Vapor Diffusion Research Articles

Evaluation of Passive Vapor Diffusion Samplers to Quantify Acetylene, Ethene, and Ethane in Groundwater

AbstractAcetylene, ethene, and ethane are products from the degradation of trichloroethene (TCE) in contaminated aquifers. However, the volatility of these gases makes it challenging to avoid excessive losses during sampling. The objective of this study was to compare the quantification of acetylene, ethene, and ethane using passive vapor diffusion (PVD) samplers vs. conventional low‐flow groundwater collection. Samples were obtained from 8 to 13 monitoring wells at three sites that show potential for biotic and abiotic degradation of TCE in fractured rock aquifers. Method reporting limits (MRLs) for the PVD samplers were 0.25 μg/L for acetylene (0.0094 μM) and 0.28 μg/L for ethene and ethane (0.0099 and 0.0092 μM, respectively); the MRLs for conventional low‐flow groundwater samples were ~40% higher. For two of the sites, the maximum concentrations of acetylene, ethene, and ethane obtained with the PVD samplers were comparable to the conventional low‐flow samples. The frequency of detection for these gases with the PVD samplers was also comparable to conventional low‐flow groundwater sampling. For one of the sites with higher levels of acetylene (maximum of 13 μg/L), the concentrations from the PVD samplers were approximately twofold higher than those with conventional low‐flow groundwater sampling. Based on robust detection of acetylene, ethene, and/or ethane, it appears likely that degradation of TCE is occurring at the three sites that were sampled. The use of PVD samplers can reduce the possibility of false negative results to provide another line of evidence in support of natural attenuation.

Numerical investigation on cooperative evaporation from microdroplet array on heated substrate

The evaporative heat and mass transport characteristics from an array of continuously fed microdroplet on a heated substrate are investigated numerically by a Multiphysics model, which incorporates heat conduction, buoyant flow, Marangoni flow, Stefan flow, and vapor diffusion. The effects of droplet spacing, contact angle, and droplet size on the evaporation rate, heat flux, and convection strength were analyzed in detail with a fixed thermal and vapor concentration boundary condition. The results revealed the existence of extremely strong convection current in the ambient gas domain for evaporation from droplet array. This convection effect dominates the vapor transport process, overcomes the suppression effect from neighboring droplet, and causes the total evaporation rate to exceed the prediction from traditional diffusion-based model by up to ten times. The strength of the convective vapor transport is characterized by a dimensionless parameter, which increases first from 2.3 to 7 and then decrease to 4 with increasing contact angle from 30° to 150°, but remains invariant at 6.3 for hemispherical droplet irrespective of the change in droplet dimension. Finally, the numerical results demonstrate potential for microdroplet array evaporation to resolve the thermal management challenge of ultrahigh power electronics with heat flux up to 1 kW/cm2.

Drying in nanoporous media with Kelvin effect: Capillary imbibition against evaporation by smoothed particle hydrodynamics method

Understanding drying processes in nanoporous media is of great importance in many technological and industrial situations. To better understand how gas moves through clayey rocks, of interest for underground disposal of radioactive wastes, we propose using pore-scale direct numerical simulations. In this study, we use the Smoothed Particle Hydrodynamics method, which has proved to be an effective approach for simulating complex fluid dynamics within porous media at the nanoscale. Our simulations consider capillary-dominated two-phase flow with evaporation and condensation at liquid–gas interfaces, coupled to the diffusion of water vapor in the gas phase, as well as the Kelvin effect, which is a specific feature of nanopores. Our evaporation-condensation model is validated against analytical solutions. The size of the compact support of kernel function and the particle density required to obtain accurate and stable results of capillary pressure are investigated. Drying regimes, capillary-driven and evaporated-driven, are explored. A specific effort is made to highlight the influence of the Kelvin effect on desaturation and the creation of preferential paths for gas flow as well as its impact on drying rate. The role of condensation due to local vapor concentration conditions is also emphasized.

