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Pulse transit time

Gregory B Gajda, Stephen H Bly
Guidelines for prevention of peripheral nerve stimulation from exposure to low frequency magnetic fields have been developed by standard-setting bodies. Exposure limits or reference levels (RLs) are typically set in terms of the maximum root-mean-square amplitude of a sinusoidal waveform; however, environmental flux densities are often periodic, non-sinusoidal waveforms. This work presents a procedure for deriving RLs for any generalized periodic waveform using the empirical nerve-stimulation threshold data obtained from human volunteer MRI experiments...
June 2017: Health Physics
Yan Zhang, Yinsheng Xu, Chenyang You, Dong Xu, Junzhou Tang, Peiqing Zhang, Shixun Dai
Chemical stoichiometric Ge-As-S glasses were prepared, and their thermal properties, refractive index (n), optical bandgap, Raman gain, and femtosecond laser damage were examined. Results revealed that the n and density (ρ) of the glasses decreased as Ge concentration increased, whereas the bandgap and glass transition temperature (Tg) increased. The Raman gain coefficients (g<sub>R</sub>) of the samples were calculated on the basis of spontaneous Raman scattering spectra. g<sub>R</sub> decreased from 2...
April 17, 2017: Optics Express
Chenxi Yang, Negar Tavassolian
This work proposes a novel method of pulse transit time measurement. The proximal arterial location data is collected from seismocardiogram (SCG) recordings by placing a MEMS accelerometer on the chest wall. The distal arterial location data is recorded using an acoustic sensor placed inside the ear. The performance of distal location recordings is evaluated by comparing SCG-acoustic and SCG-Photoplethysmogram (PPG) measurements. PPG and acoustic performances under motion noise are also compared. Experimental results suggest comparable performances for the acoustic-based and PPG-based devices...
April 24, 2017: IEEE Journal of Biomedical and Health Informatics
Jan Menser, Kyle Daun, Thomas Dreier, Christof Schulz
The temporal luminescence behavior of silicon atoms during and after laser-heating of gas-borne silicon nanoparticles was investigated. Silicon nanoparticles were formed in the exhaust stream of a microwave plasma reactor at 100 mbar. The observed prompt atomic line intensities correspond with thermal excitation of the evaporated species. A prompt signal at 251.61 and 288.15 nm originating from the 3s<sup>2</sup>3p<sup>2</sup>→3s<sup>2</sup>3p4s transitions showed a lifetime of 16 ns that matches the documented excited-state lifetime for the respective transitions...
April 10, 2017: Applied Optics
A A Ünal, A Parabas, A Arora, J Ehrler, C Barton, S Valencia, R Bali, T Thomson, F Yildiz, F Kronast
The antiferromagnetic to ferromagnetic phase transition in FeRh can be induced globally by either heating the material above its phase transition temperature or applying a combination of external stimuli (such as mechanical strain, electric/magnetic fields) on the material preheated close to its transition temperature. On the other hand, to locally induce this phase transition is more desirable for applications and requires a confined source of energy such as a focused laser beam. Here we combine laser excitation with X-ray magnetic imaging to determine the effect of laser heating on the local and transient magnetization of FeRh using time-resolved photoelectron emission microscopy...
April 4, 2017: Ultramicroscopy
M Ouali, S Coulibaly, M Taki, M Tlidi
We investigate the spatio-temporal dynamics of a ring cavity filled with a non-instantaneous Kerr medium and driven by a coherent injected beam. We show the existence of a stable mixed-mode solution that can be either extended or localized in space. The mixed-mode solutions are obtained in a regime where Turing instability (often called modulational instability) interacts with self-pulsing phenomenon (Andronov-Hopf bifurcation). We numerically describe the transition from stationary inhomogeneous solutions to a branch of mixed-mode solutions...
March 6, 2017: Optics Express
Hasan Obeid, Hakim Khettab, Louise Marais, Magid Hallab, Stéphane Laurent, Pierre Boutouyrie
BACKGROUND: Carotid-femoral pulse wave velocity (PWV) (cf-PWV) is the gold standard for measuring aortic stiffness. Finger-toe PWV (ft-PWV) is a simpler noninvasive method for measuring arterial stiffness. Although the validity of the method has been previously assessed, its accuracy can be improved. ft-PWV is determined on the basis of a patented height chart for the distance and the pulse transit time (PTT) between the finger and the toe pulpar arteries signals (ft-PTT). METHOD: The objective of the first study, performed in 66 patients, was to compare different algorithms (intersecting tangents, maximum of the second derivative, 10% threshold and cross-correlation) for determining the foot of the arterial pulse wave, thus the ft-PTT...
