Travel Time Of Pulse Research Articles

Group velocity of light in internal conical refraction.

We calculated the group velocity of light in internal conical refraction in a biaxial crystal as a function of the direction of the electric displacement vector, or the vibration direction, of its carrier wave. Our method represents group velocity through the electromagnetic fields of light, rather than its wave normal or ray direction. The travel time of a light pulse traversing a parallel plate biaxial crystal in internal conical refraction is found to vary as a sinusoidal function of twice the vibration angle of the light wave. Our method distinguishes the four directions of the two optic axes in monoclinic and triclinic crystals. Numerical examples are given for K N b O 3 at the wavelength of 400nm, and for S n 2 P 2 S 6 at the wavelength of 550nm.

Space object identification via polarimetric satellite laser ranging

Low Earth orbits are becoming congested. The rapid identification and precise orbit determination of space objects is mandatory for space management. Satellite laser ranging (SLR) enables precise orbit determination by measuring the two-way photon travel time of laser pulses from a ground station to satellites equipped with retroreflectors. Here we propose polarization-modulated SLR, where specially designed retroreflectors positioned on a satellite switch the polarization state of received polarized photons and reflect them back to a ground station for analysis. Satellite identifiers can be coded into arrays of reflectors with different polarizing properties, while the orbit determining capability of conventional SLR is maintained. We design, build and test polarized light-switching retroreflector assemblies and investigate the feasibility of accurate signal measurement from SLR ground stations. The approach is passive, straightforward to integrate and requires no electricity. Polarization-modulated SLR could contribute to increasing demands of space object monitoring, for example of mega-constellations or during cluster launches.

Asteroids for μHz gravitational-wave detection

A major challenge for gravitational-wave (GW) detection in the $\ensuremath{\mu}\mathrm{Hz}$ band is engineering a test mass (TM) with sufficiently low acceleration noise. We propose a GW detection concept using asteroids located in the inner Solar System as TMs. Our main purpose is to evaluate the acceleration noise of asteroids in the $\ensuremath{\mu}\mathrm{Hz}$ band. We show that a wide variety of environmental perturbations are small enough to enable an appropriate class of $\ensuremath{\sim}10\text{ }\text{ }\mathrm{km}$-diameter asteroids to be employed as TMs. This would allow a sensitive GW detector in the band $(\mathrm{few})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\text{ }\text{ }\mathrm{Hz}\ensuremath{\lesssim}{f}_{\mathrm{GW}}\ensuremath{\lesssim}(\mathrm{few})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }\mathrm{Hz}$, reaching strain ${h}_{c}\ensuremath{\sim}{10}^{\ensuremath{-}19}$ around ${f}_{\mathrm{GW}}\ensuremath{\sim}10\text{ }\text{ }\ensuremath{\mu}\mathrm{Hz}$, sufficient to detect a wide variety of sources. To exploit these asteroid TMs, human-engineered base stations could be deployed on multiple asteroids, each equipped with an electromagnetic transmitter/receiver to permit measurement of variations in the distance between them. We discuss a potential conceptual design with two base stations, each with a space-qualified optical atomic clock measuring the round-trip electromagnetic pulse travel time via laser ranging. Trade space exists to optimize multiple aspects of this mission: for example, using a radio-ranging or interferometric link system instead of laser ranging. This motivates future dedicated technical design study. This mission concept holds exceptional promise for accessing this GW frequency band.

Validation of Continuous Monitoring System for Epileptic Users in Outpatient Settings

Epilepsy is a chronic disease with a significant social impact, given that the patients and their families often live conditioned by the possibility of an epileptic seizure and its possible consequences, such as accidents, injuries, or even sudden unexplained death. In this context, ambulatory monitoring allows the collection of biomedical data about the patients’ health, thus gaining more knowledge about the physiological state and daily activities of each patient in a more personalized manner. For this reason, this article proposes a novel monitoring system composed of different sensors capable of synchronously recording electrocardiogram (ECG), photoplethysmogram (PPG), and ear electroencephalogram (EEG) signals and storing them for further processing and analysis in a microSD card. This system can be used in a static and/or ambulatory way, providing information about the health state through features extracted from the ear EEG signal and the calculation of the heart rate variability (HRV) and pulse travel time (PTT). The different applied processing techniques to improve the quality of these signals are described in this work. A novel algorithm used to compute HRV and PTT robustly and accurately in ambulatory settings is also described. The developed device has also been validated and compared with other commercial systems obtaining similar results. In this way, based on the quality of the obtained signals and the low variability of the computed parameters, even in ambulatory conditions, the developed device can potentially serve as a support tool for clinical decision-taking stages.

