This paper describes a nickel-based cellular material, which has the strength of titanium and the density of water. The material's strength arises from size-dependent strengthening of load-bearing ...nickel struts whose diameter is as small as 17 nm and whose 8 GPa yield strength exceeds that of bulk nickel by up to 4X. The mechanical properties of this material can be controlled by varying the nanometer-scale geometry, with strength varying over the range 90-880 MPa, modulus varying over the range 14-116 GPa, and density varying over the range 880-14500 kg/m
. We refer to this material as a "metallic wood," because it has the high mechanical strength and chemical stability of metal, as well as a density close to that of natural materials such as wood.
Both community variation and phosphorus (P) fractions have been extensively studied in aquatic ecosystems, but how P fractions affect the mechanism underlying microbial beta diversity remains ...elusive, especially in sediment cores. Here, we obtained two sediment cores to examine bacterial and archaeal beta diversity from mesotrophic lakes Hongfeng Lake and Aha Lake, having historically experienced severe eutrophication. Utilizing the Baselga’s framework, we partitioned bacterial and archaeal total beta diversity into two components: species turnover and nestedness, and then examined their sediment-depth patterns and the effects of P fractions on them. We found that total beta diversity, species turnover or nestedness consistently increased with deeper sediment layers regarding bacteria and archaea. Notably, there were parallel patterns between bacteria and archaea for total beta diversity and species turnover, which is largely underlain by equivalent processes such as environmental selection. For both microbial taxa, total beta diversity and species turnover were primarily constrained by metal oxide-bound inorganic P (NaOH-Pi) and sediment total phosphorus (STP) in Hongfeng Lake, while largely affected by reductant-soluble total P or calcium-bound inorganic P in Aha Lake. Moreover, NaOH-Pi and STP could influence bacterial total beta diversity by driving species nestedness in Hongfeng Lake. The joint effects of organic P (Po), inorganic P (Pi) and total P fractions indicated that P fractions are important to bacterial and archaeal beta diversity. Compared to Po fractions, Pi fractions had greater pure effects on bacterial beta diversity. Intriguingly, for total beta diversity and species turnover, archaea rather than bacteria are well-explained by Po fractions in both lakes, implying that the archaeal community may be involved in Po mineralization. Overall, our study reveals the importance of P fractions to the mechanism underlying bacterial and archaeal beta diversity in sediments, and provides theoretical underpinnings for controlling P sources in biodiversity conservation.
Information on the chemical composition of phosphorus (P) fractions in sediments is fundamental to understanding P bioavailability and eutrophication in lake ecosystems. Phosphorus fractions and its ...bioavailability in sediments cores of Lake Hongfeng, southwest China, were investigated using a chemical sequential extraction scheme. Relationships between P fractions, P bioavailability and particle sizes were discussed. P fractions concentrations were ranked in the order: Residual-P > NaOH–rP > NaOH–NRP > HCl–P > BD–P > NH₄Cl–P, and all of them decreased with increasing sediment depth. Statistical analysis showed that concentrations of bioavailable P (BAP) which includes the NH₄Cl–P, BD–P, NaOH–rP and NaOH–NRP fractions ranged from 404.68 to 1,591.99 mg/kg and accounted for 26.8–71.8 % of the concentrations of total phosphorus (TP) in the top 5 cm sediments, whereas in the whole sediment cores, their concentrations ranged from 239.70 to 1,591.99 mg/kg and accounted for 26.8–76.0 % of TP. The results suggested that the sediments were a large potential source of P for algae blooms in Lake Hongfeng. Phosphorus fractions and their potential bioavailability were influenced by the sediment particle sizes, especially the bioavailability of the NH₄Cl–P fraction, which was strongly affected by the presence of fine particle sizes in the sediments.
In order to improve the stabilization of closed-cell aluminum foams during preparation process, a horizontal steady uniform magnetic field was imposed. The three-dimensional microscopic drainage ...model of closed-cell aluminum foam has been developed, in which the surface viscosity was incorporated into the boundary conditions to quantify the mobility of the gas–liquid interface. The predicted results by the model agree well with the experimental data from literatures. The numerical results show that the uniform magnetic field has particularly suppression effect on the drainage flow in aluminum foam. And this effect increases with the increasing magnetic induction intensity. The suppression effect of magnetic field on drainage at the bottom of aluminum foam is higher than that at the top and middle of aluminum foam. For different stages of the drainage process, applying the magnetic field in the early stage is more effective than in the later stage. For different preparation methods, the application of magnetic field to powder metallurgy method has the best effect, followed by blowing foaming method and melting foaming method. Different combinations of particle concentration and magnetic induction intensity can achieve the same suppression effect. In the preparation of aluminum foam, it is suggested to combine magnetic field with the particles to improve the suppression efficiency of drainage behavior. The critical magnetic induction intensity is proposed. Under this critical condition, the magnetic field can completely replace the particles. Furthermore, the critical magnetic induction intensity shows linear relationship with the logarithm of Boussinesq number.
