bluuebunny/crossref_metadata_2025 huggingface dataset:
Isotopic evidence for temperate oceans during the Cambrian Explosion
Authors: Wotte Thomas , Skovsted Christian B. , Whitehouse Martin J. , Kouchinsky Artem
Published: April 2019

The Cambrian Explosion was a key event in the evolution of life on Earth. This event took place at a time when sea surface temperatures have been proposed to reach about 60 °C. Such high temperatures are clearly above the upper thermal limit of 38 °C for modern marine invertebrates and preclude a major biological revolution. To address this dichotomy, we performed in situ δ18O analyses of Cambrian phosphatic brachiopods via secondary ion mass spectrometry (SIMS). The δ18Ophosphate data, which are considered to represent the most primary δ18Oseawater signature, were identified by evaluating the diagenetic alteration of the analyzed shells. Assuming ice-free conditions for the Cambrian ocean and no change in δ18Oseawater (-1.4‰ to -1‰; V-SMOW) through time, our temperatures vary between 35 °C ± 12 °C and 41 °C ± 12 °C. They are thus clearly above (1) recent subequatorial sea surface temperatures of 27 °C–35 °C and (2) the upper lethal limit of 38 °C of marine organisms. Our new data can therefore be used to infer a minimal depletion in early Cambrian δ18Oseawater relative to today of about -3‰. With this presumption, our most pristine δ18Ophosphate values translate into sea surface temperatures of about 30 °C indicating habitable temperatures for subequatorial oceans during the Cambrian Explosion.
Studying the rigidity of red blood cells induced by Plasmodium falciparum infection
Authors: Paul Apurba , Ramdani Ghania , Tatu Utpal , Langsley Gordon , Natarajan Vasant
Published: April 2019

We study the effect of different chemical moieties on the rigidity of red blood cells (RBCs) induced by Plasmodium falciparum infection, and the bystander effect previously found. The infected cells are obtained from a culture of parasite-infected RBCs grown in the laboratory. The rigidity of RBCs is measured by looking at the Brownian fluctuations of individual cells in an optical-tweezers trap. The results point towards increased intracellular cyclic adenosine monophosphate (cAMP) levels as being responsible for the increase in rigidity.
Robust calculation of slopes in detrended fluctuation analysis and its application to envelopes of human alpha rhythms
Authors: Nolte Guido , Aburidi Mohammed , Engel Andreas K.
Published: April 2019

Detrended fluctuation analysis (DFA) is a popular method to analyze long-range temporal correlations in time series of many different research areas but in particular also for electrophysiological recordings. Using the classical DFA method, the cumulative sum of data are divided into segments, and the variance of these sums is studied as a function of segment length after linearly detrending them in each segment. The starting point of the proposed new method is the observation that the classical method is inherently non-stationary without justification by a corresponding non-stationarity of the data. This leads to unstable estimates of fluctuations to the extent that it is impossible to estimate slopes of the fluctuations other than by fitting a line over a wide range of temporal scales. We here use a modification of the classical method by formulating the detrending as a strictly stationary operation. With this modification the detrended fluctuations can be expressed as a weighted average across the power spectrum of a signal. Most importantly, we can also express the slopes, calculated as analytic derivatives of the fluctuations with respect to the scales, as statistically robust weighted averages across the power spectra. The method is applied to amplitudes of brain oscillations measured with magnetoencephalography in resting state condition. We found for envelopes of the the alpha rhythm that fluctuations as a function of time scales in a double-logarithmic plot differ substantially from a linear relation for time scales below 10 seconds. In particular we will show that model selections fail to determine accurate scaling laws, and that standard parameter settings are likely to yield results depending on signal to noise ratios than on true long range temporal correlations.
Right hemisphere occipital rTMS impairs working memory in visualizers but not in verbalizers
Authors: Hilbert Sven , McAssey Michaela , Bühner Markus , Schwaferts Patrick , Gruber Monika , Goerigk Stephan , Taylor Paul Christopher John
Published: April 2019

Distinguishing between verbal and visual working memory processes is complicated by the fact that the strategy used is hard to control or even assess. Many stimuli used in working memory tasks can be processed via verbal or visual coding, such as the digits in the digit span backwards task (DSB). The present study used repetitive transcranial magnetic stimulation (rTMS) to examine the use of visual processing strategies in the DSB. A total of 47 German university students took part in the study, 23 spontaneously using a verbal processing strategy and 24 using a visual strategy. After rTMS to the right occipital cortex, visualizers showed a significantly stronger mean performance decrease compared to verbalizers. The results indicate that the visual cortex is more critical for visualizers compared to verbalizers in the DSB task. Furthermore, the favored processing modality seems to be determined by the preference for a cognitive strategy rather than the presentation modality, and people are aware of the applied strategy. These findings provide insight into inter-individual differences in working memory processing and yield important implications for laboratory studies as well as clinical practice: the stimulus does not necessarily determine the processing and the participant can be aware of that.
A patient tumour-on-a-chip system for personalised investigation of radiotherapy based treatment regimens
Authors: Kennedy R. , Kuvshinov D. , Sdrolia A. , Kuvshinova E. , Hilton K. , Crank S. , Beavis A. W. , Green V. , Greenman J.
Published: April 2019

