bluuebunny/crossref_metadata_2025_split huggingface dataset:
Maser Effects in Recombination Lines: the case of Eta Carinae
Authors: Abraham Zulema , Beaklini Pedro P. B. , Falceta-Gonçalves Diego 
Published: July 2018

AbstractPopulation of high quantum number states can differ from their LTE values at high densities (Ne ~106− 108cm−3) and temperatures of the order of 104K. In this case, the intensity of recombination lines can be strongly amplified. The amount of amplification depends on density and temperature, and it is different for different quantum numbers, allowing the determination of the physical and kinematic conditions of the emitting region through the observation of recombination lines of different quantum numbers. This was the case of the massive binary system η Carinae. This system was observed with ALMA in the recombination lines H21α, H28α, H30α, H40α and H42α and the continuum at the frequencies of the corresponding lines. The continuum spectrum was characteristic of a compact HII region, becoming optically thin at around 300 GHz. From the intensity and width of the recombination lines we concluded that the not-resolved emission region, assumed spherically symmetric, is a shell of 40 AU radius and 4 AU width, expanding at velocities between 20 and 60 km s−1, with density of 107cm−3and temperature of 17000 K.
6.7 GHz Methanol Masers Observation with Phased Hitachi and Takahagi
Authors: Takefuji Kazuhiro , Sugiyama Koichiro , Yonekura Yoshinori , Saito Tagiru , Fujisawa Kenta , Kondo Tetsuro 
Published: July 2018

AbstractFor the high-sensitivity 6.7 GHz methanol maser observations, we developed a new technology for coherently combining the two signals from the Hitachi 32 m radio telescope and the Takahagi 32 m radio telescope of the Japanese VLBI Network. Furthermore, we compared the SNRs of the 6.7 GHz maser spectra for two methods. One is a VLBI method and the other is the newly developed digital position switching, which is a similar technology to that used in noise-cancelling headphones. We report the phase-up technique and the observation.
A Face-on Accretion System in High Mass Star-Formation: Possible Dusty Infall Streams within 100 Astronomical Unit
Authors: Motogi Kazuhito , Hirota Tomoya , Sorai Kazuo , Yonekura Yoshinori , Sugiyama Koichiro , Honma Mareki , Niinuma Kotaro , Hachisuka Kazuya , Fujisawa Kenta , Walsh Andrew J. 
Published: July 2018

AbstractWe report on interferometric observations of a face-on accretion system around the high mass young stellar object, G353.273+0.641. The innermost accretion system of 100-au radius was resolved in a 45-GHz continuum image taken with the Jansky Very Large Array. Our SED analysis indicated that the continuum could be explained by optically-thick dust emission. 6.7 GHz CH3OH masers associated with the same system were also observed with the Australia Telescope Compact Array. The masers showed a spiral-like, non-axisymmetric distribution with a systematic velocity gradient. The line-of-sight velocity field is explained by an infall motion along a parabolic streamline that falls onto the equatorial plane of the face-on system. The streamline is quasi-radial and reaches the equatorial plane at a radius of 16 au. The physical origin of such a streamline is still an open question and will be constrained by the higher-resolution thermal continuum and line observations with ALMA long baselines.
First Galactic Maser Observations on Ventspils Radio Telescopes – Instrumentation and Data Reduction
Authors: Shmeld Ivar , Aberfelds Artis , Bērziņš Kārlis , Bezrukovs Vladislavs , Bleiders Mārcis , Orbidans Artūrs 
Published: July 2018

AbstractVentspils International Radio Astronomy Centre (VIRAC) has two fully steerable Cassegrean System 32 and 16 m radio telescopes. After renovation and modernization program the Galactic masers, particularly CH3OH research and monitoring program became one of the most important realized on these telescopes. Both telescopes are equipped with broadband cryogenic receivers covering 4.5-8.8 GHz frequency band. Digital backend consisting from DBBC-2 (Digital Base Band Convertor developed by HAT-LAB, Italy) and FLEXBUFF (data storage system based on commercially available server system) is used for data digitalization and registration. A special program complex for spectral line data reduction and correction was developed and implemented.
Maser Theory: Old Problems and New Insights
Authors: Gray M. D. 
Published: July 2018

