bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of process parameters on the quality of PLA products fabricated by fused deposition modeling (FDM): surface roughness and tensile strength
Authors: Altan Mirigul , Eryildiz Meltem , Gumus Beril , Kahraman Yusuf 
Published: April 2018

Abstract
This study investigates the effects of process parameters on the quality of products fabricated by fused deposition modeling (FDM), such as surface roughness and tensile strength. Polylactic acid (PLA) samples were built on a FDM machine at various layer thicknesses, nozzle temperature and deposition head velocity. The effect of cooling the samples during the process was also considered. The experimental study was performed according to a mixed type Taguchi L16 orthogonal array. The effectiveness of each parameter was also discussed by an analysis of variance (ANOVA). The tensile strength results were compatible with the optical images of the fracture surfaces while the surface roughness results were compatible with the surface topography of the parts along the thickness. The two dominant quality characteristics were found to be layer thickness and deposition head velocity. Lower layer thickness values yielded higher tensile strength and lower surface roughness. Use of a cooling fan and nozzle temperature were found to be the least effective parameters. Finally, the results indicated that tensile strength and surface quality of the FDM samples improved about 25 %, and 12 %, respectively at optimal process conditions.
Supplementary finite element analysis in experimental testing of total hip stems
Authors: Kluess Daniel , Lange Hans-E. , Heyer Horst , Sander Manuela , Mittelmeier Wolfram , Bader Rainer 
Published: April 2018

Abstract
Before an implantable medical device passes market clearance, a number of mechanical tests need to be conducted in order to verify the mechanical safety of the product. With regard to total hip replacement stems, these are subject to fatigue tests both in the proximal region of the neck as well as in the distal region of the shaft. Despite these tests, we experienced two clinical fractures of the same product in our clinic. It was shown that these fractures were initiated by a laser engraving of the manufacturer with subsequent crack growth. The basic question raised in the present work was to find out why fracture may not have occurred during experimental preclinical testing. Hence, a supplementary finite element analysis was conducted considering the same hip stem under the prescribed conditions of the test standard in different variations. It was found that the choice of orientation and side (left or right leg) strongly influences stress in the hip stem which has not yet been prescribed in test standards. Depending on the side, only compressive stress may be acting in the experimental situation on the locations under risk, thereby inhibiting clinically relevant crack growth and concealing an actual fracture risk.
Ratcheting testing of polytetrafluoroethylene (PTFE) under multiple-step compression
Authors: Wang Wei , Zheng Xiaotao , Ma Linwei , Lin Wei , Yu Jiuyang 
Published: April 2018

Abstract
Uniaxial stress-controlled ratcheting experiments of PTFE (polytetrafluoroethylene) under cyclic compressive loads with multiple load steps were performed. The influence of stress rate, temperature, stress amplitude, loading sequence and peak holding on the compressive ratcheting behavior have been discussed systematically. Results indicate that ratcheting deformation increases significantly when enhancing temperature and stress amplitude and reducing stress rate. Only a slight, accumulated deformation occurs during the first 20 or so cycles at room temperature (RT), but it always turns to shakedown. Moreover, ratcheting strain is clearly influenced by the loading sequence. When greater compressive deformation was obtained during the prior load step due to a greater stress level (such as higher temperature or a lesser stress rate), increased compressive strain hardening and deformation resistance could be produced, which in turn restricts or even reduces ratcheting deformation in the pursuing load step. It is of great interest that no initial cyclic stress strain curve was observed under cyclic compression at peak holding time. This indicates that creep recovery due to anelastic relaxation decreases the ratcheting rate of PTFE material under compressive creep-fatigue conditions. This research provides an important testing approach and data for PTFE material subjected to repeated compressive loads influenced by temperature modulation.
Natürliche Baummortalität in Mitteleuropa: Mortalitätsraten und -muster im Vergleich
Authors: Hülsmann Lisa , Bugmann Harald , Meyer Peter , Brang Peter 
Published: April 2018

