scholarly journals Robustness to bad frames in angular differential imaging: a local weighting approach

2020 ◽  
Vol 634 ◽  
pp. A2 ◽  
Author(s):  
Olivier Flasseur ◽  
Loïc Denis ◽  
Éric Thiébaut ◽  
Maud Langlois
Keyword(s):  
Adaptive Optics ◽  
Signal To Noise Ratio ◽  
Poor Quality ◽  
Estimation Errors ◽  
Temporal Modeling ◽  
Local Fluctuations ◽  
Image Patches ◽  
Spatio Temporal ◽  
Differential Imaging ◽  
The Impact

Context. The detection of exoplanets by direct imaging is very challenging. It requires an extreme adaptive-optics (AO) system and a coronagraph as well as suitable observing strategies. In angular differential imaging, the signal-to-noise ratio is improved by combining several observations. Aims. Due to the evolution of the observation conditions and of the AO correction, the quality of the observations may vary significantly during the observing sequence. It is common practice to reject images of comparatively poor quality. We aim to decipher when this selection should be performed and what its impact on detection performance is. Methods. Rather than discarding a full image, we study the local fluctuations of the signal at each frame and derive weighting maps for each frame. These fluctuations are modeled locally directly from the data through the spatio-temporal covariance of small image patches. The weights derived from the temporal variances can be used to improve the robustness of the detection step and reduce estimation errors of both the astrometry and photometry. The impact of bad frames can be analyzed by statistically characterizing the detection and estimation performance. Results. When used together with a modeling of the spatial covariances (PACO algorithm), these weights improve the robustness of the detection method. Conclusions. The spatio-temporal modeling of the background fluctuations provides a way to exploit all acquired frames. In the case of bad frames, areas with larger fluctuations are discarded by a weighting strategy and do not corrupt the detection map or the astrometric and photometric estimations. Other areas of better quality are preserved and are included to detect and characterize sources.

scholarly journals Different Models, Different Outcomes? A Comparison of Approaches to Land Use Modeling in the Dutch Limes

Heritage ◽  
2021 ◽  
Vol 4 (3) ◽  
pp. 2081-2104
Author(s):  
Philip Verhagen ◽  
Maurice de Kleijn ◽  
Jamie Joyce
Keyword(s):  
Land Use ◽  
Roman Empire ◽  
Local Population ◽  
Population Increase ◽  
Temporal Modeling ◽  
Land Use Modeling ◽  
Agent Based ◽  
Spatio Temporal ◽  
The Impact ◽  
Agricultural Demand

Current advances in spatial simulation bring unprecedented possibilities for spatio-temporal modeling. In this paper, we focus on modeling the impact of settlement on land use in the Roman period in the Dutch river area, on the northern frontier of the Roman Empire. During this period, the area witnessed a strong population increase that put more demands on the available land to produce food, not only for the local population, but also for the soldiers stationed on the frontier and the citizens of the newly founded towns. We compare an agent-based model (ABM) of agricultural production in the region (ROMFARMS), and a model using the Past Land Use Scanner (PLUS. Both were used to estimate the effects of increased agricultural demand through simulations of food production, taking into account the available workforce and the productivity and availability of suitable land. However, how should we evaluate the model outcomes? What are the advantages and limitations of each? We discuss issues of scale, temporal resolution and model inputs, together with questions of technical implementation and validation. In this way, we aim to point the way to future researchers to implement these approaches effectively in other contexts.

Aperture shapes and the effectiveness of ground-based large and extremely large telescopes

2020 ◽  
Vol 496 (4) ◽  
pp. 5414-5422
Author(s):  
Armen V Hakobyan
Keyword(s):  
Adaptive Optics ◽  
Signal To Noise Ratio ◽  
Optical Power ◽  
Optical Transmittance ◽  
Circular Aperture ◽  
Point Spread Functions ◽  
Light Gathering ◽  
Observational Mode ◽  
Large Telescopes ◽  
The Impact

