Search

We report initial results of a large radial velocity survey of K dwarfs up to a distance of 50 pc from the Solar System, to look for stellar, brown dwarf, and jovian planets using radial velocities from the CHIRON spectrograph on the CTIO/SMARTS 1.5m telescope. We identify three new exoplanet candidates orbiting host stars in the K dwarf survey, and confirm a hot Jupiter from TESS orbiting TOI 129. Our techniques are confirmed via five additional known exoplanet orbiting K dwarfs, bringing the number of orbital solutions presented here to 9, each hosting an exoplanet candidate with a minimum mass of 0.5--3.0 $M_{jup}$. In addition, we provide a list of 186 nearby K dwarfs with no detected close companions that are ideal for more sensitive searches for lower mass planets. This set of stars is used to determine CHIRON's efficiency, stability, and performance for radial velocity work. For K dwarfs with V = 7--12, we reach radial velocity precisions of 5--20 ms$^{-1}$ under a wide range of observing conditions. We demonstrate the stability of CHIRON over hours, weeks, and years using radial velocity standards, and describe instrumental capabilities and operation modes available for potential users., Published in The Astronomical Journal. 17 pages, 8 figures, 5 tables

Proxima Centauri is our nearest stellar neighbor and one of the most well-studied stars in the sky. In 2016, a planetary companion was detected through radial velocity measurements. Proxima Centauri b has a minimum mass of 1.3 Earth masses and orbits with a period of 11.2 days at 0.05 AU from its stellar host, and resides within the star's Habitable Zone. While recent work has shown that Proxima Centauri b likely does not transit, given the value of potential atmospheric observations via transmission spectroscopy of the closest possible Habitable Zone planet, we reevaluate the possibility that Proxima Centauri b is a transiting exoplanet using data from the Transiting Exoplanet Survey Satellite (TESS). We use three sectors (Sectors 11, 12, and 38 at 2-minute cadence) of observations from TESS to search for planets. Proxima Centauri is an extremely active M5.5 star, emitting frequent white-light flares; we employ a novel method that includes modeling the stellar activity in our planet search algorithm. We do not detect any planet signals. We injected synthetic transiting planets into the TESS and use this analysis to show that Proxima Centauri b cannot be a transiting exoplanet with a radius larger than 0.4 R$_\oplus$. Moreover, we show that it is unlikely that any Habitable Zone planets larger than Mars transit Proxima Centauri., Comment: 14 pages, 5 figures, accepted for publication in Frontiers in Astronomy and Space Sciences

The theory of substellar evolution predicts that there is a sharp mass boundary between lithium and non-lithium brown dwarfs, not far below the substellar-mass limit. The imprint of thermonuclear burning is carved on the surface lithium abundance of substellar-mass objects during the first few hundred million years of their evolution, leading to a sharp boundary between lithium and non-lithium brown dwarfs, so-called, the lithium test. New optical spectroscopic observations of the binaries DENIS+J063001.4-184014 and DENIS+J225210.7-173013 obtained using the 10.4-m Gran Telescopio de Canarias are reported here. They allow us to re-determine their combined optical spectral types (M9.5 and L6.5, respectively) and to search for the presence of the LiI resonance doublet. The non detection of the LiI feature in the combined spectrum of DENIS\,J063001.4$-$184014AB is converted into estimates for the depletion of lithium in the individual components of this binary system. In DENIS\,J225210.7$-$173013AB we report the detection of a weak LiI feature which we tentatively ascribe as arising from the contribution of the T3.5-type secondary. Combining our results with data for seven other brown dwarf binaries in the literature treated in a self-consistent way, we confirm that there is indeed a sharp transition in mass for lithium depletion in brown dwarfs, as expected from theoretical calculations. We estimate such mass boundary is observationally located at 51.48$^{+0.22}_{-4.00}$ $M_\mathrm{Jup}$, which is lower than the theoretical determinations., 12 pages, 6 figures, accepted for publication in MNRAS

We re-evaluate the outer edge of orbital stability for possible exomoons orbiting the radial velocity planet discovered in the HD 23079 system. In this system, a solar-type star hosts a Jupiter-mass planet in a nearly circular orbit in the outer stellar habitable zone. The outer stability limit of exomoons is deduced using $N$-body and tidal migration simulations considering a large range of initial conditions, encompassing both prograde and retrograde orbits. In particular, we extend previous works by evaluating many values in the satellite mean anomaly to identify and exclude regions of quasi-stability. Future observations of this system can make use of our results through a scale factor relative to the currently measured minimum mass. Using a constant time lag tidal model (Hut 1981), we find that plausible tidal interactions within the system are insufficient to induce significant outward migration toward the theoretical stability limit. While current technologies are incapable of detecting exomoons in this system, we comment on the detectability of putative moons through Doppler monitoring within direct imaging observations in view of future research capacities., 10 pages, 5 figures, 2 tables; accepted for publication in PASA

Discrete Stiffness Tailoring (DST) is a novel manufacturing concept where stiffness tailoring is achieved using discrete changes in ply angle to favourably redistribute stresses. Resulting performance increases can be exploited to potentially achieve lightweight rapidly manufacturable structures, uninhibited by the minimum tow-turning radii which limit continuous fibre steering approaches. An efficient two-stage optimisation routine is implemented to design a DST minimum-mass stiffened aircraft wing panel subject to buckling and manufacturing feasibility constraints. The panel is manufactured and compression tested to failure, extending the DST design concept to component level for the first time. A weight reduction of 14.4% is achieved compared to a constant stiffness optimum, through redistribution of load to the stiffener region. The optimum design removes material from the skin, between stiffeners. Experimentally, the optimised tailored panel achieved a buckling load, without failure, within 5% of that predicted, validating both the methodology and modelling.

