Effects of a Free Adsorbate Boundary on the Description of an Argon Adsorbed Film on Graphite below the Bulk Triple Point.

Monte Carlo simulations have been carried out to study argon adsorption on graphite at temperatures below the bulk triple point temperature, Ttr(bulk) = 83.8 K. Two models for graphite have been used to investigate the effects of an adsorbate patch with a free boundary on the layering temperatures, the two-dimensional (2D)-triple point and the 2D-critical point for the three adsorbate layers on the surface. The first model (S-model) has a planar surface of infinite extent in the two directions parallel to the surface, and the second is a finite (2D-patch model). Although simulations using both models describe the characteristic temperatures, only the 2D-patch model can represent the experimental isotherms accurately, and the condensation pressures at which first-order transitions occur, while simulations with the S-model yield many unphysical substeps that are not observed experimentally in the first layer adsorbate, which leads to a poor description of higher adsorbate layers. These results support the interpretation that boundary growth of an adsorbate patch is the mechanism for argon adsorption at temperatures below the bulk triple point temperature. Combining the results derived from this simulation study for temperatures below the bulk triple point temperature, with results reported in the literature for temperatures above Ttr(bulk) and experimental data, we have constructed a generic pattern for the adsorption isotherms of simple gases on graphite at temperatures ranging from well below the bulk triple point temperature up to the bulk critical temperature, a comprehensive description not widely recognized in the literature.

Transcriptome analysis of blastoderms exposed to prolonged egg storage and short periods of incubation during egg storage.

BACKGROUND: Cool temperature egg storage prior to incubation is a common practice in the broiler industry; however, prolonged egg storage causes increased embryonic mortality and decreased hatchability and growth in surviving chicks. Exposing eggs to short periods of incubation during egg storage (SPIDES) reduces the adverse consequences of prolonged storage. SPIDES increases blastodermal cell viability by reducing apoptosis, though the counteracting mechanisms are unclear. To define the impact of prolonged storage and SPIDES, transcriptome analysis compared gene expression from blastoderms isolated from eggs exposed to the following treatments: control (CR, stored at 17 °C for 4 days), prolonged storage (NSR, stored at 17 °C for 21 days), SPIDES (SR, stored at 17 °C for 21 days with SPIDES), and incubated control (C2, stored at 17 °C for 4 days followed by incubation to HH (Hamburger-Hamilton) stage 2, used as the ideal standard development) (n = 3/group). Data analysis was performed using the CLC Genomics Workbench platform. Functional annotation was performed using DAVID and QIAGEN Ingenuity Pathway Analysis. RESULTS: In total, 4726 DEGs (differentially expressed genes) were identified across all experimental group comparisons (q < 0.05, FPKM> 20, |fold change| > 1.5). DEGs common across experimental comparisons were involved in cellular homeostasis and cytoskeletal protein binding. The NSR group exhibited activation of ubiquitination, apoptotic, and cell senescence processes. The SR group showed activation of cell viability, division, and metabolic processes. Through comparison analysis, cellular respiration, tRNA charging, cell cycle control, and HMBG1 signaling pathways were significantly impacted by treatment and potential regulatory roles for ribosomal protein L23a (RPL23A) and MYC proto-oncogene, BHLH transcription factor (MYC) were identified. CONCLUSIONS: Prolonged egg storage (NSR) resulted in enriched cell stress and death pathways; while SPIDES (SR) resulted in enriched basic cell and anti-apoptotic pathways. New insights into DNA repair mechanisms, RNA processing, shifts in metabolism, and chromatin dynamics in relation to egg storage treatment were obtained through this study. Although egg storage protocols have been examined through targeted gene expression approaches, this study provided a global view of the extensive molecular networks affected by prolonged storage and SPIDES and helped to identify potential upstream regulators for future experiments to optimize egg storage parameters.

Characterization of non-graphitized carbon blacks: a model with surface crevices.

