bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control and enhancement of multiband high harmonic generation by synthesized laser fields
Authors: Bruner Barry D , Narovlansky-Uzan Ayelet J , Arusi-Parpar Talya , Orenstein Gal , Shonfeld Assaf , Dudovich Nirit 
Published: August 2021

Abstract
High harmonic generation (HHG) spectroscopy has emerged as an invaluable tool for studying electronic dynamics and structure in crystals. The primary challenges are imposed by the multiple degrees of freedom of the underlying dynamics as well as the low efficiency of the HHG process. Here we show that when the HHG process is driven by a synthesized bichromatic field, its efficiency can be significantly enhanced, increasing the photon flux by 1–2 orders of magnitude. The bichromatic field enhances the signal on a microscopic level by manipulating the tunnel ionization and subsequent electron dynamics driven by the synthesized laser waveform. We examine the scaling of the HHG yield on the field parameters, and observe a pronounced dependence on the HHG energy. Importantly, our study reveals that the different spectral regimes are dictated by different generation mechanisms as well as multiple bands in which the dynamics evolve. Our work demonstrates that shaped laser fields serve as a powerful approach to control multiband electron currents in solids, probe their origin, and enhance the efficiency of the HHG process.
Review of porosity uncertainty estimation methods in computed tomography dataset
Authors: Jaques Victory A J , Plessis Anton Du , Zemek Marek , Šalplachta Jakub , Stubianová Zuzana , Zikmund Tomáš , Kaiser Jozef 
Published: August 2021

Abstract
X-ray computed tomography is a common tool for non-destructive testing and analysis. One major application of this imaging technique is 3D porosity identification and quantification, which involves image segmentation of the analysed dataset. This segmentation step, which is most commonly performed using a global thresholding algorithm, has a major impact on the results of the analysis. Therefore, a thorough description of the workflow and a general uncertainty estimation should be provided alongside the results of porosity analysis to ensure a certain level of confidence and reproducibility. A review of current literature in the field shows that a sufficient workflow description and an uncertainty estimation of the result are often missing. This work provides recommendations on how to report the processing steps for porosity evaluation in computed tomography data using global thresholding, and reviews the methods for the estimation of the general uncertainty in porosity measurements.
Spatially discrete Boussinesq equation: integrability, Darboux transformation, exact solutions and continuum limit
Authors: Zhao Hai-qiong , Zhou Tong 
Published: August 2021

Abstract
The intimate connection between discrete and continuous integrable systems may yield deep insight into some inherent discreteness of physical phenomena. In this paper, a spatially discrete Boussinesq equation is investigated. The integrability of the spatially discrete model is confirmed by showing the existence of Lax pair and infinite number of conservation laws. The Darboux transformation is expressed in terms of Casorati type determinant. Further, by combining the Darboux transformation with different solutions of eigenfunction, we provide a comprehensive approach to construct various types of exact solutions to the spatially discrete Boussinesq equation, such as multi-soliton solutions, periodic solutions, rational solutions and more generally their interaction solutions. Lastly, we prove that the theory of spatially discrete Boussinesq equation including the Lax pair, the conservation laws, the Darboux transformation and the exact solutions converges to the corresponding theory of the Boussinesq equation in the continuum limit.
Optical system research of multi-object fiber spectroscopic survey telescope
Authors: Bai Hua , Su Ding-Qiang , Liang Ming , Shectman Stephen A. , Yuan Xiang-Yan , Cui Xiang-Qun 
Published: August 2021

Abstract
In the first part of this paper, four different Cassegrain optical systems with their correctors are designed and studied for multi-object fiber slit spectroscopic survey. The aperture in 6.5 m and field of view 3° are taken for these optical systems. Assuming observation wavelength range is 0.365–0.95 μm, the maximum zenith distance for observing is 60°, the maximum diameter of these lenses is 1.66 m, the altitude of the telescope site is 2500 m, two correctors are composed of 4-piece lenses and the other two are 5-piece lenses. The results obtained are: f-ratio about 3.7, the image quality for all four systems with EE80D ≤ 0.60″, the linear diameter of the focal surface is about 1.2 m and 11 000 fibers can be set on it. Considering the limit of size of fused silica and optical glass, the maximum diameter for lens is about 1.7 m. Such a 6.5 m telescope is about the largest one if using the above correctors. Considering the multi-object spectroscopic survey is greatly important, we also studied some telescope optical systems having their aperture near or larger than 10 m used for the multi-object fiber spectroscopic survey. Such ideas are introduced in the last section of this paper.
Masses for free-floating planets and dwarf planets
Authors: Gould Andrew , Zang Wei-Cheng , Mao Shude , Dong Su-Bo 
Published: August 2021

