ALBERT

Description: Intertidal habitats provide numerous ecosystem services, including the sequestration and storage of carbon, a topic of great recent interest owing to land-cover transitions and climate change. Mangrove forests and seagrass meadows form a continuum of intertidal habitats, alongside unvegetated mudflats and sandbars, however, studies that consider the carbon stocks across these spatially-linked, threatened ecosystems are limited world-wide. This paper presents the results of a field-based carbon stock assessment of aboveground, belowground and sediment organic carbon stock to a depth of 1 m at Chek Jawa, Singapore. It is the first study of ecosystem carbon stocks of both vegetated and unvegetated intertidal habitats in the tropics. Ecosystem carbon stock was 497 Mg C ha -1 in the mangrove forest and 138 Mg C ha -1 in the seagrass meadow. Sediment organic carbon stock dominated the total storage in both habitats, constituting 62% and 〉99% in the mangrove forest and seagrass meadow respectively. In the adjacent mudflat and sandbars, which had no vegetative components, sediment organic carbon stock ranged from 124-143 Mg C ha -1 , suggesting that unvegetated habitats have a carbon storage role on the same order of importance as seagrass meadows. This study reinforces the importance of sediment in carbon storage within the intertidal ecosystem, and demonstrates the need to consider unvegetated habitats in intertidal ‘blue carbon’ stock assessments. This article is protected by copyright. All rights reserved.

Description: Fluid inclusions of the H 2 O-NaCl-CaCl 2 system are notorious for their metastable behavior during cooling and heating processes, which can render microthermometric measurement impossible or difficult and interpretation of the results ambiguous. This paper addresses these problems through detailed microscopic examination of synthetic solutions during cooling and warming runs, development of methods to enhance nucleation of hydrates, and comparison of microthermometric results with different degrees of metastability with values predicted for stable conditions. Synthetic H 2 O-NaCl-CaCl 2 solutions with different NaCl/(NaCl+CaCl 2 ) ratios were prepared and loaded in fused silica capillaries and glass-sandwiched films for microthermometric studies; pure solutions were used with the capillaries to simulate fluid inclusions, whereas alumina powder was added in the solutions to facilitate ice and hydrate crystallization in the sandwiched samples. The phase changes observed and the microthermometric data obtained in this study have led to the following conclusions that have important implications for fluid inclusion studies: 1) most H 2 O-NaCl-CaCl 2 inclusions that appear to be completely frozen in the first cooling run to -185°C actually contain large amounts of residual solution, as also reported in some previous studies; 2) inability of H 2 O-NaCl-CaCl 2 inclusions to freeze completely may be related to their composition (low NaCl/(NaCl+CaCl 2 ) ratios) and lack of solid particles; 3) crystallization of hydrates, which is important for cryogenic Raman spectroscopic studies of fluid inclusion composition, can be greatly enhanced by finding an optimum combination of cooling and warming rates and temperatures; and 4) even if an inclusion is not completely frozen, the melting temperatures of hydrohalite and ice are still valid for estimating the fluid composition. This article is protected by copyright. All rights reserved.

Description: Crystallization experiments were conducted in a new type of hydrothermal diamond-anvil cell (HDAC; type V) using LiAlSi 2 O 6 ( S ) gel and H 2 O ( W ) as starting materials. A total of 21 experiments were performed at temperatures up to 950°C and pressures up to 788 MPa. In the samples with relatively low W / S ratios, many small crystals formed in the melt phase during cooling. In those with high W / S ratios, only a few crystals with smooth surfaces crystallized from the aqueous fluid in the presence of melt droplets, which were gradually consumed during crystal growth, indicating rapid transfer of material from the melt to the crystals through the aqueous fluid. The nucleation of crystals started at 710 (±70)°C and 520 (±80) MPa, and crystal growth ended at 570 (±40)°C and 320 (±90) MPa, with the cooling P-T path within the stability field of spodumene + quartz in the S - W system. The observed linear crystal growth rates in the aqueous phase, calculated by dividing the maximum length of a single crystal by the duration of the entire growth step, were 4.7 × 10 −6 and 5.7 × 10 −6 cm s −1 for the cooling rates of 0.5 and 1°C min −1 , respectively. However, a rapid crystal growth rate of 3.6 × 10 −5  cm s −1 in the aqueous fluid was observed when the components were supplied by nearby melt droplets. Our results show that when crystals nucleate in the aqueous fluid instead of the melt phase, there are fewer nuclei formed, and they grow much faster due to the low viscosity of the aqueous fluid, which accelerates diffusion of components for the growth of crystals. Therefore, the large crystals in granitic pegmatite can crystallize directly from aqueous fluids rather than hydrosilicate melt.

Description: A numerical investigation on flow distribution and pressure drop characteristics in a plate-fin heat exchanger is presented. Influences from length and width of the distribution channel were particularly investigated. Flow distribution in the studied model was improved by increasing the length or reducing the width of the distribution channel, but at the cost of an increased pressure drop. The relationship of flow distribution and pressure drop was analyzed by the porous medium approach. A dynamic balance phenomenon was observed and further studied. Based on the results, a novel strategy for the attainment of flow uniformity, which causes negligible pressure drop variation, was proposed. Finally, a performance effectiveness factor was developed for predicting the effect of the proposed strategy on the performance of plate-fin heat exchangers. Flow distribution and pressure drop characteristics in a plate-fin heat exchanger are studied for the first time. Based on the effects of distribution channel dimensions, a new strategy for improving the performance of the heat exchanger is proposed. A performance effectiveness factor was developed for predicting the effect of the proposed approach.

