Using neural networks as a prediction method, we attempt to demonstrate that forecasting of the Sun’s sunspot time series can be extended to the spatio-temporal case. We employ this machine-learning ...method to forecast not only in time but also in space (in this case, latitude) on a spatio-temporal dataset representing the solar sunspot diagram extending to a total of 142 years. The analysis shows that this approach seems to be able to reconstruct the overall qualitative aspects of the spatial-temporal series, namely the overall shape and amplitude of the latitude and time pattern of sunspots. This is, as far as we are aware, the first time that neural networks have been used to forecast the Sun’s sunspot butterfly diagram, and although the results are limited in the quantitative prediction aspects, it points to the way to use the full spatio-temporal series as opposed to just the time series for machine-learning approaches to forecasting. Additionally, we use the method to predict that the upcoming Cycle 25 maximum sunspot number will be around
R
25
=
57
±
17
. This implies a very weak cycle and, in fact, the weakest cycle on record.
Steel fiber-reinforced concrete (SFRC) with hooked-end steel fibers was created for use in urban furniture to protect against blast and impact loads. Due to the variety of impact loads that these ...structures may experience, it is necessary to assess the impact of high strain rates on the flexural behavior of SFRC. This study involved testing SFRC beams with 1% volume content of hooked-end fibers, which were 30 mm long and had an aspect ratio of 80. The beams were tested at different strain rates and in a three-point loading configuration. Four strain rates were tested, ranging from 10−6 to 10−2 s−1, and impact tests were conducted using a drop weight impact test machine and varying drop heights, corresponding to strain rates ranging from 1 to 20 s−1. Two load cells were used to measure the total impact force and one reaction force, which were then used to assess the inertial force. Two accelerometers measured the maximum acceleration at the midspan of the beams. The results included quasi-static and dynamic load-deflection relationships, dynamic flexural tensile strength, and failure mode of SFRC specimens, as well as the relationship between the inertial force and strain rate. The study revealed that deflection capacity and flexural tensile strength increased with loading rate. The study also provides dynamic to static property ratios, such as flexural tensile strength and fracture energy, which are compared with those recommended by the CEB-FIP Model Code and other researchers.
The nature of the constitutive contact force law utilized to describe contact–impact events in solid contact interfaces plays a key role in predicting the response of multibody mechanical systems and ...in the simulation of engineering applications. The goal of this work is to present a comparative study on the most relevant existing viscoelastic contact force models. In the sequel of this process, their fundamental characteristics are examined and their performances evaluated. Models developed based on the Hertz contact theory and augmented with a damping term to accommodate the dissipation of energy during the impact process, which typically is a function of the coefficient of restitution between the contacting solids, are considered in this study. In particular, the identified contact force models are compared in the present study for simple solid impact problems with the sole purpose of comparing the performance of the various models and examining the corresponding system behavior. The outcomes indicate that the prediction of the dynamic behavior of contacting solids strongly depends on the selection of the contact force model.
•A comparative study of viscoelastic contact force models is presented.•The dissipated energy is defined in terms of the restitution coefficient.•The contact force models are numerically and experimentally analyzed.
The Colours of the Outer Solar System Origins Survey is acquiring near-simultaneous g, r, and J photometry of unprecedented precision with the Gemini North Telescope, targeting nearly 100 ...trans-Neptunian objects (TNOs) brighter than mr = 23.6 mag discovered in the Outer Solar System Origins Survey. Combining the optical and near-infrared photometry with the well-characterized detection efficiency of the Colours of the Outer Solar System Origins Survey target sample will provide the first flux-limited compositional dynamical map of the outer solar system. In this paper, we describe our observing strategy and detail the data reduction processes we employ, including techniques to mitigate the impact of rotational variability. We present optical and near-infrared colors for 35 TNOs. We find two taxonomic groups for the dynamically excited TNOs, the neutral and red classes, which divide at g − r 0.75. Based on simple albedo and orbital distribution assumptions, we find that the neutral class outnumbers the red class, with a ratio of 4:1 and potentially as high as 11:1. Including in our analysis constraints from the cold classical objects, which are known to exhibit unique albedos and r − z colors, we find that within our measurement uncertainty our observations are consistent with the primordial solar system protoplanetesimal disk being neutral class dominated, with two major compositional divisions in grJ color space.
The compressive behavior of steel-fiber-reinforced-concrete (SFRC) is dependent on the loading rate. This research investigates, experimentally and analytically, the effect of loading rate on the ...compressive behavior of SFRC designed to be used in prefabricated urban protective furniture. For this purpose, cylinder SFRC specimens were subjected to modified instrumented-drop-weight-impact tests at four dropping heights and quasi-static tests with four different strain rates. The inertia force was analytically obtained and also experimentally measured. The results demonstrate that by increasing the strain rate, elastic modulus, compressive strength, and energy dissipation capacity have increased. Three different models were proposed for predicting each mechanical characteristic, one in the range of quasi-static and the others in the range of impact corresponding to the split Hopkinson pressure bar and drop-weight-impact tests. The experimental dynamic to static ratios obtained for SFRC properties were discussed and compared with those proposed by present study and from other researchers. Three proposed models significantly improve the prediction the dynamic increase factor values in terms of compressive strength, modulus of elasticity and toughness.
