Hydrostatic Response Research Articles

Hydrostatic pressure effect on excited state properties of room temperature phosphorescence molecules: A QM/MM study

Stimulus-responsive organic room temperature phosphorescence (RTP) materials exhibit variations in their luminescent characteristics (lifetime and efficiency) upon exposure to external stimuli, including force, heat, light and acid-base conditions, the development of stimulus-responsive RTP molecules becomes imperative. However, the inner responsive mechanism is unclear, theoretical investigations to reveal the relationship among hydrostatic pressures, molecular structures and photophysical properties are highly desired. Herein, taking the Se-containing RTP molecule (SeAN) as a model, based on the dispersion corrected density functional theory (DFT-D), the combined quantum mechanics and molecular dynamics (QM/MM) method and thermal vibration correlation function (TVCF) theory, the influences of hydrostatic pressure on molecular structures, transition properties as well as lifetimes and efficiencies of RTP molecule are theoretically studied. Results show that extended lifetime and enhanced efficiency are observed at 2 Gpa compared with molecule at normal pressure, and this is related with the small reorganization energy and large oscillator strength. Moreover, due to the small energy gap (0.34 eV) and remarkable spin-orbit coupling (SOC) constant (8.56 cm-1) between first singlet excited state and triplet state, fast intersystem crossing (ISC) process is determined for molecule at 6 Gpa. Furthermore, the intermolecular interactions are visualized using independent gradient model based on Hirshfeld partition (IGMH) and the changes of molecular packing modes, SOC values, lifetimes and efficiencies with pressures are detected. These results reveal the relationship between molecular structures and RTP properties. Our work provides theoretical insights into the hydrostatic pressure response mechanism and could promote the development new efficient stimulus-responsive molecules.

Hydrostatic pressure response of semiconducting GaSb applying a semi-empirical approach

In addition to experimental investigations, semi-empirical approaches prove valuable for replicating experimental results and predicting material behavior under high-pressure conditions. This study investigates the variation of unit cell volume in cubic zinc blende Gallium antimonide (GaSb) up to the phase transition pressure, relying solely on structural parameters from literature measurements at ambient conditions. The research extends to inspect the impact of high pressure on various properties, including mass density, bulk modulus, bulk sound wave velocity, microhardness, first-order pressure derivative of the isothermal bulk modulus, Grüneisen parameter, and Debye temperature for the GaSb compound. The bulk modulus and microhardness show nearly linear increases with pressure, while sound wave velocity and Debye temperature exhibit nonlinear variations. The first-order pressure derivative of the bulk modulus and Grüneisen parameter gradually decreased in the material under study. Similar trends under pressure are found in literature for materials with different crystallographic structures. Additionally, the study predicts and analyzes extra physical parameters of GaSb, comparing them with existing literature data.

Orientation effects, hydrostatic response, and figures of merit in 2–2-type composites based on relaxor-ferroelectric single crystals

The article reports new results on the hydrostatic performance of laminar piezo-active composites based on domain-engineered relaxor-ferroelectric single crystals (SCs) with the perovskite-type structure. Layers of the composites are either single-crystal poled along [011] (where rotations of the main crystallographic axes around two co-ordinate axes are considered) or porous polymer, with aligned spheroidal pores. These composites are described by 2–2–0 connectivity. An influence of the rotation of the main crystallographic axes and porosity is analyzed, and maxima of the hydrostatic piezoelectric coefficient figure of merit and electromechanical coupling factor of the composites are found as functions of a few parameters. New diagrams are built to show regions of the large (over 1000 pC/N) at variations of two rotation angles in the single-crystal layers. Large values of the hydrostatic figure of merit ∼ (10−10 – 10−9) Pa−1 and electromechanical coupling factor are achieved in specific volume-fraction and rotation-angle ranges. These and other large values of the hydrostatic parameters of the studied 2–2-type composites are important for effective hydroacoustic applications.

