Pulse Reflection Research Articles

Evaluating Photoplethysmogram as a Real-Time Cognitive Load Assessment during Game Playing

ABSTRACTAccurate evaluation for user experience during computer game playing is very important in optimizing game design to improve the gaming experience. When evaluating user experiences, the concept of cognitive load is crucial for dynamically responding to game players’ mental status. In our former studies, the photoplethysmogram (PPG)-based Stress-Induced Vascular Response Index (sVRI) shows better sensitivity and reliability in measuring cognitive loads compared with heart-rate variation, blood pressure, and galvanic skin response. In this study, we use memory matrixes and Pop Cap’s tower defense game Plants vs. Zombies as cognitive tasks and use sVRI to assess players’ cognitive load dynamically during the real-time computer games. Evaluations on cognitive tasks verified the usability of sVRI in comparison with other indexes derived from PPG, such as heartbeat interval, area under curve, digital pulse amplitude, reflection index, and inflection point area ratio. Our findings indicate the potential of sVRI for assessing game players’ mental workload in real time.

Design of a new reflectance pulse oximeter by obtaining the optimal source-detector space

Pulse oximetry is an important medical monitoring technique. Interest in the use of reflectance mode of pulse oximeters has been grown for monitoring the arterial oxygen saturation (SaO2). The design sensor has an effective role in improvement of reflective pulse oximeters performance. In this study, the light propagation in tissue has been analyzed for development of reflection pulse oximetry. After analyzing theory, the optimal source-detector space was determined and a revision on SaO2 formulation calculated with Lambert–Beer law performed to reduce the errors. The new type of reflectance pulse oximeter was designed based on the theory calculation and then calibrated by in vivo experiments. The detecting signal have least dependence on changes in scattering properties of the tissue for obtained optimal space. One of the advantages of this design is reduction of influence of unconscious movement. In this novel design, calibration and validation experimental results show the repeatability potential and accuracy of the system.

Transformation of the airy pulse at temporary jump of the dielectric permittivity of the medium

The spatio-temporal problem of interaction of the Airy electromagnetic pulse and a plane dielectric layer is solved in the case of a permittivity sharp change in a layer at zero moment of time. Expressions for the field inside the layer are obtained and the influence of the starting parameter on the position of the pulse inside the layer is shown. The evolution of the pulse in media with different refractive index is analyzed. A comparative analysis of the interaction of the Airy pulse with a plane layer between two dielectric media with a dielectric layer is carried out. The influence of pulse reflections from the layer boundaries on its shape and location is analyzed. From the analysis of the obtained results it follows that the choice of the initial space-time parameter affects the location of the pulse in the layer, and the transition of the signal to a medium with a larger (lower) permittivity results in the amplitude increase of oscillations and the main lobe shape change.

Enhancement of high harmonic generation by multiple reflection of ultrashort pulses

In recent studies it has been shown that by combining the fundamental laser frequency with its low-order harmonics, significant enhancement of high harmonic intensity can be achieved. Since the laser pulse reflected from a plasma inherently contains low-order harmonics, a second reflection from a fresh plasma surface leads to the increase of spectral intensity. In this work, we have made an extensive study of multiple reflections of a short pulse between two solid density plasma walls at oblique incidence, with the help of 1D and 2D particle-in-cell simulations. A loosely focused pulse is considered that can propagate between two flat foils over consecutive reflections without significant loss of intensity. It is shown that in the weakly relativistic regime the intensity of 10th to 30th harmonics can be amplified by three orders of magnitude.

ANALYSIS OF A TWO-CRYSTAL DELAY LINE FOR FEMTOSECOND PULSES OF THE X-RAY FREE ELECTRON LASER

Using the methods of statistical optics the formation of delayed X-ray pulses in the diffraction reflection of an incident pulse with an arbitrary degree of temporal coherence from a system of parallel crystals with different lattice periods is considered. The results are of interest for constructing delay lines in experiments with a time resolution of the pump-and-probe type and realizing of the self-seeding mode to increase the degree of temporal coherence of the X-ray free-electron laser radiation.
 A rigorous theory of dynamic diffraction in Bragg geometry is applied to the diffraction reflection of short X-ray pulses from a system of two parallel crystals with arbitrary thicknesses, and also, for a system of two pairs of parallel crystals. The dependence of the delay time and the intensity of the delayed pulses on the thickness of the crystals and the distances between them are analyzed. Since the pulses from the X-ray free electron laser have high spatial coherence, i.e. a small angular divergence, but very poor temporal coherence, special attention is paid to the effect of the degree of temporal coherence on the width of the energy spectrum of the incident pulses and on the influence of this width on the intensity of the delayed pulses.

