bluuebunny/crossref_metadata_2025 huggingface dataset:
Cobalt‐Tungsten‐Boron as an Active Electrocatalyst for Water Electrolysis
Authors: Cao Guo‐Xuan , Xu Ning , Chen Zheng‐Jun , Kang Qing , Dai Hong‐Bin , Wang Ping
Published: July 2017

Electrochemically splitting water to produce clean hydrogen fuel requires high‐performance electrocatalysts. Here, we report transition metal‐boron alloy Co‐W−B is an active electrocatalyst for water electrolysis. The Co‐W−B catalyst can be readily deposited on nickle foam (NF) using a simple electroless plating method. A combination of phase/chemical state/microstructural analyses of the Co‐W−B electrocatalyst was conducted using XRD, TEM, Raman spectroscopy and XPS techniques. The properly annealed Co‐W−B/NF catalyst with an optimal composition exhibits a low overpotential along with a high stability for the hydrogen evolution reaction (HER) in alkaline solution, which is among the best reported levels for non‐noble HER catalysts. In addition, the Co‐W−B/NF catalyst also shows moderate activity towards the oxygen evolution reaction (OER). These study results highlight the potential of transition metal‐boron alloys as high‐performance and low‐cost electrocatalyst for water splitting.
Electrocatalysts Derived from Metal–Organic Frameworks for Oxygen Reduction and Evolution Reactions in Aqueous Media
Authors: Qian Yuhong , Khan Inayat Ali , Zhao Dan
Published: July 2017

Electrochemical energy conversion and storage devices such as fuel cells and metal–air batteries have been extensively studied in recent decades for their excellent conversion efficiency, high energy capacity, and low environmental impact. However, sluggish kinetics of the oxygen‐related reactions at air cathodes, i.e., oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are still worth improving. Noble metals such as platinum (Pt), iridium (Ir), ruthenium (Ru) and their oxides are considered as the benchmark ORR and OER electrocatalysts, but they are expensive and prone to be poisoned due to the fuel crossover effect, and may suffer from agglomeration and leaching after long‐term usage. To mitigate these limits, it is highly desirable to design alternative ORR/OER electrocatalysts with prominent performance. Metal–organic frameworks (MOFs) are a class of porous crystalline materials consisting metal ions/clusters coordinated by organic ligands. Their crystalline structure, tunable pore size and high surface area afford them wide opportunities as catalytic materials. This Review covers MOF‐derived ORR/OER catalysts in electrochemical energy conversion, with a focus on the different strategies of material design and preparation, such as composition control and nanostructure fabrication, to improve the activity and durability of MOF‐derived electrocatalysts.
Optimal allocation of wind turbine generator in active distribution network
Authors: Li Ke , Tai Nengling , Zhang Shenxi , Sakis Meliopoulos A. P.
Published: July 2017

Nowadays, more and more wind turbine generators (WTGs) are being integrated into power systems. In this paper, an optimal WTG allocation model with the objective of minimizing the annual cost is proposed. The model can take into account the time‐sequential correlation between the wind speed and load demand, as well as four kinds of active management measures, i.e. regulating the on‐load tap changer of the transformer, curtailing the output power of WTG, regulating the power factor of WTG, and managing the demand side. The time‐sequential correlation is handled by the joint probability distribution method. A hybrid solving strategy combining the fuzzy adaptive particle swarm optimization algorithm and primal‐dual interior point method is developed to get the optimal solutions. Case studies carried out on the IEEE 33‐bus active distribution network verify the feasibility of the developed model and the high efficiency of the proposed solving strategy. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
The impact of the CT saturation on the HVDC protection and its countermeasure
Authors: Cao Wenbin , Qi Xuanwei , Zhang Kanjun , Yin Xianggen , Zhang Zhe , Guo Qian
Published: July 2017

Converter protection, including bridge differential protection and valve short‐circuit protection, frequently malfunctions during the disturbance from an AC system, such as the short‐circuit fault and the inrush current, which severely threatens the safe and stable operation of an AC/DC hybrid power system. This paper analyzes the cause of such maloperation based on mechanism analysis and simulation tests. It is found that saturation of the current transformer in the delta winding of the YD converter transformer during the disturbance of the AC system is the main reason for this sort of maloperation. To solve this problem, this paper proposes a countermeasure by introducing the zero‐sequence circulating current as the restraint current of the bridge differential protection. The time difference between the increase of the zero‐sequence circulating current and the rise of the bridge differential current is utilized to determine whether to apply the proposed countermeasure. Simulation tests indicate that this countermeasure can improve the reliability of the bridge differential protection during the disturbance in the AC system, without affecting the sensitivity and operation speed of the bridge differential protection for the internal fault. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
Slicing the pie: how big could carbon dioxide removal be?
Authors: Psarras Peter , Krutka Holly , Fajardy Mathilde , Zhang Zhiqu , Liguori Simona , Dowell Niall Mac , Wilcox Jennifer
Published: July 2017

