Hydrostatic Pressure Dependence Research Articles

Band structure in a one-dimensional photonic crystal with a defect of Ga[formula omitted]Al[formula omitted]As

This study calculates the photonic band structures in a one-dimensional photonic crystal composed alternating GaAs and air layers through the plane wave expansion method. When examining the hydrostatic pressure and temperature dependence of the GaAs dielectric function, the photonic band structure clearly shifts to higher frequencies as the pressure increases at a given temperature. Further, if a Ga1−xAlxAs defect is introduced, it is placed within the photonic band gap in defective modes that are sensitive to Al concentrations and hydrostatic pressure. As the pressure increases, the dielectric constant of the GaAs semiconductor decreases, causing the defective mode to shift towards higher frequencies.

Effects of U-Mo irradiation creep coefficient on the mesoscale mechanical behavior in U-Mo/Al monolithic fuel plates

Abstract The fuel foils in U-Mo/Al monolithic fuel plates will evolve into porous media owing to the formed gas bubbles. Three-dimensional finite element simulations are implemented for the thermo-mechanical behavior in U-Mo/Al monolithic fuel plates with different U-Mo irradiation creep coefficients, and the results of mesoscale normal stress, bubble volume fraction and bubble pressure in the fuel foil are obtained. In the simulations, the mechanistic fission gas swelling model is adopted, considering the dependence of external hydrostatic pressure. The mesoscale normal stress refers to the effective normal stress in the skeleton of porous fuel foil, which relates to the fuel fracture. The numerical results indicate that an irradiation creep coefficient of 2000 × 10−31 m3/MPa can be identified for the current U-10Mo fuel foil, because the calculated fuel-foil thickness increments match well with the experimental data. The influences of U-Mo irradiation creep coefficient on its bubble volume fraction and pore pressure are significant in the vicinity of fuel foil edges and corners. The dangerous regions locate near the fuel foil corners, surrounding the points with maximum mesoscale normal stresses. The enlarged irradiation creep coefficient will result in stress relaxation on the whole, but the through-thickness creep strain components can be heavily magnified. When the irradiation creep coefficient increases from 10 × 10−31 m3/MPa to 1000 × 10−31 m3/MPa, the maximum mesoscale normal stresses will decrease from 58.04 MPa to 28.04 MPa, with a reduction of ∼52%; while the corresponding through-thickness creep strain components increase by ∼5%. With an increase of irradiation creep coefficient from 1000 × 10−31 m3/MPa to 2000 × 10−31 m3/MPa, the maximum mesoscale normal stresses increase by ∼9%, and the corresponding through-thickness creep strain components increase by ∼219%. The irradiation creep performance should be optimized and an extreme large creep coefficient is not a good choice, because the creep-induced damage might degrade the mesoscale strength of the fuel foil.

High magnetic field phase diagram and failure of the magnetic Grüneisen scaling in LiFePO4

We report the magnetic phase diagram of single-crystalline LiFePO$_4$ in magnetic fields up to 58~T and present a detailed study of magneto-elastic coupling by means of high-resolution capacitance dilatometry. Large anomalies at \tn\ in the thermal expansion coefficient $\alpha$ imply pronounced magneto-elastic coupling. Quantitative analysis yields the magnetic Gr\"uneisen parameter $\gamma_{\rm mag}=6.7(5)\cdot 10^{-7}$~mol/J. The positive hydrostatic pressure dependence $dT_{\rm N}/dp = 1.46(11)$~K/GPa is dominated by uniaxial effects along the $a$-axis. Failure of Gr\"uneisen scaling below $\approx 40$~K, i.e., below the peak temperature in the magneto-electric coupling coefficient [\onlinecite{toft2015anomalous}], implies several competing degrees of freedom and indicates relevance of recently observed hybrid excitations~[\onlinecite{yiu2017hybrid}]. A broad and strongly magnetic-field-dependent anomaly in $\alpha$ in this temperature regime highlight the relevance of structure changes. Upon application of magnetic fields $B||b$-axis, a pronounced jump in the magnetisation implies spin-reorientation at $B_{\rm SF} = 32$~T as well as a precursing phase at 29~T and $T=1.5$~K. In a two-sublattice mean-field model, the saturation field $B_{\rm sat,b} = 64(2)$~T enables the determination of the effective antiferromagnetic exchange interaction $J_{\rm af} = 2.68(5)$~meV as well as the anisotropies $D_{\rm b} = -0.53(4)$~meV and $D_{\rm c} = 0.44(8)$~meV.