ANALYSIS OF A TWO-CRYSTAL DELAY LINE FOR FEMTOSECOND PULSES OF THE X-RAY FREE ELECTRON LASER

Using the methods of statistical optics the formation of delayed X-ray pulses in the diffraction reflection of an incident pulse with an arbitrary degree of temporal coherence from a system of parallel crystals with different lattice periods is considered. The results are of interest for constructing delay lines in experiments with a time resolution of the pump-and-probe type and realizing of the self-seeding mode to increase the degree of temporal coherence of the X-ray free-electron laser radiation.
 A rigorous theory of dynamic diffraction in Bragg geometry is applied to the diffraction reflection of short X-ray pulses from a system of two parallel crystals with arbitrary thicknesses, and also, for a system of two pairs of parallel crystals. The dependence of the delay time and the intensity of the delayed pulses on the thickness of the crystals and the distances between them are analyzed. Since the pulses from the X-ray free electron laser have high spatial coherence, i.e. a small angular divergence, but very poor temporal coherence, special attention is paid to the effect of the degree of temporal coherence on the width of the energy spectrum of the incident pulses and on the influence of this width on the intensity of the delayed pulses.

Cross-phase-modulation-induced temporal reflection and waveguiding of optical pulses

Cross-phase modulation (XPM) is commonly viewed as a nonlinear process that chirps a probe pulse and modifies its spectrum when an intense pump pulse overlaps with it. Here we present an alternative view of XPM in which the pump pulse creates a moving refractive-index boundary that splits the probe pulse into two parts with distinct optical spectra through temporal reflection and refraction inside a dispersive nonlinear medium. The probe even undergoes a temporal version of total internal reflection for sufficiently intense pump pulses, a phenomenon that can be exploited for making temporal waveguides. We investigate the practical conditions under which XPM can be exploited for temporal reflection and waveguiding. The width and shape of the pump pulses as well as the nature of the medium dispersion at the pump and probe wavelengths (normal versus anomalous) play important roles. The super-Gaussian shape of a pump pulse is particularly helpful because of the relatively sharp edges of the super-Gaussian shape. When the pump wavelength lies in the anomalous-dispersion regime, the pump pulse can form a soliton, whose unique properties can be exploited to our advantage. We also discuss a potential application of XPM-induced temporal waveguides for compensating for timing jitter.

A Technique for Detecting Subpicosecond Reflection or Transmission Kinetics

A double-modulation technique was developed and tested experimentally for the detection of the kinetics of reflection of subpicosecond pulses of probe near-IR radiation from a sample (or transmission through it) after the action of exciting radiation pulses. A probe signal is detected at a frequency that is equal to the sum of stabilized unequal frequencies of interrupting exciting and probe radiations, thus permitting the elimination of the contribution of scattered exciting radiation from the valid signal. When detecting the semiconductor- sample reflectance kinetics with a time resolution of 0.13 ps, the reflection sensitivity ΔR/R = 5 × 10–6 was reached.

Opto-acoustic microscopy reveals adhesion mechanics of single cells.

Laser-generated GHz-ultrasonic-based technologies have shown the ability to image single cell adhesion and stiffness simultaneously. Using this new modality, we here demonstrate quantitative indicators to investigate contact mechanics and adhesion processes of the cell. We cultured human cells on a rigid substrate, and we used an inverted pulsed opto-acoustic microscope to generate acoustic pulses containing frequencies up to 100 GHz in the substrate. We map the reflection of the acoustic pulses at the cell-substrate interface to obtain images of the acoustic impedance of the cell, Zc, as well as of the stiffness of the interface, K, with 1 μm lateral resolution. Our results show that the standard deviation ΔZc reveals differences between different cell types arising from the multiplicity of local conformations within the nucleus. From the distribution of K-values within the nuclear region, we extract a mean interfacial stiffness, Km, that quantifies the average contact force in areas of the cell displaying weak bonding. By analogy with classical contact mechanics, we also define the ratio of the real to nominal contact areas, Sr/St. We show that Km can be interpreted as a quantitative indicator of passive contact at metal-cell interfaces, while Sr/St is sensitive to active adhesive processes in the nuclear region. The ability to separate the contributions of passive and active adhesion processes should allow gaining insight into cell-substrate interactions, with important applications in tissue engineering.

