Moderate Pressure Range Research Articles

Exploration of AB3Si3 (A = Na/K/Rb/Cs) compounds under moderate pressure.

We discovered the composition of ternary AB3Si3 (A = Na/K/Rb/Cs) compounds in the moderate pressure range of 0-100 GPa using first-principles structural prediction and systematically analyzed their structures, stability, electronic and optical properties within the framework of density functional theory. The AB3Si3 compounds exhibit a diverse phase diagram, including nine structures that are selected based on formation energies, along with a known clathrate RbB3Si3 structure with Pm3̄n symmetry. All predicted phases are thermodynamically and dynamically stable within the studied pressure range. In particular, the KB3Si3 compound with a direct band gap of 1.0 eV is identified as a promising candidate for photovoltaic materials beyond silicon-based materials, among which boron atoms form a unique regular octahedral structure; in contrast, NaB3Si3 and RbB3Si3 compounds are shown to have metallicity. Our findings enrich crystal structures of alkali-metal borosilicides and provide valuable insights into their potential applications.

Validation of thermal–hydraulic system code improved by advanced drift-flux correlation using bundle data at moderate pressure conditions

The accurate prediction of the interfacial drag force is essential to predict the void fraction in a reactor core during the transient and accident phases of nuclear reactors. The key to accurate prediction is to provide reliable drift-flux parameters in calculating the interfacial drag force. The authors previously developed a drift-flux correlation to improve the interfacial drag force prediction accuracy under low-flow and low-pressure conditions. In the present study, the authors demonstrated the validity of the interpolation scheme at a moderate pressure range in the drift-flux correlation and quantified its uncertainty using the experimental data measured in a 5 × 5 rod bundle for the pressures of 0.25, 0.41, 2, 5, and 7 MPa at the multi-purpose Hitachi utility steam test leading facility (HUSTLE). The validated drift-flux correlation was implemented into the RELAP5/MOD3 code and numerical analyses were also performed to reproduce the HUSTLE experimental data. The numerical calculations using the modified RELAP5/MOD3 code showed improved prediction accuracy compared to the calculations by the original RELAP5/MOD3 with the Chexal-Lellouche correlation (e.g., EPRI correlation) in the tested pressure range. The uncertainty of the distribution parameter in the drift-flux correlation was estimated using the HUSTLE database. Next, a numerical analysis was done for the differential pressure in the reactor core in a small break LOCA integral test conducted with the ROSA/large scale test facility (LSTF) by the former Japan Atomic Energy Research Institute. This analysis showed that the predictions with the improved RELAP5/MOD3 agreed with the ROSA/LSTF data within the uncertainty at a 95 % confidence level. It was concluded that the improved RELAP5/MOD3 with the new drift-flux correlation could predict the water level of a reactor core during accident scenarios.

Effects of helium adsorption in carbon nanopores on apparent void volumes and excess methane adsorption isotherms

A void volume, which is measured by helium expansion tests and used in the calculation of methane adsorption amounts, is always overestimated due to helium adsorption. In this study, by comparing void volumes of carbon nanopores determined under different temperatures and pressures using GCMC (Grand Canonical Monte Carlo) simulation, suitable experimental conditions for helium expansion tests are obtained. Five volumes, including one apparent volume Vapp, three referred volumes Vref and one physical volume Vphy, are recognized. The apparent volume Vapp corresponds to the volume directly determined under traditional experimental conditions, while three referred volumes are determined at 500 K with different pressure ranges (low, moderate, high). The physical volume is calculated by multiplying a pore width and a surface area. Besides, a volume determined by using a helium probe is named an accessible volume Vacc and used as a criterion for a determined volume through mass balance. It is found that use of a void volume determined under traditional experimental conditions or a physical volume leads to negative adsorption amounts at high pressures. Considering an economic effect and measurement accuracy, determining a void volume by helium expansion tests within a moderate pressure range at 500 K is suggested. Excess isotherms of methane calculated by the suggested volume are more appropriate and of great physical meanings for further investigation of adsorption mechanisms.

