Pressure measurements in the microcirculation with active and passive transducers

Accurate pressure measurements in harsh environments are necessary to accommodate distributed jet engine control using various feedback schemes communicating with the Full Authority Digital Engine Control (FADEC) unit. Active combustion control requires feedback to the engine control system in order to adjust the quantity, timing, and placement of fuel charges. Understanding the complex interaction of air and fuel during combustion will help scientists design and construct quieter, safer, faster and more powerful aircraft engines and other propulsion systems. Current state-of-the-art pressure measurement instruments used in jet engines may employ MEMS-based silicon or silicon carbide sensors arranged in a variety of configurations, some of which may be coupled to optical fibers. Although the measurement signals are generally not distorted by the engine's electromagnetic fields, measurements obtained through current methods may be compromised due the high temperature range, its rapid rate of change, g-levels and lifespan issues. Alternatively, intrinsic optical fiber properties may be exploited because a silica fiber acts as a pre-stressed optically anisotropic force-deformation element when subjected to an applied load. Pre-stressing the fiber during the drawing process enables positive (tension) and negative (compression) forces to be quantified. In this paper we present a technique to perform static and fast transient pressure measurements using a single optical fiber as a pressure-sensing element. Since fused silica has a frequency response on the order of 100 kHz and an annealing temperature in excess of 1100 o C, optical fiber makes an excellent candidate for combustion engine applications. Linearly polarized light is phase-modulated and then transmitted through the optical fiber, which has a reflective coating sputtered onto the terminating surface. The polarization state of the transmitted and reflected light is altered through the silica fiber by the intrinsic static birefringence inherent in fused silica and by an additional amount determined by the applied load. By examining the interaction of polarized light with the silica fiber, the amount of molecular deformation and thus the applied pressure may be obtained. Phase modulation creates an infinite series of sine waves so that a Fourier-Bessel expansion may be used to separate signals of interest from noise using offset homodyning signal recovery techniques. Ratio analysis of the dc and harmonic signals yields the optical phase retardance and mathematically relates this quantity to the applied pressure by the Stress-optic rule. Several prototype phase-modulated stress-induced birefringence based fiber-optic high-temperature pressure sensors were recently developed at NASA Glenn Research Center to operate at temperatures in excess of 600 o C for an absolute pressure range from 14 psia to 1029 psia. This paper presents the design theory, fabrication methods and laboratory test results obtained with these prototypes.

In this paper, the vibration behavior of atomic force microscopy (AFM) micro-cantilever (MC) with a piezoelectric layer in the non-contact mode considering the axial load in the air medium was studied. In the dynamic modes of AFM nano-robot, parameters such as amplitude, frequency and motion phase are used as feedback factors in the control system in order to extract sample surface information and the nanoparticle voltage. Consequently, to extract these parameters, the vibration analysis of the MCs of this nano-robot is essential. Additionally, because of the wide-spread applications of oblique MCs, applying the axial and transverse forces into the model is absolutely necessary. In order to simulate the AFM four-layered piezoelectric MC with the axial displacement, Timoshenko beam theory as well as modified couple stress theory has been used. Considering the axial displacement in the modeling not only leads to more degrees of freedom, but also has increased the amount of calculations. To extract the equations of the system, energy method has been used, and then, the FEM was applied to discrete the equations. To verify the accuracy of the results, the frequency and time responses of FEM have been compared with the results of the 3D mode simulation obtained by COMSOL software and experimental results. The comparison of results indicates that modifying the modeling by considering the axial displacement has increased the accuracy of the frequency and time responses. The error percentage of the first frequency response is 0.42% and the error percentage of the time response is 0.0053%. Furthermore, to examine the effect of MC geometry on its vibrational behavior, frequency and time responses of three common geometries of AFM MCs have been extracted. The results illustrate the improvement of modeling in all three geometries. Then, the sample surface topography of MCs at the first and second excitation frequencies in contact with rectangular roughnesses demonstrated the decline of time delay at the second excitation frequency. The results of the topography simulation in the air environment show that the roughness’s trend is better at the second mode than at the first mode. Finally, the effect of MC angle on the topography of the rectangular MC surfaces in contact with the rectangular roughness in 2D and 3D modes was examined in the presence and the absence of axial load. The results show that in the presence of the axial displacement in modeling, by increasing of MC angle, the topography quality increases drastically.