Challenges Presented by Cuffless Measurement of Blood Pressure if Adopted for Diagnosis and Treatment of Hypertension

The global health burden presented by hypertension is providing increased motivation for improved means of collection of blood pressure (BP) data. A growing area of research and commercial activity is the use of wearable devices to provide BP data using non-invasive cuffless techniques. The accelerated progress in recent years, particularly relating to connectivity of smartphone technology, has promoted the availability of consumer devices that provide values of BP. The main types of devices are wrist-worn, watch-type devices with sensors that typically record a photoplethysmography (PPG) signal, sometimes also with an electrocardiography (ECG) signal. The general underlying concept of the cuffless BP measurement in most device types is the association of BP and the travel time of the arterial pulse between two locations, determined from the time delay between the ECG and PPG signals. Other methods may involve additional analysis of the PPG waveform features. Experimental data are presented to illustrate the challenges presented by cuffless BP techniques in obtaining reliable BP measurements when the change in BP is caused by different stimuli affecting cardiac and vascular mechanisms. These effects influence the association of the measured and physiological BP change, thus presenting significant challenges and potential limitations in the use of cuffless BP devices for the diagnosis and treatment of hypertension.

Restoring light transmission of dusty glass surfaces on the Moon

Abstract The Lunar Laser Ranging Retro-reflectors (LRR) allow for the precise measurement of the travel time of laser pulses from the Earth to the lunar surface and back. Dust accumulation on the LRRs scatters the reflected light used for laser interferometry measurements leading to a reduction in the return signal amplitude by a factor of ≃ 10. We report on a series of experiments utilizing a method of an iterative application and removal of an acrylic adhesive kapton tape to remove lunar dust simulant from a glass substrate. The effectiveness of adhesive tape was determined by measuring the transmission of an expanded laser beam through a glass substrate with a dusted surface. Calibration data was obtained before the glass was exposed to any dust, and light transmission was measured after each iteration of adhesive removal using a power meter. The procedure was repeated using heavy gloves while keeping the glass substrate at 120 ° C to simulate the temperature conditions of a lunar day on the surface. A third test was conducted at room temperature in high-vacuum to ensure functionality in the lunar environment. These experiments show that glass substrates can be restored to 98 ± 2 % of their original transmission using the adhesive tape method. Therefore the light that travels into and out of the quartz surface of the LLRs can be restored up to 96 ± 4 % of their initial transmission.

Optimization of the pre-tension and separation distance for measurement of the dynamic elastic modulus and macromolecular orientation of a polypropylene monofilament via the sonic velocity method.

Using a fiber orientation degree measurement instrument (i.e., a dynamic modulus tester), 28 groups of averaged sonic pulse travel times in a polypropylene monofilament were measured and recorded under five pre-tensions across eight separation distances. The zero-time (or delay time) T0, sonic velocity C, sonic modulus E, Hermans orientation factor F, and orientation angle θ were calculated via two- and multi-point methods. The good agreement observed between the scatter plots of calculated data and the regression lines shows that the multi-point method provides reliable, accurate determination of the sonic modulus (or the dynamic elastic modulus) and the orientation parameters. Surprisingly, the zero-time for sonic pulse propagation depends significantly on the separation distance in practice, although it does not in theory. For easy and rapid measurement or relative comparisons using the two-point method, the optimal range of pre-tension is 0.1 gf/den-0.2 gf/den, and the optimal separation distances are 200 mm and 400 mm. The two-point method is appropriate for industrial applications, while because of its greater accuracy, the multi-point method is preferred for scientific research.

Detection of Low Cardiac Index using a Polyvinylidene Fluoride-Based Wearable Ring and Convolutional Neural Networks.

This study investigated the use of a wearable ring made of polyvinylidene fluoride film to identify a low cardiac index (≤2 L/min). The waveform generated by the ring contains patterns that may be indicative of low blood pressure and/or high vascular resistance, both of which are markers of a low cardiac index. In particular, the waveform contains reflection waves whose timing and amplitude are correlated with pulse travel time and vascular resistance, respectively. Hence, the pattern of the waveform is expected to vary in response to changes in blood pressure and vascular resistance. By analyzing the morphology of the waveform, our aim was to create a tool to identify patients with low cardiac index. This was done using a convolutional neural network which was trained on data from animal models. The model was then tested on waveforms that were collected from patients undergoing pulmonary artery catheterization. The results indicate high accuracy in classifying patients with a low cardiac index, achieving an area under the receiver operating characteristics and precision-recall curves of 0.88 and 0.71, respectively.