Novel lead-free 2–1–2 composite: predicted high piezoelectric sensitivity and significant hydrostatic response

A parallel-connected composite with 2–1–2 connectivity and two lead-free single-crystal (SC) components is proposed. Its high piezoelectric sensitivity is highlighted and its large hydrostatic parameters are described. The first type of composite layer represents a ferroelectric domain-engineered [001]-poled [Li, (K, Na)](Nb, Ta)O3 SC. In the second type of composite layer, piezoelectric Li2B4O7 SC rods in the form of an elliptic cylinder are regularly aligned in a large polymer matrix. The effective electromechanical properties of the composite were found in three stages, using the effective field and matrix methods that are applicable to piezoelectric media. A new orientation effect was studied, linked with rotations of SC rod bases in the polymer medium that forms the second type of layer. Since these rotations are in a Li2B4O7 SC with a unique elastic and piezoelectric anisotropy, the second type of layer exhibits a noticeable influence on the piezoelectric performance and hydrostatic response of the composite. A variation of the aspect ratio of the Li2B4O7 rod base becomes another important factor that can improve the hydrostatic parameters of the composite. Some effective parameters of related 2–1–2 composites were compared for different polymer components. Three diagrams were first constructed for the high-performance 2–1–2 [Li, (K, Na)](Nb, Ta)O3/Li2B4O7/polyethylene composite to show the ranges of rotation angles and volume fractions that correspond to the longitudinal piezoelectric voltage coefficient > 500 mV m N−1, hydrostatic piezoelectric coefficient > 200 mVm N−1 and hydrostatic figure of merit >10−11 Pa−1. These effective parameters are important in piezoelectric sensors and hydroacoustic and other applications of novel lead-free composites.

Assessment of chronic limb threatening ischemia using thermal imaging

ObjectivesCurrent chronic limb threatening ischemia (CLTI) diagnostics require expensive equipment, using ionizing radiation or contrast agents, or summative surrogate methods lacking in spatial information. Our aim is to develop and improve contactless, non-ionizing and cost-effective diagnostic methods for CLTI assessment with high spatial accuracy by utilizing dynamic thermal imaging and the angiosome concept. ApproachDynamic thermal imaging test protocol was suggested and implemented with a number of computational parameters. Pilot data was measured from 3 healthy young subjects, 4 peripheral artery disease (PAD) patients and 4 CLTI patients. The protocol consists of clinical reference measurements, including ankle- and toe-brachial indices (ABI, TBI), and a modified patient bed for hydrostatic and thermal modulation tests. The data was analyzed using bivariate correlation. ResultsThe thermal recovery time constant was on average higher for the PAD (88%) and CLTI (83%) groups with respect to the healthy young subjects. The contralateral symmetry was high for the healthy young group and low for the CLTI group. The recovery time constants showed high negative correlation to TBI (ρ = -0.73) and ABI (ρ = -0.60). The relation of these clinical parameters to the hydrostatic response and absolute temperatures (|ρ|<0.3) remained unclear. ConclusionThe lack of correlation for absolute temperatures or their contralateral differences with the clinical status, ABI and TBI disputes their use in CLTI diagnostics. Thermal modulation tests tend to augment the signs of thermoregulation deficiencies and accordingly high correlations were found with all reference metrics. The method is promising for establishing the connection between impaired perfusion and thermography. The hydrostatic modulation test requires more research with stricter test conditions.

Remarkable response of hollow thermoplastic microspheres-elastomer matrix composites in uniaxial tension

In the last few years, the mechanical response of hollow thermoplastic microsphere-elastomer matrix composites has been investigated. The large majority of the studies focuses on their compressive properties and particularly on the stress-strain response. In the present paper, large strain uniaxial tension experiments are conducted on thermoplastic microsphere filled polyurethane elastomer. Six volume fractions are considered. Thanks to a two-camera setup and digital image correlation measurements, the remarkable volumetric behaviour is highlighted. First, the hydrostatic pressure vs. volume change response during a loading-unloading cycle consists of a hysteresis loop, and its size is directly related to the volume fraction of microspheres in the composite. Second, this loop admits a complex shape with several extrema. This remarkable response can be considered as the macroscopic signature of the complex microstructural phenomena involved during deformation.