Natural tree mortality in Central Europe: a comparison of mortality rates and patterns
Mortality is one of the key processes of forest dynamics. Yet, its investigation is challenging since trees can reach high ages, and tree death is the result of several interacting drivers. Long-term monitoring data from unmanaged forests are of great importance for studying mortality. Such data from strict forest reserves in Switzerland and Germany were used in this study to 1) derive mortality rates for 18 wooden species, and 2) build species-specific mortality models. Estimated mortality rates were highly variable among the reserves, and were particularly high in stands with many young trees and a high share of short-living pioneer species. For the calculation of accurate and comparable mortality rates, adjustments towards the same caliper threshold and mortality period are necessary. Models that predict the mortality probability of individual trees can be built based on stem diameter and basal area growth. Such models revealed that small and slow growing trees had the highest mortality risk. In addition, mortality patterns featured species-specific differences. Short-living species experienced high overall mortality probability. Shade-intolerant species showed a more pronounced mortality risk at small diameter and slow growth than shade-tolerant species. Competition as well as drought and frost were identified as the dominant drivers of tree mortality in the Swiss and German reserves. Pronounced age-related mortality due to senescence was not present, in contrast to a primeval beech forest in Ukraine. In the reserves, mortality rates and patterns should become more and more similar to those of primeval forests; however, it will require several decades or centuries of undisturbed forest development to reach identical successional stage.
Searching for Cool Dust. II. Infrared Imaging of The OH/IR Supergiants, NML Cyg, VX Sgr, S Per, and the Normal Red Supergiants RS Per and T Per∗
Authors: Gordon Michael S. , Humphreys Roberta M. , Jones Terry J. , Shenoy Dinesh , Gehrz Robert D. , Helton L. Andrew , Marengo Massimo , Hinz Philip M. , Hoffmann William F. 
Published: April 2018

Abstract
New MMT/MIRAC (9–11 μm), SOFIA/FORCAST (11–37 μm), and Herschel/PACS (70 and 160 μm) infrared (IR) imaging and photometry is presented for three famous OH/IR red supergiants (NML Cyg, VX Sgr, and S Per) and two normal red supergiants (RS Per and T Per). We model the observed spectral energy distributions (SEDs) using radiative-transfer code DUSTY. Azimuthal average profiles from the SOFIA/FORCAST imaging, in addition to dust mass distribution profiles from DUSTY, constrain the mass-loss histories of these supergiants. For all of our observed supergiants, the DUSTY models suggest that constant mass-loss rates do not produce enough dust to explain the observed infrared emission in the stars’ SEDs. Combining our results with Shenoy et al. (Paper I), we find mixed results with some red supergiants showing evidence for variable and high mass-loss events while others have constant mass loss over the past few thousand years.
OGLE-2017-BLG-0482Lb: A Microlensing Super-Earth Orbiting a Low-mass Host Star
Authors: Han C. , Hirao Y. , Udalski A. , Lee C.-U. , Bozza V. , Gould A. ,   and, Abe F. , Barry R. , Bond I. A. , Bennett D. P. , Bhattacharya A. , Donachie M. , Evans P. , Fukui A. , Itow Y. , Kawasaki K. , Koshimoto N. , Li M. C. A. , Ling C. H. , Matsubara Y. , Miyazaki S. , Munakata H. , Muraki Y. , Nagakane M. , Ohnishi K. , Ranc C. , Rattenbury N. , Saito T. , Sharan A. , Sullivan D. J. , Sumi T. , Suzuki D. , Tristram P. J. , Yamada T. , Yonehara A. ,   (The MOA Collaboration), Mróz P. , Poleski R. , Kozłowski S. , Soszyński I. , Pietrukowicz P. , Skowron J. , Szymański M. K. , Ulaczyk K. , Pawlak M. , Rybicki K. , Iwanek P. ,   (The OGLE Collaboration), Albrow M. D. , Chung S.-J. , Hwang K.-H. , Jung Y. K. , Kim D. , Kim W.-T. , Kim H.-W. , Ryu Y.-H. , Shin I.-G. , Shvartzvald Y. , Yee J. C. , Zhu W. , Cha S.-M. , Kim S.-L. , Kim D.-J. , Lee D.-J. , Lee Y. , Park B.-G. , Pogge R. W. ,   (The KMTNet Collaboration)
Published: April 2018

