Application Of Hydrostatic Pressure Research Articles

Gradual pressure-induced enhancement of magnon excitations in CeCoSi

CeCoSi is an intermetallic antiferromagnet with a very unusual temperature-pressure phase diagram: at ambient pressure it orders below $T_{\mathrm{N}} = 8.8$ K, while application of hydrostatic pressure induces a new magnetically ordered phase with exceptionally high transition temperature of $\sim40$ K at 1.5 GPa. We studied the magnetic properties and the pressure-induced magnetic phase of CeCoSi by means of elastic and inelastic neutron scattering (INS) and heat capacity measurements. At ambient pressure CeCoSi orders into a simple commensurate AFM structure with a reduced ordered moment of only $m_{\mathrm{Ce}} = 0.37(6)$ $\mu_{\mathrm{B}}$. Specific heat and low-energy INS indicate a significant gap in the low-energy magnon excitation spectrum in the antiferromagnetic phase, with the CEF excitations located above 10 meV. Hydrostatic pressure gradually shifts the energy of the magnon band towards higher energies, and the temperature dependence of the magnons measured at 1.5 GPa is consistent with the phase diagram. Moreover, the CEF excitations are also drastically modified under pressure.

Effect of chemical and external hydrostatic pressure on magnetic and magnetocaloric properties of Pt doped Ni2MnGa shape memory Heusler alloys

The magnetocaloric effect (MCE) on Ni2−xPtxMnGa (x = 0.2, 0.3 and 1.0) shape memory Heusler alloys around martensite phase transition temperature (TM) is investigated by varying chemical pressure (Pt concentration). The magnetic entropy change (ΔSM) decreases with increasing chemical pressure for various external applied magnetic fields up to 3 T, and the width of thermal hysteresis increases with the increases of Pt concentration. The effect of hydrostatic pressure on both TM and ΔSM for Ni1.8Pt0.2MnGa is also investigated. We observed that the application of hydrostatic pressure increases TM (3.5 K/GPa) and stabilizes the martensite phase. The maximum magnetic entropy change (ΔSmax) of 9.31 J Kg−1 K-1is observed for a field change of 9 T at ambient pressure for Ni1.8Pt0.2MnGa. Further, the application of external pressure leads to the decrease of ΔSmax to 5.52 J Kg−1 K−1 at 0.91 GPa.

Measurement and comparison of multi-scale structure in heat and pressure treated corn starch granule under the same degree of gelatinization

In order to popularize the application of high hydrostatic pressure (HHP) in staple food, the different impact of HHP (from 300 to 600 MPa) and heat treatment (from 60 to 75 °C) on corn starch (80 wt%) under the same DG was investigated. Granule morphology, crystalline characteristics, short-range ordered structure and lamellae structure was examined with a combination of SEM, CLSM, XRD, ATR-FTIR, and SAXS. Results obtained demonstrated Heat-Treated starch appeared endo- and exo-corrosion with more collapses and destructiveness, whereas just endo-corrosion with a dense periphery was induced by HHP. Under the same degree of gelatinization (DG), the long-range and short-range structure sustained more ordered in Pressure-Treated starch than Heat-Treated starch. Further, Heat-Treated starch exhibited more flawed semi-crystalline lamellae. The larger DG, the thicker amorphous lamellae thickness (da) of Heat-Treated starch and Pressure-Treated starch was. Moreover, when DG up to 70%, the increase of da in Heat-Treated starch was more obvious. Heat treatment was shown to be more severe than HHP to disrupt the lamellae. The loss of semi-crystalline structure order occurs more violent than crystalline structure for corn starch. It is of value to reveal that heat and HHP treatment led to similar change trend for multi-scale structural features, whereas the change extent was quite various. This study was potential to provide a theoretical basis to improve the quality of novel starch-based food.

