Pore Hydration Research Articles

Luminescent properties of nanocomposite - Bi12SiO20, filled with C6H9EuO6 × H2O

The work presents the results of the study of the photoluminescence spectra of the (111) growth surface of an opal - Bi12SiO20 matrix nanocomposite filled with europium (III) acetate hydrate (C6H9EuO6 × H2O). An increase in the integral luminescence intensity of the matrix composite opal - Bi12SiO20: Eu3+ compared to composite opal: Eu3+ was found. The measured photoluminescence spectra of the Bi3+ ions in the opal pores indicate its participation in optical processes as a co-activator of luminescence. A change in the character of the splitting of the main luminescence bands of Eu3+ ions in the region of 575–635 nm and the integral luminescence intensity after dehydration of the crystalline hydrate in opal pores has been established.

Micromechanical tests of tetrahydrofuran hydrate using atomic force microscope

<p indent="0mm">The mechanical properties of micro- or nano-scale hydrate are of great significance to reveal the interaction between hydrate and sediment skeleton in pores under the external loads and to evaluate the macroscopic mechanical behavior of hydrate deposits in nature. In this paper, the tetrahydrofuran (THF) hydrate samples are analyzed by the atomic force microscope and the silica (SiO₂) microspheres colloidal probe with a diameter of 5 μm. The relationship between the press-in depth, contact time, and contact force is obtained at the temperature in the range from −30°C to −10°C and at driving speed of 0.5–20 μm/s. The adhesion force between SiO₂ microsphere and THF hydrate is also measured. The result shows that the plastic deformation of the THF hydrate occurs during the indentation, and the phase transformation induced by the indentation can further enhance this plastic behavior. At the same temperature and contact force, a greater press-in depth was observed at a lower indentation rate or higher temperature. The THF hydrate exhibited greater plasticity and lower strength. The yield stress of the THF hydrate has a threshold, which can be one of the important reasons for strain hardening and strain softening of macroscopic hydrate sediments. According to the modified power-rate rheological (PLR) viscoelastic model, the viscoelasticity of a THF hydrate is significant at a low driving rate and relatively high temperature. The adhesion force between the microsphere and THF hydrate was caused by the liquid-like layer and decomposed liquid on its surface, and it was 1.1–2.5 μN, which was closely related to the contact area before they separated.

Study of hydrate occupancy, morphology and microstructure evolution with hydrate dissociation in sediment matrices using X-ray micro-CT

Abstract Hydrate occupancy, morphology and spatial distribution in sediment pore can significantly affect the physical properties of hydrate-bearing sediment, but their evolutions with hydrate dissociation under various brine saturations are not well understood. X-ray micro-CT is employed to image the pore-scale dynamic process of methane hydrate dissociation in both sediments with different brine saturations. On the basis of processing and statistical analysis of X-ray CT images, several topological parameters, including volume, shape factor, fractal dimension and Euler characteristic of individual hydrate cluster, are selected to quantify hydrate occupancy, morphology and microstructure evolution with hydrate dissociation in the host sediments. Results show that the degree of brine saturation within the sediments can exert a significant impact on hydrate pore occupancy, morphology and microstructure connectedness during hydrate dissociation. In contrary to those of fully brine-saturated sediment, the topological parameters of individual hydrate cluster usually experience more dramatic changes with hydrate dissociation in partially brine-saturated sediment. It is inferred that in partially brine-saturated sediment the isolated hydrate clusters occupying in pore bodies are dissociated earlier in the initial experimental stage, and the dissociation of interpore hydrate frameworks interconnected through pore throats get dominated when hydrate saturation declines below a critical threshold value. On the other hand, in fully brine-saturated sediment the kinetics of pore-scale hydrate dissociation exhibit a completely opposite trend.