The current global dependence on fossil fuels to meet energy needs continues to increase. If a 2°C warming by 2100 is to be prevented, it will become important to adopt strategies that not only avoid CO2 emissions but also allow for the direct removal of CO2 from the atmosphere, enabling the intervention of climate change. The primary direct removal methods discussed in this review include land management and mineral carbonation in addition to bioenergy and direct air capture with carbon capture and reliable storage. These methods are discussed in detail, and their potential for CO2 removal is assessed. The global upper bound for annual CO2 removal was estimated to be 12, 10, 6, and 5 GtCO2/year for bioenergy with carbon capture and reliable storage (BECCS), direct air capture with reliable storage (DACS), land management, and mineral carbonation, respectively—giving a cumulative value of ~35 GtCO2/year. However, in the case of DACS, global data on the overlap of low‐emission energy sources and reliable CO2 storage opportunities—set as a qualification for DAC viability—were unavailable, and the potential upper bound estimate is thus considered conservative. The upper bounds on the costs associated with the direct CO2 removal methods varied from approximately $100/tCO2 (land management, BECCS, and mineral carbonation) to $1000/tCO2 for DACS (again, these are the upper bounds for costs). In this review, these direct CO2 removal technologies are found to be technically viable and are potentially important options in preventing 2°C warming by 2100. WIREs Energy Environ 2017, 6:e253. doi: 10.1002/wene.253

This article is categorized under:

Bioenergy > Climate and Environment

Energy and Climate > Climate and Environment

Energy and Development > Climate and Environment
Indexing ages of antelope jackrabbits and other Leporids using x‐ray
Authors: Altemus Maria M. , Babb Randall D. , Brown David E. , Cataldo Lynne , Heffelfinger Jim , Klima Karen , O'Brien James , Mulligan Grant
Published: July 2017

The ability to determine wildlife age classes is important for wildlife management and the key to understanding the life histories of species. We used radiograph images of the epiphyseal cartilage at the distal end of the radius and the age‐class criteria developed by Lechleitner (1959) for black‐tailed jackrabbits (Lepus californicus) to determine age classes for antelope jackrabbits (L. alleni) between 2011–2016. Using 2 known‐age antelope jackrabbits, we found that 3 developmental phases similar to those identified by Lechleitner (1959; class 1 [juvenile: <7 months], class 2 [subadult: 7–11.4 months], and class 3 [adult: >11.4 months]) were also applicable to radiographs of forelegs of antelope jackrabbits. Although requiring some interpretive experience, we consider this technique superior to other lagomorph aging methods because radiographs can be obtained from live and dead animals. Using this method, biologists can determine ages of individuals in the population, which would help to estimate recruitment rates and predict population changes. © 2017 The Wildlife Society.
Dissolved organic carbon (DOC) input to the soil: DOC fluxes and their partitions during the growing season in a cool‐temperate broad‐leaved deciduous forest, central Japan
Authors: Chen Siyu , Yoshitake Shinpei , Iimura Yasuo , Asai Chiyuki , Ohtsuka Toshiyuki
Published: July 2017

Dissolved organic carbon (DOC) plays an important role in C cycling in forest ecosystems. Here we measured the concentrations and fluxes of DOC in a cool‐temperate broad‐leaved deciduous forest (Takayama Forest) to quantify the contribution of DOC from different forest water flux conditions. Mean DOC concentration during the growing season increased in the sequence from bulk precipitation (2.98 ± 0.45 mg L−1), throughfall above dwarf bamboo (6.84 ± 0.45 mg L−1), throughfall below dwarf bamboo (7.08 ± 0.42 mg L−1), stemflow (15.05 ± 0.98 mg L−1), and litter leachate (21.33 ± 1.01 mg L−1). Litter leachate DOC concentration, being high in spring and autumn, which was fairly correlated with the amount of litterfall of bamboo and trees. In stemflow, the DOC concentration was high during early summer and gradually decreased, in addition, it also showed dramatic variation among different plant species. Litter leachate (72.5%) accounted for most of the DOC input to the soil during the growing season (311.5 kg C ha−1 7 months−1), while stemflow (1.6%) contributed the least. A great quantity of precipitation at the study site was associated with a subsequent high atmospheric contribution of DOC flux (8.6%), which was more than half of throughfall (16.5%). The high input of DOC to the soil and andisol soil characteristics at the Takayama Forest suggest that the DOC fluxes are vital to the soil carbon sequestration. Therefore, DOC fluxes should be taken into account when the carbon balance is assessed at forest ecosystems.
The influence of residual apixaban on bleeding complications during and after catheter ablation of atrial fibrillation
Authors: Mukai Yutaro , Wada Kyoichi , Miyamoto Koji , Nakagita Kazuki , Fujimoto Mai , Hosomi Kouichi , Kuwahara Takeshi , Takada Mitsutaka , Kusano Kengo , Oita Akira
Published: July 2017

Background

The periprocedural protocol for atrial fibrillation (AF) ablation commonly includes anticoagulation therapy. Apixaban, a direct oral anticoagulant, is currently approved for clinical use; however, little is known about the effects of residual apixaban concentration on bleeding complications during/after AF ablation. Therefore, we measured residual apixaban concentration by using mass spectrometry and examined the anticoagulant's residual effects on bleeding complications.

Methods

Fifty‐eight patients (Mean age of 64.7±12.5 years; 31 males, 27 females) were enrolled and administered apixaban twice daily. We analyzed trough apixaban concentration, activated clotting time (ACT), heparin dose, and bleeding complications during/after AF ablation. Apixaban concentrations were directly measured using mass spectrometry.