The cut-off mass ratio is under debate for contact binaries. In this paper, we present the investigation of two contact binaries with mass ratios close to the low mass ratio limit. It is found that the mass ratios of VSX J082700.8+462850 (hereafter J082700) and 1SWASP J132829.37+555246.1 (hereafter J132829) are both less than 0.1 ($q\sim0.055$ for J082700, and $q\sim0.089$ for J132829). J082700 is a shallow contact binary with a contact degree of $\sim$19%, and J132829 is a deep contact system with a fillout factor of $\sim$70%. The $O-C$ diagram analysis indicated that both the two systems manifest long-term period decrease. In addition, J082700 exhibits a cyclic modulation which is more likely resulted from Applegate mechanism. In order to explore the properties of extremely low mass ratio contact binaries (ELMRCBs), we carried out a statistical analysis on contact binaries with mass ratios of $q\lesssim0.1$ and discovered that the values of $J_{spin}/J_{orb}$ of three systems are greater than 1/3. Two possible explanations can interpret this phenomenon. One is that some physical processes, unknown to date, are not considered when Hut presented the dynamically instability criterion. The other is that the dimensionless gyration radius ($k$) should be smaller than the value we used ($k^2=0.06$). We also found that the formation of ELMRCBs possibly has two channels. The study of evolutionary states of ELMRCBs reveals that their evolutionary states are similar with those of normal W UMa contact binaries., 26 pages, 9 figures, and 4 tables, accepted by ApJ

Planets grow via the collisional accretion of small bodies in a protoplanetary disk. Such small bodies feel strong gas drag and their orbits are significantly affected by the gas flow and atmospheric structure around the planet. We investigate the gas flow in the protoplanetary disk perturbed by the gravity of the planet by three-dimensional hydrodynamic simulation. We then calculate the orbital evolutions of particles in the gas structure obtained from the hydrodynamic simulation. Based on the orbital calculations, we obtain the collision rate between the planet and centimeter to kilometer sized particles. Our results show that meter-sized or larger particles effectively collide with the planet due to the atmospheric gas drag, which significantly enhances the collision rate. On the other hand, the gas flow plays an important role for smaller particles. Finally, considering the effects of the atmosphere and gas flow, we derive the new analytic formula for the collision rate, which is in good agreement with our simulations. We estimate the growth timescale and accretion efficiency of drifting bodies for the formation of a gas-giant solid core using the formula. We find the accretion of sub-kilometer sized bodies achieve a short growth timescale (~0.005 Myr) and a high accretion efficiency (~1) for the core formation at 5 au in the minimum mass solar nebula model., Accepted for publication in The Astrophysical Journal

The extensive timespan of modern radial velocity surveys has made the discovery of long-period substellar companions more common in recent years, however measuring the true masses of these objects remains challenging. Astrometry from the Gaia mission is expected to provide mass measurements for many of these long-period companions, but this data is not yet available. However, combining proper motion data from Gaia DR2 and the earlier Hipparcos mission makes it possible to measure true masses of substellar companions in favourable cases. In this work, we combine radial velocities with Hipparcos-Gaia astrometry to measure the true masses of two recently discovered long-period substellar companion candidates, HD 92987 B and HD 221420 b. In both cases, we find that the true masses are significantly higher than implied by radial velocities alone. A $2087 \pm 19$ m s$^{-1}$ astrometric signal reveals that HD 92987 B is not close to its $17$ $M_J$ minimum mass but is instead a $0.2562 \pm 0.0045$ $M_\odot$ star viewed at a near-polar orbital inclination, whereas the $22.9 \pm 2.2$ $M_J$ HD 221420 b can be plausibly interpreted as a high-mass "super-planet" or a low-mass brown dwarf. With semi-major axes of $\sim$10 AU both companions are interesting targets for direct imaging, and HD 221420 b in particular would be a benchmark metal-rich substellar object if it proves possible to directly detect. Our results demonstrate the power of Hipparcos-Gaia astrometry for studying long-period planet and brown dwarf candidates discovered from radial velocity surveys., 25 pages, 10 figures, 7 tables. Published in AJ. Minor textual revisions compared to version 1

The non-detection of zero-metallicity stars in ultra-faint dwarf galaxies (UFDs) can be used to constrain the Initial Mass Function (IMF) of the first (PopIII) stars by means of a statistical comparison between available data and predictions from chemical evolution models. To this end we develop a model that follows the formation of isolated UFDs, calibrated to best reproduce the available data for the best studied system: Bo��tes I. Our statistical approach shows that UFDs are the best suitable systems to study the implications of the persisting non-detection of zero-metallicity stars on the PopIII IMF, i.e. its shape, the minimum mass ($m_{min}$), and the characteristic mass ($m_{ch}$). We show that accounting for the incomplete sampling of the IMF is essential to compute the expected number of long-lived PopIII stars in inefficiently star-forming UFDs. By simulating the Color Magnitude Diagram of Bo��tes I, and thus take into account the mass-range of the observed stars, we can obtain even tighter constrains on $m_{min}$. By exploiting the 96 stars with measured metallicities ($\rm i < 19$) in the UFDs represented by our model, we demonstrate that: $m_{ch} > 1 \rm M_{\odot}$ or $m_{min} > 0.8 \rm M_{\odot}$ at $99\%$ confidence level. This means that a present day IMF for PopIII stars is excluded by our model, and a top-heavy PopIII IMF is strongly favoured. We can limit $m_{min} > 0.8 \rm M_{\odot}$ independent of the PopIII IMF shape by targeting the four UFDs Bo��tes I, Hercules, Leo IV and Eridanus II with future generation instruments, such as ELT/MOSAIC ($\rm i < 25$), which can provide samples of >10\,000 stars., Accepted by MNRAS

