Arrival Phase Research Articles

Gain and Phase Calibration of Uniform Rectangular Arrays Based on Convex Optimization and Neural Networks

A calibration method based on convex optimization (CVX) and neural networks is proposed for the large planar arrays of phased array three-dimensional imaging sonar systems. The method only needs an acoustic calibration source at an unknown position in the far field, and the direction of arrival (DOA) and gain and phase error are jointly estimated. The method uses a CVX algorithm to solve an optimization problem and initially estimates the DOA of the calibration source robustly. Subsequently, according to the estimation results, a neural network is used for fitting to obtain off-grid DOA estimation of the calibration source. Thereafter, spatial matched filtering is performed to obtain the gain and phase residual estimations. The root mean square error (RMSE) of the beam pattern calibrated by the method for uniform planar arrays can reach a value of 4.9542 × 10−5. The experimental results demonstrate the efficiency of the proposed method for gain and phase calibration.

Simulation method of X-ray pulsar observation signal at spacecraft

The simulation of X-ray pulsar observation signals at spacecraft is of great significance in verifying pulsar signal processing methods and navigation schemes. The efficiency of pulsar signal simulation algorithm can be significantly improved by establishing the relationship between photon arrival time and phase at spacecraft. At present, the frequency change of the received pulsar signal is not considered in the model for the relation between photon arrival time and phase at spacecraft, which leads the calculation accuracy to decrease greatly. To solve this problem, a model for the relation between photon arrival time and phase is established with the first derivative and second derivative of frequency taken into consideration. Based on this model, a new simulation method of observation pulsar signal at a spacecraft is proposed, which not only ensures high efficiency, but also improves the simulation accuracy. The proposed method is verified from three aspects. Firstly, the correctness of the proposed method is proved by comparing the cumulative pulse profile from the simulation data with the standard pulse profile, and the results show that the standard pulse profile can be recovered by the simulation data from the proposed method. Secondly, through the comparison of experimental results with the observational data from RXTE (Rossi X-ray timing Explorer), the correctness of the proposed method is further verified. The experimental comparison results show that the absolute difference in searched frequency between simulated data and observational data for the Crab pulsar is less than 10<sup>–4</sup>, which sufficiently validates the method. Finally, the simulation efficiency and accuracy of the proposed method are compared with those of other methods to prove the superiority of the proposed method over the existing methods. The comparison results show that the simulation speed of the proposed method can be increased by up to 3 orders of magnitude compared with that of the iterative method or the method of establishing the real-time photon arrival rate function at the spacecraft, which ensures the high efficiency of the signal simulation algorithm. And comparing with the case without considering the frequency change, the Pearson correlation coefficient is increased by up to 350.0%, significantly improving the calculation accuracy. The proposed method can be used to verify the X-ray pulsar signal processing and navigation algorithms.

Target Localization by Mobile Handheld UHF RFID Reader and IMU

In this paper we design and construct a mobile handheld human operated device used to guide the user towards the desired RFID-tagged target, and at the same time provide estimations of the distance and the angle from the user to the target. The main components of the device are a UHF RFID reader operating with one antenna and an Inertial Measurement Unit (IMU), used to measure rotation angles. During the movement of the operator, phase of arrival and rotation angle data are collected by the RFID reader and the IMU respectively. A particle filter algorithm leverages the collected data to estimate the distance and angle of the operator, with respect to his/her current pose. As more iterations are completed, the fusion of multiple measurements improves the estimation performance. Experimental results show a mean angle estimation error of ~6°, and distance estimation error less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5m$ </tex-math></inline-formula> when the user approaches the target after few iterations. Recorded computational time is small-enough to enable real time tracking-applications.

