Search Results (4,001)

Background/Objectives: Glaucomatous neuropathy, a progressive deterioration of retinal ganglion cells, is the leading cause of irreversible blindness worldwide. While elevated intraocular pressure (IOP) is a well-established modifiable risk factor, increasing attention is being directed towards IOP-independent factors, such as vascular alterations. Color Doppler imaging (CDI) is a prominent technique for investigating blood flow parameters in extraocular vessels. This prospective, nonrandomized clinical trial aimed to assess the impact of ab externo canaloplasty on ocular blood flow parameters in patients with primary open-angle glaucoma (POAG) at a three-month follow-up. Methods: Twenty-five eyes of twenty-five patients with early or moderate POAG underwent canaloplasty with simultaneous cataract removal. CDI was used to measure peak systolic velocity (PSV), end-diastolic velocity (EDV), and resistive index (RI) in the ophthalmic artery (OA), central retinal artery (CRA), and short posterior ciliary arteries (SPCAs) before and after surgery. Results: The results showed a significant reduction in IOP and improvement in mean deviation at three months post-surgery. Best corrected visual acuity and retinal nerve fiber layer thickness significantly increased at each postoperative control visit. However, no significant changes were observed in PSV, EDV, and RI in the studied vessels. Conclusions: In conclusion, while canaloplasty effectively reduced IOP and medication burden, it did not significantly improve blood flow parameters in vessels supplying the optic nerve at three months post-surgery. Careful patient selection considering glaucoma severity and vascular risk factors is crucial when choosing between canaloplasty and more invasive procedures like trabeculectomy. Further larger studies are needed to comprehensively analyze this issue. Full article

Free-space optical (FSO) communication with unmanned aerial vehicles (UAVs) as relays is a promising technology for future aeronautical communication systems. In this paper, a multiple UAV-based aeronautical communication system is proposed, wherein a hybrid FSO/radio frequency (RF) link is established to connect the Airborne Warning and Control System (AWACS) with the mobile ground station (GS). Initially, we consider the velocity variance of both AWACS and the mobile GS, along with the influence of the Doppler effect. Furthermore, four relay selection modes are proposed, and exact closed expressions are derived for the end-to-end outage probability and bit error rate (BER) of the considered system. Numerical simulations demonstrate the impact of velocity variance variation on system performance. Additionally, we analyze the applicability of these four relay modes under different platform mobility characteristics through simulation results, while discussing the optimal numbers and the deployment altitude of UAVs. Finally, effective design guidelines that can be useful for aeronautical communication system designers are presented. Full article

Background/Objectives: The thyroid gland has an important influence on the heart. Long-term exposure to high levels of thyroid hormones may lead to cardiac hypertrophy and dysfunction. The aim of the study was to evaluate the morphological and functional changes in the left ventricle in patients with hyperthyroidism caused by Graves’ disease (GD) in comparison with healthy individuals, as well as to investigate potential differences in these parameters in GD patients in relation to the presence of orbitopathy. Methods: The prospective study included 39 patients with clinical manifestations and laboratory confirmation of GD and 35 healthy controls. All participants underwent a detailed echocardiographic examination. The groups were compared according to demographic characteristics (age and gender), heart rate and echocardiographic characteristics. Results: The patients with hyperthyroidism caused by GD had significantly higher values of left ventricular diameter, left ventricular volume and left ventricular mass compared to the healthy controls. In addition, hyperthyroidism significantly influenced the left ventricular contractility and led to the deterioration of the systolic and diastolic function, as shown together by longitudinal strain, color Doppler and tissue Doppler imaging. However, the patients with GD and orbitopathy showed better left ventricular function than those without orbitopathy. Conclusions: Besides the confirmation of previously known findings, our study indicates possible differences in echocardiographic parameters in GD patients in relation to the presence of orbitopathy. Further investigation with larger samples and meta-analyses of data focused on the evaluation of echocardiographic findings in the context of detailed biochemical and molecular analyses is required to confirm our preliminary results and their clinical significance. Full article