We infer the progenitor mass distribution for 22 historic core-collapse supernovae (CCSNe) using a Bayesian hierarchical model. For this inference, we use the local star formation histories to estimate the age for each supernova (SN). These star formation histories often show multiple bursts of star formation; our model assumes that one burst is associated with the SN progenitor and the others are random bursts of star formation. The primary inference is the progenitor age distribution. Due to the limited number of historic SNe and highly uncertain star formation at young ages, we restrict our inference to the slope of the age distribution and the maximum age for CCSNe. Using single-star evolutionary models, we transform the progenitor age distribution into a progenitor mass distribution. Under these assumptions, the minimum mass for CCSNe is $M_\textrm {min}~=~8.60^{+0.37}_{-0.41}\ \mathrm M_\odot$ and the slope of the progenitor mass distribution is $\alpha = -2.61^{+1.05}_{-1.18}$. The power-law slope for the progenitor mass distribution is consistent with the standard Salpeter initial mass function (α = −2.35). These values are consistent with previous estimates using precursor imaging and the age-dating technique, further confirming that using stellar populations around SN and supernova remnants is a reliable way to infer the progenitor masses.

We present an analysis of 1524 spectra of Vega spanning 10 years, in which we search for periodic radial velocity variations. A signal with a periodicity of 0.676 days and a semi-amplitude of ~10 m/s is consistent with the rotation period measured over much shorter time spans by previous spectroscopic and spectropolarimetric studies, confirming the presence of surface features on this A0 star. The timescale of evolution of these features can provide insight into the mechanism that sustains the weak magnetic fields in normal A type stars. Modeling the radial velocities with a Gaussian process using a quasi-periodic kernel suggests that the characteristic spot evolution timescale is ~180 days, though we cannot exclude the possibility that it is much longer. Such long timescales may indicate the presence of failed fossil magnetic fields on Vega. TESS data reveal Vega's photometric rotational modulation for the first time, with a total amplitude of only 10 ppm, and a comparison of the spectroscopic and photometric amplitudes suggest the surface features may be dominated by bright plages rather than dark spots. For the shortest orbital periods, transit and radial velocity injection recovery tests exclude the presence of transiting planets larger than 2 Earth radii and most non-transiting giant planets. At long periods, we combine our radial velocities with direct imaging from the literature to produce detection limits for Vegan planets and brown dwarfs out to distances of 15 au. Finally, we detect a candidate radial velocity signal with a period of 2.43 days and a semi-amplitude of 6 m/s. If caused by an orbiting companion, its minimum mass would be ~20 Earth masses; because of Vega's pole-on orientation, this would correspond to a Jovian planet if the orbit is aligned with the stellar spin. We discuss the prospects for confirmation of this candidate planet., 17 pages, 8 figures, 5 tables; accepted for publication in The Astronomical Journal

We present the new results of our long-term observational project to detect the small variations in the orbital periods of low-mass and short-period eclipsing binaries. About 120 new precise mid-eclipse times were obtained for three relatively well-known dwarf eclipsing binaries: SDSS J143547.87+373338.5 (P = 0.126 d), NSVS 07826147 (0.162 d), and NSVS 14256825 (0.110 d). Observed-minus-calculated (O-C) diagrams of these systems were analyzed using all accurate timings, and, where possible, new parameters of the light-time effect were calculated. For the first time, we derive (or improve upon previous findings with regard to) the short orbital periods of 13 and 10 years of possible third bodies for SDSS J143547.87+373338.5 and NSVS 07826147, respectively. In these binaries, our data show that period variations can be modeled simply on the basis of a single circumbinary object. For the first two objects, we calculated the minimum mass of the third components to be 17 MJ, and 1.4 MJ respectively, which corresponds to the mass of a brown dwarf or a giant planet. For NSVS 14256825, the cyclical period changes caused by a single additional body cannot be confirmed by our recent eclipse time measurements. More complex behavior connected with two orbiting bodies, or yet unknown effects, should be taken into account., 7 pages, 4 figures, Accepted in Astronomy&Astrophysics

This work involves the design optimization of metal&ndash, ceramic through the thickness of functionally graded material (FGM) plates subjected to thermomechanical loadings. Constrained optimization was performed for minimum mass and minimum material cost of the FGM plates. The design process of FGM plate structures requires a good choice of metal and ceramic materials and the adequate definition of the components volume fractions through the thickness direction in order to accomplish a certain structural behavior, while optimizing the material costs and/or the plate mass. Here, the optimization problems are solved with the simulated annealing (SA) algorithm, not requiring the calculation of the derivatives of the objective or constraint functions. Constrained single objective optimization cases are studied, and validated with alternative solutions, considering the p-index and the FGM plate thickness as design variables. New optimization cases, involving additionally the metal and ceramic materials as design variables, are presented both for benchmark purposes and to demonstrate the suitability of the SA algorithm to solve those optimization problems.

Using the Hamilton Echelle Spectrograph at Lick Observatory, we have obtained precise radial velocities (RVs) of a sample of 373 G- and K-giant stars over more than 12 years, leading to the discovery of several single and multiple planetary systems. The RVs of the long-period (~53 years) spectroscopic binary $\epsilon$ Cyg (HIP 102488) are found to exhibit additional regular variations with a much shorter period (~291 days). We intend to improve the orbital solution of the $\epsilon$ Cyg system and attempt to identify the cause of the nearly periodic shorter period variations, which might be due to an additional substellar companion. We used precise RV measurements of the K-giant star $\epsilon$ Cyg from Lick Observatory, in combination with a large set of RVs collected more recently with the SONG telescope, as well as archival data sets. Our Keplerian model to the RVs characterizes the orbit of the spectroscopic binary to higher precision than achieved previously, resulting in a semi-major axis of $a = 15.8 \mathrm{AU}$, an eccentricity of $e = 0.93$, and a minimum mass of the secondary of $m \sin i = 0.265 M_\odot$. Additional short-period RV variations closely resemble the signal of a Jupiter-mass planet orbiting the evolved primary component with a period of $291 \mathrm{d}$, but the period and amplitude of the putative orbit change strongly over time. Furthermore, in our stability analysis of the system, no stable orbits could be found in a large region around the best fit. Both of these findings deem a planetary cause of the RV variations unlikely. Most of the investigated alternative scenarios, such as an hierarchical triple or stellar spots, also fail to explain the observed variability convincingly. Due to its very eccentric binary orbit, it seems possible, however, that $\epsilon$ Cyg could be an extreme example of a heartbeat system., Comment: 17 pages, 13 figures, accepted to A&A