High pressure investigation of an organic three-dimensional Dirac semimetal candidate having a diamond lattice

$(\mathrm{ET}){\mathrm{Ag}}_{4}{(\mathrm{CN})}_{5}$ [ET = BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene] is a rare example of organic conductors that crystallizes in a diamond structure due to the tetrahedral arrangement of neighboring ET molecules. Because each ET has a $+1$ site charge, the band is half filled, which in combination with strong Coulomb interactions, turn $(\mathrm{ET}){\mathrm{Ag}}_{4}{(\mathrm{CN})}_{5}$ into a Mott insulator. Recently, it was realized that this material may realize a nodal Dirac semimetal with a diamondlike lattice, whose state can be induced by suppressing the strong electron correlations. In this report, we present high pressure transport and optical studies on $(\mathrm{ET}){\mathrm{Ag}}_{4}{(\mathrm{CN})}_{5}$. Our transport study indicates that the activation energy is highly suppressed by the application of hydrostatic pressure. At high pressures, the system varies from activated behavior into Coulomb gap variable range hopping.

Magnetotransport properties of tellurium under extreme conditions

This study investigates the transport properties of a chiral elemental semiconductor tellurium (Te) under magnetic fields and pressure. Application of hydrostatic pressure reduces the resistivity of Te, while its temperature dependence remains semiconducting up to 4 GPa, contrary to recent theoretical and experimental studies. Application of higher pressure causes structural as well as semiconductor-metal transitions. The resulting metallic phase above 4 GPa exhibits superconductivity at 2 K along with a noticeable linear magnetoresistance effect. On the other hand, at ambient pressure, we identified metallic surface states on the as-cleaved ($10\overline{1}0$) surfaces of Te. The nature of these metallic surface states has been systematically studied by analyzing quantum oscillations observed in high magnetic fields. We clarify that a well-defined metallic surface state exists not only on chemically etched samples that were previously reported, but also on as-cleaved ones.

Hydrostatic Pressure Regulates Oxidative Stress through microRNA in Human Osteoarthritic Chondrocytes.

Hydrostatic pressure (HP) modulates chondrocytes metabolism, however, its ability to regulate oxidative stress and microRNAs (miRNA) has not been clarified. The aim of this study was to investigate the role of miR-34a, miR-146a, and miR-181a as possible mediators of HP effects on oxidative stress in human osteoarthritis (OA) chondrocytes. Chondrocytes were exposed to cyclic low HP (1–5 MPa) and continuous static HP (10 MPa) for 3~h. Metalloproteinases (MMPs), disintegrin and metalloproteinase with thrombospondin motif (ADAMTS)-5, type II collagen (Col2a1), miR-34a, miR-146a, miR-181a, antioxidant enzymes, and B-cell lymphoma 2 (BCL2) were evaluated by quantitative real-time polymerase chain reaction qRT-PCR, apoptosis and reactive oxygen species ROS production by cytometry, and β-catenin by immunofluorescence. The relationship among HP, the studied miRNA, and oxidative stress was assessed by transfection with miRNA specific inhibitors. Low cyclical HP significantly reduced apoptosis, the gene expression of MMP-13, ADAMTS5, miRNA, the production of superoxide anion, and mRNA levels of antioxidant enzymes. Conversely, an increased Col2a1 and BCL2 genes was observed. β-catenin protein expression was reduced in cells exposed to HP 1–5 MPa. Opposite results were obtained following continuous static HP application. Finally, miRNA silencing enhanced low HP and suppressed continuous HP-induced effects. Our data suggest miRNA as one of the mechanisms by which HP regulates chondrocyte metabolism and oxidative stress, via Wnt/β-catenin pathway.

Pressure tuning of the anomalous Hall effect in the chiral antiferromagnet Mn3Ge

We report on the pressure evolution of the giant anomalous Hall effect (AHE) in the chiral antiferromagnet Mn$_3$Ge. The AHE originating from the non-vanishing Berry curvature in Mn$_3$Ge can be continuously tuned by application of hydrostatic pressure. At room temperature, the Hall signal changes sign as a function of pressure and vanishes completely at $p=1.53$ GPa. Even though the Hall conductivity changes sign upon increasing pressure, the room-temperature saturation value of 23 ${\rm \Omega^{-1}cm^{-1}}$ at 2.85 GPa is remarkably high and comparable to the saturation value at ambient pressure of about 40 ${\rm \Omega^{-1}cm^{-1}}$. The change in the Hall conductivity can be directly linked to a gradual change of the size of the in-plane components of the Mn moments in the non-collinear triangular magnetic structure. Our findings, therefore, provide a route for tuning of the AHE in the chiral antiferromagnetic Mn$_3$Ge.