April 4, 2017: Journal of Hypertension
Steffen Eich, Moritz Plötzing, Markus Rollinger, Sebastian Emmerich, Roman Adam, Cong Chen, Henry Cornelius Kapteyn, Margaret M Murnane, Lukasz Plucinski, Daniel Steil, Benjamin Stadtmüller, Mirko Cinchetti, Martin Aeschlimann, Claus M Schneider, Stefan Mathias
The evolution of the electronic band structure of the simple ferromagnets Fe, Co, and Ni during their well-known ferromagnetic-paramagnetic phase transition has been under debate for decades, with no clear and even contradicting experimental observations so far. Using time- and spin-resolved photoelectron spectroscopy, we can make a movie on how the electronic properties change in real time after excitation with an ultrashort laser pulse. This allows us to monitor large transient changes in the spin-resolved electronic band structure of cobalt for the first time...
March 2017: Science Advances
Marit H N van Velzen, Arjo J Loeve, Sjoerd P Niehof, Egbert G Mik
Photoplethysmography (PPG) is a widely available non-invasive optical technique to visualize pressure pulse waves (PWs). Pulse transit time (PTT) is a physiological parameter that is often derived from calculations on ECG and PPG signals and is based on tightly defined characteristics of the PW shape. PPG signals are sensitive to artefacts. Coughing or movement of the subject can affect PW shapes that much that the PWs become unsuitable for further analysis. The aim of this study was to develop an algorithm that automatically and objectively eliminates unsuitable PWs...
March 30, 2017: Medical & Biological Engineering & Computing
Konda Srinivasa Rao, Anil Kumar Chaudhary
We report the comparative study of photoacoustic (PA) fingerprint spectra, thermal decomposition, and stability mechanism of some phenyl and bis series energetic compounds named 1-(2-methoxy,-3,5-dinitrophenyl)-1H-1,2,3-triazole ( S5), 1-(3-methoxy, 2, 6 dinitrophenyl) 1H-1, 2, 3 triazole ( S10), 1-(4-nitrophenyl)-1H-1,2,3-triazole ( S8), and 2,6-bis ((4-(nitromethyl)-1H-1,2,3-triazol-1-yl)methyl) pyridine ( S9). Fourth harmonic wavelength, i.e., 266 nm of pulse duration 7 ns and 10 Hz repetition rate obtained from Q-switched Nd: YAG laser, was used to record the thermal PA spectra of these compounds under controlled pyrolysis condition in the range of 30-350 ℃...
January 1, 2017: Applied Spectroscopy
Xianglei Kong, Xiaodi Bao
RATIONALE: Graphene has been found to be a versatile precursor for the generation of mono-endohedral metallofullerenes (EMFs) of alkali and alkali earth metal atoms. Thus, it is important to investigate whether graphene is also a good precursor for the generation of EMFs including multi-metal atoms or some transition metal atoms. METHODS: Experiments were performed on a 7.0 T Fourier transform ion cyclotron resonance (FT ICR) mass spectrometer. Laser ablation mass spectra were obtained by laser irradiation on mixtures of graphene and LaCl3 , YCl3 or HAuCl4 on a stainless steel plate...
March 24, 2017: Rapid Communications in Mass Spectrometry: RCM
Thomas M Fiedler, Mark E Ladd, Andreas K Bitz
At ultra-high fields, the assessment of radiofrequency (RF) safety presents several new challenges compared to low-field systems. Multi-channel RF transmit coils in combination with parallel transmit techniques produce time-dependent and spatially varying power loss densities in the tissue. Further, in ultra-high-field systems, localized field effects can be more pronounced due to a transition from the quasistationary to the electromagnetic field regime. Consequently, local information on the RF field is required for reliable RF safety assessment as well as for monitoring of RF exposure during MR examinations...
March 20, 2017: NeuroImage
Gregory Lemberskiy, Steven H Baete, Martijn A Cloos, Dmitry S Novikov, Els Fieremans
A diffusion measurement in the short-time surface-to-volume ratio (S/V) limit (Mitra et al., Phys Rev Lett. 1992;68:3555) can disentangle the free diffusion coefficient from geometric restrictions to diffusion. Biophysical parameters, such as the S/V of tissue membranes, can be used to estimate microscopic length scales non-invasively. However, due to gradient strength limitations on clinical MRI scanners, pulsed gradient spin echo (PGSE) measurements are impractical for probing the S/V limit. To achieve this limit on clinical systems, an oscillating gradient spin echo (OGSE) sequence was developed...
May 2017: NMR in Biomedicine
Stephen E Derenzo
This paper demonstrates through Monte Carlo simulations that a practical positron emission tomograph with (1) deep scintillators for efficient detection, (2) double-ended readout for depth-of-interaction information, (3) fixed-level analog triggering, and (4) accurate calibration and timing data corrections can achieve a coincidence resolving time (CRT) that is not far above the statistical lower bound. One Monte Carlo algorithm simulates a calibration procedure that uses data from a positron point source. Annihilation events with an interaction near the entrance surface of one scintillator are selected, and data from the two photodetectors on the other scintillator provide depth-dependent timing corrections...
