Amplitude Maps Research Articles

Quantitative mapping of cerebrovascular reactivity amplitude and delay with breath-hold BOLD fMRI when end-tidal CO2 quality is low.

Cerebrovascular reactivity (CVR), the ability of cerebral blood vessels to dilate or constrict in order to regulate blood flow, is a clinically useful measure of cerebrovascular health. CVR is often measured using a breath-hold task to modulate blood CO2 levels during an fMRI scan. Measuring end-tidal CO2 (PETCO2) with a nasal cannula during the task allows CVR amplitude to be calculated in standard units (vascular response per unit change in CO2, or %BOLD/mmHg) and CVR delay to be calculated in seconds. The use of standard units allows for normative CVR ranges to be established and for CVR comparisons to be made across subjects and scan sessions. Although breath-holding can be successfully performed by diverse patient populations, obtaining accurate PETCO2 measurements requires additional task compliance; specifically, participants must breathe exclusively through their nose and exhale immediately before and after each breath hold. Meeting these requirements is challenging, even in healthy participants, and this has limited the translational potential of breath-hold fMRI for CVR mapping. Previous work has focused on using alternative regressors such as respiration volume per time (RVT), derived from respiratory belt measurements, to map CVR. Because measuring RVT does not require additional task compliance from participants, it is a more feasible measure than PETCO2. However, using RVT does not produce CVR in standard units. In this work, we explored how to achieve CVR maps, in standard units, when breath-hold task PETCO2 data quality is low. First, we evaluated whether RVT could be scaled to units of mmHg using a subset of PETCO2 data of sufficiently high quality. Second, we explored whether a PETCO2 timeseries predicted from RVT using deep learning allows for more accurate CVR measurements. Using a dense-mapping breath-hold fMRI dataset, we showed that both rescaled RVT and rescaled, predicted PETCO2 can be used to produce maps of CVR amplitude and delay in standard units with strong absolute agreement to ground-truth maps. However, the rescaled, predicted PETCO2 regressor resulted in superior accuracy for both CVR amplitude and delay. In an individual with regions of increased CVR delay due to Moyamoya disease, the predicted PETCO2 regressor also provided greater sensitivity to pathology than RVT. Ultimately, this work will increase the clinical applicability of CVR in populations exhibiting decreased task compliance.

Mapping the amplitude and phase of dissolved 129Xe red blood cell signal oscillations with keyhole spectroscopic lung imaging.

To assess the regional amplitude and phase of dissolved 129Xe red blood cell (RBC) signal oscillations in the lung vasculature with keyhole spectroscopic imaging and to compare with previous methodology, which does not account for oscillation phase. 129Xe gas transfer was measured with a four-echo 3D radial spectroscopic imaging sequence. Keyhole reconstruction-based RBC signal oscillation amplitude mapping was applied retrospectively to data acquired from 28 healthy volunteers, 4 chronic thromboembolic pulmonary hypertension (CTEPH) patients, and 5 patients who were hospitalized due to COVID-19 pneumonia and had residual lung abnormalities. Using a sliding window keyhole reconstruction, maps of RBC oscillation amplitude were corrected for regional phase difference. Repeatability of the phase-adjusted oscillation amplitude was assessed in 8 healthy volunteers across three scans. With sliding window keyhole reconstruction, regional phase differences were observed in the RBC signal oscillations: mean phase = (0.27 ± 0.19) rad in healthy volunteers, (0.24 ± 0.13) rad in CTEPH patients, and (0.33 ± 0.19) rad in patients with post-COVID-19 residual lung abnormality. The oscillation amplitude and phase maps were more heterogeneous (i.e., they showed increased coefficient of variation) for the CTEPH patients. The RBC oscillation amplitude was repeatable, and the mean three-scan coefficient of variation was smaller when the phase adjustment was made (0.07 ± 0.04 compared with 0.16 ± 0.05). Sliding window keyhole reconstruction of radial dissolved 129Xe imaging reveals regional phase differences in the RBC oscillations, which are not captured when performing two phase keyhole reconstruction. This regional phase information may reflect the hemodynamic effect of the cardiac pulse wave in the pulmonary microvasculature.