Hydrostatic high strain rate loading response of closed-cell polymeric foams as a function of mass density

Closed cell polymeric foams are widely used in naval structures as sandwich core material owing to their lightweight and high energy absorption capabilities. There has been a great push towards understanding their material response under multiple loading scenarios, however, the loading scenarios have been limited to uniaxial or multiaxial in air loadings at different strain rates. Here, the hydrostatic elastic response and yield behavior of PVC foams with varying mass densities under a high strain rate hydrostatic loading state have been investigated. A novel underwater high strain rate loading facility is utilized to subject these foams to near blast strain rate hydrostatic loading. Using the 3-D Digital Image Correlation (DIC) technique in conjunction with ultra-high-speed photography, full-field volumetric deformation data is obtained. The dynamic loading data is obtained using a piezoelectric pressure sensor. This enables the measurement of material yield strength and bulk modulus for these materials under high strain rate hydrostatic loading conditions. The foams demonstrate increment in bulk modulus and yield strength under high strain rate loading. Further, the increment observed is highly sensitive to the material bulk mass density.

Bone Remodeling Process Based on Hydrostatic and Deviatoric Strain Mechano-Sensing.

A macroscopic continuum model intended to provide predictions for the remodeling process occurring in bone tissue is proposed. Specifically, we consider a formulation in which two characteristic stiffnesses, namely the bulk and shear moduli, evolve independently to adapt the hydrostatic and deviatoric response of the bone tissue to environmental changes. The formulation is deliberately simplified, aiming at constituting a preliminary step toward a more comprehensive modeling approach. The evolutive process for describing the functional adaptation of the two stiffnesses is proposed based on an energetic argument. Numerical experiments reveal that it is possible to model the bone remodeling process with a different evolution for more than one material parameter, as usually done. Moreover, the results motivate further investigations into the subject.

The hydrostatic control of load-induced height changes above subglacial Lake Vostok

Abstract Lake Vostok, East Antarctica, represents an extensive water surface at the base of the ice sheet. Snow, ice and atmospheric pressure loads applied anywhere within the lake area produce a hydrostatic response, involving deformations of the ice surface, ice–water interface and particle horizons. A modelling scheme is developed to derive height changes of these surfaces for a given load pattern. It is applied to a series of load scenarios, and predictions based on load fields derived from a regional climate model are compared to observational datasets. Our results show that surface height changes due to snow-buildup anomalies are damped over the lake area, reducing the spatial standard deviation by one-third. The response to air pressure variations, in turn, adds surface height variability. Atmospheric pressure loads may produce height changes of up to $\pm$ 4 cm at daily resolution, but decay rapidly with integration time. The hydrostatic load response has no significant impact neither on ICESat laser campaign biases determined over the lake area nor on vertical particle movements derived from GNSS observations.

Torsion, energy magnetization, and thermal Hall effect

We study the effective action of hydrostatic response to torsion in the absence of spin connections in gapped $(2+1)$-dimensional topological phases at low temperatures. In previous studies, a torsional Chern-Simons term with a temperature-squared (${T}^{2}$) coefficient was proposed as an alternative action to describe the thermal Hall effect with the idea of balancing the diffusion of heat by a torsional field. However, the question remains whether this action leads to a local bulk thermal response that is not suppressed by the gap. In our hydrostatic effective action, we show that the ${T}^{2}$ bulk term is invariant under variations up to boundary terms considering the geometry dependence of local temperature, which precisely describes the edge thermal current. Furthermore, there are no local boundary diffeomorphism anomalies or bulk inflow thermal currents at equilibrium, and also there is no edge-to-edge adiabatic thermal current pumping upon changing the gravitational background. These results are consistent with exponentially suppressed thermal current for gapped phases.

