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The aortic-femoral arterial stiffness gradient, defined as the ratio of femoral-ankle pulse wave velocity to carotid-femoral pulse-wave velocity, demonstrates good between-day reliability in young healthy adults.
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The laser-produced plasma channel may be a promising means of producing an efficient compact soft-x-ray laser. The plasma parameters in such a plasma waveguide are calculated with a self-similar model. It is shown that nonequilibr...
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The laser-produced plasma channel may be a promising means of producing an efficient compact soft-x-ray laser. The plasma parameters in such a plasma waveguide are calculated with a self-similar model. It is shown that nonequilibrium underdense plasmas and candidate ions for recombination laser schemes can be obtained. As an example, the laser gains of the transition 1s3d-1s2p of He-like N ions are calculated for given pumping energies and initial gas densities. (C) 1997 Optical Society of America.
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Based on the geometrical acoustic approximation, we study theoretically the phonon focusing at the (100) face of silicon with a thin oxide overlayer. The oxide layer is assumed to be isotropic elastically and the focusing factors ...
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Based on the geometrical acoustic approximation, we study theoretically the phonon focusing at the (100) face of silicon with a thin oxide overlayer. The oxide layer is assumed to be isotropic elastically and the focusing factors of both the Rayleigh-surface and pseudosurface phonons are calculated for several values of k (wave number) x h (thickness of the oxide layer). As kh increases we find that the strong focusing region of Rayleigh-surface phonons in between two caustic directions becomes narrow and moves toward the [110] direction. Also the directions around the [110] axis, where the pseudosurface phonons are allowed to exist, are diminished and eventually their spatial intensity distribution disappears. [References: 19]
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Objectives: To compare noninvasive methods to assess pulse wave velocity (PWV) with the invasive gold standard in terms of absolute values, age-related changes, and relationship with subclinical organ damage.
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The property of three-wave-interaction solitons to preserve their shape upon nonlinear interaction with an arbitrary-shaped radiation is proposed for the creation of all-optical switching devices. It is shown that three-wave-inter...
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The property of three-wave-interaction solitons to preserve their shape upon nonlinear interaction with an arbitrary-shaped radiation is proposed for the creation of all-optical switching devices. It is shown that three-wave-interaction solitons can be used for optical switching in a polarization-gate geometry. This new all-optical logic gate combines the advantages of soliton switching devices with the short length of a second-order nonlinear interaction. Feasibility of an all-optical logic gate based on two 1.5-cm-long beta-barium berate crystals and with the intensity of the control pulse 190 MW/cm(2) is demonstrated. (C) 1998 Optical Society of America. [References: 13]
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Background: The brachial-ankle pulse wave velocity (baPWV) is more likely to be influenced by high blood pressure than carotid-femoral pulse wave velocity (cfPWV), since baPWV includes some peripheral arterial components, which ha...
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Background: The brachial-ankle pulse wave velocity (baPWV) is more likely to be influenced by high blood pressure than carotid-femoral pulse wave velocity (cfPWV), since baPWV includes some peripheral arterial components, which have less cushioning against high pressure than central arteries, in addition to central arterial components. So, it is feared that reliability of baPWV will decline in patients with high systolic blood pressure (SBP). Methods: We studied 114 patients with acute brain infarction or transient ischemic attack who underwent both baPWV and cfPWV measurements. We investigated the influence of SBP on discordance between baPWV and cfPWV results in patients with a slightly high SBP. Results: 114 patients were divided into accordance and discordance groups by matching both pulse wave velocity (PWV) results. The percentage of an abnormal cfPWV was higher in the accordance group (p＜0.001). However, the percentage of an abnormal baPWV was higher in the discordance group (p＝0.001). The brachial artery systolic blood pressure (bSBP) was categorized into two groups (＜144 mmHg bSBP, and ≥144 mmHg bSBP) based on 144 mmHg bSBP. The central artery systolic blood pressure (cSBP) also was categorized into two groups (＜133 mmHg cSBP, and ≥133 mmHg cSBP) based on 133 mmHg cSBP. In multivariate analysis, after adjusting for confounding factors, ＜144 mmHg bSBP was independently associated with the discordance of PWV findings (p＝0.037). However, ＜133 mmHg cSBP was not associated with the discordance of PWV findings. Conclusions: It was found that baPWV was more affected by bSBP, and resulted in an abnormal finding in spite of a normal finding of the cfPWV measurement in the same subject with ＜144 mmHg bSBP. Our study suggests that cfPWV is more useful than baPWV to estimate the arterial stiffness in patients with a slightly higher bSBP.
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In high-power pulse-tube refrigerators, the pulse tube itself can be very long without too much dissipa?tion of acoustic power on its walls. The pressure amplitude, the volume-flow-rate amplitude, and the time phase between them e...
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In high-power pulse-tube refrigerators, the pulse tube itself can be very long without too much dissipa?tion of acoustic power on its walls. The pressure amplitude, the volume-flow-rate amplitude, and the time phase between them evolve significantly along a pulse tube that is about a quarter-wavelength long. Proper choice of length and area makes the oscillations at the ambient end of the long pulse tube optimal for driving a second, smaller pulse-tube refrigerator, thereby utilizing the acoustic power that would typ?ically have been dissipated in the first pulse-tube refrigerator's orifice. Experiments show that little heat is carried from the ambient heat exchanger to the cold heat exchanger in such a long pulse tube, even though the oscillations are turbulent and even when the tube is compactly coiled.
