Apparent Flux Research Articles

Validation and evaluation of the CPFD modeling of dense particle flow velocity: Taking particle flow around an obstacle as an example

The computational particle fluid dynamic (CPFD) method is a common approach to simulating dense particle flow, but the direct validation of the CPFD model using the particle velocity distribution is lacking. Taking particle flow around an obstacle as an example, the accuracy of the CPFD method in the simulation of the dense particle velocity field was validated and evaluated in the present study. The particle flow field was experimentally visualized using a quasi-2D flow channel and the particle velocity distribution was measured by a newly-proposed stained-particle image velocimetry technique. The simulated particle velocity using the CPFD method was compared with the measured data and the results indicated that the CPFD method was capable of accurately predicting the particle flow velocity distribution as well as the overall parameters such as the apparent mass flux if the CPFD model parameters were properly adopted. The sensitivity analysis of the simulated particle velocity to the key CPFD parameters was conducted and the results showed that the simulated particle velocity distribution was quite sensitive to the particle pack volume fraction, while the particle stress model parameters and particle-to-wall restitution coefficients show less and close sensitivity in the dense particle flow situations. The recommended model parameters were given in the present study. It is also found that multiple choices of the model parameter combinations could all give accurate overall mass flow predictions but might lead to very different flow velocity distributions with a prediction error even higher than 45%. One should directly verify the CPFD simulated flow velocity using the experimental data if the flow field study was desired.

Fundamental modeling and experimental validation of hydrogen and oxygen transport through mixed ionic and electronic conducting membranes

Hydrogen transporting mixed ionic and electronic membranes offer tremendous opportunities for process intensification and energy savings in various applications such as reaction chemistries and heat/energy generation. Over the past several decades there has been significant advancement in the membrane materials science to produce improved molecular transport, but commercial adoption is still limited. To escalate implementation, a fundamental understanding of the solid state membrane transport and the water splitting phenomenon would bridge the gap for process conceptualization and design. This work presents a fundamental transport model, which quantifies the contribution of the water splitting phenomenon to the overall observed apparent flux of hydrogen and oxygen through ionic and electronic conducting membranes. The model predictions are rigorously validated against experimental data gathered in parallel. Membranes tested were based on the composition La0.87Sr0.13CrO3-δ-La5.4WO12-δ. These measurements include both apparent hydrogen/oxygen fluxes and the water splitting contributions over a range of operating conditions that included varying temperatures, hydrogen partial pressures, and hydration gradients across the membrane.

Neocalanus cristatus (Copepoda) From a Deep Sediment-Trap: Abundance and Implications for Ecological and Biogeochemical Studies

We studied seasonal variations of the mesozooplankton swimmer community collected by a sediment trap moored at 873 m in the Kuroshio–Oyashio Transition region off the east coast of Japan from 5 August 2011 to 23 June 2013, with sampling bottles rotating at 26-day intervals. The total flux of mesozooplankton swimmers varied between 0 and 11.1 individuals m–2 d–1, with a mean of 3.1 individuals m–2 d–1 during the sampling period. In total, 89 taxa were found in the trap material, of which copepods comprised 87.1% of all swimmers on average. Among the Copepoda, Neocalanus cristatus was the most dominant taxon (76.2% of copepods on average during the sampling period), and all of them were stage C5 copepodite to adult. The species composition of the swimmers closely reflected the mesopelagic mesozooplankton of the Oyashio region. Because all N. cristatus observed in the trap were stage C5 to adult, its flux represents a time series of variations in life history and response to environmental changes at the depth of the sediment trap. The fluxes of Neocalanus species (N. cristatus, N. flemingeri, and N. plumchrus) reflected ontogenetic vertical migration, but may have been overestimates of active fluxes if they included dormant individuals that accidentally entered the sediment trap. The apparent active carbon flux of Neocalanus species ranged from 0 to 22.3 mg C m–2 d–1 during the sampling period, with a mean value of 4.9 mg C m–2 d–1.

