Assessing bottom water anoxia within the Late Devonian Woodford Shale in the Arkoma Basin,southern Oklahoma

Comparing the concentration of molybdenum (Mo) (ppm) and total organic carbon (TOC) (wt%) within sediments allows interpretation of the relative degrees of bottom water restriction within the geologic record. The Woodford Shale is interpreted as transgressive systems tract (TST) grading into highstand systems tract (HST). The lowermost Woodford preserves a Mo-TOC signal that is consistent with a restricted basin that periodically received influxes of water consistent with rising sea levels flowing into restricted sub-basins that became isolated by localized conditions. The middle Woodford preserves a signal that indicates an increased ventilation at the sediment-water interface persisting until the maximum flooding surface. The presence of phosphate nodules in the uppermost Woodford suggests sufficient oxygen to retain the Mo in solution and indicates active upwelling and circulation with the Paleotethys.It is also possible to document changing ventilation patterns, non-destructively, within a basin by utilizing changing trends in redox-sensitive trace metals (Mo, Ni, and Cu) and an approximation of the degree of pyritization (aDOP) based on an idealized formula for pyrite (FeS₂). This chemofacies approach produces a qualitatively similar interpretation to the changing Mo-TOC signal and can evaluate lateral trends in bottom water ventilation where destructive sampling is not permitted. Distal regions preserve the greatest degree of bottom water ventilation. Proximal regions preserve highly variable conditions with more restricted conditions being common in the lowermost Woodford Shale and ventilation improving upsection.Interpreting changing levels of bottom water anoxia enable greater degrees of precision in targeting potential hydrocarbon resources. Furthermore, this information improves our understanding of the changing environmental conditions of the Woodford Shale. The Framvaren Fjord is a reasonable modern analog for bottom water restriction in the lowermost portion of the Woodford Shale. The Cariaco Basin is a good modern analog for bottom water restriction in the middle and uppermost Woodford Shale.     

Ventilation of the North Pacific subtropical pycnocline and mode water formation

The annual subduction rate of the North Pacific was calculated based on isopycnally averaged hydrographic climatology (HydroBase), high-resolution winter mixed-layer climatology (NWMLC), and various wind stress climatologies from ship reports, numerical weather prediction products, and satellite products. The calculation was performed using Lagrangian coordinates in the same manner as in previous works, except a less smoothed oceanic climatology (HydroBase and NWMLC) was used instead of a World Ocean Atlas. Differences in the wind stress climatologies have very little effect on subduction rate estimates. The subduction rate census for density classes showed peaks corresponding to subtropical mode water (STMW), central mode water (CMW), and eastern subtropical mode water (ESTMW). The deeper mixed layer and the associated sharper mixed-layer fronts in the present climatology resulted in a larger lateral induction, which boosted the subduction rate, especially for the potential density anomaly (σ_θ) range of the lighter STMW (25.0 < σ_θ < 25.2 kg m⁻³) and lighter CMW (26.0 < σ_θ < 26.2 kg m⁻³), compared to previous estimates. The renewal time of permanent pycnocline water was estimated as the volume of water divided by the subduction rate for each σ_θ class: 2–4 years for ESTMW (24.5 < σ_θ < 25.2 kg m⁻³), 2 years for the lighter STMW (25.0 < σ_θ < 25.3 kg m⁻³), 5–9 years for the denser STMW (25.3 < σ_θ < 25.6 kg m⁻³), 10–20 years for the lighter CMW (26.0 < σ_θ < 26.2 kg m⁻³), 20–30 years for the middle CMW (26.2 < σ_θ < 26.3 kg m⁻³), and 60 years or longer for the denser CMW (26.3 < σ_θ < 26.6 kg m⁻³). A comparison of the water volume and subduction rate in potential temperature–salinity (θ–S) space indicated that the upper permanent pycnocline water (25.0 < σ_θ < 26.2 kg m⁻³) was directly maintained by nondiffusive subduction of winter surface water, including STMW and lighter CMW. The lower permanent pycnocline water (26.2 < σ_θ < 26.6 kg m⁻³) may be maintained through the subduction of fresher and colder water from the subarctic–subtropical transition region and subsequent mixing with saltier and warmer water. Diagnosis of the potential vorticity (PV) of the subducted water demonstrated that the low PV of STMW was mainly due to the large subduction rate, whereas that of both ESTMW and CMW was due mainly to the small density advection rate (cross-isopycnal flow). Additionally, a relatively large subduction rate probably contributes to the low PV of part of the lighter CMW (ESTMW) formed in the region around 38°N and 170°W (28°N and 145°W), which is characterized by a relatively thick winter mixed layer and an associated mixed-layer front, causing a large lateral induction rate.     

