bluuebunny/crossref_metadata_2025 huggingface dataset:
A posteriori error estimator based on derivative recovery for the discontinuous Galerkin method for nonlinear hyperbolic conservation laws on Cartesian grids
Authors: Baccouch Mahboub
Published: March 2017

In this article, we develop and analyze a new recovery‐based a posteriori error estimator for the discontinuous Galerkin (DG) method for nonlinear hyperbolic conservation laws on Cartesian grids, when the upwind flux is used. We prove, under some suitable initial and boundary discretizations, that the ‐norm of the solution is of order , when tensor product polynomials of degree at most are used. We further propose a very simple derivative recovery formula which gives a superconvergent approximation to the directional derivative. The order of convergence is showed to be . We use our derivative recovery result to develop a robust recovery‐type a posteriori error estimator for the directional derivative approximation which is based on an enhanced recovery technique. The proposed error estimators of the recovery‐type are easy to implement, computationally simple, asymptotically exact, and are useful in adaptive computations. Finally, we show that the proposed recovery‐type a posteriori error estimates, at a fixed time, converge to the true errors in the ‐norm under mesh refinement. The order of convergence is proved to be . Our theoretical results are valid for piecewise polynomials of degree and under the condition that each component, , of the flux function possesses a uniform positive lower bound. Several numerical examples are provided to support our theoretical results and to show the effectiveness of our recovery‐based a posteriori error estimator. © 2016 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 1224–1265, 2017
An Optimised Method for Routine Separation and Quantification of Major Alkaloids in Cortex Cinchona by HPLC Coupled with UV and Fluorescence Detection
Authors: Holmfred Else , Cornett Claus , Maldonado Carla , Rønsted Nina , Hansen Steen Honoré
Published: March 2017

Introduction

Authentication of herbal products to ensure efficacy and safety require efficient separation and quantification of constituents. Standard assays for Cinchona bark used for the treatment of malaria and production of quinine, either use only spectrophotometry to detect two pairs of diastereoisomers of quinine and cinchonine type alkaloids (European Pharmacopoeia, Ph.Eur.) or liquid chromatography primarily optimised for detection of the four major alkaloids. However, numerous minor alkaloids occur in Cinchona and related species and efficient separation including gradient elution is necessary in order to obtain the full pattern of constituents in bark samples.

Objective

To develop an optimised HPLC method for separation and quantitative analysis of the four major alkaloids in Cinchona bark using UV detection.

Methodology

Dimethyl sulphoxide (DMSO) extracts of 50 mg of pulverised barks were prepared using ultrasonication. The chromatographic separation was performed on an XB‐C18 column packed with 2.6 μm particles. Gradient elution using an ammonium formate buffer and methanol as organic modifier over 26 min was based on non‐chiral separation of the diastereoisomers and the high solvent selectivity of methanol. Post column UV detection was performed at 250 nm and 330 nm. Fluorescence detection was performed using 330 nm for excitation and 420 nm for emission.

Results

The optimised HPLC method facilitates efficient separation and quantification of the four major alkaloids in 26 min with a limit of quantification of 5 μg/g from 50 mg bark sample.

Conclusion

The optimised HPLC method offers a simple and efficient quantification of the four major alkaloids. Copyright © 2017 John Wiley & Sons, Ltd.
Adsorption of phenazine dyes using poly(hydroxamic acid) hydrogels from aqueous solutions
Authors: Saraydın Dursun , Işıkver Yasemin , Karadağ Erdener
Published: March 2017

Swelling and adsorption properties of poly(hydroxamic acid), (PHA) hydrogels in aqueous solutions of some phenazine dyes such as Neutral Red, Safranin T, and Janus Green have been investigated. PHA hydrogels containing N,N′ methylenebisacrylamide or ethyleneglycoldimethacrylate were used in experiments on swelling, diffusion and adsorption of the dyes. The equilibrium swelling (Seq) values of PHA hydrogels in aqueous solutions of the phenazine dyes were calculated as 2.16–33.25 g g−1. Swelling kinetic parameters such as initial swelling rate, swelling rate constant, and maximum swelling were found. Dye diffusion into hydrogels was found to be non‐Fickian in character. Diffusion coefficients are ranged 1.32 × 10−6 cm2 s−1 − 44.70 × 10−6 cm2 s−1. Adsorption of the phenazine dyes onto PHA hydrogels was studied by batch technique. PHA hydrogels in the phenazine dye solutions showed the dark coloration. The data was found that Freundlich isotherm model fits. According the Freundlich constants, the adsorption isotherms are of S‐type in Giles classification. All swelling and binding parameters for PHA‐EGDMA were found to be higher than those for PHA‐NNMBA. The type of crosslinker influenced the swelling, binding, and sorption more than the type of dye. Finally, it can be said that PHA hydrogels may be used a sorbent for removal of dyes. POLYM. ENG. SCI., 58:310–318, 2018. © 2017 Society of Plastics Engineers
Characterization of valley flows within two confluent valleys under stable conditions: observations from the KASCADE field experiment
Authors: Duine Gert‐Jan , Hedde Thierry , Roubin Pierre , Durand Pierre , Lothon Marie , Lohou Fabienne , Augustin Patrick , Fourmentin Marc
Published: March 2017