Fundamental effective temperature measurements for eclipsing binary stars – III. SPIRou near-infrared spectroscopy and CHEOPS photometry of the benchmark G0V star EBLM J0113+31

Abstract EBLM J0113+31 is moderately bright (V=10.1), metal-poor ([Fe/H] ≈−0.3) G0V star with a much fainter M dwarf companion on a wide, eccentric orbit (=14.3 d). We have used near-infrared spectroscopy obtained with the SPIRou spectrograph to measure the semi-amplitude of the M dwarf’s spectroscopic orbit, and high-precision photometry of the eclipse and transit from the CHEOPS and TESS space missions to measure the geometry of this binary system. From the combined analysis of these data together with previously published observations we obtain the following model-independent masses and radii: M1 = 1.029 ± 0.025M⊙, M2 = 0.197 ± 0.003M⊙, R1 = 1.417 ± 0.014R⊙, R2 = 0.215 ± 0.002R⊙. Using R1 and the parallax from Gaia EDR3 we find that this star’s angular diameter is θ = 0.0745 ± 0.0007 mas. The apparent bolometric flux of the G0V star corrected for both extinction and the contribution from the M dwarf (<0.2 per cent) is ${\mathcal {F}}_{\oplus ,0} = (2.62\pm 0.05)\times 10^{-9}$ erg cm−2 s−1. Hence, this G0V star has an effective temperature Teff, 1 = 6124 K ± 40 K (rnd.) ± 10 K (sys.). EBLM J0113+31 is an ideal benchmark star that can be used for “end-to-end” tests of the stellar parameters measured by large-scale spectroscopic surveys, or stellar parameters derived from asteroseismology with PLATO. The techniques developed here can be applied to many other eclipsing binaries in order to create a network of such benchmark stars.

Investigating the contribution of extended radio sources to the Epoch of Reionization power spectrum

ABSTRACT We investigate the contribution of extended radio sources such as Centaurus A, and Galactic supernova remnants (SNRs) to our ability to detect the statistical 21-cm signal from the Epoch of Reionisation (EoR) with the Murchison Widefield Array (MWA). These sources are typically ignored because they are in highly attenuated parts of the MWA primary beam, however, in aggregate, these sources have apparent flux densities of $10\, \rm {Jy}$ on angular scales we expect to detect the 21-cm signal. We create bespoke multicomponent 2D Gaussian models for Galactic SNRs and for Centaurus A, and simulate the visibilities for two MWA snapshot observations. We grid those visibilities and then Fourier transform them with respect to frequency, averaging them both spherically and cylindrically to produce the 1D and 2D power spectra. We compare the simulated 1D power spectra to the expected 21-$\rm {cm}$ power spectrum. We find that although these extended sources are in highly attenuated parts of the MWA primary beam pattern, collectively they have enough power (∼104−105 $\rm {mK^2}\, {\it h^{-3}} \, \rm {Mpc^{3}}$) on EoR significant modes $(|{\boldsymbol k}| \lesssim 0.1\, h\, \rm {Mpc^{-1}})$ to prohibit detection of the 21-$\rm {cm}$ signal (∼104 $\rm {mK^2}\, {\it h^{-3}} \, \rm {Mpc^{3}}$). We find that $50{-}90{{\ \rm per\ cent}}$ of sources must be removed in order to reduce leakage to a level of $\sim 10{-}20{{\ \rm per\ cent}}$ of the 21-$\rm {cm}$ power spectrum on EoR significant modes. The effects of wide-field extended sources will have implications on the detectability of the 21-$\rm {cm}$ signal for the MWA and with the future Square Kilometre Array (SKA).

Evaluation of the Potential Release Risk of Internal N and P from Sediments—A Preliminary Study in Two Freshwater Reservoirs in South China

Growing evidence has demonstrated the influence of internal nitrogen (N) and phosphorus (P) on harmful algae blooms in eutrophic freshwater ecosystems. However, the main controlling factors for internal N and P release risks, and whether these factors vary as environmental conditions change, remains poorly understood. We evaluated potential release risks of N and P from sediments in two freshwater reservoirs in Beihai City, southern China, by evaluating apparent nutrient fluxes during simulated static incubation experiments at two temperatures (15 °C and 25 °C). Sediments were analyzed to determine their basic properties as well as N and P fractions. Results showed that the main controlling factors of the apparent fluxes in dissolved total P, soluble reactive P, total N, and ammonium were related to sediment adsorption properties, redox properties, and microbial-mediated properties (e.g., water-extractable P, total inorganic N, redox-sensitive P, total organic carbon, organic P). The primary controlling factors for apparent N and P fluxes were dependent on the form of N and P and changed with temperature. The results suggest that care should be taken when simply using total N and P contents in sediments to evaluate their internal nutrient release risks.