Development of personalised cancer models to predict response to radiation would benefit patient care; particularly in malignancies where treatment resistance is prevalent. Herein, a robust, easy to use, tumour-on-a-chip platform which maintains precision cut head and neck cancer for the purpose of ex vivo irradiation is described. The device utilises sintered discs to separate the biopsy and medium, mimicking in vivo microvascular flow and diffusion, maintaining tissue viability for 68 h. Integrity of tissues is demonstrated by the low levels of lactate dehydrogenase release and retained histology, accompanied by assessment of cell viability by trypan blue exclusion and flow cytometry; fluid dynamic modelling validates culture conditions. An irradiation jig is described for reproducible delivery of clinically-relevant doses (5 × 2 Gy) to newly-presenting primary tumours (n = 12); the addition of concurrent cisplatin is also investigated (n = 8) with response analysed by immunohistochemistry. Fractionated irradiation reduced proliferation (BrdU, p = 0.0064), increased DNA damage (ƴH2AX, p = 0.0043) and caspase-dependent apoptosis (caspase-cleaved cytokeratin-18) compared to control; caspase-dependent apoptosis was further increased by concurrent cisplatin compared to control (p = 0.0063). This is a proof of principle study showing the response of cancer tissue to irradiation ex vivo in a bespoke system. The novel platform described has the potential to personalise treatment for patients in a cost-effective manner with applicability to any solid tumour.
5-HTT independent effects of fluoxetine on neuroplasticity
Authors: Levy Marion J. F. , Boulle Fabien , Emerit Michel Boris , Poilbout Corinne , Steinbusch Harry W. M. , Van den Hove Daniel L. A. , Kenis Gunter , Lanfumey Laurence
Published: April 2019

Selective serotonin reuptake inhibitors are among the most prescribed antidepressants. Fluoxetine is the lead molecule which exerts its therapeutic effects, at least in part, by promoting neuroplasticity through increased brain-derived neurotrophic factor (BDNF)/tropomyosin-related receptor kinase B (TrkB) signalling. It is unclear however, to which extent the neuroplastic effects of fluoxetine are solely mediated by the inhibition of the serotonin transporter (5-HTT). To answer this question, the effects of fluoxetine on neuroplasticity were analysed in both wild type (WT) and 5-Htt knock-out (KO) mice. Using Western blotting and RT-qPCR approaches, we showed that fluoxetine 10 µM activated BDNF/TrkB signalling pathways in both CD1 and C57BL/6J mouse primary cortical neurons. Interestingly, effects on BDNF signalling were observed in primary cortical neurons from both 5-Htt WT and KO mice. In addition, a 3-week in vivo fluoxetine treatment (15 mg/kg/d; i.p.) increased the expression of plasticity genes in brains of both 5-Htt WT and KO mice, and tended to equally enhance hippocampal cell proliferation in both genotypes, without reaching significance. Our results further suggest that fluoxetine-induced neuroplasticity does not solely depend on 5-HTT blockade, but might rely, at least in part, on 5-HTT-independent direct activation of TrkB.
ASYMMETRIC LEAVES1 and REVOLUTA are the key regulatory genes associated with pitcher development in Nepenthes khasiana
Authors: Dkhar Jeremy , Pareek Ashwani
Published: April 2019

Nepenthes develops highly specialized insect-eating organs called pitchers that provide adequate insect-derived nutrients to the plants to offset low nutrient availability in their natural habitat. But so far, the molecular basis of Nepenthes pitcher development remains largely unknown. In an attempt to unravel the underlying mechanisms of pitcher formation, we made morphological observations of the developing N. khasiana leaf and performed RNA-seq to identify genes controlling pitcher development. Histology and scanning electron microscopy photomicrographs show that pitcher formation in N. khasiana occurs early in development and shares anatomical features with the young in-rolled leaf base lamina. Analysis of the RNA-seq data indicated that the modification of the leaf into a pitcher is associated with the altered expressions of leaf polarity genes ASYMMETRIC LEAVES1 (AS1) and REVOLUTA (REV). In fact, both genes displayed exclusive or relatively higher expressions in the tip of the leaf that later developed into a pitcher. We propose that NkAS1 may act to inhibit lamina outgrowth and promote the formation of the tendril. Increased NkREV expression may have been involved in the formation of the N. khasiana pitcher. This dataset will allow further research into this area and serve as the basis for understanding Nepenthes pitcher development.
Extinction risks of a Mediterranean neo-endemism complex of mountain vipers triggered by climate change
Authors: Ahmadi Mohsen , Hemami Mahmoud-Reza , Kaboli Mohammad , Malekian Mansoureh , Zimmermann Niklaus E.
Published: April 2019

Climate change is among the most important drivers of biodiversity decline through shift or shrinkage in suitable habitat of species. Mountain vipers of the genusMontiviperaare under extreme risk from climate changes given their evolutionary history and geographic distribution. In this study, we divided allMontiviperaspecies into three phylogenetic-geographicMontiviperaclades (PGMC; Bornmuelleri, Raddei and Xanthina) and applied an ensemble ecological niche modelling (ENM) approach under different climatic scenarios to assess changes in projected suitable habitats of these species. Based on the predicted range losses, we assessed the projected extinction risk of the species relative to IUCN Red List Criteria. Our result revealed a strong decline in suitable habitats for all PGMCs (63.8%, 79.3% and 96.8% for Xanthina, Raddei and Bornmuelleri, respectively, by 2070 and under 8.5 RCP scenario) with patterns of altitudinal range shifts in response to projected climate change. We found that the mountains close to the Mediterranean Sea are exposed to the highest threats in the future (84.6 ± 9.1 percent range loss). We also revealed that disjunct populations ofMontiviperawill be additionally highly isolated and fragmented in the future. We argue that leveraging climate niche projections into the risk assessment provides the opportunity to implement IUCN criteria and better assess forthcoming extinction risks of species.
Atomistic and experimental study on thermal conductivity of bulk and porous cerium dioxide
Authors: Malakkal Linu , Prasad Anil , Oladimeji Dotun , Jossou Ericmoore , Ranasinghe Jayangani , Szpunar Barbara , Bichler Lukas , Szpunar Jerzy
Published: April 2019

