Despite being only one-atom thick, defect-free graphene is considered to be completely impermeable to all gases and liquids
. This conclusion is based on theory
and supported by experiments
that ...could not detect gas permeation through micrometre-size membranes within a detection limit of 10
to 10
atoms per second. Here, using small monocrystalline containers tightly sealed with graphene, we show that defect-free graphene is impermeable with an accuracy of eight to nine orders of magnitude higher than in the previous experiments. We are capable of discerning (but did not observe) permeation of just a few helium atoms per hour, and this detection limit is also valid for all other gases tested (neon, nitrogen, oxygen, argon, krypton and xenon), except for hydrogen. Hydrogen shows noticeable permeation, even though its molecule is larger than helium and should experience a higher energy barrier. This puzzling observation is attributed to a two-stage process that involves dissociation of molecular hydrogen at catalytically active graphene ripples, followed by adsorbed atoms flipping to the other side of the graphene sheet with a relatively low activation energy of about 1.0 electronvolt, a value close to that previously reported for proton transport
. Our work provides a key reference for the impermeability of two-dimensional materials and is important from a fundamental perspective and for their potential applications.
Glioma is one of the most common and aggressive malignant primary brain tumors with high recurrence rate and mortality rate and heavily depends on the angiogenesis. LncRNA H19 has many diverse ...biological functions, including the regulation of cell proliferation, differentiation and metabolism. Here, we aimed to investigate the molecular mechanism of lncRNA H19 affecting angiogenesis in glioma, which could help to uncover potential target for glioma therapy. RT-qPCR analysis was performed to detect the expression of lncRNA H19 and miR-138 in HEB, U87, A172 and U373 cell lines. MTT assay was used to evaluate the cell viability. To evaluate the migration and invasion after lncRNA H19 knockdown, Transwell and wound healing assay were employed. After lncRNA H19 knockdown, protein expression of HIF 1α and VEGF was detected by western blot and tube formation was assessed. For the prediction and validation of the interaction between lncRNA H19 and miR-138, bioinformatics and luciferase assay were performed. We investigated the regulatory roles and downstream molecular mechanisms of lncRNA H19 in glioma by knockdown H19, which inhibited the proliferation, migration and angiogenesis of glioma cells. Moreover, miR-138 acted as a target of H19 as detected by luciferase reporter assays. Meanwhile, HIF-1α was also a target of miR-138 and miR-138 could also regulate the proliferation, migration and angiogenesis of glioma cells by targeting HIF-1α and affecting the expression of VEGF in turn. Our findings identified an upregulated lncRNA H19 in glioma cells, which could promote proliferation, migration, invasion and angiogenesis via miR-138/HIF-1α axis as a ceRNA. This study provided a new opportunity to advance our understanding in the potential mechanism of lncRNA in glioma angiogenesis.
At very small twist angles of ∼0.1°, bilayer graphene exhibits a strain-accompanied lattice reconstruction that results in submicron-size triangular domains with the standard, Bernal stacking. If the ...interlayer bias is applied to open an energy gap inside the domain regions making them insulating, such marginally twisted bilayer graphene is expected to remain conductive due to a triangular network of chiral one-dimensional states hosted by domain boundaries. Here we study electron transport through this helical network and report giant Aharonov-Bohm oscillations that reach in amplitude up to 50% of resistivity and persist to temperatures above 100 K. At liquid helium temperatures, the network exhibits another kind of oscillations that appear as a function of carrier density and are accompanied by a sign-changing Hall effect. The latter are attributed to consecutive population of the narrow minibands formed by the network of one-dimensional states inside the gap.
In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field ...(IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.
The eleventh generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2009 by the International Association of Geomagnetism and Aeronomy Working Group V-MOD. It ...updates the previous IGRF generation with a definitive main field model for epoch 2005.0, a main field model for epoch 2010.0, and a linear predictive secular variation model for 2010.0–2015.0. In this note the equations defining the IGRF model are provided along with the spherical harmonic coefficients for the eleventh generation. Maps of the magnetic declination, inclination and total intensity for epoch 2010.0 and their predicted rates of change for 2010.0–2015.0 are presented. The recent evolution of the South Atlantic Anomaly and magnetic pole positions are also examined.