Deploying electrical systems for aircraft propulsion have been identified as a potential solution, for reducing the environmental impact of the increasing air transport usage. However, the implementation of this system needs to be done at a suitable voltage and current combination. The aim of this work is to propose a clear procedure, for deriving a suitable voltage and current for an electrical propulsion system, based on the aircraft dimensions and thrust requirement. The approach presented, considers feasibility and minimum mass as boundary and target respectively. The results show that the fan configuration and thrust requirement directly influence the choice of optimal voltage and current. This is due to the varied impact on device sizes and overall propulsion system performance. Major drivers of the selected voltage and current are the loading coefficient, speed and torque requirement of the fan. The knowledge of these is a requirement to arrive at an optimal voltage for the propulsion system

A new multi-fidelity modelling-based probabilistic optimisation framework for composite structures is presented in this paper. The multi-fidelity formulation developed herein significantly reduces the required computational time, allowing for more design variables to be considered early in the design stage. Multi-fidelity models are created by the use of finite element models, surrogate models and response correction surfaces. The accuracy and computational efficiency of the proposed optimisation methodology are demonstrated in two engineering examples of composite structures: a reliability analysis, and a reliability-based design optimisation. In these two benchmark examples, each random design variable is assigned an expected level of uncertainty. Monte Carlo Simulation (MCS), the First-Order Reliability Method (FORM) and the Second-Order Reliability Method (SORM) are used within the multi-fidelity framework to calculate the probability of failure. The reliability optimisation is a multi-objective problem that finds the optimal front, which provides both the maximum linear buckling load and minimum mass. The results show that multi-fidelity models provide high levels of accuracy while reducing computation time drastically.

Reduction of structural weight provides significant benefits in many engineering applications. While methods to optimise structural shape and topology of both continuous solids and discrete frame structures have existed for a while, the advent of additive layer manufacturing processes has enabled more complex geometries to be feasible. In this paper, a periodic spaceframe structure is designed for minimum mass and maximum effective flexural and torsional rigidities. A method of parametrising the spaceframe through its constituent unit cells is proposed, and Genetic Algorithm (GA) multi-objective optimisation is used to optimise its topology, size and geometry as a generic structure. The superior performance of the topology optimised periodic spaceframe is highlighted in terms of structural rigidity, large deformation capability, buckling and vibrational modal analysis in compare to equivalent beam structures of identical weight and comparable domain. The results show that the proposed method can effectively generate lightweight substitute structures of great mechanical performance in many beam structures applications, such as: aircraft wing spars. The periodic spaceframe is applied into a conventional aircraft wing structure to demonstrate the possibilities of promoting weight saving in the design of civil aircraft wings. Keywords: Periodic structures, Multi-objective topology optimization, Structural analysis, Aircraft wing structure

Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S.Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC)., Our nearest neighbor, Proxima Centauri, hosts a temperate terrestrial planet. We detected in radial velocities evidence of a possible second planet with minimum mass mc sin ic = 5.8 ± 1.9M⊕ and orbital period Pc = 5.21–0.22 +0.26 years. The analysis of photometric data and spectro-scopic activity diagnostics does not explain the signal in terms of a stellar activity cycle, but follow-up is required in the coming years for confirming its planetary origin. We show that the existence of the planet can be ascertained, and its true mass can be determined with high accuracy, by combining Gaia astrometry and radial velocities. Proxima c could become a prime target for follow-up and characterization with next-generation direct imaging instrumentation due to the large maximum angular separation of ~1 arc second from the parent star. The candidate planet represents a challenge for the models of super-Earth formation and evolution. Copyright © 2020 The Authors, some rights reserved., M.D. acknowledges financial support from Progetto Premiale 2015 FRONTIERA funding scheme of the Italian Ministry of Education, University, and Research. P.G. acknowledges financial support from the Italian Space Agency (ASI) under contract 2014-025-R.1.2015 to INAF. D.B. acknowledges financial support from INAF and Agenzia Spaziale Italiana (ASI grant no. 2014-025-R.1.2015) for the 2016 PhD fellowship programme of INAF. H.R.A.J. is supported by UK STFC grant ST/R006598/1. J.S.S. and P.A.P.R. acknowledge support by FONDECYT grant 1161218 and partial support from CONICYT project Basal AFB-170002. M.J.L.-G., N.M., C.R.-L., E.R., G.A., and J.F.G. acknowledge financial support from Spanish MINECO AYA2016-79425-C3-3-P, AYA2017-84390-C2-1-R (co-funded by FEDER), ESP2017-87143R, and ESP2017-87676-C05-02-R and the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). G.A.-E. research is funded via grant ST/P000592/1 "Astronomy Research at Queen Mary"granted by the Science and Technology Facilities Council/United Kingdom.