A state-dependent constitutive model for methane hydrate-bearing sediments inside the stability region

The presence of methane hydrate in soil pores alters the stress–strain and volumetric behaviour of soil. The extent of this alteration is affected by initial temperature and pore pressure when hydrate is formed inside the thermodynamically stable region. In this paper, a state-dependent critical state model is developed for methane hydrate-bearing sediments (MHBS) within the theoretical framework of bounding surface plasticity. A phase parameter is newly introduced into the constitutive model to account for the coupled effects of temperature and pore pressure on the mechanical behaviour of MHBS. This unique feature of the proposed model enables it to capture the behaviour of MHBS inside the methane hydrate stability region. A non-associated flow rule is adopted and a modified dilatancy expression is proposed considering the degree of hydrate saturation, phase parameter and stress state of MHBS. To verify the new model, computed results are compared to measured results of drained triaxial tests on MHBS with different morphologies and at different effective confining stresses, degrees of hydrate saturation and phase states inside the stability region. The comparison reveals that the model is capable of capturing the key features such as the evident strain-softening behaviour due to hydrate degradation and the change in stress–strain and volumetric behaviour of MHBS at different initial conditions inside the stability region.

Hydrate dissociation conditioned to depressurization below the quadruple point and salinity addition

Techniques have been developed to evaluate the hydrate dissociation behaviour in a brine system by reducing pressure below the quadruple point. Experimentally, hydrate with low initial pressure and temperature is dissociated by a deep depressurization method (DDM) in a one-dimensional (1D) model to evaluate the gas and water production. Theoretically, simulation techniques have been developed to determine the two-phase relative permeability, permeability variation, intrinsic hydrate reaction constant by piecewisely fitting the experimental measurements with consideration of the temperature depression induced by NaCl. Subsequently, the existing semi-empirical permeability reduction models are compared with the simulated average permeabilites to identify the occurrence of hydrate in pores. It is shown from experiments that salinity enhances the potential of gas recovery by enhancing the dissociation driving force (i.e., increasing equilibrium pressure and decreasing equilibrium temperature). Temperature decreases almost in a constant rate at sensible heat dominant stages, while, after reaching the freezing point, it is decreased lowly and even recovered slightly due to heat conduction from boundary and ice fusion. By approximating the energy contributions, it is found that sensible heat is supplied for hydrate dissociation at the initial stage and that heat conduction from boundary and ice fusion accelerates hydrate dissociation at the final stage. It is concluded that the salinity lowers the freezing point from −1.7 to −1.3 °C in the experiment. For numerical simulation, the newly developed dissociation model is found to be able to not only identify fluid flow mechanisms and kinetic hydrate dissociation, but also reproduce ice fusion. With hydrate dissociation and water production, salinity continuously decreases and finally becomes less than its initial value. The Kozeny grain center-filling model is found to be able to capture the permeability variation, implying that hydrate tends to be pore filling dominant in the experiments. The fluid flow and hydrate dissociation kinetics are found to play a dominant role above the freezing point, while, below the freezing point, the significance of heat conduction from boundary and ice fusion is enhanced during the experiments.

Unifying photocycle model for light adaptation and temporal evolution of cation conductance in channelrhodopsin-2

Although channelrhodopsin (ChR) is a widely applied light-activated ion channel, important properties such as light adaptation, photocurrent inactivation, and alteration of the ion selectivity during continuous illumination are not well understood from a molecular perspective. Herein, we address these open questions using single-turnover electrophysiology, time-resolved step-scan FTIR, and Raman spectroscopy of fully dark-adapted ChR2. This yields a unifying parallel photocycle model integrating now all so far controversial discussed data. In dark-adapted ChR2, the protonated retinal Schiff base chromophore (RSBH+) adopts an all-trans,C=N-anti conformation only. Upon light activation, a branching reaction into either a 13-cis,C=N-anti or a 13-cis,C=N-syn retinal conformation occurs. The anti-cycle features sequential H+ and Na+ conductance in a late M-like state and an N-like open-channel state. In contrast, the 13-cis,C=N-syn isomer represents a second closed-channel state identical to the long-lived P480 state, which has been previously assigned to a late intermediate in a single-photocycle model. Light excitation of P480 induces a parallel syn-photocycle with an open-channel state of small conductance and high proton selectivity. E90 becomes deprotonated in P480 and stays deprotonated in the C=N-syn cycle. Deprotonation of E90 and successive pore hydration are crucial for late proton conductance following light adaptation. Parallel anti- and syn-photocycles now explain inactivation and ion selectivity changes of ChR2 during continuous illumination, fostering the future rational design of optogenetic tools.

