Wave Delay Research Articles

Examining cerebrovascular burden across the cognitive continuum in older adults with and without evidence of amyloidosis

AbstractBackgroundThis work characterized cerebrovascular health in human subjects spanning the cognitive spectrum with and without presence of Aβ using different neuroimaging techniques (Fig1).MethodsSubjects (n=70) were clinically characterized into four groups: cognitively unimpaired (CU), CU‐Declining (at‐risk of progressing to clinical mild MCI based on traditional neuropsychological data), clinical MCI, and clinical dementia (Fig2). MRI: Vascular imaging: Whole‐brain 4D‐Flow data were acquired to characterize cerebrovascular health. pCASL with three post labeling delays was used to provide transit time corrected CBF maps. Structural imaging: T1‐weighted and T2‐FLAIR images were also collected for quantification of intracranial, hippocampal and white matter hyperintensity volumes. Hemodynamic measurements were extracted from intracranial arteries including the petrous ICAs, BA, MCAs, and veins SSS. Quantified flow parameters included: total cerebral blood flow, trans‐capillary pulse wave delay, and flow pulsatility index (PI). Trans‐capillary pulse wave delay was defined as the time shift between arterial and venous cardiac waveforms. PET: Aβ burden was assessed using 11C‐PiB PET imaging. Amyloid positivity (A‐, A+) was established as mean cortical PiB DVR >1.16. For A+ participants, amyloid time (i.e., estimated duration A+) was estimated using the sampled iterative local approximation algorithm. Differences were assessed using ANOVA followed by post‐hoc analysis (P<0.05 significance).ResultsMicro‐vascular tissue perfusion was statically higher in A+/CU when compared to other A+ groups in the GM, WM, and hippocampus (Fig3 and 4). Trans‐capillary pulse wave delay was statistically longer in A+/CU when compared to A+/CU‐Declining, A+/MCI, and A+/dementia (Fig5A). For A‐ groups trans‐capillary pulse wave delay was similar; yet, flow PI was statistically higher in A‐/CU‐Declining and A‐/MCI when compared to A‐/CU in the ICAs and MCAs (Fig5 C, D). Flow PI in A+/CU was higher than in A‐/CU.ConclusionsDecreased micro‐vascular tissue perfusion and shorter trans‐capillary pulse wave delay in A+ subjects with cognitive alterations (e.g. CU‐Declining, MCI, Dementia) compared to A+/CU indicates decreased metabolism and increased small vessel stiffness may contribute to cognitive decline and/or are induced by amyloidosis. In contrast, for A‐ subjects significant differences in arterial flow pulsatility index between A‐/CU, CU‐Declining, and MCI suggests macro‐vascular arterial stiffness contributes to cognitive decline.

Active Control of Electromagnetically Induced Transparency Analogy in Spoof Surface Plasmon Polariton Waveguide

Metamaterial analogues of electromagnetically induced transparency (EIT) enable a unique avenue to endow a coupled resonator system with quantum interference behavior, exhibiting remarkable properties in slow-wave and highly sensitive sensing. In particular, tunable and ultracompact-chip-integrated EIT-like effects reveal fantastic application prospects in plasmonic circuits and networks. Here, we demonstrate an electrically tuned on-chip EIT analogue by means of dynamic EIT modules side-coupled to ultrathin corrugated metallic strips supporting spoof surface plasmon polaritons (SSPPs). By embedding PIN diodes into the subradiant mode, on-to-off control of the destructive coupling between the radiative and subradiant modes results in dynamic chip-scale EIT-like behavior under the change of the bias voltage, allowing for an electrically tunable group delay of the surface waves. The physical mechanism of the active modulation is elucidated with the coupled mode theory. In addition, the cascaded capacity performed by installing multiple EIT modules with an interval of equivalent wavelength are also characterized on a planar plasmonic waveguide. The proposed system will pave a versatile route toward dynamic control in chip-scale functional devices.

Impaired fertility in 4930590J08Rik mutant male mice is associated with defective sperm energy metabolism.