Understanding swarm earthquakes in Southeast Aceh, Sumatra

The cause of the swarm earthquakes occurring from September until November 2020 remains unclear. The swarm activities are close to the Tripa active fault but also close to Mt. Bendahara. This study offers the analysis of seismic P and S wave arrivals and relocate the hypocenter of the swarm. We analysed the hypocentre distribution that recorded by Badan Meteorologi Klimatologi dan Geofisika (BMKG) from July 2020 to January 2021. The arrival of P and S-wave from 103 events was used obtain 1-D seismic velocity model. The earthquake used for this study consisted of at least 6 phases of seismic arrivals with the azimuthal gap angle less than 180 degree. The different velocities occurred in the upper and lower of the crustal thickness of 0 – 40 km. The Vp values are about 5.0 – 7.0 km/s and 3.0 – 5.0 km/s for Vs value while the Vp/Vs ratio are ranging from 1.5 to 1.7. Our preliminary results indicate that the potential swarm activities near to Mt. Bandahara maybe triggered by an unknown fault activity as no volcanic activity was reported.

High precision positioning algorithm based on carrier phase and time of arrival

Carrier phase positioning technology is widely used in global navigation satellite systems (GNSS) but not applied to wireless orthogonal frequency division multiplex (OFDM) systems. Carrier phase technology has a high resolution, which can improve the positioning accuracy of wireless cellular networks. Applying the carrier phase to a wireless mobile positioning system has some problems, such as continuous phase tracking, accurate integer ambiguity resolution, positioning errors caused by non-line-of-sight (NLOS) and so forth. This paper offers a positioning technique combining the time-of-arrival (TOA) and carrier phase to solve the above problems. Based on Bayesian theory, a two-step position estimator is introduced in our scheme to solve the terminal position. Besides, an NLOS identification and suppression scheme is proposed to enhance the robustness of the algorithm. Experiments show that even in the NLOS environment, the joint positioning algorithm using TOA and carrier phase can effectively improve the positioning accuracy.

Seismic phases of 25 April 2015 (Mw 7.8) Earthquake and 12 May 2015 (Mw 7.3) Earthquake Predicted by AK135 Model - A comparison

A strong Mw 7.8 (depth = 8.2 km) earthquake initiated ~80 km northwest of the Kathmandu on 25 April of 2015 was followed by the Mw 7.3 (depth = 15 km) earthquake on 12 May. The seismic phases of these earthquakes were predicted at Kakani, Kathmandu seismic station (27.80°N and 85.28°E) using software model AK135 . The model predicts 21 arrivals for Gorkha earthquake with first p phase arriving at incident angle 82.65° in 11.516 seconds and final phase SKIKSSKIKS in 3270.791 seconds with incident angle 0.02°. Similarly, for the Dolakha earthquake 27 arrivals are predicted with the first arrival p phase at incident angle 74.35° in 14.504 seconds and final arrival SKIKSSKIKS phase at incident angle 0.03° in 3268.823 seconds. The 5 depth phases and 8 core phases predicted are similar for both the earthquakes while 8 and 12 mantle phases are predicted for Gorkha earthquake and Dolakha earthquake respectively. In addition, two crustal phases (Pn, Sn) were predicted only for Dolakha earthquake. The additional phases are critically refracted seismic phases indicating the existence of the Moho discontinuity between the crust and upper mantle. Their existence for Dolakha earthquake could be the indication of different geological provinces of the source region of the earthquakes, differing in age, crustal thickness, temperature, and tectonic stress. The ratio of P wave ad S wave velocity is found to be 1.67 for the regions. These seismic phases reflect their sensitivity to different layers of the earth and carry information about the geometrical and physical properties of discontinuities inside the earth.

The Direction of Arrival Location Deception Model Counter Duel Baseline Phase Interferometer Based on Frequency Diverse Array

With the emergence and development of the passive localization, the radiation source is more visible for the location system which endangers their survival. Therefore, there is an urgent demand for the radio frequency (RF) stealth technology. An effective method to realize RF stealth is location deception, therefore, for the passive localization system, this paper proposes a direction of arrival (DOA) location deception method using the frequency diverse array (FDA) against the dual baseline phase interferometer. Since the direction-finding of the dual baseline phase interferometer is based on the received signal with fixed frequency, the FDA signal has a deception effect on the interferometer owing to the introduction of the small frequency increment. Considering the influence of the frequency increment sequence on the deception effect, we derive the optimizations of the DOA location deception via the average location deviation for the sampling time in the case of no noise and noise, respectively. Besides, considering the time dependency of the beam, we investigate the average SNR (ASNR) and the corresponding CRLB to verify the proposed method. Numerical examples and simulations show that the proposed method can counter the interferometer by realizing location deception.

