Hysteresis and scanning curves in linear arrays of mesopores with two cavities and three necks. classification of the scanning curves

Adsorption of argon at 87K in a linear array of slit mesopores composed of two cavities and three necks has been investigated using Grand Canonical Monte Carlo simulation. Hysteresis and scanning was found to depend on the relative size of the necks and cavities and on whether the necks are wider or narrower than the critical width that demarcates cavitation from pore blocking. There are 26 possible combinations for the linear array. By considering the behaviour of hysteresis scanning curves, we are able to identify four distinct groups: (I) Group 1: The descending scanning spans the boundary curve of the hysteresis loop due to stretching of the condensate in the small cavity. (ii) Group 2: The descending curve partially spans the loop and returns to the adsorption boundary. This occurs either because the condensate stretches in the small cavity, followed by evaporation via a pore blocking mechanism; or because the condensate evaporates as the meniscus recedes in the large neck that joins the two cavities. (iii) Group 3: The descending curve spans the loop as in Group 1 but there is a small sub-loop associated with emptying and filling of the large neck connecting the large cavity to the surrounding gas. (iv) Group 4: The descending scanning curve is similar to that in Group 2; but when the large cavity of the array is filled with adsorbate, and the small cavity is empty (except for an adsorbed film) the ascending curve partially spans the loop. This happens when molecular layers build-up in the small cavity (c.f. stretching of condensate in a descending scan) is followed by condensation, which results in the scanning curve returning to the desorption boundary (c.f. evaporation of the condensate and return to the adsorption boundary). There is also a sub-loop which has similar characteristics to those in Group 3

An improved model for N2 adsorption on graphitic adsorbents and graphitized thermal carbon black - the importance of the anisotropy of graphene

Computer simulations of N adsorption on graphite frequently use the 10-4-3 equation with Steele’s molecular parameters to describe the dispersive-repulsive interaction between a molecule and graphite. This model assumes that graphite is a uniformly homogeneous continuum solid, and its derivation implies the following assumptions: (1) the solid is built from stacked, equally spaced graphene layers, (2) there is an infinite number of layers, and (3) the carbon atom molecular parameters are invariant for all layers (collision diameter of 0.34 nm and reduced well depth of interaction energy of 28 K). Despite the fact that this model can give an acceptable description of experimental data for this system, there are experimental observations that simulation results fail to account for. First, the isotherm does not exhibit a step in the sub-monolayer coverage region at 77 K, which is attributed to a transition from the supercritical state of the adsorbate to the commensurate state, and therefore fails to reproduce the cusp and heat spike in the experimental isosteric heat curve versus loading at close to monolayer coverage. Second, the simulation results overpredict the experimental data in the multilayer region. These discrepancies suggest that (1) the absence of lateral corrugation in the 10-4-3 potential misses the commensurate to incommensurate transition and (2) the long-range solid-fluid potential, experienced by the second and higher layers onwards, is too strong. Here we examine a revised graphite potential model that incorporates three features absent from the 10-4-3 model: (1) an energetic corrugation of the potential arising from the discrete atom structure of the adsorbent, (2) the unequal spacing of the graphene layers due to the anisotropic force field acting on graphene layers at the surface, and (3) the different polarizabilities of carbon atoms in graphite, parallel and normal to the graphene surface. These features are corroborated by a number of experimental measurements and quantum-mechanical calculations: (1) the Low-Energy Electron Diffraction (LEED) and Surface-Extended X-ray Absorption Fine Structure (SEXAFS) experiments show that the first adsorbate layer is smaller than predicted by the 10-4-3 model with the traditional molecular parameters suggested by Steele, and (2) the potential well depth for atoms in graphene is stronger than for C-atoms in graphite. The simulation results using this revised graphite model give an improved description of the fine features of adsorption of N on graphite: the sub-step in the first layer of the isotherm, the spike in the isosteric heat curve versus loading, and the coverage at higher loadings

On the consistency of NVT, NPT, μVT and Gibbs ensembles in the framework of kinetic Monte Carlo – fluid phase equilibria and adsorption of pure component systems

This paper aims to show the consistency between simulations of fluid phase properties, obtained with various ensembles, developed within the framework of kinetic Monte Carlo (kMC) simulation: NVT (canonical), NPT (isothermal-isobaric systems), μVT (grand canonical) and Gibbs ensembles, to ensure the reliability of the kMC methodology. The advantages of the kMC scheme, as compared to the conventional Metropolis Monte Carlo, are: (1) accurate determination of the chemical potentials compared to the Widom insertion method, and (2) a rejection-free algorithm, making the implementation of the kMC scheme simpler. For internal consistency in a grand canonical ensemble simulation, we have developed a means to calculate the intrinsic chemical potential of the system accurately, which must be the same (within statistical error of the simulation) as the specified chemical potential to ensure convergence to equilibrium. We test the consistency of canonical (NVT-kMC) and grand canonical (GC-kMC) ensembles for argon adsorption at 87\ua0K and 120\ua0K in a uniform open-ended slit pore, and hence derive governing factors affecting hysteresis in the isotherm and the microscopic mechanisms of condensation and evaporation

Wintertime Synoptic Patterns of Midlatitude Boundary Layer Clouds Over the Western North Atlantic: Climatology and Insights From In Situ ACTIVATE Observations