ABSTRACT Aperture shapes in modern large and forthcoming extremely large telescopes (ELTs), with effective light-gathering sizes more than D ∼ 10 m, differ significantly from the desirable circular one. They deliver specific point spread functions, which may also differ notably from that of the fine structure of the classical Airy pattern. The optical power of such a telescope can be changed notably compared with a circular aperture with the same area. The presence of atmospheric optical turbulence complicates the effect additionally and makes it seeing- and wavelength-dependent. So, what is the impact of a non-circular pupil on telescope exploitation? It concerns the efficiency, which is an important point, especially for instruments of such a class. In this research an attempt is made to assess the values of these changes in the context of the Keck, HDRT, GMT, TMT and ELT telescopes. Relative performance characteristics (integral contrast and signal-to-noise ratio, S/N) of the telescopes, working in the seeing-limited regime, under a range of plausible turbulence conditions, for a wide (from UV to mid-IR) spectral region are obtained. The partial role of central obscuration is assessed. The effect of adaptive optics implementation in this context is also analysed. It is shown that, for instance, maximal S/N degradation due to the non-circularity of the pupil shape can be as much as $\sim 6~{{\ \rm per\ cent}}$ (TMT) to $30~{{\ \rm per\ cent}}$ (HDRT), depending on the telescope and observational mode. The numbers are comparable with or may even substantially exceed the losses that could be caused by the other parameters (e.g. residual wave-front error, optical transmittance) relevant to the quality of the optical system.

scholarly journals Impact of Co-Channel Interference on Two-Way Relaying Networks with Maximal Ratio Transmission

Electronics ◽  
2019 ◽  
Vol 8 (4) ◽  
pp. 392 ◽  
Author(s):  
Awfa Aladwani ◽  
Eylem Erdogan ◽  
Tansal Gucluoglu
Keyword(s):  
Signal To Noise Ratio ◽  
High Reliability ◽  
Symbol Error Rate ◽  
High Signal ◽  
Amplify And Forward ◽  
Estimation Errors ◽  
Channel Interference ◽  
Noise Ratio ◽  
The Impact ◽  
Ratio Transmission

Amplify-and-forward (AF) two-way relay networks (TWRNs) have become popular to provide spectrally efficient communication when range extension or energy efficiency is needed by utilizing a simple relay. However, their performance can be significantly degraded in practice due to co-channel interference (CCI) which is increasing due to growing number of wireless devices and recent cognitive and non-orthogonal multiple access techniques. With the motivation of improving the performance of AF-TWRNs, the use of maximal ratio transmission (MRT) is investigated to achieve high reliability while requiring low receiver complexity for the relay. First, the signal-to-interference-plus-noise ratio (SINR) expression is formulated and upper bounded. Then, tight lower bound expressions of outage probability (OP), sum symbol error rate (SSER), and upper bound ergodic sum rate (ESR) for each source and for the overall system are obtained. Besides, array and diversity gains are provided after deriving the asymptotic expressions of OP and SSER at high signal-to-noise ratio (SNR). Furthermore, the impact of channel estimation errors on the performance is also included. Finally, Monte Carlo simulation results which corroborate our theoretical findings are illustrated.

The Impact of Missing and Error-Prone Auxiliary Information on Sparse-Matrix Sub-Population Parameter Estimates

Methodology ◽  
2015 ◽  
Vol 11 (3) ◽  
pp. 89-99 ◽  
Author(s):  
Leslie Rutkowski ◽  
Yan Zhou
Keyword(s):  
Sparse Matrix ◽  
Small Body ◽  
Auxiliary Information ◽  
Poor Quality ◽  
Quality Data ◽  
Estimation Methods ◽  
Parameter Estimates ◽  
Population Parameter ◽  
Conditioning Model ◽  
The Impact

Abstract. Given a consistent interest in comparing achievement across sub-populations in international assessments such as TIMSS, PIRLS, and PISA, it is critical that sub-population achievement is estimated reliably and with sufficient precision. As such, we systematically examine the limitations to current estimation methods used by these programs. Using a simulation study along with empirical results from the 2007 cycle of TIMSS, we show that a combination of missing and misclassified data in the conditioning model induces biases in sub-population achievement estimates, the magnitude and degree to which can be readily explained by data quality. Importantly, estimated biases in sub-population achievement are limited to the conditioning variable with poor-quality data while other sub-population achievement estimates are unaffected. Findings are generally in line with theory on missing and error-prone covariates. The current research adds to a small body of literature that has noted some of the limitations to sub-population estimation.