Testis-specifically expressed genes are important for male reproduction according to their unique expression patterns. However, the functions of most of these genes in reproduction are unclear. Here, we showed that mouse 4930590J08Rik was a testis-specifically expressed gene. 4930590J08Rik knockout mice exhibited a delay in the first wave of spermatogenesis and a reduction of cauda epididymal sperm. Furthermore, knockout spermatozoa exhibited defective acrosome reactions and decreased progressive motility, which led to impaired in vivo fertilization. Transcriptome analysis of testes revealed that most of the differentially expressed genes in knockout testes were associated with metabolic processes. 4930590J08Rik knockout sperm exhibited oxidative phosphorylation deficiency and were highly dependent on increased anaerobic glycolysis to compensate for ATP demands. Taken together, the 4930590J08Rik-disrupted mouse partially mimics the phenotypes of human asthenospermia and oligozoospermia, which provides a new model for further understanding the pathogenesis of idiopathic male infertility.

The role of modeling scheme and model input factors uncertainty in the analysis and mitigation of backwater induced urban flood-risk

Recent flood-related disasters, which affect many areas of the world due to a combination of climate change and increasing urbanization, have prompted researchers to study catastrophic phenomena for which large-scale mitigation strategies are needed. However, lower impact flood events occur more frequently, and although these floods are relatively less destructive, they can be effectively mitigated with local protection measures. This work focuses on understanding the factors that influence the reliable modeling of these lower impact - and less studied - flood events. We propose a procedure that combines the use of a simple but effective numerical model of the last segment of Ticino River with a Global Sensitivity Analysis for an in-depth evaluation of: i) the backwater-induced flooding of an urban area in the historical city of Pavia (Northern Italy) and ii) the potential flood damage due to such events. A 1D, unsteady HEC-RAS model (termed the 3R Model) was set up and validated against historical floods. Then, the 3R Model output was compared with a hybrid 1D/2D model of the same area. Both model schemes provide reliable results and similar predictions of the flood depth and its spatial extent. The 3R Model is demonstrated to be a successful modeling approach, providing a computational cost that is always less than one-tenth of the cost of the hybrid 1D/2D for the simulated floods. The Morris method of sensitivity analysis was performed to identify the most influential factors affecting the results of the 3R Model to help inform local policies aimed at flood risk reduction. The Morris results highlight that the maximum water level of the Po river has a dominant role in determining the flood magnitude for the whole area, with an influence at the control points in the floodplain that is more than triple that of the Ticino maximum flow rate. A Damage Index quantifying the housing loss due to the urban flood extent was introduced and analyzed using the Morris method. The results show that the predicted flood damage is strongly influenced by the uncertainty in the roughness coefficient of the floodplains. The contemporaneity of the floods on the Ticino and Po Rivers was also influential, playing a key role in flood severity within the urban area. A 5-hour delay of the Ticino flood wave (maximum flow rate of 2000 m3/s) with respect to that of the Po River (maximum stage level of 59.8 m a.s.l.) reduces the water level in the flooded area by 8 cm. These results will help the development of flood risk reduction strategies.

Improvement of Surface Acoustic Wave Delay Lines Using c-Axis Tilted AlScN Thin Film

Improvement of Surface Acoustic Wave Delay Lines Using c-Axis Tilted AlScN Thin Film

Relation between Mass Sensitivity and Complex Power Flow in Love Wave Sensors.

In this paper, we investigate the connection between average power flows in Love wave waveguides with the mass sensitivity of Love wave sensors. In fact, loading with a Newtonian liquid gives rise to two extra power flows, in the transverse direction towards the loading Newtonian liquid. The first is an active power flow feeding viscous losses in the Newtonian liquid and the second is a reactive power flow that is responsible for the phase delay of the Love wave and consequently for the changes in phase velocity of the Love wave. Since loading with a lossless mass also leads to changes in the phase velocity, we assert that mass sensitivity of Love wave sensors is connected to the average reactive power flow, in the transverse direction , bouncing back and forth, between the interior of the waveguide and the loading Newtonian liquid. Subsequently, we found the thickness of the effective surface layer of mass that is equivalent to loading with a semi-infinite Newtonian liquid. The analytical formulas developed in this paper are illustrated by the results of numerical calculations performed for an exemplary Love wave waveguide composed of a PMMA surface layer deposited on an ST-Quartz substrate.