In this study, we propose to realize high-performance inertial Micro-Electro-Mechanical Systems (MEMS) mass sensors by the thick oxide as a mask layer fabrication technique. This method enables to reduce the air-gap to sub-μm in capacitively transduced MEMS with optical lithography and has been used to fabricate high aspect ratio sub-μm air-gap bulk mode MEMS mass sensors. MEMS devices have been designed and fabricated with the gap size as small as ~400 nm for ~38 μm thick SOI-based resonators (~95:1). Due to the conical characteristic of the gap, the mean air-gap has also been estimated as ~868 nm with 46 μm depth, which results in ~ 53:1 aspect ratio for the silicon test wafers that have been treated under the same conditions with the SOI-based devices. COMSOL simulation results and fabricated MEMS resonators coherently show that MEMS devices exhibit Lame mode at 4.099 MHz resonance frequency with the estimated quality factor around 20,000, and extensional mode at 4.467 MHz with the estimated quality factors around 18,000 in the air. The motional resistance has been estimated as small as 27.28 Ω for the Lame mode operating at 40 V. In this study, two different bulk modes have been considered as sensitive and uniform mass sensors for the detection of airborne particles. Then, minimum mass measurement capability of both modes has been experimentally estimated as 0.51 ng and 0.47 ng for Lame and extensional modes, respectively. The latter, a proof-of-concept mass measurement has been conducted to deduce the resonance frequency shifts of both modes upon an added mass. This work demonstrates optimization of the thick oxide mask layer fabrication technique and realization of high aspect ratio bulk-mode MEMS mass sensors.

In the work, as a research object, a protective device of a domed form is used which is used by pyrotechnic units to localize an emergency situation in the event of an explosion inside a small hazardous object. It is noted that one of the most problematic places of its application is the development of recommendations, implementation of which should ensure the prevention of the development of an emergency event up to a level of emergency on such priority effects as the number of victims and the number of victims. It is shown that the definition of such recommendations, providing localization of the consequences of an emergency in the case of an explosion of a small explosive object inside a specialized protective device, requires the obtaining of a mathematical model of localization of the focal point of an emergency. This model should provide an assessment of the strength of the technical means of localization of fragments and become the basis for the correction of existing operational procedures in the case of its application by pyrotechnic units. In the course of the study, the Eulerian-Lagrangian approach is used, which would allow obtaining a mathematical model of localization with the help of a dome-shaped form of the consequences of emergency situations in the event of an explosion inside a small-sized dangerous object. In practice, a mathematical model is implemented in a finite element packet using the library of the ANSYS/AUTODYN computer system. This allows not to create an actual new package of applications every time, as was done before to describe similar models. Due to this, an assessment of the strength of the technical means of localization of fragments is provided. In comparison with similar well-known models, the developed mathematical model allows to estimate the size of the minimum thickness of the protective device. It allows to withstand the explosion of a small-sized explosive object and to determine the minimum mass of the protective equipment taking into account the operational capabilities of the combat calculation of the pyrotechnic unit.

Although M dwarfs are known for high levels of stellar activity, they are ideal targets for the search of low-mass exoplanets with the radial velocity (RV) method. We report the discovery of a planetary-mass companion around LSPM J2116+0234 (M3.0 V) and confirm the existence of a planet orbiting GJ 686 (BD+18 3421; M1.0 V). The discovery of the planet around LSPM J2116+0234 is based on CARMENES RV observations in the visual and near-infrared channels. We confirm the planet orbiting around GJ 686 by analyzing the RV data spanning over two decades of observationsfrom CARMENES VIS, HARPS-N, HARPS, and HIRES. We find planetary signals at 14.44 and 15.53 d in the RV data for LSPM J2116+0234 and GJ 686, respectively. Additionally, the RV, photometric time series, and various spectroscopic indicators show hints of variations of 42 d for LSPM J2116+0234 and 37 d for GJ 686, which we attribute to the stellar rotation periods. The orbital parameters of the planets are modeled with Keplerian fits together with correlated noise from the stellar activity. A mini-Neptune with a minimum mass of 11.8 M orbits LSPM J2116+0234 producing a RV semi-amplitude of 6.19 m s, while a super-Earth of mass 6.6 M orbits GJ 686 and produces a RV semi-amplitude of 3.0 m s. Both LSPM J2116+0234 and GJ 686 have planetary companions populating the regime of exoplanets with masses lower than 15 M and orbital periods, L.S. acknowledges support from the Deutsche Forschungsgemeinschaft under DFG DR 281/32-1. CARMENES is an instrument for the Centro Astronomico Hispano-Aleman de Calar Alto (CAHA, Almeria, Spain). CARMENES is funded by the German Max-Planck-Gesellschaft (MPG), the Spanish Consejo Superior de Investigaciones Cientificas (CSIC), the European Union through FEDER/ERF FICTS-2011-02 funds, and the members of the CARMENES Consortium (Max-Planck-Institut fur Astronomie, Instituto de Astrofisica de Andalucia, Landessternwarte Konigstuhl, Institut de Ciencies de l'Espai, Insitut fur Astrophysik Gottingen, Universidad Complutense de Madrid, Thuringer Landessternwarte Tautenburg, Instituto de Astrofisica de Canarias, Hamburger Sternwarte, Centro de Astrobiologia and Centro Astronomico Hispano-Aleman), with additional contributions by the Spanish Ministry of Economy, the German Science Foundation through the Major Research Instrumentation Programme and DFG Research Unit FOR2544 >Blue Planets around Red Stars>, the Klaus Tschira Stiftung, the states of Baden-Wurttemberg and Niedersachsen, and by the Junta de Andalucia. Data were partly obtained with the MONET/South telescope of the MOnitoring NEtwork of Telescopes, funded by the Alfried Krupp von Bohlen und Halbach Foundation, Essen, and operated by the Georg-August-Universitat Gottingen, the McDonald Observatory of the University of Texas at Austin, and the South African Astronomical Observatory. Data were partly collected with the 90 cm telescope at Sierra Nevada Observatory (SNO) operated by the Instituto de Astrofifica de Andalucia (IAA). We acknowledge financial support from the Spanish Ministry for Science, Innovation and Universities (MCIU) AYA2015-69350-C3-2-P, ESP2016-80435-C2-1-R, ESP2016-80435-C2-2-R, AYA2016-79425-C3-1/2/3-P, ESP2017-87676-C05-02-R, ESP2017-87143-R, BES-2017-082610, SEV-2015-0548-17-2, Generalitat de Catalunya/CERCA programme; Agencia de Gestio d'Ajuts Universitaris i de Recerca of the Generalitat de Catalunya through grant 2018FI_B_00188, and the Israel Science Foundation through grant 848/16. This work makes use of data from the HARPS-N Project, a collaboration between the Astronomical Observatory of the Geneva University (lead), the CfA in Cambridge, the Universities of St. Andrews and Edinburgh, the Queens University of Belfast, and the TNG-INAF Observatory; from observations obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation; from observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 183.C-0437(A) and 072.C-0488(E); from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.