Comparative analysis of four universal estimation methods of nitrogen and phosphorus fluxes in lake sediments

湖泊沉积物-水界面营养盐释放是研究湖泊环境行为的重点关注对象，但目前对于湖泊通量的估算方法选择缺乏横向定量比较.以南京莫愁湖为研究对象，在冬春夏3季采用静态释放培养法、机械搅拌培养法、流动培养法和间隙水浓度扩散模型法4种常见的湖泊通量培养方法进行氮磷释放对比实验.结果表明，非扩散模型法（静态释放、机械搅拌、流动培养）在冬季存在负通量，随着气温升高，夏季通量估算值为正，且该3种方法通量数值差异不显著.间隙水扩散模型法在三季实验中结果数值无负值，对比非扩散模型组具有显著差异，约低一个数量级.不同方法在培育过程中溶解氧和pH变化差异显著，流动培养法最为稳定.4种方法的通量结果在不同季节变化趋势具有显著相关性，非扩散模型法估算结果作为表观通量值，适用于计算湖泊沉积物营养盐释放总量，其中静态释放法结果稳定性较差，平行组相对标准偏差最高达70%；流动培养法稳定性最好，平行组相对标准偏差最高仅21%.扩散模型法估算结果作为理论释放值，在估算浅水湖泊通量时低于实际释放通量，适于探究深水湖泊沉积物间隙水动态释放过程，有助于分析湖泊沉积物性质.不同培养方法，有其侧重点，根据不同湖泊状况，应选取合适方法进行通量估算.;Nutrient releasing at the sediment-water interface (SWI) is the focus of environmental behavior research in lakes, but there is a lack of lateral quantitative comparison in the methods used to estimate lake fluxes. In this paper, Lake Mochou in Nanjing was taken as the research object, and four common lake flux estimation methods, such as static release method, mechanical agitation method, flow cultivation method and pore water concentration diffusion model method, were used to conduct comparative experiments on nitrogen and phosphorus release in winter, spring and summer. The results showed that the non-diffusion model (static release, mechanical agitation and flow cultivation) had negative flux in the winter, and the estimated flux was positive in the summer with the increase in temperature, and there was no significant difference in the flux values between the three methods. The results of the pore water diffusion model method showed no negative values in the three-season tests, which were significantly different from those of the non-diffusion model groups with about one order of magnitude lower. There were significant differences in dissolved oxygen and pH among different methods, and the flow cultivation method was the most stable. The flux results of the four methods were significantly correlated with each other in different seasons. As the apparent flux value, the estimation results of the non-diffusion model method were suitable for calculating the total nutrient release of lake sediments. The static release method showed poor stability, and the relative standard deviation of the parallel group was up to 70%. The flow cultivation method had the best stability, and the relative standard deviation of the parallel group was only 21%. As the theoretical release value, the estimated result of the diffusion model is lower than the actual release flux of shallow lake flux, which is suitable for exploring the dynamic release process of sediment interstitial water in deep-water lakes and helpful for analyzing the properties of lake sediments. Different cultivation methods have their own emphases. According to different lake conditions and experimental needs, appropriate methods should be selected for flux estimation.

Pre-straining alters hydrogen-assisted cracking site and local hydrogen diffusivity in a nitrogen-doped duplex steel

The pre-deformation effects of hydrogen embrittlement on nitrogen-doped duplex stainless steel were investigated using tensile testing. Hydrogen pre-charging and pre-straining were adopted, which increased the yield strength, but decreased the ductility. Silver decoration revealed that diffusible hydrogen was preferentially located in the ferrite or grain boundaries of the undeformed steel, whereas the 22% pre-strained steel had diffusible hydrogen in austenite. When deformed, the preferential plastic deformation path of the steel was in the ferrite; hence, the apparent diffusivity in ferrite decreased, while the austenite had a relatively high apparent hydrogen flux. Pre-straining suppressed macroscopic hydrogen diffusion and local diffusion in ferrite and austenite by increasing the dislocation density. The degree of the suppression of the local diffusion was more significant in ferrite than austenite. The changes in dislocation and hydrogen behaviors associated with pre-straining altered the cracking sites in the austenite and ferrite, and decreased hydrogen embrittlement susceptibility.