Automotive millimeter-wave (MMW) synthetic aperture radar (SAR) systems can achieve high-resolution images of detection areas, providing environmental perceptions that facilitate intelligent driving. However, curved path is inevitable in complex urban road environments. Non-uniform spatial sampling, brought about by curved path, leads to cross-coupling and spatial variation deteriorates greatly, significantly impacting the imaging results. To deal with these issues, we developed an Extended Omega-K Algorithm (EOKA) for an automotive SAR with a curved path. First, an equivalent range model was constructed based on the relationship between the range history and Doppler frequency. Then, using azimuth time mapping, the echo data was reconstructed with a form similar to that of a uniform linear case. As a result, an analytical two-dimensional (2D) spectrum was easily derived without using of the method of series reversion (MSR) that could be exploited for EOKA. The results from the parking lot, open road, and obstacle experimental scenes demonstrate the performance and feasibility of an MMW SAR for environmental perception. Full article

Currently, research related to the visualization of cutaneous vascular changes to heat stress depending on age and gender is limited to methods such as laser Doppler flowmetry and plethysmography, which do not provide any spatially resolved information at high resolution. On the other hand, optical coherence tomography is a real-time, noninvasive, non-contact technique that can visualize internal structures at the level of a few microns and is widely used in ophthalmology to visualize retinal structures, for example. However, the use of OCT in the investigation of skin vasculature heat stress is limited, with no study being conducted with different genders and different age groups. In this study, we propose biospeckle optical coherence tomography (bOCT), which visualizes the structural changes along a temporal scale to visualize the dynamic changes within the skin under heat stress. Heat stress was applied by applying a USB hot pad (40 °C) for five minutes to the palmar forearm of the dominant hand. A swept-source OCT (SS-OCT) operating with a central wavelength of 1310 nm, a bandwidth of 125 nm, and a sweep frequency of 20 kHz was used to obtain OCT structural images at 12.5 fps. From the one hundred OCT structural images recorded for 8 s, the biospeckle image was calculated as a ratio of the standard deviation to the mean of the images. The biospeckle images were obtained before heating, soon after heating, and after 5 min of rest. A total of 20 subjects with an equal number of male and female participants, with 10 in their 20s and the other 10 in their 30s or older, participated in the experiments. The average biospeckle contrast results were compared for significant differences under the three different conditions of before heating, soon after heating, and after rest for different depths, age differences, and genders. With heating, across all subjects at shallow depths within 200 µm or so, possibly in the epidermis–dermis border region, a significant difference was observed in the average contrast between the before-heating and after-rest conditions, with no significant difference seen in the deeper regions. With respect to age groups irrespective of gender, there was only a significant difference in the average contrast between soon after heating and before heating for the younger group, while for the older group, there was significant difference between before heating and soon after heating as well as between before heating and after 5 min of rest. This result suggests that age plays a larger role in the control of vascular dynamics. With respect to gender and irrespective of age, there was significant difference between males and females for both soon after heating and after 5 min of rest, with no significant difference found for before heating. These differences could be explained by hormonal differences that play a larger role in the vascular dynamics of the control of skin under heat stress, though the clear mechanism behind the reason for these gender differences is not clearly understood yet. As for both gender and age, because of the smaller sample size for age and gender combined, more studies are needed to obtain statistically reliable results. In total, our results obtained using bOCT demonstrate that bOCT could be successfully implemented in the study of the environmental effects on skin tissue, and we believe this has potential implications in therapeutic use such warm water immersion. Full article

Hibernating mammals experience severe hemodynamic changes over the torpor–arousal cycle, with oxygen consumption reaching peaks during the early stage of torpor to re-enter arousal. Melatonin (MT) can improve mitochondrial function and reduce oxidative stress and inflammation. However, the regulatory mechanisms of MT action on the vascular protective function of hibernators are still unclear. Morphology, hemodynamic, mitochondrial oxidative stress, and inflammatory factors of the carotid artery were assessed in ground squirrels who were sampled during summer active (SA), late torpor (LT), and interbout arousal (IBA) conditions. Changes were assessed by methods including hematoxylin and eosin staining, color Doppler ultrasound, ELISA, Western blots, and qPCR. Changes in arterial blood and serum melatonin were also measured by blood gas analyzer and ELISA, whereas mitochondrial oxidative stress and inflammation factors of primary vascular smooth muscle cells (VSMCs) were assessed by qPCR. (1) Intima-media carotid thickness, peak systolic velocity (PSV), end diastolic blood flow velocity (EDV), maximal blood flow rate (Vmax) and pulsatility index (PI) were significantly decreased in the LT group as compared with the SA group, whereas there were no difference between the SA and IBA groups. (2) PO₂, oxygen saturation, hematocrit and PCO₂ in the arterial blood were significantly increased, and pH was significantly decreased in the LT group as compared with the SA and IBA groups. (3) The serum melatonin concentration was significantly increased in the LT group as compared with the SA and IBA groups. (4) MT treatment significantly reduced the elevated levels of LONP1, NF-κB, NLRP3 and IL-6 mRNA expression of VSMCs under hypoxic conditions. (5) Protein expression of HSP60 and LONP1 in the carotid artery were significantly reduced in the LT and IBA groups as compared with the SA group. (6) The proinflammatory factors IL-1β, IL-6, and TNF-α were reduced in the carotid artery of the LT group as compared with the SA and IBA groups. The carotid artery experiences no oxidative stress or inflammatory response during the torpor–arousal cycle. In addition, melatonin accumulates during torpor and alleviates oxidative stress and inflammatory responses caused by hypoxia in vitro in VSMCs from ground squirrels. Full article