Pore habit of methane hydrate and its evolution in sediment matrix – Laboratory visualization with phase-contrast micro-CT

Abstract Describing the pore habit of methane hydrate in sediment matrices is essential for understanding natural distribution of methane hydrate, methane trace (transport and solidification) in the hydrate stability zone, physical properties of hydrate-bearing sediments, and the associated influence on potential gas production. Pore habit visualization in natural media at pore scale even with laboratory synthesized cores has been challenging due to the similar densities of methane hydrate from pore liquid. In this work, we used phase-contrast assisted micro-CT with potassium iodine-doped brine to visualize four phases: sand particles, pore fluid, methane hydrate and methane gas. This study visualizes the pore habit of methane hydrate at various stages including during hydrate formation in excess-gas systems, its evolution after brine injection to replace pore fluid, and hydrate formation in excess-water systems. Hydrate tends to adopt round and smooth surfaces when in contact with water while exhibits relatively angular interfaces when in contact with methane gas. Hydrate formation in excess-gas systems results in a partial cementing and partial mineral-coating pore habit, while hydrate in excess-water systems develops mainly as pore-filling, and locally cementing or mineral-coating where big gas pockets exist at the initial state. Pore liquid replacement from methane gas to brine triggers a shift of hydrate pore habit towards pore-filling. Methane hydrate evolution over time produces bigger hydrate particles but with less contact area with sand particles. The effects of hydrate pore habit become less important as hydrate particle size exceeds the pore size. Additionally, hydrate formation could trap residual methane gas and brine as inclusions.

Membrane‐Facilitated Allosteric Modulation of GABAA Receptor by Farnesol: An In Silico Modeling and Simulation Study

ObjectiveGABAA receptors (GABAARs) are ligand‐gated ion channels that can be activated by γ‐aminobutyric acid (GABA) and allosterically modulated by several antiepileptic drugs and endogenous neurosteroids. Using electrophysiology (patch‐clamp) and HEK cells expressing human α1β3γ2 GABAARs, our team demonstrated positive allosteric receptor modulation (PAM) by farnesol, an endogenous isoprenol. Furthermore, farnesol attenuated seizures in vivo using mouse models of GABAAR‐dependent seizures. Here, we present a computational study that provides a structural basis for the observed farnesol‐mediated allosteric modulation of GABAARs and illustrates the plausible role of membrane in facilitating access and binding of the ligand.MethodsThe membrane partitioning of farnesol were investigated in dimyristoyl phosphatidylcholine model membrane system by steered molecular dynamics (MD) and Umbrella Sampling simulations using NAMD2.12 software. To investigate farnesol's PAM mechanism, we initially constructed a computerized heteropentameric model of the human α1β3γ2 GABAAR in which two GABA molecules were sequentially docked to the extracellular orthosteric sites at the β+α‐interfaces. Subsequently, we used this GABA‐docked model to build two additional models: 1) farnesol docked at the transmembrane lipid‐facing neurosteroid‐binding site, and 2) 10 mol% farnesol molecules placed randomly in the bulk membrane around the receptor. The energetically favorable location and orientation of farnesol within the bilayer suggested the neurosteroid binding site as a potential allosteric site. Each model was subjected to 1 μs all‐atom MD simulations totaling 3 μs.ResultsThe mechanism of channel activation by farnesol was characterized by examining dynamic structural variables including global twisting of the channel, tilting of the extracellular domain, and configuration of the ion pore including pore radius, hydration status, and electrostatic potential. We observed the channel pore opening associated with an increased flux of water molecules and pore hydration that supports the conductance (or open state) of GABAAR with farnesol docked to the neurosteroid‐binding site. Remarkably, in the bulk simulation with multiple ligand molecules around the receptor, one of the farnesol molecules reached the neurosteroid binding site via lateral diffusion followed by binding in a configuration identical to the docking simulation. The membrane interactions of farnesol seemed to play an apparent role in its access and binding.ConclusionsThis study provides a structural basis for the positive allosteric modulation of the GABAAR by farnesol in atomistic details consistent with both in vitro and in vivo data. This structural and dynamic model for the PAM of GABAAR may benefit the design of novel therapeutics targeting transmembrane allosteric sites of the GABAAR in both health and disease.Support or Funding InformationNational Institutes of Health – R15GM13129This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Tracking Pore Hydration in Channelrhodopsin by Site-Directed Infrared-Active Azido Probes.