Integrated Seismic Attributes as a Tool to Delineate the Oligocene Channels Architecture, Baltim Field, Offshore Central Nile Delta, Egypt

The hydrocarbons in the Nile Delta area are produced from both clastic and non-clastic reservoirs, with ages ranging from the Early Cretaceous to the Plio-Pleistocene. The study area is situated in Baltim field offshore, Central Nile Delta, approximately 10 kilometers off the Egyptian coast (Fig. 1). The main producing reservoir in Baltim field is Abu Madi Formation (Miocene age) as there were many discoveries in the last decades resulting in most of the area had been considered as a brown field. Nowadays, the Oligocene section is considered as the hope for new hydrocarbon potentiality in the deep section (below Miocene). Among the drilled sedimentary sequence in the Nile Delta, Tineh Formation (Oligocene age) contains multiple levels of reservoir rocks with high-quality reservoirs including: Satis-1, Satis-3, Notus-1, Tineh-1, Atoll-1 & Salamat-1 (Fig. 2). This work's objective is to delineate the different channels of the Oligocene section in trial to add more reserves to the field. One of the main challenges for the exploration of these deep reservoirs is to delineate the reservoir geometry itself. A strong tool for improving bed thickness imaging and mapping, geologic discontinuities and channel delineation is the spectral decomposition technique providing more details than the conventional amplitude extractions. So, in this work, we applied the spectral decomposition tool to track the geometric dimensions of the Oligocene channels. RGB color blending performed from 10, 16, and 20 Hz represents the most significant geological features to get a better picture of the channel’s geometry. After determining the channel’s boundary by using the RGB blending, the channel geo-body was extracted. This technique helps in reducing the uncertainties of hydrocarbon exploration. Consequently to the integration between RMS amplitude maps and the channel geo-body that was extracted from the spectral decomposition, Oligocene channels became clearer and the boundaries well defined.

Mapping of chromite occurrence in a meta-ultramafic complex by magnetometric prospecting, Sul-Riograndense Shield (Southern Brazil)

This study presents the use of terrestrial magnetometry method in the characterization of a metamorphic and chromium-mineralized ultramafic body in the São Sepé region (RS). Several serpentinite exposures were recognized in the study area, characterized by a very evident schistosity marked by amphiboles and micas. The most preserved rocks are gray to dark green in color, silky to the touch and with folds and variable fracturing. The chromite present in serpentinites is associated with magnetite, and occurs in the form of small lenses. 1677 reading lines were made perpendicular to the main direction of the meta-ultramafic body, with 25m spacing between measurement points. The magnetometric maps revealed high-intensity anomalies related to meta-ultramafic rocks. 1677 reading lines were made perpendicular to the main direction of the meta-ultramafic body, with 25m spacing between measurement points. The magnetometric maps revealed high-intensity anomalies related to meta-ultramafic rocks. The results revealed the existence of highly magnetic individualized lenses orientated according to NE / SW, related to regional deformation events, with remobilization and mineral reconcentration. The direct relationship between high magnetization and chromite/ferro-chromite concentrations allows relatively detailed mapping of potentially mineralized areas, revealing dimensions more significant than the limits of the meta-ultramafic sequence defined in the geological map. The results indicate that the analytical signal amplitude map is a highly recommended product for planning sampling actions and reserve quantification, improving classical geological mapping.