Wind patterns in main and tributary valley systems undergo diurnal variations that are very dependent on the valley's dimensions. Characterizing the down‐valley winds is important for pollutant dispersion studies. It is also a challenge for numerical simulations. This paper uses KASCADE (KAtabatic winds and Stability over CAdarache for Dispersion of Effluents) observations to describe down‐valley flow development and characteristics in two intersecting, shallow valleys of different sizes located in the pre‐alpine region of southeast France. The Durance Valley and its tributary valley, the Cadarache Valley, are different in depth (200 and 100 m depth, respectively), slope (0.2 and 1.2°), width (5–8 and 1–2 km) and length (>50 and 6 km). Both down‐valley flows were dominant features for the period of measurements. The distinct valley scales lead to different characteristics: the smaller Cadarache down‐valley wind is primarily thermally driven and attains wind speeds of up to 1–4 m s−1 with its jet nose at around 30 m in height above ground. The flow at that height initiates 2 h after sensible heat flux turnover, a time‐scale which relates to a linear wave solution for along‐valley winds. The Durance down‐valley wind involves larger scales –for both terrain features and large‐scale circulation –and is related to a mountain‐to‐plain circulation. Therefore its onset occurs with a delay of ∼6 h after sunset. It reaches speeds of 4–8 m s−1 and a depth of 175–225 m above ground. Its highest occurrence is just after sunrise. Between the two valley winds, a shear layer is observed, the origin of which could be a combination of a Cadarache valley flow return current and a Durance down‐valley wind stream redirected by orography.
Rapid and sensitive determination of multiple endocrine‐disrupting chemicals by ultrasound‐assisted in situ derivatization dispersive liquid–liquid microextraction coupled with ultra‐high‐performance liquid chromatography/tandem mass spectrometry
Authors: Wei Na , Zheng Zhenjia , Wang Yuhua , Tao Yanduo , Shao Yun , Zhu Shuyun , You Jinmao , Zhao Xian‐En
Published: March 2017

Rationale

Endocrine‐disrupting chemicals (EDCs) in environment samples and food stuffs are an increasing serious public health issue due to their potency to interfere and deregulate several aspects of the endocrine system. Because of their extremely low abundance, it remains a challenging task to develop a sensitive detection method.

Methods

4'‐Carbonyl chloride rosamine (CCR) was used as a derivatization reagent for EDCs for the first time. A new ultrasound‐assisted in situ derivatization/dispersive liquid‐liquid microextraction (UA‐DLLME with in situ derivatization) method for multiple EDCs including five estrogens, two alkylphenols, eight bisphenols, seven parabens and triclosan coupled with ultra‐high‐performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) has been developed and validated.

Results

The ionization efficiency of EDCs was greatly enhanced through the introduction of a permanent charged moiety of CCR into the derivatives during electrospray ionization (ESI)‐MS analysis. The main variables potentially affecting the UA‐DLLME with in situ derivatization process are optimized. The recoveries and matrix effects of 23 EDCs for the spiking samples were in the range of 83.0–116.0% and 85.8–114.6%, respectively. Good method reproducibility was achieved.

Conclusions

The limits of detection (LODs) for 23 EDCs were 0.05–0.40 ng/L and 0.03–0.25 ng/g (dry weight, d.w.) for environment samples and food stuffs, respectively. The proposed method has been demonstrated to be suitable for simultaneous determination of multiple EDCs in real samples with high sensitivity, speediness, and good sample clean‐up ability. Copyright © 2017 John Wiley & Sons, Ltd.
A key recovery attack on an error‐correcting code‐based lightweight security protocol
Authors: Erguler Imran
Published: March 2017

One interesting radio‐frequency identification (RFID) application type is RFID searching that aims to hear a specific RFID tag from a large group of tags, that is, ability of detecting whether a target RFID tag is nearby. Very recently, a lightweight protocol using error‐correcting codes has been proposed by Chen et al. to provide a solution in this field. The authors give a detailed analysis of their protocol in terms of security, privacy, communication overhead, and hardware cost, and they claim that it is a realizable scheme with fulfilling security and privacy requirements. In this study, however, we investigate the security aspects of this protocol and clearly demonstrate its security flaws that completely allow an adversary to exploit the system. In particular, by using linear properties of error‐correcting coding, we first describe a tag tracing attack that undermines untraceability property, which is one of the design objectives. Then along with its implementation details, we present a key recovery attack that dramatically reduces the search space of a tag's secret key and show that an adversary can compromise it in convenient time by only querying this tag for several times. As an illustrative example, we retrieve the secret key of the protocol in 2 h for the suggested linear block code
. Copyright © 2017 John Wiley & Sons, Ltd.
The process of self‐regulation in adolescents: A narrative approach
Authors: Conover Kelly , Daiute Colette
Published: March 2017