Location Accuracy Improvement of Long-range Lightning Detection Network In China by Compensating Ground Wave Propagation Delay

Very low frequency (VLF) electromagnetic waves distort along the long propagation path, and that causes the arrival time of the signals measured by the long-range lightning system to be delayed. In this paper, based on the propagation correction method by compensating the peak time delay of the ground wave, the location accuracy of the long-range lightning detection network in China is greatly improved. The improvement of the relative location accuracy and location offsets are evaluated by comparing with the Advanced Direction Time Lightning Detection System (ADTD) datasets. It shows that the mean relative accuracy is improved from 7.74 km to 4.32 km, and the median relative accuracy is improved from 7.28 km to 2.46 km. The mean westwards offset of the total lightning location data drops from 2.05 km to 0.93 km, and the mean southwards offset drops from 1.19 km to 0.63 km. In addition, it is found that the location accuracy will be greatly improved if the observation site affected by the terrain is removed. The mean relative location accuracy is further improved to 4.11 km and the median to 2.32 km.

Broadband Control of Group Delay Using the Brewster Effect in Metafilms

We propose and verify a method for controlling the frequency dependence of the group delay of electromagnetic waves over a broad frequency range using the Brewster effect in single-layer metamaterials with finite thickness, here referred to as metafilms. When the metafilm's reflectance vanishes regardless of the incident frequency, the group delay can be large near its resonance frequency while maintaining the transmittance close to unity regardless of the incident frequency. Furthermore, when several reflectionless metafilms are stacked together, the total group delay should be given as the sum of the individual group delays. In this study, we realize reflectionless metafilms by arranging the meta-atoms so that the Brewster effect occurs regardless of the incident frequency. We evaluate in numerical simulations and experiments the frequency dependence of the transmittance and of the group delay of a three-layer metamaterial composed of reflectionless metafilms with different resonance frequencies, and find that the total transmittance and group delay of this metamaterial agree respectively with the product of the transmittances and the sum of the group delays of the constituent metafilms.

Strength Properties of the Heat-Resistant Inconel 718 Superalloy Additively Manufactured by Direct Laser Deposition Method under Shock Compression

By recording and analyzing complete wave profiles using the VISAR laser interferometer, measurements of the Hugoniot elastic limit and critical fracture stresses were carried out under the spalling conditions of the heat-resistant Inconel 718 alloy, additively manufactured by direct laser deposition, at shockwave loading up to ~6.5 GPa using a light-gas gun. For comparison, similar experiments were performed with the Inconel 718 alloy made by the traditional method of vacuum induction melting. The process of the delay of an elastic compression wave during its propagation through the sample and the dependence of the spall strength on the strain before fracture in the range 105–106 s−1 were investigated. To identify the anisotropy of the strength properties of the material under study, two series of experiments were carried out on loading additively manufactured samples along and perpendicular to the direction of the deposition. The measurements performed showed that the additively manufactured Inconel 718 alloy demonstrates weak anisotropy of strength properties for both the initial and thermal-treated samples. The thermal treatment leads to a noticeable increase in the Hugoniot elastic limit and the spall strength of the samples at low strain rates. For all types of samples, there is an increase in the spall strength with an increase in the strain rate. The spall strength measured for the cast alloy practically coincides with the strength of the as-received additive alloy and is noticeably lower than the strength of the thermal-treated additive alloy over the entire range of the strain rates. The process of the decay of the elastic precursor in the cast alloy occurs much faster than in the additive one, and the minimum values of the Hugoniot elastic limit are measured for thick samples in the cast alloy.

Low-frequency Lamb wave mixing for fatigue damage evaluation using phase-reversal approach

Fatigue damage is difficult to detect and evaluate non-destructively, specifically at its early stages (before the macro-crack formation). In this study, fatigue damage is evaluated based on the growth rate of the combinational harmonics generated by mixing of two fundamental symmetric mode (S0) of Lamb waves in the low frequency range. The incorporation of the phase reversal approach to the wave mixing method could potentially improve the evaluation of the combinational and second harmonics and avoid the influence of other undesirable harmonics. A series of parametric case studies are carried out using the three-dimensional (3D) finite element (FE) method to investigate the effects of the excitation frequencies and time delay of the incident waves in wave mixing on the transient response of a weakly-nonlinear material. The numerical results and experimental results show that the sum combinational harmonic and second harmonics are sensitive to weak material nonlinearities. Further experiments on damaged samples by cyclic loading demonstrate that the sum combinational harmonic has much better sensitivity to the progressive fatigue damage than the the second harmonics. In general, the outcomes of this study indicate that the damage evaluation of early stage fatigue damage is feasible and effective with the wave mixing method using the S0 waves generated at low frequency, and the phase-reversal approach improves considerably the quality of experimental results in the fatigue damage evaluation.