Abstract
The mass and distance functions of free-floating planets (FFPs) would give major insights into the formation and evolution of planetary systems, including any systematic differences between those in the disk and bulge. We show that the only way to measure the mass and distance of individual FFPs over a broad range of distances is to observe them simultaneously from two observatories separated by

D
~
O
(
0.01

au
)

(to measure their microlens parallax π
E) and to focus on the finite-source point-lens (FSPL) events (which yield the Einstein radius θ
E). By combining the existing KMTNet 3-telescope observatory with a 0.3 m 4 deg2 telescope at L2, of order 130 such measurements could be made over four years, down to about M ∼ 6 M
⊕ for bulge FFPs and M ∼ 0.7 M
⊕ for disk FFPs. The same experiment would return masses and distances for many bound planetary systems. A more ambitious experiment, with two 0.5 m satellites (one at L2 and the other nearer Earth) and similar camera layout but in the infrared, could measure masses and distances of sub-Moon mass objects, and thereby probe (and distinguish between) genuine sub-Moon FFPs and sub-Moon “dwarf planets” in exo-Kuiper Belts and exo-Oort Clouds.
Effects of resistivity on standing shocks in low angular momentum flows around black holes
Authors: Singh Chandra B. , Okuda Toru , Aktar Ramiz 
Published: August 2021

Abstract
We study two-dimensional low angular momentum flow around a black hole using the resistive magnetohydrodynamic module of PLUTO code. Simulations have been performed for the flows with parameters of specific angular momentum, specific energy and magnetic field which may be expected for the flow around Sgr A*. For flows with lower resistivity η = 10−6 and 0.01, the luminosity and shock location on the equator vary quasi-periodically. The power density spectra of luminosity variation show peak frequencies which correspond to the periods of 5 × 105, 1.4 × 105 and 5 × 104 s. These quasi-periodic oscillations (QPOs) occur due to interaction between the outer oscillating standing shock and the inner weak shocks occurring at the innermost hot blob. While for cases with higher resistivity η = 0.1 and 1.0, the high resistivity considerably suppresses the magnetic activity such as MHD turbulence and the flows tend to be steady and symmetric with respect to the equator. The steady standing shock is formed more outward compared with the hydrodynamical flow. The low angular momentum flow model with the above flow parameters and with low resistivity has a possibility to explain long-term flares of Sgr A* with frequencies ∼ one per day and ∼ 5 – 10 days in the latest observations by Chandra, Swift and XMM-Newton monitoring of Sgr A*.
Optical monitoring and intra-day variabilities of BL Lac Objects OJ 287
Authors: Yuan Yu-Hai , Fan Jun-Hui , Wu Hong , Hao Jing-Meng , Huang Wei-Rong , Liu Xiao-Lan , Huang Hong-Ren 
Published: August 2021

Abstract
Using the 1.26 m National Astronomical Observatory-Guangzhou University Infrared/Optical Telescope (NGT), we monitor one BL Lac object, OJ 287. For this source, we obtain 15 094 gri observations (4900 at g band, 5184 at r band and 5010 at i band) in 155 nights from 2014 December 13 to 2019 March 15. Based on the upper observations, we obtain the following results. (1) The total variation amplitude is ∼2.3 mag. (2) There are intra-day variabilities (IDVs). The IDV timescales (Δ T) are in the range from 7.69 min (Δ m = 0.06 ± 0.02 mag) to 371.09 min (Δ m = 0.26 ± 0.04 mag). (3) There are strong correlations between Δ T and Δ m, Δ m = (2.91 ± 0.66) × 10−4ΔT + (0.08 ± 0.009), with r = 0.52, p = 5.33 × 10−5. (4) There are intra-day periods in this source, with the period P ≈ 94 min on 2017 December 10. When we supplement the observations from the literature, we can obtain that the long-term period is about 12.02 ± 0.41 yr. (5) The spectral properties of OJ 287 show the bluer-when-brighter behavior, whatever state the source is at.
Lunar cratering asymmetries with high lunar orbital obliquity and inclination of the Moon
Authors: Li Hua-Cheng , Zhang Nan , Yue Zong-Yu , Zhang Yi-Zhuo 
Published: August 2021