COSMOGLOBE DR1 results

We present the first model of full-sky polarized synchrotron emission that is derived from all WMAP and Planck LFI frequency maps. The basis of this analysis is the set of end-to-end reprocessed COSMOGLOBE Data Release 1 (DR1) sky maps presented in a companion paper, which have significantly lower instrumental systematics than the legacy products from each experiment. We find that the resulting polarized synchrotron amplitude map has an average noise rms per 2° full width at half maximum (FWHM) beam of 3.2 μK at 30 GHz. This is 30% lower than the recently released BEYONDPLANCK model that included only LFI+WMAP Ka–V data, and 29% lower than the WMAP K-band map alone. The mean B-to-E power spectrum ratio is 0.39 ± 0.02, with amplitudes consistent with those measured previously by Planck and QUIJOTE. Assuming a power law model for the synchrotron spectral energy distribution and using the T–T plot method, we find a full-sky inverse noise-variance-weighted mean of the synchrotron polarized spectral index of βs = −3.07 ± 0.07 from the COSMOGLOBE DR1 K band and 30 GHz, in good agreement with previous estimates. In summary, the novel COSMOGLOBE DR1 synchrotron model is both more sensitive and systematically cleaner than similar previous models, and it has a more complete error description that is defined by a set of Monte Carlo posterior samples. We believe that these products are preferable over previous Planck and WMAP products for all synchrotron-related scientific applications, including simulations, forecasting, and component separation.

Evaluation of Photodynamic Therapy-combined Intravitreal Bevacizumab in Age-related Macular Degeneration

Aim: It was aimed to compare treatment results of photodynamic therapy (PDT) and PDT-combined intravitreal bevacizumab injection (PDT+IVB) in patients with age-related macular degeneration (AMD). Material and Methods: 63 eyes of 55 patients with neovascular AMD were included. Group 1 consisted of 40 eyes of 35, group 2 consisted of 23 eyes of 20 patients. Visual acuity (VA), intraocular pressure measurement and fundus examination were performed. Pattern Electroretinography P50 amplitude and edema map values (EMV) were measured with Heidelberg Retina Tomograph (HRTII). Results: VA increased in 14, remained unchanged in 17, decreased in 9 eyes in Group 1 (PDT). The PERG P50 amplitudes were compared with values of pre-treatment, and found increased as 10.6%, 11.98%, and 8.46% and HRTII EMV were 5.86%, 4.88%, and 11.22% at 1st, 3rd, and 6th months, respectively. In Group 2 (PDT+IVB), VA improved in 9, remained unchanged in 8, decreased in 6 eyes. PERG P50 amplitudes were decreased as 10.15%, 5.8%, and 0.1% and HRTII EMV were decreased as 13.07%, 12.17%, and 14.87% at 1st, 3rd, and 6th months, respectively. Conclusion: Verteporfin and PDT are effective and safe methods that preserve VA in subfoveal choroidal neovascular membranes due to neovascular AMD.

Second-harmonic generation microscopy with synthetic aperture and computational adaptive optics

Second-harmonic generation (SHG) microscopy is a powerful label-free imaging tool widely used to visualize collagen and muscle in biological tissues. However, traditional laser-scanning SHG microscopy requiring voxel scanning is time-intensive. Wide-field SHG microscopy was designed to bypass this restriction, but its application to deep tissue imaging is limited due to vulnerability to scattering and sample-induced aberrations. We introduce synthetic aperture SHG (SA-SHG) microscopy to attenuate the effect of multiple scattering noises. Our SA-SHG method coherently integrates amplitude and phase maps of wide-field SHG fields taken for different illumination angles, thereby enhancing the signal-to-noise ratio. We also develop computational adaptive optics SHG (CAO-SHG) microscopy to computationally correct the sample-induced aberrations. Our algorithm optimizes SHG fields’ aperture synthesis to identify aberration maps, enabling the restoration of diffraction-limited imaging. We successfully apply this approach to real biological samples, demonstrating its potential for high-resolution imaging in complex biological environments.