Cerium dioxide (CeO2) is a surrogate material for traditional nuclear fuels and an essential material for a wide variety of industrial applications both in its bulk and nanometer length scale. Despite this fact, the underlying physics of thermal conductivity (kL), a crucial design parameter in industrial applications, has not received enough attention. In this article, a systematic investigation of the phonon transport properties was performed using ab initio calculations unified with the Boltzmann transport equation. An extensive examination of the phonon mode contribution, available three-phonon scattering phase space, mode Grüneisen parameter and mean free path (MFP) distributions were also conducted. To further augment theoretical predictions of the kL, measurements were made on specimens prepared by spark plasma sintering using the laser flash technique. Since the sample porosity plays a vital role in the value of measured kL, the effect of porosity on kL by molecular dynamics (MD) simulations were investigated. Finally, we also determined the nanostructuring effect on the thermal properties of CeO2. Since CeO2 films find application in various industries, the dependence of thickness on the in-plane and cross-plane kL for an infinite CeO2 thin film was also reported.
Analysis of climate variability, trends, and prediction in the most active parts of the Lake Chad basin, Africa
Authors: Mahmood Rashid , Jia Shaofeng , Zhu Wenbin
Published: April 2019

An understanding of climate variability, trends, and prediction for better water resource management and planning in a basin is very important. Since the water resources of the Lake Chad basin (LCB) are highly vulnerable to changing climate, in the present study, a combination of trend analysis methods was used to examine the climate variability and trends for the period of 1951–2015 using observed and Climate Research Unit (CRU) data, and a combination of spectral analysis techniques was used for the prediction of temperature and precipitation using CRU data. Eighty-four percent of the temperature time series indicated extremely strong signals of increasing trends (α = 0.001) and 25–38% of the precipitation time series indicated strong decreasing trends (α = 0.05). Temperature is expected to increase and precipitation is expected to decrease in the future. However, surprisingly, in some regions located in the South, the temperature was predicted to decrease slightly in 2021–2030 relative to 2006–2015. This decrease might occur because these regions are highly protected natural resource areas and forests are frequently present. On the whole, the temperature was predicted to increase by 0.65–1.6 °C and precipitation was predicted to decrease by 13–11% in the next two decades (i.e., 2016–2025 and 2026–2035) relative to 1961–1990. Periodic analysis showed a 20- to 25-year cycle in precipitation in all basins and a 40- to 45-year cycle in temperature but only in the Chari-Logone basin.
Quantification of allelic differential expression using a simple Fluorescence primer PCR-RFLP-based method
Authors: Zhao Changzhi , Xie Shengsong , Wu Hui , Luan Yu , Hu Suqin , Ni Juan , Lin Ruiyi , Zhao Shuhong , Zhang Dingxiao , Li Xinyun
Published: April 2019

Allelic differential expression (ADE) is common in diploid organisms, and is often the key reason for specific phenotype variations. Thus, ADE detection is important for identification of major genes and causal mutations. To date, sensitive and simple methods to detect ADE are still lacking. In this study, we have developed an accurate, simple, and sensitive method, named fluorescence primer PCR-RFLP quantitative method (fPCR-RFLP), for ADE analysis. This method involves two rounds of PCR amplification using a pair of primers, one of which is double-labeled with an overhang 6-FAM. The two alleles are then separated by RFLP and quantified by fluorescence density. fPCR-RFLP could precisely distinguish ADE cross a range of 1- to 32-fold differences. Using this method, we verified PLAG1 and KIT, two candidate genes related to growth rate and immune response traits of pigs, to be ADE both at different developmental stages and in different tissues. Our data demonstrates that fPCR-RFLP is an accurate and sensitive method for detecting ADE on both DNA and RNA level. Therefore, this powerful tool provides a way to analyze mutations that cause ADE.
Interaction of RNA viruses of the natural virome with the African malaria vector, Anopheles coluzzii
Authors: Nanfack-Minkeu Ferdinand , Mitri Christian , Bischoff Emmanuel , Belda Eugeni , Casademont Isabelle , Vernick Kenneth D.
Published: April 2019