A coupled elastic constitutive model for high porosity sandstone

An elastic constitutive model is developed to predict the mechanical unloading response for high porosity sandstone. The resulting model is sufficiently complex to represent known mechanical response, yet reasonably straightforward to calibrate. A mechanical dataset from a suite of true triaxial tests on Castlegate sandstone is used to develop, calibrate, and validate the model, which incorporates the experimentally observed evolutions of the elastic bulk and shear moduli with stress and plastic strain. Furthermore, to properly represent the hydrostatic unloading response, a coupled term is required, in which the plastic volume strain (accumulated during both hydrostatic and deviatoric loading) modifies the nonlinear stress dependence of the bulk modulus. Omission of this coupling term causes significant over prediction of the plastic volume strain and bulk modulus after complete unloading. However, the coupled term is not required to model deviatoric response and shear modulus evolution. While a suite of 28 tests was used to develop the model, only one carefully controlled test is required to calibrate the model for a chosen high porosity sandstone.

Sensitivity of an infinite-strip-shaped polyvinylidene fluoride film in an underwater plane sound field

The sensitivity of an infinite-strip-shaped polyvinylidene fluoride (PVDF) film in an underwater plane sound field is analyzed in this paper. The high-frequency sensitivity is characterized by the resonances of the symmetrical in-plane stress modes with traction-free boundary conditions at the ends of the film and by the anti-resonances due to the superposition of the stress components. The low-frequency sensitivity exhibits a simple hydrostatic response. The directional property of the in-plane stress component, generated by the incident sound across the thickness, has two contributions. The first is from the aperture and dipolar functions of the incident sound pressure over the PVDF surfaces and at the two ends of the film. The second is from an amplitude modulation by an angle-dependent gain. The directional property of the in-plane stress component by the sound pressure at the two ends of the film is only controlled by the dipolar function, and that of the stress component in the thickness direction is only determined by the aperture function. The illustration of the frequency and directional features of the PVDF film may advance understanding of the mechanisms involved in generating the voltage output of PVDF by an incident sound field.

Design and characterization of the carbon fiber tube reinforced polymer composite for full ocean depth submersibles

The large difference between in-plane and out-of-plane mechanical properties limits the application of traditional composite honeycombs in submersibles. In this work, the carbon fiber tube reinforced polymer composite (CTPC) which have lightweight characteristic and high hydrostatic strength is designed and manufactured. The combination between epoxy resin and carbon fiber tube inhibits the buckling failure and improves the bearing capacity of the tube. Resin binds carbon fiber tubes and forms a stable stress transmission path between them. The hydrostatic response of the CTPC has been investigated by simulation and test. The measured results show good agreement with the simulation. Due to its high hydrostatic bearing capacity and lightweight, the CTPC can be used as a new type of buoyancy material in submersibles.

Experiments in measuring dynamic hydrostatic constitutive properties of soft materials

An experimental investigation is conducted to develop, analytically model, and test a novel facility to obtain the dynamic hydrostatic constitutive properties and behavior of soft materials. The novel facility is an underwater shock tube consisting of two aluminum sections and an optically-clear acrylic section in between, all filled with water. A striker-piston configuration is used to provide an axial shock loading to one end of the assembly. Dynamic pressure sensors provide pressure data along the entire length of the assembly, including at the specimen location in the acrylic section. 3D Digital Image Correlation (DIC) is used in conjunction with high-speed photography to provide full-field deformation data of the specimen to obtain volumetric strain. The mismatch in acoustic impedance between the aluminum and the acrylic sections causes a reduction in the amplitude of the pressure pulse by 33%. The pressure pulse also undergoes appreciable dispersion in the acrylic section. Fluid-structure interaction (FSI) models are considered and applied to understand the dispersion characteristics of the axially propagating pressure pulse. The dynamic hydrostatic constitutive response of closed-cell polyvinyl chloride (PVC) foam is obtained at a volumetric strain rate of 100s−1. The bulk modulus at this strain rate for H130 PVC foam is measured to be 106.97 ± 3.11MPa. This is more than double that of the quasi-static (0.001s−1) value of 46.71 ± 1.91MPa, indicating a strong effect of strain rate on the material's response. The buckling pressure is also found to be strain rate dependent, with the dynamic buckling occurring at 3.09 ± 0.12MPa and quasi-static buckling occurring at 1.39 ± 0.17MPa.