Dose-dependent changes in orientation amplitude maps in the cat visual cortex after propofol bolus injections

A general intravenous anesthetic propofol (2,6-diisopropylphenol) is widely used in clinical, veterinary practice and animal experiments. It activates gamma- aminobutyric acid (GABAa) receptors. Though the cerebral cortex is one of the major targets of propofol action, no study of dose dependency of propofol action on cat visual cortex was performed yet. Also, no such investigation was done until now using intrinsic signal optical imaging. Here, we report for the first time on the dependency of optical signal in the visual cortex (area 17/area 18) on the propofol dose. Optical imaging of intrinsic responses to visual stimuli was performed in cats before and after propofol bolus injections at different doses on the background of continuous propofol infusion. Orientation amplitude maps were recorded. We found that amplitude of optical signal significantly decreased after a bolus dose of propofol. The effect was dose- and time-dependent producing stronger suppression of optical signal under the highest bolus propofol doses and short time interval after injection. In each hemisphere, amplitude at cardinal and oblique orientations decreased almost equally. However, surprisingly, amplitude at cardinal orientations in the ipsilateral hemisphere was depressed stronger than in contralateral cortex at most time intervals. As the magnitude of optical signal represents the strength of orientation tuned component, these our data give new insights on the mechanisms of generation of orientation selectivity. Our results also provide new data toward understanding brain dynamics under anesthesia and suggest a recommendation for conducting intrinsic signal optical imaging experiments on cortical functioning under propofol anesthesia.

Transient Stability of Multiple Phase-Locked-Loop-Type Voltage Source Converters System Based on Amplitude Mapping Model

Compared to the traditional power grids, the multiple converters integration system are more vulnerable to the disturbances from transient events. However, the high-order characteristics of the system model is still a barrier not ignored. Inspired by averaging method of nonlinear vibration, the amplitude mapping model (AMM) is firstly proposed to evaluate the transient stability for multiple phase-locked-loop-type (PLL-type) voltage source converters (VSCs) system in this paper. Specifically, the origin and meaning of amplitude mapping model is introduced. Next, the mathematical model of the PLL-type VSCs system is derived. Based on AMM, the stability evaluation strategy of the PLL-type VSCs system is obtained. After that, the influence of key parameters, including the system gSCR, d-axis current reference, and PLL control parameters, on the system stability and the coupling effect between the VSCs are analyzed. Finally, a 6-VSCs 14-nodes system is applied to verify the correctness of the method proposed in this paper.

Reservoir Structural and Stratigraphical Evaluation of Sapele Deep Field, Niger Delta, Southern Nigeria.

Throughout the course of a field's existence, the oil and gas industry has not been very good at determining and forecasting how the stratigraphical and structural makeup of reservoirs will affect fluid flow. With harder-to-find reserves and growing development costs, it is critical to have a comprehensive plan in place to identify and reduce risks and uncertainties related to the stratigraphical and structural framework of reservoirs. Improving predictive capability is therefore the main task of our day. The research area's outlined strata thickens from north to south. On the other hand, the research area's considerable fault density is revealed by the structural interpretation. There is a noticeable throw to these faults, which may provide a route for the migration and deposit of hydrocarbons. Anticlines, which are important components of the majority of the Niger Delta's massive oil fields and have the potential to have several pay horizons, are typical structural types. The two defined horizons in the research region contain Sweet Spots (Bright spots), according to the Root-Mean Square Amplitude map analysis. 3D seismic cube and well log data were used to assess the research area's reservoir structural and stratigraphical framework. The study region is located between 50 33' 42.22" E and 50 53' 54.43" N.

Cerebral microcirculatory pulse wave propagation and pulse wave amplitude mapping in retrospectively gated MRI