Results

Bleeding complications were observed in 19 patients (delayed hemostasis at the puncture site, 16; hematuria, 3; hemosputum, 1). No patient required blood transfusion. The mean trough apixaban concentration was significantly lower in patients with bleeding complications than without (152.4±73.1 vs. 206.8±98.8 ng/mL respectively, P=0.037), while the heparin dose to achieve ACT>300 s was significantly higher in patients with bleeding complications (9368.4±2929.0 vs. 7987.2±2135.2 U/body respectively, P=0.046). Interestingly, a negative correlation was found between the trough apixaban concentration and the heparin dose to achieve ACT>300 s (P=0.033, R=‐0.281).

Conclusions

Low residual plasma apixaban is associated with a higher incidence of bleeding complications during/after AF ablation, potentially because of a greater heparin requirement during AF ablation.
Low Plasma Testosterone is Associated with Elevated Cardiovascular Disease Biomarkers
Authors: Pastuszak Alexander W. , Kohn Taylor P. , Estis Joel , Lipshultz Larry I.
Published: July 2017

Background

The relation between testosterone (T) plasma concentration and cardiovascular (CV) risk is unclear, with evidence supporting increased risk in men with low and high T levels. Few studies have assessed CV risk as a function of plasma T levels using objective biomarkers.

Aim

To determine the relation between T levels and high-sensitivity CV risk biomarkers.

Methods

Ten thousand forty-one male patients were identified in the database of a commercial clinical laboratory performing biomarker testing. Patients were grouped by total T concentration and associations with the following biomarkers were determined: cardiac troponin I (cTnI), endothelin-1 (ET-1), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), interleukin-17A, N-terminal pro–B-type natriuretic peptide (NTproBNP), high-density lipoprotein (HDL) cholesterol, high-sensitivity C-reactive protein (hs-CRP), hemoglobin A1c (HbA1c), and leptin.

Outcomes

Association of CV risk markers with levels of T in men.

Results

The median age of the cohort was 58 years (interquartile range = 48–68), and the median plasma T level was 420 ng/dL (interquartile range = 304–565); T levels did not vary with patient age. An inverse relation between plasma T levels and CV risk was observed for 9 of 10 CV markers: cTnI, ET-1, IL-6, TNF-α, NTproBNP, HDL cholesterol, hs-CRP, HbA1c, and leptin. Even after adjusting for age, body mass index, HbA1c, hs-CRP, and HDL cholesterol levels, the CV markers IL-6, ET-1, NTproBNP, and leptin were significantly associated with a T level lower than 250 ng/dL.

Clinical Implications

Men with low T levels could be at increased risk for increased CV disease as seen by increased CV risk markers.

Strength and Limitations

This study was performed in a group of 10,041 men and is the first study to examine CV risk associated with circulating T levels using a large panel of 10 objective biomarkers. This study is limited by an absence of clinical data indicating whether men had pre-existing CV disease or other CV risk factors.

Conclusion

Men with low plasma T levels exhibit increases in CV risk markers, consistent with a potential increased risk of CV disease.
New paradigm in advanced composite and nanocomposite design
Authors: Owuor Peter Samora , Hart Amelia C. , Lou Jun , Tiwary Chandra Sekhar , Ajayan Pulickel M.
Published: July 2017

Advanced composite materials are characterized by lightweight and unusually high stiffness, strength, modulus, etc. [ 1 , 2 ]. Their application field keeps on expanding as cheaper methods for synthesizing raw materials are found. Composite materials are now found in virtually all facets of applied materials [3] . Unlike a few decades ago when their application was limited to small parts; for example spoilers, failings, bonnets, etc., currently a new generation of airplane fuselage and wings are completely made of high-performance fiber reinforced composites [ 4 – 6 ]. The inherent high specific strength, low density, chemical and corrosion resistance [7] make them ideal for future applications. Typically, composite materials consist of a combination of two or more materials that are mixed with an aim of achieving a specific structural properties [8] . An effective composite should be able to optimize the properties of the individual components as one.
The contribution of fish studies to the “number sense” debate
Authors: Agrillo Christian , Bisazza Angelo
Published: July 2017

Leibovich et al. propose that number sense is not innate but gradually emergent during ontogeny following experience. We argue that this hypothesis cannot be reasonably tested in humans, in which the contribution of neural maturation and experience cannot be experimentally manipulated. Studies on animals, especially fish, can more effectively provide critical insights into the innate nature of numerical abilities.
Multitudes are adaptable magnitudes in the estimation of number
Authors: Durgin Frank H.
Published: July 2017

Visual number comparison does not require participants to choose a unit, whereas units are fundamental to the definition of number. Studies using magnitude estimation rather than comparison show that number perception is compressed dramatically past about 20 units. Even estimates of 5–20 items are increasingly susceptible to effects of visual adaptation, suggesting a rather narrow range in which subitizing-like categorization processes blend into greater reliance on adaptable magnitude information.
Selecting the model that best fits the data
Authors: van Woerkom Willemijn , Zuidema Willem
Published: July 2017