A Theory for the Balance between Warm Rain and Ice Crystal Processes of Precipitation in Mixed-Phase Clouds

Abstract Mixed-phase clouds contain both supercooled cloud liquid and ice crystals. In principle, precipitation may be initiated either by the liquid phase or by the ice phase. Ice crystals may grow by vapor diffusion to become snow (“ice crystal process”), forming “cold” precipitation. Equally, cloud droplets, when large enough, coalesce to form “warm” precipitation by the “warm rain process.” Warm rain could be supercooled and freeze as “warm” graupel. In the present paper, a new simplified theoretical analysis is provided to examine the microphysical system consisting of three species of hydrometeor, namely, cloud liquid, “cold ice” (crystals, snow), and “warm rain” (frozen or supercooled). This is obtained by nondimensionalizing and simplifying the evolution equations for the mass of each species. Analytical formulas are given for equilibria. Feedback analysis shows that the sign of the feedback is linked to the abundance of precipitation, with a neutral surface in the 3D phase space. The system’s precipitation amount explodes while in the initial unstable regime, crossing the neutral surface and approaching the equilibrium point that is a stable attractor. Positive and negative feedbacks are elucidated. In a standard case, the cold ice mass is about 1000 times larger than the warm rain mass. To illustrate the physical behavior of the theory, sensitivity tests are performed with respect to environmental conditions (e.g., aerosol, updraft speed) and microphysical parameters (e.g., riming and sedimentation rates for cold ice). Cold ice prevails, especially in fast ascent, due to its low bulk density, favoring slow sedimentation and a wide cross-sectional area for riming. Significance Statement The theory elucidates how the ice phase can prevail in the precipitation from any mixed-phase clouds with supercooled cloud liquid and crystals. The ice phase radically suppresses cloud liquid by riming when active and “wins” the competition against coalescence. This prevalence of ice is shown to arise from the low bulk density of snow. The cloud is viewed as a system of negative and positive feedbacks that prevail in realms of stability and instability in a 3D phase space.

Refolding, Crystallization, and Crystal Structure Analysis of a Scavenger Receptor Cysteine-Rich Domain of Human Salivary Agglutinin Expressed in Escherichia coli

Scavenger receptors are a protein superfamily that typically consists of one or more repeats of the scavenger receptor cysteine-rich structural domain (SRCRD), which is an ancient and highly conserved protein module. The expression and purification of eukaryotic proteins containing multiple disulfide bonds has always been challenging. The expression systems that are commonly used to express SRCRD proteins mainly consist of eukaryotic protein expression systems. Herein, we established a high-level expression strategy of a Type B SRCRD unit from human salivary agglutinin using the Escherichia coli expression system, followed by a refolding and purification process. The untagged recombinant SRCRD was expressed in E. coli using the pET-32a vector, which was followed by a refolding process using the GSH/GSSG redox system. The SRCRD expressed in E. coli SHuffle T7 showed better solubility after refolding than that expressed in E. coli BL21(DE3), suggesting the importance of the disulfide bond content prior to refolding. The quality of the refolded protein was finally assessed using crystallization and crystal structure analysis. As proteins refolded from inclusion bodies exhibit a high crystal quality and reproducibility, this method is considered a reliable strategy for SRCRD protein expression and purification. To further confirm the structural integrity of the refolded SRCRD protein, the purified protein was subjected to crystallization using sitting-drop vapor diffusion method. The obtained crystals of SRCRD diffracted X-rays to a resolution of 1.47 Å. The solved crystal structure appeared to be highly conserved, with four disulfide bonds appropriately formed. The surface charge distribution of homologous SRCRD proteins indicates that the negatively charged region at the surface is associated with their calcium-dependent ligand recognition. These results suggest that a high-quality SRCRD protein expressed by E. coli SHuffle T7 can be successfully folded and purified, providing new options for the expression of members of the scavenger receptor superfamily.

Experimental Analysis of Moisture-Dependent Thermal Conductivity, and Hygric Properties of Novel Hemp-shive Insulations with Numerical Assessment of Their In-Built Hygrothermal and Energy Performance.