Assessment of CO2 Adsorption Capacity under Moderate Pressure Range on Activated Carbon Produced from Coconut Endocarp

Assessment of CO₂ Adsorption Capacity under Moderate Pressure Range on Activated Carbon Produced from Coconut Endocarp

Tuning Optical and Electronic Properties in Low-Toxicity Organic-Inorganic Hybrid (CH3NH3)3Bi2I9 under High Pressure.

Low-toxicity, air-stable methylammonium bismuth iodide (CH3NH3)3Bi2I9 has been proposed as a candidate to replace lead-based perovskites as highly efficient light absorbers for photovoltaic devices. Here, we investigated the effect of pressure on the optoelectronic properties and crystal structure of (CH3NH3)3Bi2I9 up to 65 GPa at room temperature. We achieved impressive photoluminescence enhancement and band gap narrowing over a moderate pressure range. Dramatic piezochromism from transparent red to opaque black was observed in a single crystal sample. A structural phase transition from hexagonal P63/ mmc to monoclinic P21 at 5.0 GPa and completely reversible amorphization at 29.1 GPa were determined by in situ synchrotron X-ray diffraction. Moreover, the dynamically disordered MA+ organic cations in the hexagonal phase became orientationally ordered upon entering into the monoclinic phase, followed by static disorder upon amorphization. The striking enhancement of conductivity and metallization under high pressure indicate wholly new electronic properties.

Moderate pressure plasma source of nonthermal electrons

Plasma sources of electrons offer control of gas and surface chemistry without the need for complex vacuum systems. The plasma electron source presented here is based on a cold cathode glow discharge (GD) operating in a dc steady state mode in a moderate pressure range of 2–10 torr. Ion-induced secondary electron emission is the source of electrons accelerated to high energies in the cathode sheath potential. The source geometry is a key to the availability and the extraction of the nonthermal portion of the electron population. The source consists of a flat and a cylindrical electrode, 1 mm apart. Our estimates show that the length of the cathode sheath in the plasma source is commensurate (~0.5–1 mm) with the inter-electrode distance so the GD operates in an obstructed regime without a positive column. Estimations of the electron energy relaxation confirm the non-local nature of this GD, hence the nonthermal portion of the electron population is available for extraction outside of the source. The use of a cylindrical anode presents a simple and promising method of extracting the high energy portion of the electron population. Langmuir probe measurements and optical emission spectroscopy confirm the presence of electrons with energies ~15 eV outside of the source. These electrons become available for surface modification and radical production outside of the source. The extraction of the electrons of specific energies by varying the anode geometry opens exciting opportunities for future exploration.

Effects of textural and surface characteristics of metal-organic frameworks on the methane adsorption for natural gas vehicular application

In this work, methane adsorption and textural and surface characteristics of selected 46 microporous metal-organic frameworks and 6 other adsorbents were measured experimentally. The objective of this work is to identify either the most relevant characteristics or a combination of multiple properties, which will qualify a given sample to be a good methane uptake material in a moderate pressure range (up to 70 bar) and at 298 K. It is found that there is an overall linear tendency between maximum excess methane adsorption and BET specific surface area. The micropore volume correlates to the maximum excess methane adsorption as well, irrespective of the chemistry and functionalities of materials. In addition, micropore size distribution has an impact on methane uptake. When considering the total methane uptake, special attention should be paid to the effect from packing density. The evaluation also focuses on the discussion of deliverable capacity and concludes that optimal adsorption enthalpy is desired to avoid large amount of methane retained at the minimum desorption pressure in practical vehicular applications.

Pressure-induced superconductivity and its scaling with doping-induced superconductivity in the iron pnictide with skutterudite intermediary layers.