Accurate static and dynamic pressure measurements in liquids, such as fuel, oil, and hydraulic fluid, are critical to the control and health monitoring of turbomachinery and aerospace systems. This work presents a theoretical and experimental study of the frequency response of pressure transducers and pressure measurement systems in liquid media. First, we theoretically predict the frequency response of pressure transducers based upon a lumped-parameter model. We then present a liquid-based dynamic pressure calibration test apparatus that validates this model by performing several critical measurements. This system first uses a vibrating liquid column to dynamically calibrate and experimentally determine the frequency response of a test pressure transducer, measurement system or geometry. Second, this calibration system experimentally extracts the bulk modulus of the fluid and the percent of entrained and/or dissolved air by volume. Bulk modulus is determined by measuring the speed of sound within the liquid and through static pressure loading while measuring the deflection of the liquid column. Bulk modulus and the entrained/dissolved gas content within the liquid greatly impact the observed frequency response of a pressure transducer or geometry. Gases, such as air, mixed or dissolved into a fluid can add substantial damping to the dynamic response of the fluid measurement system, which makes measurement of the bulk modulus and entrained and/or dissolved air critical for accurate measurement of the frequency response of a system when operating with a liquid media. All experimental results are compared to theoretical predictions.

<h3>Abstract</h3> The sensing of abiotic stress, mechanical injury, or pathogen attack by a single plant tissue results in the activation of systemic signals that travel from the affected tissue to the entire plant, alerting it of an impending stress or pathogen attack. This process is essential for plant survival during stress and is termed systemic signaling. Among the different signals triggered during this process are calcium, electric, reactive oxygen species (ROS) and hydraulic signals. These are thought to propagate at rapid rates through the plant vascular bundles and to regulate many of the systemic processes essential for plant survival. Although the different signals activated during systemic signaling are thought to be interlinked, their coordination and hierarchy remain to be determined. Here, using a combination of advanced whole-plant imaging and hydraulic pressure measurements, we studied the activation of all four systemic signals in wild type and different <i>Arabidopsis thaliana</i> mutants subjected to a local high light (HL) stress or wounding. Our findings reveal that in response to wounding systemic changes in membrane potential, calcium, ROS, and hydraulic pressure are coordinated by glutamate receptor-like (GLR) proteins 3.3 and 3.6, while in response to HL the respiratory burst oxidase homolog D-driven systemic ROS signal could be separated from systemic changes in membrane potential and calcium levels. We further determine that plasmodesmata functions are required for systemic changes in membrane potential, calcium, and ROS during systemic signaling. Our findings shed new light on the different mechanisms that integrate different systemic signals in plants during stress. <h3>Significance statement</h3> The ability of plants to transmit a signal from a stressed or wounded tissue to the entire plant, termed systemic signaling, is key to plant survival during conditions of environmental stress. At least four different systemic signals are thought to be involved in this process: electric, calcium, reactive oxygen and hydraulic. However, how are they coordinated and whether they can be stress-specific is mostly unknown. Here we report that different types of stimuli can induce different types of systemic signals that may or may not be linked with each other. We further reveal that hydraulic waves can be actively regulated in plants in response to wounding, and that proteins that regulate plasmodesmata pores play a key role in systemic signaling.

Smoking is widespread among the young working population in Russia. Moreover, e-cigarettes are very popular among smokers as an alternative to traditional ones. The purpose of the study was to establish the effect of traditional cigarettes and modern e-cigarettes on the physiological characteristics of smokers, namely young people aged 18–21. Materials and Methods. The study involved young people agd 18–21 with at least 1 year of smoking experience and non-smokers. The trial participants were organized into three groups: a control group (non-smokers) and two experimental groups (traditional cigarette smokers and e-cigarette smokers). The research methods included physical tests, such as a breathing test, pressure measurements at rest, at load and after smoking, and calculation of cardiovascular state parameters. Results. During the experiment, no changes in blood pressure were observed in e-cigarette smokers.In traditional cigarette smokers, an increase in systolic blood pressure was observed at load. However, diastolic blood pressure was normal. It indicated a decrease in the distensibility of arterial vessels. An increase in heart rate was noted in both cigarette and e-cigarette smokers at load and immediately after smoking. The predominance of the sympathetic influence on the cardiovascular system was determined in all trial subjects. The obtained data indicated a violation in cardiovascular system activity in all subjects before and after exercise, and after smoking. At the same time, cardiovascular system activity deteriorated in the experimental groups after smoking. Under normal conditions and after exercise, all trial subjects showed tension in their adaptation mechanisms. After smoking in both experimental groups cardiovascular system adaptation potential was unsatisfactory. Conclusion. An assessment of physical parameters in smokers revealed a negative impact of tobacco and e-cigarettes on the cardiovascular system, namely on heart rate, regulation of cardiovascular system activity, adaptation mechanisms, which was likely to increase with smoking history.