Carbon nanotube with pressure inducing pseudogaps: Kondo effect study

The Kondo effect of a T-shape ligation between a single-wall carbon nanotube (SWNT) and a magnetic impurity is investigated theoretically. Hydrostatic pressure is applied, which leads to the opening of a gap in the density of states of a zigzag metallic nanotube. The effect of the pressure can be modeled by the Peierls instability; in this work, we consider the out-of-plane distortion. We use the tight-binding approach to calculate the SWNT Green’s functions with the application of hydrostatic pressure. We investigate the disappearance of the Kondo peak as the gap opens. A strong influence of the pressure on the conductance is found, which is explained by the displacement of the Kondo peak from the chemical potential. The Kondo effect was reproduced using the atomic approach with U→∞ developed previously.

Modulation of GPCR Function by Membrane Lipids and Water

G‐protein‐coupled receptors (GPCRs) are integral membrane proteins that regulate a wide range of normal and disease‐related physiological processes. Our understanding of the role of soft matter such as membrane lipids and cellular water on activation and regulation of the GPCR function remains incomplete. In the standard biochemical model, GPCRs behave as primarily agonist dependent bimodal switches, with little influence of the surrounding medium. However, using the visual receptor rhodopsin as a model GPCR, we show that water drives rhodopsin to a partially disordered, solvent‐swollen conformational ensemble upon light absorption, rendering the standard model obsolete [1], [2]. We placed rhodopsin under varying degrees of osmotic stress using polyethylene glycol solutes and investigated the activation equilibrium response using UV‐Visible spectroscopy. Our results show a flood of ~ 80 water molecules into the rhodopsin interior during photoactivation, a result supported by atomistic molecular dynamics simulations [3]. Furthermore, the osmolyte effects on rhodopsin activation are size dependent: large osmolytes back shift the equilibrium to inactive metarhodopsin‐I (MI), while small osmolytes forward‐shift the equilibrium to active metarhodopsin‐II (MII). We attribute these size effects to varying degrees of osmolyte penetration into the rhodopsin core. Large polymers behave similarly to ideal osmolytes and dehydrate rhodopsin, while smaller polymers wriggle into the rhodopsin interior and stabilize the open MII conformation of rhodopsin. Besides osmotic pressure, the application of hydrostatic pressure also back shifts the metarhodopsin equilibrium but for fundamentally different reasons. Integrating the two force‐based methods together with neutron scattering experiments indicates that the active state of rhodopsin is more hydrated yet simultaneously more structurally collapsed [4]. At the same time, the active GPCR undergoes dynamic volume fluctuations and solvent coupling, which give rise to greater thermal volume. Our results necessitate a new understanding of GPCR activation in which the surrounding soft matter is paramount in governing conformational energy landscapes.Support or Funding InformationNSF (MCB 11817862 and CHE 1904125) and US NIH (EY012049 and EY02604)

The effect of high pressure treatment on the quality of chicken breast meat

In the present work, the effect of high pressure processing (HPP) (0, 100, 200 and 300 MPa) and different treatment time (5 and 10 minutes) on the moisture uptake, cooking yield, colour and texture, as well as microbial population of chicken breast fillets was investigated. The application of high hydrostatic pressure resulted in a modification of quality parameters of chicken breast meat. By increasing pressure and time of the treatment the moisture uptake was reduced: samples treated with 300 MPa for 10 min had the lowest moisture uptake values. Cooking yield was not affected by HPP treatments. Increased pressure affected the colour by increasing L*, a* and b* values (only HPP treatment of 100 MPa in duration of 5 and 10 minutes did not affect colour of chicken breast meat). Lower pressures (100 and 200 MPa) tenderized, whereas elevated pressure (300 MPa) increased hardness in chicken breast fillets. Higher level of pressure (300 MPa) reduced bacteria count by about 3.0 – 5.3 log (CFU/g), depending on the microorganism and duration of the process.