This qualitative study utilized a narrative approach to explore the process of self‐regulation in adolescents and to examine the functions of various relational genres on psychological state and context expressions in this process. Nineteen participants, who live in high‐risk settings were recruited from a youth development and life skills program located at an urban public high school in the United States. The goal of this project is to craft a process method for research and practice on adolescents' self‐regulation while providing evidence for self‐regulation being a complex process. This research uses an exploratory study design with a narrative approach, utilizing text message based activities in the method. Findings from the plot analysis suggest that for adolescents, the process of self‐regulation begins as highly emotional and then becomes a more emotionally and cognitively balanced process. In addition, adolescents utilize different strategies to resolve conflict situations across different contexts and relational genres.
Catechol-O-methyltransferase gene promoter methylation as a peripheral biomarker in male schizophrenia
Authors: Gao S. , Cheng J. , Li G. , Sun T. , Xu Y. , Wang Y. , Du X. , Xu G. , Duan S.
Published: March 2017

As an epigenetic modification, DNA methylation may reflect the interaction between genetic and environmental factors in the development of schizophrenia (SCZ). Catechol-O-methyltransferase (COMT) gene is a promising candidate gene of SCZ. In the present study, we investigate the association of COMT methylation with the risk of SCZ using bisulfite pyrosequencing technology. Significant association between DNA methylation of COMT and the risk of SCZ is identified (P = 1.618e−007). A breakdown analysis by gender shows that the significance is driven by males (P = 3.310e−009), but not by females. DNA methylation of COMT is not significantly associated with SCZ clinical phenotypes, including p300 and cysteine level. No interaction is found between COMT genotypes and the percent methylation of this gene. Receiver operating characteristic (ROC) curve shows that DNA methylation of COMT is able to predict the SCZ risk in males (area under curve [AUC] = 0.802, P = 1.91e−007). The current study indicates the clinical value of COMT methylation as a potential male-specific biomarker in SCZ diagnosis.
Cognitive control and reward/loss processing in Internet gaming disorder: Results from a comparison with recreational Internet game-users
Authors: Dong G. , Li H. , Wang L. , Potenza M.N.
Published: March 2017

Although playing of Internet games may lead to Internet gaming disorder (IGD), most game-users do not develop problems and only a relatively small subset experiences IGD. Game playing may have positive health associations, whereas IGD has been repeatedly associated with negative health measures, and it is thus important to understand differences between individuals with IGD, recreational (non-problematic) game use (RGU) and non-/low-frequency game use (NLFGU). Individuals with IGD have shown differences in neural activations from non-gamers, yet few studies have examined neural differences between individuals with IGD, RGU and NLFGU. Eighteen individuals with IGD, 21 with RGU and 19 with NFLGU performed a color-word Stroop task and a guessing task assessing reward/loss processing. Behavioral and functional imaging data were collected and compared between groups. RGU and NLFGU subjects showed lower Stroop effects as compared with those with IGD. RGU subjects as compared to those with IGD demonstrated less frontal cortical activation brain activation during Stroop performance. During the guessing task, RGU subjects showed greater cortico-striatal activations than IGD subjects during processing of winning outcomes and greater frontal brain during processing of losing outcomes. Findings suggest that RGU as compared with IGD subjects show greater executive control and greater activations of brain regions implicated in motivational processes during reward processing and greater cortical activations during loss processing. These findings suggest neural and behavioral features distinguishing RGU from IGD and mechanisms by which RGU may be motivated to play online games frequently yet avoid developing IGD.
Advanced Hip Osteoarthritis Causing Autonomic Dysreflexia and Severe Spasticity in a Patient With Spinal Cord Injury: A Case Report
Authors: Bickelhaupt Brittany , Richard Megan , Trbovich Michelle
Published: March 2017

The life expectancy of persons with spinal cord injury (SCI) is increasing due to advances in medicine and technology. As a result, there is a higher incidence of age‐associated illnesses in this population. Degenerative joint disease is a common age‐associated illness that causes pain and thus, in persons with SCI above the T6 level, can serve as a noxious stimulus to trigger autonomic dysreflexia (AD). This is a case report of severe bilateral hip osteoarthritis (OA) causing unyielding AD in a person with tetraplegia leading to bilateral girdle stone surgeries. Hip OA as an etiology for AD has not previously been reported and is important to recognize as this population continues to age and to develop age‐associated diseases.

Level of Evidence

V
Playing with Fire: International Criminal Law, Transitional Justice, and the Implementation of the Colombian Peace Agreement
Authors: Urueña René
Published: March 2017

On November 30, 2016, after much uncertainty, the Colombian Congress finally approved a historic peace deal between the Colombian government and the Fuerzas Armadas Revolucionarias de Colombia (FARC), bringing to an end the country's fifty-year conflict. This peace deal was a historical achievement, and had important ramifications for international law, as discussed in a recent AJIL Unbound symposium. But once the spotlights were off, the government was faced with the daunting challenge of implementing the complex, lengthy accord. In particular, the government had to draw up and pass through Congress the legal and constitutional framework for the transitional justice process—a key component of the peace deal. It is there, in the subtle details of domestic criminal law, where the balance between peace and justice must be achieved.
Leon Pinsker'sAutoemancipation!and the Emergence of German as a Language of Jewish Nationalism
Authors: Volovici Marc
Published: March 2017