Abstract
We report the discovery of a planetary system in which a super-Earth orbits a late M-dwarf host. The planetary system was found from the analysis of the microlensing event OGLE-2017-BLG-0482, wherein the planet signal appears as a short-term anomaly to the smooth lensing light curve produced by the host. Despite its weak signal and short duration, the planetary signal was firmly detected from the dense and continuous coverage by three microlensing surveys. We find a planet/host mass ratio of q ∼ 1.4 × 10−4. We measure the microlens parallax

from the long-term deviation in the observed lensing light curve, but the angular Einstein radius

cannot be measured because the source trajectory did not cross the planet-induced caustic. Using the measured event timescale and the microlens parallax, we find that the masses of the planet and the host are

and

, respectively, and the projected separation between them is

au. The estimated distance to the lens is

kpc. The discovery of the planetary system demonstrates that microlensing provides an important method to detect low-mass planets orbiting low-mass stars.
Kepler’s Earth-like Planets Should Not Be Confirmed without Independent Detection: The Case of Kepler-452b
Authors: Mullally Fergal , Thompson Susan E. , Coughlin Jeffrey L. , Burke Christopher J. , Rowe Jason F. 
Published: April 2018

Abstract
We show that the claimed confirmed planet Kepler-452b (a.k.a., K07016.01, KIC 8311864) cannot be confirmed using a purely statistical validation approach. Kepler detects many more periodic signals from instrumental effects than it does from transits, and it is likely impossible to confidently distinguish the two types of events at low signal-to-noise. As a result, the scenario that the observed signal is due to an instrumental artifact cannot be ruled out with 99% confidence, and the system must still be considered a candidate planet. We discuss the implications for other confirmed planets in or near the habitable zone.
A Search for Technosignatures from 14 Planetary Systems in the Kepler Field with the Green Bank Telescope at 1.15–1.73 GHz
Authors: Margot Jean-Luc , Greenberg Adam H. , Pinchuk Pavlo , Shinde Akshay , Alladi Yashaswi , MN Srinivas Prasad , Bowman M. Oliver , Fisher Callum , Gyalay Szilard , McKibbin Willow , Miles Brittany , Nguyen Donald , Power Conor , Ramani Namrata , Raviprasad Rashmi , Santana Jesse , Lynch Ryan S. 
Published: April 2018

Abstract
Analysis of Kepler mission data suggests that the Milky Way includes billions of Earth-sized planets in the habitable zone of their host stars. Current technology enables the detection of technosignatures emitted from a large fraction of the Galaxy. We describe a search for technosignatures that is sensitive to Arecibo-class transmitters located within ∼420 ly of Earth and transmitters that are 1000 times more effective than Arecibo within ∼13000 ly of Earth. Our observations focused on 14 planetary systems in the Kepler field and used the L-band receiver (1.15–1.73 GHz) of the 100 m diameter Green Bank Telescope. Each source was observed for a total integration time of 5 minutes. We obtained power spectra at a frequency resolution of 3 Hz and examined narrowband signals with Doppler drift rates between ±9 Hz s−1. We flagged any detection with a signal-to-noise ratio in excess of 10 as a candidate signal and identified approximately 850,000 candidates. Most (99%) of these candidate signals were automatically classified as human-generated radio-frequency interference (RFI). A large fraction (>99%) of the remaining candidate signals were also flagged as anthropogenic RFI because they have frequencies that overlap those used by global navigation satellite systems, satellite downlinks, or other interferers detected in heavily polluted regions of the spectrum. All 19 remaining candidate signals were scrutinized and none were attributable to an extraterrestrial source.
A Case Study of On-the-fly Wide-field Radio Imaging Applied to the Gravitational Wave Event GW151226
Authors: Mooley K. P. , Frail D. A. , Myers S. T. , Kulkarni S. R. , Hotokezaka K. , Singer L. P. , Horesh A. , Kasliwal M. M. , Cenko S. B. , Hallinan G. 
Published: April 2018