Using a digital simulation method, we analyzed the relationship between natural frequency (fn) and damping coefficient (Zeta) of the catheter-manometer system required for high-fidelity measurement of the pulmonary arterial pressure. The pulmonary artery pressure waveform was obtained with a catheter-tip transducer and it was fed into a dynamic simulator programmed on a computer. The original waveform and the output of the simulator were compared and judged visually for the fidelity. From this analysis, the combination of fn and Zeta was obtained and was plotted on a fn-Zeta diagram. It showed as an area, which was convex on the left side and open on the right side. The left-convex endpoint was located at a damping coefficient of about 0.7. At a lower heart rate, this area was extended to the lower frequency side, while, at a higher heart rate, this area was limited to the higher frequency side. The fn-Zeta diagram was also constructed theoretically by calculating the relations between natural frequencies and damping coefficients of a second order system with the amplitude and phase error tolerance set at +/-5% respectively.

Functional failure analysis of a thermal–hydraulic passive system by means of Line Sampling

Stator can assembly is one of difficult issues in the manufacturing of AP1000 nuclear reactor coolant pumps. A new measurement and control system is developed to ensure precise assembly of the ultrathin stator can with large length to thickness ratio on the stator core. The system includes three parts: hydraulic pressure measurement and control, deformation measurement of the can and displacement measurement of valve core. Since deformation of the can is hard to measure, a new method by measuring the bulge displacement of the can is proposed. With the help of the system, the loading path can be accurately controlled and the deformation can be precisely measured. The system provides possibility for the detailed study of assembly process. Finally, the feasibility of the system in the experiment rig of a reduced scale is verified.

An optical sensor system for an aerospace application that demonstrates a multi-measurement capability from a single, generic processing module is presented. The principle is applied to two diverse sensing tasks: proximity and hydraulic pressure measurements.

The pressure distribution on systems with wings and blades is an important indication of the systems performance. However, measuring these distributions is currently challenging. A specially instrumented wing or blade must be used to replace the existing one in the system in order to obtain these measurements. This is prohibitively expensive and time consuming. Pressure belts overcome these challenges, by being able to conform to airfoil geometries and gather pressure measurements from existing blades or wing. In this paper, 3 different manufacturing techniques were explored to construct pressure belts and their performance was assessed in a wind tunnel. The results suggest additive manufacturing is a promising technique and the distributions measured from the belt were ver similar to those of the airfoil.

Cardiovascular pressure measurement in safety assessment studies: Technology requirements and potential errors

Before any analysis of the intracranial pressure waveform can be carried out it is important that an accurate reproduction of the waveform is recorded. Any pressure measuring system which relies on a pressure wave being transmitted to a transducer via a fluid-filled catheter is susceptible to resonance or damping of the original signal. This study was carried out to determine the amount of signal distortion caused by resonance and damping in the catheter-transducer systems in clinical use for intracranial and arterial pressure measurement at the Institute of Neurological Sciences in Glasgow.

The fibre-optic distributed vibration sensor (hDVS) is considered a disruptive technology for geophysical measurements. Previous works have demonstrated the use of the hDVS for a number of applications, such as vertical seismic profiling (VSP), pressure measurement and flow monitoring. We present results of monitoring a stimulation treatment with both downhole geophones and hDVS. This work compares the microseismic activity acquired with both systems and gives an insight on the maturity of the technology for hydraulic-fracturing monitoring. In particular, a direct comparison between traces validates the hDVS as a single component measurement and permits study of the system’s frequency response. Analysis of the entire monitoring job shows that 3.5% of the events recorded on the downhole array are visible in the fibre data.

In this chapter, the properties of the transfer function and frequency response of first and second order systems are studied on some examples from electrical circuit laws. We show that their properties are governed by the poles (i.e., the zeros of the denominator) of the transfer function which is a rational fraction. A geometric argument based on the location of the poles of the transfer function in the complex plane allows a qualitative interpretation of the behavior of the frequency response with varying frequency. This geometric interpretation is easily generalized to situations with any number of zeros and poles. It proves useful for the understanding of the general behavior of filters. The study begins here with the simplest system, the first order system. Then the second order circuit system is presented thoroughly. The logarithmic Bode representation of the frequency gain is introduced and its advantages demonstrated. The quality factor Q of a resonant circuit is defined.

The work aims to study the root mean square (RMS) responses to acceleration input for four state variables: the msvertical acceleration, the mspitch angular acceleration and the front and rear deflections of the suspensions. A half-car two degree-of-freedom model of semi-active control scheme is analyzed and compared with the conventional passive suspension system. Frequency response of the transfer function for the heave, pitch of the sprung mass and suspension deflections are initially compared and then mean square analysis is utilized to see the effect of semi-active scheme. Results indicate that significant improvements were achieved in the sprung mass heave and pitch responses using semi-active control scheme. However results for the rear and front suspension deflection show that there are limiting values of damping coefficient beyond which, the semi-active scheme becomes disadvantageous than the passive system.