Effects of porous fuel structure on the irradiation-induced thermo-mechanical coupling behavior in monolithic fuel plates

A UMo/Al monolithic fuel plate is composed of UMo fuel meat and Al cladding. These fuel plates with a high uranium density have a promising prospect to be used in advanced research and test reactors. Under the neutron irradiation environments, nuclear fissions occur to result in heat generation in the fuel meat; accumulation of fission-induced solid and gaseous products will lead to irradiation swelling; irradiation creep of UMo will affect the mechanical interactions between the fuel meat and the cladding. Especially, intragranular and intergranular gas bubbles will make the fuel meat evolve into a porous structure, and the fuel porosity and pore pressure will change continuously with the irradiation time. As a result, a complex irradiation-induced multi-scale thermo-mechanical coupling behavior needs to be simulated for optimal design and safety evaluation of UMo/Al monolithic fuel plates. In this study, a theoretical model for fuel porosity evolution is developed, based on a fission gas swelling model with the grain recrystallization, the resolution of intergranular gas atoms and the dependence of hydrostatic pressure involved. Moreover, the computation method of microscopic interfacial normal stress is established, with consideration of fuel porosity and pore pressure. The evolution model of fuel porosity is introduced into three-dimensional finite element simulation of the irradiation-induced multi-scale thermo-mechanical coupling behavior, which correlates the current thermal conductivity of UMo fuel with the fuel temperature and porosity. The distribution and evolution disciplines of thermo-mechanical variables in the fuel plate are obtained at different irradiation time. In addition, the effects of fuel porosity on the temperature, the main deformation and microscopic interfacial normal stresses are investigated. Simultaneously, the effects of surface heat transfer coefficient on the thermo-mechanical behavior are analyzed. The research results indicate that the porous fuel structure and fission-gas induced pore pressure become the main fracture mechanisms of monolithic fuel plates.

Evaluation of Hydrostatic Pressure Dependence of Bulk Creep of Polycarbonate by Molecular Dynamics Simulation

Evaluation of Hydrostatic Pressure Dependence of Bulk Creep of Polycarbonate by Molecular Dynamics Simulation

Theoretical Modeling of Polymer Translocation: From the Electrohydrodynamics of Short Polymers to the Fluctuating Long Polymers.

The theoretical formulation of driven polymer translocation through nanopores is complicated by the combination of the pore electrohydrodynamics and the nonequilibrium polymer dynamics originating from the conformational polymer fluctuations. In this review, we discuss the modeling of polymer translocation in the distinct regimes of short and long polymers where these two effects decouple. For the case of short polymers where polymer fluctuations are negligible, we present a stiff polymer model including the details of the electrohydrodynamic forces on the translocating molecule. We first show that the electrohydrodynamic theory can accurately characterize the hydrostatic pressure dependence of the polymer translocation velocity and time in pressure-voltage-driven polymer trapping experiments. Then, we discuss the electrostatic correlation mechanisms responsible for the experimentally observed DNA mobility inversion by added multivalent cations in solid-state pores, and the rapid growth of polymer capture rates by added monovalent salt in -Hemolysin pores. In the opposite regime of long polymers where polymer fluctuations prevail, we review the iso-flux tension propagation (IFTP) theory, which can characterize the translocation dynamics at the level of single segments. The IFTP theory is valid for a variety of polymer translocation and pulling scenarios. We discuss the predictions of the theory for fully flexible and rodlike pore-driven and end-pulled translocation scenarios, where exact analytic results can be derived for the scaling of the translocation time with chain length and driving force.

Tunable transmittance spectrum in one-dimensional photonic crystals composed of HgBa2Ca2Cu3O8+δ/GaAs with a defective GaAs layer

In this work, the transmittance spectrum of a defective one-dimensional photonic crystal is numerically calculated using the transfer matrix method and two-fluid model. The photonic crystal is embedded in air and composed alternating layers of a superconductor (HgBa2Ca2Cu3 O8+δ) and a semiconductor (GaAs) with GaAs defects. The dependence of hydrostatic pressure on the critical temperature of the superconductor, dielectric function of the semiconductor, angular frequency of the transverse optical phonons, and thickness of the semiconductor layer is determined. By increasing the pressure, the photonic band gap width increases and the defect mode shifts to larger frequencies. When the thickness of the superconductor increases while the pressure and thickness of the semiconductor layers are kept constant, the PBG width also increases but the defect mode shifts to shorter frequencies. Moreover, when considering two GaAs defects, the coupling between the defect modes decreases as the separation of the defects increases.