Abstract This paper presents an integrated approach for an ultimate high-performance safety toe cap with significant milestones in slim design and weight saving. The study of crashworthiness ...properties was performed through impact-crash test conditions exploring the potential of applicant solutions by the combination of an advanced high-strength steel and enhanced geometric stiffening models. The structural response for a significant thickness reduction was assessed and it provides an evolved discussion for improvements in energy absorption capacity. The present case study focuses on two geometric models from the S3 slim toe cap development by prototypes made of a martensitic 1200 steel alloy. The comparison of results is complemented using numerical simulation models with mathematical description of the dynamic plasticity behaviour by applying a constitutive Cowper-Symonds equation with fundamental parameters for material strain-rate dependence.
This paper presents a review on the formability evaluation of AHSS, enhancing necking-based failure criteria limitations. Complementary fracture/damage constitutive modeling approaches specifically ...tailored to formability evaluation, validated through numerical and experimental methods, are also subjects of research. AHSS are widely processed through sheet metal forming processes. Although an excellent choice when lightweight, high-strength, and ductility are critical factors, their multi-phase microstructure accentuates forming challenges. To accurately model forming behavior, necking-based failure criteria as well as direct fracture models require improvements. As a necking-based failure model, the conventional forming limit diagram/curve (FLD/FLC) presents limitations in estimating direct fracture (surface cracks, edge cracks, shear cracks), as well as deformation histories under non-linear strain paths. Thus, significant research efforts are being made towards the development of advanced fracture constitutive models capable of predicting fracture scenarios without necking, which are more frequently observed in the realm of AHSS. Scientific community research is divided into several directions aiming at improving the forming and fracture behavior accuracy of parts subjected to sheet metal forming operations. In this review paper, a comprehensive overview of ductile fracture modeling is presented. Firstly, the limitations of FLD/FLC in modeling fracture behavior in sheet metal forming operations are studied, followed by recent trends in constitutive material modeling. Afterwards, advancements in material characterization methods to cover a broad range of stress states are discussed. Finally, damage and fracture models predicting failure in AHSS are investigated. This review paper supplies relevant information on the current issues the sheet metal forming community is challenged with due to the trend towards AHSS employment in the automotive industry.
The rapid increase of space debris poses a risk to space activities, so it is vital to develop countermeasures in terms of space surveillance to prevent possible threats. The current Space ...Surveillance Network is majorly composed of radar and optical telescopes that regularly observe and track space objects. However, these measures are limited by size, being able to detect only a tiny amount of debris. Hence, alternative solutions are essential for securing the future of space activities. Therefore, this paper proposes the design of a payload camera breadboard for space surveillance to increase the information on debris, particularly for the under-catalogued ones. The device was designed with similar characteristics to star trackers of small satellites and CubeSats. Star trackers are attitude devices usually used in satellites for attitude determination and, therefore, have a wide potential role as a major tool for space debris detection. The breadboard was built with commercial off-the-shelf components, representing the current space-camera resolution and field of view. The image sensor was characterized to compute the sensitivity of the camera and evaluate the detectability performance in several simulated positions. Furthermore, the payload camera concept was tested by taking images of the night sky using satellites as proxies of space debris, and a photometric analysis was performed to validate the simulated detectability performance.
The effectiveness of local laser heat treatment technology to enhance the in situ formability of steels and aluminum alloys has already been widely acknowledged for the one-step forming of components ...with simple shape geometries. The present study demonstrates that this technology is also able to significantly improve the formability of a complex shaped multi-forming industrial part. An industrial grade advanced-high strength Dual-Phase DP1000 steel is used to analyze the multi-forming of a complex part to determine the most appropriate local laser heat treatment parameters and optimize in situ softening by correlating yield strength, ultimate tensile strength, elongation at fracture, strain hardening exponent and instantaneous strain hardening with local temperature dynamics during the laser treatment. Additionally, numerical simulation analysis using Autoform software is carried out to validate the selected heat affected zone and the in situ softening, ensuring that they are appropriate for improving the formability of the industrial part. These findings are then expanded to study the experimental forming of five in situ laser heat treated models, followed by comparative analysis with a benchmark. This study provides an insight and fundamental guidelines to perform in situ laser heat treatment on complex industrial parts leading to the production of the industrial multi-formed component with optimized formability.
In 2020, the Geophysical and Astronomical Observatory of the University of Coimbra will celebrate the 95th anniversary of its first spectroheliographic observation. Keeping a daily service of solar ...observations since then, making almost a century, led to one of the largest continuous solar data collections in the world. This long–term solar database is essential for studies where solar activity is involved. This work reviews the development of synoptic observations made at the Observatory of Coimbra since 1925 and presents a summary of some of the principal stages of the Observatory’s history since its founding in 1772. We refer the main technical improvements and present some perspectives for the near future. One of the most significant upgrades was the installation of a CCD camera in 2007. The transition from photographic emulsion to digital recording methods allowed the development of image analysis algorithms to process solar images and improved data sharing with other institutions. This upgrade enabled also to carry–out modern climate and space weather studies. This valuable advancement makes it possible to create a new catalogue of solar observations to be published in the future.
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