Experimental isotherms for argon and nitrogen adsorption on two non-graphitized carbon substrates, Carbopack B and Cabot BP280, do not obey Henry's Law in the range of pressures accessible to the most sensitive MKS pressure transducers. At high pressures, close to the bulk coexistence pressure (P0), the isotherms at temperatures below the bulk triple point temperature cross the P0 axis at a finite loading, a behaviour which is interpreted as incomplete wetting. It was found that the adsorbed density at P0 for Cabot BP280 is lower than that for Carbopack B which is, in turn, only slightly lower than that for the highly graphitized Carbopack F, suggesting that there is a long-range effect of the surface structure in non-graphitized carbon blacks, in the accumulation of higher layers, especially for Cabot BP280. We have carried out extensive Monte Carlo simulations to compare experimental observations with a molecular model for substrate surfaces decorated with crevices of molecular dimensions. From the analysis of the experimental data, it was found that the typical width of crevices is of the order of 0.65-0.9 nm. In the high pressure region, the crossing of the P0 axis by isotherms at temperatures below the bulk triple point temperature can be explained by an adsorbate structure which is less dense and more disordered than the fcc structure of the bulk crystal, with a consequent raising of the coexistence pressure between the adsorbate and the gas phase above P0. Adsorbate loading at the point where the isotherm crosses the P0 axis for Cabot BP280 is lower than for Carbopack B which can be attributed to a higher concentration of crevices leading to a lower adsorbate density and an irregular arrangement of atoms at the interface separating the adsorbed phase and the gas phase. This results in weaker gas-adsorbate interactions which supresses the build-up of higher layers. We suggest that the use of the adsorbed density at the bulk coexistence pressure, at temperatures below the bulk triple point temperature, can be a useful tool for assessing the presence and concentration of surface crevices on non-graphitized carbon black.

A simulation study of the low temperature phase diagram of the methane monolayer on graphite: a test of potential energy functions.

We have used molecular simulation with two intermolecular potential models, TraPPE-UA and TraPPE-EH, the latter of which accounts for the tetrahedral shape, to study the effects of shape on methane adsorption on graphite. Both models give good descriptions of the vapour-liquid equilibria in the bulk phase, but adsorption on graphite is better described by the TraPPE-EH model. Molecular configurations in the monolayer, show the variation with temperature of the registry sites for the carbon and hydrogen atoms of the methane molecules. At temperatures below 70 K, the centre of mass (COM) of the molecules is in registry with the centre of the carbon hexagons. For temperatures above 70 K, a commensurate monolayer is initially formed as at low temperatures, then as the loading is increased the first layer remains in registry, but the COM of the methane molecules in the first layer shifts to the top of the graphite carbon atoms with the C-H bond pointing to carbon atoms in the second shell of a C-hexagon. At temperatures above 93 K, the first adsorbate layer goes through these two commensurate states and then undergoes a transition to an incommensurate solid. Finally, for temperatures greater than 110 K methane behaves like a pseudo spherical molecule.

Nonwetting/Prewetting/Wetting Transition of Ammonia on Graphite.

Simulations of ammonia adsorption on graphite were carried out over a range of temperatures to investigate the transition from nonwetting to wetting. The process is governed by a subtle interplay between the various interactions in the system and the temperature. At temperatures below the bulk triple point, the system is nonwetting; above the triple point, we observed continuous wetting, preceded by a prewetting region in which the so-called thin-to-thick film transition occurs. This system serves as an excellent example of wetting/nonwetting behavior in an associating fluid as a function of temperature because the heat of sublimation (or condensation) is greater than the isosteric heat of adsorption at zero loading. The nonwetting-to-wetting transition (NW/W) is also strongly affected by the adsorbate-adsorbate interaction, which becomes important when this contribution to the isosteric heat is of a similar magnitude to the heat of condensation. An appropriate indicator of a NW/W transition at a given loading is therefore the difference between the isosteric heat and the heat of sublimation (or condensation). Our simulation results show the "thin-to-thick" film transition in the temperature range between 195 and 240 K, which has not been previously explained. Above 240 K, continuous wetting occurs. This study provides a basis for a better understanding of adsorption in a range of systems because ammonia is an intermediate between simple molecules, such as argon, and strongly associating fluids, such as water.

On the transition from partial wetting to complete wetting of methanol on graphite.