СКАНИРОВАНИЕ ОТДЕЛЬНО СТОЯЩИХ ДЕРЕВЬЕВ С ПОМОЩЬЮ 3D SENSE И ИХ РЕКОНСТРУКЦИЯ В САПР

Harvesters are state-of-the-art high-performance forestry machines that carry out a series of continuous operations, such as felling, pruning, and so on. During the alignment process of the harvester head to capture the trunk, the operator requires a large number of observations, judgments and multiple operations, which leads to loss of time and fuel. In order to increase operational efficiency and reduce operating costs, before cutting a tree, it is advisable to obtain a scan in the form of a point cloud. We suggest using a 3D Sense laser scanner for this, which is a non-contact measuring system. 
 The distance between the scanner and the tree is determined by the travel time of the laser light pulse: a pulsed laser beam is emitted and reflected if it encounters an object. Based on these measurements, it is possible to optimize tree felling and increase the automation of harvesters, which will lead to increased efficiency in the use of various resources However, the natural environment poses problems for any computer read task. This article presents the results of scanning single-standing trees surrounded by foliage and branches.

Evaluating the limit of gas phase responsivity with a liquids-coupled ultrasonic tomographic array

An ultrasonic tomographic array system was developed to measure oil/water/gas phase fraction in multiphase flows. This system interrogates fluids with a ring-array of ultrasonic transducers to generate tomographic images and sound speed profiles of the fluid. Gas entrained within the flow presents a signal transmission challenge for this system, due to reflections at liquid/gas interfaces and absorption of ultrasonic energy. Techniques were developed using physical models and machine learning based algorithms to extend the operating envelope of this system in multiphase fluid flows containing gas entrained in the flow. The array system measures the travel time of the ultrasonic pulses between transceiver pairs. As the signal-to-noise (SNR) at the receiver decreases due to the absorption of the signal due to the presence of gas in the fluid, the variance of the travel time measurement increases. Travel time measurements may also be distorted by reflections at liquid/gas phases leading to longer ray paths between transducer pairs. The upper limit of gas phase measurements is evaluated using physical models for the travel time of pulses between transceiver pairs. Machine learning techniques are applied to determine the gas phase fraction and increase accuracy of the liquids-phase fraction measurements of the system.

Construction of a didactic system for wave propagation speed determination in liquids

Abstract This work shows the construction, calibration and validation of a system to determine sound speed in liquids. We used the pulse method for the measurements. Piezoelectric transducers are used to transmit and receive acoustic wave pulses. The pulse travel time is determined by a counter implemented in a logic programmable device (FPGA). Initially the system is calibrated using pure water. We performed measurements in NaCl and CuSO4 solutions at different concentrations. The system detected speed variations of approximately 1.0 m/s in relation to the concentrations. Therefore, from didactical point of view, it is possible to perform experiments where small changes in the impurities concentration can be detected and measured. Further, the construction or even the enhancement of the system may be stimulant to students devoted to electronic instrumentation.

HISTORY AND APPLICATIONS OF SPACE-BORNE LIDARS

Abstract. LIDAR (Light Detection and Ranging) is a laser altimeter system that determines the distance by measuring pulse travel time. The data from the LIDAR systems provide unique information on the vertical structure of land covers. Compared to ground-based and airborne LIDARs providing a high-resolution digital surface model, space-borne LIDARs can provide important information about the vertical profile of the atmosphere in a global scale. The overall objective of these satellites is to study the elevation changes and the vertical distribution of clouds and aerosols. In this paper an overview on the space-borne laser scanner satellites are accomplished and their applications are introduced. The first space-borne LIDAR is the ICESat (Ice, Cloud and land Elevation Satellite) satellite carrying the GLAS instrument which was launched in January 2003. The CALIPSO (the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations, 2006), CATS-ISS (the Cloud-Aerosol Transport System, 2015), ADM-Aeolus (Atmospheric Dynamics Mission, 2018), and ICESat-2 (Ice, Cloud and land Elevation Satellite-2, 2018) satellites were respectively lunched and began to receive information about the vertical structure of the atmosphere and land cover. In addition, two ACE (The Aerosol-Cloud-Ecosystems, 2022) and EarthCARE (Earth Clouds, Aerosols and Radiation Explorer, 2021) space-borne satellites were planned for future. The data of the satellites are increasingly utilized to improve the numerical weather predictions (NWP) and climate modeling.

Effects of Bio-Impedance Sensor Placement Relative to the Arterial Sites for Capturing Hemodynamic Parameters.