In recent years, with the increased interest in smart home technology and the increased need to remotely monitor patients due to the pandemic, demand for contactless systems for vital sign measurements has also been on the rise. One of these kinds of systems are Doppler radar systems. Their design is composed of several choices that could possibly have a significant impact on their overall performance, more specifically those focused on the measurement of cardiac activity. This review, conducted using works obtained from relevant scientific databases, aims to understand the impact of these design choices on the performance of systems measuring either heart rate (HR) or heart rate variability (HRV). To that end, an analysis of the performance based on hardware architecture, carrier frequency, and measurement distance was conducted for works focusing on both of the aforementioned cardiac parameters, and signal processing trends were discussed. What was found was that the system architecture and signal processing algorithms had the most impact on the performance, with FMCW being the best performing architecture, whereas factors like carrier frequency did not have an impact.This means that newer systems can focus on cheaper, lower-frequency systems without any performance degradation, which will make research easier. Full article

The Solar System Boundary Exploration (SSBE) mission is the focal point for future far-reaching space exploration. Due to the SSBE having many scientific difficulties that need to be studied, such as a super long space exploratory distance, a super long flight time in orbit, and a significant communication data delay between the ground and the probe, the probe must have sufficient intelligence to realize intelligent autonomous navigation. Traditional navigation schemes have been unable to provide high-accuracy autonomous intelligent navigation for the probe independent of the ground. Therefore, high-accuracy intelligent astronomical integrated navigation would provide new methods and technologies for the navigation of the SSBE probe. The probe of the SSBE is disturbed by multiple sources of solar light pressure and a complex, unknown environment during its long cruise operation while in orbit. In order to ensure the high-accuracy position state and velocity state error estimation for the probe in the cruise phase, an autonomous intelligent integrated navigation scheme based on the X-ray pulsar/solar and target planetary Doppler velocity measurements is proposed. The reinforcement Q-learning method is introduced, and the reward mechanism is designed for trial-and-error tuning of state and observation noise error covariance parameters. The federated extended Kalman filter (FEKF) based on the Q-learning (QLFEKF) navigation algorithm is proposed to achieve high-accuracy state estimations of the autonomous intelligence navigation system for the SSBE probe cruise phase. The main advantage of the QLFEKF is that Q-learning combined with the conventional federated filtering method could optimize the state parameters in real-time and obtain high position and velocity state estimation (PVSE) accuracy. Compared with the conventional FEKF integrated navigation algorithm, the PVSE navigation accuracy of the federated filter integrated based the Q-learning navigation algorithm is improved by 55.84% and 37.04%, respectively, demonstrating the higher accuracy and greater capability of the raised autonomous intelligent integrated navigation algorithm. The simulation results show that the intelligent integrated navigation algorithm based on QLFEKF has higher navigation accuracy and is able to satisfy the demands of autonomous high accuracy for the SSBE cruise phase. Full article