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X-waves are one type of limited diffracting waves which have many potential applications in the enlargement of the field depth in acoustic imaging systems. However, the generation of X-waves ultrasonic fields in real-time need a c...
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X-waves are one type of limited diffracting waves which have many potential applications in the enlargement of the field depth in acoustic imaging systems. However, the generation of X-waves ultrasonic fields in real-time need a complex and expensive technology which involves precise and specific voltage time distributions for the excitation of each distinct array element. In order to overcome the high cost and technology, we proposed the new approach by approximating the excitation driving pulse from rectangular to triangular driving pulse and chose the pulses with the minimal optimization result as approximation driving pulses due to L2 curve criterion. The calculation of X-wave acoustic fields is based on the spatial impulse response approach, a new, simplified and exact solution algorithm to calculate of spatial pulse response is described in the paper, it is determined by intersection line of transducer apertures and the projected of spherical waves, which can reduce the calculation time. From these results of calculation of X-wave acoustic fields, the accuracy of the X-wave simulation can be improved by the new approach. A tradeoff is obtained between the cost of implementation of classical 0-order X-waves and the precision of approximation with the simple pulsed electrical driving.
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Pulse wave velocity (PWV) is the most widely used measurement of arterial stiffness in clinical practice. This study aimed to evaluate and compare the relationships between carotid-femoral pulse wave velocity (cfPWV) and brachial-...
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Pulse wave velocity (PWV) is the most widely used measurement of arterial stiffness in clinical practice. This study aimed to evaluate and compare the relationships between carotid-femoral pulse wave velocity (cfPWV) and brachial-ankle PWV (baPWV) and the presence of carotid plaque. This study was designed cross-sectionally and included 6027 participants from a community-based cohort in Beijing. Logistic regression analyses were performed to evaluate and compare the associations of cfPWV and baPWV with the presence of carotid plaque. The mean (SD) cfPWV and baPWV were 8.55?±?1.83 and 16.79?±?3.36, respectively. The prevalence of carotid plaque was 45.26% ( n =?2728). Both cfPWV (per 1?m/s increase: OR?=?1.11, 95% CI: 1.07–1.16) and baPWV (OR?=?1.04, 95% CI: 1.02–1.06) were independently associated with carotid plaque after adjusting for various confounders. Compared with bottom quartile (cfPWV ≤7.31?m/s and baPWV ≤14.44?m/s), the top quartile of cfPWV and baPWV had a significantly higher prevalence of carotid plaque (for cfPWV: OR?=?1.59, 95% CI: 1.32–1.92; for baPWV: OR?=?1.53, 95% CI: 1.26–1.86). However, the relationship of baPWV and carotid plaque was nonlinear, with a positive trend only when baPWV?<?16.85?m/s. When comparing relationships between PWV indices and carotid plaque in one model, both cfPWV and baPWV were significantly associated with carotid plaque in participants with baPWV?<?16.85?m/s; however, only cfPWV was independently associated with carotid plaque in participants with baPWV ≥16.85?m/s. Both cfPWV and baPWV were significantly associated with carotid plaque in the Chinese community-based population. Furthermore, cfPWV was more strongly correlated with carotid plaque than baPWV in participants with baseline baPWV ≥16.85?m/s.
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Mud pulse telemetry (MPT) is one of the essential means to ensure a high transmission rate of downhole data. Continuous-wave mud pulse has a high transmission rate, strong stability, and outstanding adaptability, the most widely u...
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Mud pulse telemetry (MPT) is one of the essential means to ensure a high transmission rate of downhole data. Continuous-wave mud pulse has a high transmission rate, strong stability, and outstanding adaptability, the most widely used downhole data transmission mode. One factor that restricts the high transmission rate of downhole data is the quality of the pressure wave generation signal. However, there is a lack of complete mathematical modeling research methods. Based on CFD theory, a numerical model of the integration of pulse generator and upstream and downstream pipelines was established for the first time, as well as the corresponding grid division process, which was to simulate the pressure wave generation and propagation process under drilling conditions, and the sensitivity analysis of parameters was carried out. The results show that the pressure drop curve derived from the thin-wall throttling theory is not the actual pressure wave, so the optimization results have a particular theoretical error. In fact, with the periodic change of the flow area, the upstream and downstream synchronously generate compression waves and expansion waves, which propagate and gradually decay. The amplitude of pressure wave increases with the increase of displacement and density but decreases sharply with the increase of gap height. Meanwhile, the amplitude does not change with the frequency and viscosity, but it aggravates the propagation attenuation of the pressure wave. Moreover, it is observed that the pressure wave is not a perfect sine wave in the case of sinusoidal rotor rotation, which needs further study. The research results of this paper provide a technical means for the optimization of downhole pressure wave generation, transmission, and noise reduction and help improve the transmission rate of downhole data.
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