Abstract
Accurate estimation of cratering asymmetry on the Moon is crucial for understanding Moon evolution history. Early studies of cratering asymmetry have omitted the contributions of high lunar obliquity and inclination. Here, we include lunar obliquity and inclination as new controlling variables to derive the cratering rate spatial variation as a function of longitude and latitude. With examining the influence of lunar obliquity and inclination on the asteroids population encountered by the Moon, we then have derived general formulas of the cratering rate spatial variation based on the crater scaling law. Our formulas with addition of lunar obliquity and inclination can reproduce the lunar cratering rate asymmetry at the current Earth-Moon distance and predict the apex/ant-apex ratio and the pole/equator ratio of this lunar cratering rate to be 1.36 and 0.87, respectively. The apex/ant-apex ratio is decreasing as the obliquity and inclination increasing. Combining with the evolution of lunar obliquity and inclination, our model shows that the apex/ant-apex ratio does not monotonically decrease with Earth-Moon distance and hence the influences of obliquity and inclination are not negligible on evolution of apex/ant-apex ratio. This model is generalizable to other planets and moons, especially for different spin-orbit resonances.
Revisiting pulsar velocities using Gaia Data Release 2
Authors: Yang Meng , Dai Shi , Li Di , Tsai Chao-Wei , Zhu Wei-Wei , Zhang Jie 
Published: August 2021

Abstract
Precise measurements of neutron star (NS) velocities provide critical clues in regard to the supernova physics and evolution of binary systems. Based on Gaia Data Release 2 (DR2), we selected a sample of 24 young (< 3 Myr) pulsars with precise parallax measurements and measured the velocity of their local standard of rest (LSR) and the velocity dispersion among their respective local stellar groups. The median velocity difference between thus calculated LSRs and the Galactic rotation model is ∼ 7.6 km s−1, small compared to the typical velocity dispersion of ∼ 27.5 km s−1. For pulsars off the Galactic plane, such differences grow significantly to as large as ∼40 km s−1. More importantly, the velocity dispersion of stars in the local group of low-velocity pulsars can be comparable to their transverse velocities, suggesting that the intrinsic velocities of NS progenitors should be taken into account when we consider their natal kicks and binary evolution. We also examined the double NS system J0737–3039A/B, and measured its transverse velocity to be

26

−
13

+
18

km s−1 assuming nearby Gaia sources are representative of their birth environment. This work demonstrated the feasibility and importance of using Gaia data to study the velocity of individual systems and velocity distribution of NSs.
Stellar activity cycles as revealed by long-term beat-like patterns from light curves of Kepler
Authors: Han Heng-Geng , Cui Kai-Ming , Liu Ji-Feng , Yang Hui-Qin , Fang Xuan , Zhao Rui-Ning 
Published: August 2021

Abstract
Stellar activity cycles have been found on many stars through different methods. Although in debate, an empirical relation has been found where a period of stellar activity cycle P
cyc is positively correlated with rotation period P
rot along some segregated branches. In this work, we built a systematic process to search for the Kepler objects that are analogous to the long-term solar brightness variations and investigate their possible origins. After a rigorous selection, we obtained 43 objects that all exhibit clear long-term beat-like patterns and their variability (amplitude of rotational modulation) periods and rotation periods were derived. Due to the 4-year duration of the Kepler mission, our targets are located in the region where the cycle periods are longer than ∼1 yr and shorter than ∼2.5 yr. However, all of our targets exhibit clear and notable quasi-periodic variations in variability, yet we cannot confirm any linear trends that were predicted by previous research independently. This may suggest that in the Kepler realm of the P
cyc–P
rot diagram, these relations would mix with each other or the beat-like patterns may not be related to the stellar cycle unless other evidence is provided.
Three pulsars discovered by FAST in the globular cluster NGC 6517 with a pulsar candidate sifting code based on dispersion measure to signal-to-noise ratio plots
Authors: Pan Zhichen , Ma Xiao-Yun , Qian Lei , Wang Lin , Yan Zhen , Luo Jin-Tao , Ransom Scott M. , Lorimer Duncan R. , Jiang Peng 
Published: August 2021