Mosquitoes are colonized by a little-studied natural virome. Like the bacterial microbiome, the virome also probably influences the biology and immunity of mosquito vector populations, but tractable experimental models are lacking. We recently discovered two novel viruses in the virome of wild Anopheles and in colonies of the malaria vector Anopheles coluzzii: Anopheles C virus and Anopheles cypovirus. Here, we describe biological interactions between these two viruses and An. coluzzii mosquitoes. Viral abundance varies reproducibly during mosquito development. DNA forms of these viruses were not detected, and thus viral persistence is likely based on vertical transmission of RNA genomes. At least Anopheles C virus is vertically transmitted by an intraembryonic route. Relative abundance of the two viruses is inversely correlated in individual mosquitoes. One possible mechanism for this could be interactions with host immunity, and functional genomic analysis indicated differential influence of at least the Toll and JAK/STAT immune signaling pathways upon the viruses. The nonrandom distributions and interactions with host immunity suggest that these and other members of the natural virome may constitute a source of unrecognized heterogeneity in mosquito vector populations.
Potent and PPARα-independent anti-proliferative action of the hypolipidemic drug fenofibrate in VEGF-dependent angiosarcomas in vitro
Authors: Majeed Yasser , Upadhyay Rohit , Alhousseiny Sara , Taha Tarek , Musthak Adham , Shaheen Yanal , Jameel Mohtashim , Triggle Chris R. , Ding Hong
Published: April 2019

Angiosarcomas are highly aggressive tumors of endothelial origin, which carry a poor prognosis. Fenofibrate is a hypolipidemic drug, which acts by activating the transcription factor PPARα. It has also been widely reported to have ‘anti-cancer’ activity. The current study investigated its effect in a murine VEGF-dependent angiosarcoma cell-line, MS1 VEGF. The study utilised assays to monitor cell proliferation and viability, apoptosis, cell cycle progression, mitochondrial membrane potential, changes in protein expression, and changes in miRNA expression using microarrays. Fenofibrate showed potent anti-proliferative action in MS1 VEGF angiosarcoma cells, without inducing apoptosis. It enriched cells in G2/M cell cycle phase and hyperpolarised mitochondria. Other PPARα activators failed to mimic fenofibrate action. Inhibitors of PPARα and NFκB failed to reverse the inhibitory effect of fenofibrate and their combination with fenofibrate was cytotoxic. Fenofibrate downregulated the expression of key VEGF-effector proteins, including Akt, ERK, Bcl-2 and survivin, and a chemical inhibitor screen discovered relevance of these proteins to cell proliferation. A miRNA microarray revealed that fenofibrate differentially regulated cellular miRNAs with known roles in cancer and angiogenesis. The data raise the possibility that fenofibrate could be useful in angiosarcoma therapy, especially considering its well-established clinical safety and tolerability profile.
An advanced near real dynamicin vitrohuman stomach system to study gastric digestion and emptying of beef stew and cooked rice
Authors: Wang Jingjing , Wu Peng , Liu Minghui , Liao Zhenkai , Wang Yong , Dong Zhizhong , Chen Xiao Dong
Published: April 2019

A near real dynamicin vitrohuman stomach (new DIVHS) system has recently been advanced in this study, based on the previous rope-drivenin vitrohuman stomach model (RD-IV-HSM).
Calculating transition dipole moments of phosphorescent emitters for efficient organic light-emitting diodes
Authors: Babazadeh Mohammad , Burn Paul L. , Huang David M.
Published: April 2019

Quantum-chemical calculations show that the direction of the transition dipole moment of organometallic phosphorescent emitters is sensitive to molecular geometry.
Effects of egg phosvitin on mucosal transcriptional profiles and luminal microbiota composition in murine colon
Authors: Li Mei , Zhang Qinjun , Wang Ruihan , Lu Mei , Xu Xueming , Liu Xuebo , Duan Xiang
Published: April 2019

The effects of egg phosvitin on epithelial gene expression, abundance of bacteria in colon and their correlation have been explored.
Inhibiting degradation of cellulose dissolved in ionic liquids via amino acids
Authors: Yang Jiming , Lu Xingmei , Yao Xiaoqian , Li Yao , Yang Yongqing , Zhou Qing , Zhang Suojiang
Published: April 2019

By adding l-arginine, cellulose degradation was inhibited in [C4mim]Cl with a 90% regeneration rate after 24 h at 130 °C.
Self-assembly of Au nano-islands with tuneable organized disorder for highly sensitive SERS
Authors: Fusco Zelio , Bo Renheng , Wang Yuling , Motta Nunzio , Chen Hongjun , Tricoli Antonio
Published: April 2019

A thermophoretically driven Au aerosol deposition process is used for the self-assembly of thin films consisting of plasmonic nano-islands (NIs) with a controllable and highly reproducible degree of disorder resulting in long-range periodicity with self-similar properties and stochastically distributed hot-spots, benefitting their applications as SERS substrates.
Secondary eclipse of the hot Jupiter WASP-121b at 2 μm
Authors: Kovács Géza , Kovács Tamás
Published: April 2019

Ground-based observations of the secondary eclipse in the 2MASS K band are presented for the hot Jupiter WASP-121b. These are the first occultation observations of an extrasolar planet that were carried out with an instrument attached to a 1 m class telescope (the SMARTS 1.3 m). We find a highly significant eclipse depth of (0.228 ± 0.023)%. Together with other planet atmosphere measurements, including the Hubble Space Telescope near-infrared emission spectrum, current data support more involved atmosphere models with species producing emission and absorption features, rather than simple smooth blackbody emission. Analysis of the time difference between the primary and secondary eclipses and the durations of these events yields an eccentricity of e = 0.0207 ± 0.0153, which is consistent with the earlier estimates of low or zero eccentricity, but with a smaller error. Comparing the observed occultation depth in the K band with the one derived under the assumption of zero Bond albedo and full heat redistribution, we find that WASP-121b has a deeper observed occultation depth than predicted. Together with the sample of 31 systems with K-band occultation data, this observation lends further support to the idea of inefficient heat transport between the day and night sides for most of the hot Jupiters.
A new radio molecular line survey of planetary nebulae
Authors: Bublitz J. , Kastner J. H. , Santander-García M. , Bujarrabal V. , Alcolea J. , Montez R.
Published: April 2019