G-Protein-Coupled Receptors are Solvent-Swollen in the Functionally Active State

G-protein-coupled receptors (GPCRs) are transmembrane receptors that play critical roles in a number of physiological signaling processes. In the standard biochemical model, GPCRs behave as primarily agonist-dependent bimodal switches, with little influence of the surrounding medium. However, using the visual receptor rhodopsin as a model GPCR, we show that water drives rhodopsin to a partially disordered, solvent-swollen conformational ensemble upon light absorption, rendering the standard model obsolete. We placed rhodopsin under varying degrees of osmotic stress using polyethylene glycol solutes and investigated the activation equilibrium response using UV-visible spectroscopy. Our results show a flood of ∼80 water molecules into the rhodopsin interior during photoactivation, a result supported by atomistic MD simulations [1]. Furthermore, the osmolyte effects on rhodopsin activation are size-dependent: large osmolytes back shift the equilibrium to inactive metarhodopsin-I (MI), while small osmolytes forward-shift the equilibrium to active metarhodopsin-II (MII). We attribute these size effects to varying degrees of osmolyte penetration into the rhodopsin core. Large polymers behave similarly to ideal osmolytes and dehydrate rhodopsin, while smaller polymers wriggle into the rhodopsin interior and stabilize the open MII conformation of rhodopsin. Besides osmotic pressure, the application of hydrostatic pressure also back shifts the metarhodopsin equilibrium but for fundamentally different reasons. Integrating the two force-based methods together with neutron scattering experiments [2] indicates that the active state of rhodopsin is more hydrated yet more locally collapsed. At the same time, the active GPCR undergoes volume fluctuations and solvent coupling, which give rise to greater thermal volume. The combined force-based results necessitate a new understanding of GPCR activation in which the surrounding soft matter is paramount in governing conformational energy landscapes. [1] N. Leioatts et al. (2014) Biochemistry 53, 376−385. [2] S.M.D.C. Perera et al. (2018) J. Phys. Chem. Lett.9, 7064−7071.

Behavior of photoluminescence energy in polar ZnCdO/ZnO quantum wells under hydrostatic and uniaxial pressures: Linear and nonlinear piezoelectric contributions

Abstract Dependence of the photoluminescence (PL) energy ( E P L ) in polar ZnCdO/ZnO quantum wells (QWs) on hydrostatic and uniaxial pressures are investigated as regards the Cd concentration of the structures and their physical dimension. The calculations are carried out within the framework of the effective mass and envelope function approximations. The built-in electric field is incorporated into the calculations using a piezoelectric polarization expression up to a nonlinear regime. It is found that the nonlinearity in piezoelectric polarization, under the effect of the hydrostatic pressure, leads to a large built-in electric field up to 5 MV/cm in consequence of the high lattice mismatch existing in the structures. The resulting quantum confined Stark effect causes a decreasing d E P L ∕ d p from 23.6 meV/GPa down to even negative values, such as − 6 . 46 meV/GP, for the QWs up to 50 A in width. A linear relationship between E P L at ambient pressure E P L , 0 and d E P L ∕ d p is obtained in both cases of the hydrostatic and uniaxial pressure applications. It is seen that the relationship is universal in view of the Cd concentration.

Nonlinear pressure effect on the electronic states induced by a defect layer in a Multi-Quantum wells structure

The application of the hydrostatic pressure modifies the height of the barrier, the effective masses and the thicknesses of the Multi-Quantum Wells (MQWs) constituting. We apply a hydrostatic pressure on a perfect GaAs/GaAlAs MQWs; this pressure modifies the structure of the electronic band, which leads to modification of the energies of the electrons states. So in order to show the effect of the external pressure on the proposed structure, we studied the variation of the electronic transmission as a function of the energy of the incoming electronic wave, for different applied pressure values. The electronic states are moving towards low energies when we increase the hydrostatic pressure. Besides, the application of hydrostatic pressure on MQW structure with defect layer, shows the important sensitivity of the induced electrons defect states on the intensity of the applied pressure.