The use of lime as a binder in hemp-lime considerably increases the drying time of hemp-lime after casting. Furthermore, lime is a non-renewable mineral resource. As such, this paper explores the effectiveness of using an alternative non-mineral binder instead of lime to formulate a novel hemp-shive insulation. The moisture-dependent thermal conductivity, adsorption isotherm, vapour diffusion resistance factor, and in-built hygrothermal performance of four variants of a novel bio-based insulation were investigated. The hygrothermal performance of the novel hemp-shive insulation was compared with that of a previously developed novel hemp-lime insulation. No significant variation in thermal conductivity of hemp-shive insulations between the equilibrium moisture contents (EMC) at 0% and 50% relative humidity (RH) was observed, but there was a substantial increase in thermal conductivity hemp-shive insulations when the material reached the EMC at 98% RH. The average dry thermal conductivity values of hemp-shive and hemp-lime insulations were also similar. The adsorption isotherms of hemp-shive insulations were determined at 0%, 20%, 50%, 70%, 90%, and 98% relative humidity steps. At 98% RH, the moisture adsorption capacity of hemp-shive insulations was 4-to-5-times higher than that of hemp-lime insulation. Hemp-shive insulations' vapour diffusion resistance factor (µ value) was about double the µ value of hemp-lime insulation. Hemp-shive insulations exhibited 4-to-5-times higher water absorption resistance than that of hemp-lime insulation. Numerically determined porosity values of hemp-shive agree with the values of wood-based insulation materials of similar density. Finally, using all experimentally acquired data as inputs, dynamic whole-building hygrothermal simulations were carried out and the results show that novel hemp-shive insulation materials perform at a similar level to the hemp-lime insulation in terms of heating and cooling energy demand but require 45% less energy for humidification. However, the relative humidity inside the hemp-shive wall remains higher than 70%, which can potentially induce mould growth.

Study on the mechanism of sessile droplets evaporation enhanced by the electric field

The evaporation characteristics of a sessile droplet under a direct current electric field were numerically investigated, and a numerical model was developed based on the arbitrary Lagrange-Euler method, combining the flow, heat transfer, vapour transport, and electrostatic equations. The simulations were validated to be in good agreement with previously reported experiments. The results demonstrate that the electric field can enhance the evaporation of the sessile droplet with different evaporative cooling numbers (initial electric field intensity E0 = 280 kV·m−1; 32.9% decrease in the evaporation time for water) by the following three methods: increasing the surface area of the droplet evaporation (2.6%) through the electric-field-induced deformation, improving the heat transfer efficiency between the droplet and substrate (droplet average temperature increases by 2.3 K) through the internal vortex, and by enhancing the shearing effect on the vapour layer (450.3% increase in vapour diffusion distance dc) through the external vortex. Additionally, the evaporation of a sessile water droplet undergoing thermocapillary convection is further enhanced under the electric field (E0 = 280 kV·m−1; 20.0% decrease in the evaporation time). As the inhomogeneous temperature distribution inside the droplet was eliminated by thermocapillary convection, the evaporation efficiency was dominated by the increased surface area of the droplet evaporation and the enhanced shearing effect on the vapour layer. These results will provide a better understanding of the electro-hydrodynamic enhanced droplet evaporation.

Numerical simulation and environmental impact assessment of oil vapor diffusion in surrounding residential areas before/after vapor recovery at petrol stations

ABSTRACT Oil vapor emitted during refueling process has caused serious issues of air pollution, especially the environmental impact in surrounding residential areas. Most petrol stations have installed oil vapor recovery systems, but some stations did not properly maintain or switch on them. With the increasing emphasis on ecological environmental protection, it is more crucial to investigate the internal mechanism of vapor-air mass transfer. In this study, a computational fluid dynamic (CFD) model was developed and verified to analyze the effects of wind speed, vehicles number, and residential layout on oil vapor diffusion in residential areas. Simultaneously, the effectiveness of oil vapor recovery was assessed by comparing contamination before and after recovery. Results indicate that wind speed greatly affects the area and location of excess emission areas (EEAs). As the wind speed increases from 2 m/s to 4 m/s, highest concentration, distance to buildings and width of EEAs decreases by 49.1%, 43.8%, and 33.3%, respectively, and EEAs disappear at the wind speed of 6 m/s. Vehicles number has a more significant effect on the symmetry of EEAs, and EEAs become gradually symmetrical as the number increases from 3 to 12. Further, the enclosure layout proves to be an effective layout for protecting residential air, with a minimum concentration of 0.18 mg/m3. Notably, the effectiveness of oil vapor recovery is remarkable, with a purification rate of 98.5%. These findings can offer a valuable guidance for controlling air pollution in residential areas and enhancing the environmental protection level of petroleum enterprises.