AbstractMaser theory continues to be driven by advances in observational techniques. Here, I consider the responses to VLBI with space-Earth baselines and cross-correlation spectroscopy (a re-consideration of coherence properties), routine observation in full-Stokes polarization (a re-casting of the polarization transfer equations), and long-term variability monitoring (3-D modelling of irregular domains).
The bursting variability of 6.7 GHz methanol maser of G33.641-0.228
Authors: Kojima Y. , Fujisawa K. , Motogi K. 
Published: July 2018

AbstractFrom 2014 to 2015, we conducted a total of 469 days observation of the 6.7 GHz methanol maser in a star forming region G33.641-0.228, known to be a bursting maser source. As a result, eleven bursts were detected. On MJD 57364, the flux density grew by more than six times w.r.t the day before. Moreover, during the largest burst, the flux density repeatedly increased and decreased rapidly with time-scale as short as 0.24 day. Since these characteristics of the burst are similar to the solar burst, we speculate that the burst of the 6.7 GHz methanol maser in G33.641-0.228 might occur with a similar mechanism of the solar burst.
Variability of Water Masers in W49N: Results from Effelsberg Long-term Monitoring Programme
Authors: Kramer Busaba H. , Menten Karl M. , Kraus Alex 
Published: July 2018

AbstractWe present the results from an ongoing long-term monitoring of the 22 GHz H2O maser in W49N with the 100-m Effelsberg radio telescope from February 2014 to September 2017. The unique Effelsbergs spectral line observation capability provides a broad velocity range coverage from −500 to +500 km s−1 with a spectral resolution better than 0.1 km/s. Following the strong major outburst in W49N in late 2013, we have started a long-term monitoring programme at Effelsberg. The major outburst feature (up to 80,000 Jy at VLSR − 98 km s−1) faded away by June 2014. However, we found that the site is still active with several high velocity outbursts (both blue and redshifted). Some features appear at extremely high velocities (up to ±280 km s−1) and show rapid flux variations within a 1-2 month period. This sub-year scale variability implies that the water masers could be excited by episodic shock propagation caused by a high-velocity protostellar jet.
A Circumstellar Disk in IRAS 23151+5912?
Authors: Trinidad Miguel A. , Rodríguez-Esnard Tatiana , Masqué Josep M. 
Published: July 2018

AbstractWe present radio continuum and water maser observations toward the high-mass star-forming region IRAS 23151+5912 from the VLA and VLBA archive, respectively. We detected a continuum source, which seems to be a hypercompact HII region. In addition, a water maser group about 4″ south from the continuum source was detected. We present preliminary results of the analysis of three observations epochs of the water masers, which are tracing an arc-like structure. However, its kinematics is quite complex, since while one section of the structure seems to be moving away from one center, another section seems to be approaching.
Sardinia Radio Telescope (SRT) observations of Local Group dwarf galaxies
Authors: Tarchi A. , Castangia P. , Surcis G. , Brunthaler A. , Menten K. M. , Pawlowski M. S. , Melis A. , Casu S. , Murgia M. , Trois A. , Concu R. , Henkel C. , Darling J. 
Published: July 2018

AbstractThe dwarf galaxies in the Local Group (LG) reveal a surprising amount of spatial structuring. In particular, almost all non-satellite dwarfs belong to one of two planes that show a very pronounced symmetry. In order to determine if these structures in the LG are dynamically stable or, alternatively, if they only represent transient alignments, proper motion measurements of these galaxies are required. A viable method to derive proper motions is offered by VLBI studies of 22-GHz water (and 6.7-GHz methanol) maser lines in star-forming regions.In 2016, in the framework of the Early Science Program of the Sardinia Radio Telescope (SRT), we have conducted an extensive observational campaign to map the entire optical body of all the LG dwarf galaxies that belong to the two planes, at C and K band, in a search for methanol and water maser emission.Here, we outline the project and present its first results on 3 targets, NGC 6822, IC 1613, and WLM. While no luminous maser emission has been detected in these galaxies, a number of interesting weaker detections has been obtained, associated with particularly active star forming regions. In addition, we have produced deep radio continuum maps for these galaxies, aimed at investigating their star forming activity and providing an improved assessment of star formation rates in these galaxies.
Optimal insurance control for insurers with jump-diffusion risk processes
Authors: Tian Linlin , Bai Lihua 
Published: July 2018