Leibovich et al. argue that that none of the experiments they review really establishes that human adults, infants, or nonhuman animals are sensitive to numerosity independent of a range of continuous quantities. We do not dispute their claim that the empirical record is inconclusive but argue that model-based data analysis does offer a way to make progress.
The quest for magnetic massive stars in the Magellanic Clouds
Authors: Nazé Y. , Bagnulo S. , Walborn N. R. , Morrell N. , Wade G. A. , Szymanski M. K. , Townsend R. H. D.
Published: July 2017

The Of?p category was introduced more than 40 years ago to gather several Galactic stars with some odd properties. Since 2000, spectropolarimetry, high-resolution spectroscopy, long-term photometry, and X-ray observations have revealed their nature: magnetic oblique rotators - they all have magnetic fields that confine their winds. Several Of?p stars have now been detected in the Magellanic Clouds, likely the prototypes of magnetic massive stars at low metallicity. This contribution will present the most recent photometric, spectroscopic, and spectropolarimetric data, along with the first modeling of these objects.
X-rays from colliding winds in massive binaries
Authors: Nazé Yaël , Rauw Gregor
Published: July 2017

In a massive binary, the strong shock between the stellar winds may lead to the generation of bright X-ray emission. While this phenomenon was detected decades ago, the detailed study of this emission was only made possible by the current generation of X-ray observatories. Through dedicated monitoring and observations at high resolution, unprecedented information was revealed, putting strong constraints on the amount and structure of stellar mass-loss.
Quantitative spectroscopic analyses in the IACOB+OWN project: Massive O-type stars in the Galaxy with the current Gaia information
Authors: Holgado Gonzalo , Simón-Díaz Sergio , Barbá Rodolfo
Published: July 2017

We present the results from the quantitative spectroscopic analysis of ~280 likely single O stars targeted by the IACOB and OWN surveys. This implies the largest sample of Galactic O-type stars analyzed homogeneously to date. We used the iacob-broad and iacob-gbat tools (see Simón-Díaz et al. 2011,2015) to obtain the complete set of spectroscopic parameters which can be determined from the optical spectrum of O-type stars: projected rotational velocity (v sin i), macroturbulence velocity (vmac), effective temperature (Teff), gravity (logg), wind-strength (logQ), helium abundance (YHe), microturbulence (ξt), and the exponent of the wind-law (β).
Disentangling rotational velocity distribution of stars
Authors: Curé Michel , Rial Diego F. , Cassetti Julia , Christen Alejandra
Published: July 2017

Rotational speed is an important physical parameter of stars: knowing the distribution of stellar rotational velocities is essential for understanding stellar evolution. However, rotational speed cannot be measured directly and is instead the convolution between the rotational speed and the sine of the inclination angle vsin(i). The problem itself can be described via a Fredhoml integral of the first kind. A new method (Curé et al. 2014) to deconvolve this inverse problem and obtain the cumulative distribution function for stellar rotational velocities is based on the work of Chandrasekhar & Münch (1950). Another method to obtain the probability distribution function is Tikhonov regularization method (Christen et al. 2016). The proposed methods can be also applied to the mass ratio distribution of extrasolar planets and brown dwarfs (in binary systems, Curé et al. 2015).

For stars in a cluster, where all members are gravitationally bounded, the standard assumption that rotational axes are uniform distributed over the sphere is questionable. On the basis of the proposed techniques a simple approach to model this anisotropy of rotational axes has been developed with the possibility to “disentangling” simultaneously both the rotational speed distribution and the orientation of rotational axes.
Mass-ejection events in Be stars triggered by coupled nonradial pulsation modes
Authors: Baade D. , Rivinius Th. , Pigulski A. , Carciofi A. ,   BEST
Published: July 2017

Be stars (for an in-depth review see Rivinius, Carciofi & Martayan 2013) rotate at ⩾80% of the critical velocity and are multi-mode nonradial pulsators. Magnetic dipole fields are not detected, and binaries with periods less than 30 days are rare. The name-giving emission lines form in a Keplerian decretion disk, which is viscously re-accreted and also radiatively ablated unless replenished by outburts of unknown origin.

Months-long, high-cadence space photometry with the BRITE-Constellation nanosatellites (Pablo et al. 2016) of about 10 early-type Be stars reveals the following (cf. Baade et al. 2016a, Baade et al. 2016b):

○

Many Be stars exhibit 1 or 2 so-called Δ frequencies, which are differences between two nonradial-pulsation (NRP) frequencies and much lower (mostly less than 0.1 c/d) than the parent frequencies. The associated light curves are roughly sinusoidal. The amplitudes can exceed that of the sum of the parent amplitudes.

○

Conventional beat patterns also occur.

○

Amplitudes of both Δ and beat frequencies can temporarily be enhanced. Around phases of maximal amplitude the mean brightness is in- or decreased, and the scatter can be enhanced.

○

During high-activity phases (outbursts), broad and dense groups of numerous spikes arise in the power spectra. The two strongest groups often have a frequency ratio near 2. The phase coherence seems to be low.

○

Time coverage (less than half a year) is not yet sufficient to infer whether two Δ or beat frequencies can combine to cause long-lasting (years) superoutbursts (cf. Carciofi et al. 2012).

From these observations it is concluded:

•

The variable mean brightness and the increased Δ-frequency amplitude and scatter trace the amount of near-circumstellar matter.

•

Increase or decrease of mean brightness is aspect-angle dependent (pole-on vs. equator-on).

