Triple oxygen isotope systematics of evaporation and mixing processes in a dynamic desert lake system

Triple oxygen isotope measurements are a novel and promising tool in geochemical and hydrological research. This study investigates the combined hydrogen-deuterium and triple oxygen isotope hydrology at the Salar del Huasco, a highly dynamic salt lake system located on the Altiplano Plateau, N-Chile. The region has a semiarid climate that shows strong seasonal and diurnal variability in relative humidity, temperature, and wind conditions. The Salar del Huasco receives inflow from multiple surface sources and groundwater. Episodic flooding after rare rainfall events imposes seasonal fluctuations of the groundwater table and, thus, the lake level. Applying the Craig and Gordon (C-G) evaporation model for triple oxygen isotope data measured along series of increasingly evaporated lakes and ponds within the salar demonstrates the capability to resolve the individual fundamental hydrologic processes of recharge evaporation, simple (pan) evaporation, and transient mixing with surface and subsurface floodwater. Regarding the stream and spring sources, mixing of different generations of recharge is clearly distinguishable from pre-evaporation of a single recharge event. These processes are not resolvable by δ2H and δ18O measurements alone. We also show that accurate monitoring of the isotopic composition of ambient water vapour and an estimate of the wind turbulence coefficient in the C-G model are critical aspects required to quantify the hydrologic balance. The wind turbulence coefficient, here 0.54, may be determined accurately from on-site evaporation experiments by fitting evaporation trajectories to the d-excess, δ18O and residual fraction data.

Experimental Study on the Viscoelastic Flow Mixing in Microfluidics

Background: The study of blood flow in vessels is always crucial to understand cardiovascular diseasessuch as arrhythmias, coronary artery disease and deep vein thrombosis. A viscoelastic fluid in a microchannelis modeled for the blood flow study.Methods: In this paper, we modeled the blood flow through a viscoelastic fluid in a microfluidic channel.The flow properties, especially the flow pattern and transient mixing of two fluid streams in a T-shapedmicrochannel, are experimentally studied.Results: It was found that the viscoelastic fluid has a transiently unstable flow pattern compared to thenormal Newtonian fluid, and the mixing is also increased due to its elastic property. Similar to the pulsatileblood flow, the fluid is driven under a periodically pulsed stimulus, and the flow pattern and transient mixingare compared at different flow rates and driving period conditions.Conclusions: The integration of microfluidic technology with the blood flow research could provide a newapproach to understand the related disease mechanism, which can also be used to analyze the drug mixingand delivery in the blood flow.

Direct Numerical Simulation of a Warm Cloud Top Model Interface: Impact of the Transient Mixing on Different Droplet Population

Turbulent mixing through atmospheric cloud and clear air interface plays an important role in the life of a cloud. Entrainment and detrainment of clear air and cloudy volume result in mixing across the interface, which broadens the cloud droplet spectrum. In this study, we simulate the transient evolution of a turbulent cloud top interface with three initial mono-disperse cloud droplet population, using a pseudo-spectral Direct Numerical Simulation (DNS) along with Lagrangian droplet equations, including collision and coalescence. Transient evolution of in-cloud turbulent kinetic energy (TKE), density of water vapour and temperature is carried out as an initial value problem exhibiting transient decay. Mixing in between the clear air and cloudy volume produced turbulent fluctuations in the density of water vapour and temperature, resulting in supersaturation fluctuations. Small scale turbulence, local supersaturation conditions and gravitational forces have different weights on the droplet population depending on their sizes. Larger droplet populations, with initial 25 and 18 μ m radii, show significant growth by droplet-droplet collision and a higher rate of gravitational sedimentation. However, the smaller droplets, with an initial 6 μ m radius, did not show any collision but a large size distribution broadening due to differential condensation/evaporation induced by the mixing, without being influenced by gravity significantly.