Abstract
We report the discovery of three new pulsars in the globular cluster (GC) NGC 6517, namely NGC 6517 E, F and G, made with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The spin periods of NGC 6517 E, F and G are 7.60 ms, 24.89 ms and 51.59 ms, respectively. Their dispersion measures are 183.29, 183.713 and 185.3 pc cm−3, respectively, all slightly larger than those of the previously known pulsars in this cluster. The spin period derivatives are at the level of 1 × 10 – 18 s s−1, which suggests these are recycled pulsars. In addition to the discovery of these three new pulsars, we updated the timing solutions of the known isolated pulsars, NGC 6517 A, C and D. The solutions are consistent with those from Lynch et al. but with smaller timing residuals. From the timing solution, NGC 6517 A, B (position from Lynch et al.), C, E and F are very close to each other on the sky and only a few arcseconds from the optical core of NGC 6517.With currently published and unpublished discoveries, nine pulsars have been discovered in NGC 651, ranking it 6th for GCs with the most known pulsars. The discoveries take advantage of the high sensitivity of FAST and a new algorithm used to check and filter possible candidate signals.
Statistical investigation on the formation of sunspot light bridges
Authors: Li Fu-Yu , Chen Yu-Hao , Song Yong-Liang , Hou Zhen-Yong , Tian Hui 
Published: August 2021

Abstract
Light bridges (LBs) are bright lanes that divide one sunspot umbra into two or more parts. Though frequently observed in sunspots, their formation mechanisms have rarely been studied and thus are not well understood. Here we present results from the first statistical investigation on the formation of LBs. Using observations with the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we identified 144 LBs within 71 active regions (ARs) over the whole year of 2014. The formation processes of these LBs can be categorized into three groups: penumbral intrusion (type-A), sunspot merging (type-B) and umbral-dot emergence (type-C). The numbers of events in these three categories are 74, 57 and 13, respectively. The duration of the LB formation process is mostly less than 40 hours, with an average of ∼20 hours. Most LBs have a maximum length of less than 20″. For type-A LBs, we found a positive correlation between the LB length and the duration of the LB formation process, suggesting a similar speed of penumbral intrusion in different sunspots.
CALLISTO facilities in Peru: spectrometer commissioning and observations of type III solar radio bursts
Authors: Rengifo Javier Alonso , Loaiza-Tacuri Verónica , Bazo José , Guevara Day Walter Robert 
Published: August 2021

Abstract
The Astrophysics Directorate of CONIDA has installed two radio spectrometer stations belonging to the e-CALLISTO network in Lima, Peru. Given their strategic location near the Equator, it is possible to observe the Sun evenly throughout the whole year. The receiver located at Pucusana, nearby the capital city of Lima, took data from October 2014 until August 2016 in the metric and decimetric bands looking for radio bursts. During this period, this e-CALLISTO detector was unique in its time-zone coverage. To asses the suitability of the sites and the performance of the antennas, we analyzed the radio ambient background and measured their radiation pattern and beamwidth. To demonstrate the capabilities of the facilities for studying solar dynamics in these radio frequencies, we have selected and analyzed type III Solar Radio Bursts. The study of this kind of burst helps to understand the electron beams traversing the solar corona and the solar atmospheric density. We have characterized the most common radio bursts with the following mean values: a negative drift rate of –25.8 ± 3.7 MHz s−1, a duration of 2.6 ± 0.3 s and 35 MHz bandwidth in the frequency range of 114 to 174 MHz. In addition, for some events, it was possible to calculate a global frequency drift which on average was 0.4 ± 0.1 MHz s−1.
Analysis of alcohol abuse using improved artificial intelligence methods
Authors: Kumari D , Swetapadma A 
Published: August 2021