AbstractIn this paper, we model the surplus process as a compound Poisson process perturbed by diffusion and allow the insurer to ask its customers for input to minimize the distance from some prescribed target path and the total discounted cost on a fixed interval. The problem is reduced to a version of a linear quadratic regulator under jump-diffusion processes. It is treated using three methods: dynamic programming, completion of square and the stochastic maximum principle. The analytic solutions to the optimal control and the corresponding optimal value function are obtained.
Pyrite Oxidation Drives Exceptionally High Weathering Rates and Geologic CO2 Release in Mountaintop‐Mined Landscapes
Authors: Ross Matthew R. V. , Nippgen Fabian , Hassett Brooke A. , McGlynn Brian L. , Bernhardt Emily S. 
Published: July 2018

AbstractWeathering is the ultimate source of solutes for ecosystems, controls chemical denudation of landscapes, and drives the geologic carbon cycle. Mining and other land‐moving operations enhance physical weathering by bringing large volumes of shattered bedrock to the surface. Yet, the relative influence of these activities on chemical weathering remains poorly constrained. Here we show that catchments impacted by mountaintop removal coal mining have among the highest rates of chemical weathering ever reported. Mined catchments deliver more than 7,600 kg·ha−1·year−1 of dissolved solids downstream. The chemical signatures of these exceptionally high weathering rates reflect the product of sulfuric acid weathering of carbonate‐bearing rock, driven by the oxidation of pyritic materials. As this strong acid rapidly weathers surrounding carbonate materials, H+ ions are consumed and Ca2+, Mg2+, and HCO3− ions are exported to balance the elevated SO42− exports, generating alkaline mine drainage. The sulfate exports from pyrite oxidation in mountaintop‐mined catchments account for ~5–7% of global sulfate derived from pyrite, despite occupying less than 0.006% of total land area. Further, the suite of weathering reactions liberate 100–450 kg of rock‐derived C·ha−1·year−1 as CO2, with an additional 90–150 kg C·ha−1·year−1 of C released when HCO3− reaches the ocean. This rock C release contributes to the high carbon costs of coal combustion.
Elastic Properties of Fractured Rock Masses With Frictional Properties and Power Law Fracture Size Distributions
Authors: Davy P. , Darcel C. , Le Goc R. , Mas Ivars D. 
Published: July 2018

AbstractWe derive the relationships that link the general elastic properties of rock masses to the geometrical properties of fracture networks, with a special emphasis to the case of frictional crack surfaces. We extend the well‐known elastic solutions for free‐slipping cracks to fractures whose plane resistance is defined by an elastic fracture (shear) stiffness ks and a stick‐slip Coulomb threshold. A complete set of analytical solutions have been derived for (i) the shear displacement in the fracture plane for stresses below the slip threshold and above, (ii) the partitioning between the resistances of the fracture plane on the one hand and of the elastic matrix on the other hand, and (iii) the stress conditions to trigger slip. All the expressions have been checked with numerical simulations. The Young's modulus and Poisson's ratio were also derived for a population of fractures. They are controlled both by the total fracture surface for fractures larger than the stiffness length lS (defined by ks and the intact matrix elastic properties) and by the percolation parameter of smaller fractures. These results were applied to power law fracture size distributions, which are likely relevant to geological cases. We show that if the fracture size exponent is in the range −3 to −4, which corresponds to a wide range of geological fracture networks, the elastic properties of the bulk rock are almost exclusively controlled by ks and the stiffness length, meaning that the fractures of size lS play a major role in the definition of the elastic properties.
Interseismic Strain Accumulation on Faults Beneath Los Angeles, California
Authors: Rollins Chris , Avouac Jean‐Philippe , Landry Walter , Argus Donald F. , Barbot Sylvain 
Published: July 2018