On Shear-Driven Ventilation of Snow

A series of experiments have been made in a wind tunnel to investigate the ventilation of snow by shear. We argue that the zero-plane displacement can be used as a convenient indicator of ventilation, and that this can be obtained from measurements of mean velocity profiles in conditions of zero pressure gradient. Measurements made over a natural snow surface show a zero-plane displacement depth of less than 5 mm, but practical considerations preclude extensive use of snow for these measurements. Instead, the influence of permeability is investigated using reticulated foams in place of snow. We demonstrate that the foam and snow have similar structure and flow-relevant properties. Although the surface of the foam is flat, the roughness lengths increase by two orders of magnitude as the permeability increases from 6 × 10⁻⁹ to 160 × 10⁻⁹ m². The zero-plane displacement for the least permeable foams is effectively zero, but more than 15 mm for the most permeable foams. Our data compare well to the few studies available in the literature. By analogy to conditions over snow surfaces, we suggest that shear-driven ventilation of snow is therefore limited to the upper few millimetres of snow surfaces.     

Decadal and multi-decadal variability of Labrador Sea Water in the north-western North Atlantic Ocean derived from tracer distributions: Heat budget, ventilation, and advection

Time series of profiles of potential temperature, salinity, dissolved oxygen, and planetary potential vorticity at intermediate depths in the Labrador Sea, the Irminger Sea, and the Iceland Basin have been constructed by combining the hydrographic sections crossing the sub-arctic gyre of the North Atlantic Ocean from the coast of Labrador to Europe, occupied nearly annually since 1990, and historic hydrographic data from the preceding years since 1950. The temperature data of the last 60 years mainly reflect a multi-decadal variability, with a characteristic time scale of about 50 years. With the use of a highly simplified heat budget model it was shown that this long-term temperature variability in the Labrador Sea mainly reflects the long-term variation of the net heat flux to the atmosphere. However, the analysis of the data on dissolved oxygen and planetary potential vorticity show that convective ventilation events, during which successive classes of Labrador Sea Water (LSW) are formed, occurring on decadal or shorter time scales. These convective ventilation events have performed the role of vertical mixing in the heat budget model, homogenising the properties of the intermediate layers (e.g. temperature) for significant periods of time. Both the long-term and the near-decadal temperature signals at a pressure of 1500 dbar are connected with successive deep LSW classes, emphasising the leading role of Labrador Sea convection in running the variability of the intermediate depth layers of the North Atlantic. These signals are advected to the neighbouring Irminger Sea and Iceland Basin. Advection time scales, estimated from the 60 year time series, are slightly shorter or of the same order as most earlier estimates, which were mainly based on the feature tracking of the spreading of the LSW₉₄ class formed in the period 1989-1994 in the Labrador Sea.     

青藏铁路通风路堤室内模型试验研究

正在建设中的青藏铁路即将穿越 5 5 0km的多年冻土区 ,冻土问题是青藏铁路面临的首要工程问题。出于铁路建设中保护冻土的原则 ,对通风路堤这一新的、主动保护冻土的路堤结构形式进行了几何相似比为 1∶4的大型室内试验 ,试验所得的路堤土体温度场分布及土体温度的变化结果表明 ,通风路堤能够有效地降低路堤土体的温度 ,从而达到保护天然地基冻土的目的。但是 ,温度场的分布在通风路堤内并不对称 ,及沿路堤中轴线的两侧左右不对称 ,这样可能会影响到下伏冻土温度的差异 ,从而引起不均匀冻胀、沉降变形。另一方面 ,暖季较高的气温条件下 ,通风管两端的进出口需要堵塞或关闭 ,以免造成土体吸热量较多而引起较大的沉降 ,但由于青藏高原很短的融化期 ,这一影响还有待现场试验工程的验证。     