Structural stability of human butyrylcholinesterase under high hydrostatic pressure

Human butyrylcholinesterase is a nonspecific enzyme of clinical, pharmacological and toxicological significance. Although the enzyme is relatively stable, its activity is affected by numerous factors, including pressure. In this work, hydrostatic pressure dependence of the intrinsic tryptophan fluorescence in native and salted human butyrylcholinesterase was studied up to the maximum pressure at ambient temperature of about 1200 MPa. A correlated large shift toward long wavelengths and broadening observed at pressures between 200 and 700 MPa was interpreted as due to high pressure-induced denaturation of the protein, leading to an enhanced exposure of tryptophan residues into polar solvent environment. This transient process in native butyrylcholinesterase presumably involves conformational changes of the enzyme at both tertiary and secondary structure levels. Pressure-induced mixing of emitting local indole electronic transitions with quenching charge transfer states likely describes the accompanying fluorescence quenching that reveals different course from spectral changes. All the pressure-induced changes turned irreversible after passing a mid-point pressure of about 400 ± 50 MPa. Addition of either 0.1 M ammonium sulphate (a kosmotropic salt) or 0.1 M lithium thiocyanate (a chaotropic salt) to native enzyme similarly destabilized its structure.

Comparative study of the pressure dependence of optical-phonon transverse-effective charges and linewidths in wurtzite InN

We investigate the hydrostatic pressure dependence of the zone center optical phonons of $c$-plane and $a$-plane wurtzite InN epilayers grown on GaN substrates. The longitudinal to transverse mode splitting for the ${A}_{1}$ and ${E}_{1}$ modes was found to increase with increasing pressure, whereas the associated transverse effective charge decreases for both modes as ${e}_{T}^{*}({A}_{1})=2.93--9.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}P$ and ${e}_{T}^{*}({E}_{1})=2.80--10.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}P$ (in units of elementary charge and $P$ in GPa). These observations are well in line with results for other II--VI, III--V, and group-IV semiconductor compounds as far as the relation between the magnitude and sign of the pressure derivative of ${e}_{T}^{*}$ and the bond ionicity is concerned. As the latter increases so does $|\ensuremath{\partial}{e}_{T}^{*}/\ensuremath{\partial}P|$ with a sign change from positive to negative for bond ionicities around ${f}_{i}=0.46$ for compounds with anions belonging to the first row of the Periodic Table. A comparison of the results for InN and other nine tetrahedrally bonded compounds indicate that the pressure behavior of the transverse effective charge is mainly determined by the strength of the Pauli repulsion between cation valence electrons and those of the anion core. We also perform ab initio calculations in order to address the origin of the observed increase in linewidth of the ${E}_{2}^{\text{high}}$ mode which is found to arise from a pressure-induced increase in the rate of two-phonon decay processes. This broadening is associated with tuning into resonance of a steep edge in the two-phonon density of states around 460 ${\mathrm{cm}}^{\ensuremath{-}1}$ with the frequency of the ${E}_{2}^{\text{high}}$ mode.

A gas tension device for the mesopelagic zone

Gas Tension Devices (GTDs) are used to acquire accurate and stable measurements of gas tension, or total dissolved air pressure of the gases dissolved in water. GTDs operate by measuring the barometric pressure of a small sample volume of air separated from the water by a gas-permeable membrane resting on a rigid permeable support. Existing GTDs use a compressible polydimethylsiloxane (PDMS) membrane which exhibit several undesirable features: the membrane collapses with increasing hydrostatic pressure, which reduces the permeability; a collapsed membrane increases the response; collapse and expansion generate large transient signals [McNeil et al. 2006a]. Also, reverse osmosis becomes a problem at depths greater than approximately 330 m in seawater. We present a new GTD that solves the hydrostatic pressure-generated transients and changing response times, and alleviates reverse-osmosis. These improvements allow the new GTD to be used in the mesopelagic zone. The new GTD uses a custom designed small diameter (4 cm) thin (130 µm) incompressible composite Teflon-AF 2400 membrane. It can operate to a depth of at least 1000 m with a depth-independent response time of approximately 35 min. We estimated the hydrostatic pressure dependence of Henry's Law solubilities as we characterized the new Teflon-membrane GTD using data collected in the laboratory. Field testing occurred on two APL/UW Gas-Profiling Floats deployed in the Eastern Tropical North Pacific (ETNP) for 15 days during May 2014. The floats profiled between the surface and 400 m depth, sampling gas tension within the Oxygen Deficient Zone. The gas tension-profiles from the two GTDs were validated against gas tension derived from independent N2:Ar and Ar concentrations measured by mass spectrometry, agreeing to within ± 0.6% and ± 0.4%.