Finite element models of whole gas turbine engines, also known as Whole Engine Models (WEM), which consist of three-dimensional solid elements are not commonly used in design optimization studies due to the high computational cost of solving them for many designs. WEMs consisting of two-dimensional shell elements can be a suitable replacement for high-fidelity solid WEMs as they approximate the responses well while being significantly quicker to solve. However, in a surrogate-assisted optimization study, the accumulation of errors in the shell WEM evaluations can result in the construction of a surrogate model that can be somewhat misleading compared to the solid WEM response surface. Such a surrogate model could return promising designs that, when validated using solid WEMs, turn out to be sub-optimal or infeasible. A novel approach which combines medial meshing and multi-fidelity surrogate modelling techniques is proposed to increase the feasibility of conducting whole engine optimization studies. We demonstrate the workflow for generating medial meshes on an engine intercasing geometry. The accuracy of medial mesh simulations with respect to solid mesh simulations are evaluated and discussed in the context of their suitability as a source of low-fidelity structural information for multi-fidelity surrogate models. The impact of this combination of techniques is subsequently illustrated using two case studies. The first case study is the optimization of an intermediate compressor casing for minimum mass with constraints on the casing stiffness. The results show that the multi-fidelity approach is able to find optimum designs that are equivalent to the expensive single-fidelity approach of using only solid mesh evaluations but at a significantly lower computational cost. The second case study is the optimization of a whole engine geometry. This case study serves to demonstrate the effectiveness of the multi-fidelity approach for solving realistic design problems.

We construct equilibrium models of uniformly and differentially rotating hybrid hadron-quark stars using equations of state (EOSs) with a first-order phase transition that gives rise to a third family of compact objects. We find that the ratio of the maximum possible mass of uniformly rotating configurations - the supramassive limit - to the Tolman-Oppenheimer-Volkoff (TOV) limit mass is not EOS-independent, and is between 1.15 and 1.31,in contrast with the value of 1.20 previously found for hadronic EOSs. Therefore, some of the constraints placed on the EOS from the observation of the gravitational wave event GW170817 do not apply to hadron-quark EOSs. However, the supramassive limit mass for the family of EOSs we treat is consistent with limits set by GW170817, strengthening the possibility of interpreting GW170817 with a hybrid hadron-quark EOSs. We also find that along constant angular momentum sequences of uniformly rotating stars, the third family maximum and minimum mass models satisfy approximate EOS-independent relations, and the supramassive limit of the third family is approximately 16.5 % larger than the third family TOV limit. For differentially rotating spheroidal stars, we find that a lower-limit on the maximum supportable rest mass is 123 % more than the TOV limit rest mass. Finally, we verify that the recently discovered universal relations relating angular momentum, rest mass and gravitational mass for turning-point models hold for hybrid hadron-quark EOSs when uniform rotation is considered, but have a clear dependence on the degree of differential rotation., 19 pages, 14 figures, submitted to EPJA Topical Issue "First joint gravitational wave and electromagnetic observations: Implications for nuclear and particle physics"

The placement of early-type dwarf galaxies (dSphs and dEs) with respect to the Potential Plane defined by pressure-supported late-type dwarf galaxies (dIs and BCDs) has been determined from surface brightness profiles. dEs and the most luminous dSphs lie on the Plane, suggesting that they emerged from late-type dwarfs that converted most of their gas into stars. However, there is a critical value of the potential at which dSphs start to fall systematically below the Plane, with the deviation growing as the potential becomes shallower. The displacements are attributed to depletion of baryons through gas loss, smaller galaxies having lost proportionately more gas. The critical potential corresponds to an escape velocity of 50 $\pm$ 8 km/s, which is what is expected for gas with a temperature of 13,000 $\pm$ 4,000 K, typical of a low-metallicity HII region. This suggests that photoionization was responsible for instigating the loss of gas by galaxies with potentials shallower than the critical value, with evacuation occurring over a few tens of millions of years. Extreme ratios of dynamical to luminous masses observed for the smallest dSphs are an artifact of mass loss. Because the efficiency with which gas was converted into stars was lower for dSphs with shallower potentials, there should be a minimum baryonic mass for a galaxy below which the stellar mass is negligible. Gross extrapolation of the trend of inferred gas masses with stellar masses suggests a value between 500 and 10,000 M$_\odot$. The corresponding dynamical mass is below 10$^6$ M$_\odot$., Accepted: MNRAS, 2019 March 19

Shaping building objects is conditioned by many interrelated factors, both architectural and structural. Modern tools for shaping structures working in the environment of Rhinoceros 3D such as Grasshopper and Karamba 3D enable algorithmic-aided shaping structures, while allowing the free flow of information between the geometric model and structural model. The aim of the research is to use these tools to test the curvilinear steel bar roofs’ structures shaped based on Catalan surfaces as well as to select the most efficient structure. Three types of roof structures were analyzed: cylindroid shape, conoid shape, and hyperbolic paraboloid shape. In order to find the most preferred structural form, evolutionary structural optimization was carried out, which allowed, among others, to determine optimal discretization of the base surface, as well as optimal positions of supporting columns. As the optimization criterion, the minimum mass of the structure was assumed. The most effective structure turned out to be a structure based on hyperbolic paraboloid supported by multi-branch columns. The use of a roof with the above structure is beneficial not only because of the low weight of the structure compared to the analyzed structures, but also due to the possibility of using flat panels on the roof.

