation extremes with similar changing tendencies and magnitudes of about 45 mm day−1 and 230 mm at the global scale, respectively. The reanalyses and merged products underestimate the intensity of precipitation extremes. The selected six datasets behave differently in various regions. For the percentile-based frequency of precipitation extremes, NCEP2 performs well in regions of the Southeast Asian (SEA) and Amazon (AMZ), while WFDEI better matches GPCC over East North America (ENA) and North Australia (NAU) in both spatial patterns and temporal changes with correlation coefficients of 0.84 and 0.90, respectively. For the intensity features of annual precipitation extremes, NCEP2 performs better than other four datasets over regions of SEA, AMZ and West Africa (WAF). ERAI and WFDEI are consistent with GPCC in ENA and NAU with correlations coefficients of the intensity between ERAI (WFDEI) and GPCC are 0.82 (0.77) and 0.78 (0.64) for ENA and NAU, respectively. For the intensity of seasonal precipitation extremes, GPCC shows the highest estimates in regions of SEA, AMZ, ENA and WAF. ERAI and WFDEI perform better in reproducing the spatial patterns of seasonal precipitation extremes in all regions. NCEP2 (ERAI and WFDEI) show(s) consistent temporal variability of seasonal precipitation extremes with GPCC in regions of AMZ and WAF (ENA and NAU). Overall, there are large discrepancies in the absolute values of daily precipitation among datasets, and performances of non-gauged-based precipitation datasets in capturing the spatiotemporal variability of precipitation extremes are dependent on seasons, regions, and time periods. [ABSTRACT FROM AUTHOR]

Using the observed daily precipitation data across East China, this paper analyzes spatiotemporal changes of annual and seasonal extreme precipitation indices during 1960–2015. Effects of changes in atmospheric circulation on seasonal extremes were also detected by using the singular value decomposition method. Results show that amount of annual, spring and summer extreme precipitation over East China showed a significant increase with a maximum changing rate of 7.2, 3.2 and 5.4 mm decade−1, and the stations with upward tendency mainly located in the southern part of East China. Preceding sea surface temperature of the Indian Ocean and the Equatorial Pacific Ocean shows great influences on spring extreme precipitation over East China through modulating anomalous anticyclones and winds, especially over the downstream of the south of East China. Summer extreme precipitation is statistically significantly correlated with the western North Pacific subtropical high (WPSH) and positive anomalies of 500 hPa geopotential heights. Anomalously strong WPSH combining with two blocking highs in mid-latitude regions tends to trigger more extreme precipitation events in the Yangtze River Basin but less in the Yellow River Basin. [ABSTRACT FROM AUTHOR]

The inherent disadvantages of untreated carbon felt (pristine-CF) still restrict the vanadium redox flow battery (VRFB) from further improving in electrochemical performances. To solve this problem, the carbon felt (CF) decorated with bismuth hydrogen edetate (Bi(HEDTA)) complex was synthesized and studied as anode for VRFB. The cyclic voltammetry curve reflects the great improvement in electrochemical reversibility by reducing the peak potential difference from 0.73 to 0.50 V. Electrochemical impedance spectrum shows the better charge transfer process by reducing the charge transfer resistance from 7.14 to 1.13 Ω. The VRFB assembled by the CF modified with Bi(HEDTA) exhibits an energy efficiency of 66.25% at a current density of 160 mA cm−2, which is 11.76% higher than that of the pristine system. Moreover, the mechanism of Bi(HEDTA) involved in the anodic half-reaction of VRFB has been put forward. The results demonstrate that not only the metal but also the ligand of the complex are significant for improving the electrochemical activity of the reaction towards V3+/V2+ redox couple. In more detail, the oxygen-containing functional groups in the ligand could increase the wettability of the CF as well as act as the active sites, and the metal could decrease the evolution of hydrogen at the same time. Therefore, the effective combination of the respective functions of ligand and metal, makes Bi(HEDTA) a feasible ornament of the CF for VRFB. [ABSTRACT FROM AUTHOR]