The synoptic evolution of boundary layer clouds over the western North Atlantic is described by means of a regime classification based on Self-Organizing Maps. The analysis is able to capture events with low and high low-cloud coverage. High-cloud coverage days are associated with cold-air outbreaks (CAOs). The combination of cold and dry conditions gives rise to an enhancement of surface heat fluxes during CAO, consistent with an increase in cloud fraction. In addition, prevailing winds during CAO days explain the occurrence of a synoptic maximum in cloud droplet number concentration, linked to transport of continental aerosol over the ocean. Overall, the dynamics of midlatitude low clouds substantially differ from archetypal stratocumulus clouds regimes

Boundary Layer Structures Over the Northwest Atlantic Derived From Airborne High Spectral Resolution Lidar and Dropsonde Measurements During the ACTIVATE Campaign

The Planetary Boundary Layer Height (PBLH) is essential for studying the lower atmosphere and its interaction with the surface. Usually, it contains a mixed layer (ML) with vertically well-mixed (i.e., nearly constant) specific humidity and potential temperature. Over the ocean, the PBL is usually coupled (vertically well-mixed) and the ML height (MLH) is usually close to PBLH, hence the MLH estimated from the measurements of aerosol backscatter by a lidar is traditionally compared with PBLH determined from radiosondes/dropsondes. However, when the PBL is decoupled (not vertically well mixed), the MLH differs from the PBLH. Here we used dropsondes' thermodynamic profile to evaluate the airborne High-Spectral-Resolution Lidar—Generation 2 (HSRL-2) estimation of MLH and PBLH in airborne field campaign over the northwestern Atlantic (ACTIVATE) from 2020 to 2022. We show that the HSRL-2 has excellent MLH estimation compared to the dropsondes. We also improved the HSRL-2 estimation of PBLH. Further data analysis indicates that these conclusions remain the same for cases with different cloud fractions, and for decoupled PBLs. These results demonstrate the potential of using HSRL-2 aerosol backscatter data to estimate both marine MLH and PBLH and suggest that lidar-derived MLH should be compared with radiosonde/dropsonde-determined MLH (not PBLH) in general

Large-Eddy Simulations of Marine Boundary Layer Clouds Associated with Cold-Air Outbreaks during the ACTIVATE Campaign. Part II: Aerosol–Meteorology–Cloud Interaction

Aerosol effects on micro/macrophysical properties of marine stratocumulus clouds over the western North Atlantic Ocean (WNAO) are investigated using in situ measurements and large-eddy simulations (LES) for two cold-air outbreak (CAO) cases (28 February and 1 March 2020) during the Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE). The LES is able to reproduce the vertical profiles of liquid water content (LWC), effective radius reff and cloud droplet number concentration Nc from fast cloud droplet probe (FCDP) in situ measurements for both cases. Furthermore, we show that aerosols affect cloud properties (Nc, reff, and LWC) via the prescribed bulk hygroscopicity of aerosols (¯κ) and aerosol size distribution characteristics. Nc, reff, and liquid water path (LWP) are positively correlated to ¯κ and aerosol number concentration (Na) while cloud fractional cover (CFC) is insensitive to ¯κ and aerosol size distributions for the two cases. The realistic changes to aerosol size distribution (number concentration, width, and the geometrical diameter) with the same meteorology state allow us to investigate aerosol effects on cloud properties without meteorological feedback. We also use the LES results to evaluate cloud properties from two reanalysis products, ERA5 and MERRA-2. Compared to LES, the ERA5 is able to capture the time evolution of LWP and total cloud coverage within the study domain during both CAO cases while MERRA-2 underestimates them

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Spatially-coordinated airborne data and complementary products for aerosol, gas, cloud, and meteorological studies: The NASA ACTIVATE dataset

The NASA Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) produced a unique dataset for research into aerosol-cloud-meteorology interactions. An HU-25 Falcon and King Air conducted systematic and spatially coordinated flights over the northwest Atlantic Ocean. This paper describes the ACTIVATE flight strategy, instrument and complementary dataset products, data access and usage details, and data application notes

Investigation of metformin as a radiation sensitizer in pancreatic cancer.

253 Background: Clinical study demonstrates that diabetic patients taking metformin while undergoing chemotherapy and/or radiation for localized pancreatic cancer have improved overall survival compared to diabetics not taking metformin or non-diabetic patients (Sadeghi, Clin Cancer Res 2012). Metformin may act as a radiosensitizer through direct effects on cancer cells and/or indirect effects on the host, such as the inhibition of hepatic gluconeogenesis or inflammation (Pollak, Clin Cancer Res 2012). In vitro study demonstrates that the direct effects of metformin include suppression of mTOR, G2/M cell cycle arrest, and toxicity to cancer stem cells with resultant increase in chemo and radiosensitivity, though some of these studies employed supra-physiologic doses of metformin (1-10mM) instead of physiologic doses (10uM) (Song, Sci Rep 2012; Sanli, IJROBP 2010). Methods: MiaPaCa-2 human pancreatic cancer cells were grown in physiologic (5mM) or supra-physiologic (25mM) glucose media. After exposure to metformin (10uM or 10mM) for 3-7 days in cell culture, phosphorylation of AMPK, a target of metformin, was measured by western blot and radiation survival was determined by clonogenic survival assay. Results: MiaPaCa-2 cells grown in 5mM glucose media with metformin have higher levels of AMPK phosphorylation than those grown in 25mM glucose media or without metformin. Radiation clonogenic survival was similar between cells exposed to any of the treatment conditions, including differences in glucose concentration and/or presence of metformin. Conclusions: MiaPaCa-2 pancreatic cancer cells do not demonstrate enhanced radiosensitivity to metformin in vitro. Future studies will investigate whether K-Ras wild-type cell lines exhibit enhanced radiosensitivity to metformin in vitro and whether metformin acts as a radiosensitizer in vivo