Design aspects of a CMC coating-like system for hot surfaces of aero engine components

Ceramic Matrix Composite (CMC) is an emerging material system that can be a game changer in the aerospace industry, both civil and military. CMCs components are, in fact, lighter and less prone to fatigue failure in a high temperature environment. However, at high temperatures, the diffusion of oxygen and water vapour inside the CMC can have detrimental effects. Therefore, the presence of protective coating is necessary to extend the life of CMC components. In the present work, a three-layers coating, consisting of a silicon bond (BND), adhesively bonded to the CMC, an Environment Barrier Coating (EBC) and a softer layer 3 (LAY3), is investigated for a CMC component. An aero-engine high pressure turbine seal segment was considered. Two design aspects are covered: (i) creep law is determined and calibrated in environment Abaqus from the experimental data of each coating layer available in the open literature, to provide a suitable instrument for the creep relaxation analyses of hot components; (ii) thickness sensitivity study of each layer of the coating is conducted to minimise the interface stresses of coating with substrate in order to mitigate cracking and removal/spalling phenomena when exposed to temperature gradients and to increase their service life. These two different aspects are combined together to predict the coating stress field as a function of service time.

Deciphering the adaptive conformational evolution of dihydrophenazine derivatives in the confined space of a semi-rigid macrocyclic host

Exploring the conformational evolution of organic molecules is a long-pursuit theme in the field of chemistry. Herein, interests are endeavored to unveil the conformational evolution of conformationally flexible dihydrophenazines with environment-sensitive and continuously-changeable fluorescence in the confined space exerted by the semi-rigid macrocyclic host ExBox4+. Co-crystals of the ExBox4+ and dihydrophenazines are obtained via vapor diffusion, facilitating direct clarification of the structural variations of the host and guests. The adaptive ground-state conformational evolution of the guests is fully deciphered via 1H NMR titration, crystallography analysis as well as systematic theoretical calculations. In contrast to the much smaller structural change of the well-noted conformationally adaptive host, the conformational variation in the central dihedral angle of the guest can be up to 22° in the crystal of the host-guest complex, which is completely different from the cases when ExBox4+ interacting with the rigid guests. Dynamic information encryption has been further achieved by harnessing the distinct fluorescence behaviors before and after host-guest complexation. This work not only provides new insights into the understanding of mutual interactions between a semi-rigid host and conformationally flexible guests, but also offers an alternative scheme for advanced information encryption based on the luminescent host-guest complexes.

Single ammonia droplet combustion in a high-pressure environment in microgravity

Since ammonia is a carbon neutral fuel, it is expected to be widely utilized in the near future. Although there have been many researches on ammonia combustion, no research has been conducted on ammonia droplet combustion, which is a fundamental research on spray combustion, because ammonia is in a gaseous state at room temperature and atmospheric pressure. This study investigated the combustion characteristics of single ammonia droplets in microgravity for the first time. Single ammonia droplets were formed in high pressure air and were successfully ignited in microgravity. In an early stage of burning, the droplet vaporized with an almost constant vaporization rate of 0.87–1.0 mm2/s. After such a quasi-steady period, the vaporization rate decreased over time. In accordance with the decrease in the vaporization rate, the flame standoff ratio also decreased over time. After that, the droplet exhibited unique phenomena such as droplet disruption, puffing, or droplet re-expansion although the fuel was initially pure. These types of unique behavior are caused by the diffusion of water vapor, a combustion product, to the droplet surface, and dissolution and accumulation of water on the droplet surface. Since water has a lower volatility than ammonia, the concentration of dissolved water at the droplet surface increases rapidly as the droplet diameter decreases. As a result, the vaporization of ammonia is suppressed and the flame standoff ratio decreases. Additionally, as the water concentration at the droplet surface increases, the boiling point at the droplet surface also increases, resulting in superheating of the liquid ammonia and homogeneous bubble nucleation. The growth of bubbles caused droplet disruption, puffing, and droplet re-expansion.