The transition from partial wetting to complete wetting for methanol adsorbed on a highly graphitized thermal carbon black, Carbopack F, over a range of temperature from the triple point at 185 K to 298 K, was investigated using Monte Carlo simulation and high-resolution experiments. At 190 K, (above the triple point) both the experimental and simulated adsorption isotherms cut the P/P0 axis at a finite loading; a feature of partial wetting that has not been recognized previously in the literature. This occurs because most O- and H-atoms in the second layer of the adsorbate point towards the adsorbent surface to form hydrogen bonds with molecules in the first layer and therefore the interface between the bilayer adsorbed film and the gas phase consists mainly of methyl groups, preventing the system from forming higher layers. At temperatures above 263 K, methanol adsorption increases with pressure and wets the surface as the pressure approaches the bulk coexistence pressure P0. This is because the O-H and O-CH3 bonds of methanol in the region above the second layer have random orientation, and adsorption in higher layers takes place via hydrogen bonding. From extensive simulations of methanol adsorption on adsorbents of different strength over a wide temperature range, a parametric map has been constructed which identifies the regions of non-wetting, partial wetting and complete wetting. For a given surface strength, wetting is favoured at higher temperatures, and at a given temperature there is a transition from non-wetting on weakly adsorbing substrates to either partial wetting or to complete wetting on strong adsorbents at temperatures below or above the roughening temperature Tr of 260 K.

On the microscopic origin of the temperature evolution of isosteric heat for methane adsorption on graphite.

Understanding methane adsorption is fundamental to understanding gas storage and gas separation technologies. Detailed analyses of methane adsorption on non-porous substrates are pivotal for understanding the intrinsic interactions between the methane molecule and the adsorbent. In this paper, we particularly address the isosteric heat, which is a crucial parameter that characterizes the energetics of such systems. We have used grand canonical Monte Carlo simulations to study methane adsorption on graphite over a range of temperatures (from 50 K to 110 K). Our simulation results show good agreement with experimental data for the 2D phase transition, the 2D triple and critical points in the first layer obtained from low energy electron diffraction, neutron scattering and heat capacity measurements. On the basis of this agreement, we present a detailed microscopic picture of isosteric heat and its evolution with temperature. Our results show that the origin of the cusp and spike in the isosteric heat curve and their shift with temperature are associated with the balance of entropic and enthalpic contributions between the first and second layer.

Alcohol and healthy ageing: a challenge for alcohol policy.

OBJECTIVES: This paper presents findings of a qualitative study of older people's use of alcohol during retirement and identifies ways that an improved understanding of older people's drinking can inform policy approaches to alcohol and active and healthy ageing. STUDY DESIGN: Qualitative semi-structured interviews conducted with a self-selecting sample of retired people. METHODS: Participants were recruited from three geographical locations in the West of Scotland. A quota sampling design was used to ensure a broad spread of participants in terms of socio-economic position, age and gender. In total 40 participants were interviewed and the data analysed thematically using Braun and Clarke's (2006) approach. RESULTS: Amongst those who used alcohol, it was most often framed in terms of pleasure, relaxation, socialising and as a way to mark the passage of time. Alcohol was often associated with social occasions and interactions both in private and in public spaces. There were also many examples of the use of imposed routines to limit alcohol use and of a decreasing volume of alcohol being consumed as participants aged. This suggests that older people are often active in constructing what they regard as 'healthier' routines around alcohol use. However, processes and circumstances associated with ageing can lead to risk of social isolation and/or increased alcohol consumption. Such processes include retirement from paid work and other 'biographical disruptions' such as caring for a partner, bereavement and/or loss of social networks. CONCLUSIONS: These findings highlight processes that can result in changes in drinking habits and routines. Whilst these processes can be associated with a reduction or cessation of alcohol use as people age, they can also be associated with increased risk of harmful alcohol consumption. Fractured or disrupted routines, particularly those associated with bereavement or the burden of caring responsibilities, through increasing the risk of loneliness and isolation, can construct increased risk of harmful alcohol consumption. These findings reframe the pathway of risk between ageing and alcohol-related harm by highlighting the vulnerability to harmful drinking practices brought by fracture or sudden change of routine. The findings point to a role for public health in supporting the reconstruction of routines that provide structure and meaning and can be used to actively manage the benefits and harms associated with drinking.