Simultaneous measurement of human auditory nerve and brainstem potentials: Effects of upward spread of excitation

Acoustic clicks evoke strong synchrony of auditory-nerve (AN) fibers, thereby eliciting a compound action potential (CAP); however, synchrony is reduced by the delay of the cochlear traveling wave. Upward-frequency chirps compensate for this delay, resulting in larger CAPs evoked by chirps than clicks. Our model simulations of CAPs suggest that chirps presented at high intensities (100 dB peSPL) adapt basal AN fibers via upward spread of excitation of low-frequency chirp components. This adaptation results in less-than-or-equal-to CAP amplitudes and distorted CAP morphology compared to CAPs evoked by clicks. Simulations show that these effects on CAP amplitude and morphology can be avoided by reducing the amplitude of the low-frequency components of the chirp (i.e., modified chirp). Here we present CAPs from 12 young adults with NH, which for high stimulus intensities, exhibit reduced amplitudes and broader CAP morphology for chirps than clicks, whereas CAP amplitudes for modified chirps exceed those for clicks, consistent with model simulations. The distorted CAP morphology in response to high-level chirps is consistent with adaptation of AN responses and broad cochlear excitation. Interestingly, the deleterious effects of high-level chirps on CAP amplitude and morphology are reduced or absent in simultaneous recordings of the auditory brainstem response.

DeepShake: Shaking Intensity Prediction Using Deep Spatiotemporal RNNs for Earthquake Early Warning

Abstract We propose a deep spatiotemporal recurrent neural network, DeepShake, to project future shaking intensity directly from current ground-motion observations. DeepShake is a network-based forecasting model, able to predict future shaking intensity at all stations within a network given previously measured ground shaking. The model is not given any a priori knowledge of station locations; instead, it learns wave propagation amplitudes and delays solely from training data. We developed DeepShake with the 35,679 earthquakes from the 2019 Ridgecrest sequence. Tasked with alerting for modified Mercalli intensity (MMI) IV+ shaking on 3568 validation earthquakes at least 5 s in advance, DeepShake achieves an equal error rate of 11.4%. For the Mw 7.1 earthquake that hit Ridgecrest on 5 July 2019, DeepShake was able to provide targeted alerts to all stations inside the network 5 s prior to the arrival of MMI IV+ waveforms. DeepShake demonstrates that deep spatiotemporal neural networks can effectively provide one-step earthquake early warning with reasonable accuracy and latency.

Automatic Distance and Angle Measurement Tool using Atmega8535 Microcontroller based Ultrasonic Sensor for Conventional X-Ray Medical Device

The aim of this research is to design an ultrasonic distance and angel detecting device by utilizes time delay of wave reflected. The ultrasonic echo waves were then converted into electrical echo pulses. This distance and angle detecting device can later be used on conventional X-ray modality. This distance and angle detecting device was designed based on ultrasonic sensor and an Atmega8535 microcontroller. Distance measurements was carried out vertically and horizontally with variations ranging from 90 cm to 130 cm with a 10 cm increment factor. While angle measurements were performed manually at angle variations of 10 ° to 30 ° with an increment factor of 5 °. The performance of the tool showed that the relative error value on vertical measurement was 0.10% with the greatest accuracy of 99.97%. While the horizontal measurement relative error was 0.10% and the highest relative accuracy recorded at 99.97%. Meanwhile, on the angle measurement, it was found that the relative error was0.39% with the highest relative accuracy of 99.72%.