To analyze cerebral arteriovenous pulse propagation and to generate phase-resolved pulse amplitude maps from a fast gradient-echo sequence offering flow-related enhancement (FREE). Brain MRI was performed using a balanced steady-state free precession sequence at 3T followed by retrospective k-space gating. The time interval of the pulse wave between anterior-, middle- and posterior cerebral artery territories and the superior sagittal sinus were calculated and compared between and older and younger groups within 24 healthy volunteers. Pulse amplitude maps were generated and compared to pseudo-Continuous Arterial Spin Labeling (pCASL) MRI maps by voxel-wise Pearson correlation, Sørensen-Dice maps and in regards to signal contrast. The arteriovenous delays between all vascular territories and the superior sagittal sinus were significantly shorter in the older age group (11 individuals, ≥ 31 years) ranging between 169 ± 112 and 246 ± 299 ms versus 286 ± 244 to 419 ± 299 ms in the younger age group (13 individuals) (P ≤ 0.04). The voxel-wise pulse wave amplitude values and perfusion-weighted pCASL values correlated significantly (Pearson-r = 0.33, P < 0.01). Mean Dice overlaps of high (gray) and low (white matter) regions were 73 ± 3% and 59 ± 5%. No differences in image contrast were seen in the whole brain and the white matter, but significantly higher mean contrast of 0.73 ± 0.23% in cortical gray matter in FREE-MRI compared to 0.52 ± 0.12% in pCASL-MRI (P = 0.01). The dynamic information of flow-related enhancement allows analysis of the cerebral pulse wave propagation potentially providing information about the (micro)circulation on a regional level. However, the pulse wave amplitude reveals weaknesses in comparison to true perfusion-weighting and could rather be used to calculate a pulsatility index.

Arc fault detection method based on voltage characteristic energy amplitude and phase mapping distribution distances

Arc fault detection method based on voltage characteristic energy amplitude and phase mapping distribution distances

Marine Geophysical Survey of a Medieval Shipwreck in Shallow Waters Using an Autonomous Surface Vehicle: A Case Study from Avaldsnes, Norway

This study demonstrates the successful use of a single-channel chirp system mounted on an Autonomous Surface Vehicle (ASV) for detecting and mapping a partly buried medieval ship found in water approximately one meter (m) deep in a dynamic, intertidal environment at Avaldsnes, south-western Norway. The ASV's fast mobilization and access to areas otherwise difficult to reach, makes it an efficient, low-cost, and non-invasive platform for examining the seafloor and subsurface with high-resolution seismic data, acquired in a dense grid. Line spacing of 0.25 m allowed for the generation of a detailed 3D data cube, enabling effective interpretation of both acoustic vertical sections and horizontal amplitude maps. This approach empowered accurate identification of the outline of the wooden hull and provided information about ship dimensions and maximum burial depth. Structural elements observed in the geophysical datasets, including the keelson, raiders, and maststep, corroborates with findings from previous diving investigations and photogrammetry documentation. Moreover, the geophysical survey offers valuable additional knowledge of the buried ship remains, revealing a slight tilt of the keel and a substantial object buried in close proximity to the stern, probably the rudder or another wreck-related artefact.

A CPG-based framework for flexible locomotion control and propulsion performance evaluation of underwater undulating fin platform

The black ghost knifefish is considered to possess central pattern generators (CPGs), which generates rhythms in neural circuits, coordinating the deformation of its elongated fin to achieve efficient and agile locomotion. Current biomimetic robots imitating the locomotion of the black ghost knifefish and using an undulating propulsion control method face significant challenges in adapting their swimming gaits to different environments and tasks. To overcome this limitation, this study conducted biomimetic robot research that extended from morphology to neurobiology and mimicked the CPG to construct a unified framework based on coupled Hopf oscillators. Meanwhile, an amplitude mapping function and a novel coupling method for the CPG-based control framework are proposed. The advantages of the proposed control framework are the ability to modulate different control parameters and replicate different swimming gaits, including forward, hovering, and backward swimming, realising seamless gait transitions. The control framework was tested on a specially designed undulating fin platform to evaluate the propulsion performance by modulating the control parameters, including amplitude, frequency, and phase difference. The experimental results demonstrate that the proposed CPG-based control framework achieves multimodal locomotion, enabling rapid and smooth transitions between swimming gaits, thus enhancing the robot's adaptability and stability in variable swimming environments.