•

Increased amounts of near-circumstellar matter are due to rotation-assisted mass ejections caused by coupled NRP modes.

•

Observations do not constrain the location of the coupling (atmosphere or stellar interior).

•

Broad frequency groups do not represent stellar pulsation modes but circumstellar variability.

•

Be stars later than B5 are less active and may in some cases even behave differently.
The formation of Wolf-Rayet stars in the SMC is not dominated by mass transfer
Authors: Shenar Tomer , Hainich R. , Todt H. , Sander A. , Hamann W.-R. , Moffat A. , Eldridge J. J. , Pablo H. , Oskinova L. , Richardson N.
Published: July 2017

We analyzed spectra of all Wolf-Rayet stars in the Small Magellanic Cloud (SMC). We find that, unlike predicted, mass-transfer in binaries is not needed to explain their formation.
Testing the Wind-shock Paradigm for B-Type Star X-Ray Production with θ Car
Authors: Doyle T. F. , Petit V. , Cohen D. , Leutenegger M.
Published: July 2017

We present Chandra X-ray grating spectroscopy of the B0.2V star, θ Carina. θ Car is in a critical transition region between the latest O-type and earliest B-type stars, where some stars are observed to have UV-determined wind densities much lower than theoretically expected (e.g., Marcolino et al. 2009). In general, X-ray emission in this low-density wind regime should be less prominent than for O-stars (e.g., Martins et al. 2005), but observations suggest a higher than expected X-ray emission filling factor (Lucy 2012; Huenemoerder et al. 2012); if a larger fraction of the wind is shock-heated, it could explain the weak UV wind signature seen in weak wind stars, but this might severely challenge predictions of radiatively-driven wind theory.

We measured the line widths of several He-, H-like and Fe ions and the f/i ratio of He-like ions in the X-ray spectrum, which improves upon the results from Nazé et al. (2008) (XMM-Newton RGS) with additional measurements (Chandra HETG) of Mgxi and Sixiii by further constraining the X-ray emission location. The f/i ratio is modified by the proximity to the UV-emitting stellar photosphere, and is therefore a diagnostic of the radial location of the X-ray emitting plasma. The measured widths of X-ray lines are narrow, <300 km s−1 and the f/i ratios place the X-rays relatively close to the surface, both implying θ Car is a weak wind star. The measured widths are also consistent with other later-type stars in the weak wind regime, β Cru (Cohen et al. 2008), for example, and are smaller on average than earlier weak wind stars such as μ Col (Huenemoerder et al. 2012). This could point to a spectral type divide, where one hypothesis, low density, works for early-B type stars and the other hypothesis, a larger fraction of shock-heated gas, explains weak winds in late-O type stars. Archival IUE data still needs to be analyzed to determine the mass loss rate and hydrodynamical simulations will be compared with observations to determine which hypothesis works for θ Car.
Proper Motions of η Carinae’s Outer Ejecta and Its Eruptive History
Authors: Kiminki Megan M. , Reiter Megan , Smith Nathan
Published: July 2017

η Carinae, the most extreme luminous blue variable in our Galaxy, underwent a Great Eruption in the 1800s and ejected significant mass into the well-known bipolar Homunculus. But η Car's outer ejecta, a spread of dense, nitrogen-rich knots outside the Homunculus, have led to suspicion that the Great Eruption was not this star's first major mass-loss event. We have measured proper motions for nearly 800 distinct features in the outer ejecta using 21 years of HST WFPC2 and ACS imaging. With motions measured across sixteen baselines, we find that the outer ejecta are expanding ballistically and belong to three age groups: one dating to the mid-1200s, another to the mid-1500s, and a third to the early 1800s, associated with but perhaps predating the peak of the Great Eruption. These three age groups are separated in space and radial velocity. There is no evidence for interaction between the dense ejecta that could be powering η Car's soft X-ray shell, which is instead likely driven by fast, rarefied ejecta from the Great Eruption striking the older dense ejecta. The thirteenth-century event was strikingly asymmetric, ejecting mass almost entirely to one side of the star. The sixteenth-century event displays bipolar symmetry, but along a different axis than the current Homunculus. These observations provide constraints on theoretical models of η Car's behavior, as viable models must explain the repetition, timescale, and asymmetry of these major mass-loss events. For more details, see Kiminki, Reiter, & Smith (2016, MNRAS, 463, 845).
Wind inhibition by X-ray irradiation in high-mass X-ray binaries
Authors: Krtička Jiří , Kubát Jiří , Krtičková Iva
Published: July 2017

Winds of hot massive stars are driven radiatively by light absorption in the lines of heavier elements. Therefore, the radiative force depends on the wind ionization. That is the reason why the accretion powered X-ray emission of high-mass X-ray binaries influences the radiative force and may even lead to wind inhibition. We model the effect of X-ray irradiation on the stellar wind in high-mass X-ray binaries. The influence of X-rays is given by the X-ray luminosity, by the optical depth between a given point and the X-ray source, and by the distance to the X-ray source. The influence of X-rays is stronger for higher X-ray luminosities and in closer proximity of the X-ray source. There is a forbidden area in the diagrams of X-ray luminosity vs. the optical depth parameter. The observations agree with theoretical predictions, because all wind-powered high-mass X-ray binary primaries lie outside the forbidden area. The positions of real binaries in the diagram indicate that their X-ray luminosities are self-regulated.
Line-Driven Ablation of Circumstellar Disks
Authors: Kee Nathaniel Dylan , Owocki Stan , Kuiper Rolf , Sundqvist Jon
Published: July 2017