Background: Gestational diabetes mellitus (GDM) is the most common complication in pregnancy, representing a serious risk for the mother and fetus. Identifying new biomarkers to ameliorate the screening and improving GDM diagnosis and treatment is crucial. During the last decade, a few studies have used speckle tracking echocardiography (STE) for assessing the myocardial deformation properties of fetuses (FGDM) and infants (IGDM) of GDM women, providing not univocal results. Accordingly, we performed a meta-analysis to examine the overall influence of GDM on left ventricular (LV) and right ventricular (RV) global longitudinal strain (GLS) in both FGDM and IGDM. Methods: All echocardiographic studies assessing conventional echoDoppler parameters and biventricular strain indices in FGDM and IGDM vs. infants born to healthy pregnant women, selected from PubMed and EMBASE databases, were included. The studies performed on FGDM and IGDM were separately analyzed. The subtotal and overall standardized mean differences (SMDs) in LV-GLS and RV-GLS in FGDM and IGDM studies were calculated using the random-effect model. Results: The full texts of 18 studies with 1046 babies (72.5% fetuses) born to GDM women and 1573 babies of women with uncomplicated pregnancy (84.5% fetuses) were analyzed. Compared to controls, FGDM/IGDM were found with a significant reduction in both LV-GLS [average value −18.8% (range −11.6, −24.2%) vs. −21.5% (range −11.8, −28%), p < 0.05)] and RV-GLS [average value −19.7% (range −13.7, −26.6%) vs. −22.4% (range −15.5, −32.6%), p <0.05)]. Large SMDs were obtained for both LV-GLS and RV-GLS studies, with an overall SMD of −0.91 (95%CI −1.23, −0.60, p < 0.001) and −0.82 (95%CI −1.13, −0.51, p < 0.001), respectively. Substantial heterogeneity was detected for both LV-GLS and RV-GLS studies, with an overall I² statistic value of 92.0% and 89.3%, respectively (both p < 0.001). Egger’s test gave a p-value of 0.10 for LV-GLS studies and 0.78 for RV-GLS studies, indicating no publication bias. In the meta-regression analysis, none of the moderators (gestational age, maternal age, maternal body mass index, maternal glycosylated hemoglobin, white ethnicity, GDM criteria, ultrasound system, frame rate, FGDM/IGDM heart rate, and anti-diabetic treatment) were significantly associated with effect modification in both groups of studies (all p > 0.05). The sensitivity analysis supported the robustness of the results. Conclusions: GDM is independently associated with biventricular strain impairment in fetuses and infants of gestational diabetic mothers. STE analysis may allow for the early detection of subclinical myocardial dysfunction in FGDM/IGDM. Full article

Future communication systems must support high-speed mobile scenarios, while the mainstream Orthogonal Frequency Division Multiplexing (OFDM) technology faces severe inter-carrier interference in such environments. Therefore, the adoption of Orthogonal Time–Frequency Space (OTFS) modulation in 6G systems is an effective solution. The widely used single-pilot channel estimation in OTFS systems is susceptible to path loss and inaccurate fading coefficient estimation, leading to reduced estimation accuracy, signal distortion, and degraded overall system communication quality. To address this problem, this paper proposes a Constant-Amplitude Zero-Autocorrelation (CAZAC) sequence-based multi-pilot OTFS channel estimation scheme. The proposed method inserts multiple low-power pilots in the delayed Doppler domain (DD) and employs joint signal processing at the receiver to effectively suppress noise, thereby significantly improving the accuracy and reliability of channel estimation. Additionally, this paper analyzes the impact of CAZAC sequence length on estimation performance and provides reasonable parameter selection recommendations. In summary, this work proposes an innovative solution to the channel estimation challenge in OTFS systems, laying a solid theoretical foundation for the realization of future high-speed mobile communication technologies such as 6G, with important academic value and application prospects. Full article

Vascular liver diseases (VLDs) include different pathological conditions that affect the liver vasculature at the level of the portal venous system, hepatic artery, or venous outflow system. Although serological investigations and sometimes histology might be required to clarify the underlying diagnosis, imaging has a crucial role in highlighting liver inflow or outflow obstructions and their potential causes. Cross-sectional imaging provides a panoramic view of liver vascular anatomy and parenchymal patterns of enhancement, making it extremely useful for the diagnosis and follow-up of VLDs. Nevertheless, multiparametric ultrasound analysis provides information useful for differentiating acute from chronic portal vein thrombosis, distinguishing neoplastic invasion of the portal vein from bland thrombus, and clarifying the causes of venous outflow obstruction. Color Doppler analysis measures blood flow velocity and direction, which are very important in the assessment of VLDs. Finally, liver and spleen elastography complete the assessment by providing intrahepatic and intrasplenic stiffness measurements, offering further diagnostic information. Full article