Impact of an Amaranth-Sorghum Grains Product on Nutrient Intake of Children Aged 6-23 Months in Kiandutu Slums, Thika, Kenya

10.37512/700 ◽  
2020 ◽  
Keyword(s):  
Nutrition Education ◽  
Nutrient Intake ◽  
Controlled Trial ◽  
Poor Quality ◽  
Control Group ◽  
Composite Flour ◽  
Monthly Basis ◽  
Sorghum Flour ◽  
Baseline Characteristics ◽  
The Impact

Poor quality complementary foods contribute to undernutrition in children aged 6-23 months. Therefore, there is need to explore foods that will provide adequate nutrients for this age group. This study aimed at determining the impact of a sorghum-amaranth composite flour porridge on nutrient intake of children aged 6-23 months. A randomized controlled trial was conducted at Kiandutu slum, Thika, Kenya. Children in the control group (CG), received a maize-sorghum flour while those in the treatment group (TG) received an amaranth-sorghum flour. The sample size per study group was 73 mother-child pairs. The children in the TG received Kcal 1000 worth of porridge/day while those in the CG received Kcal 266.8/day. Mothers of children in both groups were given nutrition education at baseline, and monthly, for six months. Food intake data was taken at baseline, then monthly for six months. Descriptive statistics were used to describe nutrient intake. Chi square and Mann Whitney U test were was used to compare the baseline characteristics of the two groups and their nutrient intake, respectively. At baseline characteristics of the two groups were similar. On a monthly basis, nutrient intake in the TG was significantly higher for a majority of the nutrients than in the CG. The product can contribute to preventing under-nutrition in children aged 6-23 months.

scholarly journals Pyramidal Framework: Guidance for the Next Generation of GIS Spatial-Temporal Models

2021 ◽  
Vol 10 (3) ◽  
pp. 188
Author(s):  
Cyril Carré ◽  
Younes Hamdani
Keyword(s):  
Conceptual Models ◽  
Future Generations ◽  
Temporal Data ◽  
Temporal Modeling ◽  
Temporal Models ◽  
Gis Data ◽  
Spatio Temporal ◽  
New Interpretation ◽  
Conventional Literature

Over the last decade, innovative computer technologies and the multiplication of geospatial data acquisition solutions have transformed the geographic information systems (GIS) landscape and opened up new opportunities to close the gap between GIS and the dynamics of geographic phenomena. There is a demand to further develop spatio-temporal conceptual models to comprehensively represent the nature of the evolution of geographic objects. The latter involves a set of considerations like those related to managing changes and object identities, modeling possible causal relations, and integrating multiple interpretations. While conventional literature generally presents these concepts separately and rarely approaches them from a holistic perspective, they are in fact interrelated. Therefore, we believe that the semantics of modeling would be improved by considering these concepts jointly. In this work, we propose to represent these interrelationships in the form of a hierarchical pyramidal framework and to further explore this set of concepts. The objective of this framework is to provide a guideline to orient the design of future generations of GIS data models, enabling them to achieve a better representation of available spatio-temporal data. In addition, this framework aims at providing keys for a new interpretation and classification of spatio-temporal conceptual models. This work can be beneficial for researchers, students, and developers interested in advanced spatio-temporal modeling.

scholarly journals Spatio-Temporal Variation Characteristics of Snow Depth and Snow Cover Days over the Tibetan Plateau

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 307
Author(s):  
Chi Zhang ◽  
Naixia Mou ◽  
Jiqiang Niu ◽  
Lingxian Zhang ◽  
Feng Liu
Keyword(s):  
Tibetan Plateau ◽  
Snow Cover ◽  
Snow Depth ◽  
Feedback Effect ◽  
Effect Of Temperature ◽  
The Tibetan Plateau ◽  
Reanalysis Dataset ◽  
Spatio Temporal ◽  
The Impact ◽  
Main Factor