AbstractGeodetic data show that the Los Angeles metropolitan area is undergoing 8–9 mm/year of north‐south tectonic shortening associated with the Big Bend of the San Andreas Fault. This shortening has been linked to multiple damaging twentieth century thrust earthquakes as well as possible Mw ≥ 7.0 Holocene thrust events beneath central Los Angeles. To better characterize this seismic hazard, we assess how this shortening is being accommodated by interseismic strain accumulation on subsurface faults, incorporating detailed seismology‐ and geology‐based models of fault geometry and the low‐stiffness Los Angeles sedimentary basin. We find that strain accumulation on local strike‐slip faults likely contributes no more than 1–2 mm/year of the shortening. We formally invert the geodetic data for the pattern of interseismic strain accumulation on the north dipping Sierra Madre, Puente Hills, and Compton thrust faults and a master decollement. We explore the impact of the assumed material model, strain accumulation on faults to the west and east, and other model assumptions. We infer that the three faults slip at 3–4 mm/year over the long term and are currently partially or fully locked and accruing interseismic strain on their upper sections. This locking implies an annual deficit of seismic moment, 1.6 + 1.3/−0.5 × 1017 Nm/year in total, which is presumably balanced over the long‐term average by the moment released in earthquakes. The depth distribution of moment deficit accumulation rate matches that of seismicity rates in Los Angeles to first order, in part, because the models incorporate the blind nature of the Puente Hills and Compton Faults.
Revisited Asian Monsoon Hydroclimate Response to Volcanic Eruptions
Authors: Gao C. C. , Gao Y. J. 
Published: July 2018

AbstractA multiproxy study of the climatic impact after the 1815 Tambora eruption in China found substantial discrepancies among the historical documents, proxy reconstructions, and model simulations. To understand whether the discrepancies are associated with regional‐scale heterogeneous hydroclimate responses or the specialty of an individual volcanic event, we revisit the Asian monsoon hydroclimate response to volcanic eruptions over the past five centuries using an independent warm season precipitation reconstruction. The composite results show a bipolar pattern of increased precipitation over the Yangtze‐Huaihe River valley and decreased precipitation over South China after the tropical eruptions, which agree with the instrumental observations of the El Chichón and Pinatubo eruptions. We could therefore reject the latter possibility and suggest that an overall drying response in the tree‐ring‐based Monsoon Asia Drought Atlas after tropical volcanic perturbations is an oversimplified conclusion. The hydroclimate responses suggest a combined influence of weakened East Asian and South Asian summer monsoons and an intensified East Asian subtropical westerly jet stream during its southward migration. Proxy reconstructions may be biased due to the sampling coverage and data sensitivities, and a combined analysis using different proxies is critical to form a balanced view of the important relationship between volcanic radiative perturbation and monsoon hydroclimate.
Multiple Factors Explaining the Deficiency of Cloud Profiling Radar on Detecting Oceanic Warm Clouds
Authors: Liu Dongyang , Liu Qi , Liu Guosheng , Wei Junbo , Deng Shumei , Fu Yunfei 
Published: July 2018

AbstractThe Cloud Profiling Radar (CPR) detecting efficiency on low‐level clouds is affected by many situations, including surface clutter, spatial resolution, and radar sensitivity. These factors can uniquely or jointly result in missed detections of oceanic single‐layer warm clouds. Fifty‐seven percent of missed detections are attributed to a single factor, and the rest are attributed to two or more factors that are indistinguishable. For missed warm clouds above 1 km, 30% result from the nonovercast effect, while the CPR range resolution is the major cause for the overcast ones. In particular, 18.4% are attributed exclusively to specific cloud microphysics, which is characterized by droplet effective radius (DER) and cloud optical thickness (COT). Compared to COT, the CPR detection is more dependent on DER, with a critical value standing around 10 μm. It is only for larger DER that the effects from COT turn to arise. Given liquid water path, clouds with larger DER and smaller COT are more likely to generate sufficient reflectivity and be detected than their counterpart. For clouds with the same DER and COT, opposite detecting results are primarily determined by the different droplet size distributions that lead to a variable reflectivity across the CPR detecting limit. Over global oceans, total miss rate of cloud occurrences approaches 0.73, while the loss rate of cloud water mass is 0.42 due to the smaller liquid water path of CPR‐missed clouds. The CPR‐missed detections also lead to uncertainties in cloud radiative forcing estimations. A notable overestimation of shortwave cloud forcing at 160% is found at bottom and top of atmosphere.
Primary Production and Calcification Rates of Algae‐Dominated Reef Flat and Seagrass Communities
Authors: Perez D. I. , Phinn S. R. , Roelfsema C. M. , Shaw E. , Johnston L. , Iguel J. 
Published: July 2018