Hydrostratigraphic decomposition of fluvio-deltaic sediments inferred from seismic geomorphology and geophysical well logs in the Pannonian Basin, Hungary

Heterogeneity and anisotropy of lithological units influences hydraulic conductivity on several scales. The purpose of this study is to develop a novel method supporting hydrostratigraphic classification by considering horizontal and vertical variations of sand content in relation with the paleo-depositional environment. The workflow was applied for the uppermost ca. 1800 m thick fluvio-deltaic deposits (Great Plain Aquifer) of late Neogene to Quaternary age basin-fill succession in the eastern part of the Pannonian basin in Hungary. Five combined 3D seismic volumes, seven master horizons, and 30 well logs were analyzed. First, RMS amplitude maps were extracted to interpret the seismic geomorphological features and depositional architectures. Their associated lithology was inferred from wireline logs (GR and SP) by calculating the shale volume and the net-to-gross sand ratio for 30 m thick intervals. These were used to calibrate the seismic facies as a proxy for the horizontal distribution of sand versus shale. This method allowed the identification of sand bodies, i.e.: deltaic lobes, complex channel belts, simple fluvial channels behaving as aquifers, and the dominantly muddy delta plain to flood plain suits as aquitard. The vertical pattern of sand distribution was also evaluated. Three major stratiform and some corridor-like minor hydrostratigraphic units were defined instead of the former regional (basin) scale aquifer unit. 1) Laterally extended interval of stacked deltaic lobes of high sand ratios and high rate of connectedness, at the bottom of the studied interval. 2) General presence of extended muddy floodplains with anastomosing river systems, characterized by 100–200 m wide channels, low sand ratio, and limited connectedness: 3) widespread meandering and/or braided river systems with high sand ratios and high connectedness in the Quaternary. Within unit 2) spatially and temporally variable appearance of major 500–3600 m wide meandering channel belts produce locally high sand-ratio corridors in the NE-SW direction. A workflow adapted from the oil-and-gas industry was successfully applied to distinguish units of varying sand content and hydraulic conductivity. This approach can be used on basin to local scale to build a spatially complex facies-based model of hydrostratigraphy. Thus, a robust heterogeneous geological model serves as a base for investigating fluid flow on the required scale.

Single-shot experimental-numerical twin-image removal in lensless digital holographic microscopy

Lensless digital holographic microscopy (LDHM) offers very large field of view label-free imaging crucial, e.g., in high-throughput particle tracking and biomedical examination of cells and tissues. Compact layouts promote point-of-case and out-of-laboratory applications. The LDHM, based on the Gabor in-line holographic principle, is inherently spoiled by the twin-image effect, which complicates the quantitative analysis of reconstructed phase and amplitude maps. Popular family of solutions consists of numerical methods, which tend to minimize twin-image upon iterative process based on data redundancy. Additional hologram recordings are needed, and final results heavily depend on the algorithmic parameters, however. In this contribution we present a novel single-shot experimental-numerical twin-image removal technique for LDHM. It leverages two-source off-axis hologram recording deploying simple fiber splitter. Additionally, we introduce a novel phase retrieval numerical algorithm specifically tailored to the acquired holograms, that provides twin-image-free reconstruction without compromising the resolution. We quantitatively and qualitatively verify proposed method employing phase test target and cheek cells biosample. The results demonstrate that the proposed technique enables low-cost compact LDHM imaging with enhanced precision, achieved through the elimination of twin-image errors. This advancement opens new avenues for more accurate technical and biomedical imaging applications using LDHM, particularly in scenarios where cost-effective and portable imaging solutions are desired.

A multi-functional arbitrary timing generator based on a digital-to-time converter.

This paper proposes a new high-resolution digital-to-time converter architecture based on a field programmable gate array and digital-to-analog converter (DAC). A real-time algorithm of time--amplitude mapping is proposed, which converts the vertical resolution of the DAC to the timing resolution and realizes the ultra-high resolution timing signal generation. Moreover, the relationship between the timing resolution and the vertical resolution and the sampling rate of DAC is discussed. Based on this, arbitrarily distributed random timing signals and editable timing signal sequence functions are realized. This method is verified in the experiment on Xilinx XCKU040 and Texas Instrument DAC37J82. Furthermore, a timing resolution of 1ps is realized. A time range of 4.2ns to 999s, an editable sequence length of 1-128k, and excellent nonlinear performance are achieved. In addition, functions for arbitrarily distributed random timing signals and signal bursts are tested. This method can be flexibly deployed on existing hardware and satisfy almost all test requirements.