Structure-activity correlation in transfection promoted by pyridinium cationic lipids.

The efficiency of the transfection of a plasmid DNA encoding a galactosidase promoted by a series of pyridinium lipids in mixtures with other cationic lipids and neutral lipids was assessed in CHO-K1 cells. We identify key molecular parameters of the lipids in the mixture - clog P, lipid length, partial molar volume - to predict the morphology of the lipid-DNA lipoplex and then correlate these same parameters with transfection efficiency in an in vitro assay. We define a Transfection Index that provides a linear correlation with normalized transfection efficiency over a series of 90 different lipoplex compositions. We also explore the influence of the same set of molecular parameters on the cytotoxicity of the formulations.

On the explanation of hysteresis in the adsorption of ammonia on graphitized thermal carbon black.

We present a Monte Carlo simulation and experimental study of ammonia adsorption on graphitized thermal carbon black. Our new molecular model for the adsorbent is composed of basal plane graphene surfaces with ultrafine pores grafted with hydroxyl groups at the junctions between graphene layers. The simulated adsorption isotherms and isosteric heats are in good agreement with the experimental data of Holmes and Beebe, and the simulations reproduce the unusual experimental hysteresis of ammonia adsorption on an open graphite surface for the first time in the literature. The detailed mechanisms of adsorption and desorption, and the origin of hysteresis, are investigated by the microscopic analysis of the adsorbate structures to show that restructuring occurs during adsorption. The main results from this work are: (i) at the triple point, ammonia adsorbs preferentially around the functional groups to form clusters in the ultrafine pores and spills-over onto the basal plane as the loading is increased; followed by a 2D condensation on the graphite surface to form a bilayer adsorbate; (ii) at the boiling point, adsorption occurs on the basal plane due to the increasing importance of thermal fluctuations (an entropic effect); (iii) the isosteric heat is very high at zero loading due to the strong interaction between ammonia and the functional groups, decreases steeply when the functional group is saturated, and eventually reaches the heat of condensation as the fluid-fluid interaction increases.

Existence of ultrafine crevices and functional groups along the edge surfaces of graphitized thermal carbon black.

Adsorption of different gases on graphitized thermal carbon black (GTCB) has been studied with a new molecular model to examine the consequences of micropore crevices and functional groups at the junctions between adjacent basal planes. Adsorption was simulated in the Grand Canonical Monte Carlo ensemble and the theoretical Henry constants were calculated by Monte Carlo volume integration over the Boltzmann factor of the solid-fluid potential. The simulation results are in good agreement with high-resolution experimental isotherms for argon on mineralogical graphite measured by Lopez-Gonzalez et al.1 From detailed inspection of the argon isotherms at extremely low coverages, we find two distinct Henry law regions, separated by a plateau (suggesting saturation of the stronger sites) that spans over a few decades of pressure. The first Henry law region is attributed to adsorption in the ultrafine crevices at the junctions between two adjacent basal planes, and the second region corresponds to adsorption on the basal plane, as confirmed by the theoretical Henry constant. The simulated isosteric heat and snapshots of molecular configurations show that argon adsorbs preferentially in the ultrafine crevices where there is a deep potential well due to overlap from the opposite pore walls. Similar behavior was found for other nonassociating fluids (Ar, N2, and CO2); however, for associating fluids (NH3 and H2O), the strong sites for adsorption and nucleation come from the combined effects of functional groups and ultrafine crevices, since the latter cannot alone account for the observed adsorption.

Adsorption on ordered and disordered duplex layers of porous anodic alumina.