This article examines the role of the German language in early Jewish nationalism. It focuses on the publication, reception, and afterlife of the pamphletAutoemancipation!, published in 1882 by Leon Pinsker, a Russian Jewish doctor. The first Jewish nationalist pamphlet to be written in German by a Russian Jew, its rhetoric and terminology tapped into various Jewish and European discourses of emancipation. Pinsker not only challenged the legal-political conception of emancipation as it had been commonly used in German-Jewish discourse, but also mobilized its social and revolutionary connotations, which had been associated with radical European political movements since 1848. Moreover,Autoemancipation!marked a shift in Jewish political culture with regard to the potential function of the German language. Since the late eighteenth century and through the nineteenth century, German had a controversial status in Central and Eastern European Jewish societies given its association with Jewish Enlightenment, religious reform, secularization, and assimilation. Pinsker was the first to use German as a transnational language aimed at promoting the Jewish national cause. In this respect,Autoemancipation!set in motion a process whereby German became the chief language of Jewish nationalist activism.
Finding Hope in Synthetic Biology
Authors: TAKALA TUIJA
Published: March 2017

For some, synthetic biology represents great hope in offering possible solutions to many of the world’s biggest problems, from hunger to sustainable development. Others remain fearful of the harmful uses, such as bioweapons, that synthetic biology can lend itself to, and most hold that issues of biosafety are of utmost importance. In this article, I will evaluate these points of view and conclude that although the biggest promises of synthetic biology are unlikely to become reality, and the probability of accidents is fairly substantial, synthetic biology could still be seen to benefit humanity by enhancing our ethical understanding and by offering a boost to world economy.
Safeguarding Confidentiality in Electronic Health Records
Authors: SHENOY AKHIL , APPEL JACOB M.
Published: March 2017

Electronic health records (EHRs) offer significant advantages over paper charts, such as ease of portability, facilitated communication, and a decreased risk of medical errors; however, important ethical concerns related to patient confidentiality remain. Although legal protections have been implemented, in practice, EHRs may be still prone to breaches that threaten patient privacy. Potential safeguards are essential, and have been implemented especially in sensitive areas such as mental illness, substance abuse, and sexual health. Features of one institutional model are described that may illustrate the efforts to both ensure adequate transparency and ensure patient confidentiality. Trust and the therapeutic alliance are critical to the provider–patient relationship and quality healthcare services. All of the benefits of an EHR are only possible if patients retain confidence in the security and accuracy of their medical records.
Reversing the Marginalization of Global Environmental Politics in International Relations: An Opportunity for the Discipline
Authors: Green Jessica F. , Hale Thomas N.
Published: March 2017

Despite the increasing urgency of many environmental problems, environmental politics remains at the margins of the discipline. Using data from the Teaching, Research, and International Policy (TRIP) project, this article identifies a puzzle: the majority of international relations (IR) scholars find climate change among the top three most important policy issues today, yet fewer than 4% identify the environment as their primary area of research. Moreover, environmental research is rarely published in top IR journals, although there has been a recent surge in work focused on climate change. The authors argue that greater attention to environmental issues—including those beyond climate change—in IR can bring significant benefits to the discipline, and they discuss three lines of research to correct this imbalance.
The Role of Social Group Membership on Classroom Participation
Authors: Yaylacı Şule , Beauvais Edana
Published: March 2017

Active and cooperative learning is integral to many social science classes, as it increases student motivation, improves communication skills, and stimulates creative thinking. Many political science departments break large lectures down into smaller, weekly tutorial groups to foster active learning. But do all students participate equally in active, participatory learning? We use an original dataset measuring self-reported participation and a number of important predictors (student gender, race, and language proficiency) collected from 700 undergraduate students in 91 political science tutorials. We find that participation does vary across social groups, even when controlling for psychological and some contextual factors. Female students participate significantly less than males, racial minorities report speaking less frequently than white students, and students with lower English-proficiency (the language of instruction) also participate less. In light of these findings, we offer suggestions for instructors on how to motivate all students to find their voice in the classroom.
e-MERLIN Radio Continuum Measurements of OB Star Winds in CYG OB2
Authors: Morford Jack , Prinja Raman , Fenech Danielle
Published: March 2017

Here, we report on the first results from the e-MERLIN Cyg OB2 Radio Survey (COBRaS), which is designed to exploit e-MERLIN’s enhanced capabilities to conduct deep-field mapping of the tremendously rich Cyg OB2 association. The project aims to deliver the most detailed radio census of the most massive OB association in the northern hemisphere. There exists considerable evidence for clumping in the winds of hot stars, which has hugely important consequences for mass-loss determinations. The amount of mass lost from a massive star is a crucial parameter required for stellar and cluster evolution models that are paramount to our understanding of the formation and evolution of massive star clusters. Presenting some of the first 20cm (L band) detections of massive stars in Cyg OB2, both accurate mass-loss determinations and constraints upon clumping within their winds are made. These data substantially increase the observational detections of the outer wind of massive stars and in combination with other observations at different wavelengths, COBRaS will greatly advance our knowledge of clumping as a function of radial distance around massive stars.
Evolved massive stars in W33 and in GMC G23.3 − 0.3
Authors: Messineo M. , Clark J. S. , Figer D. F. , Menten K. M. , Kudritzki R.-P. , Najarro F. , Rich R. M. , Ivanov V. D. , Valenti E. , Trombley C. , Chen C.-H. R. , Davies B. , MacKenty J. W.
Published: March 2017