Accurate measurement of the heart pulse waveform based on blood volume changes inside the arteries is crucial for reliable estimation of hemodynamic parameters such as blood pressure and cardiac output. Placement of blood volume sensors such as bio-impedance sensors close to the arterial sites is essential for the accurate measurement of the pulse waveform. The effect of sensor location relative to the wrist arteries on the pulse waveform had not been studied previously on human subjects. In this paper, we explore the effect of arterial and off-arterial placement of the bio-impedance sensor on important pulse waveform features such as pulse transit time (PTT), which is the travel time of the arterial pressure pulse between two sensors, and diastolic peak error (DPE), a measure of pulse signal sharpness. Placing the current injection and voltage sensing electrodes of a bio-impedance sensor on the radial artery provide greater accuracy for such features. We find that arterial PTT has a significantly lower standard deviation compared to off-arterial PTT indicating better signal quality. Similarly, we observe that DPE is much smaller for arterial bio-impedance which confirms our expectations. Based on these features, the location of the artery can be determined using an array of sensors placed around the artery.

ICESat/GLAS Altimetry Measurements: Received Signal Dynamic Range and Saturation Correction.

NASA's Ice, Cloud, and land Elevation Satellite (ICESat), which operated between 2003 and 2009, made the first satellite-based global lidar measurement of Earth's ice sheet elevations, sea-ice thickness and vegetation canopy structure. The primary instrument on ICESat was the Geoscience Laser Altimeter System (GLAS), which measured the distance from the spacecraft to Earth's surface via the roundtrip travel time of individual laser pulses. GLAS utilized pulsed lasers and a direct detection receiver consisting of a silicon avalanche photodiode (Si APD) and a waveform digitizer. Early in the mission, the peak power of the received signal from snow and ice surfaces was found to span a wider dynamic range than planned, often exceeding the linear dynamic range of the GLAS 1064-nm detector assembly. The resulting saturation of the receiver distorted the recorded signal and resulted in range biases as large as ~50 cm for ice and snow-covered surfaces. We developed a correction for this "saturation range bias" based on laboratory tests using a spare flight detector, and refined the correction by comparing GLAS elevation estimates to those derived from Global Positioning System (GPS) surveys over the calibration site at the salar de Uyuni, Bolivia. Applying the saturation correction largely eliminated the range bias due to receiver saturation for affected ICESat measurements over Uyuni and significantly reduced the discrepancies at orbit crossovers located on flat regions of the Antarctic ice sheet.

Pulse wave analysis with diffusing-wave spectroscopy.

Hypertension is a major risk factor for cardiovascular disease and thus at the origin of many deaths by e.g. heart attack or stroke. Hypertension is caused by many factors including an increase in arterial stiffness which leads to changes in pulse wave velocity and wave reflections. Those often result in an increased left ventricular load which may result in heart failure as well as an increased pulsatile pressure in the microcirculation l to damage to blood vessels. In order to specifically treat the different causes of hypertension it is desirable to perform a pulse wave analysis as a complement to measurements of systolic and diastolic pressure by brachial cuff sphygmomanometry. Here we show that Diffusing Wave Spectroscopy, a novel non-invasive portable tool, is able to monitor blood flow changes with a high temporal resolution. The measured pulse travel times give detailed information of the pulse wave blood flow profile.

Acoustic mode based internal tide tomography from the PhilSea 2009 experiment

The Philippine Sea 2009 experiment transmitted low frequency broadband sound pulses to a mode resolving array located at 185 km. The entire experiment was conducted over a period of one month, during which, most of the transmissions took place every 5 min, and the rest every 3 h. This talk estimates the travel times of the mode pulses and inverts them for the internal tide induced sound speed variability across the propagation path. A first order perturbation theory approach models mode travel times as range-averaged function of the sound speeds. Depending on the propagation distance, the contributions from some internal tide wavelengths are enhanced while others suppressed in the mode travel times. The talk shows the month-long time-series of the mode peak arrival times and estimates a spectrum for the observations. The presentation then derives an expression to relate the spectral components of the mode arrival times in terms of the internal tide spatial wavenumbers. The magnitude of the arrival time spectral components at the tide frequencies are used to invert for the respective internal tides across the propagation path. The tomographic inverse for the internal tides are compared with CTD measurements at the receiver and the source arrays.