A unified model for the uniaxial and hydrostatic pressure dependence of Tc in YBa2Cu3Ox (x ≈ 6.95–7.0)

Though the uniaxial and hydrostatic pressure dependence of Tc yield important insight into the superconductivity of YBa2Cu3Ox (x ≈ 6.95–7.0), the understanding of the origin of the pressure effect on this system remains lack of a unified model explanation in a quantitative manner. In order to develop a unified model, we performed first-principles calculations for YBa2Cu3O7 under pressure to distinguish the core factors including holes concentration and tetragonality and further combined the two factors with the charge-transfer model to determine the Tc. The role of tetragonality was identified in determining the uniaxial pressure effect significantly but not as prominent as holes concentration in producing the superconductivity of YBa2Cu3Ox (x ≈ 6.95–7.0). The results under pressure from the unified model based on the newly defined tetragonality and holes concentration are in good accordance with that from experiments. With this unified model, we predicted that the better superconductivity in YBa2Cu3Ox (x ≈ 6.95–7.0) may appear through 0.025 compression along b axis or 0.025 stretching along a axis.

Modeling Belt Press Filter Performance in Fine Suspension Dewatering

The principles of suspension dewatering using drainage on belt press filters are considered. A relationship describing the dependence of hydrostatic pressure, which is the driving force of the process, on time and the initial conditions, is proposed and experimentally confirmed. The equations for the calculation of the belt speed depending on the load on solids and for the solution of the reciprocal problem, which is represented by the determination of the capacity of the filter in solids at various belt speeds, are derived based on this. The calculated data, which were obtained from the results of laboratory studies on dewatering using the drainage of model suspensions, indicate that the capacity in solids at the belt speed of 0.35 m/s is 6.8–15.7 t/h. These data do not contradict the results of the pilot-scale tests.

Optical properties and exciton binding energy and related parameters of CdTe: Pressure-induced effects

The present paper reports on the hydrostatic pressure dependence of the direct and indirect energy band-gaps, refractive index, static and high-frequency dielectric constants, exciton banding energy and exciton Bohr radius for CdTe in the zinc-blende structure. The applied pressure is taken in the range 0–30 kbar. The calculations are performed using a pseudopotential approach. At zero pressure, our results show a good accord with experiment for most studied optical properties. Nevertheless, for exciton binding energy and Bohr radius the use of Adachi's expression [S. Adachi, Properties of Group-IV, III–V, and IIVI Semiconductors, Wiley, Chichester, 2005] has given poor results as compared to experiment. In this respect, a modified Adachi's expression formula have been proposed and found to give meaningful accord with experiment. Upon compression up to 30 kbar, the material of interest is found to remain a direct (Г-Г) band-gap semiconductor. All optical features being studied here have shown a monotonic behavior under compression. The present study can be useful for infrared applications.

On the ability of classic scaled particle theory to reproduce the cavity contact correlation function of water over a large hydrostatic pressure range

The cavity contact correlation function G(RC) represents the density of liquid molecules in contact with the surface of a spherical cavity of RC radius normalized to the bulk density. Recently, the G(RC) function of water has been determined in the TIP4P water model at 25 °C and over a large range of hydrostatic pressure, by means of Monte Carlo simulations [Floris, J. Mol. Liq. 218 (2016) 166]. It is shown that classic scaled particle theory relationships are able to reproduce in a satisfactory way the hydrostatic pressure dependence of G(RC) by using only two input data: the experimental density of water, and the effective hard sphere diameter of water molecules, 2.8 Å, assumed to be pressure-independent. No further information is needed, even though G(RC) should reflect structural features of water.

Pressure Dependence of Fiber Bragg Grating Inscribed in Perfluorinated Polymer Fiber

We investigate the hydrostatic pressure dependence of the Bragg wavelength of a fiber Bragg grating (FBG) inscribed in a perfluorinated graded-index (PFGI-) polymer optical fiber (POF) at 1550 nm. At 0.5 MPa, the Bragg wavelength increased with time and became almost constant ~150 min later. Such a long time constant probably originates from the unique structure of the PFGI-POF, which has a thick overcladding around its core and cladding. The pressure-dependence coefficient without considering the time constant was estimated to be 1.3 nm/MPa; this is over five times the values of other types of POF-FBGs. This indicates that by removing the overcladding of the PFGI-POF, fast-response high-sensitivity pressure sensing will be feasible. Once the Bragg wavelength became constant at 0.5 MPa, the pressure-dependence coefficient of the Bragg wavelength was measured to be −0.13 nm/MPa, the absolute value of which was comparable with those of other POF-FBGs, but with an opposite sign.