Field experiments were conducted on wheat to study the effects of foliar-applied iodine(I) alone, Zn (zinc) alone, and a micronutrient cocktail solution containing I, Zn, Se (selenium), and Fe ...(iron) on grain yield and grain concentrations of micronutrients. Plants were grown over 2 years in China, India, Mexico, Pakistan, South Africa, and Turkey. Grain-Zn was increased from 28.6 mg kg–1 to 46.0 mg–1 kg with Zn-spray and 47.1 mg–1 kg with micronutrient cocktail spray. Foliar-applied I and micronutrient cocktail increased grain I from 24 μg kg–1 to 361 μg kg–1 and 249 μg kg–1, respectively. Micronutrient cocktail also increased grain-Se from 90 μg kg–1 to 338 μg kg–1 in all countries. Average increase in grain-Fe by micronutrient cocktail solution was about 12%. The results obtained demonstrated that foliar application of a cocktail micronutrient solution represents an effective strategy to biofortify wheat simultaneously with Zn, I, Se and partly with Fe without yield trade-off in wheat.
Geomagnetic data assimilation merges past and present-day observations of the Earth’s mag-netic field with numerical geodynamo models and the results are used to initialize forecasts.We present a new ...‘proxy model’ that can be used to test, or rapidly prototype, numerical tech-niques for geomagnetic data assimilation. The basic idea for constructing a proxy is to capturethe conceptual difficulties one encounters when assimilating observations into high-resolution,3-D geodynamo simulations, but at a much lower computational cost. The framework of usingproxy models as ‘gate-keepers’ for numerical methods that could/should be considered formore extensive testing on operational models has proven useful in numerical weather predic-tion, where advances in data assimilation and, hence, improved forecast skill, are at least inpart enabled by the common use of a wide range of proxy models. We also present a largeset of systematic data assimilation experiments with the proxy to reveal the importance oflocalization and inflation in geomagnetic data assimilation.
Two-dimensional crystals with angstrom-scale pores are widely considered as candidates for a next generation of molecular separation technologies aiming to provide extreme, exponentially large ...selectivity combined with high flow rates. No such pores have been demonstrated experimentally. Here we study gas transport through individual graphene pores created by low intensity exposure to low kV electrons. Helium and hydrogen permeate easily through these pores whereas larger species such as xenon and methane are practically blocked. Permeating gases experience activation barriers that increase quadratically with molecules' kinetic diameter, and the effective diameter of the created pores is estimated as ∼2 angstroms, about one missing carbon ring. Our work reveals stringent conditions for achieving the long sought-after exponential selectivity using porous two-dimensional membranes and suggests limits on their possible performance.
Phosphorene and its derivatives so far have attracted substantial research interest due to its promising properties for developing nanoscale electronic devices. Here, we present a theoretical ...investigation on the functionalized features, such as the improved electronic structure and carrier mobility, for armchair-edged single walled black phosphorus nanotubes (PNTs) with the substitutional doping of low-concentration transition-metal atoms (Ti, Mn, Fe, and Ni). They are predicted to be exceptional magnetic semiconductors (MSCs), such as half-semiconductor or bipolar MSC. Their spin-resolved carrier mobility at room temperature holds doping element- dependence as well as carrier and spin polarity. Particularly, the difference by two orders of magnitude for carrier mobility emerges due to different TM doping. More interestingly, the carrier mobility in armchair PNTs serving as the channel material of a spin field effect transistor is predicted to be modified strongly by a gate voltage. The enhanced carrier mobility and its gate voltage direction-dependent behavior, as well as the more obvious carrier and spin polarity of mobility, can be observed clearly under gate voltage, which further facilitates the separation of different carriers and spin states and also suggests that realistic carrier mobility is gate voltage-dependent in a field effect transistor.
Abstract
Electron-electron interactions play a critical role in many condensed matter phenomena, and it is tempting to find a way to control them by changing the interactions’ strength. One possible ...approach is to place a studied system in proximity of a metal, which induces additional screening and hence suppresses electron interactions. Here, using devices with atomically-thin gate dielectrics and atomically-flat metallic gates, we measure the electron-electron scattering length in graphene and report qualitative deviations from the standard behavior. The changes induced by screening become important only at gate dielectric thicknesses of a few nm, much smaller than a typical separation between electrons. Our theoretical analysis agrees well with the scattering rates extracted from measurements of electron viscosity in monolayer graphene and of umklapp electron-electron scattering in graphene superlattices. The results provide a guidance for future attempts to achieve proximity screening of many-body phenomena in two-dimensional systems.
PDF