Certain planetary nebulae (PNe) contain shells, filaments, or globules of cold gas and dust whose heating and chemistry are likely driven by UV and X-ray emission from their central stars and from wind-collision-generated shocks. We present the results of a survey of molecular line emission in the 88–236 GHz range from nine nearby (<1.5 kpc) planetary nebulae spanning a range of UV and X-ray luminosities, using the 30 m telescope of the Institut de Radioastronomie Millimétrique. Rotational transitions of thirteen molecules, including CO isotopologues and chemically important trace species, were observed and the results compared with and augmented by previous studies of molecular gas in PNe. Lines of the molecules HCO+, HNC, HCN, and CN, which were detected in most objects, represent new detections for four planetary nebulae in our study. Specifically, we present the first detections of 13CO (1–0, 2–1), HCO+, CN, HCN, and HNC in NGC 6445; HCO+ in BD+30°3639; 13CO (2–1), CN, HCN, and HNC in NGC 6853; and 13CO (2–1) and CN in NGC 6772. Flux ratios were analyzed to identify correlations between the central star and/or nebular UV and X-ray luminosities and the molecular chemistries of the nebulae. This analysis reveals a surprisingly robust dependence of the HNC/HCN line ratio on PN central star UV luminosity. There exists no such clear correlation between PN X-rays and various diagnostics of PN molecular chemistry. The correlation between HNC/HCN ratio and central star UV luminosity demonstrates the potential of molecular emission line studies of PNe for improving our understanding of the role that high-energy radiation plays in the heating and chemistry of photodissociation regions.
Updated extraction of the APOGEE 1.5273 μm diffuse interstellar band: a Planck view on the carrier depletion in dense cores
Authors: Elyajouri M. , Lallement R.
Published: April 2019

Context. Constraining the spatial distribution of diffuse interstellar band (DIB) carriers and their links with gas and dust are mandatory steps in understanding their role in interstellar chemistry.

Aims. The latest SDSS/APOGEE data release, DR14, has provided an increased number of stellar spectra in the H band and associated stellar models using an innovative algorithm known as the Cannon. We took advantage of these novelties to extract the 15 273 Å near-infrared DIB and to study its link with dust extinction and emission.

Methods. We modified our automated fitting methods dedicated to hot stars and used in earlier studies with some adaptations motivated by the change from early- or intermediate-type stars to red giants. A new method has also been developed to quantify the upper limits on DIB strengths. Careful and thorough examinations were carried out of the DIB parameters, the continuum shape, and the quality of the adjustment of the model to the data. We compared our DIB measurements with the stellar extinctions, AV, from the Starhorse database. We then compared the resulting DIB–extinction ratio with the dust optical depth derived from Planck data, both globally and separately for nearby off-plane cloud complexes.

Results. Our analysis has led to the production of a catalog containing 124 064 new measurements of the 15 273 Å DIB, allowing us to revisit the correlation between DIB strength and dust reddening. The new data clearly reveal that the sky-averaged 15 273 Å DIB strength is linearly correlated with AV over two orders as reported by earlier studies but leveling off with respect to extinction for highly reddened lines of sight behind dense clouds. The comparison with Planck individual optical depths reveals in a conspicuous way this DIB depletion in the dense cores and shows it applies to all off-plane dense clouds. Using selected targets located beyond the Orion, Taurus, and Cepheus clouds, we derived empirical relationships between the DIB–extinction ratio and the Planck dust optical depth for the three cloud complexes. Their average is similar to the DIB carrier depletion measured in the dark cloud Barnard 68.

Conclusions. APOGEE measurements confirm the ubiquity of the 15 273 Å DIB carrier decrease with respect to dust grains in dense cloud cores, in a manner that can be empirically related to the dust optical depth reached in the cloud. They also show that the ratio between the DIB equivalent width and the extinction AV for sightlines with τ(353GHz) ≲ 2 × 10−5 that do not contain dense molecular gas is about four times higher than the constant limit towards which the ratio tends for very long sightlines with many diffuse and dense phases distributed in distance.
The relation between 5780 and 5797 diffuse interstellar bands, CH/CH+
molecules, and atomic or molecular hydrogen
Authors: Weselak T.
Published: April 2019

Correlations between column densities of neutral and molecular hydrogen and strengths of major 5780 and 5797 Å diffuse interstellar bands (DIBs) based on spectra of 66 OB stars were analyzed. We confirm that the 5797 Å DIB is more tightly correlated with column density of molecular hydrogen while the 5780 DIB – with that of atomic hydrogen. This leads to a reasonably tight relation between the molecular fraction of H2 and equivalent width ratio of the 5797 and 5780 major diffuse bands with correlation coefficient equal to 0.77 ± 0.05. Column densities of CH and CH+ molecules were used to analyze correlations between abundances of CH/CH+ molecules and strengths of the major 5780 and 5797 DIBs. The 5780 DIB is better correlated with the column density of methydyline cation than the 5797 DIB. A relation with correlation coefficient equal to 0.95 ± 0.02 based on precise column densities, between column densities of CH and H2 molecules, is also presented; in other words, the column densitiy ratio in the case of H2 and CH molecules in the ISM is equal to (2.01 ± 0.09) × 107.
Critical angular velocity and anisotropic mass loss of rotating stars with radiation-driven winds
Authors: Gagnier D. , Rieutord M. , Charbonnel C. , Putigny B. , Espinosa Lara F.
Published: April 2019

Context. The understanding of the evolution of early-type stars is tightly related to that of the effects of rapid rotation. For massive stars, rapid rotation combines with their strong radiation-driven wind.