Pressure-induced superconductivity is oberserved in Ca10(Pt3As8)(Fe2As2)5 by in situ high-pressure resistance and magnetic susceptibility measurements. Scaling of the pressure-induced and doping-induced superconductivity shows that the electronic phase diagrams of the pressurized and chemically doped 10–3–8 compound are similar in the moderate pressure and doping range but are disparate at higher pressure and heavy doping.

A model used for Hugoniot prediction of material at high-temperature along isobaric path

A model was derived in this paper to calculate the high-temperature Hugoniot of solid material along isobaric path by using an enthalpy-based equation of state (EOS) model. It provides a way and complements the Mie-Grüneisen EOS for studying high-temperature Hugoniot of materials. The Hugoniot of tungsten at 1223 K in moderate pressure range (0–10 GPa) and the Hugoniot of molybdenum at 1673 K in high pressure range (10∼300 GPa) were calculated using the presented model. The calculated results fit in with the literature data. The model can satisfactorily predict the Hugoniot of solid at high temperature over a wide pressure range. The model was also extended to predict the Hugoniot of porous materials with high initial temperature along isobaric path; and the Hugoniots of multi-component solids and porous materials at high temperature were also calculated combining with the pressure equilibrium method.

Pressure-sensing based on photothermally coupled operation of micromechanical beam resonator

Here, we demonstrate the pressure-sensing scheme based on the photothermal effect in the miniaturized beam resonator in the moderate pressure range. Since the resonance frequency of the small beam resonator under thermal stress can be easily modulated by the convective cooling of the gas molecules, the pressure change has been monitored by tracking the frequency shift under constant optical power. Our experimental measurements as well as the analytical model show that the described technique ensures the fast response to the external pressure variation with high responsivity as well as much sought-after scalability, desirable for many technological applications.

Development and performance evaluation of Proton Exchange Membrane (PEM) based hydrogen generator for portable applications

This paper presents the development of key components, specifications, configuration and operation characteristics of an 80 l/h Proton Exchange Membrane (PEM) water electrolyzer system for portable application. The developed PEM water electrolyzer can produce 80 l/h hydrogen (purity > 99.99%) with moderate pressure range up to 500 kPa (73 psi) at an operating current of 100 A with energy efficiency of 77.48%. The reliability in operation of developed PEM water electrolyzer system is tested for running the stack about 3000 h with 100 A current. The results indicate the reasonable stability of MEA fabrication and cell design method.

Nanoparticle interface driven microstructural evolution and crystalline phases of polypropylene: The effect of nanoclay content on structure and physical properties

Significant differences in the microstructure occur when the polypropylene matrix dispersed with 4 wt.% and 8 wt.% nanoclay. In neat polypropylene, α-crystals nucleate in the low to moderate crystallization pressure range of (∼0.1–60 MPa), while γ-phase nucleates at crystallization pressure of ∼60–200 MPa. In contrast to neat polypropylene, the presence of nanoclay in the polymer matrix, promotes the formation of γ-phase at ambient crystallization pressure of 0.1 MPa. Nanoclay and pressure-induced crystallization governs phase evolution and microstructure of polypropylene and is associated with change in the thermodynamic and physical properties such as equilibrium melting point and glass transition temperature. This change in equilibrium melting point and glass transition temperature points toward thermodynamic interaction between polymer-nanoparticle and nanoparticle interface-driven microstructural evolution. The dependence of equilibrium melting point on crystallization pressure and spherulite size on undercooling delineates two distinct regimes which are ascribed to dominant α- and γ-phases of polypropylene. However, the effect of nanoparticles is less dramatic when nanoclay content is increased from 4 wt.% to 8 wt.% implying that the effect maximizes at ∼4 wt.% nanoclay.