Determining the role of diffusion and basement flux in controlling 4He distribution in sedimentary basin fluids

The transport of helium from the crystalline continental basement and overlying Phanerozoic sedimentary formations to the near surface can be controlled by both diffusive and advective processes. The relative role of each is vital to helium resource prediction, and important in quantifying the residence times of fluids relevant to groundwater resources, hydrocarbon systems, geologic repositories for nuclear waste and carbon sequestration. The Williston Basin, North America, is a prominent sedimentary basin, providing an excellent natural laboratory to assess these processes. Here, we report noble gas isotopic and composition data for 28 gas samples from natural gas wells that sample different stratigraphic horizons down to the basement (Cretaceous to the Cambrian). Helium isotope ratios show a resolvable mantle 3He component (up to 4.7%) in most samples. Neon isotopic compositions of the Cambrian samples are consistent with a crystalline basement gas contribution. Both helium and neon isotopic observations provide evidence for the contribution of conservative noble gases from the crystalline basement or deeper into the overlying sedimentary basin. 4He groundwater concentrations in the sedimentary formations, calculated from 4He/20Ne values in gas samples, are in excess of in situ U+Th 4He production in some shallow units and depleted in others, providing further evidence of cross formation gas contributions.The highest 4He groundwater concentrations can be compared with the results obtained from a fully-coupled vertical scale transport model characterising diffusive-dominated transport through a static groundwater column. The model includes the 4He flux into the basin from the Precambrian basement and quantifies the apparent basement 4He flux to be between 0.8 - 1.6 × 10−6 mol 4He/m2 yr, comparable to the steady-state flux estimated for the average continental crust (1.47 × 10−6 mol 4He/m2 yr) (Torgersen, 2010). The lithologies in which 4He concentrations are significantly lower than the reference model predictions are consistent with a history of water flooding and produced water disposal in those formations over decades of hydrocarbon production. While an advective component cannot be ruled out, this work demonstrates the importance of both diffusion and the basin architecture development in controlling 4He flux into and out of different lithologies. The assumption of negligible 4He loss from the top surface of a lithology is often made when determining the 4He age of its groundwater. In the Williston Basin, this study shows that deeper lithologies may reach steady state at different stages of basin development, with shallower lithologies sometimes also showing significant 4He loss from their top surface. In the Williston Basin, 4He diffusive loss from the target lithology must be considered to accurately interpret 4He groundwater residence times and accumulation potential.

High-resolution distribution of internal phosphorus release by the influence of harmful algal blooms (HABs) in Lake Taihu

The Mechanisms driving phosphorus (P) release in sediment of shallow lakes is essential for managing harmful algal blooms (HABs). Accordingly, this study conducted field monitoring of labile P, iron (Fe), sulfur (S), and dissolved manganese (Mn) in different biomass of algae in Lake Taihu. The in-situ technique of ZrO-Chelex-AgI (ZrO-CA) diffusive gradients in thin-films (DGT) and high-resolution dialysis sampler (high resolution-Peeper (HR-Peeper)) were used to measure labile P, Fe, S, and dissolved Mn, as well as their apparent diffusion fluxes at the sediment-water interface (SWI). In addition, the distribution of iron-reducing bacteria (IRB) and sulfate-reducing bacteria (SRB) in sediments was also detected. Results showed that high HABs biomass promoted the reduction of sulfate into labile S, however, IRB is the dominant species. Thus, labile Fe concentrations greatly exceeded labile S concentrations across all sites, indicating that microbial iron reduction (MIR) is the principal pathway for ferric iron reduction. Furthermore, the simple relationship analysis revealed the principal influence P migration and transformation is the Fe–P in high algal biomass sites, while Fe and Mn redox reactions did not significantly influence labile P mobilization in low algal areas.

