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Symmetry ◽  
2022 ◽  
Vol 14 (1) ◽  
pp. 156
Author(s):  
Andriette Bekker ◽  
Johannes T. Ferreira ◽  
Schalk W. Human ◽  
Karien Adamski

This research is inspired from monitoring the process covariance structure of q attributes where samples are independent, having been collected from a multivariate normal distribution with known mean vector and unknown covariance matrix. The focus is on two matrix random variables, constructed from different Wishart ratios, that describe the process for the two consecutive time periods before and immediately after the change in the covariance structure took place. The product moments of these constructed random variables are highlighted and set the scene for a proposed measure to enable the practitioner to calculate the run-length probability to detect a shift immediately after a change in the covariance matrix occurs. Our results open a new approach and provides insight for detecting the change in the parameter structure as soon as possible once the underlying process, described by a multivariate normal process, encounters a permanent/sustained upward or downward shift.


Sensors ◽  
2021 ◽  
Vol 21 (23) ◽  
pp. 8107
Author(s):  
Dobromir Pressyanov ◽  
Pavel Stavrev

A method for the retrospective evaluation of the integrated activity concentration of 133Xe during radioxenon plumes and the moment of the plume’s center is proposed and explored by computer modeling. The concept is to use a specimen of polycarbonate material (a stack of Makrofol N foils of thickness 120 µm and 40 µm in 1 L non-hermetic Marinelly beaker) that is placed in the environment or in a controlled nuclear or radiopharmaceutical facility. On a regular basis or incidentally, the specimen may be retrieved and gamma spectrometry in two consecutive time intervals with durations of 8 h and 16 h is performed. To assess the performance of the method, 133Xe plumes of various integrated activity concentrations and with a duration of up to 10 h are simulated and analyzed, assuming that the measurement starts with a delay of up to one day after the moment of the plume center. It is found that the deviation between the estimates by the method and their true values are within a few percent. Depending on the delay, events of integrated 133Xe activity concentration 250–1000 Bq h m−3 might be qualitatively identified. At levels >10,000 Bq h m−3, the uncertainty of the quantitative estimates might be ≤10%.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Caio Ponte ◽  
Humberto A. Carmona ◽  
Erneson A. Oliveira ◽  
Carlos Caminha ◽  
Antonio S. Lima ◽  
...  

AbstractWe investigate, through a data-driven contact tracing model, the transmission of COVID-19 inside buses during distinct phases of the pandemic in a large Brazilian city. From this microscopic approach, we recover the networks of close contacts within consecutive time windows. A longitudinal comparison is then performed by upscaling the traced contacts with the transmission computed from a mean-field compartmental model for the entire city. Our results show that the effective reproduction numbers inside the buses, $$Re^{bus}$$ R e bus , and in the city, $$Re^{city}$$ R e city , followed a compatible behavior during the first wave of the local outbreak. Moreover, by distinguishing the close contacts of healthcare workers in the buses, we discovered that their transmission, $$Re^{health}$$ R e health , during the same period, was systematically higher than $$Re^{bus}$$ R e bus . This result reinforces the need for special public transportation policies for highly exposed groups of people.


2021 ◽  
Vol 28 (5) ◽  
pp. 1-9
Author(s):  
Noor Atinah Ahmad ◽  
◽  
Mohd Hafiz Mohd ◽  
Kamarul Imran Musa ◽  
Jafri Malin Abdullah ◽  
...  

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19 disease, which has become pandemic since December 2019. In the recent months, among five countries in the Southeast Asia, Malaysia has the highest per-capita daily new cases and daily new deaths. A mathematical modelling approach using a Singular Spectrum Analysis (SSA) technique was used to generate data-driven 30-days ahead forecasts for the number of daily cases in the states and federal territories in Malaysia at four consecutive time points between 27 July 2021 and 26 August 2021. Each forecast was produced using SSA prediction model of the current major trend at each time point. The objective is to understand the transition dynamics of COVID-19 in each state by analysing the direction of change of the major trends during the period of study. The states and federal territories in Malaysia were grouped in four categories based on the nature of the transition. Overall, it was found that the COVID-19 spread has progressed unevenly across states and federal territories. Major regions like Selangor, Kuala Lumpur, Putrajaya and Negeri Sembilan were in Group 3 (fast decrease in infectivity) and Labuan was in Group 4 (possible eradication of infectivity). Other states e.g. Pulau Pinang, Sabah, Sarawak, Kelantan and Johor were categorised in Group 1 (very high infectivity levels) with Perak, Kedah, Pahang, Terengganu and Melaka were classified in Group 2 (high infectivity levels). It is also cautioned that SSA provides a promising avenue for forecasting the transition dynamics of COVID-19; however, the reliability of this technique depends on the availability of good quality data.