The Effect of Packaging Type on The Shelf Life of Fresh Bread Premix Flour Based on Modified Flour

Ready-to-use flour products or premixes consist of several components of flour ingredients that are put together. This study aims to determine the quality of the effect of packaging type on the shelf life of the resulting premix flour. This study used modified rice, namely pre-cooked rice and germinated rice. The results showed that after the premix flour storage test, the shelf life of fresh bread premix flour stored using PP (Polypropylene) packaging at RH 65, 70, 75, and 80% was 0.6 years. While the product stored using HDPE (high-density polyethylene) packaging was 0.4 years at RH 65, 70, 75, and 80%. Meanwhile, white bread premix flour that uses aluminium foil packaging at the same RH, which is 65-80%, has a shelf life of 3.2 years. This is because the higher the RH of storage, the greater the pressure difference between the inside and outside of the packaging. The greater the difference in air pressure outside and inside the package, the greater the increase in the rate of diffusion of water vapor from the environment to the food product. This study shows that 65% RH is ideal for storing white bread premix flour because it has a longer shelf life.

Periodically-Poled Lithium Tantalate Ridge Waveguides for Efficient Nonlinear Frequency Conversion in the Near UV

Optical damage resistant ridge waveguides for blue and near UV wavelengths have been fabricated using high-temperature Zr and Zn diffusion doping and vapor transport equilibration (VTE) of congruent LiTaO3 crystals. For both dopants high optical damage thresholds >10 MW/cm2 for 532 nm light were demonstrated at room temperature, which can be increased by a factor ~3 when heating the samples to ~150°C. Ridge waveguides with low optical losses of ~0.4 dB/cm were fabricated using diamond-blade dicing. First-order periodic poling with grating periods of ~3 μm can be used for efficient nonlinear frequency conversion for both SHG (800 nm pump) or SPDC (400 nm pump) processes.

Model of non-stationary non-isothermal diffusion of corrosion inhibitors in polymeric film

Efficiency of film compositions with a complex of inhibitors at protection of equipment against corrosion is shown. The leading role of diffusion in formation of a protective layer on a substrate is revealed. Relevance of development of model of diffusion of inhibitors of corrosion to a substrate at the expense of the most hostile environment is proved. The specified model will provide calculation of concentration of inhibitor for various types of hostile environment (alkaline, acid) and establishment of necessary thermodynamic characteristics of a polymeric basis. The film on the basis of latex DMMA containing contact and flying water-soluble inhibitors of corrosion was investigated. Methyl Methacrylate latex belongs to the hydrophilic polymers differing in abnormal diffusion. Speed of diffusion of vapors of water through latex films up to 3 mm thick is experimentally established. Assumptions are entered and the mathematical model of an element of a polymeric film added with entry and boundary conditions according to service conditions is developed. Experimental values of the functions describing diffusion of water and inhibitor approximated the bicubic interpolation polynomial realized by standard algorithm of MatLab library. The decision is carried out in a CFD package of modeling Comsol Multiphysics, at the same time the computing grid contained 2128 elements. It is defined that diffusion is complicated by the conformational transformations of macromolecules of a polymeric matrix directly depending on temperature. Change of coefficient of diffusion of a film at endurance in water owing to change of a conformational condition of macromolecules of a film from temperature is experimentally established. It is established that the current of the first minutes is established a gradient of temperatures which results in stationary value of medium-volume temperature of a film. Water diffusion as inertial process establishes a gradient of concentration with orientation of lines of current towards a zone of defect of a film on a substrate. The gradient of concentration of inhibitor grows more slowly, than concentration of water that is caused by initiation of formation of the "inhibitor + water" complex. In process of inhibitor exhaustion directly in a defect zone, its diffusion from the nearby intact areas is excited that raises a functional stock of an anticorrosive covering. Results of comparison of the data on quantitative structure of a polymeric film received experimentally and calculation for model are given, their convergence is shown.