Aims. The aim of this paper is to investigate two questions that are prerequisite to the study of the evolution of massive rapidly rotating stars: (i) What is the critical angular velocity of a star when radiative acceleration is significant in its atmosphere? (ii) How do mass and angular momentum loss depend on the rotation rate?

Methods. To investigate fast rotation, which makes stars oblate, we used the 2D ESTER models and a simplified approach, the ω-model, which gives the latitudinal dependence of the radiative flux in a centrifugally flattened radiative envelope.

Results. We find that radiative acceleration only mildly influences the critical angular velocity, at least for stars with masses lower than 40 M⊙. For instance, a 15 M⊙ star on the zero-age main sequence would reach criticality at a rotation rate equal to 0.997 the Keplerian equatorial rotation rate. We explain this mild reduction of the critical angular velocity compared to the classical Keplerian angular velocity by the combined effects of gravity darkening and a reduced equatorial opacity that is due to the centrifugal acceleration. To answer the second question, we first devised a model of the local surface mass flux, which we calibrated with previously developed 1D models. The discontinuity (the so-called bi-stability jump) included in the Ṁ − Teff relation of 1D models means that the mass flux of a fast-rotating star is controlled by either a single wind or a two-wind regime. Mass and angular momentum losses are strong around the equator if the star is in the two-wind regime. We also show that the difficulty of selecting massive stars that are viewed pole-on makes detecting the discontinuity in the relation between mass loss and effective temperature also quite challenging.
Exoplanet atmospheres with GIANO
Authors: Guilluy G. , Sozzetti A. , Brogi M. , Bonomo A. S. , Giacobbe P. , Claudi R. , Benatti S.
Published: April 2019

Context. The study of exoplanetary atmospheres is key to understanding the differences between their physical, chemical, and dynamical processes. Until now, the bulk of atmospheric characterization analyses have been conducted on transiting planets. On a number of sufficiently bright targets, high-resolution spectroscopy (HRS) has also been successfully tested for nontransiting planets mainly by using spectrographs mounted on 8 and 10 m class ground-based telescopes.

Aims. The aim of this analysis is to study the dayside of the nontransiting planet HD 102195b using the GIANO spectrograph mounted at the Telescopio Nazionale Galileo (TNG), and thereby demonstrate the feasibility of atmospheric characterization measurements. In particular, we wish to demonstrate the possibility of molecular detection with the HRS technique for nontransiting planets using 4 m class telescopes.

Methods. Our data-analysis technique exploits the fact that the Doppler-shifted planetary signal changes on the order of many kilometers per second during the observations, in contrast with the telluric absorption which is stationary in wavelength. This allows us to effectively remove the contamination from telluric lines in the GIANO spectra while preserving the features of the planetary spectrum. The emission signal from the atmosphere of HD 102195b is then extracted by cross-correlating the residual GIANO spectra with models of the planetary atmosphere.

Results. We detect molecular absorption from water vapor at the 4.4σ level of statistical significance. We also find convincing evidence for the presence of methane, which is detected at the 4.1σ level. This is the first detection of methane obtained with the HRS technique. The two molecules are detected with a combined significance of 5.3σ, at a semi-amplitude of the planet radial velocity KP = 128 ± 6 km s−1. We estimate a true planet mass of MP = 0.46 ± 0.03 MJ and constrain the orbital inclination in the range 72.5° < i < 84.79° (1σ). Our analysis indicates a noninverted atmosphere for HD 102195b. This is expected given the relatively low temperature of the planet, inefficient to keep TiO/VO in gas phase. Moreover, a comparison with theoretical model expectations corroborates our detection of methane, and a cursory confrontation with chemical model predictions published in the literature suggests that the detected methane and water signatures could be consistent with a low C/O ratio for HD 102195b. Finally, as HD 102195 is one to three magnitudes fainter in the K-band than the nontransiting systems studied until now with 8 m telescopes, our study opens up the possibility for atmospheric characterization of a larger sample of exoplanets.
Average motion of emerging solar active region polarities
Authors: Schunker H. , Birch A. C. , Cameron R. H. , Braun D. C. , Gizon L. , Burston R. B.
Published: April 2019

Aims. Our goal is to constrain models of active region formation by tracking the average motion of active region polarity pairs as they emerge onto the surface.

Methods. We measured the motion of the two main opposite polarities in 153 emerging active regions using line-of-sight magnetic field observations from the Solar Dynamics Observatory Helioseismic Emerging Active Region (SDO/HEAR) survey. We first measured the position of each of the polarities eight hours after emergence, when they could be clearly identified, using a feature recognition method. We then tracked their location forwards and backwards in time.

Results. We find that, on average, the polarities emerge with an east-west orientation and the separation speed between the polarities increases. At about 0.1 days after emergence, the average separation speed reaches a peak value of 229 ± 11 ms−1, and then starts to decrease. About 2.5 days after emergence the polarities stop separating. We also find that the separation and the separation speed in the east-west direction are systematically larger for active regions that have higher flux. The scatter in the location of the polarities increases from about 5 Mm at the time of emergence to about 15 Mm at two days after emergence.