Earthquake-enhanced permeability – evidence from carbon dioxide release following the ML 3.5 earthquake in West Bohemia

The West Bohemia/Vogtland region is characterized by earthquake swarm activity and degassing of CO2 of mantle origin. A fast increase of CO2 flow rate was observed 4 days after a ML 3.5 earthquake in May 2014 in the Hartoušov mofette, 9 km from the epicentres. During the subsequent 150 days the flow reached sixfold of the original level, and has been slowly decaying until present. Similar behavior was observed during and after the swarm in 2008 pointing to a fault-valve mechanism in long-term. Here, we present the results of simulation of gas flow in a two dimensional model of Earth's crust composed of a sealing layer at the hypocentre depth which is penetrated by the earthquake fault and releases fluid from a relatively low-permeability lower crust. This simple model is capable of explaining the observations, including the short travel time of the flow pulse from 8 km depth to the surface, long-term flow increase and its subsequent slow decay. Our model is consistent with other analyse of the 2014 aftershocks which attributes their anomalous character to exponentially decreasing external fluid force. Our observations and model hence track the fluid pressure pulse from depth where it was responsible for aftershocks triggering to the surface where a significant long-term increase of CO2 flow started 4 days later.

Hysteresis effects in organic matter turnover in a tropical floodplain during a flood cycle

Tropical inland waters are increasingly recognized for their role in the global carbon cycle, but uncertainty about the effects of such systems on the transported organic matter remains. The seasonal interactions between river, floodplain, and vegetation result in highly dynamic systems, which can exhibit markedly different biogeochemical patterns throughout a flood cycle. In this study, we determined rates and governing processes of organic matter turnover. Multi-probes in the Barotse Plains, a pristine floodplain in the Upper Zambezi River (Zambia), provided a high-resolution data set over the course of a hydrological cycle. The concentrations of oxygen, carbon dioxide, dissolved organic carbon, and suspended particulate matter in the main channel showed clear hysteresis trends with expanding and receding water on the floodplain. Lower oxygen and suspended matter concentrations prevailed at longer travel times of water in the floodplain, while carbon dioxide and dissolved organic carbon concentrations were higher when the water spent more time on the floodplain. Maxima of particulate loads occurred before highest water levels, whereas the maximum in dissolved organic carbon load occurred during the transition of flooding and flood recession. Degradation of terrestrial organic matter occurred mainly on the floodplain at increased floodplain residence times. Our data suggest that floodplains become more intense hotspots at prolonged travel time of the flood pulse over the floodplain.

Impact of Wood Sample Shape and Size on Moisture Content Measurement Using a GPR-Based Sensor

Nondestructive, GPR-based real-time sensors have been shown to be an effective tool for measuring moisture content in wood samples within the forest products industry. Moisture content is derived from either the early time electromagnetic pulse amplitude or the pulse travel time through the wood sample. When used on samples that are comparable in size to the sensor antenna and wavelength within the sample, the GPR sensor will measure a moisture content that is dependent on the sample shape and size. In this study, we look at a cylindrical sample, representative of a typical wood log sample. We have used numerical modeling with both simplified, unshielded Hertzian dipole antennas and a realistic shielded GPR antenna system to estimate these effects. The numerical modeling shows that for measurements performed on the sides or ends of small diameter logs, the curvature of the log, and closeness of the log boundaries has a significant impact on the early time amplitude and signal travel time through the log that result in reduced accuracy in moisture content measurements. Wood logs have electrical properties that are anisotropic and vary radially within the log. Our numerical models are assumed to be isotropic and homogeneous. GPR data acquired on the ends of wood logs show similar dependency on log diameter to those observed in the modeling, and numerical model results compare reasonably well with data measured on measured logs. The numerical modeling results also demonstrate the importance of using realistic shielded antenna models in this application.

Reconstruction of reflector images using the C-SAFT method with account for the anisotropy of the material of the test object

A modification of the combined SAFT (C-SAFT) method for reconstructing reflector images in a test object, which consists of several regions with different acoustic properties, in particular, anisotropy properties, is proposed. A method for the direct construction of a family of rays, which exit from the point where a transmitter is positioned, is used to calculate the ray trajectories with consideration for the anisotropy. After the family of rays is constructed, it is possible to analyze their attribution to a certain acoustic scheme and to approximate the calculated delays on the spatial grid of the region of iterest (ROI). This will allow one to calculate the pulse travel time from a transmitter to any point of the ROI and back to the receiver and to use the C-SAFT method for reconstructing reflector images. During processing of echo signals that were calculated in the CIVA program, the efficiency of the proposed method was demonstrated. Accounting for the anisotropy in a model experiment increased the focusing quality when reconstructing images of side-drilled holes in a specimen with a repair weld.