Nonvolatile Reconfigurable Electromagnetically Induced Transparency with Terahertz Chalcogenide Metasurfaces

AbstractMetasurface analog of electromagnetically induced transparency (EIT) provides a compact platform for generating a narrow‐band transmission window with very sharp spectral features. They hold promise for many appealing applications including ultrasensitive detectors, slow‐light devices, nonlinear optical devices etc. In particular, reconfigurable EIT metasurfaces are crucial for expanding the capability of light field control, which are promising for terahertz (THz) communications and optical networks. Yet, the investigation on reconfigurable EIT metasurfaces with nonvolatile operation remains scarce. Here, reversible switching of the metasurface‐induced transparency in the THz spectrum is experimentally realized. The reconfigurable response (reversible spectral shift) is obtained by integrating a nonvolatile chalcogenide phase change material, Ge2Sb2Te5 (GST225) into the meta‐atoms. A giant reversible switching of EIT takes place under an excitation of nanosecond laser pulses, showing a reconfigurable group delay of the THz waves. The proposed reconfigurable THz metadevices may provide a new route for the ultrafast laser induced switching and reconfigurable slow‐light devices.

Dual-directional group delays during optical topological transitions in black phosphorus-based asymmetric hyperbolic metamaterials.

We theoretically study the optical properties of TM waves when their magnetic field direction is perpendicular to the armchair and zigzag optical axes of black phosphorus, respectively. It is found that hyperbolic dispersion and elliptic dispersion coexist in periodically arranged black phosphorus multilayers. Interestingly, by tilting the symmetric multilayers to be asymmetric, the elliptical part of the original two dispersions disappears as the wavelength increases. As such only the hyperbolic dispersion remains, showing an optical topological transition. In the region of the topological transition, a large transmitted group delay (3ps) and a reflected group delay (0.2ps) of the TM waves occurs simultaneously. The corresponding group velocities are slowed down to approximately c/1000 and c/100 (c is the speed of light in a vacuum), respectively. This dual-directional group delays significantly increase the wave-matter interaction so that nonreciprocal perfect absorptions can be realized in the mid-infrared band. Such asymmetrical black phosphorus hyperbolic metamaterials can be applied to the directional, tunable, and nonreciprocal perfect absorbers and also to devices based on strong wave-matter interactions.

Determination of the difference in gravitational potentials in the Earth's field based on the measurement of the gravitational delay of light waves in an optical fiber

Determination of the difference in gravitational potentials in the Earth's field based on the measurement of the gravitational delay of light waves in an optical fiber

Parker Solar Probe detects solar radio bursts related with a behind–the–limb active region

Context.The interpretation of solar radio bursts observed by Parker Solar Probe (PSP) in the encounter phase plays a key role in understanding intrinsic properties of the emission mechanism in the solar corona. Lower time–frequency resolution of the PSP receiver can be overcome by simultaneous ground–based observations using more advanced antennas and receivers.Aims.In this paper we present such observations for which the active active region 12 765, begetter of type III, J, and U solar bursts, was within sight of ground–based instruments and behind the solar limb of the PSP spacecraft.Methods.We used a subarray of the Giant Ukrainian Radio Telescope to get the spectral properties of radio bursts at the frequency range of 8–80 MHz, as well as the PSP radio instruments with a bandwidth of 10.5 kHz–19.2 MHz, during solar observations on June 5, 2020.Results.We directly detected the radio events initiated by the active region behind the solar limb of the PSP spacecraft, using special conditions in the solar corona, due to the absence of active regions from the PSP side. Following the generation mechanism of solar radio emission, we refined the density model for the solar corona above the active region 12765 responsible for the radio bursts. Based on the PSP spacecraft position near the Sun and delays of radio waves between space– and ground–based records, we found the corresponding radio responses on the PSP spectrogram.Conclusions.The absence of sunspots from the PSP side contributes to the propagation of radio waves from a dense loop of the Sun to quiet regions with low densities, through which PSP instruments can detect the radiation.