We conducted infrared spectroscopic observations of bright stars in the direction of the molecular clouds W33 and GMC G23.3 − 0.3. We compared stellar spectro-photometric distances with parallactic distances to these regions, and we were able to assess the association of the detected massive stars with these molecular complexes. The spatial and temporal distributions of the detected stars enabled us to locate sources of ionizing radiation and to gather precise information on the star formation history of these clouds. The studied clouds present different distributions of massive stars.
Evidence for the non-destruction of the Most Massive Molecular Clouds even after they have given Birth to Massive Star Clusters
Authors: Zaragoza-Cardiel J. , Beckman J. , Font J. , Camps-Fariña A. , García-Lorenzo B. , Serrano-Borlaff A.
Published: March 2017

We have combined observations of the Antennae galaxies from the radio interferometer ALMA and from the optical interferometer GHαFaS (Galaxy Hα Fabry-Perot System). The two sets of observations have comparable angular and spectral resolutions, enabling us to identify 142 giant molecular clouds (GMCs) and 303 Hii regions. We have measured, and compared, their basic physical properties (radius, velocity dispersion, luminosity). We study the mass functions of Hii regions and GMCs, where a double population of Hii regions due to a double population of GMCs is found. Using the velocity dispersion measurements, we claim that the difference between the regimes is the nature of the dominant binding force. For the regions in the lower mass range, the dominant force is the external pressure, while in the higher mass range it is the internal gravity of the clouds. We have applied the same method to similar observations (GHαFaS & ALMA) of Arp 236 and NGC 1614 finding similar results.
Stellar feedback from a massive Super Star Cluster in the Antennae merger
Authors: Herrera Cinthya N. , Boulanger Francois
Published: March 2017

Stellar feedback from massive stars can unbind and disperse large amount of molecular gas, affecting the star formation efficiency. Based on ALMA and VLT observations in the Antennae galaxies we study a massive (~ 107 M⊙) and young (~ 3 Myr) SSC, B1, associated with compact molecular and ionized emission, which suggests that it is embedded in its parent cloud. However, we found contradictories and puzzling results on the structure and dynamics of the matter around the cluster, indicating that SSC B1 is not embedded in its parent cloud after all. We propose that radiation pressure was highly enhanced at the early stages of the SSC formation, disrupting the parent cloud in < 3 Myr. We show evidences of outflowing gas from the parent cloud in the more extended CO gas. Higher angular resolution observations are needed to validate this interpretation and to understand the origin and fate of the component seen to be associated with SSC B1.
Self-shielding clumps in starburst clusters
Authors: Palouš Jan , Wünsch Richard , Ehlerová Soňa , Tenorio-Tagle Guillermo
Published: March 2017

Young and massive star clusters above a critical mass form thermally unstable clumps reducing locally the temperature and pressure of the hot 107 K cluster wind. The matter reinserted by stars, and mass loaded in interactions with pristine gas and from evaporating circumstellar disks, accumulate on clumps that are ionized with photons produced by massive stars. We discuss if they may become self-shielded when they reach the central part of the cluster, or even before it, during their free fall to the cluster center. Here we explore the importance of heating efficiency of stellar winds.
Bayesian Inference of Kinematics and Mass Segregation of Open Cluster
Authors: Shao Z. , Xie X. , Chen L. , Zhong J. , Hou J. , Lin C-C.
Published: March 2017

Based on the Bayesian Inference (BI) method, the Mixture-Model approach is improved to combine all kinematic data, including the coordinative position($\vec{x}$), proper motion ($\vec{\mu}$) and radial velocity(v), to separate the motion of the cluster from field stars, as well as to determine the intrinsic kinematic status and dynamical effects of the cluster, such as the mass segregation, anisotropy etc.. Meanwhile, the membership probability of individual stars are estimated as by product results. This method has been testified by simulation of toy models and also successfully used for well studied open clusters, such as M67 and NGC188. It is expected to largely help the studies of open clusters while combine the coming GAIA data.
Bimodal regime in young massive clusters leading to subsequent stellar generations
Authors: Wünsch Richard , Palouš Jan , Tenorio-Tagle Guillermo , Muñoz-Tuñón Casiana , Ehlerová Soňa
Published: March 2017

Massive stars in young massive clusters insert tremendous amounts of mass and energy into their surroundings in the form of stellar winds and supernova ejecta. Mutual shock-shock collisions lead to formation of hot gas, filling the volume of the cluster. The pressure of this gas then drives a powerful cluster wind. However, it has been shown that if the cluster is massive and dense enough, it can evolve in the so–called bimodal regime, in which the hot gas inside the cluster becomes thermally unstable and forms dense clumps which are trapped inside the cluster by its gravity. We will review works on the bimodal regime and discuss the implications for the formation of subsequent stellar generations. The mass accumulates inside the cluster and as soon as a high enough column density is reached, the interior of the clumps becomes self-shielded against the ionising radiation of stars and the clumps collapse and form new stars. The second stellar generation will be enriched by products of stellar evolution from the first generation, and will be concentrated near the cluster center.
Variability Survey of ω Centauri in the Near-IR: Period-Luminosity Relations
Authors: Navarrete C. , Catelan M. , Contreras Ramos R. , Gran F. , Alonso-García J. , Dékány I.
Published: March 2017