Mass is a key parameter in understanding the evolution and eventual fate of hot, luminous stars. Mass loss through a wind driven by UV-scattering forces is already known to reduce the mass of such stars by 10−10 − 10−4 M⊙/yr over the course of their lifetimes. However, high-mass stars already drive such strong winds while they are still in their accretion epoch. Therefore, stellar UV-scattering forces will efficiently ablate material off the surface of their circumstellar disks, perhaps even shutting off the final accretion through the last several stellar radii and onto a massive protostar. By using a three-dimensional UV-scattering prescription, we here quantify the role of radiative ablation in controlling the disk’s accretion rate onto forming high-mass stars. Particular emphasis is given to the potential impact of this process on the stellar upper mass limit.
The VLT-FLAMES Tarantula Survey
Authors: Vink Jorick S. , Evans C.J. , Bestenlehner J. , McEvoy C. , Ramírez-Agudelo O. , Sana H. , Schneider F. ,   VFTS
Published: July 2017

We present a number of notable results from the VLT-FLAMES Tarantula Survey (VFTS), an ESO Large Program during which we obtained multi-epoch medium-resolution optical spectroscopy of a very large sample of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). This unprecedented data-set has enabled us to address some key questions regarding atmospheres and winds, as well as the evolution of (very) massive stars. Here we focus on O-type runaways, the width of the main sequence, and the mass-loss rates for (very) massive stars. We also provide indications for the presence of atop-heavyinitial mass function (IMF) in 30 Dor.
Pre-SN neutrino emissions from ONe cores in the progenitors of CCSNe
Authors: Kato Chinami , Yamada S. , Nagakura H. , Furusawa S. , Takahashi K. , Umeda H. , Yoshida T. , Ishidoshiro K.
Published: July 2017

In order to investigate the distinguishability about the progenitors of FeCCSNe and ECSNe, we calculate the luminosities and spectra of their pre-SN neutrinos and estimate the number of events at neutrino detectors.
Observations of Bright Massive Stars Using Small Size Telescopes
Authors: Beradze Sopia , Kochiashvili Nino
Published: July 2017

The size of a telescope determines goals and objects of observations. During the latest decades it becomes more and more difficult to get photometric data of bright stars because most of telescopes of small sizes do not operate already. But there are rather interesting questions connected to the properties and evolution ties between different types of massive stars. Multi-wavelength photometric data are needed for solution of some of them. We are presenting our observational plans of bright Massive X-ray binaries, WR and LBV stars using a small size telescope. All these stars, which are presented in the poster are observational targets of Sopia Beradze’s future PhD thesis. We already have got very interesting results on the reddening and possible future eruption of the massive hypergiant star P Cygni. Therefore, we decided to choose some additional interesting massive stars of different type for future observations. All Massive stars play an important role in the chemical evolution of galaxies because of they have very high mass loss - up to 10−4M⊙/a year. Our targets are on different evolutionary stages and three of them are the members of massive binaries. We plan to do UBVRI photometric observations of these stars using the 48 cm Cassegrain telescope of the Abastumani Astrophisical Observatory.
Massive Stars in M31
Authors: Lomax Jamie R. , Peters Matthew , Wisniewski John , Dalcanton Julianne , Williams Benjamin , Lutz Julie , Choi Yumi , Sigut Aaron
Published: July 2017

Massive stars are intrinsically rare and therefore present a challenge to understand from a statistical perspective, especially within the Milky Way. We recently conducted follow-up observations to the Panchromatic Hubble Andromeda Treasury (PHAT) survey that were designed to detect more than 10,000 emission line stars, including WRs, by targeting regions in M31 previously known to host large numbers of young, massive clusters and very young stellar populations. Because of the existing PHAT data, we are able to derive an effective temperature, bolarimetric luminosity, and extinction for each of our detected stars. We report on preliminary results of the massive star population of our dataset and discuss how our results compare to previous studies of massive stars in M31.
ALMA Observation of Mass Loss from Massive Stars
Authors: Gunawan D. Y. A. Setia , Curé M. , Kanaan S. , Puls J. , Najarro F. , Sundqvist J. , Diez M. M. Rubio , Whyborn N.
Published: July 2017

We present a pilot study of using the Atacama Large Millimeter/sub-millimeter Array (ALMA) continuum observations to constrain the density structure in the intermediate wind zone of massive stars, in which the wind is extremely sensitive to clumping.
Massive stars in young VVV clusters
Authors: Alegría S. Ramírez , Borissova J. , Chené A.-N.
Published: July 2017

The role of massive stars in the Galactic evolution is crucial. During their lifetime these stars change the kinematics around them through stellar winds, affect the formation of new stars, ionise and chemically enrich the media with the final supernova explosion. But the census of both massive stars and their host clusters is still poor. We expect that still ~100 of galactic massive stellar clusters remains unknown (Hanson & Popescu, 2008).
Progenitors of binary black hole mergers detected by LIGO
Authors: Postnov Konstantin , Kuranov Alexander
Published: July 2017