March 22, 2017: Physics in Medicine and Biology
Jing Liu, Yuan-Ting Zhang, Xiao-Rong Ding, Wen-Xuan Dai, Ni Zhao
Pulse transit time (PTT) has been widely studied as an index of blood pressure (BP) changes. In recent years, some prototypes of PTT-based wearable BP measurement devices have been developed, which can relieve users from the discomfort caused by the inflating cuff used in auscultatory and oscillometric BP measurement techniques. However, in the common practice for PTT detection, multi-site sensor implementation on human body is required, making it difficult for the integration of wearable devices. Since multi-wavelength (MW) photoplethysmogram (PPG) signals carry blood pulsation information of different blood vessels embedded in different skin depths, the time difference between different wavelength PPG signals collected at the same body site can be treated as a special PTT on a short length of blood vessels beneath the skin...
August 2016: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
Ying Teng, Lanlan Jiang, Yingting Fan, Yu Liu, Dayong Wang, Abuliti Abudula, Yongchen Song
The density driven convection phenomenon is expected to have a significant and positive role in CO2 geological storage capacity and safety. The onset and development of density-driven convective on the core scale is critical to understand the mass transfer mechanism. In this paper, laboratory experiments were conducted to investigate the density-driven convective in a vertical tube. The deuterium oxide (D2O)/manganese chloride (MnCl2) water solution in water or brine were as an analog for CO2-rich brine in original brine...
March 14, 2017: Magnetic Resonance Imaging
Pavan Miriyala, N P Sukumaran, B Nagender Nath, P B Ramamurty, A V Sijinkumar, B Vijayagopal, V Ramaswamy, Tyson Sebastian
Chemical weathering and the ensuing atmospheric carbon dioxide consumption has long been considered to work on geological time periods until recently when some modelling and natural records have shown that the weathering-related CO2 consumption can change at century to glacial-interglacial time scale. Last glacial to interglacial transition period is a best test case to understand the interplay between Pco2-temperature-chemical weathering when a pulse of rapid chemical weathering was initiated. Here we show, from a high resolution 54 ka record from the Andaman Sea in the northern Indian Ocean, that the chemical weathering responds to deglacial to mid-Holocene summer monsoon intensification in the Myanmar watersheds...
March 17, 2017: Scientific Reports
Maria Chernysheva, Anastasia Bednyakova, Mohammed Al Araimi, Richard C T Howe, Guohua Hu, Tawfique Hasan, Alessio Gambetta, Gianluca Galzerano, Mark Rümmeli, Aleksey Rozhin
The complex nonlinear dynamics of mode-locked fibre lasers, including a broad variety of dissipative structures and self-organization effects, have drawn significant research interest. Around the 2 μm band, conventional saturable absorbers (SAs) possess small modulation depth and slow relaxation time and, therefore, are incapable of ensuring complex inter-pulse dynamics and bound-state soliton generation. We present observation of multi-soliton complex generation in mode-locked thulium (Tm)-doped fibre laser, using double-wall carbon nanotubes (DWNT-SA) and nonlinear polarisation evolution (NPE)...
March 13, 2017: Scientific Reports
Lucie Griffon, Alessandro Amaddeo, Jorge Olmo Arroyo, Rossana Tenconi, Serena Caggiano, Sonia Khirani, Brigitte Fauroux
PURPOSE: The characterization of apneas during polysomnography (PSG) as obstructive or central is a key element of a sleep study. Pulse transit time (PTT) has demonstrated its potential as a noninvasive surrogate marker for inspiratory efforts. The aim of the study was to assess the ability of PTT to classify apneas as central or obstructive, as compared to respiratory inductance plethysmography (RIP) in children. METHODS: Overnight PSG with simultaneous PTT recording was performed on 11 consecutive children (mean age 8...
March 9, 2017: Sleep & Breathing, Schlaf & Atmung
Wen-Xuan Dai, Yuan-Ting Zhang, Jing Liu, Xiao-Rong Ding, Ni Zhao
Accurate and ambulatory measurement of blood pressure (BP) is essential for efficient diagnosis, management and prevention of cardiovascular diseases (CVDs). However, traditional cuff-based BP measurement methods provide only intermittent BP readings and can cause discomfort with the occlusive cuff. Although pulse transit time (PTT) method is promising for cuffless and continuous BP measurement, its pervasive use is restricted by its limited accuracy and requirement of placing sensors on multiple body sites...
August 2016: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
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