In recent years, gating and transient ion-pathway formation in the light-gated channelrhodopsins (ChRs) have been intensively studied. Despite these efforts, a profound understanding of the mechanistic details is still lacking. To track structural changes concomitant with the formation and subsequent collapse of the ion-conducting pore, we site-specifically introduced the artificial polarity-sensing probe p-azido-l-phenylalanine (azF) into several ChRs by amber stop codon suppression. The frequently used optogenetic actuator ReaChR (red-activatable ChR) exhibited the best expression properties of the wild type and the azF mutants. By exploiting the unique infrared spectral absorption of azF [νas(N3) ∼ 2100 cm-1] and its sensitivity to polarity changes, we monitored hydration changes at various sites of the pore region and the inner gate by stationary and time-resolved infrared spectroscopy. Our data imply that channel closure coincides with a dehydration event occurring between the interface of the central and the inner gate. In contrast, the extracellular ion pathway seems to be hydrated in the open and closed states to similar extents. Mutagenesis of sites in the inner gate suggests that it acts as an intracellular entry funnel, whose architecture and composition modulate water influx and efflux within the channel pore. Our results highlight the potential of genetic code expansion technology combined with biophysical methods to investigate channel gating, particularly hydration dynamics at specific sites, with a so far unprecedented spatial resolution.

Thermal Conductivity of Frozen Sediments Containing Self-Preserved Pore Gas Hydrates at Atmospheric Pressure: An Experimental Study

The paper presents the results of an experimental thermal conductivity study of frozen artificial and natural gas hydrate-bearing sediments at atmospheric pressure (0.1 MPa). Samples of hydrate-saturated sediments are highly stable and suitable for the determination of their physical properties, including thermal conductivity, due to the self-preservation of pore methane hydrate at negative temperatures. It is suggested to measure the thermal conductivity of frozen sediments containing self-preserved pore hydrates by a KD-2 needle probe which causes very little thermal impact on the samples. As shown by the special measurements of reference materials with known thermal conductivities, the values measured with the KD-2 probe are up to 20% underestimated and require the respective correction. Frozen hydrate-bearing sediments differ markedly in thermal conductivity from reference frozen samples of the same composition but free from pore hydrate. The difference depends on the physical properties of the sediments and on changes in their texture and structure associated with the self-preservation effect. Namely, it increases proportionally to the volumetric hydrate content, hydrate saturation, and the percentage of water converted to hydrate. Thermal conductivity is anisotropic in core samples of naturally frozen sediments that enclose visible ice-hydrate lenses and varies with the direction of measurements with respect to the lenses. Thermal conductivity measurements with the suggested method provide a reliable tool for detection of stable and relict gas hydrates in permafrost.

Conformational transitions of the serotonin 5-HT3 receptor.