Water vapor assisted aramid nanofiber reinforcement for strong, tough and ionically conductive organohydrogels as high-performance strain sensors.

Conductive organohydrogels have gained increasing attention in wearable sensors, flexible batteries, and soft robots due to their exceptional environment adaptability and controllable conductivity. However, it is still difficult for conductive organohydrogels to achieve simultaneous improvement in mechanical and electrical properties. Here, we propose a novel "water vapor assisted aramid nanofiber (ANF) reinforcement" strategy to prepare robust and ionically conductive organohydrogels. Water vapor diffusion can induce the pre-gelation of the polymer solution and ensure the uniform dispersion of ANFs in organohydrogels. ANF reinforced organohydrogels have remarkable mechanical properties with a tensile strength, stretchability and toughness of up to 1.88 ± 0.04 MPa, 633 ± 30%, and 6.75 ± 0.38 MJ m-3, respectively. Furthermore, the organohydrogels exhibit great crack propagation resistance with the fracture energy and fatigue threshold as high as 3793 ± 167 J m-2 and ∼328 J m-2, respectively. As strain sensors, the conductive organohydrogel demonstrates a short response time of 112 ms, a large working strain and superior cycling stability (1200 cycles at 40% strain), enabling effective monitoring of a wide range of complex human motions. This study provides a new yet effective design strategy for high performance and multi-functional nanofiller reinforced organohydrogels.

Evaluation method for hygrothermal performance of masonry rendering mortars: Assessing moisture and mould growth risk under brazilian climate conditions

The presence of moisture in environments, when it exceeds certain limits and is associated with specific temperature ranges, can promote the growth of mould fungi inside buildings, compromising the health of occupants and leading to other harmful pathological manifestations affecting building performance. In this context, rendering mortars with paint application show significant potential to mitigate moisture ingress into building walls. This study aims to analyse normative trends related to criteria for water absorption by capillarity and resistance to vapour diffusion in masonry rendering mortars in Brazil. Additionally, we sought to identify gaps in existing standards and propose recommendations to enhance the suitability of rendering materials to the diverse climatic conditions found in the country. In this context, the results of the analysis of the hygrothermal behaviour of a wall rendering system are presented in this paper. The analysis, conducted through computational simulations, considered the climatic conditions of select Brazilian cities. Despite advancements in Brazilian standards, there are still gaps in existing norms regarding standardised criteria that allow for better selection of materials with performance compatible with their climatic context. The criteria outlined and the computational simulation method used were relevant in evaluating rendering materials under selected climatic conditions and have the potential to contribute to the development of more effective guidelines for the construction sector in Brazil.

Durability of concrete assessed via different unsaturated and steady-flow methods

Recently, there is a growing interest in how to decrease the environmental impact of concrete and to increase its durability. As concrete is mostly unsaturated during its service life, measuring unsaturated flow (through imbibition or diffusion) can provide information to assess its durability. Additionally, permeability values are often used to describe concrete’s ability to withstand the ingress of aggressive agents. However, it is not known whether the measured performance is representative of service-life behavior. In this research, the results obtained via two unsaturated flow methods (imbibition and diffusion) and two permeability tests (CEMBUREAU and Torrent method) were compared. In order to do this, 6 concrete mixes with 3 different cement types (CEM I, CEM II and CEM III) and two water to cement (w/c) ratios (0.4 and 0.7), were tested after 28 days of curing. Capillary imbibition was tested on specimens with a diameter of 100 mm and a height of 100 mm for a duration of 1 month. Furthermore, water vapour diffusion through the concrete was measured using the cup method, which consists of creating a moisture gradient by using a hygroscopic salt, with a concrete slice as a barrier. The results showed that for concrete with a w/c of 0.4 all test methods indicated that CEM III performed worse in comparison to CEM I and CEM II, which had a similar performance. However, for a w/c of 0.7, CEM III performed superior in comparison to CEM I and CEM II in the capillary imbibition test and the water vapour diffusion. This can possibly be explained by an increased tortuosity in the CEM III mix. In the gas permeability tests, CEM III performed worse compared to CEM I and CEM II.

