Pressure Sensitivity Research Articles

Lifespan psychosocial stressors, optimism, and hemodynamic acute stress response in a national sample.

To understand the association between psychosocial stressors and cardiovascular health by evaluating: (a) lifespan patterns of childhood and adulthood stressors in relation to hemodynamic acute stress reactivity and recovery and (b) the role of optimism in these associations. Participants (n = 1,092, 56% women, 21% racial/ethnic minority, Mage = 56.2) were from the Midlife in the United States Study II Biomarker Project. Lifespan profiles of psychosocial stressor exposure (low lifespan exposure, high childhood only, high adulthood only, persistent exposure) were constructed from responses to the Childhood Trauma Questionnaire and a life events inventory. Optimism was measured with the Life Orientation Test-Revised. Hemodynamic acute stress reactivity to and recovery from cognitive stressors were assessed using a standardized laboratory protocol involving continuous measurements of systolic and diastolic blood pressure (BP) and baroreflex sensitivity (BRS). Compared with the low lifespan exposure group, the high childhood- and persistent-exposure groups showed lower BP reactivity, and to a lesser extent, slower BP recovery. Persistent exposure was also associated with slower BRS recovery. Optimism did not modify the association between stressor exposure and any hemodynamic acute stress responses. However, in exploratory analyses, greater stressor exposure across all developmental periods was indirectly associated with reduced BP acute stress reactivity and slower recovery via lower optimism levels. Findings support childhood as a unique developmental period wherein high adversity exposure may exert an enduring influence on adulthood cardiovascular health by limiting individuals' capacity to cultivate psychosocial resources and altering hemodynamic responses to acute stressors. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Self-healing Au/PVDF-HFP composite ionic gel for flexible underwater pressure sensor

Ionic gels can be potentially used in wearable devices owing to their high humidity resistance and non-volatility. However, the applicability of existing ionic gel pressure sensors is limited by their low sensitivity. Therefore, it is very important to develop an ionic gel pressure sensor with high sensitivity and a wide pressure detection range without sacrificing mechanical stretchability and self-healing ability. Herein, we report an effective strategy for developing pressure sensors based on ionic gel composites consisting of high-molecular-weight polymers, ionic liquids, and Au nanoparticles. The resulting capacitive pressure sensors exhibit high pressure sensitivity, fast response, and excellent self-healing properties. The sensors composed of highly hydrophobic polymers and ionic liquids can be used to track underwater movements, demonstrating broad application prospects in human motion state monitoring and underwater mechanical operations.

Time evolution of ambient pressure sensitivity of microbubbles subharmonic response as a function of hydrostatic pressure and the filling gas

The ultrasound contrast microbubbles have shown a great ability to produce nonlinear oscillations in response to acoustic excitation which results in the generation of harmonics and subharmonics of the excitation. The subharmonic response of ½ order changes significantly with a change in hydrostatic pressure in the physiological range. This property is being investigated for subharmonic aided pressure estimation (SHAPE), a noninvasive alternative to current methods for vascular pressure measurement in critical organs. In this study, the ambient pressure sensitivity of the subharmonic response of microbubbles with different gas cores and shells was investigated over 25–700 kPa acoustic pressure and the hydrostatic pressure range of 0–25 kPa. The subharmonic showed different trends of increase and decrease with hydrostatic pressure. The sensitivity has shown gradual change over time which was observed to be related to the hydrostatic pressure magnitude and the gas core. These findings could help to calibrate the SHAPE.

An Integrated Workflow for the Probabilistic Estimation of Pressure and Saturation Changes from 4D Seismic Data: Application to the Catcher Fields, Central North Sea

We present 4D seismic inversion to reservoir pressure and saturation changes applied to data from the Catcher fields. The inversion workflow integrates data from reservoir simulation, well logs and production volumes, time-lapse time shifts and angle-stacked 4D seismic amplitudes as well as machine learning and Bayesian inversion methods. It begins with a petro-elastic model and reservoir pressure sensitivity calibration step, using well log data and time-lapse time-shifts. A machine learning inversion is then used to create an initial estimate of the reservoir property changes. This estimate is then used as prior information, in conjunction with reservoir simulation pressure data, for a stochastic Bayesian inversion workflow. We show that the Bayesian inversion benefits from the use of machine learning prior, leading to improvements in the match to the observed 4D seismic signal as well as the injected and produced water volumes. In addition to a most probable solution, stochastic sampling of the Bayesian posterior distribution also produces uncertainty estimates which are valuable in such inversion problems. With this result, we extract multiple equiprobable realisations and define conditional bounds for the pressure and saturation changes, which we recognise as helpful for reservoir management and 4D seismic data assimilation into reservoir simulation models.