AbstractMonitoring variability in coral reef primary production and calcification is needed to understand changes over time and between reef systems, which helps separate differences due to natural and/or anthropogenic factors happening now and in the future. This study measured net productivity and calcification for two reef systems at Shark Bay, Heron Reef in the southern Great Barrier Reef and Saipan Lagoon, Commonwealth of the Northern Mariana Islands. Net primary productivity and calcification were strongly correlated for reef flats with an adjusted R2 = 0.66. Night time dissolution occurred at Shark Bay reef flat with an average of −12.66 mmol CaCO3 · m−2 · hr−1, while calcification increased at night for the Saipan reef flat. For both reef flat sites, net productivity from oxygen flux was much lower than rates calculated from change in dissolved inorganic carbon. This study provided the first baseline estimates of net productivity and calcification for a reef flat and seagrass community in Saipan Lagoon. The seagrass community had the lowest productivity of all sites. However, the high presence of calcareous algae at the site highlights the need for more research on the carbonate chemistry of these habitats. All sites had high net productivity that was most likely associated with the dominant presence of algae.
Modeling Nondilute Species Transport Using the Thermodynamically Constrained Averaging Theory
Authors: Weigand T. M. , Schultz P. B. , Giffen D. H. , Farthing M. W. , Crockett A. , Kelley C. T. , Gray W. G. , Miller C. T. 
Published: July 2018

AbstractNondilute transport in porous media results in fronts that are much sharper in space and time than the corresponding transport of a conservative, nonreactive dilute species. A thermodynamically constrained averaging theory model for such situations is developed. A novel closure scheme is formulated, which is cross‐coupled between flow and transport in its most general form. Experiments are performed to investigate the effects of density, viscosity, and chemical activity. An adaptive numerical approximation method is developed to efficiently solve the formulated model. Parameter estimation is performed, and excellent agreement between laboratory data and model simulations is obtained. Accurate prediction of experimental data not used to estimate model parameters is found. It is also shown that chemical activity effects contribute to asymmetric breakthrough curves for nondilute transport in porous medium systems.
Onset Condition of Plasma Density Enhancements: A Case Study for the Effects of Meridional Wind During 17–18 August 2003
Authors: Luo Weihua , Xiong Chao , Zhu Zhengping , Mei Xuefei 
Published: July 2018

AbstractThe multisatellite observations were used to study the possible factors leading to the development of the plasma density enhancements during the August 2003 storm period. The plasma depletions and enhancements (also referred as bubbles and blobs, respectively) were observed by first satellite of the Republic of China around 345°E sector at different local time on 17 August, before the midnight after the storm sudden commencement. However, only the depletions were recorded on 18 August at the same longitude sector and at nearly the same time as that on 17 August. The motions of the bubbles and blobs displayed different characteristics on 17 August. From Challenging Mini‐satellite Payload, Gravity Recovery and Climate Experiment, and total electron content map, the equatorial ionization anomaly was inhibited and displayed more asymmetric on 17 August and became stronger on 18 August. A density enhancement near the northern crest was recorded by Gravity Recovery and Climate Experiment, and similar enhancements were found in total electron content map at low‐latitude regions of both hemispheres on 17 August. The results suggest that the meridional neutral wind is crucial and plays an important role in the development of the plasma blobs. And the variations of meridional neutral wind may be linked with the large‐scale traveling ionospheric disturbances during the disturbed periods.