Chandra Observations of the Planck Early Sunyaev–Zeldovich Sample: A Reexamination of Masses and Mass Proxies

Abstract Using Chandra observations, we derive the Y X proxy and associated total mass measurement, , for 147 clusters with z < 0.35 from the Planck early Sunyaev–Zeldovich catalog, and for 80 clusters with z < 0.22 from an X-ray flux-limited sample. We reextract the Planck Y SZ measurements and obtain the corresponding mass proxy, , from the full Planck mission maps, minimizing Malmquist bias due to observational scatter. The masses reextracted using the more precise X-ray position and characteristic size agree with the published PSZ2 values, but yield a significant reduction in the scatter (by a factor of two) in the – relation. The slope is 0.93 ± 0.03, and the median ratio, , is within the expectations from known X-ray calibration systematics. Y SZ/Y X is 0.88 ± 0.02, in good agreement with predictions from cluster structure, and implying a low level of clumpiness. In agreement with the findings of the Planck Collaboration, the slope of the Y SZ– flux relation is significantly less than unity (0.89 ± 0.01). Using extensive simulations, we show that this result is not due to selection effects, intrinsic scatter, or covariance between quantities. We demonstrate analytically that changing the Y SZ–Y X relation from apparent flux to intrinsic properties results in a best-fit slope that is closer to unity and increases the dispersion about the relation. The redistribution resulting from this transformation implies that the best-fit parameters of the – relation will be sample-dependent.

Identifying the Mechanisms behind the Positive Feedback Loop between Nitrogen Cycling and Algal Blooms in a Shallow Eutrophic Lake

Algal blooms have increased in frequency, intensity, and duration in response to nitrogen (N) cycling in freshwater ecosystems. We conducted a high-resolution sedimentary study of N transformation and its associated microbial activity in Lake Taihu to assess the accumulation rates of the different N fractions in response to algal blooms, aiming to understand the mechanisms of N cycling in lacustrine environments. Downcore nitrification and denitrification processes were measured simultaneously in situ via diffusive gradients in thin-films technique, peeper, and microelectrode devices in a region of intensified algal blooms of shallow lake. The decomposition of different biomasses of algal blooms did not change the main controlling factor on different N fractions in profundal sediment. However, the decomposition of different algal biomasses led to significant differences in the nitrification and denitrification processes at the sediment–water interface (SWI). Low algal biomasses facilitated the classic process of N cycling, with the balanced interaction between nitrification and denitrification. However, the extreme hypoxia under high algal biomasses significantly limited nitrification at the SWI, which in turn, restricted denitrification due to the lack of available substrates. Our high-resolution results combined with estimates of apparent diffusion fluxes of the different N fractions inferred that the lack of substrates for denitrification was the main factor influencing the positive feedback loop between N and eutrophication in freshwater ecosystems. Moreover, this positive feedback can become irreversible without technological intervention.

Influence of local convective heat flux on solidification, contraction and wall detachment behavior of molded chocolate during air cooling

The cooling process is an important step during chocolate production. It influences final product quality characteristics such as gloss, texture and melting behavior. Furthermore, it is a high energy consuming operation and its optimization leads to an increase in energy efficiency of the chocolate production. Dark chocolate was cooled in a pilot-scale cooling tunnel with cooling air temperatures of Tair = 2, 12 and 18 °C and air mean velocities of vin = 1.5, 3.5, and 6.0 m s−1. Convective heat transfer coefficients at the top and the bottom of the mold were received from model calculations applying a CFD model. Crystallization and detachment behavior from the mold walls were newly analyzed by measuring the damping characteristics of ultrasound waves transferring the filled molds during cooling. In addition, for this-like treated well-tempered dark chocolate, the crystallization and detachment behavior were analyzed in further detail. The convective heat transfer from the bottom of the mold increases in flow direction due to the existence of a typical mold geometry-dependent recirculating zone of the cooling air below the chocolate mold and also dependent on the local air velocity. It was shown that depending on intensity and homogeneity of the heat transfer in the air-cooling phase, the structure density of the chocolate can be increased which has a positive impact on resulting product quality characteristics. Moreover, the detachment of the chocolate from the mold wall was demonstrated to have an optimum for typical chocolate plate formats with 125 g weight at an apparent heat flux of 550 W/m2, for which the time until detachment reaches a minimum.