2013—2017年天津市大气自净能力与大气颗粒物质量浓度特征分析

基于经验公式分析了天津市2013-2017年大气自净能力,以及PM_2.5和PM₁₀质量浓度的时空分布特征,并探讨了大气自净能力与大气颗粒物PM_2.5质量浓度的关系,以期更好的理解大气环境对污染物浓度变化的影响。结果表明：时间变化上,天津市大气自净能力在午后13-14时最大,夜间最低,一年之中在采暖季（10月至翌年3月）要小于非采暖季,与之相反,天津市PM_2.5和PM₁₀质量浓度在采暖季均高于非采暖季。2017年相对于2013年,大气自净能力增加了5%,而PM_2.5质量浓度下降了34%,PM₁₀质量浓度则减少了47%。空间分布上,大气自净能力各季节均表现为沿海高于内陆,城区低于郊区的分布,天津市的PM_2.5和PM₁₀质量浓度的高值也主要集中在中南部地区,尤其是城区。大气自净能力与颗粒物浓度的分布在空间分布上有着一定的对应关系。分析表明,天津市大气自净能力日均值与PM_2.5质量浓度日均值呈负相关,两者的相关系数为-0.34,在采暖季,相关系数有所提高。通过大气自净能力与PM_2.5质量浓度变化的分析可知,重污染事件大多数发生在低大气自净能力时。     

Numerical investigation of airborne transmission of respiratory infections on the subway platform

Underground subway platforms are among the world’s busiest public transportation systems, but the airborne transmission mechanism of respiratory infections on these platforms has been rarely studied. Here, computational fluid dynamics (CFD) modeling is used to investigate the airflow patterns and infection risks in an island platform under two common ventilation modes: Mode 1- both sides have air inlets and outlets; Mode 2- air inlets are present at the two sides and outlets are present in the middle. Under the investigated scenario, airflow structure is characterized by the ventilation jet and human thermal plumes. Their interaction with the infector’s breathing jet imposes the front passenger under the highest exposure risk by short-range airborne route, with intake fractions up to 2.57% (oral breathing) or 0.63% (nasal breathing) under Mode 1; oral breathing of the infector may impose higher risks for the front passenger compared with nasal breathing. Pathogen are efficiently diluted as they travel further, in particular to adjacent crowds. The maximum and median value of intake fractions of passengers in adjacent crowds are respectively 0.093% and 0.016% (oral breathing), and 0.073% and 0.014% (nasal breathing) under Mode 1. Compared with Mode 1, the 2nd mode minimizes the interaction of ventilation jet and breathing jet, where the maximum intake fraction is only 0.34%, and the median value in the same crowd and other crowds are reduced by 23–63%. Combining published quanta generation rate data of COVID-19 and influenza infectors, the predicted maximum and median infection risks for passengers in the same crowds are respectively 1.46%–40.23% and 0.038%–1.67% during the 3–10 min waiting period, which are more sensitive to ventilation rate and exposure time compared with return air. This study can provide practical guidance for the prevention of respiratory infections in subway platforms.     

A study of ventilation transients associated with a controlled district recirculation circuit

Summary This paper discusses the development of a mathematical model to describe the unsteady airflow created and the subsequent effect on both the production and transportation of methane around the recirculation zone. Examples of the response of a single face recirculation system to various disturbances are presented and discussed.     

Experimental determination of ventilation coefficient for 1-hexanol drops in air

Two experimental techniques have been used for study of mass transfer from a drop of 1-hexanol evaporating into air. In the first technique, liquid is added to the drop by a supporting capillary. When the rate of liquid adding counterbalances the evaporation rate, the drop size remains constant and the evaporation takes place at steady state. In the second case with drop suspended from a thermocouple, the rate of evaporation is determined from variation of drop diameter with time. Since the combination of both methods should allow to measure at the broader range of experimental conditions, the differences and their impact on experimental determination of mass transfer are discussed. The results are compared with results of previous experimental and theoretical works reported in the literature.     

Erosion control for mudstone soil with ventilation and watertight resin

To accelerate the re-vegetation of exposed landslide areas, hydroseeding for soil and water conservation has been widely applied as one of the economically feasible ways. However, effect durations of different hydroseeding materials are different, the formulation density has a certain effect on plant growth and the addictives may exude. This paper presents laboratory experiments of soil erosion, exuding water quality and soil hardness by using a rainfall simulator with different conditions of slope, rainfall intensity and medication density. The results showed that soil erosion decreased significantly, suggesting a good erosion-resisting effect by the ventilation and watertight resin. No significant variation of the exuded water was observed during testing, which indicates that after gelling, the ventilation and watertight resin are unlikely to release chemical substances. It was found that high resin density will result in poor workability as well as high costs; adverse will cause the mudstone to fracture due to raindrops since cracks are common to soil surface. The weatherability after spraying and its effect on plant vegetation still need further investigation.