ω Centauri is by far the most massive globular star cluster in the Milky Way, and possibly the remnant of a dwarf galaxy. As such, it contains a large number of variable stars of different classes. Here we report on an extensive, wide-field time-series study of ω Cen in the J and KS bands, which has allowed us to study the near-IR period-luminosity relations for different variability classes, including the first such relations for the SX Phoenicis stars.
Contribution of globular clusters to halos
Authors: Bragaglia Angela
Published: March 2017

The contribution of massive star clusters to their hosting halo dramatically depends on their formation mechanism and their early evolution. Massive globular clusters in the Milky Way (and in other galaxies) have been shown to display peculiar chemical patterns (light-elements correlations and anti-correlations) indicative of a complex star formation, confirmed by photometric evidence (spread or split sequences). I use these chemical signatures to try to understand what is the fraction of halo stars originally born in globular clusters.
Cluster Assembly in Hierarchically Collapsing Clouds
Authors: Vázquez-Semadeni Enrique , González-Samaniego Alejandro , Zamora-Avilés Manuel , Colín Pedro
Published: March 2017

We discuss the mechanism of cluster formation in hierarchically collapsing molecular clouds. Recent evidence, both observational and numerical, suggests that molecular clouds (MCs) may be undergoing global, hierarchical gravitational collapse. The “hierarchical” regime consists of small-scale collapses within larger-scale ones. The latter implies that the star formation rate increases systematically during the early stages of evolution, and occurs via filamentary flows onto “hubs” of higher density, mass, and velocity dispersion, and culminates a few Myr after than the small-scale collapses have started to form stars. In turn, the small-scale collapses occur in clumps embedded in the filaments, and are themselves falling into the larger potential well of the still-ongoing large-scale collapse. The stars formed in the early, small-scale collapses share the infall motion of their parent clumps towards the larger potential trough, so that the filaments feed both gaseous and stellar material to the hubs. This leads to the presence of older stars in a region where new protostars are still forming, to a scale-free or fractal structure of the clusters, in which each unit is composed of smaller-scale ones, and to the eventual merging of the subunits, explaining the observed structural features of open clusters.
Modeling Small Stellar Populations Using Starburst99
Authors: Vázquez Gerardo A. , Leitherer Claus
Published: March 2017

In this work, we have developed a new approach to form stars from clusters first, where massive stars are formed from fractions of mass of small stellar clusters. This new approximation is based on the empirical power law found in recent years and the maximum stellar mass that can be formed in a cluster. To produce the new models we have used the most recent version of Starburst99 that incorporates the most recent stellar evolution models with rotation. At the verge of solving nearby stellar populations and observing small stellar populations across the universe, this new approach brings a new scope on trying to disentangle the nature of hyper and supermassive stars in small stellar populations. Models for NGC 3603 and NGC 604 are presented. Our most important result is a strong ionizing power from small clusters by forming enough supermassive stars in a cluster of ~ 104 M⊙.
Binary interactions and multiple stellar populations in globular clusters
Authors: Jiang Dengkai , Han Zhanwen , Li Lifang
Published: March 2017

Globular clusters (GCs) have multiple stellar populations, which show star-to-star abundance variations and multiple sequences (or spreads) in the Hertzsprung-Russell diagrams. It is explained by multiple generations of star-formation in GCs. However, the observed evidence of ongoing star-formation was not found within any clusters. Here we present a binary interactions scenario for the formation of multiple stellar populations in GCs, where GC stars were born in a single burst of star formation, but some of them are members of binary systems. Binary interactions can produce peculiar stars, e.g. the merged stars and the accretor stars. They are more massive than normal single stars in the same evolutionary stage, and they are rapidly rotating stars at the moment of their formation. Rotationally induced mixing can cause the variations of their surface chemical composition. This results in the single-generation GCs showing abundance anomalies.
The birthrates of SNe Ia in globular clusters
Authors: Wang Bo , Liu Dongdong
Published: March 2017

Globular clusters has been proposed as testbeds for type Ia supernovae (SNe Ia). In this work, using a detailed binary population synthesis approach, we studied the birthrates of SNe Ia from various progenitor models in globular clusters, including the single-degenerate model, the double-degenerate model and the Sub-Chandrasekhar model. Here, a single starburst with a total mass of 106M⊙ is assumed.
The Assembly History of the Milky Way Nuclear Star Cluster
Authors: Feldmeier-Krause A. , Neumayer N. , Schödel R. , Seth A. , de Zeeuw P. T. , Walcher C. J. , Lützgendorf N. , Kissler-Patig M. , Hilker M. , Kuntschner H.
Published: March 2017