Abstract P100: Associations Between Urinary Biomarkers at Baseline and Salt and Potassium Sensitivity: The GenSalt Study

Introduction: Salt sensitivity of blood pressure is associated with an increased risk of hypertension and cardiovascular disease. Measurement methods of salt sensitivity of BP are inconvenient thus identifying biomarkers for salt sensitivity of BP has important clinical significance. Hypothesis: The urinary excretion of dopamine, kallikrein, norepinephrine and uromodulin at baseline are associated with salt sensitivity of BP. Methods: The Genetic Epidemiology Network of Salt Sensitivity (GenSalt) (n=1887) and GenSalt Replication (n=690) studies dietary interventions included a 3-day baseline exam, 7-day low sodium feeding, a 7-day high sodium feeding, and a 7-day high sodium feeding with potassium supplementation. Baseline urinary dopamine, kallikrein, norepinephrine, and uromodulin were measured by ELISA methods. Salt and potassium sensitivity were defined as change in SBP and DBP during dietary intervention. Urinary biomarkers below limit of detection (LOD) were replaced using LOD/√2 and censored likelihood multiple imputation (CLMI). Linear models between standardized log transformed urinary biomarkers and change in SBP and DBP were assessed after adjustment for age, baseline BP, sex, education, physical activity, smoking status, alcohol intake, 24-hour sodium excretion and GenSalt cohort. Results: Norepinephrine was positively associated with SBP in CLMI models (0.10 mmHg, CI: 0.00, 0.19) and DBP in LOD/√2 models (0.31 mmHg, CI: 0.05, 0.57) and CLMI models (0.10 mmHg, CI: 0.02, 0.18) during high sodium diet. Uromodulin was associated with decreased SBP in LOD/√2 models (-0.36 mmHg, CI: -0.57, -0.14) and CLMI models (-0.19 mmHg, CI: -0.31, -0.08) during potassium supplementation. Similarly, dopamine was positively associated with DBP during high sodium diet and negatively associated with DBP during potassium supplementation. Conclusion: These data indicate urinary biomarkers dopamine, norepinephrine and uromodulin are associated with BP salt sensitivity and may be used in risk stratification.

Responsive Liquid‐Crystal Microlaser Arrays with Tactile Perception

AbstractFlexible photonics has the potential to develop artificial skins with superior sensing capabilities. As an essential skin function, the tactile simulation is, however, still challenging due to the difficulty in combining high pressure sensitivity and resolution in sensor networks. Here, this work designs flexible artificial photonic skins for the vivid tactile perception based on responsive cholesteric liquid‐crystal (CLC) vertical‐cavity microlaser arrays. Controllable liquid‐crystal molecule arrangement is explored to synthesize the elastic CLC vertical microcavity lasers, which support a strong correlation between the laser output signals and the external pressures. Large‐scale integration of the CLC microlaser‐based mechanical sensors enables the spatially resolved detection of pressures. As a proof‐of‐concept demonstration of vivid tactile simulation, the flexible photonic chip consisting of a CLC microlaser array is used to identify the contact objects. These results present a significant advance in the construction of high‐performance flexible optical sensor networks, thus providing valuable guidance for the design of novel photonic skins.