Pressure effect on the electrical resistance of Y0.77Pr0.23Ba2Cu3O7-δ single crystals

The effect of hydrostatic pressure up to 12 kbar on the electrical resistance in the basal ab-plane of optimally oxygen-doped (δ<0.1) single crystals Y1–xPrxBa2Cu3O7–δ moderately doped with praseodymium (x≈0.23) with a critical temperature Tc≈67 K. Compared to undoped single-crystal YBa2Cu3O7–δ, doping with praseodymium led to a decrease in the critical temperature by ≈24 K with a simultaneous increase in ρab (300 K) by ≈130 μΩcm. In the region of the transition to the superconducting state, several clearly pronounced peaks are observed on the dρ/dT – T curves, which indicates the presence of several phases with different critical temperatures in the sample. The application of high hydrostatic pressure leads to an increase in Tc by about 3 K. This increase slows down with increasing pressure, and the baric derivatives, dTc/dP, decrease from 0.44 K/kbar at atmospheric pressure to 0.14 K/kbar at 11 kbar. The comparatively weak change in the critical temperature under the action of hydrostatic pressure is due to the relatively small value of the orthorhombic distortion, (a–b)/a. The change in the baric derivative dTc/dP upon all-round compression of the sample is due to the fact that, along with an increase in the Debye temperature, the matrix element of the electron-phonon interaction also increases. Possible mechanisms of the effect of high pressure on Tc are discussed taking into account the presence of features in the electronic spectrum of carriers.

Effect of non-magnetic Ag-doping on magnetic and magnetofunctional properties of MnNiGe alloy

Systematic investigations on Ag-doped MnNiGe alloys of nominal compositions MnNi1−xAgxGe (x = 0.10, 0.15 and 0.20) have been performed through dc magnetic measurements in ambient as well as in high pressure conditions. All the Ag-doped alloys undergo martensitic type structural phase transition with a monotonic decrease in transition temperature with increasing Ag concentration. Room temperature x-ray powder diffraction data confirm the presence of both hexagonal and orthorhombic phase for 10% Ag-doped alloy whereas, 15% and 20% Ag-doped alloys are found to be purely hexagonal in nature. Gradual incorporation of ferromagnetic interaction with increasing Ag-concentration in otherwise antiferromagnetic alloy is clear from the magnetic investigations. Application of external hydrostatic pressure further favors ferromagnetism. In addition, these Ag-doped alloys also show a reasonably high magnetocaloric effect around the magnetic and structural transition temperatures which makes these alloys important for magnetic cooling applications. The robustness of the observed magnetocaloric properties have also been checked by high pressure measurements.

Tuning dimensionality in van-der-Waals antiferromagnetic Mott insulators TMPS3

We present an overview of our recent work in tuning and controlling the structural, magnetic and electronic dimensionality of 2D van-der-Waals antiferromagnetic compounds (Transition-Metal)PS3. Low-dimensional magnetic systems such as these provide rich opportunities for studying new physics and the evolution of established behaviours with changing dimensionality. These materials can be exfoliated to monolayer thickness and easily stacked and combined into functional heterostructures. Alternatively, the application of hydrostatic pressure can be used to controllably close the van-der-Waals interplanar gap and tune the crystal structure and electron exchange paths towards a 3D nature. We collect and discuss trends and contrasts in our data from electrical transport, Raman scattering and synchrotron x-ray measurements, as well as insight from theoretical calculations and other results from the literature. We discuss structural transitions with pressure common to all materials measured, and link these to Mott insulator-transitions in these compounds at high pressures. Key new results include magnetotransport and resistivity data in the high-pressure metallic states, which show potentially interesting qualities for a new direction of future work focussed on low temperature transport and quantum critical physics.

Effect of chemical and hydrostatic pressure on the coupled magnetostructural transition of Ni-Mn-In Heusler alloys

Ni-Mn-In magnetic shape-memory Heusler alloys exhibit generally a large thermal hysteresis at their first-order martensitic phase transition which hinder a technological application in magnetic refrigeration. By optimizing the Cu content in Ni$_2$Cu$_x$Mn$_{1.4-x}$In$_{0.6}$, we obtained a thermal hysteresis of the martensitic phase transition in Ni$_{2}$Cu$_{0.2}$Mn$_{1.2}$In$_{0.6}$ of only 6 K. We can explain this very small hysteresis by an almost perfect habit plane at the interface of martensite and austenite phases. Application of hydrostatic pressure does not reduce the hysteresis further, but shifts the martensitic transition close to room temperature. The isothermal entropy change does not depend on warming or cooling protocols and is pressure independent. Experiments in pulsed-magnetic fields on Ni$_{2}$Cu$_{0.2}$Mn$_{1.2}$In$_{0.6}$ find a reversible magnetocaloric effect with a maximum adiabatic temperature change of -13 K.