Stress-dependence of kinetic transitions at atomistic defects

The full second-rank activation volume tensors associated with vacancy migration in FCC copper and HCP titanium as well as transition events in the Σ5 (2 1 0) grain boundary in copper are calculated and analyzed. The full tensorial results quantitatively illustrate how the conventional use of an activation volume scalar in atomistic studies of the kinetic processes of complex defects can miss important stress dependencies, in that neither hydrostatic pressure nor deviatoric stress dependencies can be considered alone as dominating the response. The results speak to the importance of anisotropies in the stress-dependence of atomistic kinetics, including crystal structure anisotropy, elastic anisotropy, and defect structure or migration-path anisotropies.

Pressure-induced reinforcement of interfacial superconductivity in a Bi2Te3/Fe1+yTe heterostructure

We investigate the hydrostatic pressure dependence of interfacial superconductivity occurring at the atomically sharp interface between two non-superconducting materials: the topological insulator (TI) Bi2Te3 and the parent compound Fe1+yTe of the chalcogenide iron-based superconductors. Under pressure, a significant increase in the superconducting transition temperature Tc is observed. We interpret our data in the context of a pressure-induced enhanced coupling of the Fe1+yTe interfacial layer with the Bi2Te3 surface state, which modifies the electronic properties of the interface layer in a way that superconductivity emerges and becomes further enhanced under pressure. This demonstrates the important role of the TI in the interfacial superconducting mechanism.

A detailed comparison of two material models for concrete in the dynamic loading regime, RHT and HPG

Throughout the last decades, great attention has been given to model the dynamic behaviour of concrete. As such, numerous material models have been conceived in hydrocodes to describe the complex behaviour of this composite material subjected to large deformations leading to damage and failure. Concrete shows, for instance, strain rate dependency as well as hydrostatic pressure dependency. This article focuses on the comparison of two material models conceived for such purpose. These are the RHT model (RHT - Riedel, Hiermaier, Thoma) developed at the Fraunhofer Ernst-Mach-Institut and the HPG (HPG - Hartmann, Pietzsch, Gebbeken) model developed at the University of the Bundeswehr Munich, both of which have been proven to be successful in a variety of scenarios. They are macro-level models, i.e., they regard concrete as a homogeneous material. Both models incorporate the traditional splitting in hydrocodes of the hydrostatic and the deviatoric response. On the one hand, both material models have three pressure-dependent limit surfaces in the stress space to characterise concrete strength. These are the elastic limit surface, the failure surface and the residual strength surface, the latter being related to a damage model. Strain rate effects are inherent in the models. On the other hand, both material models use the p–α formulation in the Mie–Grüneisen equation of state. The parameters of this equation are, however, differently calculated. A final comparison of these two models is done by conducting numerical simulations where the RHT and the HPG models are used as material models. The scenario is a contact detonation as an example of a high strain rate problem. Such an in-depth and detailed comparison has not been done to date. It aims to help the user decide which material model to choose as well as to provide ideas for future development in the field of material modelling.

Dynamic Constitutive Model for Polymers Considered Hydrostatic Pressure and Strain Rate Dependency

Dynamic Constitutive Model for Polymers Considered Hydrostatic Pressure and Strain Rate Dependency

Hydrostatic pressure dependence on the collapsing of heptamer clusters in the charge ordered spinel AlV2O4

Charge frustrated spinels have engaged the interest of condensed matter studies due to the novel formation of multimer molecular sub units that lifts the degeneracy in the ground state. An exhaustive study on the stability of these molecular sub units is not available in the literature. In the present study, evidence has been obtained for the first time that hydrostatic pressure beyond 21 GPa, destabilizes the vanadium heptamer molecular sub units reversibly in the unique ambient temperature charge ordered spinel AlV2O4. The bulk modulus and its pressure derivative of the charge ordered phase are constrained. In addition a systematic structural analysis as a function of temperature shows destabilization of vanadium trimers those stack up to make the heptamer units. The crystal structure and total energy have been calculated using first principles density functional formalism (GGA approximation) as a function of pressure. The results obtained corroborate the stability of the frustrated phase beyond 20 GPa.