Large Variations in Pulse Wave Velocity and Reflection Patterns occur during a Hemodialysis Session and are not Related to the Degree of Ultrafiltration

Large Variations in Pulse Wave Velocity and Reflection Patterns occur during a Hemodialysis Session and are not Related to the Degree of Ultrafiltration

Mathematical modeling of pulse wave propagation along human aorta

Background: Physical characteristics of pulse waves, which are generated by the heart contractions and propagated along the arteries, are used in medicine for diagnostics of the blood circulation system and blood supply to the organs and tissues. At the sites with significant wave reflections the high local pressure oscillations appear that may lead to damage of the endothelium, development of atherosclerotic plaques and aortic aneurysm. Therefore, elaboration of a detailed biophysical model of the individual aorta based on tomography and determination of the dangerous sites with high wave reflections are important for medical diagnostics. Objectives: The aim of the work is to study the regularities of the pulse wave propagation and reflection along the aorta and to propose new methods for early diagnosis of disorders in the blood circulation system. Materials and methods: The measurement data on diameters and lengths of segments of aorta and its branches conducted on 5 corpses have been used. Calculations of the wave conduction and reflection coefficients are based on the linear theory of pulse waves developed by J. Lighthill. Results: It is shown that from the biophysical point of view, the aorta is an optimal waveguide, which provides almost zero local reflections of the pulse waves. Most of the branches possess negative reflection, which accelerates the blood flow and decreases the load on the heart due to the suction effect. The calculated values of the branching coefficients and pulse waves speeds correspond to the data of the previous experimental measurements. It is shown that most of the branches have an optimal Murray coefficient close to one. It implies, aorta also provides the optimal volumetric blood flow over the period of cardiac contraction with minimal energy expenses. Conclusions: Human aorta and its branches possess optimal biophysical properties, which ensure the blood flow with minimal energy consumption. Aorta as an optimal waveguide provides pulse wave propagation with almost without reflection. The proposed method of estimation of the biophysical properties of aorta as a waveguide can be useful for medical diagnostics, allowing early identification of the regions which are dangerous in terms of the progressive development of vascular pathologies in the individual geometry of the patient's vasculature.

Non-contact measurement using reflective pulse oximetry

Non-contact measurement using reflective pulse oximetry

Detection of angiospastic disorders in the microcirculatory bed using laser diagnostics technologies

The evaluation of the microcirculatory bed functional state and the identification of angiospastic disorders with related complications, when the pathological changes are reversible, have an important role in medical practice. The aim of this study was to evaluate the possibility of using optical noninvasive methods and the cold pressor test to solve this problem.A total of 33 patients with rheumatological diseases and 32 healthy volunteers were included in the study. Laser Doppler flowmetry, tissue reflectance oximetry and pulse oximetry were used as optical noninvasive methods. The parameters were recorded before, immediately after and 20[Formula: see text]min after the cold pressor test. Based on the measured parameters, the complex parameters of the microcirculatory bed were calculated.A detailed statistical analysis of the parameter changes for each individual in the two groups displayed diverse microcirculatory bed parameter responses upon cold exposure, with differing recovery of parameters after CPT. New diagnostic criteria were proposed for the identification of angiospastic disorders. According to the proposed criteria, 27 people of the volunteers group were confirmed to not display any disorders. In the patient group, however, 18 people were observed to have a relatively normal functional state of the microcirculatory bed, while 15 people were observed to have a possible tendency to angiospasm. To highlight the differences between a relatively normal state and presence of angiospastic disorders, statistical analysis of experimental data was carried out, which revealed significant differences. Further analysis of data with angiospastic disorders identified a relationship between their diagnoses and the results of laboratory studies.Thus, the evaluation of combined noninvasive optical diagnostic method use, the cold pressor test and proposed diagnostic criteria showed a positive result. This approach can be used to detect the presence of possible angiospastic disorders and related complications, as well as microcirculatory bed disorders against the background of other diseases.