The serotonin 5-HT3 receptor is a pentameric ligand-gated ion channel (pLGIC). It belongs to a large family of receptors that function as allosteric signal transducers across the plasma membrane1,2; upon binding of neurotransmitter molecules to extracellular sites, the receptors undergo complex conformational transitions that result in transient opening of a pore permeable to ions. 5-HT3 receptors are therapeutic targets for emesis and nausea, irritable bowel syndrome and depression3. In spite of several reported pLGIC structures4-8, no clear unifying view has emerged on the conformational transitions involved in channel gating. Here we report four cryo-electron microscopy structures of the full-length mouse 5-HT3 receptor in complex with the anti-emetic drug tropisetron, with serotonin, and with serotonin and a positive allosteric modulator, at resolutions ranging from 3.2 Å to 4.5 Å. The tropisetron-bound structure resembles those obtained with an inhibitory nanobody5 or without ligand9. The other structures include an 'open' state and two ligand-bound states. We present computational insights into the dynamics of the structures, their pore hydration and free-energy profiles, and characterize movements at the gate level and cation accessibility in the pore. Together, these data deepen our understanding of the gating mechanism of pLGICs and capture ligand binding in unprecedented detail.

The voltage-dependence of MscL has dipolar and dielectric contributions and is governed by local intramembrane electric field

Channels without canonical voltage sensors can be modulated by voltage acting on other domains. Here we show that besides protein dipoles, pore hydration can be affected by electric fields. In patches, both WT MscL and its V23T mutant show a decrease in the tension midpoint with hyperpolarization. The mutant exhibits a stronger parabolic dependence of transition energy on voltage, highly consistent with the favourable dielectric contribution from water filling the expanding pore. Purified V23T MscL in DPhPC droplet interface bilayers shows a similar voltage dependence. When reconstituted in an asymmetric DOPhPC/DPhPC bilayer carrying a permanent bias of ~130 mV due to a dipole potential difference between the interfaces, the channel behaved as if the local intramembrane electric field sets the tension threshold for gating rather than just the externally applied voltage. The data emphasize the roles of polarized water in the pore and interfacial lipid dipoles in channel gating thermodynamics.

Burial-driven methane recycling in marine gas hydrate systems

Natural gas hydrate may be buried with sediments until it is no longer stable at a given pressure and temperature, resulting in conversion of hydrate into free gas. This gas may migrate upward and recycle back into the hydrate stability zone to form hydrate. As of yet, however, no quantitative description of the methane recycling process has been developed using multiphase flow simulations to model burial-driven gas hydrate recycling. In this study, we present a series of 1D multiphase transport simulations to investigate the methane recycling process in detail. By invoking the effects of capillary phenomena on hydrate and gas formation in pores of varying size, we find that a free gas phase can migrate a significant distance above the bulk base of hydrate stability. Since the top of the free gas occurrence is often identified as the base of the hydrate stability zone from seismic data, our results demonstrate that not only could this assumption mischaracterize a hydrate system, but that under recycling conditions the highest hydrate saturations can occur beneath the top of the free gas occurrence. We show that the presence of pore size distributions requires a replacement zone through which hydrate saturations progressively decrease with depth and are replaced with free gas. This replacement zone works to buffer against significant gas buildup that could lead to fracturing of overlying sediments. This work provides a framework for simulating flow and transport of methane within the 3-phase stability zone from a mass conservation perspective.

Permeability variation and anisotropy of gas hydrate-bearing pressure-core sediments recovered from the Krishna–Godavari Basin, offshore India

