1,983 research outputs found
Stark shift and electric-field-induced dissociation of excitons in monolayer MoS2 and hBN/MoS2 heterostructures
Efficient conversion of photons into electrical current in two-dimensional
semiconductors requires, as a first step, the dissociation of the strongly
bound excitons into free electrons and holes. Here we calculate the
dissociation rates and energy shift of excitons in monolayer MoS2 as a
function of an applied in-plane electric field. The dissociation rates are
obtained as the inverse lifetime of the resonant states of a two-dimensional
hydrogenic Hamiltonian which describes the exciton within the Mott-Wannier
model. The resonances are computed using complex scaling, and the effective
masses and screened electron-hole interaction defining the hydrogenic
Hamiltonian are computed from first principles. For field strengths above 0.1
V/nm the dissociation lifetime is shorter than 1 ps, which is below the
lifetime associated with competing decay mechanisms. Interestingly,
encapsulation of the MoS2 layer in just two layers of hexagonal boron nitride
(hBN), enhances the dissociation rate by around one order of magnitude due to
the increased screening. This shows that dielectric engineering is an
effective way to control exciton lifetimes in two-dimensional materials
Geometry-induced asymmetric diffusion
Past work has shown that ions can pass through a membrane more readily in one
direction than the other. We demonstrate here in a model and an experiment that
for a mixture of small and large particles such asymmetric diffusion can arise
solely from an asymmetry in the geometry of the pores of the membrane. Our
deterministic simulation considers a two-dimensional gas of elastic disks of
two sizes diffusing through a membrane, and our laboratory experiment examines
the diffusion of glass beads of two sizes through a metal membrane. In both
experiment and simulation, the membrane is permeable only to the smaller
particles, and the asymmetric pores lead to an asymmetry in the diffusion rates
of these particles. The presence of even a small percentage of large particles
can clog a membrane, preventing passage of the small particles in one direction
while permitting free flow of the small particles in the other direction. The
purely geometric kinetic constraints may play a role in common biological
contexts such as membrane ion channels.Comment: published with minuscule change
Modulation of Elementary Calcium Release Mediates a Transition from Puffs to Waves in an IP3R Cluster Model
The oscillating concentration of intracellular calcium is one of the most
important examples for collective dynamics in cell biology. Localized releases
of calcium through clusters of inositol 1,4,5-trisphosphate receptor channels
constitute elementary signals called calcium puffs. Coupling by diffusing
calcium leads to global releases and waves, but the exact mechanism of inter-
cluster coupling and triggering of waves is unknown. To elucidate the relation
of puffs and waves, we here model a cluster of IP3R channels using a gating
scheme with variable non-equilibrium IP3 binding. Hybrid stochastic and
deterministic simulations show that puffs are not stereotyped events of
constant duration but are sensitive to stimulation strength and residual
calcium. For increasing IP3 concentration, the release events become modulated
at a timescale of minutes, with repetitive wave-like releases interspersed
with several puffs. This modulation is consistent with experimental
observations we present, including refractoriness and increase of puff
frequency during the inter-wave interval. Our results suggest that waves are
established by a random but time-modulated appearance of sustained release
events, which have a high potential to trigger and synchronize activity
throughout the cell
Paternal Folate Status and Sperm Quality, Pregnancy Outcomes, and Epigenetics
Scope: The effectiveness of maternal folate in reducing the risk of congenital malformations during pregnancy is well established. However, the role of the paternal folate status is scarcely investigated. The aim of this study is to investigate the evidence of associations between the paternal folate status and sperm quality, sperm epigenome, and pregnancy outcomes. Methods and results: Databases are searched up to December 2017 resulting in 3682 articles, of which 23 are retrieved for full-text assessment. Four out of thirteen human and two out of four animal studies show positive associations between folate concentrations and sperm parameters. An additional meta-analysis of four randomized controlled trials in subfertile men shows that the sperm concentration increases (3.54 95% confidence interval (CI) [−1.40 to 8.48]) after 3–6 months of 5 mg folic acid use per day compared to controls. Moreover, two out of two animal and one out of three human studies show significant alterations in the overall methylation of the sperm epigenome. One animal and one human study show associations between low folate intake and an increased risk of congenital malformations. Conclusions: This systematic review and meta-analysis shows evidence of associations between paternal folate status and sperm quality, fertility, congenital malformations, and placental weight
The effects of solidification conditions and heat treatment on the microstructure and mechanical properties of EN-AC 44400 alloy
Abstract. Improved mechanical and physical properties of an Al-Si alloy as a well-known casting alloy is strongly dependent upon the morphology of silicon particles, Al grains and also type of intermetallics which are in turn a function of alloy composition, solidification rate and heat treatment. This study aims at investigating the influence of the different solidification conditions (high pressure die, gradient and sand cast) and heat treatment on the microstructure (dendrite parameters, silicon particle morphology, intermetallic compounds), mechanical properties and fracture surface appearance of Al-9Si-4Mn alloy. To identify the features of microstructure and fracture surface analysis, a combination of optical metallography, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have been employed. The results show that the cooling rate has a strong effect on the evolution of intermetallics, morphology of the silicon and dendrite parameters. Introduction
Magnetotransport properties of a polarization-doped three-dimensional electron slab
We present evidence of strong Shubnikov-de-Haas magnetoresistance
oscillations in a polarization-doped degenerate three-dimensional electron slab
in an AlGaN semiconductor system. The degenerate free carriers
are generated by a novel technique by grading a polar alloy semiconductor with
spatially changing polarization. Analysis of the magnetotransport data enables
us to extract an effective mass of and a quantum
scattering time of . Analysis of scattering processes helps
us extract an alloy scattering parameter for the AlGaN material
system to be
The effects of solidification conditions and heat treatment on the microstructure and mechanical properties of EN-AC 44400 alloy
Abstract. Improved mechanical and physical properties of an Al-Si alloy as a well-known casting alloy is strongly dependent upon the morphology of silicon particles, Al grains and also type of intermetallics which are in turn a function of alloy composition, solidification rate and heat treatment. This study aims at investigating the influence of the different solidification conditions (high pressure die, gradient and sand cast) and heat treatment on the microstructure (dendrite parameters, silicon particle morphology, intermetallic compounds), mechanical properties and fracture surface appearance of Al-9Si-4Mn alloy. To identify the features of microstructure and fracture surface analysis, a combination of optical metallography, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have been employed. The results show that the cooling rate has a strong effect on the evolution of intermetallics, morphology of the silicon and dendrite parameters. Introduction
Extending the Intergenerational Stake Hypothesis: Evidence of an Intra‐individual Stake and Implications for Well‐being
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112209/1/jomf12203.pd
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