Pressure-dependent modifications in the LaAuSb2 charge density wave system

Hydrostatic pressure response of $\mathrm{LaAu}{\mathrm{Sb}}_{2}$ charge density wave (CDW) system is investigated using electrical transport, x-ray diffraction (XRD), and density-functional theory (DFT). Resistivity data at ambient pressure evidence a clear CDW transition at 83 K. X-ray diffraction at ambient pressure reveals that in plane and out of plane axes show opposite behavior with decreasing temperature, in particular, out of plane $c$ axis develops a distinct change at \ensuremath{\sim}250 K, much above the observed CDW transition at 83 K. The CDW transition shifts to low temperature with increasing pressure. Our resistivity data indicate a complete suppression of the CDW transition at \ensuremath{\sim}3.6 GPa. High-pressure XRD revealed a change from the linear trend for the out of plane ($c$) and the in plane ($a$) lattice parameters for pressure above 3.8 GPa. With compression, DFT indicated an anomaly in the c/a ratio around 8 GPa. The calculated electronic structure also indicated minor changes in the band structure in this pressure range. In addition, high-pressure DFT structural investigations reveal the $\mathrm{LaAu}{\mathrm{Sb}}_{2}$ system to be stable up to pressures as high as 150 GPa.

On the equivalence of self-consistent equations for nonuniform liquids: a unified description of the various modifications

A variety of self-consistent (SC) equations have been proposed for non-uniform states of liquid particles under external fields, including adsorbed states at solid substrates and confined states in pores. External fields represent not only confining geometries but also fixed solutes. We consider SC equations ranging from the modified Poisson–Boltzmann equations for the Coulomb potential to the hydrostatic linear response equation for the equilibrium density distribution of Lennard-Jones fluids. Here, we present a unified equation that explains the apparent diversity of previous forms and proves the equivalence of various SC equations. This unified description of SC equations is obtained from a hybrid method combining the conventional density functional theory and statistical field theory. The Gaussian approximation of density fluctuations around a mean-field distribution is performed based on the developed hybrid framework, allowing us to derive a novel form of the grand-potential density functional that provides the unified SC equation for equilibrium density.

Orientation effects and links between hydrostatic parameters in piezo-active 2–0–2 composites

The paper reports results on the large hydrostatic parameters of novel three-component 2–2-type composites based on [011]-poled relaxor-ferroelectric single crystals. The role of the rotation of the main crystallographic axes X and Y in forming the considerable hydrostatic piezoelectric response is studied. The composite consists of the single-crystal and 0–3 corundum ceramic/polyethylene layers that are regularly arranged along the non-polar axis. 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 and 0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3 single crystals poled along [011] of the perovskite unit cell are considered as main piezoelectric components of the composites with 2–0–2 connectivity. Links between the hydrostatic parameters (piezoelectric coefficients and squared figure of merit and electromechanical coupling factor ) are analysed by taking into account specifics of the microgeometry and elastic anisotropy of the 0–3 layer. Due to the large values of the aforementioned hydrostatic parameters, the studied 2–0–2 composites are of interest for hydroacoustic and piezoelectric energy-harvesting applications.