Abstract
In this work, artificial intelligence (AI) based method has been proposed for analysis of alcohol abuse (AA) to evaluate drug risk and find an optimal method for analysis of AA. To detect alcohol abuse, twelve input features are selected. As the number of positive classes and negative classes are imbalanced, input features are processed using synthetic minority oversampling technique (SMOTE). The selected input features are given to the AI based method to predict whether an individual uses alcohol or not. Three AI methods (logistic regression, Naïve Bayes and gradient boost) have been used from which the most suitable method is chosen as optimal method for analysis of AA. Methods used for validation of the proposed AI based method are leave one out cross validation and test sample estimate. Among the three methods used, gradient boost method performs better than other method. Gradient Boost based AI method has 97.55% accuracy to predict alcohol user. Significant achievement of the proposed work is that the accuracy (nearly 97%) to detect alcohol abuse is much more than previously (nearly 70%) suggested methods. This is due to the efficient design of AI method implemented in this work. All the feature processing work and AI algorithm design work has been done using python software.
Construction and characterization of a solar refrigeration system based on nano-graphene
Authors: Subramanian K R V , Raghu Vamshi Krishna B. V. , Nageswara Rao T 
Published: August 2021

Abstract
In this present work, we designed and fabricated a solar refrigeration system with increase in its performance compared to present refrigeration system by using different components (solar cell and Peltier module). The construction of the Peltier module was done using nano-graphene composite and its thermoelectric property was utilized for making the hot and cold junctions. A graphene composite material monolith was synthesized using solid state fabrication techniques and this constituted the junction of the Peltier module. A maximum coefficient of performance (COP) of 8.86 was achieved. ZT factor of graphene composite thermoelectric material can be further increased through modification in processing techniques and defect engineering. This will in turn increase the refrigeration COP further.
Twitter bot detection using supervised machine learning
Authors: Ramalingaiah A , Hussaini S , Chaudhari S 
Published: August 2021

Abstract
In the world of Internet and social media, there are about 3.8 billion active social media users and 4.5 billion people accessing the internet daily. Every year there is a 9% growth in the number of users and half of the internet traffic consists of mostly bots. Bots are mainly categorized into two categories: good and bad bots; good bots consist of web crawlers and chat bots whereas bad bots consist of malicious bots which make up 20% of the traffic, the reason they are not good is that they are used for nefarious purposes, they can mimic human behavior, they can impersonate legal traffic, attack IoT devices and exploit their performance. Among all these concerns, the primary concern is for social media users as they represent a large group of active users on the internet, they are more vulnerable to breach of data, change in opinion based on data. Detection of such bots is crucial to prevent further mishaps. We use supervised Machine learning techniques in this paper such as Decision tree, K nearest neighbors, Logistic regression, and Naïve Bayes to calculate their accuracies and compare it with our classifier which uses Bag of bots’ word model to detect Twitter bots from a given training data set.
Latest trend in building construction: three-dimensional printing
Authors: Babbar Atul , Rai Aryan , Sharma Ankit 
Published: August 2021

Abstract
Today world is looking towards additive manufacturing as a solution for sustainability in the construction business, one of which is three-dimensional printing that involves creating a three-dimensional (3-D) object by printing layer by layer developed digitally. Nowadays, 3-D printers have evolved so much that they can create a whole house from a pin. This technology is not only cost and time effective but also speeds up the construction rate with reduced power, material consumption, and hence reduced waste in building construction. The scope, elements, and classification of 3D printing has been discussed to highlight the work done by past researchers. This paper reviews the elements, merits, and demerits of using 3D printing in construction and evaluates it as a promising technique for sustainable development.
Simulation studies of three types of inverted pendulums via FOPID and PID controller
Authors: Kumar S , Ajmeri M 
Published: August 2021

Abstract
The inverted pendulum systems are very important problem in control literature and frequently studied. A simple and effective controller design is preferred for controlling a complex system. In this work, mathematical model of three types of inverted pendulums are derived depending upon their dynamics. Further, a fractional order PID (FOPID) controller is designed and applied for controlling and stabilizing the three types of inverted pendulums. The proposed fractional order controller is based on the fractional calculus and it is a robust controller. The responses of the pendulum system with FOPID are compared with the responses with conventional PID controllers. The overall performance of the FOPID controller is better than the conventional PID and the results are robust to the outer fast and large disturbances also.