Phase Equilibria and Thermodynamic Properties of Some Branched Alkyl Ethers

The low-temperature heat capacity and thermodynamic properties of the solid-to-solid transition and fusion of di-isobutyl ether (DIBE) were determined by adiabatic calorimetry in the temperature range from (8 to 373) K. The saturation vapor pressure of DIBE was determined by a comparative ebulliometry over the moderate pressure range from (10.8 to 99.6) kPa. A density of liquid DIBE was measured in the temperature interval from (298 to 313) K using a quartz pycnometer. The normal boiling temperature, Tn.b., the enthalpy of vaporization at T = 298.15 K and Tn.b., and the ideal gas thermodynamic functions (changes of the entropy, enthalpy, and Gibbs energy) at T = 298.15 K were derived. Appropriate thermodynamic functions over a wide temperature range from (150 to 1000) K and the standard enthalpy of formation at T = 298.15 K were computed by the methods of statistical thermodynamics (ST) and the density functional theory (DFT) on the level B3LYP/6-31G(d,p). The experimental data on the vapor pressure of DI...

Bacteriophage T5 DNA Ejection under Pressure

The transfer of the bacteriophage genome from the capsid into the host cell is a key step of the infectious process. In bacteriophage T5, DNA ejection can be triggered in vitro by simple binding of the phage to its purified Escherichia coli receptor FhuA. Using electrophoresis and cryo-electron microscopy, we measure the extent of DNA ejection as a function of the external osmotic pressure. In the high pressure range (7–16 atm), the amount of DNA ejected decreases with increasing pressure, as theoretically predicted and observed for λ and SPP1 bacteriophages. In the low and moderate pressure range (2–7 atm), T5 exhibits an unexpected behavior. Instead of a unique ejected length, multiple populations coexist. Some phages eject their complete genome, whereas others stop at some nonrandom states that do not depend on the applied pressure. We show that contrarily to what is observed for the phages SPP1 and λ, T5 ejection cannot be explained as resulting from a simple pressure equilibrium between the inside and outside of the capsid. Kinetics parameters and/or structural characteristics of the ejection machinery could play a determinant role in T5 DNA ejection.

Two-dimensional fluid model of a two-chamber plasma source

This study presents a two-dimensional fluid-plasma model developed for describing the cw regime operation of a tandem plasma source, consisting of a driver and an expansion plasma volume of different sizes. The moderate pressure range considered (tens to hundreds of milliTorr) allows a description within the drift–diffusion approximation, as employed in the model. Argon discharges maintained in a metal gas-discharge vessel are treated. The discussions stress charged-particle and electron-energy fluxes as well as the spatial distribution of their components. The main conclusions are for (i) different electron and ion fluxes resulting in a net current in the discharge; (ii) a radial ion flux prevailing over the axial one and an axial electron flux prevailing over the radial one; (iii) ion motion determined by the dc electric field and drift–diffusion electron motion influenced by thermal diffusion; (iv) plasma maintenance in the expansion plasma chamber due to charged-particle and electron-energy fluxes from the driver; (v) importance of the convective flux in the electron-energy balance; (vi) electron-energy losses for sustaining the dc electric field in the expansion plasma volume strongly predominating over the losses through collisions and (vii) electron cooling accompanied by a strong drop in the plasma density and in the potential of the dc electric field, due to the plasma expansion in a bigger volume. In general, the results show that the gas pressure range usually considered to be governed by ambipolar diffusion shows up in a different regime: a regime with a dc current, when the discharge is in a metal chamber with different dimensions in the transverse and longitudinal directions.

The thermodynamics of vaporization of ethyl tert-butyl ether, isobutyl tert-butyl ether, and di-isopropyl ether

The boiling temperatures of ethyl tert-butyl ether (ETBE), isobutyl tert-butyl ether (IBTBE), and di-isopropyl ether (DIPE) have been measured by comparative ebulliometry over the moderate pressure range 10.8 ⩽ ( P/kPa) ⩽ 101.7. The equations of the temperature dependences of the saturated vapour pressures and enthalpies of vaporization have been derived. The normal boiling temperatures of the ethers were computed to be 345.84 K, 386.06 K, and 341.64 K, respectively. The experimental data on the vapour pressure of the ethers under study were extended to the whole range of the liquid phases between critical and triple points by means of corresponding states law and combined treatment of the pT-parameters and low-temperature differences of the heat capacities of ideal gas and liquid, Δ C p = C p ∘ ( g ) - C p ∘ ( l ) , respectively.