A speakerless acoustic thermometer

Existing acoustic thermometers are often implemented using speaker-microphone systems, which are power-consuming and inconvenient to operate. Here we demonstrate a simple speakerless acoustic thermometer, which is an acoustic Fabry–Perot resonator (AFPR) consisting of a tubular acoustic waveguide and a microphone whose diaphragm acts as a reflective surface of the AFPR. Theoretical analysis shows that the resonant frequency (RF) ( fm ) at a given mode order (m) for the AFPR is a linear function of m with the slope (Δf/Δm) depending on the ambient temperature. Therefore, when the linear relationship between fm and m for the AFPR is measured, the ambient temperature can be determined from its slope. The values of fm at different m can be easily obtained by using the AFPR to detect ambient white noise rather than the sound signal from a loudspeaker. The thermometric performance of the prepared AFPR was investigated in a range of temperatures from −17 °C to 60 °C. The measured temperatures show the mean absolute error below 0.9 °C relative to those simultaneously obtained with a commercial electronic thermometer. As experimentally demonstrated in this work, the AFPR can detect extremely weak white noise in the anechoic room and thus enables to accurate measure the ambient temperature there, attributable to its ultrahigh pressure sensitivity at each RF. The advantages of simple structure, low power consumption, convenient operation, and high detection accuracy offer the AFPR outstanding applicability for on-site temperature measurements in various environments.

Temperature-induced inconsistency in the pressure sensitivity of polymer-diaphragm-based FP pressure sensors

Fiber optic Fabry-Perot Interferometer benefits many requirements in pressure sensing. The variation of pressure sensitivity of the polymer-diaphragm-based Fabry-Perot pressure sensor with temperature is studied by investigating the thermal effect of the cavity air and the diaphragm separately. FP cavity vacuum treatment and multi-curvature diaphragm simulation and experimental studies are conducted. Experimental results show that the sensor pressure sensitivity decreases with increasing temperature by 0.46nm/(kPa·°C). The diaphragm’s thermal effect is the leading cause of temperature-induced inconsistency in pressure sensitivity, accounting for 0.43nm/(kPa·°C).

Effect of bulky anions on the liquid-liquid phase transition in phosphonium ionic liquids: Ambient and high-pressure dielectric studies

Although the first-order liquid–liquid phase transition (LLT) has been reported to exist in various systems (i.e., phosphorus, silicon, water, triphenyl phosphite, etc.), it is still one of the most challenging problems in the field of physical science. Recently, we found that this phenomenon occurs in the family of trihexyl(tetradecyl)phosphonium [P666,14]+ based ionic liquids (ILs) with different anions (Wojnarowska et al in Nat Commun 13:1342, 2022). To understand the molecular structure–property relationships governing LLT, herein, we examine ion dynamics of two other quaternary phosphonium ILs containing long alkyl chains in cation and anion. We found that IL with the anion containing branched –O–(CH2)5–CH3 side chains does not reveal any signs of LLT, while IL with shorter alkyl chains in the anion brings a hidden LLT, i.e., it overlaps with the liquid-glass transition. Ambient pressure dielectric and viscosity measurements revealed a peculiar behavior of ion dynamics near Tg for IL with hidden LLT. Moreover, high-pressure studies have shown that IL with hidden LLT has relatively strong pressure sensitivity compared to the one without first-order phase transition. At the same time, the former exposes the inflection point indicating the concave-convex character of logτσ(P) dependences.

Ultrasensitive and Self-Powered Multiparameter Pressure-Temperature-Humidity Sensor Based on Ultra-Flexible Conductive Silica Aerogel.

The application of silica aerogel has been limited because of its poor mechanical properties. In order to expand the application scope of silica aerogel, this study fabricated an ultra-flexible conductive silica aerogel as a multiparameter sensor. The sample is fabricated by introducing poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) on a base of ultra-flexible silica aerogel, which was prepared by a diene synthesis reaction at atmospheric pressure. The pressure, temperature, and humidity can be converted into electrical signals. The pressure sensitivity can reach up to 54.88 kPa-1, and the detection limit is as low as 5 Pa. The temperature resolution is up to 0.1 K, and the response time of humidity is within 4 s. More importantly, the developed multiparameter sensor can be self-powered to realize multiparameter sensing of pressure, temperature, and humidity. The ultra-flexible conductive silica aerogel is a promising candidate for monitoring human activities and fire-affected areas.

Salt Taste and Salt Sensitive Hypertension in HIV.