Structural Energy Distribution and Particle Phase Stability Study of Longitudinal Dynamics of a Simple Linear Proton Accelerator

This paper presents the study of longitudinal beam dynamics of a simple linear proton accelerator and simulation results for a model linear accelerator (LINAC) using MATLAB. The study part of the transition energy, particle acceleration, transit time factor, RF factor, and momentum compaction are discussed. For the simulation, the model LINAC is built using unit cells and the unit cell consists of Quadrupole doublet and acceleration cavity. Model LINAC’s basic setup is present and the simulation is based on the single-particle analysis. The robustness of the model LINAC tested to operate varying different parameters like initial arrival phase and input energy. The criteria to measure the robustness of the model LINAC are to check the kinetic energy at the end of the LINAC and the transverse stability of the transfer matrices of each cell. The paper also presents the theoretical analysis of phase stability at both below and above transition energy. The stability of small and larger amplitude oscillations are present and simulation results for different particles each starting with different amplitudes observed, where the large amplitude oscillation falls outside of the separatrix.

Limited flexibility in departure timing of migratory passerines at the East-Mediterranean flyway

The rapid pace of current global warming lead to the advancement of spring migration in the majority of long-distance migratory bird species. While data on arrival timing to breeding grounds in Europe is plentiful, information from the African departure sites are scarce. Here we analysed changes in arrival timing at a stopover site in Israel and any links to Enhanced Vegetation Index (EVI) on the species-specific African non-breeding range in three migratory passerines between 2000–2017. Differences in wing length between early and late arriving individuals were also examined as a proxy for migration distance. We found that male redstart, but not females, advanced arrival to stopover site, but interestingly, not as a response to EVI phenology. Blackcap and barred warbler did not shift arrival timing significantly, although the arrival of blackcap was dependent on EVI. Barred warbler from the early arrival phase had longer wings, suggesting different populations. Our study further supports the existence species-specific migration decisions and inter-sexual differences, which may be triggered by both exogenous (local vegetation condition) and endogenous cues. Given rapid rate of changes in environmental conditions at higher latitudes, some migrants may experience difficulty in the race to match global changes to ensure their survival.

Climate and weather have differential effects in a high latitude passerine community

Climatic factors act on populations at multiple timescales leading to the separation of long-term climate and shorter-term weather effects. We used passerine counts from 1995 to 2019 in subarctic Alaska (Denali National Park, USA) to assess the impacts of the prior breeding season's weather on breeding season abundance and the impacts of climate measured through shifts in elevational distribution. Weather and climate appear to have had opposing effects on the abundance of some shrub-associated species as evidenced by a positive response to nesting phase temperature over a 1-year lag and a negative response to warming-induced shifts in shrub-dominated habitats over the long term. The latter response was indicated by declines in abundance which occurred in some part through portions of these populations shifting upslope of our fixed sampling frame. Overall, theabundance of species was related to one or more of the lagged effects of weather and the effects of weather alone drove nearly twofold variation in annual abundance in most species. The effect of nesting phase temperature was a strong positive predictor at both community and individual species levels, whereas arrival phase temperature had weak support at both levels. The effects of total precipitation during the nesting phase and snowmelt timing shared mixed support at community and species levels, but generally indicated higher abundance following seasons that were drier and had earlier snowmelt. Together, our findings of opposing effects of climatic variables at different timescales have implications for understanding the mechanisms of population and distributional change in passerines in the subarctic.