Conclusions. Our results reveal two phases of the emergence process defined by the rate of change of the separation speed as the polarities move apart. Phase 1 begins when the opposite polarity pairs first appear at the surface, with an east-west alignment and an increasing separation speed. We define Phase 2 to begin when the separation speed starts to decrease, and ends when the polarities have stopped separating. This is consistent with a previous study: the peak of a flux tube breaks through the surface during Phase 1. During Phase 2 the magnetic field lines are straightened by magnetic tension, so that the polarities continue to move apart, until they eventually lie directly above their anchored subsurface footpoints. The scatter in the location of the polarities is consistent with the length and timescales of supergranulation, supporting the idea that convection buffets the polarities as they separate.
Polarization of changing-look quasars
Authors: Hutsemékers D. , Agís González B. , Marin F. , Sluse D. , Ramos Almeida C. , Acosta Pulido J.-A.
Published: April 2019

If the disappearance of the broad emission lines observed in changing-look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical polarization would be expected in those objects. We then measured the rest-frame UV-blue linear polarization of a sample of 13 changing-look quasars, 7 of them being in a type 1.9-2 state. For all quasars but one the polarization degree is lower than 1%. This suggests that the disappearance of the broad emission lines cannot be attributed to dust obscuration, and supports the scenario in which changes of look are caused by a change in the rate of accretion onto the supermassive black hole. Such low polarization degrees also indicate that these quasars are seen under inclinations close to the system axis. One type 1.9-2 quasar in our sample shows a high polarization degree of 6.8%. While this polarization could be ascribed to obscuration by a moving dusty cloud, we argue that this is unlikely given the very long time needed for a cloud from the torus to eclipse the broad emission line region of that object. We propose that the high polarization is due to the echo of a past bright phase seen in polar-scattered light. This interpretation raises the possibility that broad emission lines observed in the polarized light of some type 2 active galactic nuclei can be echoes of past type 1 phases and not evidence of hidden broad emission line regions.
The luminosity–volume test for cosmological fast radio bursts
Authors: Locatelli N. , Ronchi M. , Ghirlanda G. , Ghisellini G.
Published: April 2019

We have applied the luminosity–volume test, also known as ⟨V/Vmax⟩, to fast radio bursts (FRBs). We compare the 23 FRBs, recently discovered by ASKAP, with 20 of the FRBs found by Parkes. These samples have different flux limits and correspond to different explored volumes. We put constrains on their redshifts with probability distributions (PDFs) and applied the appropriate cosmological corrections to the spectrum and rate in order to compute the ⟨V/Vmax⟩ for the ASKAP and Parkes samples. For a radio spectrum of FRBs ℱν ∝ ν−1.6, we found ⟨V/Vmax⟩ = 0.68 ± 0.05 for the ASKAP sample, that includes FRBs up to z = 0.72+0.42−0.26, and 0.54 ± 0.04 for Parkes, that extends up to z = 2.1+0.47−0.38. The ASKAP value suggests that the population of FRB progenitors evolves faster than the star formation rate, while the Parkes value is consistent with it. Even a delayed (as a power law or Gaussian) star formation rate cannot reproduce the ⟨V/Vmax⟩ of both samples. If FRBs do not evolve in luminosity, the ⟨V/Vmax⟩ values of ASKAP and Parkes sample are consistent with a population of progenitors whose density strongly evolves with redshift as ∼z2.8 up to z ∼ 0.7.
High resolution observations with Artemis–JLS
Authors: Bouratzis C. , Hillaris A. , Alissandrakis C. E. , Preka-Papadema P. , Moussas X. , Caroubalos C. , Tsitsipis P. , Kontogeorgos A.
Published: April 2019

Aims. We examined the characteristics of isolated intermediate drift bursts and their morphologies on dynamic spectra, in particular the positioning of emission and absorption ridges. Furthermore we studied the repetition rate of fiber groups. These were compared with a model in order to determine the conditions under which the intermediate drift bursts appear and exhibit the above characteristics.

Methods. We analyzed sixteen metric type IV events with embedded intermediate drift bursts, observed with the Artemis–JLS radio spectrograph from July 1999 to July 2005 plus an event on 1st August 2010. The events were recorded with the SAO high resolution (10 ms cadence) receiver in the 270–450 MHz range with a frequency resolution of 1.4 MHz. We developed cross- and autocorrelation techniques to measure the duration, spectral width, and frequency drift of fiber bursts in 47 intermediate drift bursts (IMD) groups embedded within the continuum of the sixteen events mentioned above. We also developed a semi-automatic algorithm to track fibers on dynamic spectra.