Searching for proto-planets with MUSE

Context. Protoplanetary disks contain structures such as gaps, rings, and spirals, which are thought to be produced by the interaction between the disk and embedded protoplanets. However, only a few planet candidates are found orbiting within protoplanetary disks, and most of them are being challenged as having been confused with disk features. Aims. The VLT/MUSE discovery of PDS 70 c demonstrated a powerful way of searching for still-forming protoplanets by targeting accretion signatures with medium-resolution integral field spectroscopy. We aim to discover more proto-planetary candidates with MUSE, with a secondary aim of improving the high-resolution spectral differential imaging (HRSDI) technique by analyzing the instrumental residuals of MUSE. Methods. We analyzed MUSE observations of five young stars with various apparent brightnesses and spectral types. We applied the HRSDI technique to perform high-contrast imaging. The detection limits were estimated using fake planet injections. Results. With a 30 min integration time, MUSE can reach 5σ detection limits in apparent Hα line flux down to 10−14 and 10−15 erg s−1 cm−2 at 0.075′′ and 0.25′′, respectively. In addition to PDS 70 b and c, we did not detect any clear accretion signatures in PDS 70, J1850-3147, and V1094 Sco down to 0.1′′. MUSE avoids the small sample statistics problem by measuring the noise characteristics in the spatial direction at multiple wavelengths. We detected two asymmetric atomic jets in HD 163296 with a very high spatial resolution (down to 8 au) and medium spectral resolution (R ~ 2500). Conclusions. The HRSDI technique when applied to MUSE data allows us to reach the photon noise limit at small separations (i.e., <0.5′′). With the combination of high-contrast imaging and medium spectral resolution, MUSE can achieve fainter detection limits in apparent line flux than SPHERE/ZIMPOL by a factor of ~5. MUSE has some instrumental issues that limit the contrast that appear in cases with strong point sources, which can be either a spatial point source due to high Strehl observations or a spectral point source due to a high line-to-continuum ratio. We modified the HRSDI technique to better handle the instrumental artifacts and improve the detection limits. To avoid the instrumental effects altogether, we suggest faint young stars with relatively low Hα line-to-continuum ratio to be the most suitable targets for MUSE to search for potential protoplanets.

Experimental studies on the charge transfer inefficiency of CCD developed for the soft X-ray imaging telescope Xtend aboard the XRISM satellite

We present experimental studies on the charge transfer inefficiency (CTI) of charge-coupled device (CCD) developed for the soft X-ray imaging telescope, Xtend, aboard the XRISM satellite. The CCD is equipped with a charge injection (CI) capability, in which sacrificial charge is periodically injected to fill the charge traps. By evaluating the re-emission of the trapped charge observed behind the CI rows, we find that there are at least three trap populations with different time constants. The traps with the shortest time constant, which is equivalent to a transfer time of approximately one pixel, are mainly responsible for the trailing charge of an X-ray event seen in the following pixel. A comparison of the trailing charge in two clocking modes reveals that the CTI depends not only on the transfer time but also on the area, namely the imaging or storage area. We construct a new CTI model by taking into account both transfer-time and area dependence. This model reproduces the data obtained in both clocking modes consistently. We also examine apparent flux dependence of the CTI observed without the CI technique. The higher incident X-ray flux is, the lower the CTI value becomes. It is due to a sacrificial charge effect by another X-ray photon. This effect is found to be negligible when the CI technique is used.

Magmatic Tempos in Large Hot Orogens in Comparison with Continental Margin Arcs

Geochronologic data combined with a geographic information system-based spatial analysis of plutons in the Bohemian Massif, Variscan belt, allow us to describe the apparent magma fluxes and episodic temporal pattern of plutonism, different from the cyclic pattern of continental margin arcs. The former is interpreted as reflecting a secular thermotectonic evolution of the orogen and magma sources changing from mantle-dominated to intracrustal, paralleled by increasing significance of crustal recycling at the expense of crustal growth. The analysis also suggests that crustal thickening, commonly regarded as the main cause of plutonism in collisional orogens, may be of relatively lower significance than late-stage mantle delamination.

Optical Study of PKS B1322-110, the Intra-hour Variable Radio Source

Abstract Observations with the Australia Telescope Compact Array revealed intrahour variations in the radio source PKS B1322-110. As part of an optical follow-up, we obtained Gemini Hα and Hα continuum (HαC) images of the PKS B1322-110 field. A robust 19σ detection of PKS B1322-110 in the Hα−HαC image prompted us to obtain the first optical spectrum of PKS B1322-110. With the Gemini spectrum we determine that PKS B1322-110 is a flat-spectrum radio quasar at a redshift of z = 3.007 ± 0.002. The apparent flux detected in the Hα filter is likely to originate from He ii emission redshifted precisely on the Galactic Hα narrowband filter. We set upper limits on the emission measure of the Galactic plasma, for various possible cloud geometries.