Shock-Tube Operation with Laser-Beam-Induced Diaphragm Rupture

Introduction A SHOCK tube is a fundamental experimental tool for research on shock waves and compressible fluid dynamics. The lowand high-pressure channels in a shock tube are usually separated from each other by a diaphragm. For operations in a moderate pressure range, plastic material, such as Mylar or cellophane, is used for the diaphragm. In ideal shock-tube operation, the separation should be instantly and completely removed so that a plane shock wave is generated immediately. However, in practice it takes a finite time for the diaphragm to be ruptured before the flow past the diaphragm reaches the full channel value.1,2 If only a partial area of the diaphragm is ruptured or the time required for the rupture is too long, the shock formation distance cannot be neglected, and/or the postshock pressure deviates from the ideal value. This problem becomes significant when the fill pressure difference between the

Pressure measurements within optical cells using diamond sensors: accuracy of the method below 1 GPa

The accuracy of the diamond pressure gauge has been investigated in the moderate pressure range (0–1 GPa) between 210 and 310 K. Experiments have been conducted using a sapphire anvil cell coupled to a Raman spectrometer. The temperature shift of the first-order Raman peak of diamond is very small (−7.56×10−4 cm−1/K−1.5), which confirms previous results obtained on a wider temperature range. Such a trend implies a very small shift over the studied temperature range, of the same order than the dispersion due to external factors (isotopic composition, orientation). The pressure dependence is found equal to 3.20 (±0.02) cm−1/GPa. A statistical description of the data is provided, indicating that the diamond gauge provides pressure estimates below 1 GPa with an accuracy of±39 MPa. Application of these results to science fields involved in the moderate pressure range below 1 GPa is discussed.

Phase Diagram of Nucleosome Core Particles

We present a phase diagram of the nucleosome core particle (NCP) as a function of the monovalent salt concentration and applied osmotic pressure. Above a critical pressure, NCPs stack on top of each other to form columns that further organize into multiple columnar phases. An isotropic (and in some cases a nematic) phase of columns is observed in the moderate pressure range. Under higher pressure conditions, a lamello-columnar phase and an inverse hexagonal phase form under low salt conditions, whereas a 2D hexagonal phase or a 3D orthorhombic phase is found at higher salt concentration. For intermediate salt concentrations, microphase separation occurs. The richness of the phase diagram originates from the heterogeneous distribution of charges at the surface of the NCP, which makes the particles extremely sensitive to small ionic variations of their environment, with consequences on their interactions and supramolecular organization. We discuss how the polymorphism of NCP supramolecular organization may be involved in chromatin changes in the cellular context.

Theoretical study of a molten carbonate fuel cell stack for pressurized operation

A mathematical stack model of a molten carbonate fuel cell was numerically solved for temperature, gas dynamic pressure, and cell performance. The model assumed a steady state, constant load operation for a co-flow stack with an external reformer. The numerical computation was done for a two-dimensional domain with a real size of cell specifications. The effect of two stack operation variables, gas utilization and system pressure, was thoroughly analysed. The computation results were demonstrated in the form of flow fields, temperature contours, axial profiles, and plots of characteristic values. Our analysis began with an underlying fact that a high cathode gas flow is necessary for stack temperature control. The analysis result verified the effect of stack cooling by the cathode gas, and showed various aspects of stack operation and performance under pressurization. The pressurization effect is most significant in a moderate pressure range of 1–5 atm. The gas dynamic pressure, as it inevitably increases at a high gas flow rate, is regulated by pressurization. All the pressurization effects can generally be represented using a dimensionless parameter, named a pressurization factor. The relation between gas dynamic pressure and total system pressure was clarified from the related flow equations. Copyright © 2001 John Wiley & Sons, Ltd.