Abstract
We apply a newly developed on-the-fly mosaicing technique on the Jansky Very Large Array (VLA) at 3 GHz in order to carry out a sensitive search for an afterglow from the Advanced LIGO binary black hole merger event GW151226. In three epochs between 1.5 and 6 months post-merger, we observed a 100 deg2 region, with more than 80% of the survey region having an rms sensitivity of better than 150 μJy/beam, in the northern hemisphere with a merger containment probability of 10%. The data were processed in near real time and analyzed to search for transients and variables. No transients were found but we have demonstrated the ability to conduct blind searches in a time-frequency phase space where the predicted afterglow signals are strongest. If the gravitational wave event is contained within our survey region, the upper limit on any late-time radio afterglow from the merger event at an assumed mean distance of 440 Mpc is about 1029 erg s−1 Hz−1. Approximately 1.5% of the radio sources in the field showed variability at a level of 30%, and can be attributed to normal activity from active galactic nuclei. The low rate of false positives in the radio sky suggests that wide-field imaging searches at a few Gigahertz can be an efficient and competitive search strategy. We discuss our search method in the context of the recent afterglow detection from GW170817 and radio follow-up in future gravitational wave observing runs.
The Kepler Light Curves of AGN: A Detailed Analysis
Authors: Smith Krista Lynne , Mushotzky Richard F. , Boyd Patricia T. , Malkan Matt , Howell Steve B. , Gelino Dawn M. 
Published: April 2018

Abstract
We present a comprehensive analysis of 21 light curves of Type 1 active galactic nuclei (AGN) from the Kepler spacecraft. First, we describe the necessity and development of a customized pipeline for treating Kepler data of stochastically variable sources like AGN. We then present the light curves, power spectral density functions (PSDs), and flux histograms. The light curves display an astonishing variety of behaviors, many of which would not be detected in ground-based studies, including switching between distinct flux levels. Six objects exhibit PSD flattening at characteristic timescales that roughly correlate with black hole mass. These timescales are consistent with orbital timescales or free-fall accretion timescales. We check for correlations of variability and high-frequency PSD slope with accretion rate, black hole mass, redshift, and luminosity. We find that bolometric luminosity is anticorrelated with both variability and steepness of the PSD slope. We do not find evidence of the linear rms–flux relationships or lognormal flux distributions found in X-ray AGN light curves, indicating that reprocessing is not a significant contributor to optical variability at the 0.1%–10% level.
A Solar-flux Line-broadening Analysis
Authors: Gray David F. 
Published: April 2018

Abstract
The Fourier technique of extracting rotation rates and macroturbulence-velocity dispersions from the shapes and broadening of stellar spectral lines is applied to the solar-flux spectrum. Lines with equivalent widths less than ∼0.055 Å are shown to have the advantage over stronger lines by allowing the residual transform to be followed to higher frequencies. The standard radial-tangential macroturbulence formulation fits the observations well and yields an equatorial velocity that is within a few percent of the correct rate.
On the Full-range β Dependence of Ion-scale Spectral Break in the Solar Wind Turbulence
Authors: Wang Xin , Tu Chuanyi , He Jiansen , Wang Linghua 
Published: April 2018

Abstract
The power spectrum of magnetic fluctuations has a break at the high-frequency end of the inertial range. Beyond this break, the spectrum becomes steeper than the Kolmogorov law f
−5/3. The break frequency was found to be associated with plasma beta (β). However, the full-range β dependence of the ion-scale spectral break has not been presented before in observational studies. Here we show the continuous variation of the break frequency on full-range β in the solar wind turbulence. By using measurements from the WIND and Ulysses spacecraft, we show the break frequency (f

b
) normalized, respectively, by the frequencies corresponding to ion inertial length (f

di
), ion gyroradius (

), and cyclotron resonance scale (f

ri
) as a function of β for 1306 intervals. Their β values spread from 0.005 to 20, which nearly covers the full β range of the observed solar wind turbulence. It is found that

(

) generally decreases (increases) with β, while

is nearly a constant. We perform a linear fit on the statistical result, and obtain the empirical formulas

,

, and

to describe the relation between f

b
and β. We also compare our observations with a numerical simulation and the prediction by ion cyclotron resonance theory. Our result favors the idea that the cyclotron resonance is an important mechanism for energy dissipation at the spectral break. When β ≪ 1 and β ≫ 1, the break at f

di
and

may also be associated with other processes.
The Spin Evolution of Fast-rotating, Magnetized Super-Chandrasekhar White Dwarfs in the Aftermath of White Dwarf Mergers
Authors: Becerra L. , Rueda J. A. , Lorén-Aguilar P. , García-Berro E. 
Published: April 2018