Within the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster. This cluster forms a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ~ 75% of nearby galaxies. It is, however, not fully understood how nuclear star clusters form. The Milky Way nuclear star cluster is the closest of its kind. At a distance of only 8 kpc we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster the perfect local reference object for understanding the structure and assembly history of nuclear star clusters in general. There are of the order of 107 stars within the central 10 pc of the Galactic center. Most of these stars are several Gyr old late-type stars. However, there are also more than 100 hot early-type stars in the central parsec of the Milky Way, with ages of only a few Myr. Beyond a projected distance of 0.5 pc of the Galactic center, the density of young stars was largely unknown, since only very few spectroscopic observations existed so far. We covered the central >4 pc2 (0.75 sq.arcmin) of the Galactic center using the integral-field spectrograph KMOS (VLT). We extracted more than 1,000 spectra from individual stars and identified >20 new early-type stars based on their spectra. We studied the spatial distribution of the different populations and their kinematics to put constraints on the assembly history of the Milky Way nuclear star cluster.
Chemical abundances of multiple stellar populations in massive globular clusters
Authors: Marino Anna F.
Published: March 2017

Multiple stellar populations in the Milky Way globular clusters manifest themselves with a large variety. Although chemical abundance variations in light elements, including He, are ubiquitous, the amount of these variations is different in different globulars. Stellar populations with distinct Fe, C+N+O and slow-neutron capture elements have been now detected in some globular clusters, whose number will likely increase. All these chemical features correspond to specific photometric patterns. I review the chemical+photometric features of the multiple stellar populations in globular clusters and discuss how the interpretation of data is being more and more challenging. Very excitingly, the origin and evolution of globular clusters is being a complex puzzle to compose.
The ODD Old, Super-Metal-Rich Open Cluster, NGC 6791
Authors: Boesgaard Ann Merchant , Lum Michael G. , Deliyannis Constantine P.
Published: March 2017

We report on the composition of turn-off stars in the intriguing open cluster, NGC 6791, which is old, but super-metal-rich using Keck/HIRES spectra. We find [Fe/H] = +0.30 ±0.02[O/Fe]n −0.06 ±0.02,[Mg/Fe], [Si/Fe], [Ca/Fe], and [Ti/Fe] near solar and the two Fe-peak elements, Cr and Ni, are consistent with Fe.
Massive Star Clusters in Dwarf Galaxies
Authors: Larsen Søren S.
Published: March 2017

Dwarf galaxies can have very high globular cluster specific frequencies, and the GCs are in general significantly more metal-poor than the bulk of the field stars. In some dwarfs, such as Fornax, WLM, and IKN, the fraction of metal-poor stars that belong to GCs can be as high as 20%–25%, an order of magnitude higher than the 1%–2% typical of GCs in halos of larger galaxies. Given that chemical abundance anomalies appear to be present also in GCs in dwarf galaxies, this implies severe difficulties for self-enrichment scenarios that require GCs to have lost a large fraction of their initial masses. More generally, the number of metal-poor field stars in these galaxies is today less than what would originally have been present in the form of low-mass clusters if the initial cluster mass function was a power-law extending down to low masses. This may imply that the initial GC mass function in these dwarf galaxies was significantly more top-heavy than typically observed in present-day star forming environments.
Universal and Environmental Influences on Star Clusters
Authors: Whitmore Bradley C.
Published: March 2017

There is now evidence that some aspects of compact star cluster formation and destruction are quasi-universal in nature, and some aspects depend on environment. But what do we mean by these terms, environmental and universal? Is one the dominant influence? How can things be both universal and environmentally dependent? In this contribution we first provide a brief historical overview, then examine evidence for both universality and environmental dependences, and finish by examining a new approach that both demonstrates the degree to which cluster mass functions are universal (i.e., to a level of roughly 0.2 in the Log over three orders of magnitude when normalizing by the star formation rate), and enables a method for quantifying 2nd-order environmental effects.
Star-Formation Histories of Resolved Galaxies in the Local Volume
Authors: Aloisi Alessandra
Published: March 2017

Color-magnitude diagrams of resolved stellar populations are the most powerful tool to derive the star formation histories of galaxies. In this review the method to infer star formation histories by comparing synthetic color-magnitude diagrams to deep, high-precision, multi-color photometry is briefly outlined, and our current knowledge of the star formation history of systems within the local Volume is summarized.
Intermediate-mass black holes in globular clusters: observations and simulations - Update
Authors: Lützgendorf Nora , Kissler-Patig Markus , Gebhardt Karl , Baumgardt Holger , Kruijssen Diederik , Noyola Eva , Neumayer Nadine , de Zeeuw Tim , Feldmeier-Krause Anja , van der Helm Edwin , Pelupessy Inti , Zwart Simon Portegies
Published: March 2017