Control of arrival time using structured wave packets

Scattering dynamics are examined for Gaussian and non-Gaussian wave packets with identical momentum densities. Average arrival time delays, dwell times, and phase time delays are calculated for wave packets scattering from a square barrier, and it is shown that the non-Gaussian wave packets exhibit different average arrival time delays than the Gaussian wave packets. These differences result from the non-linear terms in the momentum wave function phase of the non-Gaussian wave packets, which alters the self-interaction times of the wave packets. Control of the average arrival time delay can be achieved through adjustment of the momentum wave function phase, independent of wave packet energy and momentum density.

Performance evaluation of terminal airspace system safety, delay and predictability of Muritala Mohammed International Airport, Ikeja Lagos, Nigeria

This paper outlines a multi-dimensional user-oriented performance metrics approach in evaluating the operation of the terminal airspace system to aid in the airport and airspace planning and decision making. Safety, delay and predictability metrics contribute to the analytical framework. From the findings, the occurrence of air incidence has a high severity level at departure, and arrival phases of flight, higher likelihood at the radar room and much of the incidences were as a result of faulty equipment and inherent absence of modern airspace infrastructure. Also, in Lagos terminal airspace, the number of incidences has no close correlation with the level of traffic complexity. Total schedule arrival delay ranges from 1-392 minutes representing an average of 7.8-17.9 minutes per aircraft that arrived Lagos airport at that period. Besides, the total approach contact time ranges from 1-57 minutes, translating to 4.6-7.1 minutes per aircraft. However, variability in arrival time of 1-5 minutes is common from published airline arrival scheduled time. In the same vein, the variability of 1-5 minutes is common from approach contact times of aircraft. These figures indicate sound arrival predictability signature for Lagos airport. Also, departure time variability above 30 minutes is familiar from the ATC clearance time for the various routes under study. However, there is about or more 25% variability of more than 15 minutes, and this indicates possible inconsistency of predicting departure times from the times ATC clearance was acquired. Above all, the predictability of departure times in Lagos airport is weak compared to those of the arrival. Taken by it, this may be a sign of airspace congestion or ATC deficiencies at the Lagos airport. This is an indication of the lack of users' confidence in Nigeria's air transport industry to deliver just-in-time service.

Leveraging Deep Learning in Global 24/7 Real-Time Earthquake Monitoring at the National Earthquake Information Center

AbstractMachine-learning algorithms continue to show promise in their application to seismic processing. The U.S. Geological Survey National Earthquake Information Center (NEIC) is exploring the adoption of these tools to aid in simultaneous local, regional, and global real-time earthquake monitoring. As a first step, we describe a simple framework to incorporate deep-learning tools into NEIC operations. Automatic seismic arrival detections made from standard picking methods (e.g., short-term average/long-term average [STA/LTA]) are fed to trained neural network models to improve automatic seismic-arrival (pick) timing and estimate seismic-arrival phase type and source-station distances. These additional data are used to improve the capabilities of the NEIC associator. We compile a dataset of 1.3 million seismic-phase arrivals that represent a globally distributed set of source-station paths covering a range of phase types, magnitudes, and source distances. We train three separate convolutional neural network models to predict arrival time onset, phase type, and distance. We validate the performance of the trained networks on a subset of our existing dataset and further extend validation by exploring the model performance when applied to NEIC automatic pick data feeds. We show that the information provided by these models can be useful in downstream event processing, specifically in seismic-phase association, resulting in reduced false associations and improved location estimates.

Health system response to large scale migration: the case of Emilia-Romagna region