Abstract Permeability measurements were conducted on gas hydrate-bearing pressure-core sediments recovered from the Krishna–Godavari Basin during India's National Gas Hydrate Program Expedition 02. Pressure cores collected in the deep seabed of the Indian Ocean were cut and stored under high pressure and low temperature on the D/V Chikyu using pressure core analyzing tools. A total of 25, 1.2-m storage chambers were transferred to Japan from India for pressure core studies using pressure-core analysis tools at the National Institute of Advanced Industrial Science and Technology. The sediment core's pressure and temperature were maintained within the hydrate stability conditions during the entire process of transfer and loading into a triaxial testing apparatus called TACTT to preserve the hydrate, which can simulate the in-situ effective stress state under triaxial conditions. The hydrate saturation of the samples was in the range of 50–90%. It was found that the initial effective water permeability was in range of 0.01 mD to tens of mD, depending on the hydrate saturation and the mean particle size of the host sediment. The hydrate pore space morphology is also a critical factor, and results suggest hydrates are forming in the pore centers of sand grains as pore filling, but also as a sediment grain coating. In a first for gas hydrate-bearing pressure cores, the permeability anisotropy was established via vertical and horizontal flow tests combined with a pore fluid flow simulation. The horizontal/vertical permeability ratio was found to be 4. Additionally, the effective stress dependency of permeability was investigated by performing flow tests at different effective stresses. Due to decreasing porosity and particle crushing, the permeability dropped by approximately 90% for an effective stress increase of 10 MPa.

Surface area controls gas hydrate dissociation kinetics in porous media

This study integrates X-ray radiography and 3D computed tomography (CT) to measure xenon hydrate dissociation kinetics in a porous medium (sand) through depressurization at the quasi-isothermal condition. Before dissociation, we use X-ray CT to measure hydrate volume and surface area in the sand and find [hydrate volume]2/3 is a linear approximation of hydrate surface area regardless of differences in hydrate specific area. During dissociation, we use X-ray radiography to quantify the evolutions of hydrate volume and dissociation rate. We find [hydrate volume]2/3 (i.e., hydrate surface area) is a linear metric of hydrate dissociation rate. Additionally we observe two circumstances when dissociate rate is not linear with [hydrate volume]2/3. First, above a critical hydrate saturation of 35–45%, hydrate dissociation rate initially stays constant and then decreases with [volume]2/3. Second, the dissociation rates of patchy hydrates in large pores initially stay constant and are significantly slower than hydrates in small pores with the same sizes. Since methane hydrates in nature are patchy and heterogeneously distributed, the new knowledge will facilitate modeling of hydrates production with a simple metric of dissociation rate (i.e., [volume]2/3) and constraints of hydrate saturation and pore size.

Mapping the functional anatomy of Orai1 transmembrane domains for CRAC channel gating

Store-operated Orai1 channels are activated through a unique inside-out mechanism involving binding of the endoplasmic reticulum Ca2+ sensor STIM1 to cytoplasmic sites on Orai1. Although atomic-level details of Orai structure, including the pore and putative ligand binding domains, are resolved, how the gating signal is communicated to the pore and opens the gate is unknown. To address this issue, we used scanning mutagenesis to identify 15 residues in transmembrane domains (TMs) 1-4 whose perturbation activates Orai1 channels independently of STIM1. Cysteine accessibility analysis and molecular-dynamics simulations indicated that constitutive activation of the most robust variant, H134S, arises from a pore conformational change that opens a hydrophobic gate to augment pore hydration, similar to gating evoked by STIM1. Mutational analysis of this locus suggests that H134 acts as steric brake to stabilize the closed state of the channel. In addition, atomic packing analysis revealed distinct functional contacts between the TM1 pore helix and the surrounding TM2/3 helices, including one set mediated by a cluster of interdigitating hydrophobic residues and another by alternative ridges of polar and hydrophobic residues. Perturbing these contacts via mutagenesis destabilizes STIM1-mediated Orai1 channel gating, indicating that these bridges between TM1 and the surrounding TM2/3 ring are critical for conveying the gating signal to the pore. These findings help develop a framework for understanding the global conformational changes and allosteric interactions between topologically distinct domains that are essential for activation of Orai1 channels.