Changes in snow cover over the Tibetan Plateau (TP) have a significant impact on agriculture, hydrology, and ecological environment of surrounding areas. This study investigates the spatio-temporal pattern of snow depth (SD) and snow cover days (SCD), as well as the impact of temperature and precipitation on snow cover over TP from 1979 to 2018 by using the ERA5 reanalysis dataset, and uses the Mann–Kendall test for significance. The results indicate that (1) the average annual SD and SCD in the southern and western edge areas of TP are relatively high, reaching 10 cm and 120 d or more, respectively. (2) In the past 40 years, SD (s = 0.04 cm decade−1, p = 0.81) and SCD (s = −2.3 d decade−1, p = 0.10) over TP did not change significantly. (3) The positive feedback effect of precipitation is the main factor affecting SD, while the negative feedback effect of temperature is the main factor affecting SCD. This study improves the understanding of snow cover change and is conducive to the further study of climate change on TP.

scholarly journals Interphotoreceptor coupling: an evolutionary perspective

2021 ◽  
Author(s):  
Lorenzo Cangiano ◽  
Sabrina Asteriti
Keyword(s):  
Visual Information ◽  
Signal To Noise Ratio ◽  
Electrical Coupling ◽  
Physiological Role ◽  
Cellular Processes ◽  
Contact Points ◽  
Highly Sensitive ◽  
The Many ◽  
The Impact

AbstractIn the vertebrate retina, signals generated by cones of different spectral preference and by highly sensitive rod photoreceptors interact at various levels to extract salient visual information. The first opportunity for such interaction is offered by electrical coupling of the photoreceptors themselves, which is mediated by gap junctions located at the contact points of specialised cellular processes: synaptic terminals, telodendria and radial fins. Here, we examine the evolutionary pressures for and against interphotoreceptor coupling, which are likely to have shaped how coupling is deployed in different species. The impact of coupling on signal to noise ratio, spatial acuity, contrast sensitivity, absolute and increment threshold, retinal signal flow and colour discrimination is discussed while emphasising available data from a variety of vertebrate models spanning from lampreys to primates. We highlight the many gaps in our knowledge, persisting discrepancies in the literature, as well as some major unanswered questions on the actual extent and physiological role of cone-cone, rod-cone and rod-rod communication. Lastly, we point toward limited but intriguing evidence suggestive of the ancestral form of coupling among ciliary photoreceptors.

scholarly journals Investigating the Impact of the Bit Depth of Fluorescence-Stained Images on the Performance of Deep Learning-Based Nuclei Instance Segmentation

Diagnostics ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 967
Author(s):  
Amirreza Mahbod ◽  
Gerald Schaefer ◽  
Christine Löw ◽  
Georg Dorffner ◽  
Rupert Ecker ◽  
...  
Keyword(s):  
Deep Learning ◽  
State Of The Art ◽  
Computer Assisted ◽  
Important Criterion ◽  
Histological Image ◽  
Computer Mediated ◽  
Image Patches ◽  
Processing Techniques ◽  
The Impact ◽  
Instance Segmentation

Nuclei instance segmentation can be considered as a key point in the computer-mediated analysis of histological fluorescence-stained (FS) images. Many computer-assisted approaches have been proposed for this task, and among them, supervised deep learning (DL) methods deliver the best performances. An important criterion that can affect the DL-based nuclei instance segmentation performance of FS images is the utilised image bit depth, but to our knowledge, no study has been conducted so far to investigate this impact. In this work, we released a fully annotated FS histological image dataset of nuclei at different image magnifications and from five different mouse organs. Moreover, by different pre-processing techniques and using one of the state-of-the-art DL-based methods, we investigated the impact of image bit depth (i.e., eight bits vs. sixteen bits) on the nuclei instance segmentation performance. The results obtained from our dataset and another publicly available dataset showed very competitive nuclei instance segmentation performances for the models trained with 8 bit and 16 bit images. This suggested that processing 8 bit images is sufficient for nuclei instance segmentation of FS images in most cases. The dataset including the raw image patches, as well as the corresponding segmentation masks is publicly available in the published GitHub repository.

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