Results. The mean duration of individual fiber bursts at fixed frequency was δt ≈ 300 ms, while the instantaneous relative bandwidth was fw/f ≈ 0.90% and the total frequency extent was Δftot ≈ 35 MHz. The recorded intermediate drift bursts had frequency drift, positive or negative, with average values of df/fdt equal to −0.027 and 0.024 s−1 respectively. Quite often the fibers appeared in groups; the burst repetition rate within groups was, on average, ∼0.98 s. We distinguish six morphological groups of fibers, based on the relative position of the emission and absorption ridges. These included fibers with emission or absorption ridges only, fibers with the absorption ridge at lower or higher frequency than the emission, or with two absorption ridges above and below the emission. There were also some fibers for which two emission ridges were separated by an absorption ridge. Some additional complex groups within our data set were not easy to classify. A number of borderline cases of fibers with very high drift rate (∼0.30 s−1) or very narrow total bandwidth (∼8 MHz) were recorded; among them there was a group of rope-like fibers characterized by fast repetition rate and relatively narrow total frequency extent. We found that the whistler hypothesis leads to reasonable magnetic field values (∼4.6 G), while the Alfven-wave hypothesis requires much higher field. From the variation of the drift rate with time we estimated the ratio of the whistler to the cyclotron frequency, x, to be in the range of 0.3−0.6, varying by ∼0.05−0.1 in individual fibers; the same analysis gives an average value of the frequency scale along the loop of ∼220 Mm. Finally, we present empirical relations between fiber burst parameters and discuss their possible origin.
Far-infrared continuum absorption of forsterite and enstatite at low temperatures
Authors: Mutschke Harald , Mohr Pierre
Published: April 2019

Context. The far-infrared continuum opacity of cold dust is an important quantity for the study of debris disks in planetary systems and of protoplanetary disks. Forsterite and enstatite are considered to be the most abundant crystalline dust species in such environments.

Aims. The optical constants of these minerals at wavelengths above 80 μm, which govern the opacity, and their temperature dependence are poorly known. Our aim is to fill in this lack of information with new laboratory data.

Methods. We present spectroscopic transmission measurements on forsterite and enstatite single crystals of up to 10 mm thickness at wavelengths between 45 and 500 μm and for temperatures down to 10 K. We compare our results to literature data originating from powder transmission and from reflection spectroscopy.

Results. The imaginary parts of the refractive indices calculated from the measurements show very strong temperature dependences, which to that extent are not seen in reflection-based data or in powder measurement data. The temperature dependences can be described by a simple theoretical model taking the contributions of single-phonon absorption and phonon difference processes into account. We also observe, for the first time, enstatite absorption bands at 87.5 μm and 116.6 μm wavelengths.

Conclusions. The single-crystal optical constants of forsterite and enstatite predict an extremely small submillimeter opacity of crystalline silicate dust at low temperatures, which would make these particles almost invisible in the thermal radiation of cold dust. Thus, it is important to understand why absorption measurements with mineral powders resulted in much higher opacity values.
RPC-MIP observations at comet 67P/Churyumov-Gerasimenko explained by a model including a sheath and two populations of electrons
Authors: Wattieaux G. , Gilet N. , Henri P. , Vallières X. , Bucciantini L.
Published: April 2019

The response of the mutual impedance probe RPC-MIP on board Rosetta orbiter electrostatically modeled considering an unmagnetized and collisionless plasma with two Maxwellian electron populations. A vacuum sheath surrounding the probe was considered in our model in order to take the ion sheath into account that is located around the probe, which is immersed in the cometary plasma. For the first time, the simulated results are consistent with the data collected around comet 67P/Churyumov-Gerasimenko (67P), but strong discrepancies were identified with the previous simulations that neglected the plasma sheath around the probe. We studied the influence of the sheath thickness and of the electron populations. This work helps to better understand the initially unexpected responses of the mutual impedance probe that were acquired during the Rosetta mission. It suggests that two electron populations exist in the cometary plasma of 67P.
Investigation of the WR 11 field at decimeter wavelengths
Authors: Benaglia P. , del Palacio S. , Ishwara-Chandra C. H. , De Becker M. , Isequilla N. L. , Saponara J.
Published: April 2019

The massive binary system WR 11 (γ2-Velorum) has recently been proposed as the counterpart of a Fermi source. If this association is correct, this system would be the second colliding wind binary detected in GeV γ-rays. However, the reported flux measurements from 1.4 to 8.64 GHz fail to establish the presence of nonthermal (synchrotron) emission from this source. Moreover, WR 11 is not the only radio source within the Fermi detection box. Other possible counterparts have been identified in archival data, some of which present strong nonthermal radio emission. We conducted arcsec-resolution observations toward WR 11 at very low frequencies (150–1400 MHz) where the nonthermal emission – if existent and not absorbed – is expected to dominate. We present a catalog of more than 400 radio emitters, among which a significant portion are detected at more than one frequency, including limited spectral index information. Twenty-one of these radio emitters are located within the Fermi significant emission. A search for counterparts for this last group pointed at MOST 0808–471; this source is 2′ away from WR 11 and is a promising candidate for high-energy emission, having a resolved structure along 325–1390 MHz. For this source, we reprocessed archive interferometric data up to 22.3 GHz and obtained a nonthermal radio spectral index of − 0.97 ± 0.09. However, multiwavelength observations of this source are required to establish its nature and to assess whether it can produce (part of) the observed γ-rays. WR 11 spectrum follows a spectral index of 0.74 ± 0.03 from 150 to 230 GHz, consistent with thermal emission. We interpret that any putative synchrotron radiation from the colliding-wind region of this relatively short-period system is absorbed in the photospheres of the individual components. Notwithstanding, the new radio data allowed us to derive a mass-loss rate of 2.5 × 10−5 M⊙ yr−1, which, according to the latest models for γ-ray emission in WR 11, would suffice to provide the required kinetic power to feed nonthermal radiation processes.