Effects of magnesium ions on near-equilibrium calcite dissolution: Step kinetics and morphology

Dissolution kinetics at the aqueous solution-calcite interface at 50 °C were investigated using in situ atomic force microscopy (AFM) to reveal the influence of magnesium concentration and solution saturation state on calcite dissolution kinetics and surface morphology. Under near-equilibrium conditions, dissolved Mg²⁺ displayed negligible inhibitory effects on calcite dissolution even at concentrations of . Upon the introduction of , the solution saturation state with respect to calcite, , acted as a “switch” for magnesium inhibition whereby no significant changes in step kinetics were observed at Ω_calcite<0.2, whereas a sudden inhibition from Mg²⁺ was activated at Ω_calcite?0.2. The presence of the Ω-switch in dissolution kinetics indicates the presence of critical undersaturation in accordance with thermodynamic principles. The etch pits formed in solutions with exhibited a unique distorted rhombic profile, different from those formed in Mg-free solutions and in de-ionized water. Such unique etch pit morphology may be associated with the anisotropy in net detachment rates of counter-propagating kink sites upon the addition of Mg²⁺.     

Sources of plutonium to the tropical Northwest Pacific Ocean (1943-1999) identified using a natural coral archive

The Pu isotopes, ²³⁹Pu and ²⁴⁰Pu, were determined in annually-banded skeletons of an accurately dated (1943-1999) modern coral (Porites lobata) from Guam Island to identify historical Pu sources to the tropical Northwest Pacific Ocean. Activity concentrations of ^239+240Pu and ²⁴⁰Pu/²³⁹Pu atom ratios were determined in the dated coral bands using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Close-in fallout from the former US Pacific Proving Grounds (PPG) in the Marshall Islands and global fallout were identified as the two main sources. The Guam site was dominated by PPG close-in fallout in the 1950s, with an average ²⁴⁰Pu/²³⁹Pu atom ratio of 0.315 ± 0.005. In addition, a higher ²⁴⁰Pu/²³⁹Pu atom ratio (0.456 ± 0.020) was observed that could be attributed to fallout from the “Ivy Mike” thermonuclear detonation in 1952. The atom ratio decreased in the 1960s and 1970s due to increase in the global fallout with a low ²⁴⁰Pu/²³⁹Pu atom ratio (∼0.18). Recent coral bands (1981-1999) are dominated by the transport of remobilised Pu, with high ²⁴⁰Pu/²³⁹Pu atom ratios, from the Marshall Islands to Guam Island along the North Equatorial Current (NEC). This remobilised Pu was estimated to comprise 69% of the total Pu in the recent coral bands, although its contribution was variable over time.     

Numerical simulation of vertical ground heat exchangers: Intermittent operation in unsaturated soil conditions

The effect of varying the thermal properties of inhomogeneous unsaturated soil on the intermittent operation of a vertical ground heat exchanger (GHE) was simulated by a conjugate heat transfer simulation using a transient conductive heat transfer model. A three-phase soil model was used to introduce soil properties that vary with depth. The performance during the first few hours was significantly different from that of an analytical infinite line source model that assumes steady-state borehole conditions, although relatively good agreement was obtained thereafter. Unsaturated soil conditions afforded a 40% lower mean heat exchange rate than saturated conditions. This demonstrates the importance of considering unsaturated conditions in the design and performance evaluation of GHEs.     

Biochar application in a tropical,agricultural region: A plot scale study in Tamil Nadu,India

A plot-scale evaluation of biochar application to agricultural soils was conducted in Tirunelveli, Tamil Nadu, India, to investigate the potential of biochar to improve soil fertility and moisture content. Biochar feedstocks need to be sustainably sourced: several locally available feedstocks (rice husk, cassia stems, palm leaves and sawdust) were analysed as proposed soil amendments so that no single biomass material is depleted to maintain biochar addition. The biochars from different biomass feedstock contained >20% C and were high in macro- and micronutrients. The results suggest that an application rate of 6.6 metric tonnes ha^?1 cassia biochar was enough to initiate C-accumulation, which is reflected in an increase in OM and a net reduction in soil bulk density.     

SWDC数字航摄仪在线路工程测量中的应用研究

SWDC数字航摄仪的研制成功,改变了我国航空摄影测量一直采用传统胶片摄影仪的局面。介绍SWDC数字航摄仪系统,并对其在线路工程测量中的应用作了试验。结果表明在大比例尺图的线路工程生产中,基于SWDC数字航摄仪的GPS辅助空中三角测量方法有很大优势,能够满足我国现行航空摄影测量规范对航测生产的精度要求。     

沉积环境有机质及在铀成矿中的作用研究

通过系统研究,将沉积环境有机质分为可确定或未确定的高相对分子质量有机物质、简单物质和腐殖质3个主要部分,一般称为非腐殖质和腐殖质2个部分.非腐殖质系指那些可被列入单独的化合物类别中的有机化合物,主要包括糖、脂类和氨基酸;腐殖质系指那些很难确定的不能再分成其他化合物的有机化合物,据其溶解性质和颜色特征,腐殖质分为黄腐酸、...     