We have carried out systematic experiments and numerical simulations of the adsorption on porous anodic aluminum oxide (AAO) duplex layers presenting either an ordered or a disordered interconnecting interface between the large (cavity) and small (constriction) sections of the structured pores. Selective blocking of the pore openings resulted in three different pore topologies: open structured pores, funnel pores, and ink-bottle pores. In the case of the structured pores having an ordered interface, the adsorption isotherms present a rich phenomenology characterized by the presence of two steps in the condensation branch and the opening of one (two) hysteresis loops during evaporation for the ink-bottle (open and funnel) pores. The isotherms can be obtained by summing the isotherms measured on uniform pores having the dimensions of the constrictions or of the cavities. The numerical analysis of the three different pore topologies indicates that the shape of the junction between the two pore sections is only important for the adsorption branch. In particular, a conic junction which resembles that of the AAO pores represents the experimental isotherms for the open and funnel pores better, but the shape of the junction in the ink bottle pores does not matter. The isotherms for the duplex layers with a disordered interface display the same general features found for the ordered duplex layers. In both cases, the adsorption branches coincide and have two steps which are shifted to lower relative pressures compared to those for the ordered duplex. Furthermore, the desorption branches comprise hysteresis loops much wider than those of the ordered duplex layers. Overall, this study highlights the important role played by morphologies where there are interconnections between large and small pores.

Hysteresis loop and scanning curves of argon adsorption in closed-end wedge pores.

The hysteresis loop and scanning curves for argon adsorbed in a wedge pore with one end closed are studied with grand canonical Monte Carlo simulation. We have found multiple hysteresis loops for pores with either the narrow end or the wider end closed. In pores with the narrow end closed, adsorption and desorption exhibits a two-stage sequence of rapid change, followed by a gradual change in adsorbate density. The pore can be divided into zones of commensurate packing and junctions of incommensurate packing. A striking feature is that the sequence of these two stages is opposite for the adsorption and desorption processes. This can be explained by cohesion in the adsorbate, in which a steep condensation process is associated with the zones and a steep evaporation process is associated with the junctions between them. For pores with the wider end closed, the processes of adsorption and desorption from various zones are correlated with each other. In pores with the narrow end closed, the scanning curves trace reversibly along the segment of the isotherm, where the isotherm shows gradual change, and when the scanning curve reaches a point between the gradual change segment and the sharp change segment, the scanning curve crosses from one boundary of the hysteresis loop to the corresponding point on the other boundary. This indicates that the condensation and evaporation states are not affected by scanning but that, in scanning across the hysteresis loop, the adsorbate passes through a sequence of metastable states as the distribution of density is rearranged, without any significant change in the overall density. In contrast, for pores with the wider end closed, both the descending curve from a partially filled pore and the ascending curve are identical to the desorption branch of the corresponding pore with its narrow end closed.

An undulation theory for condensation in open end slit pores: critical hysteresis temperature & critical hysteresis pore size.

A new theory of condensation in an open end slit pore, based on the concept of temperature dependent undulation, at the interface separating the adsorbed phase and the gas-like region, is presented. The theory, describes, for the first time, the microscopic origin of the critical hysteresis temperature and the critical hysteresis pore size, properties which are not accessible to any classical theories.

Elementary excitations and crossover phenomenon in liquids.

The elementary excitations of vibration in solids are phonons. But in liquids phonons are extremely short lived and marginalized. In this Letter through classical and ab initio molecular dynamics simulations of the liquid state of various metallic systems we show that different excitations, the local configurational excitations in the atomic connectivity network, are the elementary excitations in high temperature metallic liquids. We also demonstrate that the competition between the configurational excitations and phonons determines the so-called crossover phenomenon in liquids. These discoveries open the way to the explanation of various complex phenomena in liquids, such as fragility and the rapid increase in viscosity toward the glass transition, in terms of these excitations.

On the irreversibility of the adsorption isotherm in a closed-end pore.

We present a simulation study of argon adsorption in a closed-end mesopore of uniform diameter in order to investigate the occurrence of hysteresis and propose two principal reasons for its existence: the variation in the shape and radius of curvature of the meniscus and the change in the packing of adsorbate during adsorption and desorption. This interpretation differs from classical theories that neglect both of these factors, and therefore find that adsorption-desorption in a closed-end pore is reversible. A detailed simulation study of the effects of temperature on the microscopic behavior of the adsorbate supports the interpretation proposed here.

Cleavage of huntingtin by apopain, a proapoptotic cysteine protease, is modulated by the polyglutamine tract.