The velocity/distance trade-off poses a fundamental challenge in pulsed Doppler weather radar systems and is known as the velocity/distance dilemma. Techniques such as multiple-pulse repetition frequency, staggered pulse repetition time (PRT), and pulse phase coding are commonly used to mitigate this issue. The current study evaluates the adaptability/capability of a specific type of low-capture signal called the non-uniform PRT (NPRT) through analyzing the weather target characteristics of typical velocity distributions. The spectral moments estimation (SME) signal-processing algorithm of the NPRT weather echo is designed to calculate the average power, velocity, and spectrum width of the target. A comprehensive error analysis is conducted to ascertain the efficacy of the NPRT processing algorithm under influencing factors. The results demonstrate that the spectral parameters of weather target echo with a velocity of $[-50,50]$ m/s through random-jitter NPRT signals align with radar functionality requirements (RFRs). Notably, the NPRT waveform resolves the inherent conflicts between the maximum unambiguous distance and velocity and elevates the upper limit of the maximal observation velocity. The evaluation results confirm that nonlinear radar signal processing technology can improve a radar’s detection performance and provide a new method for realizing the multifunctional observation of radar in different applications. Full article

The recent rapid development of low Earth orbit (LEO) constellation-based navigation techniques has enhanced the ability of position, navigation, and timing (PNT) services in deep attenuation and interference environments. However, existing navigation modulations face the challenges of high acquisition complexity and do not improve measurement precision at the same signal strength. We propose a pulsed orthogonal time frequency space (Pulse-OTFS) signal, which naturally converts continuous signals into pulses through a special delay-Doppler domain pseudorandom noise (PRN) code sequence arrangement. The performance evaluation indicates that the proposed signal reduces at least 89.4% of the acquisition complexity. The delay measurement accuracy is about 8 dB better than that of the traditional binary phase shift keying (BPSK) signals with the same bandwidth. It also provides superior compatibility and anti-multipath performance. The advantages of fast acquisition and high-precision measurement are verified by processing the real signal in the developed software receiver. As Pulse-OTFS occupies only one time slot of a signal period, it can be easily integrated with OTFS-modulated communication signals and used as a navigation signal from broadband LEO satellites as an effective complement to the global navigation satellite system (GNSS). Full article

Windshear is a microscale meteorological phenomenon that can be dangerous to aircraft during the take-off and landing phases. Accurate windshear detection plays a significant role in air traffic control. In this paper, we aim to investigate a machine learning method for windshear detection based on previously collected wind velocity data and windshear records. Generally, the occurrence of windshear events are reported by pilots. However, due to the discontinuity of flight schedules, there are presumably many unreported windshear events when there is no flight, making it difficult to ensure that all the unreported events are all non-windshear events. Hence, one of the key issues for machine-learning-based windshear detection is determining how to correctly distinguish windshear cases from the unreported events. To address this issue, we propose to use a positive and unlabeled learning method in this paper to identify windshear events from unreported cases based on wind velocity data collected by Doppler light detection and ranging (LiDAR) plan position indicator (PPI) scans. An optimal-transport-based optimization model is proposed to distinguish whether a windshear event appears in a sample constructed by several LiDAR PPI scans. Then, a binary classifier is trained to determine whether a sample represents windshear. Numerical experiments based on the observational wind velocity data collected at the Hong Kong International Airport show that the proposed scheme can properly recognize potential windshear cases (windshear cases without pilot reports) and greatly improve windshear detection and prediction accuracy. Full article

This paper documents a windshear case for an airport in the Qinghai-Tibet Plateau and explores, for the first time, the capability for high-resolution numerical weather simulation of the wind shear features. The windshear appears to be associated with pulses of the wind speed in a low-level easterly jet. The features are basically reproduced quite well with the high-resolution numerical model, though some discrepancies are identified, such as the maximum wind speed of the easterly jet and the magnitude of the eddy dissipation rate as compared with the actual Doppler LIDAR observations. Statistical analysis has been performed between the observation and the simulation results. The sensitivity of the modeling result to the choice of turbulence parameterization scheme has also been studied. The study result shows that it is possible to forecast the windshear feature using a high-resolution numerical weather prediction model for an airport in the complex terrain of the Plateau. Full article