Description: [1]  Experiments to determine silicate structural species in silicate-saturated aqueous fluids in equilibrium with silica polymorphs (quartz and coesite), enstatite, and enstatite + forsterite in the SiO 2 -H 2 O and MgO-SiO 2 -H 2 O systems have been carried out in-situ in the 0.4-5.4 GPa and 700˚-900˚C pressure and temperature ranges, respectively. MicroRaman spectroscopy was the structural probe. In the SiO 2 -H 2 O system (1.6-5.4 GPa/700˚-900˚C), the detected silicate species are Q o (SiO 4 4- ), Q 1 (0.5 Si 2 O 7 6- ), and Q 2 (SiO 3 2- ). The expression, 2Q 1  ⇌ Q o  + Q 2 , describes the equilibrium among these species with ∆H and ∆V-values from the isochoric temperature- and isothermal pressure-dependence of its equilibrium constant, K = X Qo •X Q2 /(X Q1 ) 2 , range from −23 to −69 kJ/mol and −1 - -2 cm 3 /mol, respectively. In the system MgO-SiO 2 -H 2 O the calculated silica solubility, using literature algorithms, is approximately 50% of that in the SiO 2 -H 2 O system at similar temperature and pressure. Only Q 1 and Q o species were detected in the MgO-SiO 2 -H 2 O fluids, whether in equilibrium with enstatite + forsterite (P 〈 3 GPa) or enstatite only (P 〉 3 GPa). The temperature- and pressure-dependence of the equilibrium constant, K = X Q1 /X Qo , for this system yields average values of ∆H = 40 ± 5 kJ/mol and ∆V = −2.3 ± 0.4 cm 3 /mol. [2]  The speciation of silicate in aqueous fluids resembles that in hydrous melts as a function of temperature and pressure at deep crustal and upper mantle temperature and pressure conditions and they become increasingly similar with depth. As the silicate speciation and solubility in the aqueous fluid depend on silicate composition, the pressure and temperature at which complete miscibility occurs will also vary with silicate composition. The structural similarity between fluids and melts will also lead to fluid/melt element partition coefficients trending toward 1, and mineral/fluid partition coefficients trending toward mineral/melt values, in the upper mantle as the silicate-H 2 O systems approach complete miscibility with increasing temperature and pressure.

Description: Article Single layers of atoms can exhibit electronic properties far removed from their three-dimensional counter parts, with much potential for spintronics. Here, the authors provide evidence of spin-orbit splitting and extrinsic quantum well states in MoS2 and MoSe2 by angle-resolved photoemission spectroscopy Nature Communications doi: 10.1038/ncomms5673 Authors: Nasser Alidoust, Guang Bian, Su-Yang Xu, Raman Sankar, Madhab Neupane, Chang Liu, Ilya Belopolski, Dong-Xia Qu, Jonathan D. Denlinger, Fang-Cheng Chou, M. Zahid Hasan

Description: Flux tube integrated Rayleigh-Taylor instability growth rates computed using the results of ionosphere data assimilation are used for the first time to investigate global plasma bubble occurrence. The study is carried out by assimilating total electron content measurements using ground based global positioning system (GPS) receivers into thermosphere ionosphere electrodynamic general circulation model, and the growth rates are calculated using standalone model run without assimilation (control run) as well as using prior (or forecast) state output of the assimilation run. The growth rates are compared with rate of change of total electron content index (ROTI), estimated from global network of GPS receivers, as well as all sky airglow observations carried out over Taiwan on the nights of 16, and 17 March 2015. In contrast to the growth rates using the control run, results using data assimilation show remarkable agreement with the ROTI. Further, the all sky images reveal intense plasma bubbles over Taiwan on the night of 16 March, when the corresponding assimilated growth rate is also pronounced. Similarly, absence of plasma bubbles in the all sky images on the night of 17 March (St. Patrick's day storm) is supported by smaller growth rates predicted by the assimilation model. Significant improvements in the calculated growth rates could be achieved because of the accurate updating of zonal electric field in the data assimilation forecast. The results suggest that realistic estimate or prediction of plasma bubble occurrence could be feasible by taking advantage of the data assimilation approach adopted in this work.

Description: Article Topological Dirac semimetals constitute a promising platform for the study of quantum Hall phenomena and Weyl fermion transport. Using high-resolution angle-resolved photoemission spectroscopy, Neupane et al. identify the topological bulk Dirac semimetal phase in a Cd 3 As 2 system. Nature Communications doi: 10.1038/ncomms4786 Authors: Madhab Neupane, Su-Yang Xu, Raman Sankar, Nasser Alidoust, Guang Bian, Chang Liu, Ilya Belopolski, Tay-Rong Chang, Horng-Tay Jeng, Hsin Lin, Arun Bansil, Fangcheng Chou, M. Zahid Hasan