Horizontal-to-Vertical Spectral Ratios and Refraction Microtremor Analyses for Seismic Site Effects and Soil Classification in the City of David, Western Panama

The City of David constitutes one of the most important commercial centers of the Republic of Panama. However, it is located on a coastal plane, close to an area with high seismic activity and has been affected by significant earthquakes (18 July 1934, Mw = 7.4 and 12 March 1962, Mw = 6.7). The goal of this study is to estimate the seismic effects and to classify the soil in the City of David. The experimental work entailed the measurement of environmental noise for H/V spectral ratio (HVSR) analyzed at 22 stations. A series of microtremor refraction studies (ReMi) at six stations distributed from north to south of the city was also performed. The stations were distributed around urban areas of the city, which are characterized by the presence of water supply, sewerage, buildings, roads, etc. The spectral analysis of environmental noise allowed the generation of three different types of maps: First, predominant frequency maps (f0) with zones composed mainly of rigid and semi-rigid soils in the southern end of the city and rigid soils in the central and northern regions. Secondly, maximum H/V amplitude maps (A0) which evidence a low range of HVSR amplitude in the city, ranging from 1.1 to 3.8. Finally, liquefaction vulnerability (Kg) maps, with values less than 2 Hz−1, representative of a low liquefaction risk. Soil classification using ReMi and calculation of the corresponding Vs30 reveal type D soils, which correlate well with results obtained using HVSR analyses. A comparison between HVSR and ReMi shows that HVSR curves that exhibit clear peaks tend to be related to ReMi stations that presented relatively large shear-wave velocity contrasts at some depth. The results from this research are intended to aid the decision-making process related to the future development of the city, as well as government level maintenance and mitigation plans.

Probabilistic Amplitude Shaping and Nonlinearity Tolerance: Analysis and Sequence Selection Method

Probabilistic amplitude shaping (PAS) is a practical means to achieve a shaping gain in optical fiber communication. However, PAS and shaping in general also affect the signal-dependent generation of nonlinear interference. This provides an opportunity for nonlinearity mitigation through PAS, which is also referred to as a nonlinear shaping gain. In this paper, we introduce a linear lowpass filter model that relates transmitted symbol-energy sequences and nonlinear distortion experienced in an optical fiber channel. Based on this model, we conduct a nonlinearity analysis of PAS with respect to shaping blocklength and mapping strategy. Our model explains results and relationships found in literature and can be used as a design tool for PAS with improved nonlinearity tolerance. We use the model to introduce a new metric for PAS with sequence selection. We perform simulations of selection-based PAS with various amplitude shapers and mapping strategies to demonstrate the effectiveness of the new metric in different optical fiber system scenarios.

Non-contact measurement of neck pulses achieved by imaging micro-motions in the neck skin.

We report a method and system of micro-motion imaging (µMI) to realize non-contact measurement of neck pulses. The system employs a 16-bit camera to acquire videos of the neck skin, containing reflectance variation caused by the neck pulses. Regional amplitudes and phases of pulse-induced reflection variation are then obtained by applying a lock-in amplification algorithm to the acquired videos. Composite masks are then generated using the raw frame, amplitude and phase maps, which are then used to guide the extraction of carotid pulse (CP) and jugular vein pulse (JVP) waveforms. Experimental results sufficiently demonstrate the feasibility of our method to extract CP and JVP waves. Compared with conventional methods, the proposed strategy works in a non-contact, non-invasive and self-guidance manner without a need for manual identification to operate, which is important for patient compliance and measurement objectivity. Considering the close relationship between neck pulses and cardiovascular diseases, for example, CA stenosis, the proposed µMI system and method may be useful in the development of early screening tools for potential cardiovascular diseases.