To provide a summary of current literature and propose potential mechanistic models to help us understand the role of HIV infection/antiretroviral therapy (ART), salt taste sensitivity (STS), and salt sensitivity of blood pressure (SSBP) in hypertension development. The epithelial sodium channel (ENaC) is the main protein/sodium channel for recognizing Na + in the tongue and mediates preference to low-medium salt concentrations in animals and humans. Considering the pressor response to oral salt in individuals with SSBP, poor STS may worsen blood pressure. Specific genetic variants in ENaC are linked to salt taste perception and hypertension. HIV infection, some ART, and specific antihypertensive drugs are associated with reduced STS and an increased liking for salty foods. Persons with HIV (PWH) on ART may have a decreased STS and are at a higher risk of developing salt-sensitive hypertension. Inflammation mediated by dietary salt is one of the drivers of poor STS and salt-sensitive hypertension among PWH.

Role of adrenomedullin2/ intermedin in pregnancy induced vascular and metabolic adaptation in mice.

Introduction: Adrenomedullin2 (AM2) shares its receptor with Calcitonin gene related peptide and adrenomedullin with overlapping but distinct biological functions. Goal of this study was to assess the specific role of Adrenomedullin2 (AM2) in pregnancy induced vascular and metabolic adaptation using AM2 knockout mice (AM2 -/-). Method : The AM2 -/- mice were successfully generated using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Nuclease Cas nine system. Phenotype of pregnant AM2 -/- mice was assessed with respect to its fertility, blood pressure regulation, vascular health and metabolic adaptations and compared to the wild type littermates (AM2 +/+). Results : Current data shows that AM2 -/- females are fertile with no significant difference in number of pups/litter compared to the AM2 +/+. However, ablation of AM2 decreases the gestational length and the total number of pups born dead or that die after birth is greater in AM2 -/- mice compared to AM2 +/+ mice (p < 0.05). Further AM2 -/- mice exhibit elevated blood pressure and elevated vascular sensitivity for the contractile responses to angiotensin two and higher serum sFLT-1 trigylcerides levels compared to AM2 +/+(p < 0.05). In addition, AM2 -/- mice develop glucose intolerance with elevated serum levels of Insulin during pregnancy compared to the AM2 +/+mice. Discussion: Current data suggests a physiological role for AM2 in pregnancy induced vascular and metabolic adaptations in mice.

Precise Sensitivity Calculation Method of SAW-Based Pressure Sensor

In this work, we propose a precise sensitivity calculation method for a surface acoustic wave (SAW)-based pressure sensor. The Tiersten–Sinha perturbation theory and finite-element method (FEM) were used to analyze the mechanical properties of a diaphragm based on piezoelectric material and achieved the pressure sensitivity distribution. Many factors affecting the pressure sensitivity could be taken into consideration by this method, including the material, the dimension of the diaphragm, as well as the position of electrodes. To prove the theoretical prediction, SAW pressure-sensing devices in ST and AT quartz diaphragm at two different thicknesses are prepared, and electrodes are patterned at different positions on the surface defined as type I and type II. Measured results confirmed the excellent consistency between theoretical and experimental results. For the group of 0.45-mm diaphragm, comparing the theoretical and the experimental results, errors of the type I and type II ST quartz sensors are 3.92% and 2.63%, and the error of the type I AT quartz sensor is only 0.96%. For the group of 0.3-mm diaphragm, errors of type I ST and AT quartz are 6.3% and 1.6%, respectively.

An FBG Temperature–Pressure Sensor Based on Diaphragm and Special-Shaped Bracket Structure

A fiber Bragg grating (FBG) sensor capable of simultaneous temperature–pressure measurement is presented and experimentally verified, which consists of a diaphragm, a special-shaped bracket, dual FBGs, and protective housing. The principle of simultaneous temperature and pressure measurement with dual FBGs is theoretically illustrated and simulated by a finite-element analysis. The experimentally investigated results demonstrate that the sensor can be employed to measure temperature and pressure in environments where the temperature ranges from 50 °C to 200 °C and the pressure ranges from 0 to 40 MPa. The temperature sensitivity of the sensor is 31.8 pm/°C with a linear correlation coefficient of 0.9997; the pressure sensitivity is 50.6 pm/MPa, the linearity is 0.21%, and the repeatability and hysteresis error are 0.024% and 0.16%, respectively. The sensor exhibits a large measuring range, high-temperature resistance, miniaturized structure, and easily multiplexed, which allows it for temperature and pressure dual parametric measurements in high-temperature and high-pressure environments such as oil and gas wells.

Ag NW-Embedded Coaxial Nanofiber-Coated Yarns with High Stretchability and Sensitivity for Wearable Multi-Sensing Textiles.