The study of intermediate-mass black holes (IMBHs) is a young and promising field of research. If IMBH exist, they could explain the rapid growth of supermassive black holes by acting as seeds in the early stage of galaxy formation. Formed by runaway collisions of massive stars in young and dense stellar clusters, intermediate-mass black holes could still be present in the centers of globular clusters, today. We measured the inner kinematic profiles with integral-field spectroscopy for 10 Galactic globular cluster and determined masses or upper limits of central black holes. In combination with literature data we further studied the positions of our results on known black-hole scaling relations (such asM•− σ) and found a similar but flatter correlation for IMBHs. Applying cluster evolution codes, the change in the slope could be explained with the stellar mass loss occurring in clusters in a tidal field over its life time. Furthermore, we present results from several numerical simulations on the topic of IMBHs and integral field units (IFUs). N-body simulations were used to simulate IFU data cubes. For the specific case of NGC 6388 we simulated two different IFU techniques and found that velocity dispersion measurements from individual velocities are strongly biased towards lower values due to blends of neighbouring stars and background light. In addition, we use the Astrophysical Multipurpose Software Environment (AMUSE) to combine gravitational physics, stellar evolution and hydrodynamics to simulate the accretion of stellar winds onto a black hole. We find that the S-stars need to provide very strong winds in order to explain the accretion rate in the galactic center.
Effects of Stellar-Mass Black Holes on Massive Star Cluster Evolution
Authors: Chatterjee Sourav , Morscher Meagan , Rodriguez Carl L. , Pattabiraman Bharat , Rasio Frederic A.
Published: March 2017

Recent observations have revealed the existence of stellar mass black hole (BH) candidates in some globular clusters (GC) in the Milky Way and in other galaxies. Given that the detection of BHs is challenging, these detections likely indicate the existence of large populations of BHs in these clusters. This is in direct contrast to the past understanding that at most a handful of BHs may remain in old GCs due to quick mass segregation and rapid mutual dynamical ejection. Modern realistic star-by-star numerical simulations suggest that the retention fraction of BHs is typically much higher than what was previously thought. The BH dynamics near the cluster center leads to dynamical formation of new binaries and dynamical ejections, and acts as a persistent and significant energy source for these clusters. We have started exploring effects of BHs on the global evolution and survival of star clusters. We find that the evolution as well as survival of massive star clusters can critically depend on the details of the initial assumptions related to BH formation physics, such as natal kick distribution, and the initial stellar mass function (IMF). In this article we will present our latest results.
Kinematic and thermal structure at the onset of high-mass star formation - ISOSS23053
Authors: Bihr Simon , Beuther Henrik , Linz Hendrik , Ragan Sarah E. , Tackenberg Jochen , Smith Rowan J. , Henning Thomas , Krause Oliver
Published: March 2017

Within the ‘earliest phases of star formation’ (EPoS) Herschel project, we observed the NH3 inversion lines of 6 very young high-mass star-forming regions at high spatial resolution (3-5″) with the JVLA. While the Herschel data provide details about the dust continuum, the ammonia data reveal the kinematics and temperatures. Here we present the exciting star-forming clump ISOSS23053 that shows multiple velocity components. We observe a prominent velocity step within the clump, which could be a sign of colliding or converging flows that triggers star formation. Furthermore, we used the JVLA in the C-array configuration to study this source in more detail and we present the first results from the new data. They support the idea of converging flows, as we observe two components in the NH3(1,1) and (2,2) line, whereas the higher excited NH3(3,3) line shows one component that links the two lower excited lines.
Water Masers Outburst in the Massive Stellar Cluster W49A
Authors: Kramer Busaba H. , Menten Karl M. , Kamiński Tomasz , Zhang Bo , Patel Nimesh A. , Kraus Alex
Published: March 2017

We report a multi-wavelength study of a recent major flare (~ 80,000 Jy at VLSR ~ -98.1 km s−1) of the 22-GHz water maser in W49A. In February 2014, we started monthly monitoring with the Effelsberg 100-m radio telescope. In May 2014, we carried out the nearly simultaneous observations of the 22-GHz transition with selected submillimeter water transitions using the IRAM 30-m telescope (at 183 GHz) and the Atacama Pathfinder Experiment (APEX) 12-m telescope (from 321 to 475 GHz). We have also performed interferometric observations using the NRAO Very Long Baseline Array (VLBA) at 22 GHz and the Submillimeter Array (SMA) at 321 and 325 GHz. One remarkable result is the detection of very high velocity emission features in several transitions. Our data also represent its first detection of the 475-GHz water transition in a star-forming region. Studying these multiple masing transitions in conjunction with theoretical modeling of their excitation not only places strong constraints on the physical conditions of the masing gas but also allows us to study their association with the embedded massive stellar cluster in W49A.
Formation of the super star cluster RCW 38 triggered by cloud-cloud collision
Authors: Fukui Yasuo
Published: March 2017

RCW 38 is the youngest super star cluster in the Galaxy and is located at a distance of 1.7 kpc. Molecular observations revealed that the cluster is associated with two molecular clouds having velocity difference of 12 km s−1. We interpret that the two clouds are colliding with each other and the collision triggered the cluster formation. The natal molecular gas still survives within ~ 0.5 pc of the central O stars which have an age of 0.1 Myrs as inferred from the collision morphology. We suggest that the high column density of one of the clouds 1023 cm−2 enabled formation of ~ 20 O stars in the cluster center and discuss the implications on massive cluster formation.