Revisiting the Climatology of Atmospheric Blocking in the Northern Hemisphere

In addition to the occurrence of atmospheric blocking,the climatology of the characteristics of blocking events,including duration,intensity,and extension,in four seasons over the Northern Hemisphere was analyzed for the period 1950-2009.The seasonality and spatial variations of these characteristics were studied according to their longitudinal distributions.In general,there were sharp discrepancies in the blocking characteristics between winter and summer,and these differences were more prominent over the Atlantic and Pacific Oceans.The blocking not only occurred more frequently but also underwent stronger amplification in winter;likewise,the blocking occurred less frequently and underwent weaker amplification in summer.There are very strong interrelationships among different blocking characteristics,suggesting that they are supported by similar physical factors.In addition,the relationship between blocking over different regions and East Asian circulation was examined.Ural-Siberia is a major blocking formation region in all seasons that may exert a downstream impact on East Asia.The impact is generally weak in summer,which is due to its lower intensity and smaller duration.However,the extratropical circulation over East Asia in summer can be disturbed persistently by the frequent occurrence of blocking over the Asian continent or the Western Pacific.In particular,the blocking frequency over the Western Pacific significantly increased during the study period.This climatological information provides a background for studying the impact of blocking on East Asian circulation under both present and future climate conditions.     

Ocean mixed layer processes in the Pacific Decadal Oscillation in coupled general circulation models

It is investigated how the Pacific Decadal Oscillation (PDO) is simulated differently among various coupled general circulation models (CGCMs), and how it is related to the heat budget of the simulated ocean mixed layer, which includes the surface heat flux and ocean heat transport. For this purpose the dataset of the climate of the 20th Century experiment (20C3M) from nine CGCMs reported to IPCC’s AR4 are used, while the MRI and MIROC models are examined in detail. Detailed analyses of these two CGCMs reveal that the PDO is mainly affected by ocean heat transport rather than surface heat flux, in particular in the MRI model which has a larger contribution of ocean heat transport to the heat budget. It is found that the ocean heat transport due to Ekman advection versus geostrophic advection contributes differently to the PDO in the western and central North Pacific. Specifically, the strength of PDO tends to be larger for CGCMs with a larger ocean heat transport in the region.     

Investigating factors in indoor transmission of respiratory disease through agent-based modeling

The transmission of respiratory diseases such as COVID-19 is exacerbated in densely populated urban areas and crowded indoor settings. Despite the majority of transmissions occurring in such settings, controlling viral spread through individual-level contacts indoors remains challenging. Experimental studies have investigated the transmission patterns of respiratory behaviors such as coughing or sneezing in controlled spatial environments. However, the effects of dynamic movement and spatial structures have been ignored, making it difficult to apply findings to urban policy and planning. To address this gap, we developed agent-based simulations to investigate individual virus inhalation patterns across multiple scenarios in a symmetrical and formulaic indoor space. We conducted sensitivity analysis using regression emulator models to identify significant factors for viral transmission. Our results indicate positive associations with viral transmission in descending order of: (1) stay time; (2) encounter frequency; and (3) initial infected population; while negative associations are: (4) mask wearing; (5) distance to infected people; (6) nearest infected people's mask wearing; and (7) distance to entrance. We also found that narrow passages between obstacles increase virus transmission from breathing. Furthermore, we conducted a case study to investigate the potential of reducing the amount of individually inhaled virus by controlling behaviors and spatial environments. Our findings suggest that mask wearing and reduced stay time can substantially reduce transmission risk, while a large number of contacts and high grouping time result in the growth of the infected population at a certain threshold. These results provide guidance for decision makers to formulate guidelines for curbing the spread of respiratory diseases in indoor spaces.     

升降轨PSInSAR地面沉降监测结果的互检验与时序融合

升降轨PSInSAR时序分析获得的同一地区2组监测结果分别为升轨和降轨下的地表形变速率与累积变形量。针对研究区地面以下沉为主,水平方向变形极为微小的特点,将视线向(line of sight,LOS)变形转换为垂向的下沉值,以此进行升降轨模式下2组观测值的比较与精度检验。在此基础上,将相干目标的2组观测序列数据融合以实现加密观测。研究结果表明:升降轨模式下沉降速率观测值的互检验精度优于2 mm;2组观测序列数据的融合结果进一步揭示了相干目标在时域上的非线性沉降特征。