Using historical salinity data from nine drought periods in the Pearl River Delta of China, this study utilized two machine learning approaches to forecast the salinity time series for multistep lead times: random forest (RF) models and extreme learning machine (ELM) models. To improve conventional RF and ELM models, three signal decomposition techniques were applied to preprocess the input time series: empirical mode decomposition (EMD), wavelet decomposition (WD) and wavelet packet decomposition (WPD). The study results indicated that in contrast to conventional RF/ELM, a hybrid RF/ELM method accompanied by decomposition techniques displayed better forecasting performance and yielded reasonably accurate prediction results. More specifically, hybrid models coupled with WPD displayed the best performance for all three forecast lead times of one, three and five days, whereas EMD underperformed both WPD and WD because of the limited predictability of the components. Both the WPD and WD hybrid models using the c o i f 5 wavelet basis performed better than those using the other two bases (db8 and sym8). In addition, ELM method performed better for conventional and WD/WPD hybrid models, whereas the RF method worked better for EMD hybrid model. The findings of the study showed that the nonstationary salinity series could be transformed into several relatively stationary components in the decomposition process, which provided more accurate salinity forecasts. The developed hybrid models coupling RF/ELM method with decomposition techniques could be a feasible way for salinity prediction. [ABSTRACT FROM AUTHOR]

Climate change and large-scale climate patterns may result in changes in probability distributions of climate variables that are associated with changes in the mean and variability, and severity of extreme climate events. In this paper, we applied a flexible framework based on the Bayesian spatiotemporal quantile (BSTQR) model to identify climate changes at different quantile levels and their teleconnections to large-scale climate patterns such as El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO) and Pacific-North American (PNA). Using the BSTQR model with time (year) as a covariate, we estimated changes in Canadian winter precipitation and their uncertainties at different quantile levels. There were some stations in eastern Canada showing distributional changes in winter precipitation such as an increase in low quantiles but a decrease in high quantiles. Because quantile functions in the BSTQR model vary with space and time and assimilate spatiotemporal precipitation data, the BSTQR model produced much spatially smoother and less uncertain quantile changes than the classic regression without considering spatiotemporal correlations. Using the BSTQR model with five teleconnection indices (i.e., SOI, PDO, PNA, NP and NAO) as covariates, we investigated effects of large-scale climate patterns on Canadian winter precipitation at different quantile levels. Winter precipitation responses to these five teleconnections were found to occur differently at different quantile levels. Effects of five teleconnections on Canadian winter precipitation were stronger at low and high than at medium quantile levels. [ABSTRACT FROM AUTHOR]

River discharge, tide, wind, topography and other factors all have great impacts on the saltwater intrusion of Modaomen Waterway (MW), a major outlet of the Pearl River Estuary. A coupled 1D-3D numerical model was applied in this study to account for the dynamic characteristics of saltwater intrusion in the MW, and the impacts of tide and river discharge on the length of saltwater intrusion were uncovered. Results are as the followings: (1) River discharge from upstream induces an obvious dilution of salinity along the MW, whereas tide can exert a positive force that pushes salt water landward. The effects of river discharge and tide on the length of saltwater intrusion can be well described by a regression function; (2) the saltwater intrusion along the MW is generally aggravated by increases in tidal range from the South China Sea. The length of saltwater intrusion usually reaches a maximum 2 or 3 days before spring tide, and the hourly length of saltwater intrusion along the MW usually slows the tidal process for approximately 4 h, which can provide important information that the pumping operation along the MW to store freshwater in the backup storages needs to be at least 3 days ahead of the spring tide so as to avoid serious impact from saltwater intrusion; (3) the length of saltwater intrusion generally decreases with increasing river discharge. In 2005, 2009 and 2010, the average river discharge from upstream was 2680, 2630 and 3160 m/s, respectively, with corresponding average lengths of saltwater intrusion of 32.7, 42.3 and 21.4 km. The inverse correlation between the water flow and the length of saltwater intrusion may provide some guidance for operations to maintain enough upstream flow to dilute the salinity and therefore satisfy the domestic water supply. [ABSTRACT FROM AUTHOR]

Extreme precipitation event is rare and mostly occurs on a relatively small local scale, which presents marked uncertainties when analyzing its characteristics. Using daily precipitation data covering 1959-2009 from 62 stations over the Pearl River Basin, the percentile method (PM) and the absolute critical value method (ACVM) are applied to define extreme precipitation thresholds (EPT), and their different impacts on the spatial-temporal distribution of extreme precipitation event were analyzed in this study. The findings of this study show: (1) Using the K-means clustering algorithm in terms of precipitation indices and the topography, longitude and latitude of each station, the whole basin is divided into eight precipitation zones. (2) The extreme indices, including extreme precipitation frequency, extreme precipitation proportion and proportion of extremely n-day precipitation, calculated by PM are markedly higher than those calculated by ACVM during five decades, which is particularly obvious in the low precipitation area such as the west-northern of the basin since more daily precipitation events are treated as extreme precipitation in this region if EPT is defined by PM. (3) The spatial distributions of extreme frequencies respectively calculated by these two methods are quite different across the basin. The spatial distribution of extreme frequencies calculated by ACVM shows a high-value center in the southeast coastal areas and a low-value center in the northwest mountain areas. However, the extreme frequencies calculated by PM distribute evenly over the basin, which is obviously inconsistent with the empirical results, an area with heavy precipitation usually has a high extreme precipitation frequency, and vice versa. [ABSTRACT FROM AUTHOR]