In this study, we investigated the influence of the Indian Ocean Dipole (IOD) on the interannual variability of tropical cyclone (TC) activity over the western North Pacific (WNP) during autumn ...(September–November) from 1961–2015. We found the number of TCs making landfall in China to be significantly negatively correlated with the IOD index, which can be attributed to shifts in the location of TC formation together with the abnormal steering flow at 500 hPa. During negative IOD autumns, TC genesis regions move obviously westward due to the westward retreat of the WNP monsoon trough. The TC activity is remarkably enhanced near South China coastal areas, which is due to a contiguous 500-hPa subtropical ridge. In contrast, during positive IOD autumns, TC genesis positions obviously shift eastward and more TCs tend to exhibit recurvature around 130°E or a westward path south of 15°N led by an equatorward movement of the 500-hPa subtropical ridge with a break near 125°E. In our examination of large-scale circulation, we found a pair of equator-symmetric anticyclones in the lower troposphere resulting from variations in the large-scale Walker circulation induced by the anomalous sea surface temperature (SST) associated with a positive IOD. The resulting Philippines anti-cyclonic anomalies are closely related to the variability of the monsoon trough over the WNP region. Furthermore, the variations in the steering flow can be explained by the suppressed (enhanced) convective activities around the Philippines and the weakened (strengthened) local meridional circulation over East Asia in positive (negative) IOD years.
Abstract
The ballistic performance of edge-clamped monolithic polyimide aerogel blocks (12 mm thickness) has been studied through a series of impact tests using a helium-filled gas gun connected to a ...vacuum chamber and a spherical steel projectile (approximately 3 mm diameter) with an impact velocity range of 150–1300 m s
−1
. The aerogels had an average bulk density of 0.17 g cm
−3
with high porosity of approximately 88%. The ballistic limit velocity of the aerogels was estimated to be in the range of 175–179 m s
−1
. Moreover, the aerogels showed a robust ballistic energy absorption performance (e.g., at the impact velocity of 1283 m s
−1
at least 18% of the impact energy was absorbed). At low impact velocities, the aerogels failed by ductile hole enlargement followed by a tensile failure. By contrast, at high impact velocities, the aerogels failed through an adiabatic shearing process. Given the substantially robust ballistic performance, the polyimide aerogels have a potential to combat multiple constraints such as cost, weight, and volume restrictions in aeronautical and aerospace applications with high blast resistance and ballistic performance requirements such as in stuffed Whipple shields for orbital debris containment application.
With XAD-series and ion exchange resins, dissolved organic matter (DOM) from Lake Hongfeng in Southwestern China Plateau was isolated into 6 fractions, i.e., humic acid (HA), fulvic acid (FA), ...hydrophobic neutrals (HON), hydrophilic acids (HIA), hydrophilic bases (HIB) and hydrophilic neutrals (HIN). Those fractions were characterized by high performance size exclusion chromatography, fluorescence spectroscopy and UV absorbance. Among the 6 fractions, FA was predominant and accounted for 51% of the total DOM. The weight-average (
M
w) and number-averaged (
M
n) molecular weight of these fractions ranged from 1688 to 2355 Da and from 1338 to 1928 Da, respectively. A strong correlation was observed between specific UV absorbance at 280 nm,
E
2/
E
3 (absorbance at 250 nm to 365 nm), and the molecular weight for DOM fractions. UV-Vis fulvic-like fluorescence peaks were found in all fractions. Protein-like fluorescence peaks existed in HON may indicate that microbial activity was severely in Lake Hongfeng. There was a significant relationship between fluorescence intensities and specific UV absorbance at 254 nm for those DOM fractions, suggesting their similar luminescence characteristics. The values of fluorescence index (
f
450/500) indicated that hydrophobic fractions may derive from terrestrial sources, and the hydrophilic fractions from microbial and terrestrial origins. Those results suggest that there were inter-relationships between molecular weight, fluorescence and absorbance characteristics, and also subtle consistencies between the hydrophilic and hydrophobic properties and the sources for these 6 fractions from Lake Hongfeng.