Abstract
The evolution of the remnant of the merger of two white dwarfs is still an open problem. Furthermore, few studies have addressed the case in which the remnant is a magnetic white dwarf with a mass larger than the Chandrasekhar limiting mass. Angular momentum losses might bring the remnant of the merger to the physical conditions suitable for developing a thermonuclear explosion. Alternatively, the remnant may be prone to gravitational or rotational instabilities, depending on the initial conditions reached after the coalescence. Dipole magnetic braking is one of the mechanisms that can drive such losses of angular momentum. However, the timescale on which these losses occur depends on several parameters, like the strength of the magnetic field. In addition, the coalescence leaves a surrounding Keplerian disk that can be accreted by the newly formed white dwarf. Here we compute the post-merger evolution of a super-Chandrasekhar magnetized white dwarf taking into account all the relevant physical processes. These include magnetic torques acting on the star, accretion from the Keplerian disk, the threading of the magnetic field lines through the disk, and the thermal evolution of the white dwarf core. We find that the central remnant can reach the conditions suitable to develop a thermonuclear explosion before other instabilities (such as the inverse beta-decay instability or the secular axisymmetric instability) are reached, which would instead lead to gravitational collapse of the magnetized remnant.
Chronique des constatations du Comité des droits de l’homme, année 2017
Authors: Duclaux de L’Estoille Marie 
Published: April 2018

Durant l’année 2017, le Comité des droits de l’homme a examiné une centaine de communications individuelles relatives à la mise en œuvre du Pacte international relatif aux droits civils et politiques. Deux thèmes sont quantitativement majoritaires : la question du non-refoulement appliquée au système de Dublin dans l’Union européenne et celle des disparitions forcées. Outre ces questions caractéristiques des droits civils et politiques, le Comité s’est penché sur des questions relatives aux droits des femmes et à l’identité de genre.
Climate change and vulnerability discourse by students at a South African university
Authors: Mugambiwa Shingirai S. , Dzomonda Obey 
Published: April 2018

Climate change is expected to pose grave consequences to communities around the world. It is predicted that many people, mostly in the developing world, will experience shortages of water and food as well as numerous health-related effects because of climate change. Therefore, rigorous global action is needed to enable developing countries to adapt to the effects of climate change. Universities play a pivotal role in addressing these issues and their impacts through research and technological innovations. Hence, assessing the extent to which university students understand climate change and its impacts displays the extent of hope in mitigating future changes in climatic conditions. This article assesses the knowledge and understanding of climate change and its impacts by students at an institution of higher learning in South Africa. This study utilised a quantitative approach and a descriptive design. The convenience method was used to obtain participants for the study. Self-administered questionnaires were utilised in a survey to collect data from the participants. A sample of 90 university students participated in the survey. Data analysis included descriptive statistics and T-tests. Reliability was measured using the Cronbach’s alpha. The study discovered that university students have low knowledge and understanding of climate change. As a result, the study concluded that if students could be well-informed about climate change issues, they could positively contribute to the development of their communities by crafting smart climate change mitigation and adaptation skills.
Effect of SiO2 Dispersion on Chlorine-Induced High-Temperature Corrosion of High-Velocity Air-Fuel Sprayed NiCrMo Coating
Authors: Sadeghi Esmaeil , Markocsan Nicolaie , Hussain Tanvir , Huhtakangas Matti , Joshi Shrikant 
Published: April 2018

NiCrMo coatings with and without dispersed SiO2 were deposited using high-velocity air-fuel technique. Thermogravimetric experiments were conducted in 5% O2 + 500 vppm HCl + N2 with and without a KCl deposit at 600°C for up to 168 h. The SiO2-containing coating showed lower weight change as a result of formation of a protective and adherent Cr-rich oxide scale. SiO2 decelerated short-circuit diffusion of Cr3+ through scale’s defects, e.g., vacancies, and promoted the selective oxidation of Cr to form the protective Cr-rich oxide scale. Furthermore, the presence of SiO2 led to less subsurface depletion of Cr in the coating, and accordingly less corrosion of the substrate. The formed corrosion product on the SiO2-free coating was highly porous, non-adherent, and thick.