We present the detection of a Warm Neptune orbiting the M-dwarf Gl378, using radial velocity measurements obtained with the SOPHIE spectrograph at the Observatoire de Haute-Provence. The star was observed in the context of the SOPHIE exoplanets consortium's subprogramme dedicated to finding planets around M-dwarfs. Gl378 is an M1 star, of solar metallicity, at a distance of 14.96 pc. The single planet detected, Gl378 b, has a minimum mass of 13.02 $\rm M_{Earth}$ and an orbital period of 3.82 days, which place it at the lower boundary of the Hot Neptune desert. As one of only a few such planets around M-dwarfs, Gl378 b provides important clues to the evolutionary history of these close-in planets. In particular, the eccentricity of 0.1 may point to a high-eccentricity migration. The planet may also have lost part of its envelope due to irradiation., 10 pages, 8 figures, accepted for publication in A&A

The article is devoted to the problem of computer modeling of rational design of tracked vehicle transmissions with multiple criteria. The problems of finding optimal geometric parameters that satisfy several quality criteria. All the complexity of the layout and the relationship of the parameters make difficult their choice, which is simplified when using approaches of mathematical optimization. Using the famous pseudo-random method LPτ-search with the author's modification made it possible to avoid problems associated with the discreteness and the number of parameters. The main optimization criteria for transmission are minimum center distance, minimum length, minimum mass, and maximum uptime probability. To solve this problem, the problem was formulated and design parameters with constraints were specified, criteria were recorded and a transformation from multicriteria to a single criterion was proposed. The approach is based on analysis of test points that obtained using LPτ-search, and further processing of the information received. The approach of transformation from many criteria to one is proposed by introducing the scale of importance by the designer and assigning the importance of each of the criteria, finding the desired solution for each trial point of relative offset, which is proposed to be used as a unifying criterion. Basic schemes and flowcharts of the algorithm elements are provided. The implementation of the computer model was carried out in the Delphi 7 environment.

The number of exoplanet detections continues to grow following the development of better instruments and missions. Key steps for the understanding of these worlds comes from their characterization and its statistical studies. We explore the metallicity-period-mass diagram for known exoplanets by using an updated version of The Stellar parameters for stars With ExoplanETs CATalog (SWEET-Cat), a unique compilation of precise stellar parameters for planet-host stars provided for the exoplanet community. Here we focus on the planets with minimum mass below 30 M$_{\oplus}$ which seems to present a possible correlation in the metallicity-period-mass diagram where the mass of the planet increases with both metallicity and period. Our analysis suggests that the general observed correlation may be not fully explained by observational biases. Additional precise data will be fundamental to confirm or deny this possible correlation., Comment: 12 pages, 9 Figures, Accepted for MNRAS

Erosion and destruction of riverbeds, foundations of flooded engineering structures are accelerated during natural phenomena, accompanied by a significant increase in the rate and wetted perimeter of river flows, the acquisition of mobility by the riverbeds’ particles. We have analyzed the interaction between a water flow and a separate stone of spherical, cylindrical, pyramidal, and other configurations. In particular, we have further developed a traditional approach to determining the force action of fluid on a solid barrier, a stone, for the case of compression of a water jet and taking into consideration the relative flow around a stone with the predefined geometrical characteristics: diameter, volume, and configuration.It has been proposed to employ the following parameters for interaction between the flow of water and rocks of various configurations: a compression ratio and a streamline coefficient. We have derived analytical dependences of the flow rate limit, which sets a stone into motion, its weight, and configuration. For spherical smooth stones these ratios are identical with the classical results. The coefficients, introduced for consideration, were categorized, depending on the configuration of a single stone, in tables and charts, which is convenient to apply when calculating bank­protecting structures. It has been proposed to use a stone shape factor, which is the ratio of the actual flow rate limit, enabling the mobility of a stone of arbitrary configuration taking into consideration its streamlining, to the flow rate limit of a spherical stone of the same mass with a reduced diameter. A shape factor should be applied as an adjustment multiplier in the calculation of the minimum mass of stones for bank­protecting structures and during hydro­engineering works. For the wedge­shaped stones a value of the adjustment coefficient can sometimes amount to 0.170, which indicates high efficiency of applying such stones compared to those of spherical shape. In addition, the proposed coefficient could be used to refine the water flow rate limit in terms of loss of stability by existing bank­protecting structure.We have identified directions for further studies: analysis of the impact interaction between configurable stones and elements of bank­protecting structures; determination of motion parameters for water­stone flows, Ерозія та руйнування русел річок, фундаментів підтоплюваних інженерних споруд пришвидшується під час стихійних явищ, супроводжуваних значним збільшенням швидкості й змоченого периметру річкових потоків, набуттям рухливості частинками русла. Проаналізовано взаємодію потоку води із окремим каменем циліндричної, сферичної, еліпсоїдної, пірамідальної та іншої конфігурації. Зокрема розвинуто традиційний підхід до визначення силової дії рідини на тверду перешкоду – камінь - для випадку стиснення струменю води й врахування відносної обтічності каменю із заданими геометричними характеристиками: діаметр, об`єм та конфігурація.Запропоновано використовувати наступні параметри взаємодії потоку води із каменями різних конфігурацій: коефіцієнт стиснення та коефіцієнт обтічності. Отримано аналітичні залежності між граничною швидкістю потоку, яка спричиняє рух каменя, його масою та конфігурацією. Для сферичних гладких каменів ці відношення співпадають із класичними результатами. Запроваджені коефіцієнти типізовано у залежності від конфігурації окремого каменя у таблицях та графіках, що є зручним для використання у розрахунках берегоукріплень. Запропоновано використовувати коефіцієнт форми каменя – відношення дійсної граничної швидкості потоку, що викликає рухливість каменю довільної конфігурації із врахуванням його обтічності – до граничної швидкості потоку сферичного каменю такої ж маси з приведеним діаметром. Коефіцієнт форми слід використовувати як коригуючий множник у розрахунках мінімальної маси каменів для берегоукріплень та у гідротехнічних роботах. Для каменів клиновидної форми значення коригуючого коефіцієнта може в окремих випадках досягати значення 0,170, що вказує на високу ефективність використання таких каменів у порівнянні із сферичними. Крім того запропонований коефіцієнт може застосовуватися для уточнення граничної швидкості потоку води, з огляду на втрату стійкості існуючого берегоукріплення.Визначено напрями подальших досліджень: аналіз ударної взаємодії конфігуративних каменів із елементами берегоукріплень; визначення параметрів руху водно- каменевих потоків, Эрозия и разрушения русел рек, фундаментов подтопляемых инженерных сооружений ускоряется во время стихийных явлений, сопровождаемых значительным увеличением скорости и смоченного периметра речных потоков, приобретением подвижности частицами русла. Проанализировано взаимодействие потока воды с отдельным камнем цилиндрической, сферической, эллипсоидной, пирамидальной и другой конфигурации. В частности развит традиционный подход к определению силового воздействия жидкости на твердую преграду – камень – для случая сжатия струи воды и учета относительной обтекаемости камня с заданными геометрическими характеристиками: диаметр, объем и конфигурация.Предложено использовать следующие параметры взаимодействия потока воды с камнями различных конфигураций: коэффициент сжатия и коэффициент обтекаемости. Получены аналитические зависимости между предельной скоростью потока, которая приводит в движение камень, его массой и конфигурацией. Для сферических гладких камней эти соотношения совпадают с классическими результатами. Введенные в рассмотрение коэффициенты типизированы в зависимости от конфигурации отдельного камня в таблицах и графиках, что удобно для использования в расчетах берегоукреплений. Предложено использовать коэффициент формы камня - отношение действительной предельной скорости потока, что вызывает подвижность камня произвольной конфигурации с учетом его обтекаемости - к предельной скорости потока сферического камня такой же массы с приведенным диаметром. Коэффициент формы следует использовать как корректирующий множитель в расчетах минимальной массы камней для береговых укреплений и в гидротехнических работах. Для камней клиновидной формы значение корректирующего коэффициента может в отдельных случаях достигать значения 0,170, что указывает на высокую эффективность использования таких камней по сравнению со сферическими. Кроме того, предложенный коэффициент может применяться для уточнения предельной скорости потока воды с точки зрения потери устойчивости существующего берегоукрепления.Определены направления дальнейших исследований: анализ ударного взаимодействия конфигуративных камней с элементами береговых укреплений; определение параметров движения водно - камневых потоков