Multistage Triaxial Tests on Laboratory‐Formed Methane Hydrate‐Bearing Sediments

AbstractA sound understanding of the geomechanical behavior of hydrate‐bearing sediments (HBSs) is essential not only for assessing reservoir and wellbore stability during methane gas production but also for projecting the impact of global warming on the stability of geological settings that contain hydrates. This study experimentally investigated the geomechanical responses of laboratory‐formed methane‐HBS to triaxial shearing under drained conditions. The hydrate pore habit formed in the sediments is noncontact‐cementing, which is different from contact‐cementing or grain‐coating hydrate pore habits formed when the excessive gas method is used. The multistage triaxial test method, which shears a single specimen under different confinements, was employed to examine its applicability in measuring geomechanical properties of the HBS. Conventional single‐stage triaxial tests were also performed to serve as baselines. The results show that both the strength and stiffness of HBS increase with increased hydrate saturation and confining stress. Shear dilatancy increases with increased hydrate saturation and decreased confining stress. The peak strength and peak/postpeak shear dilation measured using the multistage tests are comparable to those using the single‐stage tests. However, the stiffness measured in later stress stages in the multistage tests was enhanced by the stress‐strain history of earlier stages. Therefore, the multistage test offers an efficient way of measuring the strength and volumetric response of the HBS with a much smaller number of specimens than the single‐stage test. This benefits the geomechanical characterization of the HBS, as obtaining the pressure cores is extremely costly and preparing lab samples is usually sophisticated and time consuming.

Ostwald ripening changes the pore habit and spatial variability of clathrate hydrate

Clathrate hydrate is a solid crystalline compound that consists of water cages with trapped gas molecules. Methane hydrate in permafrost and marine sediments is estimated to contain 2 × 103 to 4 × 106 Gt of carbon, which makes it both a potential energy source and a liability to global warming. The transport and mechanical properties of hydrate bearing sediments (HBS), and therefore hydrate dissociation through depressurization, thermal stimulation, or CO2 injection, depend on hydrate pore habit and spatial distribution in sediments. However, the evolution of hydrate pore habit and spatial distribution in HBS are not well understood yet. Here we show experimental evidence of Ostwald ripening of gas hydrate crystals in pores and porous media. We find that (1) hydrate growth rate (under nearly isothermal conditions) versus the degree of overpressurization fits an Arrhenius-type equation, and (2) Ostwald ripening gradually changes hydrate pore habit from grain-attaching to pore-filling and increases hydrate saturation heterogeneity at both pore and core scales. The latter ultimately creates significant spatial variations of permeability and sediment strength. Our results provide insights into kinetics and pore-scale physics that determine the geophysical signature from HBS at various scales. Based on our findings of hydrate occurrence in both gas and gas-water interface, we argue that hydrate growth in natural HBS is not limited to the water liquid phase. Our observation of hydrate pore habit alteration by Ostwald ripening explains patchy saturation and heterogeneous distribution of hydrate in natural HBS, which gives physical insight to improve geophysical hydrate models in porous media.

Preparation of UHPC with Fly Ash Replaced by Rich-Silicon Iron Ore Tailing Powder

In order to raise up the the rate of multipurpose utilization of rich-silicon iron ore tailing (IOTP for short) and the preparation of ultra-high performance concrete(UHPC for short), the influence rules and mechanism of rich-silicon iron ore tailing powder replacing fly ash in UHPC were studied, the influences of different specific surface area and dosage of IOTP replacing fly ash on its strength and liquidity were tested. Moreover, the pore structure and hydration products morphology of UHPC were tested by MIP and SEM methods, respectively. The results show that when fly ash replaced by IOTP, the liquidity of UHPC will be increased. When alternative content of IOTP is less than 10%, proper specific surface area of IOTP can improve the strength and pore structure, it can get the best result when the alternative content is 5% and the specific surface area is 588m2/kg. However, when alternative content of IOTP is 15% or more, all of these properties of UHPC become worse. It proves that IOTP can be used in the preparation of UHPC and improve the properties of UHPC.

393 Evaluating Clinical Decisionmaking Using Inferior Vena Cava Ultrasound for IV vs PO Rehydration in Pediatric Emergency Department Patients With Suspected Dehydration

393 Evaluating Clinical Decisionmaking Using Inferior Vena Cava Ultrasound for IV vs PO Rehydration in Pediatric Emergency Department Patients With Suspected Dehydration