Abstract Background In Italy, recent changes in migration flows posed complex public health challenges. The Emilia-Romagna region (ERR) was one of the first regions to adopt specific policies addressing the health of newly arrived asylum seekers. In our study, we analysed the regional health system response comparing it to the regional and national guidelines, in order to assess its strengths and its critical areas. Methods In 2019, we conducted a survey among the referents of the regional clinics that provide healthcare to asylum seekers, in order to learn about local policies, challenges and best practices. A questionnaire with 35 closed and 11 open questions was administered and analysed through descriptive statistical analysis and text analysis. Results Regional policies showed good responsiveness and Local Health Authorities (LHAs) adhered to the guidelines. A special permit was introduced to grant asylum seekers access to healthcare, which also allowed integration of health data into the regional health information system. However, data integration was done in only 2 clinics out of 14. Instances of discretion in issuing the special permit were reported, due to ambiguity in the rules and inadequate training of office workers. Policies and LHAs protocols focused greatly on the arrival phase and on Communicable Diseases (CDs) surveillance. Other areas - such as protection of vulnerable groups, health promotion, NCDs - were prioritized in the national guidelines, but unevenly considered throughout the region, also due to lack of resources. Some clinics responded autonomously to these gaps with local resources. Conclusions The ERR health response to the influx of asylum seekers was rapid but incomplete. Interventions focused more on CDs surveillance than on responding to asylum seekers' health needs in terms of quality, access and equity. Areas to be strengthened include protection of vulnerable groups, health promotion and NCDs, together with coordination and long-term planning. Key messages The Emilia-Romagna region health response to the influx of asylum seekers reflects an emergency approach focused on communicable diseases, while NCDs and health promotion are relatively neglected. The health system in Emilia-Romagna needs to be strengthened in its capacity to respond to asylum seekers’ health needs. Health policies and practices should be planned to ensure equity and quality.

Fracture properties estimation using distributed acoustic sensing recording of guided waves in unconventional reservoirs

Perforation shots excite guided waves that propagate in a low-velocity unconventional shale reservoir. They have a frequency content of up to 700 Hz and are dispersive. We have analyzed horizontal crosswell perforation shots recorded by a distributed acoustic sensing (DAS) array. As guided waves propagate through a previously stimulated area, we observe a dramatic influence on the guided SH waves in the form of delayed arrival times, scattering, phase incoherency, and loss of amplitude and frequency. The leaky compressional waves undergo a gradual slowdown. Using a simple geometric analysis of the spatial locations of the distortions in the direct arrivals of the guided SH waves, we can estimate the half-lengths of the induced fractures, which range from 50% to 75% of the distance between the perforated and monitoring wells. Furthermore, we find that the propagation disturbances originate from the middle of the stimulated area. Other diffracted signals, notably from frac plugs, are clearly visible in the data. We report the first large-scale use of DAS records of guided waves. Their potential for high-resolution imaging and inversion of subsurface properties before and after hydraulic stimulation opens new possibilities for the use of seismology in optimizing production from unconventional reservoirs.

The effect of autonomous systems on the crew size of ships – a case study

ABSTRACT Recently, autonomous ships have gotten a lot more attention both in the media and in research. However, very little research has focussed on the effects of automation on the size of the crew. This paper analyses the effects of added automation on the required size and composition of the crew on a 750 TEU short sea container vessel. A Crew Analysis Algorithm is used to determine the cheapest crew composition to perform the tasks required to operate a ship. Using this algorithm, two potential automation options are investigated: automating the navigation tasks and automating the mooring tasks. Automating the navigation tasks decreases the required crew size in the normal sailing and arrival & departure phases by 3 and 1 crew members, respectively. The loading & unloading phase is unaffected. Automating the mooring tasks reduces the required crew in the arrival & departure phase to 2. It is concluded that since individual automation options do not affect the crew requirements for all travel phases, their effect on crew reduction is limited unless several options are combined. However, with a change in task assignment and different training of crew members, a reduction of the required number of crew members is possible.

Drone aggregation behavior in the social wasp Vespula germanica (Hymenoptera: Vespidae): Effect of kinship and density

Inbreeding can have negative consequences on population viability because of the reduced fitness of the progeny. In general, most species have developed mechanisms to minimize inbreeding such as dispersal and kin avoidance behavior. In the eusocial Hymenoptera, related individuals typically share a common nest and have relatively short mating periods, this could lead to inbreeding, and because of their single–locus complementary sex determination system, it may generate diploid males that could result in infertile triploid progeny representing a cost for the colony. Vespula germanica, is an eusocial wasp that has invaded many parts of the world, despite likely facing a reduced genetic pool during the arrival phases. We ask whether male wasp display specific aggregation behavior that favors genetic diversity, key to reduce inbreeding. Through a set of laboratory experiments, we investigated the effects of drone nestmateship and density on the aggregation behavior of V. germanica drones. We show that drones avoid aggregating with their nestmates at all densities while non-nestmates are avoided only at high densities. This suggests that lek genetic diversity and density could be regulated through drone behavior and in the long run minimize inbreeding favoring invasion success.