The emerging intelligent piezoresistive yarn/textile-based sensors are of paramount importance for skin-interface electronics, owing to their unparalleled features including softness, breathability, and easy integration with functional devices. However, employing a facile way to fabricate 1D sensing yarns with mechanical robustness, multi-functional integration, and comfortability is still demanded for satisfying the practical applications. Herein, a facile one-step synchronous conjugated electrospinning and electrospraying technique is innovatively employed to continuously construct an Ag NW-embedded polyurethane (PU) nanofiber sensing yarn (AENSY) with hierarchical architecture. This 1D AENSY with weavability and stretchability can be woven into AENSY textile-based sensors integrated with functions of strain and pressure sensing. In this embedded multi-scale architecture, Ag NWs are evenly embedded and locked in the oriented and twisted PU nanofiber (PUNF) scaffold, forming the hierarchical mechanical sensing layer on the surface of the AENSY with favorable stability. Meanwhile, the presence of the elastic PUNFs enhances porosity, elasticity, and considerable deformation space, which in turn endow the AENSY textile-based sensor with a gauge factor (GF) up to 1010, a pressure sensitivity up to 16.7 N-1, high stretchability up to 160%, and high stability under long-term cycles. In addition, the AENSY textile-based sensor exhibits light weight and the unique advantage of skin-friendliness with the human body, which can be directly and conformally attached to the curved human skin to monitor the various human movements. Furthermore, the weavable AENSYs can be integrated into smart textiles with sensing arrays, which are capable for spatial pressure and strain mapping. Thus, the continuous one-step developing process and the stable embedded-twisted fiber structure provide a promising strategy to develop innovative smart yarns and textiles for personalized healthcare and human-machine interfaces.

Path-integral molecular dynamics predictions of equilibrium H and O isotope fractionations between brucite and water

Precise prediction of hydrogen (H) isotope fractionations among different substances is a long-standing challenge in isotope geochemistry, as it needs treatments beyond the harmonic approximation. Path-integral molecular dynamics (PIMD) simulations have recently been proved to be valid in predicting equilibrium isotope fractionations for light elements. However, the lack of reliable force fields hinders the application of PIMD to the condensed phases. In this work, the deep potential models trained on the first-principles molecular dynamics (FPMD) data are applied to PIMD simulations to determine the D/H and 18O/16O isotope fractionation factors between brucite and water. To quantitatively assess the influence of quantum effects, the D/H and 18O/16O isotope fractionations between brucite and water are also determined under the framework of harmonic approximation.By comparing the results of the PIMD and those of harmonic calculations, we find that H and O atoms in brucite and water are strongly affected by the anharmonic effects. The accuracy of the harmonic isotope fractionations mainly depends on the cancellation percentage of the anharmonic effects on the reduced partition function ratios (RPFRs) of the two substances. The isotope fractionations predicted by PIMD simulations are close to the experimental results at high temperatures. However, at low temperatures, the predicted isotope fractionations are different from those of experiments. The discrepancies are attributed to the approximations in the density functional theory (DFT) functionals used in this work, i.e., the inaccuracy in predicting the proton positions in brucite and water. Moreover, we find that the H isotope fractionations are extremely sensitive to the change of pressure. The direction of H isotope fractionation between brucite and water (at 300 K) will be even inversed as the pressure increases to more than 3 GPa. This strong pressure sensitivity may be a common characteristic of hydrous minerals and water systems. Therefore, the extrapolated H isotope fractionations used in the studies of dehydration of subducting slabs or deep Earth H distribution based on the isotope fractionations under low pressures may need to be rechecked.