DURATION LIMIT OF LASER PULSES EMITTED FROM A Ce-DOPED CRYSTAL SHORT CAVITY

Based on the rate equation set for broadband cavities, the dependence of pulse duration on cavity and pumping parameters is analyzed. The cavity uses a Ce-doped crystal as a gain medium. Computation results show the variation of the pulse width with the change of cavity length, mirror reflectivity, pumping energy and pumping pulse duration. A significant influence of multiple-pulse operation in limiting pulse duration is realized and a pulse-width of the order 200 ps is found to be the limit for the direct generation of ultraviolet single picosecond pulses from a Ce:LLF short cavity.

Combined Dietary Nitrate and Exercise Intervention in Peripheral Artery Disease: Protocol Rationale and Design.

BackgroundPeripheral artery disease (PAD) is caused by atherosclerotic occlusions in the legs. It affects approximately 8-12 million people in the United States alone, one-third of whom suffer from intermittent claudication (IC), defined as ischemic leg pain that occurs with walking and improves with rest. Patients with IC suffer a markedly impaired quality of life and a high perception of disability. Improving pain-free walking time is a primary goal of rehabilitation in this population.ObjectiveThe nitric oxide (NO)-PAD trial is designed to compare the effects that 12 weeks of supervised exercise training, in combination with a high inorganic nitrate-content (beetroot [BR] juice) beverage or placebo (PL) beverage, has on clinical outcomes of exercise and functional capacity in two groups of PAD+IC patients: exercise training plus beetroot (EX+BR) and exercise training plus placebo (EX+PL). The primary aims of this randomized controlled, double-blind pilot study are to determine group differences following 12 weeks of EX+BR versus EX+PL in the changes for (1) exercise capacity: pain-free walking time (claudication onset time, COT), peak walk time (PWT), and maximal exercise capacity (peak oxygen uptake, VO2peak) during a maximal-graded cardiopulmonary exercise test (max CPX) and (2) functional capacity: 6-minute walk (6MW) distance. The secondary aims will provide mechanistic insights into the exercise outcome measures and will include (1) gastrocnemius muscle oxygenation during exercise via near-infrared spectroscopy (NIRS); (2) gastrocnemius muscle angiogenesis: capillaries per unit area and per muscle fiber, and relative fraction of type I, IIa, IIb, and IId/x fibers; and (3) vascular health/function via brachial artery flow-mediated dilation, lower-limb blood flow via plethysmography, and pulse wave velocity and reflection.MethodsA total of 30 subjects between 40 and 80 years of age with PAD who are limited by IC will undergo exercise training 3 days per week for 12 weeks (ie, 36 sessions). They will be randomized to either the EX+BR or EX+PL group where participants will consume a beverage high in inorganic nitrate (4.2 mmol) or a low-nitrate placebo, respectively, 3 hours prior to each training session.ResultsData collection from this study has been completed and is in the process of analysis and write-up. While the study is too underpowered—EX+BR, n=11; EX+PL, n=13—to determine between-group differences in the primary outcomes of COT, PWT, and 6MW, preliminary observations are promising with Cohen d effect sizes of medium to large.ConclusionsExercise training is currently the most effective therapy to increase functional capacity in PAD+IC. If the addition of inorganic nitrate to an exercise regimen elicits greater benefits, it may redefine the current standard of care for PAD+IC.Trial RegistrationClinicalTrials.gov NCT01684930; https://clinicaltrials.gov/ct2/show/NCT01684930 (Archived by WebCite at http://www.webcitation.org/6raXFyEcP)

Development and clinical evaluation of a new sensor design for buccal pulse oximetry in horses.