Possible formation mechanisms of massive close binary black holes that can merge in the Hubble time to produce powerful gravitational wave bursts detected during advanced LIGO O1 science run are briefly discussed. The pathways include the evolution from field low-metallicity massive binaries, the dynamical formation in globular clusters and primordial black holes. Low effective black hole spins inferred for LIGO GW150914 and LTV151012 events are discussed. Population synthesis calculations of the expected spin and chirp mass distributions from the standard field massive binary formation channel are presented for different metallicities (from zero-metal Population III stars up to solar metal abundance). We conclude that that merging binary black holes can contain systems from different formation channels, discrimination between which can be made with increasing statistics of mass and spin measurements from ongoing and future gravitational wave observations.
High-mass stars in Milky Way clusters
Authors: Negueruela Ignacio
Published: July 2017

Young open clusters are our laboratories for studying high-mass star formation and evolution. Unfortunately, the information that they provide is difficult to interpret, and sometimes contradictory. In this contribution, I present a few examples of the uncertainties that we face when confronting observations with theoretical models and our own assumptions.
Reconstructing the Scene: New Views of Supernovae and Progenitors from the SNSPOL Project
Authors: Hoffman Jennifer L. , Williams G. Grant , Leonard Douglas C. , Bilinski Christopher , Dessart Luc , Huk Leah N. , Mauerhan Jon C. , Milne Peter , Porter Amber L. , Smith Nathan , Smith Paul S.
Published: July 2017

Because polarization encodes geometrical information about unresolved scattering regions, it provides a unique tool for analyzing the 3-D structures of supernovae (SNe) and their surroundings. SNe of all types exhibit time-dependent spectropolarimetric signatures produced primarily by electron scattering. These signatures reveal physical phenomena such as complex velocity structures, changing illumination patterns, and asymmetric morphologies within the ejecta and surrounding material. Interpreting changes in polarization over time yields unprecedentedly detailed information about supernovae, their progenitors, and their evolution.

Begun in 2012, the SNSPOL Project continues to amass the largest database of time-dependent spectropolarimetric data on SNe. I present an overview of the project and its recent results. In the future, combining such data with interpretive radiative transfer models will further constrain explosion mechanisms and processes that shape SN ejecta, uncover new relationships among SN types, and probe the properties of progenitor winds and circumstellar material.
Core-Collape Supernova Progenitors: Light-Curve and Stellar-Evolution Models
Authors: Bersten Melina C.
Published: July 2017

A very active area of research in the field of core-collapse supernovae (SNe) is the study of their progenitors and the links with different subtypes. Direct identification using pre- and post-SN images is a powerful method but it can only be applied to the most nearby events. An alternative method is the hydrodynamical modeling of SN light curves and expansion velocities, which can serve to characterize the progenitor (e.g. mass and radius) and the explosion itself (e.g. explosion energy and radioactive yields). This latter methodology is particularly powerful when combined with stellar evolution calculations. We review our current understanding of the properties of normal core-collapse SNe based chiefly on these two methods.
The supergiant O + O binary system HD 166734: a new study
Authors: Gosset E. , Mahy L. , Damerdji Y. , Nitschelm C. , Sana H. , Eenens P. , Nazé Y.
Published: July 2017

We present here a modern study of the radial velocity curve and of the photometric light curve of the very interesting supergiant O7.5If + O9I(f) binary system HD 166734. The physical parameters of the stars and the orbital parameters are carefully determined. We also perform the analysis of the observed X-ray light curve of this colliding-wind binary.
The very massive star content of the nuclear star clusters in NGC 5253
Authors: Smith Linda J. , Crowther Paul A. , Calzetti Daniela
Published: July 2017

The blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters. Calzetti et al. (2015) find that the two clusters have an age of 1 Myr, in contradiction to the age of 3–5 Myr inferred from the presence of Wolf-Rayet (W-R) spectral features. We use Hubble Space Telescope (HST) far-ultraviolet (FUV) and ground-based optical spectra to show that the cluster stellar features arise from very massive stars (VMS), with masses greater than 100 M⊙, at an age of 1–2 Myr. We discuss the implications of this and show that the very high ionizing flux can only be explained by VMS. We further discuss our findings in the context of VMS contributing to He ii λ1640 emission in high redshift galaxies, and emphasize that population synthesis models with upper mass cut-offs greater than 100 M⊙ are crucial for future studies of young massive clusters.
A high-contrast imaging survey of nearby red supergiants
Authors: Scicluna Peter , Siebenmorgen Ralf , Blommaert Joris , Kemper Francisca , Wesson Roger , Wolf Sebastian
Published: July 2017

Mass-loss in cool supergiants remains poorly understood, but is one of the key elements in their evolution towards exploding as supernovae. Some show evidence of asymmetric mass loss, discrete mass-ejections and outbursts, with seemingly little to distinguish them from more quiescent cases. To explore the prevalence of discrete ejections and companions we have conducted a high-constrast survey using near-infrared imaging and optical polarimetric imaging of nearby southern and equatorial red supergiants, using the extreme adaptive optics instrument SPHERE, which was designed to image planets around nearby stars. We present the initial results of this survey, including the detection of large (500 nm) dust grains in the ejecta of VY CMa and a candidate dusty torus aligned with the maser ring of VX Sgr. We briefly speculate on the consequences for our understanding of mass loss in these extreme stars.
Recent advances in non-LTE stellar atmosphere models
Authors: Sander Andreas A. C.
Published: July 2017

In the last decades, stellar atmosphere models have become a key tool in understanding massive stars. Applied for spectroscopic analysis, these models provide quantitative information on stellar wind properties as well as fundamental stellar parameters. The intricate non-LTE conditions in stellar winds dictate the development of adequate sophisticated model atmosphere codes. The increase in both, the computational power and our understanding of physical processes in stellar atmospheres, led to an increasing complexity in the models. As a result, codes emerged that can tackle a wide range of stellar and wind parameters.

