26 research outputs found
An early Little Ice Age brackish water invasion along the south coast of the Caspian Sea (sediment of Langarud wetland) and its wider impacts on environment and people
Caspian Sea level has undergone significant changes through time with major impacts not only on the surrounding coasts, but also offshore. This study reports a brackish water invasion on the southern coast of the Caspian Sea constructed from a multi-proxy analysis of sediment retrieved from the Langarud wetland. The ground surface level of wetland is >6 m higher than the current Caspian Sea level (at -27.41 m in 2014) and located >11 km far from the coast. A sequence covering the last millennium was dated by three radiocarbon dates. The results from this new study suggest that Caspian Sea level rose up to at least -21.44 m (i.e. >6 m above the present water level) during the early Little Ice Age. Although previous studies in the southern coast of the Caspian Sea have detected a high-stand during the Little Ice Age period, this study presents the first evidence that this high-stand reached so far inland and at such a high altitude. Moreover, it confirms one of the very few earlier estimates of a high-stand at -21 m for the second half of the 14th century. The effects of this large-scale brackish water invasion on soil properties would have caused severe disruption to regional agriculture, thereby destabilizing local dynasties and facilitating a rapid Turko-Mongol expansion of Tamerlane’s armies from the east.N Ghasemi (INIOAS), V Jahani (Gilan Province Cultural Heritage and Tourism Organisation) and A Naqinezhad (University of Mazandaran), INQUA QuickLakeH project (no. 1227) and to the European project Marie Curie, CLIMSEAS-PIRSES-GA-2009-24751
Droplets Formation and Merging in Two-Phase Flow Microfluidics
Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed
Minimum-Variance Portfolios Based on CovarianceMatrices Using Implied Volatilities: Evidence
Direct Visualization of Evaporation in a Two-Dimensional Nanoporous Model for Unconventional Natural Gas
Evaporation
at the nanoscale is critical to many natural and synthetic
systems including rapidly emerging unconventional oil and gas production
from nanoporous shale reservoirs. During extraction processes, hydrocarbons
confined to nanoscopic pores (ranging from one to a few hundred nanometers
in size) can undergo phase change as pressure is reduced. Here, we
directly observe evaporation in two-dimensional (2D) nanoporous media
at the sub-10 nm scale. Using an experimental procedure that mimics
pressure drawdown during shale oil/gas production, our results show
that evaporation takes place at pressures significantly lower than
predictions from the Kelvin equation (maximum deviation of 11%). We
probe evaporation dynamics as a function of superheat and find that
vapor transport resistance dominates evaporation rate. The transport
resistance is made up of both Knudsen and viscous flow effects, with
the magnitude of the Knudsen effect being approximately twice that
of the viscous effects here. We also observe a phenomenon in sub-10
nm confinement wherein lower initial liquid saturation pressures trigger
discontinuous evaporation, resulting in faster evaporation rates
Direct Visualization of Evaporation in a Two-Dimensional Nanoporous Model for Unconventional Natural Gas
Evaporation
at the nanoscale is critical to many natural and synthetic
systems including rapidly emerging unconventional oil and gas production
from nanoporous shale reservoirs. During extraction processes, hydrocarbons
confined to nanoscopic pores (ranging from one to a few hundred nanometers
in size) can undergo phase change as pressure is reduced. Here, we
directly observe evaporation in two-dimensional (2D) nanoporous media
at the sub-10 nm scale. Using an experimental procedure that mimics
pressure drawdown during shale oil/gas production, our results show
that evaporation takes place at pressures significantly lower than
predictions from the Kelvin equation (maximum deviation of 11%). We
probe evaporation dynamics as a function of superheat and find that
vapor transport resistance dominates evaporation rate. The transport
resistance is made up of both Knudsen and viscous flow effects, with
the magnitude of the Knudsen effect being approximately twice that
of the viscous effects here. We also observe a phenomenon in sub-10
nm confinement wherein lower initial liquid saturation pressures trigger
discontinuous evaporation, resulting in faster evaporation rates
Condensation in One-Dimensional Dead-End Nanochannels
Phase
change at the nanoscale is at the heart of many biological
and geological phenomena. The recent emergence and global implications
of unconventional oil and gas production from nanoporous shale further
necessitate a higher understanding of phase behavior at these scales.
Here, we directly observe condensation and condensate growth of a
light hydrocarbon (propane) in discrete sub-100 nm (∼70 nm)
channels. Two different condensation mechanisms at this nanoscale
are distinguished, continuous growth and discontinuous growth due
to liquid bridging ahead of the meniscus, both leading to similar
net growth rates. The growth rates agree well with those predicted
by a suitably defined thermofluid resistance model. In contrast to
phase change at larger scales (∼220 and ∼1000 nm cases),
the rate of liquid condensate growth in channels of sub-100 nm size
is found to be limited mainly by vapor flow resistance (∼70%
of the total resistance here), with interface resistance making up
the difference. The condensation-induced vapor flow is in the transitional
flow regime (Knudsen flow accounting for up to 13% of total resistance
here). Collectively, these results demonstrate that with confinement
at sub-100 nm scales, such as is commonly found in porous shale and
other applications, condensation conditions deviate from the microscale
and larger bulk conditions chiefly due to vapor flow and interface
resistances