Distribution characteristics and release mechanisms of Pb in surface sediments in different aquatic environments

As a trace heavy metal, lead (Pb) has many anthropogenic applications but also produces many environmental pollution problems because of its high toxicity. In this study, we combined two in situ high-resolution sampling techniques – high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) – with the DGT-induced fluxes in sediment (DIFS) model to explore the mechanism of Pb release and resupply between sediments and pore water in the lower reaches and estuary of the Jiuxi River and the adjacent coast. An analysis of the chemical forms of Pb in the sediments showed that the content of the acid-extractable fraction (F1) was higher at the coastal site than at the other sampling sites, which indicates that Pb in the coastal sediments had greater activity and was more likely to cause Pb pollution. The apparent diffusion fluxes of Pb across the sediment-water interface (SWI) in the lower reaches, estuary and coastal zone are negative, and the absolute value of Pb flux in the estuary is several times higher than that in the other two stations, indicating a strong downward Pb diffusion trend, which may be due to water pollution caused by the nearby sewage outlet. As an insensitive element to redox, Pb did not exhibit an obvious correlation with Fe. In particular, the high Pb concentration and strong downward diffusion trend of the overlying water in the estuary caused the significant negative correlation between Pb and Fe. The calculated results of the DIFS model show that the reduced layer in the intertidal zone along the coast has the highest R value, the highest desorption rate (k−1) and the shortest response time (Tc), indicating that sediment particles in the coastal intertidal zone supply Pb to the pore water at the fastest rate; consequently, Pb pollution in the coastal zone is worthy of further attention.

Quantifying excess power from radio frequency interference in Epoch of Reionization measurements

ABSTRACT We quantify the effect of radio frequency interference (RFI) on measurements of the 21-cm power spectrum during the Epoch of Reionization (EoR). Specifically, we investigate how the frequency structure of RFI source emission generates contamination in higher order wave modes, which is much more problematic than smooth-spectrum foreground sources. Using a relatively optimistic EoR model, we find that even a single relatively dim RFI source can overwhelm the EoR power spectrum signal of $\sim 10\, {\rm mK}^2$ for modes $0.1 \ \lt k \lt 2 \, h\, {\rm Mpc}^{-1}$. If the total apparent RFI flux density in the final power spectrum integration is kept below 1 mJy, an EoR signal resembling this optimistic model should be detectable for modes $k \lt 0.9\, h\, {\rm Mpc}^{-1}$, given no other systematic contaminants and an error tolerance as high as 10 per cent. More pessimistic models will be more restrictive. These results emphasize the need for highly effective RFI mitigation strategies for telescopes used to search for the EoR.

High-resolution imaging of labile P & S in coastal sediment: Insight into the kinetics of P mobilization associated with sulfate reduction

The internal P cycling in coastal sediments during early diagenesis is of great importance to aquatic ecosystems, but its relationship with sulfate reduction is still unclear and lacks visualized evidence. In this study, diffusive gradients in thin films (Zr-oxide DGT and AgI DGT) techniques at a two-dimensional (2D) submillimeter resolution were utilized to synchronously characterize the in situ labile P and dissolved sulfide in coastal sediments around Xiamen Bay, China. The distributions of dissolved sulfide formed from sulfate reduction showed large vertical and horizontal variations, which are mainly controlled by the reactive organic carbon (OC) and redox conditions at different sampling sites. Multiple correlation analysis revealed that significant and linear correlations exist between dissolved sulfide and DGT-labile P, demonstrating that P mobilization is predominantly regulated by sulfide-dependent reductive dissolution of Fe(III)-bound P and sulfate reduction-associated OC mineralization. Both labile P and dissolved sulfide showed lower values at intertidal sites, due to oxic/suboxic conditions favoring weak sulfate reduction and strong P sequestration. Labile P accumulation during flood tides and removal during ebb tides on tidal timescales indicate that the mobilization and detention of P in surface sediment are regulated by tidal cycles and consequential S and Fe redox cycling. The apparent diffusion flux of P implies that the internal P loading can act as a P source to aquatic ecosystems.