Author(s):  
Philippe Loubaton ◽  
Xavier Mestre

We consider linear spectral statistics built from the block-normalized correlation matrix of a set of [Formula: see text] mutually independent scalar time series. This matrix is composed of [Formula: see text] blocks. Each block has size [Formula: see text] and contains the sample cross-correlation measured at [Formula: see text] consecutive time lags between each pair of time series. Let [Formula: see text] denote the total number of consecutively observed windows that are used to estimate these correlation matrices. We analyze the asymptotic regime where [Formula: see text] while [Formula: see text], [Formula: see text]. We study the behavior of linear statistics of the eigenvalues of this block correlation matrix under these asymptotic conditions and show that the empirical eigenvalue distribution converges to a Marcenko–Pastur distribution. Our results are potentially useful in order to address the problem of testing whether a large number of time series are uncorrelated or not.


Shock Waves ◽  
2021 ◽  
Author(s):  
C. J. Aouad ◽  
W. Chemissany ◽  
P. Mazzali ◽  
Y. Temsah ◽  
A. Jahami

AbstractThe evolution of the fireball resulting from the August 2020 Beirut explosion is traced using amateur videos taken during the first 400 ms after the detonation. Thirty-nine frames separated by 16.66–33.33 ms are extracted from six different videos located precisely on the map. Time evolution of the shock wave radius is traced by the fireball at consecutive time moments until about $$ t \approx 170$$ t ≈ 170  ms and a distance $$ d \approx 128$$ d ≈ 128  m. Pixel scales for the videos are calibrated by de-projecting the existing grain silos building, for which accurate as-built drawings are available, using the length, the width, and the height and by defining the line-of-sight incident angles. In the distance range $$ d \approx $$ d ≈ 60–128 m from the explosion center, the evolution of the fireball follows the Sedov–Taylor model with spherical geometry and an almost instantaneous energy release. This model is used to derive the energy available to drive the shock front at early times. Additionally, a drag model is fitted to the fireball evolution until its stopping at a time $$ t \approx 500$$ t ≈ 500  ms at a distance $$d \approx 145\pm 5$$ d ≈ 145 ± 5  m. Using the derived TNT equivalent yield, the scaled stopping distance reached by the fireball and the shock wave-fireball detachment epoch within which the fireball is used to measure the shock wave are in excellent agreement with other experimental data. A total TNT equivalence of $$ 200\pm 80\,\mathrm{t}$$ 200 ± 80 t at a distance $$ d \approx 130$$ d ≈ 130  m is found. Finally, the dimensions of the crater size taken from a hydrographic survey conducted 6 days after the explosion are scaled with the known correlation equations yielding a close range of results. A recent published article by Dewey (Shock Waves 31:95–99, 2021) shows that the Beirut explosion TNT equivalence is an increasing function of distance. The results of the current paper are quantitatively in excellent agreement with this finding. These results present an argument that the actual mass of ammonium nitrate that contributed to the detonation is much less than the quantity that was officially claimed available.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hiroyuki K. M. Tanaka ◽  
Masaatsu Aichi ◽  
Cristiano Bozza ◽  
Rosa Coniglione ◽  
Jon Gluyas ◽  
...  

AbstractTidal measurements are of great significance since they may provide us with essential data to apply towards protection of coastal communities and sea traffic. Currently, tide gauge stations and laser altimetry are commonly used for these measurements. On the other hand, muography sensors can be located underneath the seafloor inside an undersea tunnel where electric and telecommunication infrastructures are more readily available. In this work, the world’s first under-seafloor particle detector array called the Tokyo-bay Seafloor Hyper-Kilometric Submarine Deep Detector (TS-HKMSDD) was deployed underneath the Tokyo-Bay seafloor for conducting submarine muography. The resultant 80-day consecutive time-sequential muographic data were converted to the tidal levels based on the parameters determined from the first-day astronomical tide height (ATH) data. The standard deviation between ATH and muographic results for the rest of a 79-day measurement period was 12.85 cm. We anticipate that if the length of the TS-HKMSDD is extended from 100 m to a full-scale as large as 9.6 km to provide continuous tidal information along the tunnel, this muography application will become an established standard, demonstrating its effectiveness as practical tide monitor for this heavy traffic waterway in Tokyo and in other important sea traffic areas worldwide.