An unexpected imidazole-induced porphyrinylphosphonate-based MOF-to-HOF structural transformation leading to the enhancement of proton conductivity.

Post-synthetic modification of proton-conducting metal-organic frameworks (MOFs) by loading small molecules capable of generating protons into pores is an efficient approach for developing a new type of material with improved ionic conductivity. Herein, the synthesis, characterization and proton conductivity of a novel electroneutral MOF based on palladium(II) meso-tetrakis(4-(phosphonatophenyl))porphyrinate, IPCE-1Pd, are reported. The exposure of the obtained framework to imidazole by the diffusion vapor method has surprisingly led to its complete crystal-to-crystal MOF-to-HOF transformation, resulting in the formation of a novel hydrogen-bonded organic framework (HOF) IPCE-1Pd_Im, which is the first example of such kind of structural change among all known MOFs. This modification has led to an almost 25-fold increase in the proton conductivity in comparison with the pristine MOF, reaching up to 6.54 × 10-3 S cm-1 at 85 °C and 95% relative humidity, which is one of the highest values among all known porphyrin-based HOFs.

Pal power: Demonstration of the functional association of the Helicobacter pylori flagellar motor with peptidoglycan-associated lipoprotein (Pal) and its preliminary crystallographic analysis.

The bacterial flagellar motor is a molecular nanomachine, the assembly and regulation of which requires many accessory proteins. Their identity, structure and function are often discovered through characterisation of mutants with impaired motility. Here, we demonstrate the functional association of the Helicobacter pylori peptidoglycan-associated lipoprotein (HpPal) with the flagellar motor by analysing the motility phenotype of the ∆pal mutant, and present the results of the preliminary X-ray crystallographic analysis of its globular C-terminal domain HpPal-C. Purified HpPal-C behaved as a dimer in solution. Crystals of HpPal-C were grown by the hanging drop vapour diffusion method using medium molecular weight polyethylene glycol (PEG) Smear as the precipitating agent. The crystals belong to the primitive orthorhombic space group P1 with unit cell parameters a = 50.7, b = 63.0, c = 75.1 Å. X-ray diffraction data were collected to 1.8 Å resolution on the Australian Synchrotron beamline MX2. Calculation of the Matthews coefficient (VM=2.24 Å3/Da) and molecular replacement showed that the asymmetric unit contains two protein subunits. This study is an important step towards elucidation of the non-canonical role of H. pylori Pal in the regulation, or function of, the flagellar motor.

Synthesis of Long Alkyl and Fluoroalkyl Substituted Siloxane Copolymers for the Water Repellency of Rammed Earth Walls.

Rammed earth in a built environment has vapor diffusion characteristics and humidity control abilities, each of which is respectively attributed to the porous structures and the hydrophilic properties. Indeed, these structures and properties allow for the easy absorbance of water particles, hence affecting the durability of a rammed earth wall. This paper presents the water-repellency method for rammed earth walls, which utilizes siloxane copolymers containing fluorine. The water-repellent properties are investigated by measuring the contact angle, water absorption rate, and compressive strength after spray-coating with the synthesized siloxane copolymers on the surface of the rammed earth specimens under study. The water contact angle of the specimen, coated with a siloxane copolymer containing 10 mol.% of a silane monomer with a fluorine group, is about 140°. The water absorption of the specimen obtained after immersing in water for 24 h is low, at about 3.5 wt.%. In addition, the compressive strength remains more than 80% of the corresponding strength of the specimen which is not immersed in water. It is confirmed that the use of a 10% by volume of the siloxane copolymer containing the fluorine group may enhance the water-repellent performance and economic competitiveness.