Dynein pulling forces on ruptured nuclei counteract lamin-mediated nuclear envelope repair mechanisms in vivo

Recent work done exclusively in tissue culture cells revealed that the nuclear envelope (NE) undergoes ruptures leading to transient mixing of nuclear and cytoplasmic components. The duration of transient NE ruptures depends on lamins, however the underlying mechanisms and the relevance to in vivo events is not known. Here, we use C. elegans embryos to show that dynein forces that position nuclei increase the severity of lamin-induced NE ruptures in vivo. In the absence of dynein forces, lamin prevents nuclear-cytoplasmic mixing caused by NE ruptures. By monitoring the dynamics of NE rupture events, we demonstrate that lamin is required for a distinct phase in NE recovery that restricts nucleocytoplasmic mixing prior to the full restoration of NE rupture sites. We show that laser-induced puncture of the NE recapitulates phenotypes associated with NE recovery in wild type cells. Surprisingly, we find that embryonic lethality does not correlate with the incidence of NE rupture events suggesting that embryos survive transient losses of NE compartmentalization during early embryogenesis. In addition to presenting the first mechanistic analysis of transient NE ruptures in vivo, this work demonstrates that lamin controls the duration of NE ruptures by opposing dynein forces on ruptured nuclei to allow reestablishment of the NE permeability barrier and subsequent restoration of NE rupture sites.

Response of water vapour D-excess to land–atmosphere interactions in a semi-arid environment

The stable isotopic composition of water vapour provides information about moisture sources and processes difficult to obtain with traditional measurement techniques. Recently, it has been proposed that the D-excess of water vapour (dv = δ2H − 8 × δ18O) can provide a diagnostic tracer of continental moisture recycling. However, D-excess exhibits a diurnal cycle that has been observed across a variety of ecosystems and may be influenced by a range of processes beyond regional-scale moisture recycling, including local evaporation (ET) fluxes. There is a lack of measurements of D-excess in evaporation (ET) fluxes, which has made it difficult to assess how ET fluxes modify the D-excess in water vapour (dv). With this in mind, we employed a chamber-based approach to directly measure D-excess in ET (dET) fluxes. We show that ET fluxes imposed a negative forcing on the ambient vapour and could not explain the higher daytime dv values. The low dET observed here was sourced from a soil water pool that had undergone an extended drying period, leading to low D-excess in the soil moisture pool. A strong correlation between daytime dv and locally measured relative humidity was consistent with an oceanic moisture source, suggesting that remote hydrological processes were the major contributor to daytime dv variability. During the early evening, ET fluxes into a shallow nocturnal inversion layer caused a lowering of dv values near the surface. In addition, transient mixing of vapour with a higher D-excess from above the nocturnal inversion modified these values, causing large variability during the night. These results indicate d

Advection and buoyancy-induced turbulent mixing in a narrow vertical tank

We describe new experiments to examine the buoyancy-induced turbulent mixing which results from the injection of a small constant volume flux of dense fluid at the top of a long narrow vertical tank with square cross-section, in which a steady laminar upward flow of less dense fluid is present. To conserve volume of fluid in the tank, fluid leaves the tank through two small openings near the top of the tank. Dense source fluid vigorously mixes with the less dense fluid of the upward flow, such that a dense mixing region of turbulent fluid propagates downwards during the transient mixing phase of the experiment. Eventually, the transport of dense fluid associated with the buoyancy-induced turbulent flow is balanced by the transport of less-dense fluid associated with the steady upward flow, such that the mixing region evolves into a layer of finite extent which stays approximately constant in height during a statistically steady mixing phase of the experiment. With an ideal source of downward constant buoyancy flux ${B}_{s} $ at the top of the tank, tank width $d$, and speed of the upward flow ${u}_{u} $, we perform experiments with Froude numbers $\mathit{Fr}= {u}_{u} {d}^{1/ 3} / { B}_{s}^{1/ 3} $ ranging between $O(0. 01)$ and $O(1)$. The steady-state height of the mixing region and the maximum reduced gravity as found near the source of buoyancy flux at the top of the tank increase with decreasing Froude number. For the experiments with intermediate values of the Froude number, we find that the steady-state mixing region is small enough to be contained in the experimental tank, but large enough not to be dominated by developing turbulence near the source of buoyancy flux. For these experiments, we show that the key buoyancy-induced turbulent mixing properties are not significantly affected by the upward flow. We use a dye-attenuation technique to obtain vertical profiles of the time- and horizontally averaged reduced gravity to show a good agreement between the experimental profiles and the solution of a nonlinear turbulent advection–diffusion equation during the steady mixing phase. Furthermore, we discuss the characteristic time scale of the transient mixing phase. We compare our experimental results with the numerical solution of a time-dependent nonlinear turbulent advection–diffusion equation during the transient mixing phase. We also describe three reduced models for the evolution of the reduced gravity distribution in the mixing region, and we demonstrate these models’ usefulness by comparison with our experimental results and the numerical solution of the time-dependent nonlinear turbulent advection–diffusion equation.