Apoptosis has recently been recognized as a mode of cell death in Huntington disease (HD). Apopain, a human counterpart of the nematode cysteine protease death-gene product, CED-3, has a key role in proteolytic events leading to apoptosis. Here we show that apoptotic extracts and apopain itself specifically cleave the HD gene product, huntingtin. The rate of cleavage increases with the length of the huntingtin polyglutamine tract, providing an explanation for the gain-of-function associated with CAG expansion. Our results show that huntingtin is cleaved by cysteine proteases and suggest that HD might be a disorder of inappropriate apoptosis.

Comparison of blastoderm traits from 2 lines of broilers before and after egg storage and incubation.

We examined the impact of egg storage on the hatchability of eggs from 2 lines (A and B) of commercial broiler breeders with known differences in fertility (line B slightly higher) and hatchability following egg storage (line A slightly lower). Eggs from both lines were stored in a 16°C room for 3 to 4, 10 to 12, and 17 d, the blastoderms were isolated, evaluated, and statistically compared. No significant interactions (line × duration of storage) were observed in the following traits: blastoderm diameter, total and percentage of viable blastodermal cells, stage of blastoderm development, and embryo weight and stage of development after 7 d of incubation. However, significant differences were observed when comparing line averages across storage treatments (diameter and total number of blastodermal cells) and storage treatment averages across lines (percentage of viable cells, and embryo weight and stages following incubation). To ascertain the basis for the observed differences in fertility, perivitelline sperm-hole numbers were determined in eggs within 72 h of lay (3 to 4 d storage group). Eggs from line B had a significantly higher number of eggs having greater numbers of sperm holes than eggs from line A. It is concluded that no single blastoderm trait or combination of traits can be definitively associated with the inter-line differences in hatchability following storage of eggs. Alternatively, differences in PVL sperm-hole counts between lines may be associated with the reported differences in fertility between the 2 lines.

On the cavitation and pore blocking in slit-shaped ink-bottle pores.

We present GCMC simulations of argon adsorption in slit pores of different channel geometry. We show that the isotherm for an ink-bottle pore can be reconstructed as a linear combination of the local isotherms of appropriately chosen independent unit cells. Second, depending on the system parameters and operating conditions, the phenomena of cavitation and pore blocking can occur for a given configuration of the ink-bottle pore by varying the geometrical aspect ratio. Although it has been argued in the literature that the geometrical aspects of the system govern the evaporation mechanism (either cavitation or pore blocking), we here put forward an argument that the local compressibility in different parts of the ink-bottle pore is the deciding factor for evaporation. When the fluid in the small neck is strongly bound, cavitation is the governing process, and molecules in the cavity evaporate to the surrounding bulk gas via a mass transfer mechanism through the pore neck. When the pore neck is sufficiently large, the system of neck and cavity evaporates at the same pressure, which is a consequence of the comparable compressibility between the fluid in the neck and that in the cavity. This suggests that local compressibility is the measure of cohesiveness of the fluid prior to evaporation. One consequence that we derive from the analysis of isotherms of a number of connected pores is that by analyzing the adsorption branch or the desorption branch of an experimental isotherm may not lead to the correct pore sizes and the correct pore volume distribution.

Development of equations for differential and integral enthalpy change of adsorption for simulation studies.

We present equations to calculate the differential and integral enthalpy changes of adsorption for their use in Monte Carlo simulation. Adsorption of a system of N molecules, subject to an external potential energy, is viewed as one of transferring these molecules from a reference gas phase (state 1) to the adsorption system (state 2) at the same temperature and equilibrium pressure (same chemical potential). The excess amount adsorbed is the difference between N and the hypothetical amount of gas occupying the accessible volume of the system at the same density as the reference gas. The enthalpy change is a state function, which is defined as the difference between the enthalpies of state 2 and state 1, and the isosteric heat is defined as the negative of the derivative of this enthalpy change with respect to the excess amount of adsorption. It is suitable to determine how the system behaves for a differential increment in the excess phase adsorbed under subcritical conditions. For supercritical conditions, use of the integral enthalpy of adsorption per particle is recommended since the isosteric heat becomes infinite at the maximum excess concentration. With these unambiguous definitions we derive equations which are applicable for a general case of adsorption and demonstrate how they can be used in a Monte Carlo simulation. We apply the new equations to argon adsorption at various temperatures on a graphite surface to illustrate the need to use the correct equation to describe isosteric heat of adsorption.