After a brief address of the fundamentals of stellar atmosphere modeling, the current stage of clumped and line-blanketed model atmospheres will be discussed. Finally, the path for the next generation of stellar atmosphere models will be outlined. Apart from discussing multi-dimensional approaches, I will emphasize on the coupling of hydrodynamics with a sophisticated treatment of the radiative transfer. This next generation of models will be able to predict wind parameters from first principles, which could open new doors for our understanding of the various facets of massive star physics, evolution, and death.
Radiation Hydrodynamical Models for Type I Superluminous Supernovae: Constraints on Progenitors and Explosion Mechanisms
Authors: Nomoto Ken’ichi , Tolstov Alexey , Sorokina Elena , Blinnikov Sergei , Bersten Melina , Suzuki Tomoharu
Published: July 2017

The physical origin of Type-I (hydrogen-less) superluminous supernovae (SLSNe-I), whose luminosities are 10 to 500 times higher than normal core-collapse supernovae, remains still unknown. Thanks to their brightness, SLSNe-I would be useful probes of distant Universe. For the power source of the light curves of SLSNe-I, radioactive-decays, magnetars, and circumstellar interactions have been proposed, although no definitive conclusions have been reached yet. Since most of light curve studies have been based on simplified semi-analytic models, we have constructed multi-color light curve models by means of detailed radiation hydrodynamical calculations for various mass of stars including very massive ones and large amount of mass loss. We compare the rising time, peak luminosity, width, and decline rate of the model light curves with observations of SLSNe-I and obtain constraints on their progenitors and explosion mechanisms. We particularly pay attention to the recently reported double peaks of the light curves. We discuss how to discriminate three models, relevant models parameters, their evolutionary origins, and implications for the early evolution of the Universe.
The First 3D Simulations of Carbon Burning in a Massive Star
Authors: Cristini A. , Meakin C. , Hirschi R. , Arnett D. , Georgy C. , Viallet M.
Published: July 2017

We present the first detailed three-dimensional hydrodynamic implicit large eddy simulations of turbulent convection for carbon burning. The simulations start with an initial radial profile mapped from a carbon burning shell within a 15 M⊙stellar evolution model. We considered 4 resolutions from 1283to 10243zones. These simulations confirm that convective boundary mixing (CBM) occurs via turbulent entrainment as in the case of oxygen burning. The expansion of the boundary into the surrounding stable region and the entrainment rate are smaller at the bottom boundary because it is stiffer than the upper boundary. The results of this and similar studies call for improved CBM prescriptions in 1D stellar evolution models.
Students’ Growth Mindsets, Goals, and Academic Outcomes in	Mathematics
Authors: Bostwick Keiko C. P. , Collie Rebecca J. , Martin Andrew J. , Durksen Tracy L.
Published: July 2017

Abstract. The majority of educational research on the associations between growth constructs and academic outcomes has adopted a somewhat piecemeal approach, focusing on either growth mindset (implicit beliefs about intelligence) or growth goals. We explore an integrative approach to analyzing the impact of well-established and emerging growth constructs (viz. growth mindset, self-based growth goals, task-based growth goals) on academic outcomes in mathematics. Our participants were secondary school students (n = 4,411) in grades 7–9 from 19 schools in Australia. We used confirmatory factor analysis (CFA) and structural equation modeling (SEM) to test the measurement and substantive hypotheses in our study. We found that growth mindset, self-based growth goals, and task-based growth goals were well represented by an underlying growth orientation factor. Additionally, after controlling for five student background factors (e.g., sex, socioeconomic status [SES]), students’ growth orientation positively predicted mathematics engagement and achievement. These results contribute to the growing literature on educational growth constructs and academic success.
Implicit Theories About Willpower in Resisting Temptations and	Emotion Control
Authors: Bernecker Katharina , Job Veronika
Published: July 2017

Abstract. Previous research suggests that people’s implicit theories about willpower affect continuous self-control performance in the domain of strenuous mental activities. The present research expands these findings to two further domains of self-control: resisting temptations and emotion control. In Study 1, participants were either led to resist a temptation or not. Participants who believed that willpower gets depleted by resistance to temptations (limited-resource theory) performed significantly worse in a subsequent Stroop task compared to participants who believed that resisting temptations activates their willpower (nonlimited-resource theory). In Study 2, participants controlled their emotions during a funny video or were allowed to express them. Participants who believed that controlling emotions depletes willpower performed worse in a subsequent persistence task than those who believed that controlling emotions activates willpower. Results suggest that implicit theories about willpower are domain specific and sensitive to the domain of the initial self-control task rather than that of the subsequent self-control task.