Investigation of the transport, magnetic and flux pinning properties of the noncentrosymmetric superconductor TaRh2B2 under hydrostatic pressure

The bulk superconducting properties of polycrystalline TaRh2B2 under pressure are investigated with transport resistivity [ρ(T)], and dc magnetization [M(T) and M(H)] measurements up to ~3 GPa, and 1 GPa respectively. The application of hydrostatic pressure leads to a decrease in Tc for both magnetic [dTc/dP is −0.4 K/GPa (0 ≤ P ≤ 1 GPa)] and transport [(dTc/dP) is −0.02 K/GPa (0 ≤ P ≤ 1 GPa) and −0.06 K/GPa (1 ≤ P ≤ 2.5 GPa)] measurements. At 2.5 GPa the upper critical field, μ0Hc2(0), and the irreversible field, μ0Hirr(0), are found to be (11.8 ± 0.2) T and (6.5 ± 0.1) T respectively. The critical current density, Jc (at μ0H = 0 T), decreases from 6.5 × 105 A/cm2 (0 GPa) to 2.5 × 105 A/cm2 (0.9 GPa) at 4.3 K. The flux pinning and Jc(H) in TaRh2B2 are significantly affected by the application of external pressure. It is seen that surface and volume flux pinning coexist both at ambient pressure and at high pressure. We infer that the pinning energy and superconducting properties are suppressed by external pressure.

Weak antilocalization effect and high-pressure transport properties of ScPdBi single crystal

Half-Heusler compounds have attracted considerable attention due to their fantastic physical properties that include topological effects, Weyl fermions, unusual magnetism, and superconductivity. Herein, the transport properties of half-Heusler ScPdBi single crystals are studied across a wide temperature range and different magnetic fields. From the field-dependent magnetoresistance, we observe a clear weak antilocalization (WAL) effect below 200 K in the low magnetic-field region. The angle-dependent magnetoconductance and the ultralarge prefactor α extracted from the Hikami-Larkin-Nagaoka equation reveal that the WAL effect is a 3D bulk effect caused by strong spin–orbit coupling. We further studied the magnetotransport properties of the single crystal upon application of hydrostatic pressure and found that the energy gap of ScPdBi increases gradually as the hydrostatic pressure increases. Density functional theory calculations confirm that applying hydrostatic pressure decreases the lattice parameters and, consequently, enlarges the bandgap.

Modeling the Mechanical Parameters of Glaucoma.

Glaucoma is a major eye disease characterized by a progressive loss of retinal ganglion cells (RGCs). Biomechanical forces as a result of hydrostatic pressure and strain play a role in this disease. Decreasing intraocular pressure is the only available therapy so far, but is not always effective and does not prevent blindness in many cases. There is a need for drugs that protect RGCs from dying in glaucoma; to develop these, we need valid glaucoma and drug screening models. Since in vivo models are unsuitable for screening purposes, we focus on in vitro and ex vivo models in this review. Many groups have studied pressure and strain model systems to mimic glaucoma, to investigate the molecular and cellular events leading to mechanically induced RGC death. Therefore, the focus of this review is on the different mechanical model systems used to mimic the biomechanical forces in glaucoma. Most models use either cell or tissue strain, or fluid- or gas-controlled hydrostatic pressure application and apply it to the relevant cell types such as trabecular meshwork cells, optic nerve head astrocytes, and RGCs, but also to entire eyes. New model systems are warranted to study concepts and test experimental compounds for the development of new drugs to protect vision in glaucoma patients. Impact Statement The outcome of currently developed models to investigate mechanically induced retinal ganglion cell death by applying different mechanical strains varies widely. This suggests that a robust glaucoma model has not been developed yet. However, a comprehensive overview of current developments is not available. In this review, we have therefore assessed what has been done before and summarized the available knowledge in the field, which can be used to develop improved models for glaucoma research.