Combining 3D seismics, eyewitness accounts and numerical simulations to reconstruct the 1888 Ritter Island sector collapse and tsunami

The 1888 Ritter Island volcanic sector collapse triggered a regionally damaging tsunami. Historic eyewitness accounts allow the reconstruction of the arrival time, phase and height of the tsunami wave at multiple locations around the coast of New Guinea and New Britain. 3D seismic interpretations and sedimentological analyses indicate that the catastrophic collapse of Ritter Island was preceded by a phase of deep-seated gradual spreading within the volcanic edifice and accompanied by a submarine explosive eruption, as the volcanic conduit was cut beneath sea level. However, the potential impact of the deep-seated deformation and the explosive eruption on tsunami genesis is unclear. For the first time, it is possible to parameterise the different components of the Ritter Island collapse with 3D seismic data, and thereby test their relative contributions to the tsunami. The modelled tsunami arrival times and heights are in good agreement with the historic eyewitness accounts. Our simulations reveal that the tsunami was primarily controlled by the displacement of the water column by the collapsing cone at the subaerial-submarine boundary and that the submerged fraction of the slide mass and its mobility had only a minor effect on tsunami genesis. This indicates that the total slide volume, when incorporating the deep-seated deforming mass, is not directly scalable for the resulting tsunami height. Furthermore, the simulations show that the tsunamigenic impact of the explosive eruption energy during the Ritter Island collapse was only minor. However, this relationship may be different for other volcanogenic tsunami events with smaller slide volumes or larger magnitude eruptions, and should not be neglected in tsunami simulations and hazard assessment.

Measurement and analysis of Wi-MAX channel in 3.3 GHz using minimal-ray fading model

This paper presents minimal-ray a sum-of-sinusoids fading model with one direct signal and multipath signal as minimum as three in number, having phase, attenuation, and time of arrival as random variables for random scatterer area. In most of the literature, fading simulators assume independence of random phase and angle of arrival. Because of this, at the receiver side, the demodulator has to adjust the phase by trial and error method to recover the original time-variant signal which is a tedious process. If the dependency of the random phase and the angle of deviation is proved, then it is easier at the receiver side for the demodulator to adjust the phase directly. This work defines the simple relationship between the angle of deviation and random phase which can directly help at the receiver side for adjusting the deviation occurred in the transmitted signal. The statistical characteristics of the proposed model are analyzed and validity is ensured with empirical data for the Worldwide interoperability for microwave access (Wi-MAX) application. The goodness of fit is verified with the Kolmogorov–Smirnov test and the results show that it agrees best with the Ricean distribution, compared with Rayleigh distribution.

Healthcare models and challenges for refugees and asylum seekers: the response of Emilia-Romagna (Northern Italy) to the recent migration trends

to characterize healthcare for refugees and asylum seekers. a quali-quantitative study with semi-structured interviews was carried out with key informants of the regional clinics which provide health assistance to refugees and asylum seekers during the first phases of arrival. key informants of 14 health centres were interviewed across the 9 provinces of the region. the study investigated the different healthcare interventions and the quality of the relationships among the main actors involved in providing healthcare to refugees and asylum seekers. three healthcare models were identified: one involved Local Health Units (LHUs), one based on the recruitment of NGOs, and the last one formed by the combination of LHAs and General Practitioners. Challenges in guaranteeing a good level of health assistance were reported at all levels, such as specific barriers in accessing health and social services, fragmentation and lack of coordination amongst services and the poor quality of care for vulnerable groups. the healthcare for asylum seekers is characterized by various critical issues, mainly related to accessibility and coordination of health and social services. In order to guarantee health equity, it is necessary to strengthen the primary health care system and improve local governance.