We address quasinormal modes of compact objects in several alternative theories of gravity. In particular, we focus on black holes and neutron stars with scalar hair. We consider black holes in dilaton-Einstein-Gau\ss -Bonnet theory, and in a generalized scalar-Einstein-Gau\ss -Bonnet theory. In the latter case scalarized black holes arise, and we study the stability of the different branches of solutions. In particular, we discuss how the spectrum of quasinormal modes is changed by the presence of a non-trivial scalar field outside the black hole horizon. We discuss the existence of an (effective) minimum mass in these models, and how the spectrum of modes becomes richer as compared to general relativity, when a scalar field is present. Subsequently we discuss the effect of scalar hair for realistic neutron star models. Here we consider $R^2$ gravity, scalar-tensor theory, a particular subsector of Horndeski theory with a non-minimal derivative coupling, and again dilatonic-Einstein-Gau\ss -Bonnet theory. Because of the current lack of knowledge on the internal composition of the neutron stars, we focus on universal relations for the quasinormal modes, that are largely independent of the equations of state and thus the matter content of the stars., Comment: 38 pages, 14 figures

Giant, wide-separation planets often lie in the gap between multiple, distinct rings of circumstellar debris: this is the case for the HR\,8799 and HD\,95086 systems, and even the solar system where the Asteroid and Kuiper belts enclose the four gas and ice giants. In the case that a debris disk, inferred from an infrared excess in the SED, is best modelled as two distinct temperatures, we infer the presence of two spatially separated rings of debris. Giant planets may well exist between these two belts of debris, and indeed could be responsible for the formation of the gap between these belts. We observe 24 such two-belt systems using the VLT/SPHERE high contrast imager, and interpret our results under the assumption that the gap is indeed formed by one or more giant planets. A theoretical minimum mass for each planet can then be calculated, based on the predicted dynamical timescales to clear debris. The typical dynamical lower limit is $\sim$0.2$M_J$ in this work, and in some cases exceeds 1$M_J$. Direct imaging data, meanwhile, is typically sensitive to planets down to $\sim$3.6$M_J$ at 1'', and 1.7$M_J$ in the best case. Together, these two limits tightly constrain the possible planetary systems present around each target, many of which will be detectable with the next generation of high-contrast imagers., Comment: Accepted for publication in MNRAS. 16 pages, 7 figures

We report the detection of two exoplanets and a further tentative candidate around the M-dwarf stars Gl96 and Gl617A, based on radial velocity measurements obtained with the SOPHIE spectrograph at the Observatoire de Haute-Provence. Both stars were observed in the context of the SOPHIE exoplanet consortium's dedicated M-dwarf subprogramme, which aims to detect exoplanets around nearby M-dwarf stars through a systematic survey. For Gl96, we present the discovery of a new exoplanet at 73.9 d with a minimum mass of 19.66 earth masses. Gl96 b has an eccentricity of 0.44, placing it among the most eccentric planets orbiting M stars. For Gl617A we independently confirm a recently reported exoplanet at 86.7 d with a minimum mass of 31.29 earth masses. Both Gl96 b and Gl617A b are potentially within the habitable zone, though Gl96 b's high eccentricity may take it too close to the star at periapsis., 22 pages, 23 figures