The linkage between the spring subtropical Indian Ocean Dipole (SIOD) events and tropical cyclone genesis frequency over the western North Pacific (WNP) in the following summer is investigated in ...this study. It is found that their correlation is positive and statistically significant with a greater number of TCs genesis over the WNP in summer of a positive SIOD year. After removing the ENSO effects, diagnostic analysis reveals that under positive SIOD conditions the summertime WNP monsoon trough becomes intensified. Correspondingly, there are enhanced lower‐level vorticity, reduced vertical zonal wind shear, increased middle‐level relative humidity and vertical velocity over the WNP, conductive to generation of more TCs. Further examination indicates that the Mascarene high and Australian high are strengthened successively from spring to subsequent summer in a positive SIOD year, contributing to the maintenance of SIOD‐related SST dipole anomalies in southern Indian Ocean due to SST–wind–evaporation feedback mechanism. The resulting cyclonic anomaly is formed at lower troposphere over the WNP induced by the prominently enhanced cross‐equator airflows and the related Ekman upwelling. At upper troposphere, there tend to be remarkably WNP divergence anomalies of the interhemispheric vertical circulation forced by the summertime SST patterns closely associated with positive SIOD cases. By contrast, the monsoon trough is weakened and the dynamic and thermodynamic conditions are unfavourable for the WNP TC genesis in summer of a negative SIOD year, in agreement with a lower‐level anticyclonic anomaly and suppressed deep convection over the WNP forced by the SIOD‐related SST anomalies.
(a) Normalized time series of the spring (March–May) SIOD index (black line) and the following summer (June–August) WNP TC genesis frequency index (grey shadings). (b) Correlation map of the spring SIOD index and simultaneous SST (contours: 0.2). Red E and blue L in (a) denote El Niño and La Niña years, respectively. Shadings in (b) indicate the regions significant passing 99% confidence level
The temporal distribution of polycyclic aromatic hydrocarbons (PAHs) was examined in dated sediments from five lakes in Western China. The surficial concentrations of seven carcinogenic PAHs (B
aA, ...Chyr, B
bF, B
kF, B
aP, DBA and INP, hereafter denoted as PAH
7) were highly site-specific. The ΣPAH
7 concentrations generally increased from the deep layers to surface sediments. The temporal trends of ΣPAH
7 concentrations were clearly different from those reported in developed countries. From 1950s to 1980s, which PAHs started to decrease in developed countries, is the right period that PAHs started to increase rapidly in Western China. The fluxes and mass inventories suggest that the PAH
7 input over the past three decades was much more rapidly than it was before the 1980s. Source identification indicates that the PAHs were primarily from biomass burning and domestic coal combustion, and increasing vehicular and/or industrial coal combustion emission was also found.
The present manuscript provides critical information for comprehensive understanding of the temporal trends of PAHs in lake sediments from Western China and the global PAHs emission.
As a primary factor responsible for lake eutrophication, a deeper understanding of the phosphorus (P) composition and its turnover in sediment is urgently needed. In this study, P species in surface ...sediments from a Chinese large eutrophic lake (Lake Taihu) were characterized by traditional fractionation and
31
P nuclear magnetic resonance (NMR) spectroscopy, and their contributions to the overlying water were also discussed. Fractionation results show that NaOH-P predominated in the algal-dominated zone, accounting for 60.1% to total P in Zhushan Bay. Whereas, refractory fractions including HCl-P and residual-P were the main P burial phases in the macrophyte-dominated zone, the center and lakeshore. Recovery rates of the total P and organic P were greatly improved by using a modified single-step extraction of NaOH-EDTA, ranging from 22.6 to 66.1% and from 15.0 to 54.0%. Ortho-P, monoester-P, and pyro-P are identified as the major P components in the NaOH-EDTA extracts by
31
P NMR analysis. Trace amount of DNA-P appeared only in sediments from algal- and macrophyte-dominated zones, ascribing to its biological origin. The relative content of ortho-P is the highest in the algal-dominated zone, while the biogenic P including ester-P and pyro-P is the highest in the macrophyte-dominated zone. Moreover, ortho-P and pyro-P correlated positively with TP and chlorophyll a in the overlying water, whereas only significant relationships were found between monoester-P, biogenic P, and chlorophyll a. These discrepancies imply that inorganic P, mainly ortho-P, plays a vital role in sustaining the trophic level of water body and algal bloom, while biogenic P makes a minor contribution to phytoplankton growth. This conclusion was supported by the results of high proportion of biogenic P in algae, aquatic macrophytes, and suspended particulate from the published literature. This study has significant implication for better understanding of the biogeochemical cycling of endogenous P and its role in affecting lake eutrophication.
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