2021 ◽  
Author(s):  
Feng Chen ◽  
Daoman Xiang ◽  
Ying Yu ◽  
Jianxun Wang ◽  
Tian Liu

Abstract Purpose: To analyze the efficacy of three different doses of bevacizumab treatment on Threshold retinopathy of prematurity during different periods . Methods: 36 cases (72 eyes) of infants with threshold ROP were analyzed, whom were treated with intravitreal injection of 1.25 mg, 0.75 mg or 0.5 mg bevacizumab respectively from October 1st, 2016 to September 30th, 2017. After treatment, fundus examination results during five time points were recorded and classified into four grades according to the efficacy. Results: There were significant differences in the changes of fundus among the 3 groups from the 4th day to the 4th week after treatment (P<0.01). In the 1.25 mg group, there was a significant difference in the changes of fundus on the 4th day after treatment VS. the 2nd week after treatment (P<0.001). In the 0.75 mg and 0.5 mg group respectively, the changes of fundus were significantly different between each consecutive time points of the 4th day, 2nd week, 4th week and 2nd month after treatment (P<0.001,P=0.001,P=0.002; P<0.001,P=0.001,P=0.003). The proportion of normal retinal vessels respectively in 1.25 mg , 0.75 mg and 0.5 mg group is 66.67%、43.48% and 50% in the 3rd month after treatment.Conclusion: Retinal complete vascularization was slightly better in 1.25 mg group, but failed to reach a statistical significance. Based on results, the lowest dose 0.5 mg may be preferred since our final results were similar (p>0.05). Long-term follow-up of fundus changes was still needed to avoid recurrence of ROP whatever the dose of bevacizumab was uesed.


PLoS ONE ◽  
2021 ◽  
Vol 16 (8) ◽  
pp. e0256685
Author(s):  
Subhronil Mondal ◽  
Hindolita Chakraborty ◽  
Sandip Saha ◽  
Sahana Dey ◽  
Deepjay Sarkar

Studies on the large-scale latitudinal patterns of gastropod drilling predation reveal that predation pressure may decrease or increase with increasing latitude, or even show no trend, questioning the generality of any large-scale latitudinal or biogeographic pattern. Here, we analyze the nature of spatio-environmental and latitudinal variation in gastropod drilling along the Indian eastern coast by using 76 samples collected from 39 locations, covering ~2500 km, incorporating several ecoregions, and ~15° latitudinal extents. We find no environmental or latitudinal gradient. In fact, drilling intensity varies highly within the same latitudinal bin, or oceanic sub-basins, or even the same ecoregions. Moreover, different ecoregions with their distinctive biotic and abiotic environmental variables show similar predation intensities. However, one pattern is prevalent: some small infaunal prey taxa, living in the sandy-muddy substrate—which are preferred by the naticid gastropods—are always attacked more frequently over others, indicating taxon and size selectivity by the predators. The result suggests that the biotic and abiotic factors, known to influence drilling predation, determine only the local predation pattern. In the present case, the nature of substrate and prey composition determines the local predation intensity: soft substrate habitats host dominantly small, infaunal prey. Since the degree of spatial variability in drilling intensity within any time bin can be extremely high, sometimes greater than the variability across consecutive time bins, temporal patterns in drilling predation can never be interpreted without having detailed knowledge of the nature of this spatial variability within a time bin.


Author(s):  
Daniel Schanz ◽  
Matteo Novara ◽  
Andreas Schröder

We present a novel evaluation mode for Lagrangian Particle Tracking methods in general, applied to the Shake-The-Box method specifically. The aim is to attain high levels of accuracy and a removal of false (‘ghost’) tracks in flow situations, where significant amounts of particles show small relative movement with respect to each other in consecutive time-steps. An iterative approach using variable time separations is employed, which starts by tracking particles at high timeseparations, followed by an iterative reduction of time separation, while feeding the particle tracked within the previous iterations. The process allows for applying tracking parameters fine-tuned to the different flow regimes tracked within each iteration. Experimental validation was performed using a dataset on impinging jet flow, created in collaboration with the School of Mechanical Engineering of Pusan National University. Evaluation of this flow with high velocity range shows distinct advantages in reduction of ghost tracks and in tracking accuracy.


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