The use of pulse oximetry in horses is limited due to inadequate readings with conventional transmission sensor probes. The objectives of this study were to 1) develop an improved sensor design for horses to be used at an appropriate anatomical site, and 2) evaluate this design in an experimental study. In vivo experiment. A new sensor design for reflectance pulse oximetry at the buccal mucosa was developed. A conventional Nonin 2000SL sensor for transmission pulse oximetry was included into this design. Three different prototypes (N1, N2a, N2b) were constructed and used with the Nonin 2500A Vet pulse oximetry monitor. Thirteen anaesthetised warmblood horses were included into a desaturation protocol (100-70% SaO2 ). SpO2 and pulse frequency values were recorded, using SaO2 calculated from blood gas analysis and invasive pulse frequency measurements as reference methods. Bias and precision were evaluated by calculations of the root mean square deviation (Arms ). The agreement of the methods was tested with Bland-Altman analysis. The quality of the pulse frequency readings determined the quality of the SpO2 -readings. Good pulse signal strength resulted in a SpO2 -accuracy comparable to that of the original sensor (Nonin 2000SL: Arms = 3%; N1: Arms = 3.60%; N2b: Arms = 3.46%). Especially at heart rates ≤30 bpm, pulse rate readings that were about twice as high as the reference value occurred. Their exclusion from the dataset resulted in a pulse rate accuracy similar to that of the original sensor. Bland-Altman plots showed limits of agreement typical of pulse oximeters. The pulse frequency accuracy requires further improvement. The usability in clinical cases needs to be tested. The new sensor design has been shown to be suitable for buccal pulse oximetry in horses.

Tunable positive and negative group delays of light reflection from layer structures with a graphene layer

In this paper, we investigate the propagation of a light pulse reflection from the layer system with a graphene layer. We show a tunable transition between positive and negative group delays of optical pulse reflection in such a layered system controlled by the properties of the graphene layer and reveal two mechanisms to control the propagation properties of the light pulse reflected from such systems. It is demonstrated that the reflected group delays are tunable from positive to negative values in both mechanisms of resonances and the excitations of surface plasmon resonances, which are also adjusted by tuning the Fermi energy and temperature of the graphene layer. Our results are helpful to control the pulse propagations and are useful for design of graphene-based optical devices.

Harmonic generation enhancement due to interaction of few-cycle light pulses in nonlinear dielectric coating on a mirror

We theoretically investigate reflection of a few-cycle light pulse from a mirror with nonlinear dielectric coating. We employ a nonlinear equation that describes spatiotemporal evolution of a few-cycle light pulse with a broad spectrum that lies in the transparency range of nonlinear dielectric media. This model is formulated directly for the electric field without slowly varying amplitude approximation. Analytical and numerical analysis shows that counter-propagating wave interactions in thin films can strongly enhance or suppress third harmonic generation of the central frequency, whereas this effect is neglected in the framework of slowly varying amplitude approximation.

Proton energy behavior by variation of the target density in laser acceleration

Ion acceleration using a laser pulse irradiating a thin disk target is examined using three-dimensional and two-dimensional particle-in-cell simulations. A laser pulse of 620 TW, with an intensity of 5×1021 W/cm2 and a duration of 27 fs, is irradiated on to a double-layer target. Simulations are performed by varying the ion density, i.e., electron density, of the first layer with a fixed areal mass density. It is shown that the obtained proton energy increases dramatically for a certain density of the first layer, which is made of a material having a small mass over charge ratio, “light” material, such as carbon; that is, the Coulomb explosion of the target and radiation pressure acceleration act effectively above a certain density. Moreover, even for the same electron density, the reflection of the laser pulse from the first layer is small for a “light” material.

Automatic extraction of pavement markings on streets from point cloud data of mobile LiDAR

Pavement markings provide an important foundation as they help to keep roads users safe. Accurate and comprehensive information about pavement markings assists the road regulators and is useful in developing driverless technology. Mobile light detection and ranging (LiDAR) systems offer new opportunities to collect and process accurate pavement markings’ information. Mobile LiDAR systems can directly obtain the three-dimensional (3D) coordinates of an object, thus defining spatial data and the intensity of (3D) objects in a fast and efficient way. The RGB attribute information of data points can be obtained based on the panoramic camera in the system. In this paper, we present a novel method process to automatically extract pavement markings using multiple attribute information of the laser scanning point cloud from the mobile LiDAR data. This method process utilizes a differential grayscale of RGB color, laser pulse reflection intensity, and the differential intensity to identify and extract pavement markings. We utilized point cloud density to remove the noise and used morphological operations to eliminate the errors. In the application, we tested our method process on different sections of roads in Beijing, China, and Buffalo, NY, USA. The results indicated that both correctness (p) and completeness (r) were higher than 90%. The method process of this research can be applied to extract pavement markings from huge point cloud data produced by mobile LiDAR.