The change structures of precipitation and precipitation intensity and rainy days are analyzed for the Pearl River Basin (from 1959 to 2009) on the basis of a suite of 24 climatic indices derived from daily precipitation data at 62 meteorological stations with the help of the Mann-Kendall test. Contributions of seasonal precipitation and precipitation intensity class to the annual precipitation are also examined using the inverse distance weighted method. The following four conclusions can be drawn: (1) although the average annual precipitation of the entire basin does not show obvious variation, the number of annual rainy days has decreased significantly in 98.3 % of the stations. These two factors result in an obvious increase in precipitation intensity at 64.5 % of the stations. (2) No clear change trend has been found for seasonal precipitation over the entire area; however, the number of rainy days in each season has decreased significantly. In particular, the number of rainy days in the entire year and in the fall season has decreased in 98.3 and 100 % of the stations, respectively. (3) Although the number of rainy days in drizzle has decreased in 83.9 % of the stations, the number of rainy days where heavy rain and extremely heavy rain occurred increased in nearly 75.8 and 82.3 % of the stations, respectively. (4) The number of rainy days in fall and winter contributes more to the change in the number of annual rainy days than the number of rainy days in spring and summer. Heavy rain and extremely heavy rain contribute more to the change in total annual precipitation than drizzle; however, they contribute less to the change in the number of annual rainy days than drizzle. The findings in this study can provide important information for formulating water resource and eco-environment management strategies in the Pearl River Basin to policymakers and stakeholders. [ABSTRACT FROM AUTHOR]

Torrefaction is a slow pyrolysis process that is carried out in the relatively low temperature range of 220-300°C. The influence of torrefaction as a pretreatment on biomass gasification technology was investigated using a bench-scale torrefaction unit, a bench-scale laminar entrained-flow gasifier, and the analysis techniques TGA-FTIR and low temperature nitrogen adsorption. A series of experiments were performed to examine the characteristics of the torrefaction process, the properties of torrefaction products, and the effects of torrefaction on gas composition, cold gas efficiency and gasification efficiency. The results showed that during the torrefaction process the moisture content of biomass were reduced, and the wood fiber structure of the material was destroyed. This was beneficial to storage, transport and subsequent treatments of biomass in large scale. For solid products, torrefaction increased the energy density, decreased the oxygen/carbon ratio, and created a more complex pore structure. These improved the syngas quality and cold gas efficiency. Combustible gases accounted for about 50% of non-condensable gaseous torrefaction products. Effective use of the torrefaction gases can save energy and improve efficiency. Overall, biomass torrefaction technology has good application prospects in gasification processes. [ABSTRACT FROM AUTHOR]

At present, in the directed energy deposition (DED) of metals, the heat transfer of the melt pool and microstructural evolution are not fully understood. This study investigates the thermal effect on the microstructure and the mechanical properties of DED AISI 316L, using in situ optical monitoring. Five thin-wall samples were tested to determine the effect on microstructural evolution and mechanical properties with variable laser powers and scanning speeds. A comprehensive optical monitoring system with a CMOS (coaxial complementary metal oxide semiconductor) visual module and an infrared camera was adopted in analyzing the temperature gradient and the solidification rate. The emissivity of the melt pool was calibrated, using the melt pool length, extracted from the coaxial visual image. The results showed that microstructures mainly consist of the coarse columnar grain and the equiaxed grain at the top layer of AISI 316L samples. The direction of epitaxial growth of columnar grains is affected by the compromise between directional heat flux and crystallographic direction. High numerical temperature gradient and high solidification rate are beneficial to obtaining fine grain size and high yield stress. A modified microstructure map for DED AISI316L was established, which correlates the solidification parameters with a solidification microstructure. This research study, combining temperature distribution, solidification parameter, microstructure, and tensile property, provides an experimental identification of solidification parameters and the model on the solidification theory for precision control of DED process. [ABSTRACT FROM AUTHOR]