Associations in Alzheimer’s disease between intracranial vascular metrics from 4D‐flow MRI and β‐amyloid and tau PET

AbstractBackgroundCerebrovascular disease (CVD), has been linked with dementia stages of Alzheimer’s disease (AD); however, the question of whether CVD is associated with underlying AD pathophysiology remains unresolved. This work investigated the relationship between advanced MRI based cerebrovascular markers with AD biomarkers of β‐amyloid deposition and neurofibrillary tau tangles in subjects spanning the AD clinical spectrum.MethodSubjects: Study groups are summarized in figure 1. MRI: Whole brain 4D‐Flow data were acquired on a 3.0T system using a 32‐channel head coil. From 4D‐Flow images, intracranial blood flow, trans‐capillary pulse wave delay, and low frequency oscillations (LFOs) were estimated. Trans‐capillary pulse wave delay was defined as the cardiac pulse wave transit time from intracranial arteries‐to‐capillaries‐to‐veins and was measured from cardiac wave time‐to‐upstroke differences in arteries and veins. White matter hyperintensity (WMH) lesion volumes were segmented from T2‐FLAIR images using the Lesion Segmentation Toolbox in SPM12. PET: Four groups were established based on clinical diagnosis and biomarker positivity. Subjects were classified as cognitively normal (CN) or impaired (IM) (MCI or dementia) based on a clinical consensus review. Amyloid (A) (+/‐) was determined using a previously established global PiB DVR threshold >1.19 and tau (T) (+/‐) was determined using a previously established entorhinal cortex MK‐6240 SUVR threshold >1.27. Pairwise statistical differences were assessed using ANOVA followed by post‐hoc analysis (P<0.05 significance).ResultTrans‐capillary pulse wave delay was significantly longer in controls (A‐/T‐/CN) when compared with AD biomarker confirmed groups (fig 2 b) (P<0.001). Low frequency flow range and LFOs were significantly lower and diminished in A+T+ groups both cognitively normal and impaired (fig 3 P<0.001; fig 4 P=0.027, P=0.046, P=0.046). Linear regression analysis showed a weak correlation between trans‐capillary pulse wave delay and PiB and MK‐6240 (R2=0.12, R2=0.04), and between LFOs and PiB and MK‐6240 (R2=0.07, R2=0.03) (fig 5). No significant AT biomarker group differences were observed across other modalities such as traditional cardiovascular and cerebrovascular metrics, including WMH lesion volumes (fig 1).ConclusionAlthough more traditional measures of CVD were not related to biomarker groups, 4D‐Flow MRI based vascular markers suggest significant intracranial vascular stiffness and reduced autoregulation‐related vasomotion in AD biomarker positive subjects during preclinical AD.

The influence of human arterial network's frequency characteristics on a pulse wave delay estimation

The influence of human arterial network's frequency characteristics on a pulse wave delay estimation

Design and Optimization of a Novel SAW Gyroscope Structure Based on Amplitude Modulation with 1-D Phononic Crystals.

Surface acoustic wave gyroscopes (SAWGs), as a kind of all-solid-state micro-electro-mechanical system (MEMS) gyroscopes, can work normally under extremely high-impact environmental conditions. Among the current SAWGs, amplitude-modulated gyroscopes (AMGs) are all based on the same gyro effect, which was proved weak, and their sensitivity and intensity of the output are both lower than frequency-modulated gyroscopes (FMGs). However, because FMGs need to process a series of frequency signals, their signal processing and circuits are far less straightforward and simple than AMGs. In order to own both high-sensitivity and simple signal processing, a novel surface acoustic traveling wave gyroscope based on amplitude modulation is proposed, using one-dimensional phononic crystals (PCs) in this paper. In view of its specific structure, the proposed gyroscope consists of a surface acoustic wave oscillator and a surface acoustic wave delay line within a one-dimensional phononic crystal with a high-Q defect mode. In this paper, the working principle is analyzed theoretically through the partial wave method (PWM), and the gyroscopes with different numbers of PCs are also designed and studied by using the finite element method (FEM) and multiphysics simulation. The research results demonstrate that under a 1 V oscillator voltage output, the higher sensitivity of −23.1 mV·(rad/s)−1 in the linear range from −8 rad/s to 8 rad/s is reached when the gyro with three PC walls, and the wider linear range from −15 rad/s to 17.5 rad/s with the sensitivity of −6.7 mV·(rad/s)−1 with only one PC wall. Compared with the existing AMGs using metal dots to enhance the gyro effect, the sensitivity of the proposed gyro is increased by 15 to 112 times, and the linear range is increased by 4.6 to 186 times, even without the enhancement of the metal dots.