Hydrostatic Response of Deployable Hyperbolic-Paraboloid Umbrellas as Coastal Armor

This paper introduces an innovative structural system consisting of four-sided hyperbolic-paraboloid (hypar) roof umbrellas as hard countermeasures against nearshore hazards. The umbrellas line the coast and remain upright during normal operation, providing shade and shelter along the waterfront while not limiting access to the shore. A hinge at the hypar-column interface permits tilting to form a physical barrier against surge-induced coastal inundation. Analytical equations based on idealized boundary conditions are formulated in the hydrostatic regime. The equations provide insight into optimal geometric parameters and are used to validate a decoupled numerical scheme constituting smoothed particle hydrodynamics (SPH) and the finite element method (FEM). All numerical reactions concur with the analytical solutions for water inundation matching the total deployed height. A proof-of-concept study was employed to successfully illustrate the applicability of deployable hypar umbrellas as coastal armor from a structural engineering perspective. This work ultimately demonstrates the feasibility of decoupled SPH-FEM methods in modeling fluid-structure interaction involving hypar forms, while establishing a foundation for their analysis and design for coastal hazard adaptation.

Differences in gene modulation in Saccharomyces cerevisiae indicate that maturity plays an important role in the high hydrostatic pressure stress response and resistance

There is a strong relationship between the regulatory pathways to oxidative stress, longevity, and aging. High hydrostatic pressure (HHP) induces oxidative stress and activates cellular defense mechanisms. The understanding of these mechanisms is a strategy to delay damage associated with aging. Addressing resistance to stress and aging in Saccharomyces cerevisiae is a well-accepted approach since pathways involved in energy balance, damage accumulation and stress response are preserved among eukaryotes. The purpose of this study was to correlate the environmental stress response to cell maturity. HHP stress response on S. cerevisiae mother and daughter cells was evaluated through survival, reactive oxygen species (ROS) accumulation and gene expression. Mature cells were yeasts that had budded and originated at least one descendant, and young cells were the ones that did not form a bud. Mature cells were more resistant to HHP, although they showed a decrease in expression of antioxidants enzymes genes, and a higher intracellular levels of ROS. Young cells had less resistance to HHP despite a tendency of positively regulating these same antioxidant encoders. The TOR1 gene, related to aging and apoptosis, was unchanged in mother cells and showed a tendency toward increased expression in daughter cells submitted to HHP. The gene modulation differences of the mother and daughter cells indicates that maturity plays an important role in the HHP stress response and resistance. Thus, even accumulating high levels of ROS, mature cells were more tolerant to HHP stress and survived better, despite aging.

Design of active debris flow mitigation measures: a comprehensive analysis of existing impact models

Debris flows occur in mountainous areas characterized by steep slope and occasional severe rainstorms. The massive urbanization in these areas raised the importance of studying and mitigating these phenomena. Concerning the strategy of protection, it is fundamental to evaluate both the effect of the magnitude (that concerns the definition of the hazard), in terms of mobilized volume and travel distance, and the best technical protection structures (that concerns the mitigation measures) to reduce the existing risk to an acceptable residual one. In particular, the mitigation measure design requires the evaluation of the effects of debris flow impact forces against them. In other words, once it is established that mitigation structures are required, the impacting pressure shall be evaluated and it should be verified that it does not exceed barrier resistance. In this paper, the author wants to focus on the definition and the evaluation of the impacting load of debris flows on protection structures: a critical review of main existing models and equations treated in scientific literature is here presented. Although most of these equations are based on solid physical basis, they are always affected by an empirical nature due to the presence of coefficients for fitting the numerical results with laboratory and, less frequently, field data. The predicting capability of these equations, namely the capability of fitting experimental/field data, is analysed and evaluated using ten different datasets available in scientific literature. The purpose of this paper is to provide a comprehensive analysis of the existing debris flow impact models, highlighting their strong points and limits. Moreover, this paper could have a practical aspect by helping engineers in the choice of the best technical solution and the safe design of debris flow protection structures. Existing design guidelines for debris flow protection barrier have been analysed. Finally, starting from the analysis of the hydro-static model response to fit field data and introducing some practical assumptions, an empirical formula is proposed for taking into account the dynamic effects of the phenomenon.