Sodium alginate reinforced polyacrylamide/xanthan gum double network ionic hydrogels for stress sensing and self-powered wearable device applications

Strong and ductile sodium alginate (SA) reinforced polyacrylamide (PAM)/xanthan gum (XG) double network ionic hydrogels were constructed for stress sensing and self-powered wearable device applications. In the designed network of PXS-Mn+/LiCl (short for PAM/XG/SA-Mn+/LiCl, where Mn+ stands for Fe3+, Cu2+ or Zn2+), PAM acts as a flexible hydrophilic skeleton, and XG functions as a ductile second network. The macromolecule SA interacts with metal ion Mn+ to form a unique complex structure, significantly improving the mechanical strength of the hydrogel. The addition of inorganic salt LiCl endows the hydrogel with high electrical conductivity, and meanwhile reduces the freezing point and prevents water loss of the hydrogel. PXS-Mn+/LiCl exhibits excellent mechanical properties and ultra-high ductility (a fracture tensile strength up to 0.65 MPa and a fracture strain up to 1800%), and high stress-sensing performance (a high GF up to 4.56 and pressure sensitivity of 0.122). Moreover, a self-powered device with a dual-power-supply mode, i.e., PXS-Mn+/LiCl-based primary battery and TENG, and a capacitor as the energy storage component was constructed, which shows promising prospects for self-powered wearable electronics.

Leakage Characteristics of Proportional Directional Valve

This paper deals with the analysis of leakage characteristics of the proportional directional valve. These characteristics distinguish a real directional valve from an ideal one. The ideal directional valve is characterized by zero leakage due to its perfect geometry. The investigated element is the three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The spool position is measured by the inductive position sensor and processed by external electronics. Internal leakage occurs due to axial and radial clearances between the spool and the sleeve. The magnitude of axial clearances that occur at throttle edges and their effect on the directional valve leakage is the subject of research. The blocked-line pressure sensitivity curve, the leakage flow curve and the center flow curve are determined by experiment. Individual characteristics are determined for different working fluid temperatures and different supply pressures. The flow through internal leaks in the center position of the valve spool is determined by analytical calculations. The flow through internal leaks is also simulated using the Ansys Fluent software. Subsequently, the geometry of the flow simulation model is modified to take into account manufacturing tolerances. From simulation results, the effect of the manufacturing tolerance magnitude on the internal leakage of the directional valve is evaluated. Finally, simulated dependencies are compared with experimentally determined characteristics.

Ultra-high sensitivity gas pressure sensor based on cascaded Mach-Zehnder interferometer and Sagnac interferometer

A highly sensitive optical fiber gas pressure sensor based on Vernier effect of cascaded optical fiber Sagnac interferometer (SI) and Mach Zehnder interferometer (MZI) is proposed, and the sensing characteristics are verified. The SI consists of a 3 dB coupler and a section of panda fiber, and SI is used as a filter. As the sensing part, MZI has high sensitivity and good stability. It is composed of single-mode fiber, multimode fiber and quartz capillary. By controlling the length of two interferometers, their free spectrum ranges (FSR) are similar but not equal. Therefore, the cascade structure produces the Vernier effect, which can amplify the gas pressure sensitivity of the sensor. The experimental results show that the gas pressure sensitivity of a single MZI is only − 7.75 nm/MPa. The cascade structure can amplify the sensitivity to − 211.9 nm/MPa, and the magnification factor is 27.3, which is consistent with the theoretical analysis results. In addition, the proposed sensor has excellent repeatability and stability.

Fracture mechanism and failure strain of TA31 titanium alloy for deep-sea pressure hulls based on continuum damage mechanics

Titanium alloys has high fatigue resistance, high corrosion resistance, high temperature resistance, and other excellent properties, and have been widely used in deep-sea equipment and aviation industries. In this paper, the fracture mechanism and failure strain of TA31 titanium alloy, which has been widely used in deep-sea equipment, were studied experimentally and numerically in different stress states. Considering the pressure sensitivity, the Modified Johnson-Cook (MJC) model and the Bonora damage model were used to study the fracture behavior. In order to obtain the parameters of models, four types of specimens under different stress triaxiality were conducted, and a hybrid experimental-numerical approach was employed in this paper. Then, the coupled constitutive elastic–plastic-damage model was developed and implemented in ABAQUS explicit finite element analysis (FEA) code. Finally, to validate the suggested model, FEA simulation was carried out and compared with the experimental results. The comparison revealed that the Bonora model with constant parameters was not enough to predict the failure strain. The damage parameters were sensitive to the stress triaxiality. In addition, the fracture morphology was observed by scanning electron microscope (SEM), which revealed the micro-mechanism of failure for TA31 titanium alloy. It is concluded that a higher stress triaxiality and shear mechanism lead to lower plastic deformation, and will inhibit the void growth on the damage evolution.